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E1077. Radiographic Metrics of Neuraxial Deformation Stress
Authors
  1. Marios Papachristou; University of Pittsburgh Medical Center
  2. Vikas Agarwal; University of Pittsburgh Medical Center
  3. Barton Branstetter; University of Pittsburgh Medical Center
Background
Classic etiologies of cervicomedullary syndrome (CMS) such as Chiari I malformation (CM) and basilar invagination (BI) are familiar to radiologists of all specialties and levels of experience. Less familiar may be the contribution of relatively subtle craniocervical bony anatomy and alignment to the pathogenesis of CMS. Neuraxial Deformation Stress (NDS) is a general term encompassing forces acting on the brainstem neuraxis and is thought to contribute to CMS. NDS mechanisms may be subdivided into ventral brainstem compression (VBSC) and stretch-induced myelopathy (SIM). Moreover, simple radiographic measurements have been associated with prediction of symptomatic NDS: Clivo-axial angle (CXA) and Grabb’s line (pB-C2). Familiarity with these measurements and their implications can improve radiologists’ relevance to our neurosurgical colleagues and the patients we both serve.

Educational Goals / Teaching Points
1) To review mechanisms of NDS 2) To gain awareness of the association between CMS and radiographic metrics of NDS: CXA and pB-C2. 3) To learn measurement methods of CXA and pB-C2 and integrate them into clinical reports

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
MEASUREMENTS: Martin et al. (2017) reported a system of MRI landmarks for measuring CCA and pB-C2. 4 reference points: Spheno-occipital synchondrosis, Basion, Ventral cervicomedullary dura, and posterior-inferior cortex of C2 3 reference lines: Clival slope, soft tissue posterior axial line, and Basion-C2 line CLIVO-AXIAL ANGLE (CXA): CXA: angle formed between the clival slope and posterior axial line. -Considered a surrogate measurement for deformation of the brainstem neuraxis. -Normal range of 145° to 165°, +/-10° -CXA of less than 135° is considered potentially pathologic. The incidence of clivo-axial kyphosis in Chiari I patients with failed posterior fossa decompression is well documented. While craniocervical kyphosis may exacerbate symptoms in Chiari I and basilar invagination patients, abnormal CXA is associated with symptoms independent of other conditions. pB-C2: pB-C2: perpendicular distance from a line connecting the basion and postero-inferior cortex of C2 (PAL) to the ventral cervicomedullary dura -Quantifiable indicator of ventral brainstem compression related to craniocervical anatomy. -pB-C2 of 9 mm or more suggests high risk of ventral brainstem compression, requiring consideration for craniospinal reduction or trans-oral decompression, and fusion-stabilization.

Conclusion
The clinical significance of VBSC and NDS is well established in scientific literature. While initially characterized in the context of Chiari I malformation and basilar invagination, these mechanisms have now been identified as pathologic independent of these clinical entities. Likewise, the correlation of abnormal CXA and pB-C2 measurements to VBSC and NDS is being increasingly recognized in the neurosurgical community. CXA and pB-C2 are convenient to obtain and may affect clinical decision making. As such, radiologists can improve our contribution to clinical decision-making by having a basic familiarity with these measurements and reporting them when relevant.