AAOS Comprehensive Orthopaedic Review

Section 4 - Orthopaedic Oncology and Systemic Disease

Chapter 38. Benign Bone Tumors and Reactive Lesions

I. Bone

A. Osteoid osteoma—A distinctive, painful, benign osteoblastic bone tumor.


1. Demographics


a. Male to female ratio = 2:1


b. The vast majority of patients are between 5 and 30 years of age.


2. Genetics/etiology


a. Etiology is unclear, but nerve fibers associated with blood vessels within the nidus likely play a role in producing pain.


b. High prostaglandin and cyclooxygenase levels within the lesion


3. Clinical presentation (

Table 1)


a. Classic symptom is night pain relieved by aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs).


b. The pain is progressive in its severity, can be referred to an adjacent joint, and may be present for months to years prior to diagnosis.


c. Most common locations include femur, tibia, vertebral arch, humerus, and fingers; the proximal femur is the most common site, and the hip is the most common intra-articular location.


d. Usually occurs in the diaphyseal or metaphyseal regions of long bones


e. When an osteoid osteoma is the cause of a painful scoliosis, the lesion is usually at the center of the concavity of the curve.


f. Osteoid osteomas cause extensive inflammatory symptoms in the adjacent tissues (joint effusions, contractures, limp, muscle atrophy).


4. Imaging appearance (

Figure 1)


a. Round, well-circumscribed intracortical lesion with radiolucent nidus


b. Lesions usually <1 cm in diameter


c. Extensive periosteal reaction may obscure the nidus (Figure 1, A).


d. Lesions are occasionally intra-articular, subperiosteal, or medullary, and these cause less surrounding periosteal reaction.


e. Radiographic differential diagnosis includes osteomyelitis and Ewing sarcoma.


f. Intense and focal increased tracer uptake on technetium Tc 99m bone scans


g. Thin-cut CT scan is often the key to diagnosis because it frequently identifies the small radiolucent nidus (Figure 1, B).


h. MRI may show extensive surrounding edema (Figure 1, C and D).


5. Pathology



Microscopic appearance consists of uniform, thin osteoid seams and immature trabeculae (Figure 1, E and F).


Trabeculae are lined with uniform plump osteoblasts.


[Table 1. Factors Differentiating Osteoid Osteoma From Osteoblastoma]

[Figure 1. Osteoid osteomas. A, AP radiograph of a right femur shows extensive reactive bone formation and cortical thickening along the medial diaphysis. B, Axial thin-cut CT of the same patient shown in A reveals a clear radiolucent nidus with a central density that is classic for an osteoid osteoma. C, AP radiograph of a left femoral neck reveals a well-circumscribed subcortical lucency surrounded by sclerosis. D, MRI of the same patient shown in C reveals a nidus near the lateral cortex with surrounding edema. E, At low-power magnification, an osteoid osteoma has the histologic appearance of a sharply demarcated lesion (nidus) encased by dense cortical bone. F, High-power magnification shows osteoblastic rimming similar to that found in an osteoblastoma. The nuclei appear active but there is no pleomorphism. Marked vascularity is present within the stroma.]


1- to 2-mm fibrovascular rim surrounds the sharply demarcated nidus.


No pleomorphic cells, and the lesion does not infiltrate the surrounding bone


Similar in appearance to osteoblastoma but smaller in size (Table 1)


6. Treatment/outcome


a. Standard of care is percutaneous radiofrequency ablation (RFA) of the lesion. A CT-guided probe is inserted into the lesion with the temperature raised to 90°C for 4 to 6 minutes to produce a 1-cm zone of necrosis.


i. Recurrence rates after RFA are <10%.


ii. Contraindications include lesions close to the spinal cord or nerve roots.


b. Other surgical treatments have included surgical resection or burring, although the lesion must be localized preoperatively to identify its exact location.


c. In lesions around the hip, patients often require internal fixation, sometimes with bone grafting, if a large portion of cortex is removed with the lesion.


d. Long-term medical management with aspirin or NSAIDs can relieve symptoms after an average of 3 years because these lesions have self-limited growth.


e. Depending on the age of the child and duration of symptoms, removal of an osteoid osteoma associated with a painful scoliosis will allow resolution of the curve without further treatment.


B. Osteoblastoma—A rare, aggressive, benign osteoblastic tumor.


1. Demographics


a. Male to female ratio = 2:1


b. Osteoblastomas are much less common than osteoid osteomas.



Figure 2. Osteoblastomas. A, AP radiograph of the lower portion of the thoracic spine of a 17-year-old boy shows a possible lesion on the right side of the T10 vertebra. B, A CT scan of the same patient shown in A better shows the location of the osteoblastoma in the pedicle of T10. C, The histologic appearance of an osteoblastoma shows interlacing trabeculae surrounded by fibrovascular connective tissue. The tumor merges into the normal bone at the periphery of the lesion. D, Higher power magnification shows osteoblastic rimming around the trabecular bone. The osteoblasts can appear plasmacytoid.]

c. The vast majority of affected patients are between 10 and 30 years of age.


2. Genetics/etiology: unknown


3. Clinical presentation (Table 1)


a. Slowly progressive dull, aching pain of long duration that is less severe than that from an osteoid osteoma


b. Night pain is not typical, and aspirin does not classically relieve the symptoms.


c. Neurologic symptoms can occur because the spine is the most common location for osteoblastoma (posterior elements) (Figure 2, A and B).


d. Other locations include the diaphysis or metaphysis of long bones (tibia and femur) and the mandible.


e. Related swelling, muscle atrophy, and a limp may occur because the lesions are large and present for a prolonged period of time.


f. Osteoblastomas may be associated with oncogenic osteomalacia.


4. Imaging appearance


a. Radiolucent lesion 2 to 10 cm in size with occasional intralesional densities


b. Cortically based (two thirds) more often than medullary (one third)


c. Expansile with extension into the surrounding soft tissues and a rim of reactive bone around the lesion


d. 25% of the lesions have an extremely aggressive appearance and are mistaken for a malignancy.


e. Radiographic differential diagnosis includes osteosarcoma, aneurysmal bone cyst (ABC), osteomyelitis, and osteoid osteoma.


f. Three-dimensional imaging (CT, MRI) is necessary to fully evaluate the extent of the lesion prior to surgical treatment.


5. Pathology


a. Histology is similar to an osteoid osteoma but with increased giant cells.


b. Irregular seams of osteoid separated by loose fibrovascular stroma (Figure 2, C)


c. Osteoid is rimmed by prominent osteoblasts that are occasionally large and epithelioid (Figure 2, D).


d. Most commonly there is a sharp demarcation from the surrounding bone.


e. 10% to 40% are associated with secondary ABC formation.


f. Numerous mitotic figures may be present but are not atypical.


g. It is important to differentiate osteoblastoma from osteosarcoma, although giant cell tumor and ABC are also similar in appearance.


6. Treatment/outcome


a. Osteoblastoma is not self-limited and requires surgical treatment.


b. In most cases, curettage and bone grafting is adequate to achieve local control.


c. Nerve roots should be maintained when treating spinal lesions.


d. Occasionally, en bloc resection is required for lesions in the spine.


