(A) infarction of the right middle cerebral artery
(B) bilateral infarction of the anterior cerebral artery
(C) infarction of the right anterior cerebral artery
(D) bilateral infarction of the middle cerebral artery
(B) This is an unenhanced CT scan of the head. It shows a large area of hypodensity within the left medial frontal lobe. There is a similar region of hypodensity within the right medial frontal region, which is smaller in size. These findings are typical of evolving infarcts within the territory of the left and right anterior cerebral arteries (ACAs). There is no mass or midline shift. The basal cisterns are intact. The ventricles are normal in size and shape.
Infarction in the ACA distribution is uncommon and bilateral infarction is rare. ACA infarctions are cortical or subcortical and are caused by embolism. The clinical spectrum of unilateral infarction in the ACA territory is broad and may include disinhibition and hemiparesis predominant in the leg. Bilateral infarction in the ACA territories causes a profound neurological syndrome, highlighted by akinetic mutism and poor recovery. (Minagar, 886)
These are magnetic resonance images (MRIs) of the head of a 43-year-old man with a history of progressive ataxia. The most likely diagnosis is
(A) pilocytic astrocytoma
(D) These are multiple axial images of the brain MRI, with and without contrast. There is a left cerebellar mass with low signal intensity on T1-weighted images, demonstrating minimal enhancement. This mass causes compression of the fourth ventricle. There is also increased signal intensity in the subependymal region, consistent with transependymal resorption of cerebrospinal fluid (CSF). The lateral and third ventricles are dilated. These findings are consistent with obstructive hydrocephalus.