The patient was diagnosed with a left atrial appendage (LAA) aneurysm. He was urgently referred to a tertiary hospital, where surgical resection was performed successfully.

LAA aneurysms are very rare; approximately 100 cases have been reported thus far ¹. They are usually diagnosed incidentally on imaging but do predispose to atrial tachyarrhythmias and thromboembolism. Definitive treatment consists of surgical excision ² or clipping ³.

Take-home message:
The mnemonic for the differential diagnosis of anterior mediastinal mass - 5Ts:

1. Thymic lesions
2. Thyroid lesions
3. Teratoma
4. Terrible lymphoma
5. Thoracic aneurysms, which can be of aortic or cardiac origin