Arachnoid granulation

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Arachnoid granulation
Gray769-en.svg
Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc. ("Arachnoid granulation" label is at top right.)
Arachnoid granulations.jpg
Arachnoid granulations seen on autopsy, where the dura mater has been removed but the arachnoid mater is left in place.
Details
Identifiers
Latin granulationes arachnoideae
TA98 A14.1.01.205
TA2 5389
FMA 77760
Anatomical terminology

Arachnoid granulations (also arachnoid villi, and pacchionian granulations or bodies) are small outpouchings of the arachnoid mater and subarachnoid space into the dural venous sinuses of the brain. The granulations are thought to mediate the draining of cerebrospinal fluid (CSF) from the subarachnoid space into the venous system.

Contents

The largest and most numerous granulations lie along the superior sagittal sinus; they are however present along other dural sinuses as well.

Anatomy

The granulations are often situated near where cerebral veins drain into the dural sinuses. They are most prominent along the superior sagittal sinus, particularly those lodged withinin the lateral lacunae. In order of decreasing frequency, the granulations occur within the: superior sagittal sinus, transverse sinuses, superior petrosal sinuses, and straight sinus. [1]

The arachnoid granulations may be lodged within granular foveae - small pits upon the inner surface of the cranial bones. [2] [3]

Structure

The arachnoid granulations are local outpouchings of the arachnoid mater as well as the subarachnoid space enclosed within it into the dural venous sinuses. The granulations exhibit a thinner stalk that penetrates through the wall of a venous sinus, and a distended head formed within the lumen of the sinus. The head consists of a trabecular collagenous core that is largely covered by a dural cupula, except for an apical cap - some 0.3 mm in diameter - of arachnoid cells attached directly to the dural venous endothelium. [1]

Development

The granulations develop during childhood as separate arachnoid villi gradually aggregate into macroscopic clumps. [4]

Function

The arachnoid granulations are notably thought to be involved in resorption of cerebrospinal fluid, however, their function is not entirely understood. [1]

Cerebrospinal fluid resorption

The arachnoid granulations act as one-way valves. Normally the pressure of the CSF is higher than that of the venous system, so CSF flows through the villi and granulations into the blood. If the pressure is reversed for some reason, fluid will not pass back into the subarachnoid space. The reason for this is not known. It has been suggested that the endothelial cells of the venous sinus create vacuoles of CSF, which move through the cell and out into the blood. [5]

The importance of arachnoid granulations for the drainage of CSF is controversial. [6] The granulations are sparse during early life, possibly underscoring the importance of alternate mechanisms of drainage. [1] A large portion (perhaps the majority) of CSF may in fact drain through lymphatics associated with extracranial segments of cranial nerves - especially through axons of CN I (olfactory nerve) through their extension through the cribriform plate. [6]

Subarachnoid systolic overpressure dampening

A suggested alternative or additional function of the granulation may be the dispersal of the overpressure wave formed within the subarachnoid space by the pulsation of arteries during systole. As the venous sinuses are enclosed in rigid dural structures, they represent a non-distensible compartment into which subarachnoid pressure increases may be dispersed. [1]

Clinical significance

Age-related degenerative changes of the granulations and consequent decreased CSF resorption may underlie normal pressure hydrocephalus (which may in turn be pathogenetically implicated in additional age-related neurodegenerative disorders. [1]

Eponym

Occasionally, they are referred to by their old name: Pacchioni's bodies, named after Italian anatomist Antonio Pacchioni. [7]

Related Research Articles

<span class="mw-page-title-main">Cerebrospinal fluid</span> Clear, colorless bodily fluid found in the brain and spinal cord

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.

<span class="mw-page-title-main">Hydrocephalus</span> Abnormal increase in cerebrospinal fluid in the ventricles of the brain

Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment. In babies, it may be seen as a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes.