C. Parosteal osteoma—A rare, self-limited deposition of reactive bone on the surface of the cortex.


1. Demographics: adults, most commonly in their 30s or 40s


2. Genetics/etiology: no known cause, but often a history of trauma is reported


3. Clinical presentation


a. Long history of gradual swelling or dull pain


b. Occasionally, incidental radiographic findings are present.


c. Classically, osteomas are found in the craniofacial bones, but rare presentations in other parts of the skeleton include the long bones (tibia, femur), pelvis, and vertebrae.


d. Multiple osteomas are associated with Gardner syndrome (autosomal dominant), which also includes colonic polyps, fibromatosis, cutaneous lesions, and subcutaneous lesions.


4. Imaging appearance


a. Uniform radiodense lesion attached to the bone cortex with a broad base ranging from 1 to 8 cm in size (

Figure 3, A)


b. Well-defined with smooth, lobulated borders


c. No cortical or medullary invasion (best noted on CT scan) (Figure 3, B)


d. Radiographic differential diagnosis includes parosteal osteosarcoma, healed stress fracture, and osteoid osteoma.


5. Pathology


a. Histologic appearance is of mature, hypocellular lamellar bone with intact Haversian systems.


b. No atypical cells are present.


6. Treatment/outcome


a. Nonsurgical treatment is preferred for incidental or minimally symptomatic lesions.


b. Biopsy should be performed if the diagnosis is unclear.


c. Local recurrence of the lesion suggests it was initially not recognized as a parosteal osteosarcoma.


D. Bone island (enostosis)—A usually small (but occasionally large) deposit of dense, compact bone within the medullary cavity.


1. Demographics: Bone islands occur frequently in adults, but their true incidence is unknown because they are usually found incidentally.


2. Genetics/etiology: Possible arrested resorption of mature bone during endochondral ossification


3. Clinical presentation


a. This nontumorous lesion is asymptomatic and found incidentally.


b. Any bone can be involved, but the pelvis and femur are most common.


c. Osteopoikilosis is a hereditary syndrome that manifests as hundreds of bone islands throughout the skeleton, usually centered about joints.


4. Radiographic appearance


a. Well-defined, round focus of dense bone


[Figure 3. Parosteal osteoma. A, Lateral radiograph of the distal femur in a 37-year-old man reveals a heavily ossified surface lesion attached to the posterior femoral cortex. B, CT scan of the same patient reveals the relationship of the lesion to the cortex and differentiates it from myositis ossificans. An excisional biopsy revealed a parosteal osteoma.]

   within the medullary cavity usually measuring 2 to 20 mm in diameter (

Figure 4)


b. Occasionally, radiating spicules of bone around the lesion that blend with the surrounding medullary cavity are present.


c. Approximately one third of lesions show increased activity on a bone scan.


d. No surrounding bony reaction or edema on T2-weighted MRI


e. Low intensity on T1- and T2-weighted MRI


f. Radiographic differential diagnosis includes well-differentiated osteosarcoma, osteoblastic metastasis, and bone infarct.


5. Pathology


a. Bone islands appear histologically as cortical bone with a well-defined lamellar structure and haversian systems.


b. Border between the lesion and surrounding medullary bone shows no endochondral ossification.


6. Treatment/outcome—No treatment is required, but follow-up radiographs should be taken if there is any question about the diagnosis.


[Figure 4. AP radiograph of the hip of an asymptomatic 45-year-old woman with a benign-appearing lesion in the proximal femur consistent with a bone island.]


Figure 5. Enchondromas. A, AP radiograph of the right proximal humerus in a 49-year-old woman with shoulder pain reveals a calcified lesion in the metaphysis that is centrally located within the bone. The ring-like or stippled calcifications are consistent with an enchondroma. There is no endosteal erosion or cortical thickening. B, Radiograph demonstrating enchondromas in the hand of a patient with Ollier disease. Note the multiple expansile lytic lesions affecting the metacarpals and phalanges. Areas of calcified cartilage are evident within the lucent areas. C, Histologic appearance of an enchondroma. Note the normal chondrocytes in lacunar spaces with no mitotic figures.]

II. Cartilage

A. Enchondroma—A benign tumor comprised of mature hyaline cartilage and located in the medullary cavity.


1. Demographics


a. Enchondromas can occur at all ages; most common in patients age 20 to 50 years.


b. The incidence is unclear because most lesions are found incidentally.


2. Genetics/etiology—Enchondromas are thought to be related to incomplete endochondral ossification, where fragments of epiphyseal cartilage displace into the metaphysis during skeletal growth.


3. Clinical presentation


a. Most enchondromas are asymptomatic and are noted incidentally when radiographs are taken for other reasons.


b. Lesions in the small bones of the hands and feet can be painful, especially after pathologic fracture.


c. When a patient presents with an enchondroma and pain in the adjacent joint, the pain often has a cause that is unrelated to the tumor.


d. If the patient has pain and the radiographic appearance is suspicious, low-grade chondrosarcoma must be considered.


e. Half of all enchondromas occur in the small tubular bones, with the vast majority in the hands; enchondromas are the most common bone tumor in the hand.


f. Other common locations include the metaphysis or diaphysis of long bones (proximal humerus, distal femur, tibia); enchondromas are rare in the spine and pelvis.


g. Enchondromas are classified by Enneking as inactive or latent bone lesions.


h. The incidence of malignant transformation is <1%.


i. A dedifferentiated chondrosarcoma rarely develops from an enchondroma.


4. Imaging appearance


a. Enchondromas begin as well-defined, lucent, central medullary lesions that calcify over time; they appear more diaphyseal as the long bone grows.


b. The classic radiographic appearance involves rings and stippled calcifications within the lesion (Figure 5, A).


c. Lesions can be 1 to 10 cm in size.


d. Small endosteal erosion (<50% width of the cortex) or cortical expansion may be present.


e. The cortices in hand enchondromas may be thinned and expanded (Figure 5, B).


f. Cortical thickening or destruction suggests a chondrosarcoma.


g. The radiographic differential diagnosis includes a bone infarct and low-grade chondrosarcoma.


h. The radiographic appearance is more important than the pathologic appearance in differentiating an enchondroma from a low-grade chondrosarcoma.


i. Enchondromas frequently have increased up-take on bone scans due to continual remodeling of the endochondral bone within the lesion.


j. MRI is not necessary for diagnosis but shows the lesion as lobular and bright on T2-weighted images, with no bone marrow edema or periosteal reaction.


5. Pathology


a. The gross appearance is of blue-gray, lobulated hyaline cartilage with a variable amount of calcifications throughout the tumor.


b. The low-power histologic appearance is of mature hyaline cartilage lobules separated by normal marrow, which is key to differentiating an enchondroma from a chondrosarcoma.


c. Endochondral ossification encases the cartilage lobules with lamellar bone.


d. Lesions in the small tubular bones and proximal fibula are more hypercellular than lesions in other locations.


e. Enchondromas in long bones have abundant extracellular matrix but no myxoid component.


f. The cells are bland, with uniform, dark-stained nuclei; they have no pleomorphism, necrosis, mitoses, or multinucleate cells (Figure 5, C).


