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StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The brain and spinal cord space enveloped within 3 layers the membrane jointly known as the meninges, v the cranial meninges especially referring come the ar that consist of the brain. From superficial come deep, the three layers are the dura, arachnoid, and also pia—the ax “mater,” Latin because that mother, often adheres to these name (i.e., dura mater, arachnoid mater, pia mater).<1> The dura, Latin for “hard,” is written of thick connective tissue and adheres come the inner surface of the skull and vertebrae. The arachnoid is a thin wispy membrane that lies just deep come the dura and is superficial come the pia, the really thin, clean membrane that straight adheres come the surface of the mind and spinal cord. Developing from this layers are three clinically significant spaces, or potential spaces (sometimes dubbed cavities): the epidural, subdural, and also subarachnoid spaces, indigenous superficial come deep. The chief role of the meninges is to safeguard the contents of the brain and spinal cord.<2>


Structure and also Function

Epidural Space

Between the roof of the skull (i.e., calvarium) and also the superior surface of the dura potentially lies the epidural space.  when arteries and also veins run between the inner surface of the calvarium and the dura, the epidural room typically exist pathologically, since the superficial great of the dura, the periosteal layer, is securely attached to the periosteum of the skull.

Dura Mater

The outermost mater of the meninges, the dura, is composed of 2 layers: the periosteal layer the lies closest come the calvarium and also the meningeal layer the lies closest to the mind tissue. This together add to the dura gift a thick, dense, fibrous membrane the is quite inelastic. The periosteal layer is composed of fibroblasts and also osteoblasts, through a huge quantity that extracellular collagen existing within its intercellular space, providing the dura that strength.<1> These 2 layers are greatly fused, only separating to kind venous sinuses and dural reflections. Dural reflections refer to places where two face-to-face meningeal layers descend into the cranial cavity to form the septa the compartmentalize the brain. The two key dural reflections space the falx cerebri and also the tentorium cerebelli. The sickle-shaped falx cerebri is attached to the roof that the cranium and also suspends down into the interhemispheric fissure, separating the right and also left cerebral hemispheres. The “U” shame tentorium cerebelli runs transversely in between the cerebellum and occipital lobes. Importantly, over there is an opening in the falx cerebri, recognized as the tentorial incisura (sometimes referred to as the tentorial notch), that permits the midbrain to pass through right into the center cranial fossa.

Subdural Space

The subdural space is the space that possibly exists in between the meningeal layer of the dura and the arachnoid mater. Comparable to the epidural space, the subdural an are typically exists just under pathological conditions.

Arachnoid Mater

The arachnoid sits between the dura and the pia and also is one avascular membrane the is affiliated in cerebrospinal fluid (CSF) metabolism via the subarachnoid space.<2> unlike the pia mater, the arachnoid does no follow the border of the cortical sulci however bridges them. When its figure varies in between locations in the cranium, the is usually a thin, lucent membrane. The structure is composed of a superficial mesothelial layer listed below the dura, a main layer created of cell conjoined by many junction proteins, and also a deep great of less tightly packed cells with plenty of collagen yarn within their intercellular space. Evidence says that the clusters of arachnoid villi (i.e., arachnoid granulations), or sections of the arachnoid the protrude right into the dura mater, serving together a network for communication in between the systemic venous system and the CSF.

Subarachnoid Space

The subarachnoid room is the cerebrospinal fluid-filled space that exists between the arachnoid and also the pia. Within the lateral ventricles of the brain, the choroid plexus produces CSF, which passes right into the subarachnoid space via the foramina the Luschka.<3><4> since the subarachnoid space is constant between the brain and spinal cord, CSF flows v the foramen magnum under to the distal portion of the spinal cord. The primary functions of the CSF room to cushion the mind and spinal cord native trauma and also to it is provided them through nutrients and also remove waste. In enhancement to the CSF, the major arteries of the brain run v the subarachnoid space. Also, projecting into this space are arachnoid trabeculae which room strands of arachnoid mater connective tissue.

