Fibromuscular Dysplasia As a Rare Cause of Ileus and Aneurysm in Childhood

**Background:** Fibromuscular dysplasia (FMD) is a nonatherosclerotic, noninflammatory vascular disease that causes arterial narrowing, dissections, or aneurysms. It most commonly affects renal and carotid arteries but can involve mesenteric arteries. FMD is extremely rare in children, with limited literature on its presentation and management. This case highlights an unusual presentation of FMD in a young child with recurrent ileus and mesenteric artery aneurysms.

**Methods:** This is a single case report of a 21-month-old malnourished girl who presented with abdominal pain, distension, vomiting, and radiological signs of ileus (dilated small bowel loops proximal to suspected obstruction, gasless abdomen). Barium enema ruled out Hirschsprung disease. Ultrasound showed inflammatory changes in other small bowel loops. Due to worsening symptoms and persistent vomiting, laparoscopy was performed, revealing an obstructed loop of jejunum adherent to the abdominal wall. Adhesiolysis and resection showed small bowel ulcerated mucosa and proliferated vascular intima. Inflammatory disorders of the vasa vasorum and other etiologies were not identified. Laboratory tests found no evidence for autoimmunity, celiac disease, cystic fibrosis, thrombophilia, or metabolic disorders. One week later, the child again developed ileus. Due to possible Crohn disease, exclusive enteral nutrition and corticosteroid treatment were introduced without success. Four months later, a second small bowel resection was required, and a similar obstructed, thickened loop was removed, with symptomatic relief. Abdominal sonography subsequently detected a fusiform aneurysmal dilation of the superior mesenteric and hepatic artery, confirmed by computed tomography angiography (Fig. 1). Magnetic resonance imaging and cardiac sonography revealed no other aneurysms. Histologic re-evaluation of material resected at both surgeries identified arterial changes of fibromuscular dysplasia (FMD).

**Key Results:** The patient was a 21-month-old girl with recurrent ileus requiring two small bowel resections. Imaging revealed fusiform aneurysms of the superior mesenteric artery and hepatic artery. Histology confirmed intimal fibroplasia, a subtype of FMD affecting the inner arterial layer. No other aneurysms were found on MRI or cardiac sonography. Laboratory tests ruled out autoimmune, metabolic, and infectious causes. The patient was started on aspirin therapy but developed asymptomatic hepatic artery thrombosis. The case underscores the diagnostic challenge of FMD in children, as initial presentations mimicked Hirschsprung disease, chronic intestinal pseudoobstruction, and Crohn disease.

**Clinical Implications:** FMD should be considered in pediatric patients with unexplained ileus, especially when associated with vascular abnormalities such as aneurysms. Early recognition is crucial to avoid unnecessary treatments (e.g., corticosteroids for presumed Crohn disease) and to guide appropriate management. Treatment focuses on symptom control, blood pressure management, and prevention of thrombotic events. In this case, aspirin was initiated but thrombosis still occurred, highlighting the need for careful monitoring. Long-term follow-up is essential due to the risk of renal artery involvement, hypertension, and clot formation. This case adds to the limited literature on pediatric FMD and emphasizes the importance of histologic evaluation of resected bowel tissue in atypical presentations.