6. Treatment/outcome


a. Asymptomatic lesions require no treatment but should be followed with serial radiographs to ensure inactivity.


b. Rarely, when pain due to other causes is excluded, symptomatic enchondromas can be treated with curettage and bone grafting.


c. Pathologic fractures through enchondromas in small, tubular bones should be allowed to heal prior to curettage and bone grafting.


d. If radiographs are suspicious for a chondrosarcoma, then surgery is necessary.


e. A needle biopsy is not reliable to differentiate enchondroma from low-grade chondrosarcoma and should be used only if confirmation of tissue type is needed.


7. Related conditions: Ollier disease/Maffucci syndrome


a. Ollier disease is characterized by multiple enchondromas with a tendency toward unilateral involvement of the skeleton (sporadic inheritance).


b. Multiple enchondromas are thought to indicate a skeletal dysplasia with failure of normal endochondral ossification throughout the metaphyses of the affected bones.


c. Patients with multiple lesions have growth abnormalities causing shortening and bowing deformities.


d. Maffucci syndrome involves multiple enchondromas and soft-tissue angiomas.


e. Radiographically, the enchondromas have variable mineralization and often markedly expand the bone.


f. The angiomas in Maffucci syndrome can be identified on radiographs due to phleboliths (small, round calcified bodies).


g. The histologic appearance of lesions in a patient with multiple enchondromas is similar to solitary lesions in small tubular bones (hypercellular with mild chondrocytic atypia).


h. Patients with multiple enchondromas may require surgical correction of skeletal deformities at a young age.


i. There is an increased risk of malignant transformation of an enchondroma to a low-grade chondrosarcoma in patients with Ollier disease (25% to 30%).


j. Patients with Maffucci syndrome have an increased risk of malignant transformation of an enchondroma (23% to 100%) to a low-grade chondrosarcoma, as well as a high risk of developing a fatal visceral malignancy.


k. Patients with these syndromes need to be followed long-term because of the increased chance of malignancy.


B. Periosteal chondroma—A benign hyaline cartilage tumor located on the surface of the bone.


1. Demographics: Periosteal chondromas occur in patients from 10 to 30 years of age.


2. Genetics/etiology: These are rare lesions thought to arise from pluripotential cells deep in the periosteum that differentiate into chondroblasts instead of osteoblasts.


3. Clinical presentation


a. Patients present with pain, or sometimes the lesions are found incidentally in asymptomatic patients.



Figure 6. Periosteal chondroma. A, Lateral view of the right knee in a 28-year-old woman with lateral calf pain. Extraosseous calcification is seen around the proximal fibula. B, Axial CT reveals a surface lesion with a calcified rim and nondisplaced pathologic fracture in the fibula. C, MRI reveals bright signal on T2-weighted imaging and defines that this is a surface lesion without medullary involvement. A biopsy revealed a periosteal chondroma.]

b. Any bone can be involved, but the proximal humerus, the femur, and the small bones of the hand are the most common locations.


c. The lesions can grow slowly after patients reach skeletal maturity but have no malignant potential.


4. Imaging appearance


a. The classic appearance is a well-defined surface lesion that creates a saucerized defect in the underlying cortex (Figure 6).


b. The lesion ranges from 1 to 5 cm in size and is metaphyseal or diaphyseal.


c. There is a rim of sclerosis in the underlying bone.


d. The edges of the lesion often have a mature buttress of bone.


e. The amount of calcification is variable, and soft-tissue swelling may be present because of the surface location.


f. The radiographic differential diagnosis includes periosteal chondrosarcoma and periosteal osteosarcoma.


5. Pathology


a. The low-power appearance is of well-circumscribed hyaline cartilage lobules.


b. The histologic appearance is similar to that of enchondroma, with mildly increased cellularity, binucleated cells, and occasional mild pleomorphism.


6. Treatment/outcome


a. No treatment is needed for asymptomatic patients.


b. Symptomatic patients are treated with excision with a marginal margin.


c. Local recurrence is rare.


C. Osteochondroma—A benign cartilage tumor arising from the surface of the bone.


1. Demographics


a. Osteochondromas are the most common benign bone tumor.


b. The true incidence of osteochondromas is unknown because most lesions are asymptomatic.


c. Most lesions are identified in the first two decades of life.


2. Genetics/etiology


a. Osteochondromas are hamartomatous proliferations of bone and cartilage.


b. They are thought to arise from trapped growth-plate cartilage that herniates through the cortex and grows via endochondral ossification beneath the periosteum.


c. A defect in the perichondrial node of Ranvier may allow the physeal growth to extend from the surface; as the cartilage ossifies, it forms cortical and cancellous bone that is the stalk of the lesion.


3. Clinical presentation


a. Most lesions are solitary and asymptomatic.


b. Most are <3 cm in size, but they can be as large as 15 cm.


c. Depending on size and location, patients can have pain from an inflamed overlying bursa, fracture of the stalk, or nerve compression.



Figure 7. Osteochondromas. A, Sessile osteochondroma noted on an AP radiograph of the right humerus in a 14-year-old boy. AP (B) and lateral (C) radiographs of the distal femur in an 11-year-old boy reveal a pedunculated osteochondroma of the medial distal femur. The medullary portion of the lesional stalk is continuous with the medullary cavity of the distal femur. There is cortical sharing. D, AP radiograph of the right knee in an 18-year-old man with multiple hereditary osteochondromas. Note the multiple small lesions and the widened metaphysis. E, Axial CT scan of the same patient shown in Eshows the posteromedial extension of a lesion in the proximal fibula. F, At low-power magnification, the histologic appearance of an osteochondroma shows the cartilage cap with the cartilage cells arranged in columns similar to a growth plate.]

d. When close to the skin surface, they are firm, immobile masses.


e. Osteochondromas continue to grow until the patient reaches skeletal maturity.


f. The lesions most commonly occur around the knee (distal femur, proximal tibia), proximal humerus, and pelvis; spinal lesions (posterior elements) are rare.


g. Subungual exostosis arises from beneath the nail in the distal phalanx; this is a posttraumatic lesion and not a true osteochondroma.


h. Patients can present with multiple lesions (multiple hereditary exostosis).


i. The risk of malignant degeneration of a solitary osteochondroma to a chondrosarcoma is <1%.


j. Rarely, a dedifferentiated chondrosarcoma can develop from a solitary osteochondroma.


4. Imaging appearance


a. Osteochondromas can be sessile or pedunculated on the bone surface (Figure 7, A).


b. There is a higher risk of malignant degeneration in sessile lesions.


c. Lesions arise near the growth plate and appear to become more diaphyseal with time.


d. Pedunculated lesions grow away from the adjacent joint (Figure 7, B and C).


e. The medullary cavity of the bone is continuous with the stalk of the lesion.


f. The cortex of the underlying bone is continuous with the cortex of the stalk.


g. The affected bony metaphysis is often flared or widened.


h. The cartilage cap is usually radiolucent and involutes at skeletal maturity.


i. Metaplastic cartilage nodules can occur within a bursa over the cartilage cap.


j. The radiographic differential diagnosis includes parosteal osteosarcoma and myositis ossificans.


k. CT or MRI scans can better evaluate the cartilage cap and are useful when malignant degeneration is a concern.


