# Clinical Cases: Pelvic Nerves ## 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 1. **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 ![Sacral Plexus](case_01_image.jpg) *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 1. **Surgical emergency:** Urgent decompressive laminectomy and discectomy within 24-48 hours 2. **Pre-operative:** Urinary catheter placement for bladder decompression 3. **Post-operative:** Monitor for return of bladder and bowel function 4. **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 --- ## Case 2: Pudendal Nerve Entrapment ### Patient Demographics - **Age:** 52 years old - **Sex:** Female - **Occupation:** Cyclist (recreational) ### Chief Complaint Chronic perineal pain and numbness that worsens with sitting for 18 months. ### History of Present Illness The patient developed insidious onset of burning pain and numbness in the perineal region approximately 18 months ago. The symptoms are localized to the area between the anus and clitoris. Pain is rated 6-7/10 at baseline and increases to 9/10 when sitting, particularly on hard surfaces. Interestingly, she reports significant relief when sitting on a toilet seat (which does not contact the perineum). Standing and lying down also provide relief. She is an avid cyclist and notes that symptoms began shortly after she increased her training for a long-distance cycling event. She has stopped cycling for 6 months without significant improvement. She denies urinary incontinence, fecal incontinence, or sexual dysfunction, though she reports dyspareunia. MRI of the lumbar spine and pelvis were unremarkable. ### Physical Examination - **Vitals:** Within normal limits - **Neurological examination:** - Sensory: Decreased sensation to light touch over the perineum in the distribution of the pudendal nerve (vulva, perineal body, perianal region) - Motor: Normal anal sphincter tone, normal bulbocavernosus reflex - Tinel's sign: Positive tenderness with percussion over the ischial spine on the right - **Pelvic examination:** Tenderness on palpation of the right ischial spine region; no pelvic masses ### Diagnostic Studies 1. **Pudendal nerve terminal motor latency testing:** Prolonged latency on the right side consistent with nerve injury 2. **Diagnostic pudendal nerve block (CT-guided):** Significant (>50%) pain relief following injection at the ischial spine ### Diagnosis **Pudendal Nerve Entrapment** (pudendal neuralgia), likely at the level of the ischial spine. ### Anatomical Correlation The pudendal nerve (S2-S4) is the principal somatic nerve of the perineum. It follows a distinctive course that creates multiple potential sites of entrapment. After forming in the pelvis, the nerve exits through the greater sciatic foramen below the piriformis muscle, curves around the posterior aspect of the ischial spine (where a pudendal nerve block is performed), and re-enters the perineum through the lesser sciatic foramen. It then travels in the pudendal canal (Alcock's canal), a fascial tunnel on the lateral wall of the ischioanal fossa formed by the obturator fascia. The nerve provides sensory innervation to the external genitalia and perineum, motor innervation to the external urethral and anal sphincters, and motor innervation to the perineal muscles. Entrapment can occur at the sacrospinous ligament (near the ischial spine), at the entrance to or within the pudendal canal, or from direct compression (as with cycling, where the pudendal nerve is compressed between the bicycle seat and the pubic bone). The diagnosis is supported by the "Nantes criteria": pain in the pudendal nerve distribution, worsened by sitting, no sensory impairment on waking, no objective sensory loss (though it may be present), and relief with pudendal nerve block. ### Treatment 1. **Conservative management:** - Activity modification (avoid prolonged sitting, use cushion with cutout) - Physical therapy focused on pelvic floor relaxation - Medications: tricyclic antidepressants, gabapentinoids for neuropathic pain 2. **Interventional:** Serial pudendal nerve blocks with local anesthetic and corticosteroid 3. **Surgical:** Pudendal nerve decompression (release of sacrospinous ligament) if conservative measures fail