Chilaiditi Syndrome With Colonic Gastrointestinal Stromal Tumor (GIST): An Unusual Overlap.

Chilaiditi syndrome is a rare condition characterized by the interposition of the colon between the liver and diaphragm, often mimicking other abdominal pathologies. While gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the GI tract, they rarely originate from the colon. We report a 69-year-old man presenting with progressive right upper quadrant pain, low-grade fever, weight loss, altered bowel habits, sluggish bowel sounds, and a positive Murphy's sign. Initial imaging with an erect X-ray showed air under the right hemidiaphragm, prompting suspicion of intra-abdominal pathology. Contrast-enhanced computed tomography (CECT) revealed an interposed ascending colon with a heterogeneously enhancing, necrotic mass and air-fluid level, suggestive of GIST. Positron-emission tomography-computed tomography confirmed a hypermetabolic colonic mass with retroperitoneal and pelvic nodal metastases. Colonoscopy identified a friable, ulcerated lesion, and biopsy confirmed a spindle cell GIST, positive for Cluster of Differentiation 117 and Discovered on GIST-1. Surgical resection was done, after which the patient had an uncomplicated recovery and was initiated on adjuvant imatinib therapy. To the best of our knowledge, this is the first reported case of GIST arising from an interposed colonic segment without prior surgery, emphasizing the need for thorough evaluation in rare presentations.