The naso-axial line:  a new method of accurately predicting the inferior limit of the endoscopic endonasal approach to the craniovertebral junction.
BACKGROUND
The endoscopic endonasal approach (EEA) has developed as an emerging surgical corridor to the craniovertebral junction (CVJ). In addition to understanding its indications and surgical anatomy, the ability to predict its inferior limit is vital for optimal surgical planning.


OBJECTIVE
To develop a method that accurately predicts the inferior limit of the EEA on the CVJ radiologically and to compare this with other currently used methods.


METHODS
Predissection computerized tomographic scans of 9 cadaver heads were used to delineate a novel line, the naso-axial line (NAxL), to predict the inferior EEA limit on the upper cervical spine. A previously described method with the use of the nasopalatine line (NPL or Kassam line) was also used. On computerized tomographic scans obtained following dissection of the EEA, the predicted inferior limits were compared with the actual extent of dissection.


RESULTS
The postdissection inferior EEA limit ranged from the dens tip to the upper half of the C2 body, which matched the limit predicted by NAxL, with no statistically significant difference between them. In contrast to the NAxL, the NPL predicted a significantly lower EEA limit (P < .001), ranging from the lower half of the C2 body to the superior end plate of C3.


CONCLUSIONS
The novel NAxL more accurately predicts the inferior limit of the EEA than the NPL. This method, which can be easily used on preoperative sagittal scans, accounts for variations in patients' anatomy and can aid surgeons in the assessment of the EEA to address caudal CVJ pathology.
Division of Pediatric Neurosurgery, University of Florida College of Medicine Jacksonville/Wolfson Children's Hospital, Jacksonville, FL 32207, USA. philipp.aldana@jax.ufl.edu
Philipp R
PR
Aldana
Iman
I
Naseri
Emanuele
E
La Corte
D001268:Atlanto-Axial Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D002102:Cadaver; D004210:Dissection; D006801:Humans; D044583:Neuroendoscopy / Q000379:methods*; D009666:Nose / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011859:Radiography