Tentorial Incisura

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Abstract
The tentorial incisura provides the only communication between the supratentorial and infratentorial spaces (17) (Fig. 5.1). The area between the upper brainstem and the incisural edges is divided into the anterior, middle, and posterior incisural spaces (Fig. 5.2). The anterior incisural space is located anterior to the brainstem and extends upward around the optic chiasm to the subcallosal area; the middle incisural space is located lateral to the brainstem and is intimately related to the hippocampal formation in the medial part of the temporal lobe; and the posterior incisural space is located posterior to the midbrain and corresponds to the region of the pineal gland and vein of Galen. The arterial relationships in the anterior incisural space and the venous relationships in the posterior incisural space are extremely complex, since the anterior incisural space contains all of the components of the circle of Willis and the bifurcation of the internal carotid and basilar arteries, and the posterior incisural space contains the convergence of the internal cerebral and basal veins and many of their tributaries on the vein of Galen. The incisura is intimately related to the depths of the cerebrum and cerebellum, the first six cranial nerves, and the upper brainstem. Some part of the incisura is commonly exposed during the operations for aneurysms, deep tumors and arteriovenous malformations, trigeminal neuralgia, and epilepsy. Much attention has been focused on the distortions of this anatomy by herniation of the brain through the incisural space.