AAOS Comprehensive Orthopaedic Review

Section 4 - Orthopaedic Oncology and Systemic Disease

Chapter 41. Malignant Soft-Tissue Tumors

I. Soft-Tissue Sarcoma Treatment

A. Overview

 

1. Ratio of benign to malignant soft-tissue masses = 100:1 (sarcomas rare)

 

2. Males affected more than females

 

3. Extremities (upper and lower)—60% of sarcomas

 

4. 85% occur in individuals older than 15 years.

 

5. Appearance of most sarcomas on MRI is indeterminate; a biopsy is required.

 

6. Staging—The most common system is the AJCC system, which relies on histologic grade, tumor size, nodal status, and whether distant metastases are present.

 

B. Surgery

 

1. Goal is to achieve an acceptable margin to minimize local recurrence and maintain reasonable function; limb salvage procedures performed in ~90% of patients.

 

2. Sarcomas have a centripetal growth pattern.

 

3. Reactive zone around tumor includes edema, fibrous tissue (capsule), inflammatory cells, and tumor cells

 

4. "Shelling out" a sarcoma usually means excising it through the reactive zone, which leaves tumor cells behind in most cases.

 

5. Definition of surgical margins (Enneking)

 

a. Intralesional: resection through the tumor mass for gross total resection

 

b. Marginal: resection through the reactive zone

 

c. Wide: resection with a cuff of normal tissue

 

d. Radical: resection of the entire compartment (eg, quadriceps)

 

6. Amputation is indicated if necessary to resect the entire tumor, if major nerves cannot be saved, or if the patient has significant comorbidities that preclude a limb-sparing surgery.

 

7. Standard oncologic techniques are used to resect soft-tissue sarcomas.

 

a. Tourniquet without exsanguination

 

b. Excise biopsy tract

 

c. Drains distal, close, and in line with incision

 

8. Surgical resection alone of large, deep, high-grade tumors has unacceptably high rate of local recurrence—requires adjuvant treatment (radiation with or without chemotherapy).

 

9. Soft-tissue reconstruction by free or rotational tissue transfer frequently is necessary and minimizes wound complications after major resection (

Figure 1).

 

C. Radiation

 

1. Used routinely in the treatment of soft-tissue sarcoma (noted exceptions being when an amputation is performed or when the sarcoma is small, superficial, low grade, and amenable to a wide surgical resection)

 

2. Radiation can be administered by external beam techniques, brachytherapy (percutaneous flexible catheters placed directly on tumor bed and loaded with radiation sources [beads or wires] over 48 to 96 hours) (

Figure 2), or intraoperatively.

 

3. Early radiation effects: desquamation, delayed wound healing, infection. Late effects: fibrosis, fractures, joint stiffness, secondary sarcoma (depending on treatment dose, volume, and length of follow-up).

 

4. Preoperative radiation requires a lower dose (~50 Gy) than postoperative radiation (~66 Gy), decreases the surrounding edema, and helps form a thick fibrous capsule around the tumor. Surgery is delayed 3 to 4 weeks after completion of radiation.

 

5. Preoperative radiation incurs a higher wound complication rate (35%) than postoperative radiation (17%) (

Figure 3).

 

6. No difference in overall survival or functional outcomes related to timing of radiation has been reported.

 

7. External beam radiation combined with extensive periosteal stripping during tumor resection increases the risk of postradiation fracture. In these cases, consider prophylactic intramedullary or plate stabilization.

 

[Figure 1. Clinical photographs after soft-tissue sarcoma resection. A, Soft-tissue defect after wide resection of a clear cell sarcoma of the volar wrist. B, Soft-tissue reconstruction using free tissue transfer is commonly performed to minimize wound breakdown and infection, especially when the patient has had preoperative radiation.]

[Figure 2. Brachytherapy catheters are shown overlying a tumor bed after resection. A free flap was used to cover the defect.]

D. Chemotherapy

 

1. Controversial for soft-tissue sarcoma in general. (May delay local or systemic recurrent disease, but no statistically significant survival benefit at 10 years.)

