Meninges and CSF | Anatomy2Medicine
Meninges and CSF

Meninges and CSF

    • Meninges include
      • pia mater and the arachnoid (together known as the leptomeninges)

 

  • dura mater (pachymeninx).

 

    • Pia mater
      • is a delicate, highly vascular layer of connective tissue.

 

  • closely covers the surface of the brain and spinal cord.
  • Denticulate ligaments

 

        • consist of two lateral flattened bands of pial tissue.
        • adhere to the spinal dura mater with 21 attachments.

 

  • Filum terminale

 

        • consists of a nonneural band of tissue that is a condensation of the pia mater.
        • extends from the conus medullaris to the end of the dural sac and fuses with it.
    • Arachnoid
      • is a delicate, nonvascular connective tissue membrane
      • exists between the dura mater and the pia mater.

 

  • Arachnoid granulations or arachnoid villi

 

        • enter the venous dural sinuses
        • permit the one-way flow of CSF from the subarachnoid space into the venous circulation.
        • are found in large numbers along the superior sagittal sinus

 

  • Subarachnoid space

 

    • Dura mater
      • is the outermost layer of the meninges
      • consists of dense connective tissue.
      • The supratentorial dura is innervated by the trigeminal nerve (MCQ)
      • posterior fossa dura is innervated by the vagal and upper spinal nerves (MCQ)

 

  • Falx cerebri

 

        • lies between the cerebral hemispheres in the longitudinal cerebral fissure
        • contains the superior and inferior sagittal sinuses between its two layers.

 

  • Tentorium cerebelli

 

        • separates the posterior cranial fossa from the middle cranial fossa.

 

  • separates the temporal and occipital lobes from the cerebellum and infratentorial brainstem.

 

        • contains the tentorial incisure, or notch, through which the brainstem passes.

 

  • Diaphragma sellae
  • forms the roof of the hypophyseal fossa.
  • contains an aperture through which the hypophyseal stalk (infundibulum) passes.

 

      • Dural sinuses
        • are endothelium-lined, valveless venous blood channels.
    • Meningeal spaces

 

  • Spinal epidural space

 

        • is located between the dura and the vertebral periosteum.
        • contains loose areolar tissue, venous plexuses, and lymphatics.
        • may be injected with a local anesthetic to produce a paravertebral nerve block. (MCQ)

 

  • Cranial epidural space

 

        • is a potential space between the periosteal and meningeal layers of the dura.
        • contains the meningeal arteries and veins. (MCQ)

 

  • Subdural space

 

        • is a potential space between the dura and the arachnoid.

 

  • intracranially transmits the superior cerebral veins to the venous lacunae of the superior sagittal sinus.

 

        • Laceration of these “bridging veins” results in subdural hemorrhage (hematoma). (MCQ)

 

  • Subarachnoid space

 

        • is located between the pia mater and the arachnoid.
        • contains CSF.

 

  • surrounds the entire brain and spinal cord.
  • extends, in the adult, below the conus medullaris to the level of the second sacral vertebra, the lumbar cistern (MCQ)
  • Subarachnoid cisterns

 

        • are dilations of the subarachnoid space, which contains CSF.

 

  • are named after the structures over which they lie (e.g., pontine, chiasmatic, and interpeduncular cisterns).
  • Cerebellopontine angle cistern
  • receives CSF from the fourth ventricle via the lateral foramina of Luschka.

 

          • contains the facial nerve and the vestibulocochlear nerve

 

  • Cerebellomedullary cistern (cisterna magna)

 

          • is located in the midline between the cerebellum and the medulla.

 

  • receives CSF from the fourth ventricle via the median foramen of Magendie.

 

          • can be tapped for CSF (suboccipital tap).

 

  • Ambient cistern interconnects the superior and interpeduncular cisterns; contains the trochlear nerve (CN IV)
  • Ventricles

 

      • are lined with ependyma and contain CSF.

 

  • contain choroid plexus, which produces CSF at a rate of 500 ml/day. (MCQ)

 

      • communicate with the subarachnoid space via three foramina in the fourth ventricle
      • Lateral ventricles
        • are the two ventricles located within the cerebral hemispheres.
        • communicate with the third ventricle via the interventricular foramina of Monro.
        • Frontal (anterior) horn
          • is located in the frontal lobe

 

  • its lateral wall is formed by the head of the caudate nucleus.

