Simple mesothelial pericardial cyst in a rare location.

Pericardial cysts are rare and generally benign intrathoracic lesions, most frequently located in the cardiophrenic angles, but other locations have been described. We present a case of a pericardial cyst in a previously undescribed site. Our patient presented with a cyst in the interventricular septum which was discovered as an incidental finding. After surgical excision of the cyst, it was described pathologically as a simple mesothelial pericardial cyst. The explanation of this rare condition is uncertain, but some hypotheses can be outlined.