Inverted "V" sign (spinal cord)
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The inverted "V" sign, also known as the inverted rabbit ears sign, is a radiological sign described in subacute combined degeneration of the spinal cord.
It refers to the appearance of the spinal cord on axial MRI slices 1-3. On these slices in a patient with subacute combined degeneration of the spinal cord, there is bilateral high-intensity T2 signal within the posterior funiculus, resembling the appearance of an inverted letter "V" 1-3.
This sign is produced because subacute combined degeneration of the spinal cord is caused by vitamin B12 deficiency 1-3. One theory suggests that this deficiency results in an accumulation of methylmalonic acid, which leads to the synthesis of abnormal fatty acids instead of myelin 3. These are then incorporated into neuronal lipids leading to abnormal myelination 3. This process has a predilection for the dorsal columns, which lie in the posterior funiculus of the spinal cord 3, which is why an alternate name for subacute combined degeneration of the spinal cord is "funicular myelosis".