 

2. Key component of treatment for rhabdomyosarcoma and soft-tissue Ewing sarcoma/primitive neuroectodermal tumor. Studies show possible benefit for synovial sarcoma.

 

3. Common agents include ifosfamide and doxorubicin (adriamycin), which have considerable toxicity in high doses.

 

[Figure 3. Wound breakdown after preoperative radiation and surgical resection of a high-grade liposarcoma of the medial thigh.]

4. Patients with soft-tissue sarcoma commonly are older, with more comorbidities, and cannot tolerate high-dose systemic treatment.

 

E. Outcomes

 

1. The use of radiation and surgery minimizes the risk of local recurrence to <10%.

 

2. Stage is the most important factor in determining overall prognosis/outcome.

 

3. Other prognostic factors include presence of metastasis, grade, size, and depth of tumor.

 

4. Tumor grade is related to risk of metastasis (low grade, <10%; intermediate grade, 10% to 25%; high grade, >50%).

 

5. Most common site of metastasis is to the lungs.

 

6. Lymph node metastasis (~5%) occurs most frequently in rhabdomyosarcoma, synovial sarcoma, epithelioid sarcoma, and clear cell sarcoma.

 

7. The outcome of individual soft-tissue sarcoma subtypes is rarely reported; ~50% of patients with high-grade soft-tissue sarcomas die of the disease.

 

8. Resection of pulmonary metastasis can cure up to 25% of patients.

 

9. Patients require follow-up of primary site of resection (MRI with contrast, or ultrasound) and chest (radiograph or CT scan) every 3 to 4 months for 2 years, every 6 months for 3 years, and then yearly with chest studies.



II. Malignant Fibrous Histiocytoma

A. Definition and demographics

 

1. Pleomorphic in histologic appearance (recently reclassified as "undifferentiated high-grade pleomorphic sarcoma")

 

2. Most common soft-tissue sarcoma in adults 55 to 80 years of age

 

3. Male to female ratio = 2:1

 

4. More common in Caucasian than in African-American or Asian populations

 

B. Genetics/etiology—No data yet.

 

C. Clinical presentation

 

1. Usually a deep, slow-growing, painless mass

 

2. More common in the extremities (lower more common than upper) than retroperitoneum

 

3. Patients occasionally present with fever, elevated white blood cell count, and hypoglycemia.

 

D. Imaging appearance (indeterminate)—Low intensity on T1-weighted MRI; high intensity on T2-weighted MRI (

Figure 4, A and B).

 

E. Pathology

 

1. Grossly, a gray-white multinodular mass

 

2. Histologic subtypes include pleomorphic (80% to 85%), giant cell (10%), and inflammatory (<10%).

 

3. Low-power histology shows storiform or cartwheel growth pattern (Figure 4, C).

 

4. Cells are plump, spindled, and arranged around narrow vessels.

 

5. Haphazard histiocytic cells

 

6. Multinucleated eosinophilic giant cells (Figure 4, D)

 

[Figure 4. Malignant fibrous histiocytoma in a 68-year-old man who presented with a painless soft-tissue mass in the right posterior thigh. Axial T1-weighted (A) and T2-weighted (postcontrast) (B) MRI scans are indeterminate in appearance; a biopsy is required. C, Low-power histology reveals a storiform pattern with bizarre pleomorphic tumor cells and hyalinized collagen bundles consistent with malignant fibrous histiocytoma (undifferentiated high-grade pleomorphic sarcoma). D, Higher power reveals anaplastic tumor cells, multinucleated cells, and mitotic figures.]

7. Marked atypia, mitotic activity, and pleomorphism

 

F. Treatment/outcome

 

1. Radiation and wide surgical resection

 

2. Chemotherapy in selected cases

 

3. Overall 5-year survival of 50% to 60% (depending on size, grade, depth, presence of metastasis)



III. Liposarcoma

A. Definition and demographics

 

1. Composed of a variety of histologic forms related to the developmental stages of lipoblasts

 

2. Second most common soft-tissue sarcoma in adults

 

3. Occurs most commonly in patients 50 to 80 years of age

 

4. Affects males more than females

 

B. Genetics/etiology

 

1. Origin of liposarcoma is from primitive mesenchymal cells; diagnosis does not require adipose cells.

 

2. Lipomas do not predispose a patient to liposarcomas.

 

3. Histologic types include well-differentiated, myxoid (most common—50%), round cell, pleomorphic, and dedifferentiated.

