The tentorium cerebelli is a crescent-shaped fold of the dura mater, one of the three layers of meninges that protect the brain. This tent-like structure forms a partition within the cranial cavity, separating the upper cerebral hemispheres from the lower cerebellum. Its presence is significant in maintaining the brain’s anatomical structure by supporting the weight of the upper brain regions.
Anatomical Location and Structure
The tentorium cerebelli is a landmark within the skull, dividing the cranial cavity into two distinct compartments. As a dural reflection, it is a tough, fibrous sheet that extends horizontally over the posterior cranial fossa, which houses the cerebellum. This positioning creates a separation between the occipital and temporal lobes of the cerebrum above and the cerebellum and brainstem below, establishing the supratentorial and infratentorial spaces.
The fixed, convex outer border attaches firmly to the skull. Specifically, it connects to the superior borders of the petrous part of the temporal bones and along grooves on the occipital bone that house the transverse sinuses. These attachments anchor the tentorium, providing a stable platform within the cranium.
The free, inner margin of the tentorium is U-shaped and unattached. This opening is known as the tentorial notch or incisura. The brainstem, which connects the brain to the spinal cord, passes directly through this gap. The tentorial notch is a point where neurovascular structures are concentrated.
Primary Functions of the Tentorium
The primary role of the tentorium cerebelli is to bear the weight of the cerebrum’s occipital lobes, preventing them from exerting excessive pressure on the underlying cerebellum. Without this “tent,” the heavier upper portions of the brain could sag and compress the more delicate structures located in the posterior cranial fossa.
This dural fold also contributes to the compartmentalization of the cranial cavity. This separation helps to contain and direct the flow of cerebrospinal fluid (CSF) within the different cranial spaces. The structure also houses dural venous sinuses, such as the straight sinus and transverse sinuses, which are channels for draining deoxygenated blood from the brain.
Clinical Significance
The tentorium is medically relevant when intracranial pressure rises due to swelling or a space-occupying lesion like a tumor. A condition known as tentorial herniation can occur. This is a life-threatening event where a portion of the brain is forced from one compartment to another, across the edge of the tentorium. For example, the uncus of the temporal lobe can be pushed downward through the tentorial notch, compressing the brainstem.
Head injuries can cause traumatic tears in this dural fold. These injuries can damage the blood vessels that run within or alongside the tentorium, leading to intracranial bleeding. Such events can rapidly increase pressure within the skull, requiring immediate medical intervention to prevent further brain injury.
Tumors can arise directly from the cells that make up the tentorium itself. A tentorial meningioma is a tumor that grows from the meningeal layers of the tentorium. While often benign, these tumors can cause problems by compressing adjacent brain structures, such as the brainstem or cranial nerves, as they grow in size. Surgical removal is often complex due to the proximity of these delicate neurological and vascular structures.