Unusual Association of a Thymic Cyst and Thymolipoma: A Case Report

Benign thymic lesions are uncommon and mainly include thymic cysts, thymic hyperplasia, and thymolipoma. Their coexistence is exceptionally rare and may represent a significant diagnostic challenge, particularly because of the potential for confusion with malignant tumors of the anterior mediastinum. We report the case of a 68-year-old woman who presented with a large anterosuperior mediastinal mass that was radiologically suggestive of a thymoma, in the absence of clinical or biological features of myasthenia gravis. Complete surgical excision was performed, and histopathological examination revealed a multilocular thymic cyst arising in a thymolipoma, characterized by multiple cystic spaces lined by a benign epithelium and thymic parenchyma largely replaced by mature adipose tissue containing residual thymic islands with Hassall's corpuscles, without cytological atypia or evidence of invasion. This case highlights the limitations of imaging in the assessment of anterior mediastinal masses and emphasizes the pivotal role of histopathological analysis in distinguishing benign thymic lesions from malignant thymic tumors, thereby avoiding overdiagnosis and unnecessary aggressive treatment, with complete surgical resection providing an excellent prognosis.