Long-standing Renal Hydatid Cyst Mimicking an Angiomyolipoma: A Rare Case Report

Primary hydatid cyst of the kidney is very rare and accounts for 1-4% of all hydatid disease. Authors hereby reports an unusual case of an isolated, long-standing renal hydatid cyst, mimicking an angiomyolipoma on imaging. A 72-year-old female, from a rural area, presented with pain in the right flank since two years. She also complained of mild fever off and on, since one year. A 10x10 cm, non tender lump was palpated in the right flank. Ultrasonography and computerised tomography showed a large right-sided renal mass measuring 10 cms and a diagnosis of angiomyolipoma was rendered. A right sided open/simple nephrectomy was done. The kidney was large, cystic, firm and was sent for histopathological examination. On gross examination, a large, unilocular, thick- walled, cystic lesion was seen. Cut-surface showed heterogeneous, creamy coloured necrotic contents, with few nodular gelatinous masses. On microscopy, characteristic acellular, laminated structure of the ectocyst of Echinococcus granulosus was seen. Extensive calcification and ossification of the cyst wall with bone marrow production was also seen. Contents of the cyst were necrotic and no daughter cysts were seen. Adipose tissue of the bone marrow was mistaken on imaging for the lipomatous component of an angiomyolipoma. Isolated renal hydatid cyst is very uncommon and though active hydatid cysts do have characteristic radiological findings, they can be misdiagnosed as a benign renal tumours. Renal cysts or abscesses. Old cases show degenerative changes as well as calcification and are difficult to diagnose preoperatively. Surgical treatment of renal hydatid cyst depends on the size, number of cysts, exact intrarenal location and residual renal function.