Chronic Lacunar Infarct: This is the most likely diagnosis due to the asymptomatic nature and indeterminate age of the infarct. Lacunar infarcts are small and often do not produce noticeable symptoms, especially if they occur in non-eloquent areas of the brain.

Remote Embolic Infarct: This could be a possible diagnosis if the patient has a history of embolic events, such as atrial fibrillation or a patent foramen ovale. The infarct's age being indeterminate makes it plausible that it occurred at a remote time.
Hypertensive Encephalopathy with Chronic Changes: Chronic hypertension can lead to small vessel disease, resulting in asymptomatic infarcts. The indeterminate age could reflect the gradual progression of hypertensive changes.
Chronic Vasculitis: Certain forms of vasculitis, like primary central nervous system vasculitis, can cause asymptomatic infarcts. However, this would typically be accompanied by other systemic symptoms or findings.

Cerebral Amyloid Angiopathy (CAA): Although less common, CAA can cause asymptomatic infarcts, especially in the elderly. Missing this diagnosis could lead to inappropriate management and increased risk of future hemorrhages.
Moyamoya Disease: This rare condition affects the blood vessels in the brain and can lead to asymptomatic infarcts. It's crucial not to miss this diagnosis due to its significant implications for management and prognosis.
Neurosarcoidosis: Sarcoidosis can affect the central nervous system, leading to asymptomatic infarcts among other manifestations. Missing this diagnosis could result in delayed treatment of a potentially serious condition.

CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy): This is a rare, inherited condition that affects the blood vessels in the brain, leading to subcortical infarcts and leukoencephalopathy. It's an important consideration in younger patients with a family history of similar conditions.
Susac Syndrome: A rare condition characterized by microangiopathic changes in the brain, retina, and cochlea. It can cause asymptomatic infarcts and is more common in young women.
Fabry Disease: A genetic disorder that can lead to vascular dysfunction, including in the brain, resulting in asymptomatic infarcts. It's rare but important to consider due to its potential for systemic involvement and the availability of specific treatments.