High-Grade Malignant Spindle Cell Sarcoma of the Pelvis Presenting With Bloody Diarrhea and Urinary Retention: A Rare Case With a Rare Presentation.

Soft tissue sarcomas (STSs) are rare malignant tumors originating from mesenchymal cells. Extremities are the most commonly affected anatomical sites, and majority of them present as a painless mass. We present a very interesting case of high-grade spindle cell sarcoma of the pelvis manifested as urinary retention and bloody diarrhea. A 68-year-old male presented to the emergency department with abdominal pain, inability to void urine, and bloody diarrhea. Straight urinary catheterization retrieved 900 mL of urine, and a Foley catheter was placed. All laboratory workup including complete blood count, complete metabolic panel, and urinalysis were within normal limits, but computed tomography (CT) of the abdomen and pelvis with contrast was remarkable for bilateral moderate hydronephrosis and a large 14 x 9.1 cm pelvic mass fistulizing into the rectum. To better identify the extent of disease, magnetic resonance imaging (MRI) with contrast was performed, which also revealed a similar large pelvic mass fistulizing into the rectum. Core needle biopsy of the mass was performed, which showed malignant spindle and epithelioid neoplasm with necrosis consistent with high-grade sarcoma. This is a very rare presentation of STS, and, to the best of our knowledge, only few similar cases have been reported thus far.