Chapter2_Meninges and CSF

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Chapter 2

Meninges and Cerebrospinal Fluid (CSF)

I. Meninges (Figure 2-1)

are three connective t issue membranes that invest the spinal cord and brain.

consist of the pia mater and the arachnoid (together known as the leptomeninges) and the dura

mater (pachymeninx).

A. Pia mater

is a delicate, highly vascular layer of connective t issue.

closely covers the surface of the brain and spinal cord.

is connected to the arachnoid by trabeculae.

Denticulate l igaments (see Figure 2-1)

consist of two lateral f lattened bands of pial t issue.

adhere to the spinal d ura mater with 21 attachments.

1.

Filum terminale (Figure 2-2)

consists of a nonneural band of t issue that is a condensation of the pia mater.

extends from the conus medullaris to the end of the dural sac and fuses with it .

2.

B. Arachnoid

is a delicate, nonvascular connective t issue membrane between the dura mater and the pia mater.

Arachnoid granulations or arachnoid vill i

enter the venous dural sinuses and permit the one-way f low of CS F from the subarachnoid

space into the venous circulation.

are found in large numbers along the superior sagittal sinus but are associated with all

dural sinuses.

1.

Subarachnoid space (see I D 4)2.

C. Dura mater

is the outer layer of the meninges and consists of dense connective t issue.

The supratentorial dura is innervated by the tr igeminal nerve; the posterior fossa is innervated by the

vagal and upper spinal nerves.

forms three major ref lections and the walls o f the dural venous sinuses:

Falx cerebri

l ies between the cerebral hemispheres in the longi tudinal cerebral f issure.

contains the superior and inferior sagittal sinuses between its two layers.

1.

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Figure 2-1. Cross-section of the spinal cord and its meningealinvestments. The subarachnoid, subdu ral, and epidural spaces arevisible. The anterior and posterior longitudinal l igaments are seen butare not labeled. (Reprinted with permission from Carpenter MB, Sutin J:Human Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1983, p 9. )

Tentorium cerebel l i (Figure 2-3)

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.

2.

Diaphragma sellae

forms the roof of the hypophyseal fossa.

contains an aperture through which the hypophyseal stalk ( infundibulum) passes.

3.

Dural sinuses (see Figure 2-3)

are endothelium-lined, valveless venous blood channels.

4.

D. Meningeal spaces(see Figures 2-1, 2-2 and2-3)

Spinal epidural space

is located between the dura and the vertebral periosteum.

contains loose areolar t issue, venous p lexuses, and lymphatics.

1.


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may be injected with a local anesthetic to produce a paravertebral nerve block.

Cranial epidural space

is a potential space between the periosteal and meningeal layers of the dura.

contains the meningeal arteries and veins.

2.

Subdural space

is a potential space between the dura and the arachnoid.

intracranially transmits the superior cerebral veins to the venous la cunae of the superior sagittal

sinus. Laceration of these bridging veins results in subdural hemorrhage (hematoma).

Figure 2-2. Diagrammatic representations of the caudal part of the sp inal

cord and lumbar cistern. (A) Longitudinal section through the caudalvertebral column and canal showing the conus medull aris and th e lumbarcistern. Lumbar puncture is made between the spinous processes of L3

and L4 (or L4 and L5). (B) Dorsal view of the cauda equina and spinalnerves. The adult spinal cord terminates at the L1L2 interspace.(Reprinted with permission from Carpenter MB, Sut in J: Human

3.


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Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1983, p 8. )

Subarachnoid space

is located between the pia mater and the arachnoid.

contains CS F.

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 (see Figure 2-2A).

4.

Subarachnoid cisterns (see Figure 2-3)

are dilat ions 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.

a.

5.


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Figure 2-3. The subarachnoid spaces and cisterns of the b rain andspinal cord. CSF is produced in the choroid pl exuses of theventricles, exits the fourth ventricle, circulates in the subarachnoidspace, and enters the superior sagittal sinus via the arachnoidgranulations. (Reprinted with permission from Noback CR,

Strominger NL, Demarest RJ: The Human Nervous System, 4th ed.Baltimore, Will iams & Wilkins, 1991, p 68. )

contains the facial nerve (cranial nerv e [CN ] VII ) and the vestibulocochlear nerve

(CN VIII).

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.

b.


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can be tapped for CSF (suboccipital tap).

Ambient cistern

interconnects the superior and interpeduncular cisterns; contains the trochlear

nerve (CN IV ).

c.

Superior cistern

overlies the midbrain tectum.

d.

