Thallium-201 accumulation by epidermoid inclusion cyst.

An elderly male undergoing re-evaluation for coronary artery disease demonstrated an extra-cardiac focus of 201Tl accumulation during the performance of a planar myocardial perfusion scan. This corresponded to a subcutaneous lesion of the left posterior thorax found on a concurrent computerized axial tomographic (CAT) scan and upon surgical excision proved to be an "epidermoid inclusion cyst." A follow-up nuclear scan failed to reveal any residual extracardiac tracer localization. Confusing this lesion with metastatic deposits during 201Tl neoplastic evaluations can be avoided by examination of the adjacent integument.