Anatomical triangles provide neurosurgeons with the specificity required to access deep targets, supplementing more general instructions, such as craniotomy and approach. The infragalenic triangle (IGT), bordered by the basal vein of Rosenthal (BVR), precentral cerebellar vein (PCV), and the quadrangular lobule of the cerebellum, is one of a system of anatomical triangles recently introduced to guide dissection to brainstem cavernous malformations and has not been described in detail. This study aimed to quantitatively analyze the anatomical parameters of the IGT and present key nuances for its microsurgical use.

A midline supracerebellar infratentorial (SCIT) approach through a torcular craniotomy was performed on 5 cadaveric heads, and the IGT was identified in each specimen bilaterally. Anatomical measurements were obtained with point coordinates collected using neuronavigation. Three cadaveric brains were used to illustrate relevant brainstem anatomy, and 3D virtual modeling was used to simulate various perspectives of the IGT through different approach angles. In addition, 2 illustrative surgical cases are presented.

The longest edge of the IGT was the lateral edge formed by the BVR (mean ± SD length 19.1 ± 2.3 mm), and the shortest edge was the medial edge formed by the PCV (13.9 ± 3.6 mm). The mean surface area of the IGT was 110 ± 34.2 mm² in the standard exposure. Full expansion of all 3 edges (arachnoid dissection, mobilization, and retraction) resulted in a mean area of 226.0 ± 48.8 mm² and a 2.5-times increase in surface area exposure of deep structures (e.g., brainstem and thalamus). Thus, almost the entire tectal plate and its relevant safe entry zones can be exposed through an expanded unilateral IGT except for the contralateral inferior colliculus, access to which is usually hindered by PCV tributaries. Exposure of bilateral IGTs may be required to resect larger midline lesions to increase surgical maneuverability or to access the contralateral pulvinar.

The IGT provides a safe access route to the dorsal midbrain and reliable intraoperative guidance in the deep and complex anatomy of the posterior tentorial incisura. Its potential for expansion makes it a versatile anatomical corridor not only for intrinsic brainstem lesions but also for tumors and vascular malformations of the pineal region, dorsal midbrain, and posteromedial thalamus.

解剖三角形为神经外科医生提供了进入深层目标所需的特异性，补充了更一般的说明，例如开颅手术和入路。盖伦下三角 (IGT)，以罗森塔尔基底静脉 (BVR)、小脑中央前静脉 (PCV) 和小脑四角小叶为界，是最近引入的解剖三角系统之一，用于指导脑干海绵状血管瘤的解剖并且没有详细描述。本研究旨在定量分析 IGT 的解剖参数，并提出其显微外科使用的关键细微差别。

通过环型开颅手术对 5 个尸体头部进行中线小脑上幕下 (SCIT) 入路，并在每个标本的双侧鉴定出 IGT。通过使用神经导航收集的点坐标获得解剖测量结果。使用三个尸体大脑来说明相关的脑干解剖结构，并使用3D虚拟建模来模拟IGT通过不同接近角度的各种视角。此外，还介绍了 2 个说明性手术病例。

IGT 的最长边缘是 BVR 形成的外侧边缘（平均值±SD 长度 19.1 ± 2.3 mm），最短边缘是 PCV 形成的内侧边缘（13.9 ± 3.6 mm）。在标准暴露下，IGT 的平均表面积为 110 ± 34.2 mm ^{2 。}所有 3 个边缘的完全扩张（蛛网膜解剖、动员和回缩）导致平均面积为 226.0 ± 48.8 mm ²，并且深层结构（例如脑干和丘脑）的表面积暴露增加了 2.5 倍。因此，几乎整个顶盖板及其相关的安全进入区都可以通过扩大的单侧 IGT 暴露，但对侧下丘除外，进入下丘通常受到 PCV 支流的阻碍。可能需要暴露双侧 IGT 来切除较大的中线病灶，以增加手术可操作性或进入对侧枕窝。

IGT 为后侧中脑提供了安全的进入路径，并在后天幕切迹的深层和复杂的解剖结构中提供了可靠的术中指导。它的扩展潜力使其成为一个多功能的解剖走廊，不仅适用于脑干内病变，还适用于松果体区、背侧中脑和后内侧丘脑的肿瘤和血管畸形。