Adult ileo-ileal intussusception from primary small bowel leiomyosarcoma: MRI diagnostic insights with corroborative histopathology.

Adult intussusception is a rare condition and, unlike pediatric cases, is usually associated with an underlying structural lesion. Primary leiomyosarcoma of the small bowel is an exceptionally uncommon cause, with limited imaging correlations described in the literature. We report the case of a 60-year-old patient who presented with iron-deficiency anemia and intermittent abdominal pain. CT demonstrated ileo-ileal intussusception, prompting further evaluation with MRI. MRI confirmed a polypoid intraluminal mass serving as the lead point and demonstrated low signal intensity on T2-weighted imaging, diffusion restriction, and avid post-contrast enhancement. While these findings supported the presence of a solid neoplasm and facilitated confident identification and localization of the lead point, they were nonspecific and did not allow definitive tumor characterization. MRI therefore provided complementary anatomic and tissue-level information rather than a specific diagnosis. Given the high suspicion for a pathologic lead point, surgical resection was performed. Histopathologic examination established the diagnosis of leiomyosarcoma arising from the muscularis propria. Immunohistochemistry showed positivity for smooth muscle actin and negativity for c-Kit, DOG1, and S100, excluding gastrointestinal stromal tumor and other mesenchymal neoplasms. Pathology thus represented the diagnostic cornerstone. This case contributes to the limited literature describing MRI features of small bowel leiomyosarcoma presenting with adult intussusception and underscores the importance of a multimodal diagnostic approach, in which MRI serves as an adjunct to CT, while histopathology remains essential for definitive diagnosis.