Chronic Pediatric Ankle Swelling Due to an Occult Foreign Body: A Case Report.

INTRODUCTION: Chronic ankle swelling in the pediatric population presents a diagnostic challenge due to a wide range of differential diagnoses and often non-specific clinical features. Occult retained foreign bodies, particularly radiolucent organic materials, such as wood or thorns, are an under-recognized cause of persistent swelling, especially in children who walk barefoot and may not recall trivial penetrating injuries. Delayed presentation and secondary inflammatory changes frequently obscure the primary pathology, leading to prolonged diagnostic delays. CASE REPORT: We report the case of a 10-year-old boy who presented with progressive medial ankle swelling for 18 months without a definite history of trauma, infection, or cutaneous lesions. Clinical examination revealed a firm, tender peri-ankle swelling with preserved joint motion. Plain radiographs were normal, and magnetic resonance imaging (MRI) demonstrated flexor tendon tenosynovitis without identifying a causative lesion. Subsequent ultrasonography revealed a linear echogenic structure suggestive of a retained foreign body. Surgical exploration confirmed and enabled removal of a wooden foreign body measuring 1.7 × 0.3 cm, with histopathology demonstrating a chronic inflammatory foreign body reaction. The patient achieved complete symptomatic resolution post-operatively. CONCLUSION: Occult foreign bodies should be considered in the differential diagnosis of chronic pediatric ankle swelling, even in the absence of trauma history or characteristic imaging findings. Ultrasonography is a valuable diagnostic adjunct when radiographs and MRI are inconclusive. Early recognition and timely surgical intervention result in excellent outcomes and prevent unnecessary investigations and complications.