 

4. Well-differentiated variants have giant marker and ring chromosomes.

 

5. Myxoid liposarcoma is associated with a translocation between chromosomes 12 and 16.

 

C. Clinical presentation

 

1. Wide spectrum of disease depending on histologic type

 

2. Slow-growing; may become extremely large (10 to 20 cm), painless masses

 

3. Pain may occur in larger lesions.

 

4. Occur in extremities (lower [thigh] more common than upper) and retroperitoneum (15% to 20%) (present at later age)

 

5. Well-differentiated liposarcoma is essentially the same entity as atypical lipoma/atypical lipomatous tumor (some use the former term for retroperitoneal lesions and the latter term for extremity lesions).

 

6. Well-differentiated liposarcomas can rarely dedifferentiate. Watch for rapid growth of a longstanding (usually >5 years) painless mass.

 

D. Imaging appearance

 

1. Plain radiographs occasionally show foci of calcification or ossification in well-differentiated variants.

 

2. MRI appearance of well-differentiated variant is the same as a lipoma. Watch for rare areas of dedifferentiation (

Figure 5, A and B).

 

3. MRI appearance of high-grade liposarcoma is indeterminate and similar to all sarcomas (low intensity on T1-weighted images; high intensity on T2-weighted images) (

Figure 6, A and B).

 

4. Myxoid liposarcomas can metastasize to sites other than the lungs (eg, abdomen), so staging for this tumor should include a CT scan of the abdomen and pelvis as well as a chest CT scan.

 

E. Pathology

 

1. Grossly, liposarcomas are large, well-circumscribed, and lobular.

 

2. Well-differentiated liposarcoma—Low-grade tumor with lobulated appearance of mature adipose tissue (Figure 5, C).

 

3. Myxoid liposarcoma

 

[Figure 5. Well-differentiated liposarcoma. A, Coronal T1-weighted image reveals a large left retroperitoneal lipomatous lesion extending through the sciatic notch into the gluteal muscles. B, Axial T2-weighted fat-suppressed MRI scan reveals that the lesion completely suppresses with no concern for high-grade areas. C, Histology of the resected specimen reveals slight variation in the size and shape of the fat cells with hyperchromatic nuclei, consistent with a well-differentiated liposarcoma.]

[Figure 6. Myxoid liposarcoma in the left calf of a 27-year-old woman. Axial T1-weighted (A) and T2-weighted short tau inversion recovery (STIR) (B) MRI sequences reveal an indeterminate lesion that is low intensity on T1-weighted images and high intensity on T2-weighted images. There is no bony involvement, but the mass is adjacent to the proximal fibula. C, The histology reveals lipoblasts (some with signet-ring appearance), numerous capillaries, and a myxoid stroma between the tumor cells. No significant round cell component is noted.]

a. Low- to intermediate-grade tumor with lobulated appearance

 

b. Composed of proliferating lipoblasts, a plexiform capillary network, and a myxoid matrix (Figure 6, C)

 

c. Signet ring (univacuolar) lipoblasts occur at the edge of the tumor lobules.

 

d. Few mitotic figures

 

4. Round cell liposarcoma

 

a. Also considered a poorly differentiated myxoid liposarcoma

 

b. Characteristic small round blue cells

 

c. Rare intracellular lipid formation and minimal myxoid matrix

 

5. Pleomorphic liposarcoma

 

a. High-grade tumor with marked pleomorphic appearance

 

b. Giant lipoblasts with hyperchromatic bizarre nuclei

 

c. Deeply eosinophilic giant cells

 

6. Dedifferentiated liposarcoma—high-grade sarcoma (malignant fibrous histiocytoma, fibrosarcoma, leiomyosarcoma) juxtaposed to well-differentiated lipomatous lesion.

 

F. Treatment/outcome

 

1. Well-differentiated liposarcoma

 

a. Marginal resection without radiation or chemotherapy

 

b. Metastasis extremely rare

 

c. Risk of local recurrence is 25% to 50% at 10 years.

