Campbell-Walsh Urology, 11th Edition


Neoplasms of the Upper Urinary Tract


Benign Renal Tumors

Vitaly Margulis; Jose A. Karam; Surena F. Matin; Christopher G. Wood


  1. The most accurate imaging study to characterize a renal mass is:
  2. intravenous pyelography.
  3. ultrasonography.
  4. computed tomography (CT) with and without contrast enhancement.
  5. magnetic resonance imaging (MRI).
  6. renal arteriography.
  7. A hyperdense renal cyst may also be termed a:
  8. probable malignancy.
  9. Bosniak II cyst.
  10. Bosniak III cyst.
  11. Bosniak IV cyst.
  12. probable angiomyolipoma.
  13. The primary indication for fine-needle aspiration of a renal mass is which suspected clinical diagnosis?
  14. Renal cell carcinoma
  15. Renal oncocytoma
  16. Renal adenoma
  17. Renal metastasis
  18. Renal angiomyolipoma
  19. All of the following statements are TRUE about renal cysts EXCEPT:
  20. They are the most common benign renal lesions found in the kidney.
  21. They are best characterized using the Bosniak criteria to assess risk that the patient harbors a malignancy.
  22. They are best imaged using ultrasound to allow classification with the Bosniak criteria.
  23. They can harbor internal septa, calcifications, and internal debris and still be considered benign according to the Bosniak classification.
  24. They rarely require treatment.
  25. Which of the following is TRUE about renal adenoma?
  26. There is uniform agreement regarding the clinical and pathologic classification of renal adenoma.
  27. Recent studies suggest that renal adenoma may be a premalignant precursor of papillary renal cell carcinoma (RCC).
  28. They are most common in young females.
  29. They can be high grade or low grade, as long as they are smaller than 3 cm.
  30. They are usually of clear cell histology but can also be found with chromophobe and papillary cells.
  31. A diagnosis of renal adenoma:
  32. can be made primarily on the basis of histologic criteria.
  33. can be rendered only if tumor is smaller than 1 cm.
  34. is commonly made at autopsy.
  35. requires specific immunohistochemical staining.
  36. can be confirmed by electron microscopy.
  37. A healthy 62-year-old man is scheduled to undergo surgery for a 3.0-cm enhancing renal mass; CT shows it to be interpolar, exophytic, and with a central stellate scar. Which of the following best describes the most appropriate surgical strategy?
  38. A radical nephrectomy with adrenalectomy
  39. A radical nephrectomy without adrenalectomy
  40. Renal exploration with biopsy and intraoperative frozen section analysis determining radical versus partial nephrectomy
  41. Renal exploration and partial nephrectomy with intraoperative frozen section analysis of histology (if malignant, a radical nephrectomy)
  42. Partial nephrectomy
  43. A 48-year-old woman with a history of seizure disorder presents with recurrent gross hematuria and left flank pain. Abdominal CT shows a large left perinephric hematoma associated with a 3.0-cm left renal angiomyolipoma. There are also multiple right renal angiomyolipomas ranging in size from 1.5 to 6.5 cm. The next best step in management of the left renal lesion is:
  44. selective embolization.
  45. radical nephrectomy.
  46. observation.
  47. partial nephrectomy.
