The clivo-axial angle (CXA) is a measure of the angle between the clivus, a bony part of the base of the skull, and the spine. It is used to aid in the diagnosis of craniocervical instability. It is sensitive to horizontal instability and characterizes the relationship between the skull, the brainstem, and the odontoid process, including abnormalities due for example, to a compromised transverse ligament.
Definitions[edit | edit source]Also called the clivus canal angle, the clivus vertebral angle, the clivus spinal angle or the clivus cervical angle, terms and measurement methodology can vary from study to study and from neurosurgeon to neurosurgeon. In an effort to standardize terminology and measurement, a 2014 consensus statement defined the CXA as "the angle between the clivus line and the posterior axial line."
The clivus line is drawn along the lower third of the clivus, from the spheno-occipital synchondrosis to the basion; in the case of basilar invagination, it is drawn from the spheno-occipital synchondrosis to the top of the odontoid process. The posterior axial line is differentiated to reflect either the bone contour of the axis on CT, the so-called bone CXA, or the ligamentous margin of the odontoid—the soft tissue CXA. The soft tissue CXA, necessarily including thickening of the posterior ligament due to pannus, may be more pertinent in identifying possible ventral brainstem compression, and is therefore more representative of the pathology.
Epidemiology[edit | edit source]
The average CXA in healthy or nonsymptomatic population is estimated to be approximately 150 degrees. Several studies have shown that a CXA lower than 135 degrees, a frequently used cutoff, is uncommon in the healthy population (see table below) and is associated with pathological conditions such as brainstem compression in patients with rheumatoid arthritis. A consensus statement formed at the second International CSF Dynamics Symposium of the Chiari and Syringomyelia Foundation in 2013, proposed that a CXA lower than 135 degrees could be seen as “potentially pathological.”
|Study||Term||Definition||Number of healthy persons||Average CXA||standard deviation||Range|
|Bothelo & Ferreira (2013)||Clivo-canal angle (CCA)||The angle between the line extending from the top of the dorsum sellae to the basion and the line between the inferodorsal portions of C2 to the most superodorsal part of the dens.||33||148°||± 9.8°||129°-175°|
|Batista et al. (2015)||Clivus-canal angle (CCA)||Measured as the angle at the intersection of a line extending from the inferior one-third of the clivus and a line extending from the inferodorsal portion of the C-2 vertebral body to the superodorsal part of the dens||100||153.6°||± 7.6°||132.3°–173.9°|
|Bundschuh et al. (1987)||Cervicomedullary angle||Angle subtended by lines drawn parallel to the ventral surfaces of the medulla and upper cervical cord||50||155.2°||± 8,7°||135°-175°|
|Asal and Hasan (2018)||Clivo-axial angle (CAA)||The angle between the line extending from dorsum sella to basion and the line drawn along the boundary superoposterior and inferoposterior corners of the C2 vertebrae.||65||153.66°||±6.35°||139.5-169.5|
|Nagashima and Kubota (1983)||Clivo-axial angle (C-A angle)||The clivus line (line drawn along posterior surface of clivus) and the axis line (line drawn along posterior surface of axis) form the angle.||41||158.2°||± 9.8°|
Gender[edit | edit source]
Women have increased range of motion (change in CXA from flexion to extension) than men.
Ehlers-Danlos Syndrome[edit | edit source]
A unpublished study of the CXA in patients with Ehlers-Danlos syndrome and a control group of patients with cervical spondolysis found that EDS patients had an average CXA of 139.7±10.4 degrees as compared to the control group 148.9±8.4. They also had a greater change in CXA between flexion and extension: 74.6±24.4 in the EDS group vs 39.4±11.3 in controls.
Migraine[edit | edit source]
Basilar invagination[edit | edit source]
References[edit | edit source]
- Consensus statement. 2nd International CSF Dynamics Symposium, 2013.
- Henderson, Fraser C.; Henderson, Fraser C.; Wilson, William A.; Mark, Alexander S.; Koby, Myles (Jan 1, 2018). "Utility of the clivo-axial angle in assessing brainstem deformity: pilot study and literature review". Neurosurgical Review. 41 (1): 149–163. doi:10.1007/s10143-017-0830-3. ISSN 1437-2320. PMC . PMID 28258417.
- Batzdorf U, Henderson F, Rigamonti D (2016) Eds. Co-morbitidies that complicate the treatment and outcomes of chiari malformation. First edition ed. Chiari Syringomyelia Foundation Inc., Lulu
- Botelho, Ricardo Vieira; Ferreira, Edson Dener Zandonadi (Oct 2013). "Angular craniometry in craniocervical junction malformation". Neurosurgical Review. 36 (4): 603–610; discussion 610. doi:10.1007/s10143-013-0471-0. ISSN 1437-2320. PMC . PMID 23640096.
- Batista, Ulysses C.; Joaquim, Andrei F.; Fernandes, Yvens B.; Mathias, Roger N.; Ghizoni, Enrico; Tedeschi, Helder (Apr 2015). "Computed tomography evaluation of the normal craniocervical junction craniometry in 100 asymptomatic patients". Neurosurgical Focus. 38 (4): E5. doi:10.3171/2015.1.FOCUS14642. ISSN 1092-0684. PMID 25828499.
- Bundschuh, C; Modic, Mt; Kearney, F; Morris, R; Deal, C (Jul 1, 1988). "Rheumatoid arthritis of the cervical spine: surface-coil MR imaging". American Journal of Roentgenology. 151 (1): 181–187. doi:10.2214/ajr.151.1.181. ISSN 0361-803X.
- Şahan, Mehmet Hamdi; Asal, Neşe (Dec 1, 2018). "Is there a relationship between migraine disease and the skull base angles?". Ortadoğu Tıp Dergisi. 10 (4): 456–470. doi:10.21601/ortadogutipdergisi.411138.
- Nagashima, C.; Kubota, S. (1983). "Craniocervical abnormalities. Modern diagnosis and a comprehensive surgical approach". Neurosurgical Review. 6 (4): 187–197. ISSN 0344-5607. PMID 6674836.
- Casey, A. T.; Smith, F.; Davagnanam, I.; Khan, F.; Prezerakos, G. K. (Mar 1, 2019). "FM1-7 Cranio-cervical instability in ehlers-danlos syndrome employing upright, dynamic MR imaging; a comparative study". Journal of Neurology, Neurosurgery & Psychiatry. 90 (3): e22–e22. doi:10.1136/jnnp-2019-ABN.69. ISSN 0022-3050.