OA17 An unusual cause of unilateral retroperitoneal fibrosis

Abstract Background/Aims Retroperitoneal fibrosis (RPF) is a rare condition, with an incidence of around 1 per 200,000 to 500,000 per year. It is distinguished by fibro-inflammatory changes in the retroperitoneum, which typically surrounds the abdominal aorta. Idiopathic RPF is common, whilst secondary causes can result from drug therapies, infection, malignancy, or surgery. Early symptoms include dull, poorly-localised back or flank pain, and lower limb swelling. The classical focal mass of primary retroperitoneal fibrosis is typically situated over the distal aorta, anterior to the L4 and L5 vertebra. External compression of the ureter can result in hydronephrosis due to prevention of normal ureteric urinary peristalsis. Management options are limited, generally involving immunosuppression and urological surgery, often necessitating cross-specialty, multidisciplinary input. Methods We report the case of a young gentleman with no past medical or family history who presented with abdominal pain, vomiting, septic shock and metabolic acidosis. To exclude acute abdominal pathology, computed tomography (CT) abdomen and pelvis was performed. Incidentally, this found chronic inflammatory changes in the descending colon and right retroperitoneal soft tissue thickening causing severe right hydroureteronephrosis. This incidental finding of retroperitoneal fibrosis on CT scan prompted an exploration into infective, inflammatory, and malignant aetiological causes of retroperitoneal fibrosis. Results Following initial stabilisation, urological opinion was sought, which concluded that surgical intervention for ureteric stenting was unnecessary. This decision was supported by the absence of obstruction from fibrosis and the lack of signs indicating infection. No medical explanation was found for the initial presentation in extremis. Rheumatological advice was sought for consideration of biopsy and immunosuppressive therapy for this suspected primary retroperitoneal fibrosis. Upon inquiry, the patient divulged a historical occurrence of retroperitoneal fluid accumulation secondary to a paravertebral mass that mandated laparoscopic drainage four years ago overseas. Histopathological analysis of the mass confirmed the presence of tuberculosis (TB), which was treated. His recovery was complicated at that time by right-sided hydronephrosis and fibrosis necessitating decompression. This sequence of events was deemed by a radiologist to also account for the observed bowel findings in the right flank. Conclusion This case report is the first of its kind to document TB, or any infective aetiology, as being the primary cause of unilateral retroperitoneal fibrosis. Unilateral retroperitoneal fibrosis is incredibly rare, and there are only four English language case reports in the literature. Idiopathic RPF typically presents as bilateral concentric tissue around the abdominal aorta, whilst secondary causes can lead to unconventional imaging patterns, as seen in this case. It was only upon direct inquiry that the patient disclosed a prior diagnosis of TB affecting the lumbar spine. This case highlights the importance of meticulous history taking and systematic exclusion of secondary causes of RPF, prior to contemplating invasive biopsies and steroid therapy. Disclosure D. Li: None. M. Renju: None.