  48. laparoscopic exposure and renal cryoablation.
  49. Which of the following statements is TRUE regarding multiloculated cystic nephromas?
  50. They are complex cystic lesions that are typically classified as Bosniak II.
  51. They are malignant 2% to 5% of the time.
  52. They are more common in men than in women.
  53. They are characterized by bimodal age distribution.
  54. They are readily differentiated from RCC on the basis of appropriate imaging studies.
  55. Metanephric adenoma is differentiated from RCC based on all the following features EXCEPT:
  56. female predominance.
  57. benign clinical course.
  58. specific pattern on immunostain marker panel.
  59. characteristic appearance on MRI.
  60. peak incidence in the fifth decade of life.
  61. Which of the following would be considered diagnostic for renal angiomyolipoma?
  62. Hyperechoic pattern on ultrasonography
  63. Enhancement of more than 30 Hounsfield units (HU) on CT
  64. Small area of less than − 20 HU on nonenhanced CT
  65. Aneurysmal changes on renal arteriogram
  66. Positive signal on T2-weighted images of MRI
  67. Which of the following features is typically required for the diagnosis of renal adenoma in a clinical setting?
  68. Tumor size smaller than 3 cm
  69. Low to moderate grade
  70. Papillary architecture
  71. Nonconventional histology
  72. Noncentral location
  73. Which of the following tumors is most likely to be a malignant RCC?
  74. A 2.5-cm hyperechoic complex cyst, with no enhancement after intravenous administration of a contrast agent
  75. A 6.0-cm complex cyst with four thin septa
  76. A 5.0-cm cyst with thin, curvilinear calcification
  77. An 11-cm cyst with water density and a homogeneous nature
  78. A 3.0-cm tumor with fat associated with calcification
  79. A reliable finding for the diagnosis of renal oncocytoma is:
  80. trisomy of chromosomes 7 and 17.
  81. a central, stellate scar on CT.
  82. a spoke-wheel pattern on renal angiography.
  83. multiple mitochondria on electron microscopy.
  84. a hypervascular pattern.
  85. A distinctive finding for renal angiomyolipoma is:
  86. positive staining for vimentin.
  87. a unique cytokeratin expression pattern.
  88. positive staining for human melanoma black-45.
  89. multiple microsomes on electron microscopy.
  90. occasional aneuploidy.
  91. All of the following statements accurately describe mixed epithelial and stromal tumors of the kidney EXCEPT:
  92. There is a female predilection.
  93. They are associated with estrogen replacement therapy in women or with androgen ablation therapy in men.
  94. Radiologic diagnostic criteria exist for reliable differentiation from RCC.
  95. Nephron sparing with partial nephrectomy when technically feasible is appropriate.
  96. A benign clinical course is expected.
  97. A 44-year-old man undergoes left laparoscopic partial nephrectomy for a 2-cm exophytic renal mass. Final pathologic review reveals intersecting fascicles of smooth muscle with no evidence of hypercellularity, pleomorphism, or mitotic activity. Surgical margins are negative. The next step in management is:
  98. complete radical nephrectomy.
  99. adjuvant chemotherapy.
  100. adjuvant targeted therapy.
  101. observation.
  102. retroperitoneal external-beam radiation therapy.


