At major boundaries of brain regions such as the longitudinal fissure between the hemispheres, and the tentorium cerebelli between the posterior brain and the cerebellum the dura separates, folds and invaginates to make the divisions. These folds are known as dural folds, or reflections.[3]
Cranial dura mater has two layers which include a superficial periosteal layer that is actually the inner periosteum of the neurocranium (the calvarium and endocranium); and a deep meningeal layer, which is the true dura mater. The dura mater covering the spinal cord is known as the dural sac or thecal sac, and only has one layer (the meningeal layer) unlike cranial dura mater. The potential space between these two layers is known as the epidural space,[5] which can accumulate blood in the case of traumatic laceration to the meningeal arteries.
Folds and reflections
Spinal reflections and folds
The dura separates into two layers at dural reflections (also known as dural folds), 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 (falx cerebelli) 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 diaphragm covers the pituitary gland in this fossa and has an aperture for passage of the infundibulum (pituitary stalk) and hypophysial veins.
This depends upon the area of the cranial cavity: in the anterior cranial fossa the anterior meningeal artery (branch from the ethmoidal artery) is responsible for blood supply, in the middle cranial fossa the middle meningeal artery and some accessory arteries are responsible for blood supply, the middle meningeal artery is a direct branch from the maxillary artery and enter the cranial cavity through the foramen spinosum and then divides into anterior (which runs usually in vertical direction across the pterion) and posterior (which runs posterosuperiorly) branches, while the accessory meningeal arteries (which are branches from the maxillary artery) enter the skull through foramen ovale and supply area between the two foramina, and the in posterior cranial fossa the dura mater has numerous blood supply from different possible arteries:
A. posterior meningeal artery (from the ascending pharyngeal artery through the jugular foramen)
B. meningeal arteries (from the ascending pharyngeal artery through hypoglossal canal)
C. meningeal arteries (from occipital artery through jugular or mastoid foramen)
D. meningeal arteries (from vertebral artery through foramen magnum)
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 (CSF) from the brain and empty into the internal jugular vein.
Arachnoid villi, which are outgrowths of the arachnoid mater (the middle meningeal layer), 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 (V1, V2 and V3).[8] The innervation for the infratentorial dura mater are via upper cervical nerves and the meningeal branch of the vagus nerve.[9]
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. If there is a dural deficiency, then a dural substitute may be used to replace this membrane. Small gaps in the dura can be covered with a surgical sealant film.
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.[12]
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.[13]
Cerebellar tonsillar ectopia, or Chiari malformation, is a condition that was previously thought to be congenital but can be induced by trauma, particularly whiplash trauma.[14] 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.
The name dura mater derives from the Latin for tough mother (or hard mother),[15] a loan translation of Arabic أم الدماغ الصفيقة (umm al-dimāgh al-ṣafīqah), literally 'thick mother of the brain', matrix of the brain,[16][17] and is also referred to by the term "pachymeninx" (plural "pachymeninges").[16]
Additional images
Dura mater (spinal section)
Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc.
Diagrammatic transverse section of the medulla spinalis and its membranes
Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view.
Spinal cord. Spinal membranes and nerve roots. Deep dissection. Posterior view
^Gagan, Jeffrey R.; Tholpady, Sunil S.; Ogle, Roy C. (2007). "Cellular dynamics and tissue interactions of the dura mater during head development". Birth Defects Research Part C: Embryo Today: Reviews. 81 (4): 297–304. doi:10.1002/bdrc.20104. PMID18228258.
^Frank Scali; Eric S. Marsili; Matt E. Pontell (2011). "Anatomical Connection Between the Rectus Capitis Posterior Major and the Dura Mater". Spine. 36 (25): E1612–E1614. doi:10.1097/brs.0b013e31821129df. PMID21278628. S2CID31560001.