<span class="mw-page-title-main">Ventricular system</span> Structures containing cerebrospinal fluid

In neuroanatomy, the ventricular system is a set of four interconnected cavities known as cerebral ventricles in the brain. Within each ventricle is a region of choroid plexus which produces the circulating cerebrospinal fluid (CSF). The ventricular system is continuous with the central canal of the spinal cord from the fourth ventricle, allowing for the flow of CSF to circulate.

<span class="mw-page-title-main">Meninges</span> Three membranes protecting the brain

In anatomy, the meninges are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia mater. The primary function of the meninges is to protect the central nervous system.

<span class="mw-page-title-main">Pia mater</span> Delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord

Pia mater, often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. Pia mater is medieval Latin meaning "tender mother". The other two meningeal membranes are the dura mater and the arachnoid mater. Both the pia and arachnoid mater are derivatives of the neural crest while the dura is derived from embryonic mesoderm. The pia mater is a thin fibrous tissue that is permeable to water and small solutes. The pia mater allows blood vessels to pass through and nourish the brain. The perivascular space between blood vessels and pia mater is proposed to be part of a pseudolymphatic system for the brain. When the pia mater becomes irritated and inflamed the result is meningitis.

<span class="mw-page-title-main">Dura mater</span> Outermost layer of the protective tissues around the central nervous system (meninges)

In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. The other two meningeal layers are the arachnoid mater and the pia mater. It envelops the arachnoid mater, which is responsible for keeping in the cerebrospinal fluid. It is derived primarily from the neural crest cell population, with postnatal contributions of the paraxial mesoderm.

<span class="mw-page-title-main">Great cerebral vein</span>

The great cerebral vein is one of the large blood vessels in the skull draining the cerebrum of the brain. It is also known as the vein of Galen, named for its discoverer, the Greek physician Galen.

<span class="mw-page-title-main">Intracranial hemorrhage</span> Hemorrhage, or bleeding, within the skull

Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds, subarachnoid bleeds, epidural bleeds, and subdural bleeds.

<span class="mw-page-title-main">Epidural space</span> Space between the dura mater and vertebrae

In anatomy, the epidural space is the potential space between the dura mater and vertebrae (spine).

<span class="mw-page-title-main">Antonio Pacchioni</span> Italian scientist and anatomist

Antonio Pacchioni was an Italian scientist and anatomist, who focused chiefly on the outermost meningeal layer of the brain, the dura mater.

<span class="mw-page-title-main">Median aperture</span>

The median aperture is an opening at the caudal portion of the roof of the fourth ventricle. It allows the flow of cerebrospinal fluid (CSF) from the fourth ventricle into the cisterna magna. The other openings of the fourth ventricle are the lateral apertures - one on either side. The median aperture varies in size but accounts for most of the outflow of CSF from the fourth ventricle.

<span class="mw-page-title-main">Falx cerebri</span> Anatomical structure of the brain

The falx cerebri is a large, crescent-shaped fold of dura mater that descends vertically into the longitudinal fissure to separate the cerebral hemispheres. It supports the dural sinuses that provide venous and CSF drainage from the brain. It is attached to the crista galli anteriorly, and blends with the tentorium cerebelli posteriorly.

<span class="mw-page-title-main">Arachnoid mater</span> Web-like middle layer of the three meninges

The arachnoid mater is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural crest mesoectoderm in the embryo.

<span class="mw-page-title-main">Cavernous sinus</span> Sinus in the human head

The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.

<span class="mw-page-title-main">Dural venous sinuses</span> Venous channels in the dura mater

The dural venous sinuses are venous sinuses (channels) found between the endosteal and meningeal layers of dura mater in the brain. They receive blood from the cerebral veins, and cerebrospinal fluid (CSF) from the subarachnoid space via arachnoid granulations. They mainly empty into the internal jugular vein. Cranial venous sinuses communicate with veins outside the skull through emissary veins. These communications help to keep the pressure of blood in the sinuses constant.

