In an adult, the spinal cord terminates in a tapering fashion as the conus medullaris (T12-S4) at the L1-L2 vertebral level. The collection of spinal nerves below this point (eg, L3-S4) exit inferiorly through their respective intervertebral foramina and are referred to as the cauda equina (ie, horse’s tail).
Damage to or compression of the cauda equina (nerve fibers L3–S5) located below L2
Common causes include large posteromedial disk herniation, trauma, and tumors.
Functions
Innervates the lower limb, perineum, and pelvic organs
Innervates the internal and external anal sphincter
Provides parasympathetic innervation to the bladder
Clinical features
Onset: gradual, typically unilateral
Pain
Lower back pain
Severe radicular pain
Motor symptoms
Asymmetric, areflexic, flaccid paresis of the legs
Sensory symptoms
Saddle anesthesia: lack of sensitivity in the dermatomes S3–S5, affecting the areas around the anus, genitalia, and inner thighs (may be asymmetric)
Urogenital and rectal symptoms
Late onset of urinary retention
Change in bowel habits due to loss of anal sphincter control