5. Pathology


a. The gross appearance of a pedunculated lesion is similar to a cauliflower, with cancellous bone beneath the cartilage cap.


b. Histologically, the cartilage cap consists of hyaline cartilage and is organized like a growth plate with maturation to bony trabeculae (Figure 7, F).


c. There is a well-defined perichondrium around the cartilage cap.


d. The stalk consists of cortical and trabecular bone with spaces between the bone filled with marrow.


e. The chondrocytes within the lesion are uniform, without pleomorphism or multiple nuclei.


f. Thick cartilage caps imply growth but are not a reliable indicator of malignant degeneration.


6. Treatment/outcome


a. For asymptomatic or minimally symptomatic patients who are still growing, nonsurgical treatment is preferred.


b. Relative indications for surgical excision of an osteochondroma (performed by excision at the base of the stalk)


i. Symptoms secondary to soft-tissue inflammation (bursae, muscles, joint capsule, tendons)


ii. Symptoms secondary to frequent traumatic injury


iii. Significant cosmetic deformity


iv. Symptoms secondary to nerve or vascular irritation


v. Concern for malignant transformation


c. The perichondrium over the cartilage cap must be removed to decrease the likelihood of local recurrence.


d. Delaying surgical excision until skeletal maturity allows a higher chance of local control.


e. Patients with osteochondromas extending into the popliteal fossa can have pseudoaneurysms and are subject to vascular injury during excision.


7. Related condition: multiple hereditary exostoses


a. This is a skeletal dysplasia that is inherited with an autosomal dominant pattern.


b. Patients may have up to 30 osteochondromas throughout the skeleton.


c. The EXT1EXT2, and EXT3 are three genetic loci associated with this disorder.


d. Mutations in these genes are found in most affected patients, and they are considered tumor-suppressor genes.


e. Clinically, the patients have skeletal deformities and short stature.


f. The lesions are similar radiographically and histologically to solitary osteochondromas.


g. Radiographs reveal primarily sessile lesions that may grow to a very large size.


h. Metaphyseal widening is present in affected patients (Figure 7, D and E).


i. Deformities occur due to disorganized endochondral ossification in the growth plate and may require surgical correction, especially in the paired bones (radius/ulna, tibia/fibula).


j. The risk of malignant transformation is higher (~5% to 10%) in patients with this condition.


k. The most common location of a secondary chondrosarcoma is the pelvis. Usually the malignant tumors are low grade.


D. Chondroblastoma—A rare, benign bone tumor differentiated from giant cell tumor by its chondroid matrix.


1. Demographics


a. Male to female ratio = 2:1


b. 80% of patients are younger than 25 years.



Figure 8. Chondroblastoma. AP (A) and lateral (B) views of the right knee in a 19-year-old man show a well-circumscribed round lesion in the proximal tibial epiphysis extending slightly into the metaphysis. Note the sclerotic rim. C, Histologic appearance of a chondroblastoma. Note the round or oval chondroblasts (arrows). On higher power, areas of dystrophic calcification are visible around the individual cells in a "chicken-wire" pattern.]

2. Genetics/etiology


a. Chondroblastoma has been categorized as a cartilage tumor due to its areas of chondroid matrix, but type II collagen is not expressed by the tumor cells.


b. It is thought to arise from the cartilaginous epiphyseal plate.


3. Clinical presentation


a. Patients present with pain that is progressive at the site of the tumor.


b. As these tumors often occur adjacent to a joint, there can be decreased range of motion, a limp, muscle atrophy, and tenderness over the affected bone.


c. Most chondroblastomas are found in the distal femur and proximal tibia, followed by proximal humerus, proximal femur, calcaneus, and flat bones.


d. <1% develop benign pulmonary metastasis from chondroblastoma.


4. Imaging appearance


a. Chondroblastomas are small, round tumors that occur in the epiphysis or apophysis; they often extend into the metaphysis (Figure 8, A and B).


b. Most are 1 to 4 cm in size and have a sclerotic rim.


c. Most are centrally located in the epiphysis, with a small subset having a more aggressive appearance due to secondary ABC formation.


d. Cortical expansion of the bone may be present, but soft-tissue extension is rare.


e. 25% to 40% of chondroblastomas have stippled calcifications within the lesion.


f. The differential diagnosis includes giant cell tumor, osteomyelitis, and clear cell chondrosarcoma.


g. Three-dimensional imaging is not required, but a CT scan defines the bony extent of the lesion.


h. MRI shows extensive edema surrounding the lesion.


5. Pathology


a. The tumor consists of a background of mono-nuclear cells, scattered multinucleated giant cells, and focal areas of chondroid matrix.


b. The mononuclear stromal cells are distinct, round, S100+ cells with large central nuclei that can appear similar to histiocytes; the nuclei have a longitudinal groove resembling a coffee bean (Figure8, C).


c. Chicken-wire calcifications are present in a lace-like pattern throughout the tumor.


d. Mitotic figures are present but not atypical.


e. One third of chondroblastomas have areas of secondary ABC.


6. Treatment/outcome


a. Curettage and bone grafting is indicated for the treatment of chondroblastoma.



Figure 9. Chondromyxoid fibromas. A, AP radiograph of the right distal femur in a 12-year-old boy with knee pain shows an eccentric lytic lesion with a well-defined intramedullary border. A periosteal shell that is not easily seen is consistent with a chondromyxoid fibroma. B, AP radiograph of the proximal tibia in a 22-year-old woman with an eccentric lesion expanding the cortex with a visible rim. C,The histologic appearance of a chondromyxoid fibroma shows hypercellular regions at the periphery of the lobules. Note the spindled, stellate cells and myxoid stroma.]

b. Adjuvants such as phenol or liquid nitrogen are often used to decrease local recurrence.


c. The local recurrence rate is 10% to 15%.


d. Surgical resection is indicated for rare benign pulmonary metastasis.


E. Chondromyxoid fibroma (CMF)—A rare, benign cartilage tumor containing chondroid, fibrous, and myxoid tissue.


1. Demographics


a. Most CMFs occur in the second and third decades of life, but they may be seen in patients up to 75 years of age.


b. There is a slight male predominance.


2. Genetics/etiology—CMF is thought to arise from remnants of the growth plate.


3. Clinical presentation


a. Most patients present with pain and mild swelling of the affected area.


b. Occasionally the lesions are noted incidentally.


c. The most common locations are the long bones of the lower extremities (proximal tibia) and pelvis. Small bones in the hands and feet are also affected.


4. Imaging appearance


a. CMF is a lucent, eccentric lesion found in the metaphysis of long bones (Figure 9, A).


b. It can cause thinning and expansion of the adjacent cortical bone (Figure 9, B).


c. It often has a sharp, scalloped sclerotic rim.


d. Radiographic calcifications within the lesion are rare.


e. CMF ranges in size from 2 to 10 cm.


f. The radiographic differential diagnosis includes ABC, chondroblastoma, and nonossifying fibroma.


g. There is increased tracer uptake within the lesion on bone scan.


