Differential diagnosis of a ring-enhancing brain lesion in the setting of metastatic cancer and a mycotic aneurysm.

A diagnostic challenge arises when a patient presents with a ring-enhancing lesion of the brain in the setting of both metastatic cancer and a source of infection. We report a case depicting this dilemma in an 80-year-old man with a history of metastatic oral squamous cell carcinoma who presented for left-sided hemiparesis. Computed tomography and magnetic resonance imaging revealed a ring-enhancing lesion of the right parietal vertex without signs of stroke. He was also found to have an aneurysm of the right common carotid artery with abnormal surrounding soft tissue density and gas, findings suspicious for a mycotic aneurysm. The likelihood of the brain lesion being an abscess formed by septic embolization was raised, leading to the recommendation to surgically explore the brain lesion and repair the aneurysm. Nevertheless, a high index of suspicion for a brain abscess and mycotic aneurysm is necessary in this type of clinical scenario.