Comparative Cadaveric Study and Anatomic Limitations of the Nasofrontal Trephination: A Novel Endoscopic Corridor for Enhanced Exposure of The Odontoid and Occipital Condyle Regions.

BACKGROUND AND

OBJECTIVES

The endoscopic endonasal approach (EEA) serves as the primary minimally invasive route to the ventral craniovertebral junction (CVJ). However, anatomic constraints limit its caudal reach. Multiport endoscopic approaches may complement a standard EEA providing additional reach. This anatomic study evaluates the EEA's anatomic limitations in accessing the CVJ and examines how contralateral nasofrontal trephination (CNT) port may overcome these constraints.

METHODS

Thirty-two cadaveric specimens underwent EEA and CNT dissections. Key measurements included the nasoaxial line (NAxL) angle, anteroposterior frontal sinus distance, interorbital distance, and distance of odontoid process from the hard palate line. Area of exposure and surgical freedom were quantified using a surgical navigation. A clinical case treated using the CNT approach has been included to demonstrate the technique, instrument utilization, successful healing, and absence of complications.

RESULTS

CNT significantly enhanced area of exposure of both odontoid (1720.41 vs 1086.62 mm 2 , P = <.001) and occipital condyle targets (613.32 vs 446.15 mm 2 , P = <.001), while EEA provided significant greater surgical freedom for both odontoid (1121.91 vs 1030.58 mm 3 , P = <.001) and occipital condyle (888.25 vs 827.74 mm 3 , P = <.001). Frontal sinus anteroposterior distance strongly correlated with CNT odontoid exposure (r = 0.889, P < .001) but not with the occipital condyle (r = -0.009, P = .966). CNT offered a wider angle of attack compared with EEA (49.8° vs 16.5°, P = <.001). NAxL angle inversely correlated with the distance of the odontoid process from the hard palate line level (r = -0.757, P < .001), while showing no significant correlation with EEA exposure area.

CONCLUSION

CNT augments traditional EEA by enhancing inferior access during the management of complex CVJ pathologies. Although NAxL angle may provide guidance in determining the inferior extent of the EEA, anatomic variability and its poor correlation with exposure area limit its standalone utility in surgical planning.