 

d. Dedifferentiation risk is 2% for extremity lesions and 20% for retroperitoneal lesions.

 

2. Intermediate- and high-grade variants

 

a. Radiation and wide surgical resection

 

b. Chemotherapy in selected patients

 

c. Incidence of pulmonary metastasis increases with grade.

 

d. Myxoid liposarcomas with >10% round cells have higher likelihood of metastasis.

 

e. Local recurrence is higher in retroperitoneal lesions.



IV. Fibrosarcoma

A. Definition and demographics

 

1. Rare soft-tissue sarcoma of fibroblastic origin that shows no tendency toward other cellular differentiation

 

2. Occurs in adults 30 to 55 years of age

 

3. Affects males more than females

 

B. Genetics/etiology—No data yet.

 

C. Clinical presentation

 

1. Slow-growing, painless mass (4 to 8 cm) most commonly noted around the thigh or knee

 

[

Figure 7. Fibrosarcomas. A, Gross appearance of a fibrosarcoma within the muscles of the anterior thigh. There are areas of hemorrhage and cyst formation. B, High-power view of a fibrosarcoma reveals the distinct fascicular appearance of cells with little variation in size or shape. When the cells are cut in cross section, they appear round. The overall appearance is a herringbone pattern of spindle cells.]

2. Ulceration of the skin in superficial lesions

 

D. Imaging appearance (indeterminate)—Low intensity on T1-weighted MRI; high intensity on T2-weighted MRI.

 

E. Pathology

 

1. Gross appearance (Figure 7, A)

 

2. Histology

 

a. Uniform fasciculated growth pattern (herringbone) (Figure 7, B)

 

b. Spindle cells with minimal cytoplasm

 

c. Collagen fibers commonly aligned in parallel throughout tumor

 

d. Mitotic activity varies

 

F. Treatment/outcome

 

1. Wide surgical resection and radiation

 

2. Chemotherapy for selected patients

 

3. Metastasis in ~50% of high-grade lesions



V. Synovial Sarcoma

A. Definition and demographics

 

1. Distinct lesion occurring in para-articular regions

 

2. Most common soft-tissue sarcoma in young adults

 

3. Occurs most commonly in patients 15 to 40 years of age

 

4. Affects males more than females

 

B. Genetics/etiology

 

1. Characteristic translocation (X;18)

 

2. Represents the fusion of SYT with either SSX1 or SSX2

 

C. Clinical presentation

 

1. Slow-growing soft-tissue mass (3 to 5 cm)

 

2. Sometimes 2 to 4 years before a correct diagnosis

 

3. Pain in 50% of patients; some have history of trauma

 

4. Most commonly occur in para-articular regions around the knee, shoulder, arm, elbow, and foot (lower extremity in 60%)

 

5. Can arise from tendon sheaths, bursa, fascia, and joint capsule, but only rarely involves a joint (

Figure 8, A and B)

 

D. Imaging appearance

 

1. Calcification noted on plain radiographs in 15% to 20% of synovial sarcomas

 

2. MRI appearance indeterminate: low intensity on T1-weighted images; high intensity on T2-weighted images (Figure 8, A and B)

 

E. Pathology

 

1. Classically occurs as biphasic type, with epithelial cells forming glandlike structures alternating with elongated spindle cells (Figure 8, C)

 

2. Epithelial cells are large and round with distinct cell borders and pale cytoplasm.

 

3. Epithelial cells are arranged in nests or chords and stain positive with keratin.

 

[Figure 8. Synovial sarcomas. Axial T1-weighted (A) and T2-weighted (B) MRI scans of the wrist reveal a small soft-tissue mass associated with the flexor carpi radialis tendon sheath (arrow). It is indeterminate in appearance, and a biopsy revealed a synovial sarcoma. C, Histology of a biphasic synovial sarcoma showing the typical pattern of epithelial cells and fibrosarcoma-like spindle cells. D,Monophasic synovial sarcoma variant showing only spindle cells (would be keratin positive).]

