Microsurgical Pathways to Anterolateral Pons and Upper Cerebellopontine Cistern: Utilizing Supratrigeminal and Infratrigeminal Triangles

Introduction: Anatomical triangles can serve as useful landmarks guiding neurosurgeons to deep-seated targets. Among these, the supratrigeminal (STT) and infratrigeminal (ITT) triangles are yet to be explored in detail. As corridors to the anterolateral pons and upper cerebellopontine cistern, STT and ITT may provide direct access to peritrigeminal safe entry zones (SEZs). This study offers descriptive and quantitative analyses of STT and ITT, assessing their boundaries, expandability, and surgical exposure to optimize their use in microsurgical approaches. Methods: Five formalin-fixed (10 sides), latex-injected cadaveric heads underwent dissection using extended retrosigmoid craniotomy and transcerebellopontine angle approach. Neuronavigation-based measurements were used to measure the triangle dimensions under standard and expanded exposures (i.e., on the brainstem surface). Statistical analysis, using R software (v.4.4.3), compared standard versus expanded brainstem exposures. Two additional cadaver heads were used to illustrate the pertinent brainstem anatomy. Ultrahigh-resolution 7-Tesla MRI and 3D-modeling were also employed to visualize the associated white matter tracts. Results: STT is bounded medially by the cerebellar quadrangular lobule (QBL), superiorly by the tentorium, and inferiorly by the upper margin of the trigeminal nerve, with mean edge lengths of 14.3(4.7) mm, 11.1(1.6)mm, and 13.0(3.3)mm, respectively. Standard brainstem exposure through STT measured 64.6(27.6)mm 2 . Retraction of individual borders significantly increased the area: tentorium to 108.4(33.1)mm 2 (p