Dual Tumor Pathogenesis in the Gastrointestinal Tract: Synchronous Rectal Schwannoma and Gallbladder Papillary Adenocarcinoma—A Case Report

<b>Background and Clinical Significance</b>: Synchronous gastrointestinal tumors are exceptionally rare, particularly when combining histologically distinct benign and malignant components. Schwannomas represent uncommon mesenchymal tumors of the gastrointestinal tract, most frequently arising in the stomach, while rectal localization is exceedingly unusual. Papillary adenocarcinoma of the gallbladder is an aggressive malignant entity derived from intracholecystic papillary-tubular neoplasms (ICPNs). The coexistence of these two unrelated neoplasms has not been previously reported, making this case of dual tumor pathogenesis clinically and academically significant. <b>C</b><b>ase Presentation</b>: A 68-year-old female was admitted for surgical management of grade IV uterovaginal prolapse. Preoperative imaging incidentally revealed a well-circumscribed rectal wall mass and gallstones. A combined abdominopelvic operation was performed, including total hysterectomy with bilateral adnexectomy (Wiart procedure), rectosigmoid resection with colorectal anastomosis, and bipolar cholecystectomy. Intraoperatively, a firm intramural rectal lesion and a friable papillary mass in the gallbladder fundus were identified. Histopathologic examination confirmed a benign rectal schwannoma (S-100 positive, CD117/DOG-1 negative) and a papillary adenocarcinoma of the gallbladder, pT3N0M0, with clear resection margins and no lymphovascular or perineural invasion. The postoperative course was uneventful, and the patient remained disease-free at six-month follow-up. <b>Conclusions</b>: This case represents an exceedingly rare benign-malignant synchronous tumor association. The simultaneous occurrence of rectal schwannoma and gallbladder papillary adenocarcinoma underscores the importance of thorough intraoperative exploration and histopathologic evaluation. Complete resection with negative margins and multidisciplinary follow-up remains crucial for optimal outcomes and contributes to understanding dual tumor pathogenesis within the gastrointestinal tract.