Comment The differential diagnosis includes ruptured renal cell carcinoma, ruptured cyst, and arteriovenous malformation. Fluid resuscitation with 2 units of packed RBCs and crystalloid solution clinically stabilized her condition. Exploratory laparotomy and left nephrectomy confirmed the diagnosis of ruptured left kidney tumor and perirenal hematoma. Grossly, the lower pole kidney tumor was large, cystic, hemorrhagic, and nonencapsulated but fairly well demarcated and circumscribed from the rest of the renal parenchyma. The 11 7.5 7-cm tumor showed partly necrotic, yellow-tan, soft and friable tissue, closely admixed with considerable blood, with trabeculated, granular, focally cavitated, and papillary cut inner surfaces. The lower pole and midzonal parenchyma appeared compressed by the tumor. The rest of the kidney, hilar structures, and resection margins were grossly unremarkable.

Microscopic examination revealed a typical angiomyolipoma (AML) exhibiting equal amounts of mature adipocytes and large focally aneurysmal blood vessels, and predominant benign spindle-shaped smooth muscle cells arranged in streams, fascicles, and whorls. Immunostains displayed positivity to vimentin, HMB45, MART-1, and actin. Negative results were noted with keratin, epithelial membrane antigen, CD34, S-100, estrogen receptor, and progesterone receptor.

The prevalence of AML is 1 case per 10,000 to 25,000 individuals. Renal AML may initially manifest as an acute retroperitoneal hemorrhage or symptoms of a flank mass. In approximately 105 patients reported in the literature with symptomatic renal AML not associated with tuberous sclerosis, 15 have presented with a clinical picture of shock from spontaneous rupture and massive retroperitoneal hemorrhage.¹ Moreover, when associated with aneurysmal blood vessel component, the probability of AML rupture is higher than that of small aneurysms within the lesion.

Ultrasonography and CT can provide clear evidence of lipomatous formation within the tumor, while in rare cases angiography can demonstrate the existence of multiple vascular tumor compartments. Although findings by ultrasound and CT scan are fairly specific for AML, histologic examination is still necessary for a final diagnosis.^1-5 AML almost invariably follows a benign clinical course despite the presence of histologic features that typically define malignancy, such as nuclear pleomorphism and mitosis. Moreover, approximately 20 cases of AML extending into the vena cava and 40 cases spreading to regional lymph nodes at the time of diagnosis have been reported. However, by specific criterion of malignancy, these are considered multicentric rather than metastatic AMLs.^1-5

The patient recovered well and no tumor recurrence or metastasis has been found on follow-up after 4 years.

1. Lee JD, Chang HC, Chu SH, et al. Massive retroperitoneal hemorrhage from spontaneous rupture of a renal angiomyolipoma during pregnancy: a case report. J Reprod Med. 1994;39:477-480.

2. Wolfe TR. Ruptured renal angiomyolipoma presenting as renal colic. Am J Emerg Med. 1998;16:658-661.

3. May M, Seehafer M, Helke C, et al. Angiomyolipoma of the kidneys as a rare cause of retroperitoneal hemorrhage: two case reports with tuberous sclerosis Bourneville-Pringle. Urologe A. 2003;42:693-701.

4. Yigit T, Yigitler C, Gulec B, et al. Acute abdomen due to spontaneous renal angiomyolipoma rupture. Prog Urol. 2004;14:207-209.

5. Chao CH, Lin CY. Concurrent hepatic and ruptured renal angiomyolipoma in tuberous sclerosis complex. Chnag Gung Med J. 2004;27:696-700.

Contributed by CESAR V. REYES, MD, Department of Pathology; ROMAN M. SMYK, MD, Department of Surgery; and JOEL N. SLUTSKY, MD, Department of Urology, Morris Hospital, Morris, Ill.