LAUSR

We present a rare case of sodium polystyrene sulfonate crystal-induced inflammatory pseudotumour, diagnosed incidentally in an asymptomatic patient, mimicking malignancy in an extra-intestinal site without evidence of previous intestinal integrity compromise. An asymptomatic 59-year-old lady with end-stage renal failure secondary to hypertensive nephrosclerosis, dyslipidaemia and gout was electively admitted for deceased donor renal transplantation. A computed tomography (CT) scan, performed for raised CA-125 found in a previous admission, demonstrated an indeterminate pre-sacral heterogeneous solid mass, without bony destruction or adenopathy (Fig. 1a). Colonoscopy was unremarkable and CT-guided biopsy returned negative for malignancy. After multidisciplinary discussion and informed consent, the patient underwent diagnostic laparotomy and excision of the pre-sacral mass. The rectum was mobilized and the tumour was excised without compromising bowel integrity. The resected mass showed abundant irregularly shaped crystals demonstrating “fish scale” appearance, surrounded by aggregates of macrophages and chronic inflammatory cells without evidence of malignancy (Fig. 1b) consistent with sodium polystyrene sulphonate crystal-induced inflammatory pseudotumour. Upon review of the patient’s history, she had only received two 3-day oral courses of sodium polystyrene sulphonate at 12 and 1 years prior to the current presentation. Regular surveillance CT scans showed evidence of recurrence 3 years post-surgery with plans for continued surveillance. Inflammatory pseudotumours are rare, heterogenous, non-neoplastic, fibro-inflammatory mass lesions [1]. Sodium polystyrene sulfonate, otherwise known as Resonium A or Kayexalate, is commonly used for the treatment of hyperkalaemia. Previously reported patients with sodium polystyrene sulfonate-induced inflammatory pseudotumours presented with abdominal pain or change in bowel habits [2–4]. Presence of extra-intestinal sodium polystyrene sulfonate crystals suggests compromised bowel integrity but our patient was asymptomatic, had a normal colonoscopy and no previous intestinal surgeries or perforations. The only other reported extra-intestinal sodium polystyrene sulfonate-induced inflammatory pseudotumours developed from a peri-hepatic abscess near a colostomy site [2]. In our patient, sodium polystyrene sulfonate crystals may have extruded into the retro-rectal site through asymptomatic micro-perforations, possibly contributed by sorbitol in the sodium polystyrene sulfonate formulations. Inflammatory pseudotumours may result from foreign bodies such as sodium polystyrene sulfonate crystals which trigger aggregations of inflammatory cells which form tumorous lesions that mimic malignancy [2]. While inflammatory pseudotumours may be attributed to other localized pathology or systemic inflammatory conditions, there was no evidence of such in our patient. Surgery may be required for the management of inflammatory pseudotumours and to exclude malignancy [1]. Recurrence post-surgery is rare * Quan Yao Ho [email protected]