Imaging of an infected cystic lymphangioma of the forearm in an adolescent: A case report

Cystic lymphangiomas, currently classified as lymphatic malformations, are benign congenital lesions that most commonly occur in the cervicofacial region and axilla. Extremity involvement is uncommon, and secondary infection may obscure the typical imaging appearance by producing painful inflammatory swelling that mimics abscess or other soft-tissue masses. We report the case of a 14-year-old female who presented with recurrent painful erythematous swelling of the left forearm associated with fever and elevated inflammatory markers, with a history of a previous similar episode treated surgically but not documented. Ultrasound demonstrated a poorly defined superficial subcutaneous lesion composed of multiple communicating canalicular structures containing heterogeneous echogenic material, without internal Doppler flow, and associated with surrounding inflammatory hyperemia. MRI showed extensive inflammatory infiltration of the subcutaneous tissues with multiple cystic components demonstrating high STIR signal and peripheral rim enhancement. These findings suggested an infected lymphatic malformation rather than a simple abscess or vascular tumor. Complete surgical excision was performed, and histopathological examination confirmed cystic lymphangioma. This case highlights the complementary role of ultrasound and MRI in recognizing infected lymphatic malformations of the extremities and avoiding diagnostic confusion with more common acute soft-tissue lesions.