EXPLANATION AND DIAGNOSIS: EPITHELIOID ANGIOMYOLIPOMA OF THE RETROPERITONEUM

CASE REPORT A 45-year-old Caucasian woman living in Brisbane, Australia, presented to her general practitioner with increased urinary frequency and urgency over a 6-month period, not associated with haematuria or pain. Physical examination was unremarkable. Serial urine dipsticks, microscopy and cultures were normal. Pelvic ultrasound examination revealed a solid mass abutting the inferolateral aspect of the right kidney measuring up to 75 mm. Computed tomography showed the tumour at a higher resolution, and demonstrated focal involvement of the renal capsule and subjacent cortex. The radiological differential diagnosis was primary renal carcinoma, oncocytoma or connective tissue tumour (Fig. 1). The mass was removed as part of a radical nephrectomy. The resection specimen showed the tumour in retroperitoneal fat, attached to the capsular surface of the kidney, and bulging into subjacent renal parenchyma (Fig. 2). It was not encapsulated. Figures 3 and 4 show the H&E microscopic findings at medium and high power. Figure 5 demonstrates positivity of one of a panel of immunohistochemical stains (HMB45). Other stains performed but not shown included CAM5.2, vimentin, epithelial membrane antigen (EMA), CD10, CD56, synaptophysin, S-100, cytokeratin 7, cytokeratin 20 and neuron specific enolase (NSE). None of these stained positively. The patient did not have a personal or family history of tuberous sclerosis. She remains well more than 12 months after the operation.