BackgroundSegmental Absence of Intestinal Musculature (SAIM) is a rare condition associated with intestinal obstruction and perforation. Colostomy fistula as a presentation of SAIM and their association with anastomotic failure have not been previously reported. This case report aimed to raise awareness of this unique manifestation and its potential implications.Case presentationA 58-year-old male with a history of type 2 diabetes, hypertension, and lumbar hernia presented with diarrhea. Lower gastrointestinal endoscopy revealed a tumor in the rectum, for which he was diagnosed with a well-differentiated adenocarcinoma. The patient underwent a laparoscopic Hartmann operation. After the operation, an entero-entero-fistula was identified at the sigmoid colostomy site. Subsequently, laparoscopic reconstruction of the colostomy was performed, and the patient had a favorable postoperative course without complications. Histopathological examination confirmed the localized absence of the muscularis propria in the resected colon, with fibrosis and nearby ganglion cells.ConclusionsThis case highlights the rarity of a colostomy fistula as a manifestation of SAIM and emphasizes the need to consider SAIM in the differential diagnosis for such cases. The presence of SAIM-affected lesions poses a risk of anastomotic failure, underscoring the importance of assessing the risk of complications during future surgeries. Surgeons should be aware of the etiology and potential implications of SAIM to ensure appropriate management and minimize postoperative morbidity. Further studies are warranted to explore the underlying mechanisms and optimize surgical strategies for patients with SAIM and its associated complications. Increased awareness among clinicians is crucial for timely diagnoses and tailored interventions to improve patient outcomes.