<span class="mw-page-title-main">Confluence of sinuses</span> Venous sinus in the skull

The confluence of sinuses, torcular Herophili, or torcula is the connecting point of the superior sagittal sinus, straight sinus, and occipital sinus. It is below the internal occipital protuberance of the skull. It drains venous blood from the brain into the transverse sinuses. It may be affected by arteriovenous fistulas, a thrombus, major trauma, or surgical damage, and may be imaged with many radiology techniques.

<span class="mw-page-title-main">Superior sagittal sinus</span> Anatomical structure of the brain

The superior sagittal sinus, within the human head, is an unpaired dural venous sinus lying along the attached margin of the falx cerebri. It allows blood to drain from the lateral aspects of anterior cerebral hemispheres to the confluence of sinuses. Cerebrospinal fluid drains through arachnoid granulations into the superior sagittal sinus and is returned to venous circulation.

<span class="mw-page-title-main">Arachnoid trabeculae</span>

The arachnoid trabeculae are delicate strands of connective tissue that loosely connect the two innermost layers of the meninges – the arachnoid mater and the pia mater. They are found within the subarachnoid space where cerebrospinal fluid is also found.

<span class="mw-page-title-main">Glymphatic system</span> System for waste clearance in the CNS of vertebrates

The glymphatic system is a system for waste clearance in the central nervous system (CNS) of vertebrates. According to this model, cerebrospinal fluid (CSF) flows into the paravascular space around cerebral arteries, combining with interstitial fluid (ISF) and parenchymal solutes, and exiting down venous paravascular spaces. The pathway consists of a para-arterial influx route for CSF to enter the brain parenchyma, coupled to a clearance mechanism for the removal of interstitial fluid (ISF) and extracellular solutes from the interstitial compartments of the brain and spinal cord. Exchange of solutes between CSF and ISF is driven primarily by arterial pulsation and regulated during sleep by the expansion and contraction of brain extracellular space. Clearance of soluble proteins, waste products, and excess extracellular fluid is accomplished through convective bulk flow of ISF, facilitated by astrocytic aquaporin 4 (AQP4) water channels.

<span class="mw-page-title-main">Meningeal lymphatic vessels</span>

The meningeal lymphatic vessels are a network of conventional lymphatic vessels located parallel to the dural venous sinuses and middle meningeal arteries of the mammalian central nervous system (CNS). As a part of the lymphatic system, the meningeal lymphatics are responsible for draining immune cells, small molecules, and excess fluid from the CNS into the deep cervical lymph nodes. Cerebrospinal fluid and interstitial fluid are exchanged, and drained by the meningeal lymphatic vessels.

References

  1. 1 2 3 4 5 6 Standring, Susan (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice (42th ed.). New York: Elsevier. p. 413. ISBN   978-0-7020-7707-4. OCLC   1201341621.
  2. Linden Forest Edwards (1934). Anatomy for physical education, descriptive and applied. P. Blakiston's son & co., inc. p. 80. Retrieved 23 June 2012.
  3. Sir Henry Morris (1921). Morris's human anatomy. P. Blakiston's son & Company. p.  953 . Retrieved 23 June 2012.
  4. Sinnatamby, Chummy S. (2011). Last's Anatomy (12th ed.). p. 440. ISBN   978-0-7295-3752-0.
  5. McKnight, Colin D.; Rouleau, Renee M.; Donahue, Manus J.; Claassen, Daniel O. (2020-10-19). "The Regulation of Cerebral Spinal Fluid Flow and Its Relevance to the Glymphatic System". Current Neurology and Neuroscience Reports. 20 (12): 58. doi:10.1007/s11910-020-01077-9. ISSN   1534-6293. PMC   7864223 . PMID   33074399.
  6. 1 2 Norwood, Jordan N; Zhang, Qingguang; Card, David; Craine, Amanda; Ryan, Timothy M; Drew, Patrick J (7 May 2019). "Anatomical basis and physiological role of cerebrospinal fluid transport through the murine cribriform plate". eLife. 8: e44278. doi: 10.7554/eLife.44278 . PMC   6524970 . PMID   31063132.
  7. synd/392 at Who Named It?

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