Anatomy Pelvis Head Neck · Year 1 · from Anatomy Pelvis Head Neck
Case 1: Cauda Equina Syndrome
Patient Demographics
- Age: 45 years old
- Sex: Male
- Occupation: Warehouse worker
Chief Complaint
Progressive lower back pain, bilateral leg weakness, and difficulty urinating for the past 24 hours.
History of Present Illness
The patient has a 5-year history of chronic lower back pain attributed to degenerative disc disease. Three days ago, he lifted a heavy box at work and experienced sudden worsening of his back pain. Over the following 24 hours, he developed progressive bilateral leg weakness, numbness in the "saddle area" (perineum and inner thighs), and urinary retention. He attempted to void this morning but was unable to initiate urination despite a strong urge. He also reports decreased sensation when wiping after bowel movements. He denies fever, recent trauma beyond the lifting incident, or history of malignancy.
Physical Examination
- Vitals: HR 85 bpm, BP 145/90 mmHg, Temp 37.0C
- Neurological examination:
- Motor: Bilateral ankle dorsiflexion weakness (3/5), knee extension 4/5 bilaterally
- Sensory: Diminished sensation to light touch and pinprick over the perineum (S2-S5 dermatomes), posterior thighs, and perianal region (saddle anesthesia)
- Reflexes: Absent ankle jerks bilaterally, knee jerks 1+ bilaterally
- Rectal examination: Decreased anal sphincter tone, absent bulbocavernosus reflex
- Bladder scan: Post-void residual of 650 mL (bladder distension)
Imaging Workup
- MRI lumbar spine (emergent): Large central disc herniation at L4-L5 with severe compression of the cauda equina; disc material filling the spinal canal
Clinical Image
Anatomical illustration of the sacral plexus demonstrating the nerve roots that form the cauda equina.
Image Source: Wikimedia Commons - Gray's Anatomy Plate 837, Public Domain
Diagnosis
Cauda Equina Syndrome secondary to massive L4-L5 disc herniation.
Anatomical Correlation
The spinal cord typically terminates at the L1-L2 vertebral level as the conus medullaris. Below this level, the lumbar and sacral nerve roots descend through the lumbar cistern as the cauda equina (Latin for "horse's tail") before exiting through their respective intervertebral foramina. The sacral nerve roots (S2-S4) are particularly important for pelvic organ function: they provide parasympathetic innervation to the bladder (via pelvic splanchnic nerves) enabling detrusor contraction, sensory innervation to the bladder and rectum, motor innervation to the external urethral and anal sphincters (via the pudendal nerve), and sensory innervation to the perineum ("saddle area"). Compression of these nerve roots causes the classic triad of cauda equina syndrome: saddle anesthesia (S2-S5 dermatomes), bladder and bowel dysfunction (typically urinary retention followed by overflow incontinence), and bilateral leg weakness. The bulbocavernosus reflex tests the S2-S4 arc: squeezing the glans penis or clitoris should cause anal sphincter contraction. Absence of this reflex indicates sacral nerve root dysfunction.
Treatment
- Surgical emergency: Urgent decompressive laminectomy and discectomy within 24-48 hours
- Pre-operative: Urinary catheter placement for bladder decompression
- Post-operative: Monitor for return of bladder and bowel function
- Prognosis: Outcomes depend on duration and severity of compression; bladder function is often the slowest to recover and may be permanently impaired if surgery is delayed