Brown-Sequard Syndrome is caused by damage to one half of the spinal cord - either left or right. This hemitransection of the cord produces a characteristic set of clinical signs and symptoms.

The diagram opposite shows the effects of hemitransection of the cord on the right side of the individual.

The symptoms of Brown-Séquard syndrome are as follows:

* = Side of the lesion
1 = hypotonic paralysis
2 = spastic paralysis and loss of vibration and proprioception (position sense) and fine touch
3 = loss of pain and temperature sensation

In the Brown-Séquard syndrome the signs and symptoms can be explained by

1. interruption of the lateral corticospinal tracts
2. interruption of dorsal column axons
3. interruption of lateral spinothalamic tracts and anterolateral system

The segmental injury to the cord usually damages the motoneurones innervating muscles of that myotome, with a hypotonic paralysis in which the muscles are deprived of their innervation.

The spastic paralysis below the lesion is due to activity in the motoneuones that are still in contact with their muscles. The mechanisms underlying spastic paralysis will be discussed later.

Ipsilateral loss of fine touch sensation, vibration sense and proprioception below the level of the lesion is due to section of the dorsal columns

Contralateral loss of pain and temperature sensation usually occurs 2-3 segments below the level of the lesion, because the spinlothalamic system crosses the cord within a few segments of the segment of origin of the peripheral pain pathway.

As the spinothalamic tract carries the sense of crude touch, the loss of this sensation corresponds to that of the pain pathway. The patient will not be able to localize where they were touched, only that they were.

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