Pseudotumoral schistosomiasis mimicking locally advanced rectal carcinoma: a case report

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Abstract Introduction and Importance: Pseudotumoral rectal schistosomiasis is a rare complication of chronic Schistosoma mansoni infection characterized by mass-forming granulomatous inflammation and fibrosis. It may closely mimic locally advanced rectal carcinoma clinically and radiologically, creating significant diagnostic difficulty in endemic regions. Case Presentation: A 50-year-old Ethiopian man presented with rectal bleeding, lower abdominal pain, urinary intermittency, and weight loss. Laboratory investigations revealed leukocytosis with marked eosinophilia, microcytic anemia, renal impairment, and normal carcinoembryonic antigen levels. Contrast-enhanced CT and MRI demonstrated long-segment rectal wall thickening with mesorectal invasion, lymphadenopathy, and bilateral distal ureteric encasement, suggestive of cT4b rectal carcinoma. Colonoscopy showed a circumferential ulcerated rectal mass with luminal narrowing. Initial biopsies were non-diagnostic, revealing necrotic and inflammatory tissue only. Repeat deep biopsies demonstrated eosinophil-rich granulomatous inflammation with calcified Schistosoma ova and no malignancy, confirming pseudotumoral schistosomiasis. The patient developed obstructive uropathy with acute kidney injury requiring percutaneous nephrostomy and ureteric stenting and was treated with praziquantel with partial recovery. Clinical Discussion: This case highlights the diagnostic difficulty of pseudotumoral schistosomiasis due to its close resemblance to colorectal malignancy. Peripheral eosinophilia and discordant radiological–histopathological findings are key diagnostic clues. The condition may produce extensive fibrotic inflammation causing mass-forming lesions and adjacent organ compression. Deep biopsy is essential when superficial samples are non-diagnostic. Conclusion Pseudotumoral rectal schistosomiasis should be considered in the differential diagnosis of colorectal masses in endemic regions. Awareness of this entity and confirmation through adequate histopathology are essential to prevent misdiagnosis and unnecessary oncologic intervention.

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