E. M eningiomas

are benign, slow-growing, well-demarcated tumors that arise from meningotheal arachnoid cells.

comprise 20% of primary intracranial tumors and 25% of spinal tumors.

are found most frequently in the anterior cranial fossa (parasagittal 25% , convexity 20%, and basal

40%).

are histologically characterized by a whorling pattern and calcif ied psammoma bodies.

enlarge slowly and create a cavity in the adjacent brain.

occur in adults between 20 and 60 years of age, most often in women (60%).

II. Ventricles (Figure 2-4; see Figure 2-3)

are lined with ependyma and contain CSF.

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

communicate with the subarachnoid space via three foramina in the fourth ventricle.

consist of four f luid-f i l led communicating cavit ies within the brain.

A. Lateral ventricles

are the two ventricles located within the cerebral hemispheres.

communicate with the third ventricle via the interventricular foramina of Monro .

consist of f ive parts:

Frontal (anterior) horn

is located in the frontal lobe; its lateral wall is formed by the head of the caudate nucleus.

lacks choroid plexus.

1.

Body

is located in the medial port ion of the frontal and parietal lobes.

has choroid plexus.

communicates via the interventricular foramen of Monro with the third ventricle.

2.

Temporal (inferior) horn

is located in the medial part of the temporal lobe.

has choroid plexus.

3.

Occipital (posterior) horn (see Figure 1-2)4.


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is located in the parietal and occipital lobes.


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 calcif ied in adults and is

visible on x-ray f i lm and computed tomography (CT).

5.

B. Third ventricle(see Figures 1-5, 2-3, and2-4)

is a slit l ike vert ical midline cavity of the diencephalon.

communicates with the lateral ventricles via the interventricular foramina of Monro and with the fourth

ventricle via the cerebral aqueduct.

contains a pair of choroid plexuses in its roof.

C. Cerebral aqueduct (aqueduct of Sylvius)

l ies in the midbrain.

connects the third ventricle with the fourth ventricle.


Blockage leads to hydrocephalus (aqueductal stenosis).


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Figure 2-4. The ventricle system of the brain. (A) Lateral aspect. (B)Dorsal aspect. (Reprinted with permission from Carpenter MB, Sutin J:Human Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1983, p 44. )

D. Fourth ventricle(see Figures 1-5, 2-3, and2-4)

l ies between the cerebellum and the brainstem.

contains a pair of choroid plexuses in its caudal roof.


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expresses CSF into the subarachnoid space via the two lateral foramina of Luschka and the single

medial foramen of Magendie.

III. Cerebrospinal Fluid

is a clear, colorless, acellular f luid found in the subarachnoid space and ventricles.

has several features:

A. Formation

is produced by the choroid plexus at a rate of 500 ml/day. The total CSF volume equals 140 ml (see

Figures 1-5, 1-7, and 2-3).

B. 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 vill i (see Figure 2-3).

C. Circulation(see Figure 2-3)

f lows 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.

D. Compositioncontains no more than 5 lymphocytes/l and usually is sterile.

other normal values are:

pH : 7.351.

Specif ic gravity: 1.0072.

Glucose: 66% of plasma glucose3.

Total protein: < 45 mg/dl in the lumbar cistern4.

E. Normal pressure

is 80 to 180 mm of water (CSF) in the lumbar subarachnoid space when the patient is in a lateral

recumbent (decubitus) posit ion.

IV. Hydrocephalus

is dilat ion of the cerebral ventricles caused by blockage of the CSF pathways.

is characterized by excessive accumulation of CSF in the cerebral ventricles or subarachnoid space.


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A. Noncommunicating hydrocephalus

results from obstruction within the ventricles (e.g., congenital aqueductal stenosis).

B. Communicating hydrocephalus

results from blockage within the subarachnoid space (e.g., adhesions after meningit is).

C. Normal-pressure hydrocephalus

occurs when the CSF is not absorbed by the arachnoid vil l i , possibly secondary to posttraumatic

meningeal hemorrhage.

is characterized clinically by the tr iad of progressive dementia, ataxic gait, and urinary incontinence

(wacky, wobbly, and wet).

D. Hydrocephalus ex vacuo

results from a loss of cells in the caudate nucleus (e.g., Huntington disease).

E. Pseudotumor cerebri (benign intracranial hypertension)

results from increased resistance to CSF outf low at the arachnoid vil l i .

is characterized by papilledema without mass, elevated CSF pressure, and deteriorating vision. The

ventricles may be slit- l ike.

occurs in obese young women.

V. Meningitis (pl. m eningitides)

is an inf lammation of the piaarachnoid of the brain, spinal cord, or both.

A. Bacterial (pyogenic) meningitis

occurs most often in children under 5 years of age (>70% of all cases).

is characterized clinically by fever, headache, and nuchal r igidity with Kernig sign.

may result in cranial nerve palsies (CN III, CN IV, CN VI, and CN VIII) and hydrocephalus.

