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Medical Science Monitor Basic Research


An Incidental Diagnosis of Microscopic Renal Angiomyolipoma Completely Excised on Renal Biopsy: A Case Report

Challenging differential diagnosis, Rare disease

Toshiki Hyodo, Keiji Kono, Shinichi Nishi, Tomoo Itoh, Shigeo Hara

Japan Department of Diagnostic Pathology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan

Am J Case Rep 2020; 21:e921353

DOI: 10.12659/AJCR.921353

Available online: 2020-01-30

Published: 2020-03-15


BACKGROUND: Microscopic tumor foci have been detected incidentally on renal biopsy, including renal cell carcinoma and renomedullary interstitial cell tumor (medullary fibroma). A report is presented of a case of an incidental finding of microscopic renal angiomyolipoma that was diagnosed and completely excised on core needle biopsy.
CASE REPORT: A 44-year-old woman was referred to our hospital for evaluation of persistent mild proteinuria. Three years previously, she was diagnosed with Cushing’s syndrome associated with a right adrenal cortical adenoma, which was successfully treated with unilateral adrenalectomy. At the time of surgery, abdominal computed tomography (CT) showed no renal lesions. During the present admission, a renal biopsy was performed that showed minimal changes in the renal glomeruli and interstitium. Immunofluorescence showed weakly positive staining for IgM in the glomeruli and no dense deposits. A microscopic focus of a predominantly spindle-cell tumor was found in the corticomedullary region. Immunohistochemistry showed positive immunostaining for HMB-45, Melan-A, and alpha-smooth muscle actin (ASMA), which supported a diagnosis of angiomyolipoma. Abdominal ultrasound at one-year follow-up showed no evidence of residual renal tumor.
CONCLUSIONS: To our knowledge, this is the first reported case of a completely excised incidental microscopic renal angiomyolipoma. This case demonstrated that even when imaging findings are normal, renal biopsy may detect microscopic foci of primary renal tumors.

Keywords: Angiomyolipoma, Kidney Neoplasms, MART-1 Antigen