Development of Rectal Ulcer Leading to Hematochezia After Placement of SpaceOAR Hydrogel for Prostate Carcinoma: A Case Report and Review of Literature.

SpaceOAR hydrogel is a synthetic polyethylene glycol-based spacer used to reduce rectal radiation exposure in patients undergoing radiotherapy (RT) for prostate cancer. While generally safe, rare complications such as rectal ulceration have been reported. We describe a 76-year-old male patient with prostate adenocarcinoma who underwent SpaceOAR hydrogel and fiducial marker placement prior to RT. Within 10 days of the procedure, he developed severe rectal pain and hematochezia. Computerized tomography (CT) imaging showed focal proctitis adjacent to the spacer, and colonoscopy revealed a large anterior rectal ulcer with fibrotic tissue at the site of spacer placement. He was managed conservatively with antibiotics and laxatives, with complete symptom resolution. Early-onset rectal ulceration after hydrogel insertion is extremely rare, with only a few cases reported; most cases in the literature occur weeks to months later. The mechanism is likely multifactorial. In contrast to prior case reports, our patient presented within 10 days, making this one of the earliest documented cases. This highlights the need to maintain a high index of suspicion for such complications to ensure timely diagnosis and treatment, enabling prompt resumption of RT.