Posterolateral tract

At a glance

English

Posterolateral tract

Latin (TA2)

Fasciculus posterolateralis

System

Nerve

Region

Whole body

Side

Single, on the midline

About the posterolateral tract

The posterolateral tract, better known as Lissauer's tract or the dorsolateral fasciculus, is a slender band of white matter capping the tip of the posterior horn of the spinal cord. It sits where the posterior roots enter the cord, between the surface and the substantia gelatinosa. It is found at every level of the cord and is best developed in the upper cervical region. The name honours the German neurologist Heinrich Lissauer.

Its fibres are mostly thin. Many are unmyelinated, and the myelinated ones are among the last in the cord to gain their sheaths, late in fetal life. Most come from the lateral division of the posterior roots, as the central branches of small cells in the spinal ganglia; others are intrinsic fibres that begin and end in the cord. On entering, the fibres divide and run up or down within the tract for no more than one or two segments before turning into the grey matter, mostly near the level at which they entered.

They end in the superficial layers of the posterior horn, mainly the substantia gelatinosa and the marginal zone, with some reaching the nucleus proprius. The second-order neurons there send their axons across the anterior white commissure to the anterolateral part of the opposite side, where they join the spinothalamic system. That route carries pain, temperature and crude touch through the spinal lemniscus to the ventral posterolateral nucleus of the thalamus and then, by way of the internal capsule, to the somatosensory cortex of the postcentral gyrus.

Because fibres spread over a segment or two before crossing, the upper limit of lost pain sensation after a cord lesion usually lies a level or two below the injury. The tract lies outside the territory of the anterior spinal artery, so, with the posterior columns, it is spared when that artery is blocked. It has also been described as affected in the cord degeneration of pernicious anaemia.

Course and supply

Supplies

Carries entering pain, temperature and crude touch fibres a short way up or down the cord before they end in the posterior horn.

Blood supply

Lies at the back of the cord in the territory of the posterior spinal arteries, so it escapes anterior spinal artery occlusion.