Recurrent Extraperitoneal Pelvic Desmoplastic Small Round Cell Tumor Treated by Total Pelvic Exenteration: A Case Report

Abstract

Background: Desmoplastic small round cell tumour (DSRCT) is a rare, aggressive mesenchymal neoplasm that typically disseminates along the peritoneal and serosal surfaces of the abdominopelvic cavity in adolescent and young adult males. Isolated presentations confined to a non-serosal extraperitoneal pelvic space are exceptionally uncommon and pose considerable diagnostic difficulty. Case Presentation: We report the case of a 32-year-old man initially treated with tumorectomy for a retro-rectal mass. Immunohistochemistry (CD45 negative, CD99 negative, chromogranin A negative, cytokeratin AE1/AE3 positive, desmin positive, WT1 positive) supported a diagnosis of DSRCT, requiring review by multiple pathologists, although molecular confirmation of the EWSR1-WT1 fusion was not available. Despite neoadjuvant and adjuvant multiagent chemotherapy, follow-up imaging, including 18F-FDG PET-CT, demonstrated an intensely hypermetabolic recto-vesico-prostatic mass with associated hypermetabolic pelvic and retroperitoneal lymphadenopathy, consistent with locally advanced recurrence without distant metastasis. The patient underwent total pelvic exenteration comprising cystoprostatectomy, abdominoperineal amputation, ileal conduit (Bricker) urinary diversion, and pseudo-continent perineal colostomy, achieving an R0 resection. Final pathology confirmed a 4.5-cm round cell tumour infiltrating the bladder, prostate, and rectum, with five of six lymph nodes involved. The postoperative course was uneventful, with discharge on postoperative day 13. At the last clinical follow-up, the patient remained in remission and had been referred to medical oncology for discussion of adjuvant treatment. Conclusion: This case illustrates the diagnostic difficulty posed by an atypical, non-serosal extraperitoneal pelvic presentation of DSRCT and demonstrates that total pelvic exenteration can offer a potentially curative option for locally advanced or recurrent disease confined to the pelvis when undertaken within an experienced multidisciplinary team.