What are the features of extramedullary lesions?
Extramedullary lesions are lesions that compress the spinal cord from the outside.
They can be extramedullary extradural or extramedullary intradural. Either way, extramedullary lesions cause exterior compression of the spinal cord.
Because of the somatotopic organization of the spinal cord, the spinothalamic tracts and the corticospinal tracts are arranged so that the sacral fibers are the most lateral and the cervical fibers are the most medial.
Because of this, external compression of the spinal cord causes the sacral regions to be affected first, followed by the lumbar, then thoracic, and then cervical.
Thus, external compression causes ascending deficits starting in the sacral region and traveling up to one or two levels below the actual level of the lesion.