Pia Mater

The deepest class of the meninges, the pia mater, is written of two layers and, unequal the arachnoid, follows the contours of the sulci and also gyri. The external layer the the pia, described as the epipial layer, consists of collagen fibers; the inside layer, or the intima pia, includes elastic and reticular fibers.<5><6> if mesothelial cells of the epipial layer connect to the arachnoid mater via the arachnoid trabeculae, the intima pia adheres to the outermost great of neural tissue known as the glial membrane. Importantly, the cerebral pia mater creates sheaths about the blood vessels that enter and exit the brain perpendicular come the meninges, especially from the subarachnoid an are to within the mind parenchyma.<7> This sheathing creates an interstitial fluid-filled space, known as the perivascular or Virchow-Robin space, between the courage walls and the pia.


Embryology

While the dura mater, sometimes dubbed the pachymeninx, is obtained from the mesoderm, the arachnoid and also pia mater, together dubbed the leptomeninges, are acquired from the ectoderm. Specifics the development of the meninges begins with what is known as the perimedullarly mesenchyme, which has cells from both the ectoderm and also mesoderm.<1><8> The leptomeninges creates first, together cells from the neural crest differentiate into the pia and arachnoid. Subsequently, dura differentiation wake up from sclerotomes, a subdivision the the mesodermal somites. The dura differentiates indigenous the development of the skull together the venous sinuses start to develop and arises native two distinct condensations of cells in the peripheral mesenchyme; the more thick condensation forms the periosteal layer, while the thinner forms the meningeal layer.<9>


Blood Supply and Lymphatics

Epidural room and Dura Mater

While the was when thought that the dura to be avascular, that is actually extremely vascular in nature, together the significant vessels that supply it run in the epidural room deep come the skull. The major arteries that supply the dura are derived from the interior carotid, vertebral, maxillary, ascending pharyngeal, lacrimal, occipital, and ethmoidal arteries. The the arteries that supply the dura, the center meningeal artery (MMA), i beg your pardon branches from the internal carotid artery’s maxillary branch, is the many important.<1> The MMA start the cranium via the foramen spinosum and runs inside the epidural space, creating grooves versus the skull. Importantly, while the MMA provides the dura, the center cerebral artery the branches indigenous the inner carotid artery supply the brain. Venous drainage the the dura wake up via the satellite veins of the meningeal arterial trunks and the dural venous sinuses.

The dural venous sinuses space venous networks formed wherein the periosteal and meningeal class of the dura mater separate and also serve together the major pathway for venous drainage from the brain. They incorporate the remarkable sagittal sinus, worse sagittal sinus, directly sinus, and sigmoid sinus, amongst others.<1> The dural sinuses mainly drainpipe blood via the sigmoid sinuses right into the internal jugular veins. In addition to receiving blood indigenous both the brain’s internal and also external veins, the dural sinuses get CSF native the subarachnoid space.

Subdural Space

The many notable blood vessels regarded the subdural an are are the bridging veins, i m sorry pass v the subdural room transversely ~ above their method to drainpipe the cerebral hemispheres right into the dural venous sinuses. The rupturing of this veins is the many common cause of subdural hematomas.

Arachnoid Mater and Subarachnoid Space

The arachnoid mater is avascular. Locations of the subarachnoid space where over there are large gaps are described as cisternae. The approximately cistern, which surrounding the midbrain, has branches that the posterior cerebral and superior cerebellar arteries; it additionally contains the basal vein the Rosenthal. The remarkable cerebellar cistern consists of the petrosal vein and also the premium cerebellar artery. Additionally, where the arachnoid mater bridges the cerebral hemispheres deep to the falx cerebri, the subarachnoid room houses the anterior cerebral arteries.

Pia Mater

The pia mater is very vascularized and also contains networks that capillaries that nourish the brain. Additionally, the parts of the pia mater that type the perivascular room eventually fuse with the blood ship they surround.

