Retrorectal Schwannomas: Atypical Presentation and Controver
Schwannomas known as neurilemomas are benign tumors. Retrorectal schwannomas are extremely rare, accounting for 1 to 5% of all schwannomas. They are mostly asymptomatic but may present with symptoms such as pelvic pain, back pain, lower extremities pain, or constipation. Physical examination is often poor. Imaging (CT, MRI) and fine needle biopsy can often help orient the diagnosis. The treatment of choice is monoblock resection of the mass. The prognosis is good. Recurrence has been reported especially after intralesional enucleation.

A 41-year-old man complaining of pelvic pain and bilateral sciatica radiating towards the right inguinal and lumbar area for 2 years. He reported some abdominal discomfort but no urinary or neurologic symptoms were reported. Abdominal examination was poor. Rectal examination found a 3.5?cm smooth, fixed, retrorectal mass. Computed tomography revealed a 29.2 × 26?mm solid, heterogeneous pelvic mass with well-defined limits containing small calcifications. A CT-guided biopsy was performed but was inconclusive. Magnetic resonance (MR) imaging showed a 3?cm with low signal on T1-weighted image, with a high signal intensity and heterogeneous signal intensity on T2-weighted image.

Laparotomy was performed using a midline incision. A 3?cm encapsulated mass was found, and it was adherent to the right pelvic sidewall and the periosteum of the sacrum. The bladder, prostate, seminal vesicle, and rectosigmoid colon were carefully dissected free, and we performed a monoblock resection of the tumor. The follow-up was simple and the patient was discharged 3 days later.

Histological examination showed benign schwannian cells, along with an alternating Antoni A and Antoni B pattern, and areas of nuclear atypia were noted. The specimen tested positive for S100 and had one mitotic figure per 30 high-powered fields (HPF), all consistent with the diagnosis of benign (ancient) schwannoma. The patient has remained asymptomatic, with no sign of recurrence on a CT scan at 36 months of follow-up.

Source:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8121578/
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