Benign renal schwannoma: a rare entity.

To cite: Yong A, Kanodia AK, Alizadeh Y, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/bcr-2015211642 DESCRIPTION We present a case of a 55-year-old woman who presented with colicky pain on the right side of her abdomen. She had microscopic haematuria while urine cultures were negative. She had no other concomitant gynaecological or gastrointestinal symptoms. An ultrasound revealed normal kidneys apart from a prominent right renal pelvis even on postmicturition images. Non-contrast CT demonstrated a soft tissue density lesion adjoining the right renal pelvis (figure 1). The ureter was not obstructed and passed anterior to this structure. A CT urogram demonstrated mildly enhancing lobulated mass measuring approximately 5.1×4.7×2.4 cm, located outside the renal collecting system (figure 1). The right renal parenchyma was normal and the renal pelvis was draped around the lesion, without intrinsic filling defects. There was no dilation of the right ureter although there was mild dilation of the right renal pelvis. The mass was not visualised on ureteroscopy. An MRI revealed similar appearances to the CT urogram, without additional information (figure 2). Based on imaging findings, possibility of transitional cell carcinoma was thought to be unlikely. A CT-guided biopsy was performed, which resulted in sudden deterioration and dramatic drop in the patient’s blood pressure, which stabilised on intravenous fluid resuscitation. The postbiopsy CT examination revealed a large perirenal posterior retroperitoneal haematoma without any active extravasation. On histopathology, the tumour comprised of spindled cells with elongated hyperchromatic nuclei arranged in hypocellular and hypercellular zones (figure 3). Verocay bodies were noted. There was no necrosis and no evidence of mitotic activity. Immunohistochemically, the neoplasm showed positivity with S100 (figure 3). CD117 showed weak predominantly cytoplasmic