Makindo Medical Notes

🧠 About Arnold–Chiari Malformation

• A developmental abnormality of the craniocervical junction where the cerebellar tonsils herniate through the foramen magnum. ⬇️
• This can compress the brainstem and cervical spinal cord → leading to neurological symptoms of variable severity.
• Part of the spectrum of congenital hindbrain anomalies; sometimes discovered incidentally on MRI.

📌 Aetiology

• Exact cause unknown; thought to be related to mesodermal/CSF flow abnormalities during embryogenesis.
• Can be acquired after CSF shunting for hydrocephalus (excess drainage lowers pressure → downward herniation).
• Genetic predisposition suspected in familial clusters.

🧩 Clinical Presentation

• 💢 Suboccipital or upper cervical pain (often worsens with Valsalva manoeuvre e.g. coughing/sneezing).
• 🎢 Dizziness / vertigo, imbalance, and ataxia.
• 👅 Cranial nerve palsies (IX, X, XII) → dysphagia, dysarthria, hoarseness, impaired gag reflex.
• 👀 Downbeat nystagmus due to brainstem compression.
• 🦴 Syringomyelia → cape-like sensory loss, weakness, scoliosis.
• In children with Chiari II: may present with spina bifida + hydrocephalus.

🔎 Investigations

• MRI Brain & Spine = gold standard. • Demonstrates cerebellar tonsil herniation (measured in mm below foramen magnum). • Shows hydrocephalus, syrinx, and brainstem compression.
• CT head may show hydrocephalus or bony changes but is less sensitive.

⚕️ Management

• 👀 Asymptomatic / mild cases: Observation + MRI surveillance.
• 🔪 Surgery: Posterior fossa decompression (suboccipital craniectomy ± duraplasty) when there is significant brainstem compression, syrinx, or disabling symptoms.
• 💧 Hydrocephalus management: CSF shunting or endoscopic third ventriculostomy (ETV) if raised ICP present.
• 🧑‍⚕️ Multidisciplinary care: Neurosurgery, neurology, physio, OT, speech therapy.

📊 Classification of Chiari Malformations

💡 Exam Pearls

• Think Chiari I in a young patient with headache + syrinx + downbeat nystagmus.
• Chiari II is almost always associated with spina bifida (neural tube defect).
• MRI spine is essential to look for syringomyelia or tethered cord.