5. Pathology


a. On low power, the lesion is lobulated with peripheral hypercellularity.


b. Within the lobules, the cells are spindled or stellate with hyperchromatic nuclei.


c. Between the lobules are multinucleated giant cells and fibrovascular tissue.


d. Areas of myxoid stroma are present, but hyaline cartilage is rare (Figure 9, C).


e. The cellular areas may resemble chondroblastoma.


f. Areas with pleomorphic cells with bizarre nuclei are common.


g. The histologic differential diagnosis includes chondroblastoma, enchondroma, and chondrosarcoma.


6. Treatment/outcome


a. CMF is treated with curettage and bone grafting.


b. The local recurrence rate is 10% to 20%.

III. Fibrous/Histiocytic

A. Nonossifying fibroma (NOF)—A developmental abnormality related to faulty ossification rather than a true neoplasm.


1. Demographics


a. Very common skeletal lesions


b. Occur in children and adolescents (age 5 to 15 years)


c. 30% of children with open physes have nonossifying fibromas.


d. Also frequently called fibrous cortical defect or metaphyseal fibrous defect


2. Genetics/etiology—Possibly caused by abnormal subperiosteal osteoclastic resorption during remodeling of the metaphysis.


3. Clinical presentation


a. Usually an incidental finding


b. May be multifocal


i. Familial multifocal


ii. Neurofibromatosis


iii. Jaffe-Campanacci syndrome (congenital with cafe au lait pigmentation, mental retardation, and nonskeletal abnormalities involving heart, eyes, gonads)


c. Most common in long bones of lower extremity (80%)


d. Patients occasionally present with a pathologic fracture.


4. Radiographic appearance


a. Eccentric, lytic, cortically based lesions with a sclerotic rim (

Figure 10, A and B)


b. Occur in the metaphysis and appear to migrate to diaphysis as bone grows


c. May thin the overlying cortex with expansion of the bone


d. Lesions enlarge (1 to 7 cm) as patient grows.


e. As patient reaches skeletal maturity, the lesions ossify and become sclerotic.


f. Occasionally associated with secondary ABC


g. Plain radiographs are diagnostic.


h. A lesion similar in appearance to a nonossifying fibroma on the posteromedial aspect of the distal femur is an avulsive cortical irregularity, which is the result of an avulsion injury at the insertion of the adductor magnus muscle.


5. Pathology


a. Prominent storiform pattern of fibrohistiocytic cells (Figure 10, C and D)


b. Variable numbers of giant cells


c. May have areas of xanthomatous reaction with foamy histiocytes


d. Prominent hemosiderin


e. Occasional secondary ABC component


6. Treatment/outcome


a. Most treated with observation; will spontaneously regress


b. Monitor along with skeletal growth if they are large lesions.


c. When symptomatic and large, curettage and bone grafting is often necessary


d. For pathologic fractures, often allow to heal, then observe or curettage/graft


e. Internal fixation rarely needed, depending on anatomic location


B. Fibrous dysplasia—A common developmental abnormality characterized by hamartomatous proliferation of fibro-osseous tissue within the bone.


1. Demographics


a. Can be found in any age, but ~75% in patients <30 years


b. Affects females more than males


2. Genetics/etiology


a. Solitary focal or generalized multifocal inability to produce mature lamellar bone


b. Areas of the skeleton remain indefinitely as immature, poorly mineralized trabeculae.


c. Not inherited


d. Monostotic and polyostotic forms associated with activating mutations of GSα on chromosome 20q13, which produce a sustained activation of adenylate cyclase cAMP.


e. Fibrous dysplasia tissue has high expression of fibroblast growth factor (FGF)-23, which may be the cause of hypophosphatemia in patients with McCune-Albright syndrome or oncogenic osteomalacia.


3. Clinical presentation


a. Usually asymptomatic and found incidentally

b. Can be monostotic or polyostotic


c. Affects any bone, but predilection for proximal femur, rib, maxilla, tibia


[Figure 10. Nonossifying fibromas. AP (A) and lateral (B) radiographs of the distal tibia in an 11-year-old boy reveal a nonossifying fibroma that has healed after a minimally displaced pathologic fracture. It is an eccentric, scalloped lesion with a sclerotic rim. Anteriorly, the lesion is filling in with bone. C, Histologic appearance of a nonossifying fibroma. Bands of collagen fibers and fibroblasts can be seen coursing throughout the lesion. D, High-power magnification of the same specimen shown in C reveals multinucleated giant cells and hemosiderin-laden histiocytes that are characteristic of an NOF.]

d. Fatigue fractures through lesion can cause pain.


e. May have swelling around lesion


f. Severe cranial deformities, blindness with craniofacial involvement


g. Patients occasionally present with pathologic fracture


h. McCune-Albright syndrome


i. Triad of polyostotic fibrous dysplasia, precocious puberty, and pigmented skin lesions (coast of Maine)


ii. Unilateral bone lesions


iii. Skin lesions usually on same side as bone lesions


iv. 3% of patients with polyostotic fibrous dysplasia


i. Myriad endocrine abnormalities with polyostotic forms


j. Most common entity causing oncogenic osteomalacia (renal phosphate wasting due to FGF-23)


k. Mazabraud syndrome is fibrous dysplasia (usually polyostotic) associated with soft-tissue intramuscular myxomas.


4. Radiographic appearance


a. Central lytic lesions within the medullary canal—usually diaphysis/metaphysis


b. Sclerotic rim


c. May be expansile with cortical thinning


d. "Ground glass" or "shower-door glass" appearance (

Figure 11, A)


e. Bowing deformity in proximal femur (shepherd's crook) or tibia


f. Can see vertebral collapse and kyphoscoliosis


g. Long lesion in a long bone (Figure 11, B)


h. Increased activity on bone scan, but plain radiographs usually diagnostic


5. Pathology


a. Gross: yellow-white gritty tissue


b. Histology: poorly mineralized immature fibrous tissue surrounding islands of irregular, often poorly mineralized trabeculae of woven bone (Figure 11, C)


c. "Chinese letters" or "alphabet soup" appearance


d. Metaplastic bone arises from fibrous tissue without osteoblastic rimming.


e. Common mitoses


f. May have metaplastic cartilage present or areas of cystic degeneration


g. Can be associated with secondary ABC


h. Differential diagnosis includes low-grade intramedullary osteosarcoma.


6. Treatment/outcome


a. Asymptomatic patients may be observed.


b. Surgical indications include painful lesions, impending/actual pathologic fracture, severe deformity, neurologic compromise (spine).


c. Curettage and bone-graft the lesion. (Use cortical allograft, not cancellous autograft!)


d. Cancellous autografts are replaced by dysplastic bone.


e. Usually requires internal fixation to achieve pain control (intramedullary device more effective than plate) in the lower extremity


f. Osteotomies for deformity


g. Medical treatment with bisphosphonates provided good pain relief in small series.


h. In ~1% of lesions, malignant transformation to osteosarcoma, fibrosarcoma, or malignant


[Figure 11. Fibrous dysplasia. A, AP radiograph of the right proximal femur in an 18-year-old woman with groin pain. A central, lytic bone lesion with a ground glass appearance fills the femoral neck, consistent with fibrous dysplasia. B, A lateral radiograph of an elbow reveals an expansile lesion in the proximal radius with a ground glass appearance. There is no evidence of cortical destruction. C,Histologic appearance on intermediate magnification. Metaplastic bone spicules can be seen scattered haphazardly; this pattern produces the characteristic radiographic ground glass appearance of fibrous dysplasia.]


