Proximal Peril From a Distal Malignancy: Impending Colonic Perforation in Obstructing Sigmoid Adenocarcinoma

Sigmoid colon adenocarcinoma is a common cause of large bowel obstruction in elderly patients. However, progression to impending proximal colonic perforation due to distal malignant obstruction represents a rare and catastrophic complication associated with high morbidity and mortality. A 74-year-old female presented with acute constipation of five days' duration, progressive abdominal distension, nausea, vomiting, and one episode of fever. Contrast-enhanced computed tomography demonstrated diffuse dilatation of the large bowel, multiple air-fluid levels, and an irregular circumferential wall thickening of the sigmoid colon over a 6-cm segment, causing distal luminal narrowing with marked upstream dilatation and fecalization of the ileum, radiologically consistent with malignant obstruction. Emergency exploratory laparotomy revealed an obstructing sigmoid mass with gross proximal colonic distension and features of impending perforation involving the cecum and hepatic flexure. The patient underwent sigmoid resection with primary anastomosis, extended right hemicolectomy with end-to-side ileo-transverse anastomosis, omentectomy, and thorough peritoneal lavage. Histopathology confirmed a well-differentiated (Grade 1) adenocarcinoma of the sigmoid colon. Distal sigmoid malignancy can precipitate closed-loop large bowel obstruction with progressive proximal colonic dilatation, culminating in impending perforation at remote colonic segments. Early recognition and timely definitive surgical intervention are critical to prevent fatal outcomes.