Renal inflammatory myofibroblastic tumour presenting with a large retroperitoneal abscess

Inflammatory myofibroblastic tumour arising from the kidney is a rare occurrence. In this case report, we present a rare case of inflammatory myofibroblastic tumour arising from the kidney diagnosed after the presentation with a large retroperitoneal abscess for the first time in literature. A 55-year-old woman with diabetes mellitus presented to us with painful lump in the left lumbar region of the back for 1-week duration. On examination, there was a firm, diffuse lump in the left lumbar region of the back. Her inflammatory markers were high, but the serum creatinine and blood urea were within the normal range. Abdominal ultrasonography showed a distorted left kidney with a heterogeneous mass consisting cystic and solid components measuring approximately 7 × 9 × 8 cm in size. A contrast-enhanced computed tomography scan showed an 11 × 9 × 9 cm-sized low-density mass posterior to the left kidney with multiple contrast-enhancing septations which appeared posterior to but separate from the left kidney within the left renal fascia. There was breeching of the Gerota's fascia with extension posteriorly up to subcutaneous tissue. Since the radiological opinion was in favour of a complex perinephric abscess, open drainage of the abscess was performed after failed attempts of ultrasound-guided drainage. The biopsy of the abscess wall was suggestive of a renal cell carcinoma and radical nephrectomy was planned. Due to tumour invasion, the radical nephrectomy was combined with a splenectomy and the specimen sent for histology. It showed an inflammatory myofibroblastic tumour or pseudotumour with the periphery showing ulceration and abscess formation. The patient had an uneventful recovery following surgery. Thus, we report the first case of renal inflammatory myofibroblastic tumour presenting with a large retroperitoneal abscess extending to the subcutaneous tissue plane. Final diagnosis was made only after radical surgery which was curative.