Opening cranial cisterns by the anterior subtemporal keyhole approach to the superior petroclival region: anatomical study and comparative analysis

BackgroundWithout drilling the bony structures, simple incision of the tentorium dorsal to the porus of trochlear nerve by the anterior subtemporal keyhole approach provides narrow exposure in the superior petroclival region. This study was designed to measure and compare the areas of exposure, linear distances, and angles of approach in the superior petroclival region before and after opening cranial cisterns.MethodsThe study was carried out on 20 sides of cadaver heads. With the use of a navigation system, the area of exposure in the dorsum sella and clivus, the ventrolateral area of exposure in brainstem around the BA, the linear exposure of the posterior petroclinoid fold and BA trunk, and the angles of approach to BA tip were evaluated. The length of oculomotor cistern and trochlear cistern, the distance of oculomotor porus between trochlear porus, the linear exposure of the trigeminal nerve, and the angle to the most inferior medial point in clivus were also measured.ResultsThe area of exposure in the dorsum sella and clivus (157.6 ± 27.2mm2), the ventrolateral area of exposure in brainstem around BA (249.5 ± 29.7mm2), the linear exposure of the posterior petroclinoid fold (11.5 ± 0.6 mm) and BA trunk (10.3 ± 2.0 mm), and the angle of approach in the vertical axis to the BA tip (13.7° ± 1.7°) were significantly greater after opening cisterns. The angles of approach in the horizontal axis to the BA tip (24.5° ± 1.1° vs 24.7° ± 0.8°) were not statistically different. The length of oculomotor cistern and trochlear cistern, the distance of oculomotor porus and trochlear porus, the linear exposure of the trigeminal nerve, and the angle of approach to the most inferior medial point in clivus were 6.7 ± 1.3 mm, 10.7 ± 2.4 mm, 9.6 ± 2.3 mm, 15.8 ± 1.4 mm, and 13.0° ± 1.5°, respectively.ConclusionThe areas of exposure, linear distances, and the angles of approach in the superior petroclival region can be increased after opening cranial cisterns by the anterior subtemporal keyhole approach.