4. Fibrous component involves plump, malignant spindle cells with minimal cytoplasm and dark nuclei; mast cells are common in fibrous sections.

 

5. Calcification more common at periphery

 

6. Variable vascularity

 

7. Less commonly, a monophasic histology is seen (either fibrous or epithelial) (Figure 8, D).

 

F. Treatment/outcome

 

1. Wide resection and radiation

 

2. Chemotherapy used more commonly; younger patients tolerate it better.

 

3. Lymph node metastasis occurs in 20% of patients; can stage with sentinel node biopsy.

 

4. 5-year survival = 50%, 10-year survival = 25% (better in heavily calcified lesions)



VI. Epithelioid Sarcoma

A. Definition and demographics

 

1. Distinct soft-tissue sarcoma occurring in young adults that is often mistaken for a benign granulomatous process

 

2. Occurs in adolescents and young adults (10 to 35 years)

 

3. Male to female ratio = 2:1

 

B. Genetics/etiology—No data yet.

 

C. Clinical presentation

 

1. Small, slow-growing soft-tissue tumor that can be superficial or deep

 

2. Frequently involves hand, forearm, fingers; 3 to 6 cm in size (

Figure 9, A)

 

[Figure 9. Epithelioid sarcoma. A, Clinical photograph of an epithelioid sarcoma in the dorsal aspect of the distal long finger. Note the nodule in the superficial tissues. B, Low-power histology reveals a nodule with central necrosis consistent with an epithelioid sarcoma but often mistaken for a benign granulomatous process.]

3. Most common soft-tissue sarcoma in the hand/wrist

 

4. Occurs as firm, painless nodule(s); may ulcerate when superficial

 

5. When deep, attached to tendons, tendon sheaths, or fascia

 

6. Confused with granuloma, rheumatoid nodule, or skin cancer, often resulting in delay in diagnosis or inappropriate treatment

 

D. Imaging appearance

 

1. Occasional calcification within lesion

 

2. Can erode adjacent bone

 

3. MRI reveals nodule along tendon sheaths of upper or lower extremity.

 

a. Low intensity on T1-weighted images; high intensity on T2-weighted images

 

b. Indeterminate in appearance; requires biopsy

 

E. Pathology

 

1. Low-power histology reveals a nodular pattern with central necrosis within granulomatous areas (Figure 9, B).

 

2. Higher power reveals an epithelial appearance with eosinophilic cytoplasm.

 

3. Minimal cellular pleomorphism

 

4. Intercellular deposition of dense hyalinized collagen

 

5. Calcification/ossification in 10% to 20% of patients

 

6. Cells are keratin positive

 

F. Treatment/outcome

 

1. Wide surgical resection with adjuvant radiation if necessary

 

2. Regional lymph node metastasis is common. Sentinel node biopsy may be indicated.

 

3. Often mistaken for a benign lesion and inadequately excised, leading to high rate of multiple recurrences

 

4. Amputation is frequently necessary to halt spread of disease.

 

5. Late regional or systemic metastasis to lungs is common.

 

6. Overall, extremely poor prognosis



VII. Clear Cell Sarcoma

A. Definition and demographics

 

1. Rare soft-tissue sarcoma that has the ability to produce melanin

 

2. Occurs in young adults (age 20 to 40 years)

 

3. Affects females more than males

 

4. Often called "malignant melanoma of soft parts"

 

B. Genetics/etiology

 

1. Frequent translocation of chromosomes 12 and 22 (not seen in malignant melanoma)

 

2. Etiology thought to be neuroectodermal

 

C. Clinical presentation

 

1. Occurs in deep tissues associated with tendons, aponeuroses

 

[

Figure 10. Clear cell sarcoma. A, STIR sequence of the left foot reveals a soft-tissue lesion abutting the medial calcaneous. Additional views revealed involvement of the neurovascular bundle. B, Histology shows fibrous septa separating the tumor into well-defined fascicles of cells with clear cytoplasm consistent with a clear cell sarcoma.]