  1. A nephrectomy is performed in a 67-year-old man for a solid renal mass; the gross specimen is depicted in Figure 56-1Aand the microscopic findings are shown in Figure 56-1B. The pathology report states that this neoplasm has oncocytic features. The next step in management is:

FIGURE 56-1 (From Bostwick DG, Cheng L. Urologic surgical pathology. 2nd ed. Edinburgh: Mosby; 2008. A, Courtesy Philip Bomeisl, MD.)

  1. biopsy opposite kidney.
  2. ask the pathologist for a subclassification.
  3. no further follow-up required.
  4. chest CT scan.
  5. endocrine workup.
  6. A 35-year-old man has a renal mass incidentally discovered. He is asymptomatic and a left nephrectomy is planned. A biopsy is obtained and the pathologic findings are depicted in Figure 56-2and reported as metanephric adenoma. The next step in management is:

FIGURE 56-2 (From Bostwick DG, Cheng L. Urologic surgical pathology. 2nd ed. Edinburgh: Mosby; 2008.)

  1. proceed with nephrectomy.
  2. perform a partial nephrectomy.
  3. stain for Wilms tumor marker WT1.
  4. observation.
  5. obtain a chest CT scan.


  1. See Figure 56-3. A CT scan is obtained in a 23-year-old woman with hematuria. In this patient:


  1. selective renal embolization may be indicated in symptomatic lesions.
  2. there is an associated high risk for urothelial neoplasms.
  3. the renal lesions contain microscopic fat.
  4. the renal lesions commonly calcify.
  5. the renal lesions are premalignant.


  1. c. Computed tomography (CT) with and without contrast enhancement.A dedicated (thin-slice) renal CT scan remains the single most important radiographic image for delineating the nature of a renal mass. In general, any renal mass that enhances with administration of intravenous contrast material on CT should be considered a renal cell carcinoma (RCC) until proved otherwise.
  2. b. Bosniak II cyst.Category II lesions are minimally complicated cysts that are benign but have some radiologic findings that cause concern. Classic hyperdense renal cysts are small (< 3 cm), round, and sharply marginated and do not enhance after administration of contrast material.
  3. d. Renal metastasis.Fine-needle aspiration or biopsy is of limited value in the evaluation of renal masses. The major problem with this technique is the high incidence of false-negative findings in patients with renal malignancy. The primary indication for needle aspiration or biopsy of a renal mass occurs when a renal abscess or infected cyst is suspected or when differentiating RCC from metastatic malignancy or renal lymphoma.
  4. c. They are best imaged using ultrasound to allow classification with the Bosniak criteria.Contrast enhancement using imaging that utilizes contrast (CT, MRI) is critical to the Bosniak classification criteria.
  5. b. Recent studies suggest that renal adenoma may be a premalignant precursor of papillary renal cell carcinoma (RCC).Recent immunohistochemical studies suggest that renal adenomas are commonly associated with papillary RCC and may represent a premalignant precursor along a biologic continuum.
  6. c. Is commonly made at autopsy.Small, evidently benign, solid renal cortical lesions have been found at autopsy with an incidence of 7% to 23% and have been designated renal adenomas.
  7. e. Partial nephrectomy.Most renal oncocytomas cannot be differentiated from malignant RCCs on the basis of clinical or radiographic means, nor can they be reliably differentiated on frozen section at the time of surgery. Given these uncertainties about a diagnosis, and the excellent outcomes obtained with partial nephrectomy of either benign or malignant tumors, most authors have emphasized the need to treat these tumors with nephron-sparing surgery depending on the clinical circumstances.
  8. a. Selective embolization.Most patients with acute or potentially life-threatening hemorrhage will require total nephrectomy if exploration is done. If the patient has tuberous sclerosis, bilateral disease, preexisting renal insufficiency, or other medical or urologic disease that could affect renal function in the future, selective embolization should be considered. In such circumstances, selective embolization can temporize and in many cases will prove to be definitive treatment.
  9. d. They are characterized by bimodal age distribution.Multiloculated cystic nephroma is a characteristic renal lesion with a bimodal age distribution and a benign clinical course.
  10. d. Characteristic appearance on MRI.Metanephric adenoma is radiographically indistinguishable from RCC and is typically a diagnosis made postoperatively. All other answers are distinguishing features of metanephric adenoma.
  11. c. Small area of less than − 20 HU on nonenhanced CT.The presence of even a small focus of fat, as evidenced by less than − 20 HU on a nonenhanced CT scan, is diagnostic for angiomyolipoma. The findings described in a, b, and d are all suggestive, but not diagnostic, for renal angiomyolipoma.
  12. c. Papillary architecture.Most pathologists will not make the diagnosis of renal adenoma in a nonautopsy setting unless the lesion is low grade, small (< 1.0 cm), and of papillary architecture.
  13. e. A 3.0-cm tumor with fat associated with calcification. Tumors with calcification associated with fat are uncommon but are almost always malignant RCC.In this setting the fat is thought to be a reactive process related to tumor necrosis. Calcification is virtually never seen in association with angiomyolipoma. The lesions described in a to c are Bosniak II renal cysts, with risk of malignancy of less than 10%. The lesion described in d is a simple cyst and highly likely to be benign despite its large size.
  14. d. Multiple mitochondria on electron microscopy.A distinctive and diagnostic feature of renal oncocytoma is the presence of multiple mitochondria on electron microscopy. Suggestive radiographic findings including a central stellate scar on CT or spoke-wheel pattern on renal angiography have been described but can be seen with RCC and are absent in many oncocytomas. Trisomy of chromosomes 7 and 17 is found in papillary RCC, not renal oncocytoma.
  15. c. Positive staining for human melanoma black (HMB)-45.Angiomyolipoma will stain positive for HMB-45 in most cases, and this can be used to confirm the diagnosis in challenging cases. This antigen, which was originally found in association with melanoma, is expressed by most angiomyolipomas.
  16. c. Radiologic diagnostic criteria exist for reliable differentiation from RCC. Conclusive differentiation of mixed epithelial/stromal tumor from RCC or cystic Wilms tumor is not possible based on current imaging modalities.The other answers are characteristic for mixed epithelial/stromal tumors.
  17. d. Observation.Pathologic diagnosis is of renal leiomyoma with a benign clinical course. Observation is appropriate.


