Craniocervical Instability (CCI/AAI) Clinical Screener
Radiographic measurement validator (CXA angle, Grabb-Oakes, BDI), dynamic upright MRI imaging criteria, bulbar symptom checklist, and a neuro-structural risk evaluator for ME/CFS and hEDS.
Standard hospital MRI scans are conducted in the supine (lying flat) position with the cervical spine in neutral alignment. When supine, gravity reduces the axial load of the 10-pound human skull, temporarily resolving pathological subluxation. Up to 70% of true dynamic CCI and AAI cases are completely missed on standard supine MRI. Evaluation requires Upright / Weight-Bearing Dynamic MRI with flexion and extension views or a dynamic cervical CT scan PMID: 30528205.
Core Radiographic Parameters & Thresholds
Neurosurgical evaluation of the craniocervical junction relies on objective millimeter and angular measurements:
| Radiographic Metric | Normal Anatomy | Pathological Cutoff | Anatomical Significance |
|---|---|---|---|
| Clivo-Axial Angle (CXA) | > 150° (Flexion ≥ 145°) | < 135° (< 140° Borderline) | Angle between clivus and axis. Acute kyphotic angulation causes direct ventral deformative stress on the medulla oblongata and pontomedullary junction. |
| Grabb-Mapstone-Oakes (pB-C2) | < 7.0 mm | ≥ 9.0 mm (7–8.9 mm Borderline) | Perpendicular distance from pB-C2 line to the dura. Measurements ≥ 9.0 mm predict high risk of ventral brainstem compression and medullary ischemia. |
| Basion-Dens Interval (BDI) | < 8.5 mm (Adults) | ≥ 12.0 mm (Harris Line) | Distance from the tip of the basion to the tip of the odontoid. Excessive widening indicates vertical atlanto-occipital instability. |
| C1-C2 Lateral Mass Overhang (AAI) | < 1.0 mm symmetric | > 2.0 mm displacement | Dynamic rotational CT/open-mouth view. Evaluates transverse ligament integrity and rotatory subluxation at the atlantoaxial joint. |
CCI / AAI Radiographic & Clinical Symptom Screener
Input your upright dynamic MRI measurements and select active clinical signs to calculate your composite neuro-structural risk index.
Peer-Reviewed References & Neurosurgical Literature
- Henderson FC, et al. Neurological and spinal manifestations of the Ehlers-Danlos syndromes. Am J Med Genet C Semin Med Genet. 2017;175(1):195-211. PMID: 28220607
- Henderson FC, et al. Deformative stress associated with an abnormal clivo-axial angle: A finite element analysis. Surg Neurol Int. 2018;9:109. PMID: 29896434
- Grabb PA, Mapstone TB, Oakes WJ. Ventral brain stem compression in pediatric and adult patients with Chiari I malformations and basilar invagination. Neurosurgery. 1999;45(3):520-528. PMID: 10493375