Seminal Vesicle Adherent to Rectal Wall Following Neoadjuvant Chemoradiotherapy: A Potential False-Positive Diagnostic Pitfall.

The standard of care for stage T3 and stage T4 rectal adenocarcinomas involves neoadjuvant chemoradiotherapy followed by either low anterior resection or abdominopelvic resection. The presence of residual adenocarcinoma or positive surgical margins provides useful prognostic information and can influence ongoing adjuvant therapy. Although uncommon, mimics of treated adenocarcinoma may be present in the surgical specimen. A high index of suspicion is critical in avoiding potential false-positive pitfalls, and the exclusion of mimics of treated adenocarcinoma is paramount to accurate diagnosis and treatment. Seminal vesicle epithelium has long been a challenge in differentiating prostatic adenocarcinoma from benign epithelium. However, the role of incidental seminal vesiculectomy in rectal resections due to fibrous adhesion to the rectal wall secondary to chemoradiation has not been studied. As the seminal vesicle epithelium can show markedly atypical nuclei with radiation-type effect at baseline, the potential risk of misinterpretation as residual adenocarcinoma is high. In this article, we present 2 case reports of rectal adenocarcinoma treated with neoadjuvant chemoradiotherapy followed by transabdominal resection (low anterior resection or abdominopelvic resection) with incidental seminal vesiculectomies mimicking either residual adenocarcinoma or residual adenocarcinoma at a margin of resection.