Rectal Abscess Caused by Schistosoma

Authors: MIGLIORESI Lucia, LISI Daniele – Roma, Italy

We evaluated a 70-year-old male outpatient, originally from Colombia, who has been living in Italy for the past ten years. During a colonoscopy performed for proctalgia, a small rectal bump was identified above an anal fissure. MRI revealed a para-rectal elongated lesion measuring 80×35×37 mm, raising radiological suspicion of a gastrointestinal stromal tumor (GIST) or leiomyoma. The images showed that, while the lesion did not infiltrate surrounding tissues, it was compressing the prostate and the posterior rectal wall.

Ultrasound examination was performed using both a linear probe (5–13 MHz) and a convex probe (3–6 MHz) via the perineum. The lesion was successfully identified and delineated, appearing to consist of a soft, gelatinous texture with a predominantly arterial vascular pattern. (Video available on YouTube. https://youtu.be/nyjS3ZdyRk4  )

Gradual compression applied with the probe demonstrated that the mass had a clear vascular axis and a semi-solid structure.

Following the examinations, the patient was referred to the surgical team. While the possibility of an abscess or malignant tumor was excluded, no definitive diagnosis could fully explain the lesion's etiopathogenesis. The team proceeded with a para-anal incision, surgically opening the mass and extracting the bump.

Pathological analysis of the specimen revealed multiple multinucleated giant cells arranged in non-necrotizing granulomas, along with hyaline material and dense round bodies resembling Schistosoma eggs. However, serological testing of peripheral blood for schistosomiasis was negative, showing no eosinophilia or monocytosis.

During Schistosoma infection, hundreds to thousands of eggs are produced and released daily via urine and feces from the human host. Some eggs may become trapped in adjacent tissues of the rectum or bladder, where granuloma formation occurs as part of the body's inflammatory response.

Although schistosomiasis is rare in Western countries, in today’s globalized world, clinical suspicion should always be considered when evaluating patients from endemic regions, including South America, Sub-Saharan Africa, and China