hematuria. In this patient:

FIGURE 56-3

a.selective renal embolization may be indicated in symptomatic lesions.

b.there is an associated high risk for urothelial neoplasms.

c.the renal lesions contain microscopic fat.

d.the renal lesions commonly calcify.

e.the renal lesions are premalignant.

Answers

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 lifethreatening 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.

.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.

.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.

.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.

.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.

.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.

.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.

.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.

.d. Observation. Pathologic diagnosis is of renal leiomyoma with a benign clinical course. Observation is appropriate.

Pathology

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.

Imaging

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.