Nerve
Cauda equina
Descending nerve roots below the end of the spinal cord
High-yield
These are peripheral roots. Injury can cause weakness with reduced tone or reflexes in the affected distribution. Bladder disturbance and saddle sensory loss may appear in different combinations; neither follows a dependable early-versus-late rule.
Overview
The cauda equina is a loose bundle of roots traveling through cerebrospinal fluid below the conus. They arise from lower cord segments and descend to their exit levels because the spinal cord ends above the bottom of the vertebral canal.
Reference facts
- Origin
- Ventral and dorsal roots from lower lumbar, sacral and coccygeal spinal cord segments, including segments above the conus itself
- Root value
- Usually described as L2–L5, S1–S5 and Co1 roots; descriptions of its uppermost lumbar extent vary
- Course
- Descend beside the filum terminale in the lumbar cistern before reaching their corresponding exits from the vertebral canal
- Motor
- Somatic fibers to lower-limb and perineal muscles, including external sphincters; sacral roots also carry parasympathetic output to pelvic organs
- Sensory
- Sensory input from the lower limbs and perineal region, with the affected area depending on which roots are involved
Clinical correlation
New difficulty controlling or emptying the bladder, numbness around the genitals or anus, or progressive leg weakness can signal cauda equina compression and requires emergency assessment. Severe bilateral leg pain is not required, and no single symptom reliably excludes the syndrome.
Frequently asked questions
What are the roots of the cauda equina?
Usually described as L2–L5, S1–S5 and Co1 roots; descriptions of its uppermost lumbar extent vary.
What muscles does the cauda equina supply?
Somatic fibers to lower-limb and perineal muscles, including external sphincters; sacral roots also carry parasympathetic output to pelvic organs.
What is the sensory distribution of the cauda equina?
The cauda equina carries sensation from the sensory input from the lower limbs and perineal region, with the affected area depending on which roots are involved.
What is the course of the cauda equina?
Descend beside the filum terminale in the lumbar cistern before reaching their corresponding exits from the vertebral canal.