 

          • lacks choroid plexus.
        • Body
          • is located in the medial portion of the frontal and parietal lobes.
          • has choroid plexus.
          • communicates via the interventricular foramen of Monro with the third ventricle.
        • Temporal (inferior) horn

 

  • is located in the medial part of the temporal lobe.

 

          • has choroid plexus.
        • Occipital (posterior) horn
          • is located in the parietal and occipital lobes.
          • lacks choroid plexus.
        • Trigone (atrium)
          • is found at the junction of the body, occipital horn, and temporal horn of the lateral ventricle.
          • contains the glomus, a large tuft of choroid plexus, which is calcified in adults and is visible on x-ray film and CT
      • Third ventricle
        • is a slitlike vertical midline cavity of the diencephalon.
        • communicates with the
          • Lateral ventricles via the interventricular foramina of Monro
          • fourth ventricle via the cerebral aqueduct.
        • contains a pair of choroid plexuses in its roof.
      • Cerebral aqueduct (aqueduct of Sylvius)
        • lies in the midbrain.

 

  • connects the third ventricle with the fourth ventricle

 

        • lacks choroid plexus.
        • Blockage leads to hydrocephalus (aqueductal stenosis).
      • Fourth ventricle
        • lies between the cerebellum and the brainstem.
        • contains a pair of choroid plexuses in its caudal roof.
        • expresses CSF into the subarachnoid space via the
          • two lateral foramina of Luschka and
          • single medial foramen of Magendie.
    • Cerebrospinal Fluid
      • is a clear, colorless, acellular fluid
      • found in the subarachnoid space and ventricles.
      • produced by the choroid plexus at a rate of 500 ml/day.
      • The total CSF volume equals 140 ml
      • Function
        • supports and cushions the central nervous system (CNS) against concussive injury.
        • transports hormones and hormone-releasing factors.
        • removes metabolic waste products through absorption
      • the sites of greatest absorption are the arachnoid villi
      • Circulation
        • flows from the ventricles via the three foramina of the fourth ventricle into the subarachnoid space and over the convexity of the hemisphere to the superior sagittal sinus, where it enters the venous circulation.
      • Composition
        • contains no more than 5 lymphocytes
        • pH: 7.35
        • Specific gravity: 1.007
        • Glucose: 66% of plasma glucose
        • Total protein: < 45 mg/dl in the lumbar cistern
      • Normal pressure
        • is 80 to 180 mm of water (CSF) in the lumbar subarachnoid space when the patient is in a lateral recumbent (decubitus) position.

 

  • Herniation

 

      • Transtentorial (uncal) herniation
        • is protrusion of the brain through the tentorial incisure.
      • Transforaminal (tonsillar) herniation

 

  • is protrusion of the brainstem and cerebellum through the foramen magnum.

 

      • Subfalcial herniation
        • is herniation below the falx cerebri.

 

  • Circumventricular Organs (A High yield MCQ Zone for MD Entrance)

 

      • are chemosensitive zones

 

  • monitor the varying concentrations of circulating hormones in blood and CSF.

 

      • Location
        • are located in the periphery of the third ventricle
        • the area postrema is found in the floor of the fourth ventricle.
      • are highly vascularized with fenestrated capillaries
      • no blood–brain barrier (the sub- commissural organ is an exception).
      • Organum vasculosum of the lamina terminalis
        • is considered to be a vascular outlet for luteinizing hormone–releasing hormone and somatostatin.
      • Median eminence of the tuber cinereum
        • contains neurons that elaborate releasing and inhibiting hormones into the hypophyseal portal system.
      • Subfornical organ

 

  • contains neurons that project to the supraoptic nuclei and the organum vasculosum.
  • is a central receptor site for angiotensin II.

 

      • Subcommissural organ
        • is composed of specialized ependymal cells, glial elements, and a capillary bed containing nonfenestrated endothelial cells.
      • Pineal body
        • contains calcareous granules, in brain sand or acervulus, which are seen on x-ray film and CT

 

  • calcification occurs after 16 years of age.
  • contains pinealocytes (epiphyseal cells)

 

        • highly vascular with fenestrated capillaries.
        • is derived from the diencephalon.

 

  • is innervated solely via postganglionic fibers from the superior cervical ganglion of the autonomic nervous system.

 

    • Area postrema
      • consists of two small subependymal oval areas on either side of the fourth ventricle  contains modified neurons and astrocyte-like cells
      • contain fenestrated capillaries.
      • is considered to be a chemoreceptor zone that triggers vomiting in response to circulating emetic substances.
      • plays a role in food intake and cardiovascular regulation.