A giant anterior mediastinal thymolipoma mimicking dextrocardia with cardiomegaly: a case report and review of literature.

Abstract

Background: Thymolipoma is a rare benign anterior mediastinal tumour composed of thymic and adipose tissue, accounting for only 2-9% of thymic neoplasms (Mohamud et al., J Surg Case Rep 2020,2020; Shrivastava and Ntiamoah, Radiol Case Rep 15:1538-1540, 2020). Patients are often asymptomatic, and these masses are often detected incidentally. We present a case of a young male with an anterior mediastinal thymolipoma that initially mimicked dextrocardia and cardiomegaly based on findings from clinical examination and chest radiography.

Case presentation: A 22-year-old university student was incidentally noted to have abnormal findings on cardiorespiratory examination. A chest X-ray suggested dextrocardia with cardiomegaly, but further imaging revealed a large anterior mediastinal mass. Contrast-enhanced computed tomography (CT) of the chest showed a well-encapsulated, predominantly fat-density mass (approximately 24 × 15 × 12 cm) in the anterior mediastinum extending into the right hemithorax without invasion of adjacent structures. The lesion caused rightward mediastinal widening but no actual cardiac enlargement, dextroposition or lung collapse. Surgical resection via right mini-thoracotomy was performed. The Gross examination revealed a large, lobulated, encapsulated tumour with a yellow, fatty cut surface and interspersed solid areas. Histopathology confirmed the presence of mature adipose tissue with thymic lobules (cortex, medulla, and Hassall's corpuscles), consistent with thymolipoma, showing no evidence of malignancy. The patient's postoperative recovery was uneventful, and the heart resumed its normal anatomical position.

Conclusion: This case highlights that an anterior mediastinal mass, such as a thymolipoma, can masquerade as dextrocardia and cardiomegaly by distorting the mediastinal silhouette. It is essential to distinguish a mediastinal tumour from true congenital dextrocardia or pulmonary conditions, as each requires markedly different management approaches. Thorough imaging and histological evaluation ensured the correct diagnosis and curative surgical treatment. This report emphasises the importance of considering mediastinal pathology in patients with apparent dextrocardia, as detected during examination or imaging.