An 82-year-old woman presented to the emergency department with shortness of breath and personality changes. After being diagnosed with a pulmonary embolism, a head CT was ordered to evaluate for metastases and/or hemorrhage prior to starting anticoagulation.
An unenhanced head CT (A) showed increased attenuation of the anterior cerebral artery (white arrow in A). An unenhanced brain MRI (B) demonstrated restricted diffusion of the corpus callosum and bilateral frontal lobes in the distribution of the pericallosal arteries (solid arrow in B). Maximum intensity projection images from a CT angiogram (C, D) demonstrated a bihemispheric anterior cerebral artery (ACA) with abrupt cutoff of the common pericallosal artery (black arrow in C), normal variant absent left A1 segment (red arrow in D), and a hypoplastic left ACA arising from the right-sided circulation (yellow arrow in D).
The hyperdense middle cerebral artery sign is a well-known finding of acute stroke on noncontrast CT and thought to represent direct visualization of the thrombus/embolus. A hyperdense vessel can also be caused by elevated hematocrit, atherosclerosis, pseudo-hyperdensity from decreased attenuation of the adjacent brain parenchyma, and dissection.1
The ACAs have numerous variations with the standard configuration seen in just over 50% of cases.2 In the hemispheric ACA, the bilateral ACA territory is supplied by a single dominant A2 segment with hypoplasia of the contralateral A2 segment. This is in contrast to the azygous ACA in which a single A2 segment is supplied by two A1 segments.1,2
Martin A, McKnight T. JAOCR at the Viewbox: Hyperdense Bihemispheric Anterior Cerebral Artery. J Am Osteopath Coll Radiol. 2020;9(3):32.