Clinical Summary: Arnold–Chiari Type II Malformation in Adults

Introduction

Arnold–Chiari type II malformation (CM‑II) is a congenital hindbrain herniation almost always associated with myelomeningocele and hydrocephalus. With improved pediatric care, many patients survive to adulthood, presenting a range of neurological, orthopedic, and urological sequelae—whether or not they underwent posterior fossa decompression as children.

Pathophysiology of Late Symptoms

• Crowded posterior fossa → ongoing mechanical stress on brainstem and spinal cord
• Syringomyelia (40–80% of adults)
• Hydrocephalus / shunt issues
• Tethered spinal cord (scarring at myelomeningocele closure site)
• Musculoskeletal deterioration

Symptom Categories

1. Headache & Craniocervical Pain

• Occipital/suboccipital headache exacerbated by Valsalva maneuvers (coughing, straining)
• Reported in 30–60% of symptomatic adults
• May indicate progressive brainstem impaction (especially if no prior decompression)
• Recurrence after decompression → inadequate bony removal, dural scarring, or re‑herniation

2. Cranial Nerve & Brainstem Dysfunction

• Lower CN deficits (IX–XII): dysphagia, aspiration, dysarthria, vocal cord paralysis (stridor)
• Central sleep apnea – medullary respiratory center compression
• Ocular motor abnormalities: downbeat nystagmus, oscillopsia, impaired smooth pursuit
• Facial numbness, hearing loss, tinnitus (CN V, VIII)
• Surgically decompressed patients may have fewer signs but delayed recurrence possible

3. Cerebellar & Vestibular Signs

• Truncal/appendicular ataxia (multifactorial: cerebellar, proprioceptive, paraplegic)
• Intention tremor, dysmetria, titubation
• Episodic vertigo, nystagmus – may persist even after decompression

4. Syringomyelia

• Sensory: dissociated loss (pain/temperature) in “cape” distribution; dysesthetic burning pain
• Motor: segmental weakness, hand amyotrophy, spastic paraparesis/tetraparesis
• Autonomic: worsening neurogenic bladder/bowel; Horner’s syndrome
• Progression more likely in unoperated patients; decompression with duraplasty can collapse syrinx

5. Hydrocephalus & Shunt Issues

• Shunt malfunction: headache, vomiting, lethargy, cognitive slowing, Parinaud’s syndrome, sudden death
• Overdrainage / slit‑ventricle syndrome: positional headache, chronic subdural hematomas
• Unshunted patients (rare): risk of late‑onset symptomatic hydrocephalus

6. Tethered Cord Syndrome

• Back/leg pain (non‑dermatomal, worsened by flexion)
• Progressive lower limb weakness, gait decline
• Worsening scoliosis, loss of bowel/bladder control
• Surgical untethering can stabilize but recovery incomplete if long‑standing
• Common cause of late deterioration even in previously operated patients

7. Orthopedic & Musculoskeletal Deterioration

• Progressive scoliosis/kyphosis (neuromuscular + syrinx + tethering)
• Joint contractures, osteoporosis, pathological fractures
• Pressure ulcers, Charcot neuroarthropathy (insensate feet)

8. Urological & Gastrointestinal Dysfunction

• Neurogenic bladder: UTIs, vesicoureteral reflux, renal scarring, CKD
• Neurogenic bowel: constipation, fecal incontinence, prolonged colonic transit
• Late complications from bladder augmentation (stones, metabolic issues, perforation)

9. Cognitive & Psychosocial Manifestations

• Executive dysfunction, visuospatial impairment, attention deficits
• Verbal IQ relatively preserved; performance IQ depressed
• High rates of depression, anxiety, social isolation
• Worse outcomes with multiple shunt revisions or episodes of raised ICP

Impact of Prior Surgical Treatment

Posterior Fossa Decompression (PFD)

• Performed PFD: less life‑threatening lower CN crises; syrinx stabilization; but risk of late re‑stenosis
• No PFD: milder hindbrain herniation initially; may become symptomatic in adulthood (ataxia, headache, syrinx)

Shunting

• Shunt‑dependent patients need lifelong surveillance for malfunction (slit ventricles make diagnosis challenging)
• Never shunted (rare): may develop late‑onset hydrocephalus (chronic headache, cognitive decline, gait apraxia)

Tethered Cord Release

• Timely childhood release: may preserve motor/urological function for decades, but re‑tethering common
• First presentation in adulthood: often irreversible losses but surgery can prevent further decline

Acute Deterioration Triggers

• Minor head/neck trauma, general anesthesia with neck extension
• Rapid CSF loss (lumbar puncture), systemic infection/shunt colonization

Surveillance Recommendations for Adults

• Neurological exam (lower CN, cerebellar, motor/sensory level, anal reflex)
• Spine MRI (craniocervical junction + whole spine) to monitor syrinx and brainstem herniation
• Brain imaging (CT/fast MRI) for ventricular size
• Urodynamics + renal ultrasound for neurogenic bladder surveillance
• Sleep study if central sleep apnea suspected
• Neuropsychology assessment for cognitive deficits
• Multidisciplinary care: neurosurgery, urology, orthopedics, physiatry, psychology