The Disappearing Basal Ganglia Sign

The disappearing basal ganglia sign is a finding that can be seen at computed tomography (CT). It appears as a loss of the normal delineation of the basal ganglia, with the affected basal ganglia exhibiting abnormal morphologic features. This is best appreciated when a comparison is made between the affected basal ganglia and the contralateral side of the brain.

Transverse CT scans obtained without intravenous contrast material demonstrate the disappearing basal ganglia sign.Note the loss of the normal contour of the right basal ganglia. The left basal ganglia (arrow) are normal. The right insular cortex is obscured, and there is a loss of the gray matter-white matter junction.

The disappearing basal ganglia sign is representative of cerebral infarction. The sign is usually caused by incomplete to complete occlusion of the MCA as a result of thromboembolic disease. Other differential diagnostic considerations include arterial dissection, trauma, vasculitis, and hemolytic uremic syndrome. If injury occurs bilaterally, diagnostic considerations include global hypoperfusion; respiratory arrest; near drowning; strangling; barbiturate overdose; methanol toxicity; cyanide poisoning; osmotic myelinolysis; hypoglycemia; Leigh disease; mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (also known as MELAS); and infectious causes.

Transverse CT scan from the same patient described in the previous CT image but 36 hours later. The right middle cerebral artery infarct (arrows) has now matured, creating a large area of hypoattenuation in the right basal ganglia, right temporal lobe, and posterior portion of the right frontal lobe. The left basal ganglia retain normal morphologic features and attenuation.                       

Normally, the lentiform nucleus and caudate nucleus are slightly hyperattenuated when compared with the surrounding white matter. When present, a vascular insult will usually manifest at CT as areas of hypoattenuation, which occur when the normal cellular requirements are not met. Normal cell volume must be maintained with normal intra- and extracellular electrolyte concentration gradients. When there is an interruption of blood flow, cellular injury occurs. This, in turn, causes a loss of homeostasis and creates an influx of sodium, chloride, calcium, and water into the cells, thereby causing metabolic acidosis. This intracellular influx of fluid will lead to cytotoxic edema. The areas of hypoattenuation may also be interpreted as an indicator of severe focal ischemia.

Normal CT Brain.