Purpose or Case Report: ACTA2 mutation occurs in the alpha-actin gene. Since the gene product is not expressed in brain parenchyma but is a contractile protein of smooth muscle cells that make up vascular walls, structural brain findings in this disorder are postulated to be the result of mass effect from abnormal rigid arteries during development. Presented here are typical imaging findings of ACTA2 mutation to emphasize the radiologist's role in diagnosing this disease prospectively.
Methods & Materials: A 2-year-old female presented to an outside hospital with ataxia. On physical exam, her pupils were dilated and poorly reactive. A CT performed at the outside facility demonstrated low attenuation throughout the white matter, greatest in the centrum semiovale. A preliminary diagnosis of possible demyelinating or leukodystrophy was assigned, and the patient was transferred to our pediatric hospital for further evaluation.
Results: An MRI of the brain was requested which exhibited confluent T2 hyperintensity throughout the periventricular white matter. The corpus callosum was minimally foreshortened, the paramedial frontal gyri were radially oriented, the anterior of the corpus callosum was v-shaped on the axial images, and a central indentation on the anterior pons along the course of the basilar artery was apparent. MRA demonstrated a broomstick pattern of the branches of the Circle of Willis. There was high-grade stenosis of the distal left internal carotid artery and narrowing of the distal right internal carotid artery, but both internal carotid arteries were dilated proximally. A follow-up transcranial Doppler also showed the distal internal carotid artery stenosis. Flow velocity in the right middle cerebral artery was elevated.
Conclusions: ACTA2 mutation is a rare cause of encephalopathy in children. In the setting of unexplained white matter T2 hyperintensity and straightened branches of the Circle of Willis, ACTA2 mutation should be considered as a differential consideration. Corroborating structural anomalies such as those described in this case may further aid in diagnosis.