Basilar invagination

Basilar invagination is a topic that involves Spine & neurosurgeon and ENT surgeon.
Here is a presentation that summarises this topic.

1. Basilar Invagination Dr. Vijay Kumar Loya

2. Umbrella term which encompasses various congenital and acquired forms of the craniovertebral junction (CVJ) anomalies where odontoid process of C2 prolapses into foramen magnum. associated terms - Atlantoaxial impaction, upward (or superior) migration of odontoid, Basilar impression, cranial(or vertical) settling & platybasia

3. Basilar Impression PRIMARY (Congenital)- 1% Vertebral defects - (atlanto-occipital fusion) Klippel-Feil syndrome Arnold- Chiari Malformation(ACM) Syringomelia Odontoid anomalies Hypoplasia of atlas Bifid posterior arch of atlas SECONDARY (Acquired) Paget’s Disease Osteomalacia Rickets Osteogenesis Imperfecta (III,IV>I) Rheumatoid arthritis Neurofibromatosis Ankylosing Spondylitis

4. Embryology of Atlas & Axis

5. Spine develops from 42- 44 pairs of somites ( 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 8-10 coccygeal). Formation of OCJ, atlas & axis is more complex. First cx sclerotome – part of occipital condyle & tip of odontoid(proatlas)

6. Occipitalization of Atlas Usually triad of low posterior hairline, short neck, and torticollis is seen(painful torticollis). Anterior (Zone 1) most common. Lateral with neuro deficit. Wang has described four patterns of course of vertebral artery. In two of them artery travels posterior to lateral mass of C2.

7. Atlantal Arch defects Currarino classified them into A-failure of posterior fusion with midline cleft B- U/L cleft defect C- B/L cleft defect D – retained posterior tubercle E- complete arch defect. Can present with weakness, paraesthesia, transient quadriparesis, and atlantoaxial instability & basilar invagination.

8. Odontoid Anomalies A rare anomaly – Os avis can be seen with severe neurologic sequelae.

9. Os Odontoideum Hypoplasia & Aplasia associated with SED congenita II & MPS If a sclerotic oval & round ossicle ( Bergmann) seen as a gap from odontoid Can be orthotopic or Dystopic (with BI) Increased incidence in KFS, Down’s , Morquio, SED. ( Congenital theory ) Other proposed cause are of Non-union theory caused by distraction by alar ligaments – also in infection, unknown trauma, osteonecrosis. Neck pain, torticollis or suboccipital headache can be presenting symptoms. Neurologic symptoms can vary from transient paresis to frank myelopathy. Vertebrobasilar insufficency may be seen Cranial nerve involvement suggest basilar invagination.

10. Vertebral artery in these deformities

11. Down’s Syndrome with os odontoideum with basilar invagination

12. Chiari Malformation - Most common, tonsillar herniation > 5mm; if<5mm- ectopia. Seen in adolescents or adults. Syringomelia & Hydrocephalus common. Other defects - Basilar invagination, Segmentation defects, KFS, scoliosis. Associated with spinal dysraphism - myelomeningocele or inencephaly. Truly called Arnold-Chairi Malformation. Medulla, fourth ventricle and pons all displaced downward. Other abnormalities include hydrocephalus, GI/GU abnormalities.

13. 3. - spinal dysraphism with cerebellum and/or brainstem pushing out through a defect in the back of the head or neck (cranioraschis). High mortality rate with severe neurological deficits. 4. - very severe & rare. Brainstem, cerebellum fail to develop rarely.

14. Goel et.al classification of Basilar Invagination

15. New classification of Basilar Invagination Goel et.,al further classified into Group A & B A – ‘fixed’ atlantoaxial dislocation and the tip of odontoid process invaginated into foramen magnum above all radiographic lines. B – Odontoid process & clivus remained anatomically aligned. Odontoid process was above Chamberlain line but below Mcrae & Wackenheim’s line. Group A is characterised by an element of instability, Chairi malformation & slippage of facets of C1 over C2 due to oblique orientation instead of a horizontal one vis-à-vis spondylolisthesis.

16. Klippel-Feil syndrome Fusion can be of three types : (Feil et.al) I – block fusion of all cervical & upper thoracic segment II – one or two pairs of cervical vertebra III – cervical with lower thoracic or lumbar vertebra fusion

17. Three patterns of cervical fusions create a high risk for Symptomatic instability C2-C3 fusion with occipitocervical synostosis Extensive fusion of cervical vertebra with an abnormal OC junction Two fused segments with separated by an open joint space. Samartzis classification: Type I – single congenital fused cervical Type II – multiple noncontigous congenitally fused Type III – multiple contigous fused level

18. Rheumatoid arthritis Systemic disorder involves small blood vessels & synovium. Female predominance, bimodal distribution. MTP feet>Cervical Spine>MCP hand. - INVOLVEMENT Atlantoaxial>Vertical migration of odontoid>Subaxial - FREQUENCY. Mye lopathy difficult to assess due to concomitant joint destruction, neuropathy & myopathy.

19. Pathology - Synovitis - destroys facet joints, erodes dens, weakens ligamentous attachments. Characteristic pannus may form between odontoid peg & ventral dura mater that can compress spinal cord. Inflammatory destruction of lateral atlantoaxial joints can lead to vertical migration of dens ————> Flattening, softening and atrophy of medulla. Repetitive movement of atlantoaxial against the neuraxis that causes mechanical wear- and- tear phenomenon that leads to myelopathy.

20. C/F- pain at craniocervical junction or occipital headache. Compression of trigeminal nucleus with cranial settling can cause facial pain Verterbrobasilar insufficiency - tinnitus, vertigo, loss of equilibrium, visual disturbances. Bulbar involvement -diplopia, dysphasia, urinary frequency or retention. Brainstem compression - vertical nystagmus & Cheyne-Stokes respirations.

21. NURICK’S CLASSIFICATION Grade 0 - Root symptoms only or normal Grade 1 - Signs of cord compression; normal gait Grade 2 - Gait difficulties but fully employed Grade 3 - Gait difficulties prevent employment, walks unassisted Grade 4 - Unable to walk without assistance Grade 5 - Wheelchair or Bedbound Type to enter a caption.

22. RISK FACTORS - male gender, severe peripheral disease, use of steroids, and age of onset of disease. Some studies also state that subluxation of spine is associated with HLA-DW2 and HLA-B7.

23. Treatment Principles Type I – Posterior arthrodesis with anterior decompression – same sitting or seperately. Type II – posterior decompression Principles of OC fusion covered previously.

24. Anterior approach to CVJ

25. TRANSORAL ODONTOIDECTOMY

26. Endoscopic odontoidectomy