Dura

The dura mater is a tough layer of connective tissue that forms the outermost meningeal layer of the brain and spinal cord. It consists of two sublayers: an outer periosteal/endosteal layer that covers the inner skull, and an inner meningeal layer that surrounds the brain and spinal cord, along with the arachnoid and pia mater.

Although these two layers are tightly stuck together, there is a potential space between them. It's important to note that in certain areas, such as those with dural partitions or where the venous sinuses are located, these layers are separated. The dura mater has a network of venous sinuses between its two layers, including the superior sagittal sinus, inferior sagittal sinus, straight sinus, and sigmoid sinus, among others. These sinuses carry venous blood and also allow cerebrospinal fluid (CSF) to drain into them through the subarachnoid villi/granulations.

In specific areas, the inner dural layer separates from the outer periosteal layer and extends into the brain, attaching to certain bony areas. This creates partitions or folds that divide brain regions and provide support for the brain's structure. These dural partitions include the falx cerebrum, falx cerebellum, tentorium cerebellum, and diaphragma sellae.

Understanding the clinically significant spaces associated with the dura mater is crucial. These spaces include the epidural and subdural spaces. The epidural (or extradural) space refers to the space between the periosteal dural layer and the skull bone. Epidural (arterial) hemorrhages can occur in this space when the middle meningeal arteries rupture, requiring immediate neurosurgical evacuation. The subdural space, located between the dura and arachnoid mater, is where venous subdural hemorrhages can occur due to traction and rupture of bridging veins.

In terms of innervation, the dura mater receives nerve supply from the trigeminal, vagus, and first three cervical spinal nerves. Traction of dura mater below the tentorium cerebellum causes headaches that are referred to the back of the scalp and neck regions, while the dural traction or stretching above the tentorium cerebellum leads to headache felt in the head region.