Infiltrating Presacral Neuroendocrine Tumor: An Atypical Cause of Lower Gastrointestinal Bleeding

CASE REPORT An 82-year-old African American man with a history of G2 rectal neuroendocrine tumor (NET) diagnosed 15 years earlier, which was treated using hot snare polypectomy with negative margins and later complicated by histologically confirmed metastases to liver, bone, and presacrum, presented with hematochezia. Systemic therapy with lanreotide was stopped 4 months prior due to pancytopenia. Initial endoscopy revealed friable rectal mucosa with spontaneous oozing, which was treated with bipolar electrocautery. Limited visualization prompted repeat flexible sigmoidoscopy the following day (Figure 1), which showed diffuse mucosal necrosis of the rectum at 8 cm from the anal verge with mucosal openings concerning for fistula formation. Biopsy was deferred due to mucosal friability and lack of intraluminal mass. Subsequent computed tomography imaging (Figure 1) revealed that the previously known presacral NET was enlarged and infiltrating the rectum. There were necrotic changes and fistulous tracts connecting the mass and rectum. Interestingly, the location of infiltration was the same as the index tumor, which we postulate as coincidence.Figure 1.: (A) Flexible sigmoidoscopy, at 8cm proximal from rectum. Diffusely necrotic rectal mucosa with multiple openings concerning for fistula formation (green arrows). The area of prior cauterization has an adherent clot. There is no evidence of mass within the rectum. (B) Computed tomography of abdomen and pelvis, sagittal view. Large contrast‐enhancing presacral tumor with necrotic changes that is indistinguishable from rectum. A portion of the channel‐like area consistent with fistula formation extends between the mass and rectum. The tumor is exerting mass effect on other pelvic organs.Presacral NETs are typically asymptomatic or present with pelvic pain.1,2 There are no known cases of a presacral NETs presenting with lower gastrointestinal bleeding or infiltrating the rectum, resulting in necrosis.2,3 This extracolonic pathology represents an atypical cause of lower GI bleeding. DISCLOSURES Author contributions: L. Krause was primary author of this manuscript. R. Humes was editor of materials and staff advisor. L. Krause is the article guarantor. Financial disclosure: None to report. Previous presentation: This case was presented as a posted at the American College of Gastroenterology Annual Scientific Meeting, October 27, 2025; Phoenix, Arizona. All attempts have been exhausted in trying to contact the patient, next of kin, and/or parent/guardian for informed consent to publish their information, but consent could not be obtained.