  1. b. Ask the pathologist for a subclassification.Both oncocytoma and chromophobe RCC have oncocytic features. Notice the central scar on the gross specimen and the eosinophilic cytoplasm, and also the low mitotic activity on the photomicrograph. These are the hallmarks of oncocytoma. The pathology report should state with clarity what it is because the management for the two is very different.
  2. b. Perform a partial nephrectomy.Metanephric adenoma is benign and may stain positive for the Wilms tumor marker WT1. Notice the uniformity of the cells, scant cytoplasm, and no nuclear mitotic activity. The three elements of a Wilms tumor are not present.


  1. a. Selective renal embolization may be indicated in symptomatic lesions.The CT scan demonstrates multiple bilateral low-attenuation lesions. The attenuation of the majority of the lesions is similar to the low density of retroperitoneal fat and lower than the fluid in the gallbladder. This indicates that the lesions are composed of macroscopic fat and represent angiomyolipomas. There are also large cysts in the left kidney. Calcification in angiomyolipomas is unusual, and bilateral angiomyolipomas are often seen in patients with tuberous sclerosis. There is no association with urothelial neoplasms. Angiomyolipomas that are larger than 4 cm have a propensity to bleed spontaneously, and angiographically directed selective embolization of such lesions is indicated when they are symptomatic. Microscopic fat is not visible on CT.

Chapter review

  1. Loss of PKD1 and PKD2 leads to cyst formation.
  2. Simple renal cysts increase in both size and number with time. The risk factors for development of cysts include age, male gender, hypertension, and renal insufficiency.
  3. There is a higher incidence of RCC in acquired renal cystic disease. These patients also have a higher incidence of papillary adenomas. Papillary adenomas may be linked to the development of papillary renal cell carcinoma.
  4. The diagnosis of oncocytoma may be made on biopsy with reasonable assurance if the features are classic; however, on occasion it may be difficult to differentiate an RCC with oncocytic features from an oncocytoma. Under these circumstances, the lesion should be treated as though it were an RCC.
  5. Oncocytomas are derived from distal renal tubule cells. Chromophobe RCCs also originate from distal renal tubule cells.
  6. Angiomyolipomas may be difficult to differentiate from RCCs when they are lipid poor and appear more solid on CT.
  7. Multiloculated cystic nephroma is a characteristic renal lesion with a bimodal age distribution and a benign clinical course.
  8. Tumors with calcification associated with fat are uncommon but are almost always malignant RCC. In this setting the fat is thought to be a reactive process related to tumor necrosis. Calcification is virtually never seen in association with angiomyolipoma.
  9. A distinctive and diagnostic feature of renal oncocytoma is the presence of multiple mitochondria on electron microscopy.