Supracerebellar-supratrochlear and supracerebellar-infratrochlear triangles as gateways to the posterolateral midbrain and ambient cistern: descriptive and quantitative analysis of microsurgical anatomy.

Background: Anatomic triangles aid neurosurgeons in accessing deep targets. However, the supracerebellar-supratrochlear triangle (STT) and supracerebellar-infratrochlear triangle (ITT), defined by specific landmarks, remain underexplored. This study provides a descriptive and quantitative analysis of their anatomical parameters to enhance microsurgical utility.

Methods: The lateral supracerebellar-infratentorial (SCIT) approach with a retrosigmoid craniotomy was performed on 5 formalin-fixed, latex-injected, cadaveric heads, with STT and ITT identified bilaterally. Measurements were acquired using neuronavigation. Three additional cadaver brains were used to illustrate pertinent brainstem anatomy. Three-dimensional modeling and diffusion tractography visualized associated structures and fiber tracts.

Results: The longest edges of the STT and ITT are the inferior edges, formed by the trochlear nerve and quadrangular lobule, respectively (mean [SD], 15.8 [2.0] mm and 29.4 [2.8] mm, respectively). Full expansion of retractable edges increased the area of the STT from 80.6 [15.5] mm² to 159.5 [25.5] mm² and the area of the ITT from 81.1 [28.6] mm² to 244.7 [57.9] mm². The STT provides access to the quadrigeminal cistern, posterior tegmentum, and P2P and P3 segments of the posterior cerebral artery. The ITT grants access to the ambient cistern, cerebellomesencephalic fissure, anterior tegmentum, S3 segments of the superior cerebellar artery, and lateral mesencephalic vein.

Conclusions: Although the paramedian SCIT approach also reaches the posterolateral midbrain and ambient cistern, the lateral SCIT was preferred in this study because it also provides ideal access. With these approaches, the STT and ITT are secure and expandable anatomical corridors, facilitating access to intrinsic brainstem lesions, including tumors and vascular malformations.