Dura mater

The dura mater is the outermost and toughest layer of the meninges, the three protective membranes that cover the brain and spinal cord. It provides mechanical protection, supports venous sinuses, and forms structural partitions within the cranial cavity. The dura mater is composed of dense fibrous connective tissue and is richly innervated, especially within the cranial cavity.

Layers of Cranial Dura Mater

In the cranial cavity, the dura mater consists of two distinct layers:

• Periosteal layer: Adheres to the inner surface of the skull bones; acts as the internal periosteum of the cranial vault
• Meningeal layer: Lies deep to the periosteal layer; continuous with the spinal dura mater and forms dural folds and venous sinuses

These two layers are fused in most places but separate to form dural venous sinuses, which drain blood from the brain into the internal jugular veins.

Spinal Dura Mater

In the vertebral canal, the dura mater consists of only one layer (equivalent to the meningeal layer). It forms a tubular sac surrounding the spinal cord, ending at the level of the second sacral vertebra (S2). A potential space known as the epidural space lies between the spinal dura and the vertebral canal, filled with fat and venous plexuses.

Dural Reflections (Folds)

The meningeal layer of the cranial dura projects inward to form partitions that separate and support parts of the brain:

• Falx cerebri: Vertical fold separating the right and left cerebral hemispheres; attaches anteriorly to the crista galli and posteriorly to the internal occipital protuberance
• Tentorium cerebelli: Horizontal fold separating the occipital lobes from the cerebellum; contains the tentorial notch for the passage of the midbrain
• Falx cerebelli: Small vertical fold separating the two cerebellar hemispheres
• Diaphragma sellae: Small fold covering the pituitary gland within the sella turcica, with an aperture for the pituitary stalk

Dural Venous Sinuses

The separation between the periosteal and meningeal layers creates endothelial-lined venous sinuses that drain blood from the brain, meninges, and skull:

• Superior sagittal sinus: Along the superior margin of the falx cerebri
• Inferior sagittal sinus: Along the inferior margin of the falx cerebri
• Straight sinus: Formed by the union of the inferior sagittal sinus and great cerebral vein; drains into the confluence of sinuses
• Transverse sinuses: Along the tentorium cerebelli; continue as sigmoid sinuses
• Sigmoid sinuses: Drain into the internal jugular veins
• Cavernous sinuses: Located on either side of the sella turcica; receive venous blood from the orbit and face

Innervation

The cranial dura mater is innervated by branches of the trigeminal nerve (CN V), especially the ophthalmic division (V1), and also by branches from CN X and cervical spinal nerves. The spinal dura mater receives innervation from the recurrent meningeal nerves of spinal nerves. Pain-sensitive innervation of the dura is responsible for many types of headaches, especially those related to stretching or inflammation.

Blood Supply

• Middle meningeal artery: Major arterial supply to the dura; branch of the maxillary artery; enters via the foramen spinosum
• Accessory meningeal, occipital, and vertebral arteries: Provide additional vascular supply

Venous drainage follows dural veins into adjacent venous sinuses.

Development

The dura mater arises from mesenchymal cells of the neural crest and paraxial mesoderm. It is the first meningeal layer to form during embryogenesis and provides an early scaffold for brain and skull development.

Clinical Significance

• Epidural hematoma: Arterial bleeding (commonly from the middle meningeal artery) between the skull and periosteal dura; often associated with temporal bone fractures
• Subdural hematoma: Venous bleeding between the dura mater and arachnoid mater; typically due to bridging vein rupture in elderly or trauma
• Meningitis: Inflammation of the meninges may involve the dura and cause severe headache, stiffness, and systemic signs
• Dural sinus thrombosis: Clot formation within venous sinuses; presents with headache, seizures, and increased intracranial pressure
• Dural tear (durotomy): May lead to CSF leaks during neurosurgical procedures or trauma; can cause postural headaches
• Dural arteriovenous fistula: Abnormal connection between dural arteries and venous sinuses; can present with pulsatile tinnitus or hemorrhage

Imaging

• CT: Shows calcified dura or hemorrhages (e.g., epidural, subdural); useful in trauma evaluation
• MRI: Provides high-resolution images of dural folds, enhancement patterns in infection or inflammation, and venous sinus thrombosis
• MR venography: Used to visualize dural venous sinuses and detect thrombosis