Figure 12. Osteofibrous dysplasia. A, Lateral radiograph of the tibia in a skeletally immature patient reveals a cortically based lytic lesion. There are multiple lucencies surrounded by dense sclerosis consistent with osteofibrous dysplasia. There is no periosteal reaction. B, A high-power histologic section reveals woven bone arising from a fibrous stroma. The new bone is prominently rimmed by osteoblasts, thereby differentiating this from fibrous dysplasia.]

   fibrous histiocytoma occurs, with extremely poor prognosis.


C. Osteofibrous dysplasia—A nonneoplastic fibroosseous lesion affecting the long bones of young children.


1. Demographics


a. Affects males more than females


b. Usually noted in first decade of life


2. Genetics/etiology: Trisomy 7, 8, 12, and 22 have been reported.


3. Clinical presentation


a. Unique predilection for the tibia


b. Can have anterior or anterolateral bowing deformity


c. Pseudarthrosis develops in 10% to 30% of patients.


d. Patients usually present with painless swelling over anterior border of tibia.


4. Radiographic appearance


a. Eccentric, well-defined anterior tibial lytic lesions (Figure 12, A)


b. Usually diaphyseal


c. Single or multiple lucent areas surrounded by dense sclerosis


d. Confined to the anterior cortex; may expand


e. No periosteal reaction


f. Differential diagnosis: adamantinoma (radiographic appearance can be identical)


5. Pathology


a. Moderately cellular fibroblastic stroma


b. Islands of woven bone with prominent osteoblastic rimming (Figure 12, B)


c. No cellular atypia


d. May have giant cells


e. Differential diagnosis: fibrous dysplasia


6. Treatment/outcome


a. Avoid surgery if possible; brace when necessary.


b. Lesions may spontaneously regress or stabilize at skeletal maturity.


c. May need deformity correction


d. Controversy whether there is a continuum from osteofibrous dysplasia to adamantinoma, but the exact nature of this relationship is uncertain


D. Desmoplastic fibroma—An extremely rare benign bone tumor composed of dense bundles of fibrous connective tissue.


1. Demographics—Most common in patients age 10 to 30 years.


2. Genetics/etiology


a. Bone counterpart of the aggressive fibromatosis (desmoid) in soft tissue; may originate from myofibroblasts


b. Loss of 5q21-22 (gene location for familial adenomatous polyposis and Gardner syndrome) has been reported.


c. Loss of 4p and rearrangement of 12q12-13, and trisomy 8 (0%-33%), trisomy 20 (2%-25%), or both (0%-16%)


3. Clinical presentation


a. Can occur in any bone


b. Intermittent pain unrelated to activity


c. Palpable mass/swelling


4. Imaging appearance


a. Lytic lesion centrally located in metaphysis


b. Honeycomb/trabeculated appearance (

Figure 13)


c. Usually no periosteal reaction unless a fracture is present (12%)


d. May appear aggressive with cortical destruction and soft-tissue extension


e. No calcification within lesion


f. Increased activity on bone scan


5. Pathology


a. Gross: dense, white, scarlike tissue


b. Histology: abundant collagen fibrils with intermixed spindle cells


c. Appearance is hypocellular and similar to scar tissue.


d. Monotonous uniform nuclei


e. Infiltrative growth pattern—trapping native trabeculae


f. Differential diagnosis includes low-grade fibrosarcoma.


6. Treatment/outcome


a. Surgical treatment is the standard of care.


b. Thorough curettage allows good results.


c. Wide resection for expendable bones or locally recurrent lesions


d. Desmoplastic fibromas do not metastasize, but they often recur locally.


E. Langerhans cell histiocytosis—A clonal proliferation of Langerhans-type histiocytes that can have multiple clinical presentations.


1. Demographics


a. Most common in children (80% < 20 years of age)


b. Male to female ratio = 2:1


[Figure 13. Lateral (left) and AP (right) radiographs of the distal femur reveal a lytic lesion expanding the posterolateral cortex and having an internal honeycomb appearance. This is consistent with the aggressive behavior of a desmoplastic fibroma.]

2. Genetics/etiology: N/A


3. Clinical presentation


a. Previously categorized as eosinophilic granuloma, Hand-Schuller-Christian disease (chronic, disseminated), and Letterer-Siwe disease (infantile, acute)


b. Now believed to be three scenarios


i. Solitary disease (eosinophilic granuloma)


ii. Multiple bony sites


iii. Multiple bony sites with visceral involvement (lungs, liver, spleen, skin, lymph nodes)


c. Rarely, bone lesions are asymptomatic; usually, they cause localized pain/swelling/limp.


d. Can occur in any bone but most commonly skull, ribs, clavicle, scapula, vertebrae (thoracic > lumbar > cervical), long bones, pelvis


4. Radiographic appearance


a. Classic appearance is a "punched-out" lytic lesion (

Figure 14, A).


b. May have thick periosteal reaction


c. Can appear well-demarcated or permeative (Figure 14, B)


d. Commonly causes vertebral collapse (vertebra plana) when affecting the spine (Figure 14, C)


e. Great mimicker of other lesions (osteomyelitis, Ewing sarcoma, leukemia)


5. Pathology


a. The characteristic tumor cell is the Langerhans cell or histiocyte (Figure 14, D).


[Figure 14. Eosinophilic granulomas/Langerhans cell histiocytosis. A, AP radiograph of a scapula with a well-defined lytic lesion having a classic "punched-out" appearance of an eosinophilic granuloma.B, AP radiograph of a lytic lesion in the right clavicle of a child demonstrates cortical expansion, periosteal reaction, and no sclerotic edges. This is an eosinophilic granuloma, but the radiographic appearance can also be consistent with osteomyelitis or Ewing sarcoma. C, A lateral radiograph of the thoracic spine shows the classic appearance of vertebra plana in a patient with eosinophilic granuloma.D, Histologic appearance of an eosinophilic granuloma shows a mixed inflammatory infiltrate with Langerhans histiocytes having large indented nuclei, lymphocytes, and eosinophils.]

b. Histiocytes have indented nuclei (coffee bean) with eosinophilic cytoplasm.


c. Histiocytes stain with CD1A.


d. Giant cells are present.


e. Eosinophils are variable in number.


f. Mixed inflammatory cell infiltrate


g. Birbeck granules on electron microscopy (tennis rackets)


6. Treatment/outcome


a. Solitary lesions can be treated effectively with an intralesional injection of methylprednisolone acetate.


b. Curettage/bone grafting if open biopsy is being performed for diagnosis


c. In 90% of patients with vertebra plana due to Langerhans cell histiocytosis, bracing alone will correct the deformity; 10% will need corrective surgery.


d. Low-dose radiation is used in rare cases (spinal cord compression).


e. Patients with disseminated disease and visceral involvement can die of the disease. The prognosis is improving with more effective chemotherapy but worsens with increasing number of extraosseous sites of disease.

