Basilar invagination

basilar invagination / basilar impression

1. Basilar invagination (BASILAR IMPRESSION) DR.SAJIL KRISHNA K

2. Indentation of the skull floor by the upper cervical spine Tip of the odontoid is more cephalid than normal , may protrude into foramen magnum Neurological damage caused by direct pressure/ circulatory compromise of vertebral artery/ impairment o CSF Misdiagnosed as posterior fossa tumor, bulbar polio palsy, amyotrophic lateral sclerosis, spinal cord tumor, or multiple sclerosis

3. Two types Primary and secondary Primary ( incidence 1%) is the congenital structural abnormality of craniocervical junction primary may associated with other vertebral defects like, atlantooccipital fusion , klippel – feil syndrome, arnorld chiary malformation, syringomyelia , odontoid anomalies, hypoplasia of atlas, bifid posterior arch of atlas

4. Secondary is the acquired type resulting from systemic disease that cause softening of osseous structures at the base of skull such as Pagets disease osteomalacia rickets Osteogenic imperfect ( mainly type 3 and type 4) Rheumatoid arthritis Neurofibramatosis Ankylosing spondylitis

5. Clinical presentation Varies from totally asymptomatic to severe Symptoms starts usually during second and third decades ( increased ligamentous laxity and instability with age and decreased tolerance to compression spinal cord and vertebral arteries) Most have short neck, asymmetry of face or skull, torticollis (non specific) Headache in distribution of greater occipital nerve

6. DeBarros et al. divided the sign and symptoms into two categories 1) caused by pure basilar impression 2) caused by Arnold chiari malformation

7. By pure basilar impression :- primary motor and sensory disturbances such as weakness and paresthesia in the limbs, involvement of lower cranial nerves such as trigeminal, vagus , glossopharyngeal and hypoglossal nerves Due to Arnold chiari malformation had symptoms of cerebellar and vestibular disturbance such as ataxia, dizziness, and nystagmus Sexual disturbances such as impotence and reduced libido also seen

8. Higher incidence of vertebral artery anomalies seen Symptoms of vertebral artery insufficiency such as dizziness, seizures, mental deterioration and syncope

9. Radiographic findings Xrays CT MRI (functional MRI obtained with spine in flexion and then extension shows dynamics of spinal cord compression caused by vertebral instability or anomaly)

10. Measurement for diagnosing basilar impression On lateral radiograph

11. On AP radiograph / CT

12. Clark station, redlund – johnell criterion, ranawat criteria are useful to measure basilar impression in adult with rheumatoid arthritis

13. By dividing odontoid process into three equal parts in sagittal plane Positive if anterior rim of atlas is at the level of middle third( station 2) or caudal third ( station 3) Clarks stations

14. Distance between McGregor line and midpoint of caudal margin of second cervical vertebral body . Basilar invagination present if measurement less than 34 ( in men) and less than 29 ( in women). Not applicable in children Redlund - johnell criterion

15. Distance between center of second cervical pedicle and transverse axis of atlas. Basilar invagination present if distal is less than 15 mm ( in men) and less than 13 ( in women) Not applicable in children Ranawat criterion

16. Treatment Conservative in asymptomatic patients with periodic examination Surgery if clinical symptoms worsen and not based on degree of invasion. If symptoms caused by anterior impingement from odontoid , stabilization in extension by an occipital C1-2 fusion. If symptoms persists anterior excision of odontoid can be done after posterior stabilization. Posterior impingement requires suboccipital craniectomy and laminectomy C1 and possibly C2 to decompress brain stem and spinal cord Posterior fusion is recommended in addition to decompression if stability is doubtful

17. Thank you