Cauda Equina

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Introduction

The spinal cord ends around L1, consequently, the caudal nerve roots below the first lumbar root, form the cauda equina. The roots descend at an almost vertical angle to reach their corresponding foramina, gathered around the filum terminale within the spinal theca. The proximal portion of the cauda equina is said to be hypovascular hence more vulnerable if compressed . The cauda equina roots have both a dorsal and ventral root. The ventral root provides motor fibres for the efferent pathway along with sympathetic fibres. The dorsal root is composed of afferent fibres for the transmission of sensation. The functions of those nerves are:

• Sensory and motor fibres to the lower limbs.
• Sensory innervation to the saddle area.
• Voluntary control of the external anal and urinary sphincters.

Aspects of anatomical features relating to saddle sensation, bladder, bowel and sexual function are discussed below;

The first three sacral nerves, S1,2 and 3 supply multifidus and lateral cutaneous branches to the skin and fascia over the sacrum and part of the gluteal region. The 4th and 5th sacral nerves, S4 and 5, along with posterior primary ramus of the coccygeal nerve supply the skin and fascia around the coccyx. The pelvic splenic nerves to the pelvic viscera composed of parasympathetic fibres, travel in the ventral rami of S2,3 and 4. They then leave these nerves as they exit the anterior sacral foramina and pass to the pre-sacral tissue. Some pass to the pelvic viscera alongside the pelvic sympathetic supply and supply the urogenital organs and distal aspect of the large intestine. Others pass immediately into retroperitoneal tissue and into the mesentry of the sigmoid and descending colon . The pudendal nerve supplies the perineum and arises from S2,3 and 4 with its terminal branches including the dorsal nerve of the penis or clitoris.

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