2. Most common soft-tissue sarcoma of the foot; also occurs in ankle, knee, and hand

 

3. 2 to 6 cm in size

 

4. Slow-growing mass; pain in 50% of patients and present for many years prior to diagnosis

 

5. Often mistaken for a benign lesion and inadequately excised

 

D. Imaging appearance

 

1. Nonspecific appearance; may be nodular in foot

 

2. MRI: indeterminate; requires a biopsy. Low intensity on T1-weighted images; high intensity on T2-weighted images (Figure 10, A)

 

E. Pathology

 

1. Grossly, no connection to overlying skin, but may be attached to tendons

 

2. Histology shows nests of round cells with clear cytoplasm (Figure 10, B)

 

3. Uniform pattern of cells with a defined fibrous border that might be continuous with surrounding tendons or aponeuroses

 

4. Occasional multinucleated giant cells but rare mitotic figures

 

5. Intracellular melanin noted in 50% of patients with appropriate staining

 

F. Treatment/outcome

 

1. Wide surgical resection with adjuvant radiation

 

2. Local recurrence is common.

 

3. Frequent regional lymph node metastasis; consider sentinel lymph node biopsy

 

4. High rate of pulmonary metastasis with extremely poor prognosis

 

5. No effective chemotherapy



VIII. Rhabdomyosarcoma

A. Definition, demographics, and genetics

 

1. Soft-tissue sarcoma of primitive mesenchyme, occurring primarily in children

 

2. Most common soft-tissue sarcoma in children/adolescents (embryonal and alveolar types)

 

3. Embryonal type occurs in infants/children, alveolar in adolescents/young adults.

 

4. Affects males more than females

 

5. Histologic subtypes include embryonal (most common), alveolar, botryoid, and pleomorphic (affects adults 40 to 70 years of age)

 

6. In alveolar rhabdomyosarcoma, translocation between chromosome 2 and 13 is common.

 

B. Clinical presentation

 

1. Most lesions occur in head/neck, genitourinary, and retroperitoneal locations.

 

2. 15% occur in extremities (incidence equal in upper and lower)—forearm, thigh, foot, hand.

 

3. Often rapidly enlarging, deep, painless soft-tissue masses

 

4. Staging should include bone marrow biopsy.

 

C. Imaging appearance (indeterminate): low intensity on T1-weighted MRI; high intensity on T2-weighted MRI

 

D. Pathology

 

1. Immunohistochemical markers for rhabdomyosarcoma: desmin, myoglobin, MyoD1

 

2. Embryonal—Composed of small round cells that resemble normal skeletal muscle in various stages of development, with cross striations visible in 50% of patients.

 

a. Alternating dense hypercellular areas with loose myxoid areas (

Figure 11, A)

 

b. Mixture of undifferentiated, hyperchromatic cells and differentiated cells with eosinophilic cytoplasm

 

c. Matrix with minimal collagen and more prominent myxoid material

 

3. Alveolar—Aggregates of poorly differentiated round tumor cells and irregular alveolar spaces.

 

[Figure 11. Rhabdomyosarcomas. A, Histology of embryonal rhabdomyosarcoma shows undifferentiated small round cells in addition to rhabdomyoblasts in various stages of differentiation. B, Histology of alveolar rhabdomyosarcoma shows aggregates of small round tumor cells separated by fibrous septa.]

a. Cellular aggregates surrounded by dense, hyalinized fibrous septa arranged around dilated vascular spaces (Figure 11, B)

 

b. Multinucleated giant cells prominent

 

4. Pleomorphic—Loosely arranged polygonal tumor cells with eosinophilic cytoplasm.

 

a. Difficult to differentiate from other pleomorphic sarcomas

 

b. Requires either cells with cross striations or positive staining for desmin and myoglobin

 

E. Treatment/outcome

 

1. Treatment is wide surgical resection and chemotherapy.

 

2. For unresectable lesions or tumors with positive margins after surgery, radiation is indicated.

 

3. Common chemotherapy agents include vincristine, dactinomycin, cyclophosphamide.

 

4. Regional lymph node metastasis is common. May consider sentinel lymph node biopsy.

 

5. Tendency to metastasize to the bone marrow

 

6. 5-year survival of embryonal form is 80%, alveolar 60%

 

7. For pleomorphic variant in adults, treatment is wide resection and radiation. Chemotherapy is not effective—5-year survival of 25%.



