Congenital or Acquired (e.g. LP shunts, CSDH, hydrocephalus).
Chiari 1- tonsillar descent >5mm (3-5mm borderline) below foramen magnum (or McRae basion-opisthion). A/w Syrinx in >30%. (also scoliosis, hydrocephalus in <10%, small p fossa, thickened occipital bone, low lying tent, basilar invagination)
Chiari 2- tonsillar, vermian, medulla/brainstem and 4th ventricular descent. A/w cervicomedullary kinking, myelomeningocele and hydrocephalus in most cases. Numerous other associations e.g. tectal beaking etc.
Chiari 3- occpital encephalocele
Chiari 4- cerebella hypoplasia)
Chiari 0- syrinx without Chiari
1/3 asymptomatic 2/3 have pain- classically suboccipital strain headaches. May c/o limb weakness/wasting.
o/e 3 patterns:
- FM compression signs i.e. ataxia, corticospinal (usually unilateral) and sensory deficits, cerebellar signs, lower cranial nerve palsies.
- Central cord syndrome (dissociated sensory loss, occasional weakness, long tract signs.
- Cerebellar syndrome (truncal and limb ataxia, nystagmus, dysarthria).
Nystamus is classically downbeat. May have Lhermitte's sign.
Important to note presence/absence of brainstem signs e.g. dysphagia o/e, palatal movements (uvula position) and tongue wasting.
Reflexes may be brisk in Chiari but should be reduced with syrinx (LMN phenomenon). As syrinx is usually cervical 'cape like' dissociated sensory loss (loss of spinothalamic pain/temp but preserved LT/JPS/vibration) typically seen. Also loss of temperature hence injuries/ulcers (ask can they tell hot from cold water). Look for atrophy e.g. of hand and arm.
Investigations
MRI whole spine
Cine or CSF flow may be requested
Empty sella may be seen on MR
Indications for surgery
Symptoms
Syrinx
Surgical Mangement (FMD)
Small suboccipital craniectomy e.g. 1cm (max 2cm) to avoid cerebellar slumping.
In paediatrics, bony decomression alone sometimes attempted (USS can be used to assess flow).
Open dura in Y shape
Other measures controversial e.g. opening arachnoid, lysing bands, identifying obex/Magendie, diathermy/subpial dissection to tonsills and tonsillopexy) +/- duroplasty.
Bleeding from marginal sinus may be irritating. Can be packed e.g. with muslin.
Complications include: cerebellar ptosis, CSF leak, brainstem injury/stroke (e.g. PICA), apnoea/respiratory depression.
