Hans Chiari (1851-1916) was an Austrian pathologist
Definition
>5 mm tonsillar descent = classic cutoff for Chiari I, but:
-0–5 mm can still be symptomatic (in small posterior fossa)
-Tonsillar pointing is more predictive of clinical significance than absolute descent
Epidemiology
-Prevalence ↑ dramatically with modern MRI.
-Often incidental (up to 1% of MRIs).
-Association:
>connective tissue disorders (Marfan, Ehlers-Danlos)→ ligamentous laxity → more craniocervical instability
>Klippel–Feil syndrome
>Craniosynostosis
Types
One falls→ tonsils fall down
Two crowds→ crowded posterior fossa (tonsils + brainstem)
Three out→ herniates OUT into an encephalocele
Four without→ without a cerebellum
Classical 4
- 2/2 CSF flow obstruction
>Headaches (occipital, worsened by coughin/straining/sneezing)
>Tinnitus
>Tinnitus
Pulsatile→ abnormal CSF pulsation
High-Hz→ brainstem-involvement
Intermittent-pressure→ ICP spikes
>Dizziness/ imbalance
>Visual disturbances
Episodes of visual obscurations
-Syringomyelia
>paresthesias→ cape-like (dissociated anesthesia)
-Brainstem/ lower cranial nerve signs
>Dysphagia, dysarthria, sleep‑disordered breathing (central OSA), nystagmus, brisk reflexes in lower limbs
-Associated syndromes
>Syringobulbia→ facial numbness, palatal weakness
>Tethered cord syndrome (Chiari II)
>Basilar invagination/ platybasia→ worsens compression
Diagnostic imaging
-bMRI if suspicion
>c-MRI for all cases
>t&l-MRI, if suspect below cervical sx or spinal deformity
-Cine MRI = evaluates CSF flow obstruction; crucial for:
>deciding surgery in borderline cases
>assessing postoperative success
Craniocervical Angles
-Most important chiari displacement
-Other:
>CXA→ predictor of sx
>pB-C2 line→ ventral brainstem compression
>McRae line/ Chamberlain line→ basilar invagination
-Asymptomatic→ observe, avoid activities that ↑ICP (heavy straining)
>Repeat MRI (1y) if >10mm or syringomyelia
-Symptomatic
w/o syrinx→ usual care, if refractory→ surgery
w/ syrinx→ surgery
-Other indications for surgery
>Visual obscurations
>Papilledema
>LOC
>Central OSA→ CPAP
Surgery
-PFD (post fossa decompress)
>SOC + C1 laminectomy + duraplasty (controversial but ↑ decompression effectiveness)
>Sx pt improve after surgery (>70%)