Anastomosing hemangioma of the genitourinary tract: a lesion mimicking angiosarcoma.

BACKGROUND: We describe 6 cases of a poorly recognized vascular neoplasm that can simulate angiosarcoma.
DESIGN: Cases of a rare vascular tumor with a proclivity for the genitourinary tract encountered in our consultation material were prospectively collected between the year 1999 and 2008. Follow-up information was obtained when possible.
RESULTS: There were 6 tumors from 4 men (66%) and 2 women, ranging in age from 49 to 75 years (median, 59.5) involving the kidney and renal hilum (4, 66%) and testis (2). Tumors ranged from 1.3 to 1.7 cm (median, 1.6 cm) and were grossly well-marginated with a hemorrhagic mahogany spongy appearance. Microscopically, at low power they had a loosely lobulated architecture and were associated with a medium-caliber vessel (5/6, 83%). Most kidney (3/4, 75%) tumors showed minor extensions into adjacent adipose tissue. At higher magnification, the tumors consisted of anastomosing sinusoidal capillary-sized vessels with scattered hobnail endothelial cells within a framework of nonendothelial supporting cells. There was a minimal inflammatory backdrop consisting of lymphocytes but not plasma cells or acute inflammation. Mitoses were absent (5/6, 83%) or rare (1 case; in supporting cells). There was mild cytologic atypia in one of the cases but no multilayering of endothelial cells in any case. Vascular thrombi were typical (5/6, 83%) and the lesions had zones of central sclerosis with focal necrosis (5/6, 83%). Two (33%) tumors featured prominent extra-medullary hematopoiesis and 2 tumors (33%) had striking hyaline globules reminiscent of those seen in Kaposi's sarcoma. Immunohistochemistry was available on some cases and the lesions stained with CD34, CD31, and FVIII but not human herpes virus type 8, keratin AE1/3, epithelial membrane antigen, HMB45, placental alkaline phosphatase, or human chorionic gonadotropin. In all but one submitted consultation, the possibility of angiosarcoma had been raised based on the anastomosing vascular pattern. On follow-up, there were no recurrences or metastases in 5 cases (range: 8 to 36 mo; median 12 mo, mean 15 mo), and 1 patient was lost to follow-up.
CONCLUSIONS: Anastomosing hemangioma of the genitourinary tract is a rare neoplasm displaying some overlapping features of both sinusoidal hemangioma and hobnail hemangioma of soft tissue and skin. However, in our opinion, it is a unique neoplasm with a proclivity for the kidney. Its anastomosing appearance can lead to concern for angiosarcoma but, despite small numbers and limited follow-up in our series, evidence to date supports that the lesion is benign.