Multiple tumors in the pericardial cavity of an australian rock oyster, crassostrea commercialis (iredale and roughley)

A pedunculated tumor within the pericardial cavity of a Sydney rock oyster (Crassostrea commercialis) was discovered during a routine dissection. The tumor measured 5 × 4.8 × 4.5 mm, was lobulated and was attached to the dorsal parietal pericardium over the ventricle, close to the anterior aorta. Associated with it were three smaller nodular lesions, also on the parietal pericardium. All four masses were composed chiefly of vesicular connective tissue (Leydig cells of oysters) within which mild inflammatory cell infiltration and fibrosis were present. The mesothelium overlying or enveloping the tumors was moderately hyperplastic. These apparently multicentric lesions present a problem in differential diagnosis among (1) slow‐growing, multi‐centric, benign neoplasms of Leydig cell origin, (2) developmental anomaly, including hamartoma, (3) hyperplasia secondary to inflammation and repair. The authors consider the first of these possibilities to be the most acceptable. The tumors in this specimen appear to belong in a group with three similar ones previously recorded in the literature. Their precise nature in relation to neoplastic processes remains unsettled.