Peroneal neuropathy due to a popliteal aneurysm in a patient with infectious endocarditis.

We present an 18-year-old young man with the diagnosis of infective endocarditis who also suffered from concomitant knee pain. The clinical examination revealed right homonymous hemianopsia and left peroneal neuropathy. Magnetic resonance imaging studies of the knee demonstrated a lobulated saccular aneurysm in the left popliteal fossa. We diagnosed this patient as having peripheral mononeuropathy due to an aneurysm compressing the peroneal nerve in the left poplitea.