Malignant Prostatic Gastrointestinal Stromal Tumour Presenting with Acute Intestinal Obstruction and Urinary Retention: A Rare Case Report

Case Report

A 39-year-old male presented with acute intestinal obstruction and acute urinary retention. He reported a one-month history of intermittent abdominal distension, constipation, and difficulty in micturition. The patient had previously undergone a prostatic biopsy at a government tertiary care centre five years earlier, where prostatic GIST was diagnosed. He was started on imatinib therapy, following which the tumour initially regressed. He had known diabetes mellitus and a history of tuberculosis, for which he was not receiving active treatment. On presentation, the patient was catheterised for urinary retention and stabilised. Clinical and radiological evaluation revealed a large pelvic mass causing compression of both urinary and gastrointestinal structures. In view of acute obstruction and disease progression, surgical intervention was planned at Max Super Speciality Hospital, Lucknow, UP.

Intraoperative findings and procedure

A midline abdominal incision revealed a large abdominopelvic mass measuring 15.0 x 13.0 x 9.5 cm, adherent to the urinary bladder and rectum. The urinary bladder was grossly thickened and distended. The mass was abutting the bilateral ureters. There was no ascites or major vascular encasement.

Surgical steps included:

• Initial dissection between the bladder and the mass;the bladder was abutting but not involved, and planes were maintained
• Bilateral ureters were carefully dissected away from the mass up to the bladder base
• Anterior dissection was carried out up to the pubic bone
• Posteriorly, the mass was dissected from the rectum up to its mid-part; however, due to rectal wall adherence, the rectum was divided between the upper and mid-segments
• Further posterior dissection was performed up to the pelvic floor muscles
• The bladder neck was divided to expose the prostate,and the mass was excised
• The urethra was transacted at the bony level and sent for frozen section examination, which showed negative margins
• Bladder neck was anastomosed to the urethra using 4-0 polydioxanone (PDS) double-needle sutures over a Foley catheter
• Suprapubic cystostomy and colostomy were performed
• Drain placement was performed, and the abdomen was closed in layers

The surgery lasted for 8 hours, with an estimated blood loss of approximately 1 L. The postoperative course was uneventful, and the patient was discharged on postoperative Day 7 with regular follow-up.

Histopathological findings

Gross examination revealed a well-encapsulated tumour with areas of necrosis (Figure 1).

Figure 1: Gross morphology of prostatic gastrointestinal stromal tumour: A. Resected abdominopelvic mass showing a large, lobulated, irregular tumour with congested and haemorrhagic external surface; B. Cut surface of the tumour revealing a solid, grey-white to grey-tan appearance with areas of necrosis. 

Microscopic examination showed a highly cellular tumour composed of spindle and epithelioid cells arranged in storiform, fibrosarcomatous, and epithelioid patterns. Extensive areas of hypercellularity, marked cytological atypia, and frequent mitoses, including atypical forms (30–35 per 50 high-power fields), were noted (Figures 2 and 3).

Figure 2: Side-by-side photomicrographs of malignant prostatic gastrointestinal stromal tumour (haematoxylin and eosin [H&E]): A. Tumour showing extensive serpentine areas of necrosis; B. Tumour with adjacent seminal vesicle.

Figure 3: Histopathological features of malignant prostatic gastrointestinal stromal tumour (haematoxylin and eosin [H&E], ×600): A. Tumour showing atypical mitotic figures; B. Epithelioid tumour cell morphology; C. Spindle cell pattern arranged in fascicles; D. High-grade tumour area with marked cellularity and nuclear atypia. 

An initial diagnosis of malignant spindle cell tumour was considered. Immunohistochemical evaluation showed(Figure 4):