Basilar Invagination

Definition

 

Cranial prominence of odontoid into region of foramen magnum

- upper cervical spine encroaches on brain stem

 

Aetiology

 

Congenital syndromes

- Klippel Feil Syndrome

- Achondroplasia

- OI

- Downs 

- Morquio

- SED

- NF

 

Congenital abnormalities

- atlas hypoplasia

- bifid posterior arch atlas

- occipitocervical synostosis

 

Acquired

- JRA

- Rickets

- RA

 

Clinical Features

 

Become symptomatic in third decade

- neurological compression 15%

 

Xray

 

McRae's line 

- line along foramen magnum 

- Basion to Opisthion

- dens above line = basilar invagination

 

MacGregor' s Line

- hard palate to inferior aspect occiput

- < 4.5mm above line

 

Ranawat Criterion

- distance between centre of C2 pedicle & transverse axis of C1

- men < 15mm

- women < 13mm

 

MRI 

 

Delineate pathology

 

Management

 

Consider surgery if symptomatic

 

Indications

 

1.  Severe pain

 

2.  Neurology

 

3.  Progression

- basilar invagination > 5mm

 

Technique

 

Surgery complex & fraught with complications

 

1.  Fusion

- Gallie C1/2 fusion if reducible

- occipitocervical fusion if not with C1 laminectomy

 

2. Excision of odontoid