Adult Hirschsprung's disease presenting with a tubulovillous adenocarcinoma: a case report.

Introduction and importance: Hirschsprung's disease (HD) is a congenital condition typically diagnosed in infancy. Adult presentation is rare and often misinterpreted. We present a unique case of HD diagnosed at 61 years of age, associated with a synchronous tubulovillous adenoma of the rectosigmoid junction. Presentation of case: A 61-year-old man with lifelong bowel dysfunction presented with recent deterioration. He had no significant medical or surgical history. After an inconclusive colonoscopy, full-thickness rectal biopsy and sigmoidoscopy confirmed HD and identified a non-benign lesion at the rectosigmoid junction. Definitive management was achieved via an open combined abdominal and transanal approach, performed collaboratively by adult and pediatric colorectal surgeons. Intraoperatively, a clear transition zone and palpable tumor were noted. A Swenson-type dissection allowed complete excision of the carcinoma with lymphadenectomy while preserving the dentate line. A coloanal anastomosis and protective loop ileostomy were performed. The patient received adjuvant chemotherapy, and post-treatment CT imaging showed no residual disease. He is currently awaiting ileostomy reversal. Clinical discussion: Adult HD is rare and diagnostically challenging, and coexisting colorectal carcinoma adds further complexity. While chronic stasis in long-standing, untreated HD has been proposed as a potential risk factor for malignancy, the causal relationship remains unclear. This case highlights diagnostic pitfalls and the value of multidisciplinary management in adults with chronic bowel dysfunction and atypical colorectal pathology. Conclusion: This first reported case of untreated adult HD with synchronous colorectal carcinoma underscores the uncertain relationship between the two conditions and highlights the importance of multidisciplinary collaboration to achieve optimal outcomes.