Thymic Langerhan's cell histiocytosis: A rare entity in 8 Y/
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LCH is a rare disease characterized by the accumulation of abnormal Langerhans cells in various tissues or organs. It commonly involves the bone and skin in pediatric groups, whereas thymic involvement is rare. The clinical presentation for thymic involvement can range from an asymptomatic to an enlarged thymic mass causing cough, cough, chest pain, respiratory distress, and superior vena cava syndrome.

A full-term, 8-month-old boy with no personal medical or family history was referred with non-productive cough and facial skin rashes. On physical examination, he had extensive rashes on the scalp, face, chest, and upper back. The chest X-ray revealed diffuse cystic changes of both lungs and widening of the mediastinum. Chest computed tomography (CT) showed multiple cavitary nodules and subpleural thin-wall cysts. The anterior mediastinum was widened due to an enlarged thymus with multiple punctate calcifications. A skin biopsy was performed, which showed infiltrates of Langerhans cells in the superficial dermis. CD1a, Langerin, and S-100 protein were positive on immunohistochemistry. The diagnosis of Langerhans cell histiocytosis (LCH) was then made.

On Chest radiographs, thymic involvement mostly presents as a non-specific mediastinal enlargement. Punctate calcifications are highly specific for thymic LCH. In general, enlarged thymus, cysts, and punctate calcifications will be resolved after chemotherapy. Although it is a rare entity, this report emphasizes that characteristic radiological features can be observed in LCH with thymic involvement, and the recognition of the pattern can lead to prompt diagnosis.