Meningeal Lymphatic Vessels

The lymphatic system of the meninges to be recently discovered in 2015 via the usage of electron microscopy, and work is recurring to much better understand that is structure and function.<10><11> Lymphatic vessels run tangentially to the dural venous sinuses and also meningeal arteries and also connect to the deep cervical lymph nodes. Additionally, these vessels have actually been presented to absorb CSF for drainage and also are thought to play a main role in connecting the immune and also nervous solution through immune cell trafficking.


Nerves

The meninges mainly receives innervation through the vagus and trigeminal nerves, v some cervical spinal nerves contributing to a lesser degree.<2> if the dura of the anterior cranial fossa is mostly innervated by the anterior and also posterior ethmoidal nerve branches the the ophthalmic division of the trigeminal nerve, the dura that the middle cranial fossa receives nerve supply from a branch the the maxillary department of the trigeminal nerve. The tentorium cerebelli and also the posterior 3rd of the falx cerebri are primarily innervated through the tentorial nerve, i beg your pardon is additionally a branch the the ophthalmic department of the trigeminal nerve. The an initial three cervical spinal nerves, together with the cranial sympathetic trunk, mainly innervate the infratentorial dura the the posterior cranial fossa.


Surgical Considerations

Meningiomas room the most common form of cranial neoplasms and also arise indigenous the cell that make up the arachnoid villi, recognized as arachnoid lid cells. Lock are commonly benign however can present in an atypical or malignant fashion.<12> While surgical procedure is typically employed come treat meningiomas, the threat of major neurological complications had led to its steady decline, specifically when the tumor is in regions of the skull near the critical neurovascular structures.<13> The main strategy because that cranial meningioma removal is complete excision, which commonly entails the removal of the dura, bone, and also vascular sinuses that have been infiltrated by the tumor. In current decades, endoscopic and minimally invasive keyhole viewpoints to surgery have actually seen heightened implementation in pick cases. Ultimately, the operation strategy is patient-tailored and depends on each tumor’s location and also characteristics.


Clinical Significance

The meninges theatre a duty in numerous pathological conditions. Bacter meningitis (BM) is a problem where one gets inflammation the the meninges because of bacteria invading the subarachnoid space, most frequently by the pathogens Streptococcus pneumoniae and Neisseria meningitides.<14> bacterial meningitis may cause neuronal damages as a an outcome of rises in intracranial pressure and also subsequent parenchymal damages due to mind edema, hydrocephalus, and also vascular alterations. Additionally, evidence suggests that toxin released from the infiltrated pathogens may add to neuropsychological deficits — treatment centers roughly immediate antibiotic therapy.

Traumatic and atraumatic intracranial hemorrhages within different locations that the meninges are a common set of conditions that are straight related come the framework and duty of the meninges and can be classified through their details location in ~ the meningeal layers. Because that example, an epidural hematoma is the arsenal of blood in the tight potential space between the dura and also the skull (i.e., the epidural space).<15> This condition is usually brought about by the rupturing the the center meningeal artery together a an effect of the fracture the the temporal bone as a an outcome of head trauma. As the hemorrhage rapidly increases under arterial pressure, the dura peels far from the calvarium developing a lens-shaped biconvex hematoma, as seen by a CT scan. Together the hematoma compresses the underlying brain tissue, brain herniation have the right to occur and lead to fatality unless treated v surgery. Various other intracranial hemorrhages include subdural hematomas, i m sorry usually an outcome from rupturing of the bridging veins and the build-up of blood in the potential subdural space between the dura and also the arachnoid,<16> and subarachnoid hemorrhages, which take place in the subarachnoid space.

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<17> Subarachnoid hemorrhages are regularly further classified together nontraumatic (spontaneous) or traumatic; nontraumatic subarachnoid hemorrhages are usually a an outcome of a voluntary aneurysm (or rupture) of one artery in the room between the arachnoid and also the pia and present with a sudden onset headache.<18>