With Ethics Committee Approval of the experimental protocol granted by the Catholic University of Rome, Italy (protocol number P663/CE/2010 approved on July 28, 2010; subsequent amendment number P437/CE 2012 approved on May 2, 2012) we studied nine fresh nonperfused cadavers—five female and five male—median age 72 years (interquartile range 33; minimum 41, maximum 94), at the CVJ Surgery Research Center in the Department of Public Health, Institute of Legal Medicine, of our University. With the cadaver in the supine position with the head slightly extended (about 25°), a Crockard transoral distractor (Crockard Transoral Instrument Set; Codman and Shurtleff, Raynham, MA, USA) was placed in the oral cavity to expose the CVJ. The C1 tubercle was identified with the finger in all the cadavers and the position of the distractor was chosen according to fluoroscopic assessment (MPX+ portable X-ray unit; Philips Healthcare, Best, The Netherlands). We considered the NPL according to the Kassam definition and conceived a new PIA line from the inferior dental arch up to the hard palate, for preoperative transoral approach planning [11]. The radiological NPL and PIA lines were evaluated by means of X-ray and computed tomography (CT) scan (GE LightSpeed VCT 64 Slice, 1.25 mm thin; General Electric, Milwaukee, WI, USA). Subsequently two thin stainless probes mimicking the endoscopic tools (30 cm length) were inserted through the nostrils (choanae) and the oral cavity, as exposed by the Crockard distractor. The SNPL and SPIA were then radiologically evaluated and compared more as usually [10, 11]. In detail the values of the angular (°) exposure of the transoral and the transnasal approaches, in reference to the hard palate line first described by Aldane [13], were evaluated for each subject by lateral reconstructions (Fig. 1). Percentage differences (%) between the radiological and surgical NPLs were evaluated, along with the radiological and surgical NPL ratio.

The same procedure was used for determining radiological and surgical PIA values. Box plot minimum-maximum values of the NPL and PIA are reported in Tables 1a and 1b. Furthermore, we also evaluated the NAxL and compared it with the SNPL [12].

No platybasia or basilar invagination was identified radiologically, nor was jaw-opening impairment found in any of the cadavers. The collected data were statistically analyzed. A descriptive analysis of the sample was carried out by means of median, interquartile range (IQR), and range for continuous variables, and absolute and relative frequencies for qualitative variables. In order to find statistically significant differences between the two surgical approaches, we performed a Wilcoxon signed rank test. We chose to use a nonparametric test because data were not normally distributed, as demonstrated by the Shapiro-Wilk test [15]. The analysis was performed using SPSS software version 12.0 for Windows and the statistical significance level was set at P = .05.