IX. Malignant Peripheral Nerve Sheath Tumor

A. Definition and demographics

 

1. Malignant peripheral nerve sheath tumor (MPNST), or neurofibrosarcoma, is a sarcoma arising from a peripheral nerve or neurofibroma.

 

2. MPNSTs that arise from solitary neurofibromas occur in patients 30 to 55 years of age.

 

3. MPNSTs that arise in setting of neurofibromatosis type 1 (NF1) occur in patients 20 to 40 years of age

 

4. Affects males more than females in NF1 patients; male to female ratio = 1 in sporadic cases

 

B. Genetics/etiology

 

1. Most cases (50%) associated with NF1

 

2. Patients with NF1 have ~5% risk of malignant transformation (latent period of 10 to 20 years).

 

C. Clinical presentation

 

1. Slow or rapid enlargement of a long-standing benign soft-tissue mass

 

2. Pain is variable but more common in patients with NF1.

 

3. Most arise from large nerves (sciatic, sacral roots, brachial plexus) (5 to 8 cm in size).

 

D. Imaging appearance

 

1. Indeterminate MRI appearance: low intensity on T1-weighted images; high intensity on T2-weighted images (

Figure 12, A and B)

 

2. Fusiform appearance; eccentrically located within a major nerve

 

3. Serial MRI scans documenting enlargement of a previously documented benign nerve sheath tumor suggest malignant degeneration.

 

E. Pathology

 

1. Spindle cells closely resemble fibrosarcoma; pattern is sweeping fascicles (Figure 12, C).

 

2. Histology reflects Schwann cell differentiation; cells arranged asymmetrically

 

[Figure 12. Malignant peripheral nerve sheath tumor arising from a solitary neurofibroma. Coronal T1-weighted (A) and axial T2-weighted (B) images of the left neck area. The tumor (arrows) is indeterminate in appearance but involves the brachial plexus, causing decreased motor function of the left arm. C, Histology is similar to a fibrosarcoma, with spindle cells arranged in long fascicles. The nuclei, however, are wavy or comma-shaped in appearance, which is unique to MPNSTs.]

3. Spindle cells have wavy nuclei.

 

4. Dense cellular areas alternate with myxoid areas.

 

5. Mature islands of cartilage, bone, or muscle present in 10% to 15% of lesions.

 

6. Staining for S100 is positive in most tumors but usually focal.

 

7. Keratin staining is negative.

 

F. Treatment/outcome

 

1. Wide surgical resection (requires nerve resection)

 

2. Adjuvant radiation preoperatively (or postoperatively, especially if margins are close)

 

3. Chemotherapy has not been effective.

 

4. 5-year survival for MPNST in a solitary lesion is 75%; 5-year survival in a patient with NF1 is 30%.



Top Testing Facts

1. Soft-tissue sarcomas are usually categorized as indeterminate lesions on MRI (low intensity on T1-weighted images and high intensity on T2-weighted images) and require a biopsy for definitive diagnosis.

 

2. Liposarcomas (other than low-grade well-differentiated subtypes) do not have any resemblance to fat on MRI studies.

 

3. Myxoid liposarcoma has a classic 12;16 chromosomal translocation.

 

4. Synovial sarcoma has a classic X;18 chromosomal translocation.

 

5. Epithelioid sarcoma is the most common soft-tissue sarcoma found in the hand/wrist.

 

6. Common sarcomas that metastasize to regional lymph nodes include rhabdomyosarcoma, synovial sarcoma, clear cell sarcoma, and epithelioid sarcoma.

 

7. Chemotherapy has not been shown to have a proven benefit in the treatment of most soft-tissue sarcomas (exceptions from this chapter include rhabdomyosarcoma and synovial sarcoma).

 

8. Patients with a history of NF1 have a 5% chance of malignant degeneration of a neurofibroma to an MPNST.

 

9. Most high-grade soft-tissue sarcomas are treated with radiation and wide surgical resection.

 

10. Compared with postoperative radiation, preoperative radiation allows a lower dose, but wound complications are increased.



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