Cortical vein sign

Last revised by Bálint Botz on 17 Jan 2021

The cortical vein sign refers to the presence of superficial cortical veins seen on MRI and CT (particularly with contrast injection) traversing an enlarged subarachnoid space, differentiating it from the similar radiological appearance of a subdural hygroma.

Although initially proposed as a method for differentiating cerebral atrophy from subdural hygroma 1, this sign is also valid for differentiating benign enlargement of the subarachnoid spaces in infancy from subdural hygroma (which may be a sign associated with non-accidental injury2,3. In infants, an ultrasound Doppler study of the cranium, instead of brain CT or MRI, can also be used to detect the presence of these cortical veins 2,3.

The mechanism behind this sign is that in global cerebral atrophy or benign enlargement of the subarachnoid spaces in infancy, the cortical veins will still be adjacent to the inner table of the calvaria and thus visible traversing the subarachnoid space with MRI, CT or ultrasound Doppler 1-3. While in a subdural hygroma, the veins are displaced away from the inner table because the arachnoid membrane and subarachnoid space are displaced by the subdural fluid collection 1-3.

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