Common etiologic agents

In newborns (


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type of meningit is.

CSF findings (Table 2-1)

Numerous neutrophilsa.

Decreased glucose leve lb.

Elevated protein leve lc.

2.

B. Viral (lymphocytic) meningitis

is also called aseptic meningit is.

is characterized by fever, headache, and nuchal r igidity with Kernig sign.

Table 2-1. Properties of CSF in Subarachnoid Hemorrhage, Bacterial

Meningitis, and Viral Encephalitis

CSF Normal

Subarachnoid

Hemorrhage

Bacterial

Meningitis

Viral

Encephalitis

Color Clear Bloody Cloudy Clear,cloudy

Cellcount(per

mm3)

1000PML

25500lymphocytes

Protein 100mg/dl)

Slightlyelevated(45 mg/dl Normal Reduced Normal

PML = polymorphonuclear leukocytes.

In infants: cell counts


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CSF findings

Numerous lymphocytesa.

Normal glucoseb.

Normal to slightly increased proteinc.

2.

VI. Herniation (Figures 2-5, 2-6, 2-7 and 2-8)

A. Transtentorial (uncal) herniation

is protrusion of the brain through the tentorial incisure.

B. Transforaminal (tonsillar) herniation

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

C. Subfalcial herniation

is herniation below the falx cerebri.

VII. Circumventricular Organs

are chemosensit ive zones that monitor the varying concentrations of circulating hormones in blood and

CSF.

are located in the periphery of the third ventricle; the area postrema is found in the f loor of the fourth

ventricle.

are highly vascularized with fenestrated capil laries and no bloodbrain barrier (the subcommissural

organ is an exception).

include the following structures:


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Figure 2-5. Coronal section of a tumor in the sup ratentorial compartment.

(1) Anterior cerebral artery; (2) subfalcial herniation; (3) shifting of

ventricles; (4) posterior cerebral artery (compression result s in contralateral

hemianopia); (5) uncal (t ranstentorial) herniation; (6) Kernohan notch, with

damaged corticospinal and corticobulbar fibers; (7) tentorium cerebelli; (8)

pyramidal cells that give rise to the corticospinal tract; (9) tonsillar(transforaminal) herniation, which damages vital medull ary centers.

(Adapted with permission from Leech RW, Shuman RM: Neuropathology.New York, Harper & Row, 1982, p 16. )

Figure 2-6. Axial section through the midbrain and th e herniating

parahippocampal gyrus (arrows). The left oculomotor nerve is beingstretched (dilated pupil). The l eft posterior cerebral artery is compressed,resulting in a contralateral hemianopia. The right crus cerebri is damaged(Kernohan notch) by the free edge of the tentorial incisure, resulting in acontralateral hemiparesis; the Kernohan notch result s in a false l ocalizingsign. The caudal displacement of the brainstem causes rupture of the

paramedian arteries of the basilar artery. Hemorrhage into the midbrainand rostral pontine tegmentum is usuall y fatal (Duret hemorrhages). The

posterior cerebral arteries lie superior to the oculomotor nerves. (1)

Parahippocampal gyrus; (2) crus cerebri; (3) posterior cerebral artery; (4)

optic nerve; (5) optic chiasma; oculomotor nerve; (6) oculomotor nerve; (7)free edge of tentorium; (8) Kernohan notch. (Adapted with permission fromLeech RW, Shuman RM: Neuropathology. New York, Harper & Row, 1982, p19. )


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Figure 2-7. Magnetic resonance imaging scan (T1-weighted image)showing brain trauma. Epidural hematomas may cross dural attachments.Subdural hematomas do not cross dural attachments. The hyperintense

signals are caused by methemoglobin. (A) Internal capsule; (B) subdural

hematoma; (C) subdural hematoma; (D) thalamus; (E) epidural hematoma.(Reprinted with permission from Fix JD: High-Yield Neuroanatomy, 3rd ed.Philadelphia, Lippincott Will iams & Wilkins, 2005, p 27. )


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Figure 2-8. CT scan (axial section) showing an intraparenchymal

hemorrhage in the l eft frontal lobe. (A) Intraparenchymal hemorrhage; (B)

lateral ventricle; (C) internal capsule; (D) calcified glomus in the trigoneregion of the lateral ventricle. (Reprinted with permission f rom Fix JD:High-Yield Neuroanatomy, 3rd ed. Philadelph ia, Lippincott Williams &Wilkins, 2005, p 27. )

A. Organum vasculosum of the lamina terminalis

is considered to be a vascular outlet for luteinizing hormonereleasing hormone and somatostatin.

B. Median eminence of the tuber cinereum (see Figure 1-1)

contains neurons that elaborate releasing and inhibit ing hormones into the hypophyseal portal system.