IV. Cystic

A. Unicameral bone cyst (UBC)—A common, serous fluid-filled bone lesion.


1. Demographics—Most cases occur in patients younger than 20 years.



Table 2. Comparison of Clinical Presentation of Unicameral Bone Cysts and Aneurysmal Bone Cysts]


Figure 15. Unicameral bone cysts. A, AP radiograph of the proximal humerus in a 5-year-old girl shows a lytic lesion centrally located in the medullary canal of the metaphysis consistent with a unicameral bone cyst. The lesion does not expand the bone wider than the epiphyseal plate. The girl had had a prior pathologic fracture through the lesion. B, AP radiograph of a proximal femur demonstrates a lytic lesion in the metaphysis abutting the proximal femoral epiphyseal plate. The lesion is central in location and will likely require surgical treatment because of the high risk of fracture. C, Histologic appearance. A thin cyst lining consisting of fibroblasts is seen. Cementum is noted in the wall and no cellular atypia is present.]

2. Genetics/etiology


a. Thought to result from a temporary failure of medullary bone formation near the epiphyseal plate during skeletal growth


b. The cyst is active initially when adjacent to the growth plate. When medullary bone formation resumes, the cyst appears to move into the diaphysis.


c. Possible causes and precursor lesions include lymphatic/venous obstruction, intraosseous hematoma, or intraosseous synovial rest.


3. Clinical presentation (Table 2)


a. Most common presentation is a pathologic fracture after minor trauma.


b. Painful symptoms resolve when fracture heals.


c. Most common locations include the proximal humerus and proximal femur, but UBCs can occur in the ilium and calcaneus.


4. Imaging appearance


a. Purely lytic lesion located centrally in the medullary canal


b. UBCs start metaphyseal, adjacent to the growth plate, and appear to progress toward the diaphysis with bone growth (Figure 15, A).


c. Narrow zone of transition between cyst and normal bone


d. Cortical thinning but no soft-tissue extension (Figure 15, B)


e. Bone expansion does not exceed width of the physis.


f. Trabeculations occur after multiple fractures.


g. "Fallen leaf" sign is pathognomonic (fallen cortical fragment into base of empty lesion).


h. Plain radiographs are usually diagnostic, but MRI shows a well-defined zone of bright uniform signal on T2-weighted images.


5. Pathology


a. Lining of the cyst is a thin fibrous membrane: no true endothelial cells (Figure 15, C).


b. Giant cells, inflammatory cells, hemosiderin within lining


c. Clear or serous fluid within cavity (bloody after fracture)


d. 10% contain cementum spherules (calcified eosinophilic fibrinous material) in the lining.


6. Treatment/outcome


a. Natural history is to fill in with bone as the patient reaches skeletal maturity.


b. After acute fractures, the lesion will occasionally fill in with native bone (15%).


c. Standard treatment is intralesional injection of methylprednisolone acetate.


d. May require multiple injections, especially in very young children


e. Proximal femoral lesions with or without a pathologic fracture often treated with curettage/bone grafting/internal fixation


B. Aneurysmal bone cyst (ABC)—A destructive, expansile reactive bone lesion filled with multiple blood-filled cavities.


1. Demographics—75% of patients are <20 years of age.


2. Genetics/etiology


a. Reactive, nonneoplastic process of unknown etiology


b. Possibilities include a traumatic origin or a circulatory disturbance leading to increased venous pressure and hemorrhage.


c. Can arise de novo or be associated with an underlying lesion that is identifiable in 30% of cases (most commonly chondroblastoma, giant cell tumor, chondromyxoid fibroma, nonossifying fibroma, osteoblastoma, and fibrous dysplasia)


3. Clinical presentation (Table 2)


a. Pain and swelling are the most common symptoms.


b. Pathologic fracture as a presenting symptom is rare.


c. Neurologic symptoms are possible with lesions in the spine.


d. Most common locations are distal femur, proximal tibia, pelvis, spine (posterior elements).


4. Imaging appearance


a. Eccentric, lytic lesions located in the metaphysis (

Figure 16, A)


b. Can aggressively destroy/expand the cortex and extend into the soft tissues


c. Lesion can expand to greater than the width of the epiphyseal plate (Figure 16, B).


d. Usually maintains a periosteal rim around the lesion


e. Can grow contiguously across adjacent spinal segments or extend through epiphyseal plate


f. No matrix mineralization


g. MRI shows fluid-fluid levels on T2-weighted images (separation of serum and blood products) (Figure 16, C).


h. Radiographic differential diagnosis includes UBC and telangiectatic osteosarcoma.


5. Pathology


a. Blood-filled cyst without a true endothelial lining


b. Lining contains giant cells, new (woven) bone, spindle cells (Figure 16, D).


c. Solid areas are common.


d. May be histologic evidence of an underlying primary lesion


e. No cellular atypia, but mitoses are common


f. Histologic differential diagnosis includes telangiectatic osteosarcoma and giant cell tumor.


6. Treatment/outcome


a. Surgical treatment is curettage and bone grafting of the lesion.


b. Local adjuvants (eg, phenol) can be used after curettage.


c. Highest local recurrence is in patients with an open physeal plate.


d. For local recurrence, repeat curettage and grafting is indicated.


e. May resect expendable bones (proximal fibula)


f. Embolization can be useful for pelvic or spinal lesions alone or in combination with surgical treatment.


[Figure 16. Aneurysmal bone cysts. A, AP view of a proximal tibia shows an eccentric lytic lesion located in the metaphysis that expands into the soft tissues with a periosteal rim consistent with an ABC.B, AP view of a proximal humerus showing a septated expansile lesion wider than the epiphyseal plate in a very young child, consistent with an ABC. C, An axial MRI reveals the presence of fluid-fluid levels within the lesion. D, Higher power magnification of an ABC shows multinucleated giant cells within the fibrohistiocystic stroma. No cellular atypia is seen.]

V. Miscellaneous

A. Giant cell tumor—A benign, aggressive bone tumor consisting of distinct undifferentiated mononuclear cells.


1. Demographics


a. Most occur in patients 30 to 50 years of age (90% are older than 20 years)


b. Affects females more than males


2. Genetics/etiology


a. Etiology is unknown.


b. Stromal cells have alterations in the C-myc, C-fos, and N-myc oncogenes.


