The lethal fifth cardiac chamber: a rare autopsy case report of left atrial appendage aneurysm and review of literature.

Congenital left atrial appendage (LAA) aneurysm is an extremely rare condition characterized by abnormal dilatation of the LAA. We report a fatal case of a left atrial appendage aneurysm (LAAA). The presented case was a 19-year-old male who died suddenly during vigorous exercise with no relevant medical or family history. On gross examination, we observed a semi-rounded bulge at the LAA with a diameter of approximately 5 cm. Sectioning the bulge revealed an aneurysmal dilatation encompassing recent and huge lamellated mural thrombi filling its cavity. Though coronaries showed no stenosis, the mid-ventricular section of the heart showed dark and whitish areas at the lateral and posterior wall of the left ventricle, which were suspicious of myocardial infarctions. Histopathological examination depicted a thinned fibrosed wall of LAA, and the mural thrombi exhibited different stages of healing, which was confirmed using Martius Scarlet Blue stain. We identified myocardial infarctions at the suspected areas in the left ventricle, confirmed by the Masson Trichrome stain. The chronic myocardial ischemia was precipitated by the LAA aneurysmal compression of the left circumflex coronary artery as it passed along the atrioventricular groove. Seven other cases who died from LAAA complications since 1922 were reviewed. Early diagnosis and adequate management of LAAA allow survival without residual complications. Yet, this article highlighted the importance of screening for cardiac diseases in those subjected to vigorous exercise.