The dura mater has several functions and layers. The dura mater is a membrane that envelops the arachnoid mater. It surrounds and supports the dural sinuses and carries blood from the brain toward the heart. Cranial dura mater has two layers called :wikt:lamella|lamellae, a superficial layer, which serves as the skull's inner periosteum, called the endocranium and a deep layer called the meningeal layer. When it covers the spinal cord it is known as the dural sac or thecal sac. Unlike cranial dura mater, spinal dura mater only has one layer, known as the meningeal layer. The potential space between these two layers is known as the epidural space.
Folds and reflections
The dura separates into two layers at dural reflections, places where the inner dural layer is reflected as sheet-like protrusions into the cranial cavity. There are two main dural reflections:
Two other dural infoldings are the cerebellar falx and the sellar diaphragm:
The cerebellar falx is a vertical dural infolding that lies inferior to the cerebellar tentorium in the posterior part of the posterior cranial fossa. It partially separates the cerebellar hemispheres.
The sellar diaphragm is the smallest dural infolding and is a circular sheet of dura that is suspended between the clinoid processes, forming a partial roof over the hypophysial fossa. The sellar diaphgram covers the pituitary gland in this fossa and has an aperture for passage of the infundibulum and hypophysial veins.
The two layers of dura mater run together throughout most of the skull. Where they separate, the gap between them is called a dural venous sinus. These sinuses drain blood and cerebrospinal fluid from the brain and empty into the internal jugular vein. Arachnoid villi, which are outgrowths of the arachnoid mater, extend into the dural venous sinuses to drain CSF. These villi act as one-way valves. Meningeal veins, which course through the dura mater, and bridging veins, which drain the underlying neural tissue and puncture the dura mater, empty into these dural sinuses. A rupture of a bridging vein causes a subdural hematoma.
Nerve supply
The supratentorial dura mater membrane is supplied by small meningeal branches of the trigeminal nerve. The innervation for the infratentorial dura mater are via upper cervical nerves and the meningeal branch of the vagus nerve.
Clinical significance
Many medical conditions involve the dura mater. A subdural hematoma occurs when there is an abnormal collection of blood between the dura and the arachnoid, usually as a result of torn bridging veins secondary to head trauma. An epidural hematoma is a collection of blood between the dura and the inner surface of the skull, and is usually due to arterial bleeding. Intradural procedures, such as removal of a brain tumour, or treatment of trigeminal neuralgia via a microvascular decompression require that an incision is made to the dura mater. To achieve a watertight repair and avoid potential post-operative complications the dura is typically closed with sutures. In the event that there is a dural deficiency, a dural substitute may be used to replace this membrane. Small gaps in the dura can be covered with a surgical sealant film. In 2011, researchers discovered a connective tissue bridge from the rectus capitis posterior major to the cervical dura mater. Various clinical manifestations may be linked to this anatomical relationship such as headaches, trigeminal neuralgia and other symptoms that involved the cervical dura. The rectus capitis posterior minor has a similar attachment. The dura-muscular, dura-ligamentous connections in the upper cervical spine and occipital areas may provide anatomic and physiologic answers to the cause of the cervicogenic headache. This proposal would further explain manipulation's efficacy in the treatment of cervicogenic headache. The American Red Cross and some other agencies accepting blood donations consider dura mater transplants, along with receipt of pituitary-derived growth hormone, a risk factor due to concerns about Creutzfeldt–Jakob disease. Cerebellar tonsillar ectopia, or Chiari, is a condition that was previously thought to be congenital but can be induced by trauma, particularly whiplash trauma. Dural strain may be pulling the cerebellum inferiorly, or skull distortions may be pushing the brain inferiorly. Dural ectasia is the enlargement of the dura and is common in connective tissue disorders, such as Marfan syndrome and Ehlers–Danlos syndrome. These conditions are sometimes found in conjunction with Arnold–Chiari malformation. Spontaneous cerebrospinal fluid leak is the fluid and pressure loss of spinal fluid due to holes in the dura mater.
Etymology
The name derives from the Latin for tough mother , a loan translation of Arabic أم الدماغ الصفيقة, literally 'thick mother of the brain', matrix of the brain, and is also referred to by the term "pachymeninx".