3. Clinical presentation


a. Pain and swelling for 2 to 3 months are main symptoms.


b. Decreased range of motion around a joint



Figure 17. Giant cell tumors. AP (A) and lateral (B) radiographs of the wrist in a 54-year-old man reveal an expansile lesion located within the epiphysis of the distal radius. No matrix is produced, and there is no sclerotic rim. There has been a pathologic fracture through the lesion. AP (C) and lateral (D) radiographs of the distal femur in a 33-year-old woman demonstrate an aggressive lytic lesion expanding and destroying the medial and posterior cortices. The differential includes malignant bone tumors, but a biopsy revealed a giant cell tumor. E, Gross view of the resection specimen (an intralesional procedure was not deemed appropriate) from the same patient shown in C and DF, Low-power photomicrograph shows abundant multinucleated giant cells amid a background of mononuclear stromal cells (hematoxylin and eosin, ×100). G, A higher power photomicrograph shows the multinucleated giant cells with abundant nuclei. The nuclei of the stromal cells resemble those of the giant cells. No cellular atypia or matrix production is noted (hematoxylin and eoxin, ×400).]

c. Sometimes presents with a pathologic fracture (10%)


d. Located most commonly in distal femur, proximal tibia, distal radius, proximal humerus, proximal femur, sacrum, and pelvis


e. 1% of cases are multicentric.


4. Imaging appearance


a. Eccentric, lytic lesions located in the epiphysis/metaphysis of long bones


b. May arise in an apophysis


c. Lesions extend to the subchondral surface with no sclerotic rim (Figure 17, A and B).


d. Can destroy the cortex and extend into the surrounding tissues (Figure 17, C and D)


e. Located in the anterior vertebral body when involving the spine


f. Commonly have a secondary ABC component


g. May be associated soft-tissue calcifications


h. Bone scan shows increased uptake in the lesion.


i. MRI helpful only to define the extent of soft-tissue involvement, as plain radiographs are usually diagnostic.


5. Pathology


a. Gross: soft, red-brown, hemorrhage, necrosis (Figure 17, E)


b. Histology: uniformly scattered multinucleated giant cells within a background of mononuclear stromal cells (Figure 17, F and G)


c. The stromal cells represent the neoplastic cell.


d. Can have secondary changes of necrosis or fibrohistiocytic change


e. Mitoses are frequent, but there should be no cellular atypia.


f. No matrix production unless there is a pathologic fracture


g. Frequent ABC component


h. There is no histologic grading system for giant cell tumor or way to predict prognosis.


6. Treatment/outcome


a. Most lesions can be treated with thorough curettage and a high-speed burr.


b. Thorough intralesional treatment requires making a large cortical window.


c. Local adjuvants are commonly used to decrease local recurrence (phenol, cryotherapy, argon beam).


d. Can fill defect with either bone graft or methylmethacrylate (equivalent recurrence rate), with or without internal fixation, depending on the defect size


e. Can bear weight as tolerated after using methylmethacrylate; protect from weight bearing after using bone graft until consolidation


f. Local recurrence with intralesional treatment is 10% to 15%.


g. Local recurrence can be in the adjacent bone or manifest as soft-tissue masses.


h. Aggressive lesions may require resection and reconstruction.


i. Embolization should be used for large pelvic or spinal lesions alone or in combination with surgical treatment.


j. Radiation occasionally used in multiply recurrent or surgically inaccessible lesions


k. Metastasizes to the lungs in 2% of patients (benign metastasizing giant cell tumor)


i. Treatment includes thoracotomy, radiation, chemotherapy, or observation.


ii. 10% to 15% of patients with metastatic disease die of the disease.


l. Rare cases (~1%) of malignant giant cell tumor

Top Testing Facts


1. Osteoid osteoma has a radiolucent nidus with surrounding sclerosis.


2. The bone scan is always intensely positive in an osteoid osteoma.


3. Thin-cut CT scans most often identify the nidus and make the diagnosis of osteoid osteoma.


4. The proximal femur is the most common location for an osteoid osteoma.


5. Osteoid osteoma is the most common cause of a painful scoliosis in a young patient.


6. RFA is the current standard of care to treat osteoid osteoma.


7. An osteoid osteoma can be differentiated from an osteoblastoma by its smaller size and less aggressive behavior, although the histologic appearance is similar.


8. Osteoblastoma is a large radiolucent lesion that occurs most commonly in the posterior elements of the spine.


9. Parosteal osteoma must be differentiated from parosteal osteosarcoma.


10. A bone island is an inactive lesion most commonly found in the pelvis and proximal femur.



1. Enchondromas are usually asymptomatic; a painful presentation is usually due to an unrelated condition.


2. The clinical presentation and radiographic appearance are more important than the histologic appearance in differentiating enchondroma from low-grade chondrosarcoma.


3. Patients with either Ollier disease or Maffucci syndrome have an increased risk for malignant transformation of an enchondroma to a low-grade chondrosarcoma.


4. A periosteal chondroma is a surface lesion that creates a saucerized defect in the underlying cortex.


5. The medullary cavity of the underlying bone is continuous with the stalk of an osteochondroma.


6. Secondary chondrosarcomas arising from osteochondromas are low grade and occur more often in patients with multiple lesions.


7. EXT1EXT2, and EXT3 are genetic loci commonly mutated in patients with multiple hereditary exostoses.


8. Chondroblastoma most commonly occurs in the epiphyses and apophyses of long bones.


9. Chondroblastoma rarely metastasizes to the lung.


10. Chondromyxoid fibroma is a lucent, eccentric lesion with a sclerotic, scalloped rim seen in long bones, pelvis, and hands/feet.



1. Nonossifying fibromas are usually incidental findings that spontaneously regress and should be observed.


2. Nonossifying fibromas are developmental abnormalities that occur in 30% of children.


3. Nonossifying fibromas occur as scalloped lytic lesions with a sclerotic border within the metaphysis.


4. Fibrous dysplasia is a long lesion in a long bone with a ground glass appearance.


5. The histologic appearance of fibrous dysplasia is woven bone shaped like "Chinese letters" or "alphabet soup" in a cellular, fibrous stroma.


6. Polyostotic fibrous dysplasia occurs in McCune-Albright syndrome along with precocious puberty and cafe-au-lait spots.


7. Osteofibrous dysplasia affects children in the first decade, with a predilection for the anterior cortex of the tibia.


8. The histologic appearance of osteofibrous dysplasia is a cellular, fibrous stroma with prominent osteoblastic rimming around the woven bone, which differentiates it from fibrous dysplasia.


9. Langerhans cell histiocytosis is the great mimicker; think of it with lytic lesions in children.


10. In Langerhans cell histiocytosis, the histiocyte (not the eosinophil) is the tumor cell and stains with CD1A.



1. UBCs are centrally located in the metaphysis and appear to move to the diaphysis.


2. UBCs present with a pathologic fracture—rare fallen leaf sign on radiographs.


3. Treat UBCs with an intralesional steroid injection.


4. ABCs are destructive, expansile, blood-filled cysts.


5. ABCs occur around the knee, pelvis, and posterior elements of the spine.


6. At least 30% of the time, ABCs are secondary to an underlying primary bone tumor.


7. Giant cell tumors are epiphyseal or apophyseal and extend into the metaphysis and subchondral bone.


8. The mononuclear stromal cell is the neoplastic cell in giant cell tumor.


9. The treatment of giant cell tumor is careful curettage with a large cortical window (low local recurrence rate of 5% to 15%).


10. Giant cell tumor metastasizes to the lung in 2% of patients.


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