Patent foramen ovale as a preferential mechanism for increasing the likelihood of brain tumor metastasis.

Metastases are the most common tumors of the central nervous system which may lie dormant behind the brain blood- barrier sheltering from chemiotherapeutic drugs, and whose presence usually indicates a poor prognosis. Development of brain metastases includes the intravasation of the cancer cells through the tumor blood vessels, their circulation within the venous system, passing through the pulmonary filter thus reaching the systemic circulation. Patent foramen ovale (PFO) is a natural communication between the right and left atrium with a prevalence of about 25% in the general population. It may predispose to a right-to-left shunt by-passing the pulmonary filter. Recent literature suggests that the presence of a permanent shunt, large shunt, atrial septal aneurysm and/or venous valve remnants, all increase the risk of paradoxical embolism in PFO patients. The hypothesis that cancer cells may reach the brain circulation through a significant PFO, might open up new fields in brain metastases pathophysiology and prevention.