Incidental Finding of Synchronous Rectal Adenocarcinoma and Intestinal Neuroendocrine Tumor: A Case Report and Literature Review

Synchronous colorectal adenocarcinoma and neuroendocrine tumor (NET) represent a rare and unique phenomenon. These lesions are often incidental findings, typically diagnosed through histological examination rather than based on clinical symptoms, physical findings, or macroscopic appearance. We describe a case of a 83-year-old man who presented with complains of abdominal pain, intermittent subocclusive symptoms and two episodes of bleeding per rectum. Colonoscopy revealed an ulcerative infiltrating mass in the rectum. During the staging assessment, a CT of the abdomen and pelvic images showed the presence of a second tumor located in small intestine and formed a wall thickening. The patient underwent a low anterior rectal resection with total mesorectal excision and an intestinal resection. Based on histomorphology and immunohistochemistry, the rectal tumor was diagnosed as well-differentiated adenocarcinoma, whereas the intestinal tumor was diagnosed as neuroendocrine tumor. Our goal is to highlight the critical role of thorough extension assessment and meticulous intraoperative evaluation in the management of colorectal malignancies.