C. Subfornical organ

is located on the i nferior surface of the fornix at the level of the i nterventricular foramen of Monro.

contains neurons that project to the supraoptic nu clei and the organum vasculosum.

is a central receptor site for angiotensin II.

D. Subcommissural organ

is located below the posterior commissure at the junction of the third ventricle and the cerebral

aqueduct.

is composed of specialized ependymal cells, glial elements, and a capil lary bed containingnonfenestrated endothelial cells.

E. Pineal body(see Figures 1-5 and1-6)

contains calcareous granules, in brain sand or acervulus, which are seen on x-ray f i lm and CT;

calcif ication occurs after 16 years of age.

contains pinealocytes (epiphyseal cells) and is highly vascular with fenestrated capil laries.

is derived from the diencephalon.

is innervated solely via postganglionic f ibers from the superior cervical ganglion of the autonomic

nervous system.

synthesizes serotonin and melatonin. Clinical observation suggests an antigonadotrophic function.

Pinealomas may result in dorsal midbrain syndrome (see Figure 14-3A).


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Figure 2-9. CT scan (axial section) showing an epidural hematoma and askull fracture. The epidural hematoma has a classic biconvex, or lentiform,

shape. (A) Epidural hematoma; (B) skull fracture; (C) calcified pineal

gland; (D) calcified glomus in the trigone region of the l ateral ventricle.

F. Area postrema(Figure 2-9)

consists of two small subependymal oval areas on either side of the fourth ventricle rostral to the obex.

contains modif ied neurons and astrocyte-like cells surrounded by fenestrated capil laries.

is considered to be a chemoreceptor zone that tr iggers vomit ing in response to circulating emetic

substances.

plays a role in food intake and cardiovascular regulation.

Q Review Test1. A 25-ye ar-old housewife com plains of headaches of 4 months' duration. She is obese and has

bilateral papil ledem a, and her vision is deteriorating. Her opening CSF pressure is elev ated; other

CSF findings are normal. CT and magnetic resonance im aging (MRI) scans are normal. The se signs

are due to im pairme nt of CSF egress. Obstruction at which of the following loci is most likely ?

(A) Arachnoid vil l i

(B) Cerebral aqueduct

(C) Foramen of Luschka

(D) Foramen of Magendie

(E) Foramen of Monro


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View Answer

2. The total volume of CSF found in the subarachnoid space and cerebral v entricles is

(A) 110 ml

(B) 140 ml

(C) 160 ml

(D) 170 ml

(E) 190 ml

View Answer

3. Which of the following pathogens would most likely be se en in bacterial me ningitis of the

newborn?

(A) Streptococcus agalactiae

(B ) Haemophi lus inf luenzae

(C ) Neisser ia meningit ides

(D ) Streptococcus pneumoniae

(E) Herpes simplex type 2

View Answer

4. Which part of the ve ntricular system contains choroid plexus?

(A) Frontal horn

(B) Occipital horn

(C) Cerebral aqueduct

(D) Third ventricle

(E) Terminal ventricle

View Answer

5. Which one of the following circumve ntricular organs is solely inne rvate d by postganglionic fibers

from the superior cervical ganglion of the ANS?

(A) Area postrema

(B) Pineal body

(C) Organum vasculosum of the lamina terminalis

(D) Subfornical organ

(E) Subcommissural organ

View Answer

6. Choose the normal quantity of CSF daily production.

(A) 300 ml

(B) 400 ml

(C) 500 ml

(D) 600 ml

(E) 700 ml


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View Answer

7. Which one of the following tumors contains cellular whorls and psammoma bodie s?

(A) Astrocytoma

(B) Acoustic schwannoma

(C) Glioblastoma multiforme

(D) Oligodendroglioma

(E) Meningioma

View Answer

Questions 8 to 12

Match each structure or description in item s 8 to 12 with the appropriate lettere d structure shown in

the T1-weighted magnetic resonance image of a coronal section of the brain.

8. Olive

View Answer

9. It contains the trochlear nerve (CN IV)

View Answer

10. Its stenosis results in hydrocephalus

View Answer

11. Contains a calcified glomus

View Answer

12. Receive s CSF from the arachnoid vi l l i

View Answer

Questions 13 to 17


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Match each structure or description in items 13 to 17 with the appropriate lettered structure shown

on the T1-weighted magnetic resonance image of a midsagittal section of the brain.

13. Superior cistern

View Answer

14. Blockage resulting in hydrocephalus

View Answer

15. Lateral ventricle

View Answer

16. Contains the two foram ina of Luschka

View Answer

17. Receive s CSF via the foramen of Magendie

View Answer


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Chapter2_Meninges and CSF

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