Jejunal Leiomyoma Arising in a Diverticulum Mimicking a Hollow Viscus Perforation: A Diagnostic Challenge.

Small intestinal leiomyomas are rare benign smooth muscle tumors that are now infrequently encountered following the reclassification of many mesenchymal tumors as gastrointestinal stromal tumors (GISTs). They are usually asymptomatic or present with nonspecific symptoms such as abdominal pain or gastrointestinal bleeding. Acute presentation with perforation peritonitis is exceedingly rare and poses a diagnostic challenge. We report the case of a 50-year-old female who presented with fever, vomiting, and acute abdominal pain with features of localized peritonitis. Contrast-enhanced computed tomography demonstrated pneumoperitoneum with a heterogeneously enhancing large outpouching arising from a mid-jejunal loop with wall thickening and internal air foci, suggestive of complicated jejunal diverticulitis or perforated neoplasm. Emergency exploratory laparotomy revealed a diverticulum-like outpouching arising from the jejunum with localized purulent contamination. Segmental jejunal resection with primary anastomosis was performed. Microscopic examination revealed a well-circumscribed spindle cell tumor arising from the muscularis propria, composed of spindle cells arranged in fascicles with mild to moderate pleomorphism, elongated to oval nuclei, vesicular chromatin, variably prominent nucleoli, and moderate cytoplasm. Focal bizarre nuclei and increased vascular proliferation were noted without necrosis or mitotic activity. Immunohistochemistry showed positivity for smooth muscle actin (SMA) and h-caldesmon, while CD117 and DOG1 were negative, confirming leiomyoma and excluding GIST. The postoperative course was uneventful. This case highlights the diagnostic difficulty associated with rare small bowel tumors presenting as acute abdomen and emphasizes the importance of surgical exploration, histopathology, and immunohistochemistry in establishing the diagnosis and guiding management.