=====pB-C2 line=====
pB-C2 line (drawn perpendicular to a line drawn between the [[basion]] and the posterior aspect of the [[C2]] vertebral body, at the most posterior extent of the [[odontoid process]] at the dural interface). The pB-C2 line is a measure of ventral canal encroachment.

The study of Khaleel et al. demonstrates that the odontoid process in adults is anatomically different from that in children: it is longer, more posteriorly inclined, and has a greater pB-C2 line. Therefore, utilization of these parameters with previously published cutoffs in the pediatric population is not appropriate for surgical planning in adults
((Khaleel ZL, Besachio DA, Bisson EF, Shah LM. Estimation of odontoid process
posterior inclination, odontoid height, and pB-C2 line in the adult population. J
Neurosurg Spine. 2014 Feb;20(2):172-7. doi: 10.3171/2013.10.SPINE13405. Epub 2013
Dec 6. PubMed PMID: 24313675.
)).

Ladner et al. divided the pB-C2 line length into Grade 0 (< 3 mm) and Grade I (≥ 3 mm). 
Ventral canal encroachment may explain the symptomatology of selected patients with [[Chiari I malformation]]. The clinical findings presented suggest that patients with Grade I pB-C2 lines, with increased ventral canal obstruction, may experience a higher likelihood of syrinx reduction and headache resolution from decompressive surgery with duraplasty than those with Grade 0 pB-C2 lines
((Ladner TR, Dewan MC, Day MA, Shannon CN, Tomycz L, Tulipan N, Wellons JC 3rd. 
Evaluating the relationship of the pB-C2 line to clinical outcomes in a 15-year
single-center cohort of pediatric Chiari I malformation. J Neurosurg Pediatr.
2015 Feb;15(2):178-88. doi: 10.3171/2014.9.PEDS14176. Epub 2014 Dec 5. PubMed
PMID: 25479579.
)).

For Grabb et al. patients with a pB-C2 measurement of less than 9 mm do not require treatment directed at ventral brain stem compression (VBSC). In select patients with pB-C2 measurements of 9 mm or greater, reduction of VBSC may be prudent before posterior fossa decompression
((Grabb PA, Mapstone TB, Oakes WJ. Ventral brain stem compression in pediatric
and young adult patients with Chiari I malformations. Neurosurgery. 1999
Mar;44(3):520-7; discussion 527-8. PubMed PMID: 10069589.
)).