Contralateral Transmaxillary Approach versus Purely Transnasal Approach to the Petroclival Region—An Anatomical and Radiological Study

Background Dealing with petroclival lesions is challenging even for the most experienced skull base surgeons. The recently proposed contralateral transmaxillary approach (CTMA) could be advantageous as a surgical route to the petroclival region (PCR).

Objective To study the anatomical limits of CTMA to the PCR and to compare it with a purely transnasal approach (TNA).

Methods This study was divided in two parts. In the first one (anatomical), CTMA to the PCR was bilaterally performed in two silicone-injected specimens (four sides). The procedure was initiated with a contralateral Caldwell–Luc’s approach. With the aid of a 0-degree endoscope, medial maxillectomy, posterior septectomy, and wide bilateral sphenoidotomies were performed. The vidian canal was dissected, and foramen lacerum (FL) and internal carotid artery (ICA) were identified. Drilling of the middle clivus, and petrous apex medial and inferior to the ICA, was performed until the anatomical limits of PCR were reached. At the end of the dissection, TNA was performed to see whether the same anatomical limits could be reached. In the second part of the study (radiological), 10 CT scans (20 sides) were analyzed and the following parameters were measured: (1) the distance between the infraorbital foramen and internal acoustic canal on the contralateral side (IOF-IAC), typical of a CTMA; (2) the distance between the anterior nasal spine and internal acoustic canal (ANS-IAC), typical of a TNA; and (3) the angle between the before-mentioned points of reference (IOF-IAC-ANS).

Results CTMA to the PCR was successfully completed in both specimens bilaterally. Petrous apex drilling was initiated medial and deep to the paraclival ICA; early identification of the abducens nerve was paramount during this step. Further drilling was greatly facilitated by ICA mobilization, which required superior detachment of the eustachian tube, and dissection of FL. After sufficient bone drilling, the dura was opened and it was possible to clearly identify the anatomical limits of the approach: the abducens nerve superiorly, the inferior petrosal sinus inferiorly, the ICA anterolaterally, the brain stem and cerebellopontine angle medially, and the IAC posteriorly. The entry to this region was defined by the abducens nerve, the paraclival ICA, and the FL (“Gardner’s triangle”). Only 0-degree endoscopes and straight instruments were used during the whole CTMA. Following that, a TNA was performed. Reaching all the before-mentioned anatomical limits was only possible with the aid of angled endoscopes and instruments. More retraction and manipulation of the ICA were also necessary. From CT analysis, the average (±1 SD) working distance for CTMA (IOF-IAC) and TNA (ANS-IAC) was 9.67 (±0.61) cm and 10.24 (±0.81) cm, respectively (p = 0.019). The average angle between the two approaches was 21.28 (±1.67) degrees.

Conclusion CTMA to the PCR permits access to all its anatomical limits using 0-degree endoscopes and straight instruments. Performing TNA to the PCR was possible only with the aid of angled endoscopes and instruments and with increased manipulation of the ICA. CTMA to the PCR allows shorter working distance and provides a better working angle when compared with TNA.