Posterolateral tract

The posterolateral tract (fasciculus of Lissauer, tract of Lissauer, dorsolateral fasciculus) is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots.

Composition and path
It consists of fine fibers which do not receive their medullary sheaths until toward the close of fetal life.

It is usually regarded as being formed by some of the fibers of the posterior nerve roots, which ascend for a short distance in the tract and then enter the posterior column, but since its fibers are myelinated later than those of the posterior nerve roots, and do not undergo degeneration in locomotor ataxia, they are probably intersegmental in character.

In addition it contains great numbers of fine non-medullated fibers derived mostly from the dorsal roots but partly endogenous in origin.

These fibers are intimately related to the substantia gelatinosa which is probably the terminal nucleus.

The non-medullated fibers ascend or descend for short distances not exceeding one or two segments, but most of them enter the substantia gelatinosa at or near the level of their origin.

Clinical significance
During a complete occlusion of the ventral artery of the spinal cord, it is the only tract spared along with the dorsal columns.

Eponym
The tract of Lissauer was named after German neurologist Heinrich Lissauer (1861-1891).