Ventricular System

A. The choroid plexus is a specialized structure that projects into the lateral, third, and fourth ventricles of the brain. It consists of infoldings of blood vessels of the pia mater that are covered by modified ciliated ependymal cells. It secretes the CSF. Tight junctions of the choroid plexus cells form the blood-CSF barrier.

B. Ventricles contain CSF and choroid plexus.

1. The two lateral ventricles communicate with the third ventricle through the interventricular foramina of Monro.

2. The third ventricle is located between the medial walls of the diencephalon. It communicates with the fourth ventricle through the cerebral aqueduct.

3- The cerebral aqueduct connects the third and fourth ventricles. It has no choroid plexus. Blockage of the cerebral aqueduct results in hydrocephalus.

4. The fourth ventricle communicates with the subarachnoid space through three outlet foramina.

C. Hydrocephalus is dilation of the cerebral ventricles caused by blockage of the CSF pathways. It is characterized by excessive accumulation of CSF in the cerebral ventricles or subarachnoid space.

1- Noncommunicating hydrocephalus results from obstruction within the ventricles (e.g., congenital aqueductal stenosis).

2. Communicating hydrocephalus results from blockage within the subarachnoid space (e.g., adhesions after meningitis).

3. Normal-pressure hydrocephalus occurs when the CSF is not absorbed by the arachnoid villi. It may occur secondary to posttraumatic meningeal hemorrhage. Clinically, it is characterized by the triad of progressive dementia, ataxic gait, and urinary incontinence. (Remember: wacky, wobbly, and wet.)

4. Hydrocephalus ex vacuo results from a loss of cells in the caudate nucleus (e.g., Huntington's d isease).

5. Pseudotumor cerebri (benign intracranial hypertension) results from increased resistance to CSF outflow at the arachnoid villi. It occurs in obese young women and is characterized by papilledema without mass, elevated CSF pressure, and deteriorating vision. The ventricles may be slit-1 ike.

III. CEREBROSPINAL FLUID is a colorless acellular fluid. It flows through the ventricles and into the subarachnoid space.

A. Function

1. CSF supports the central nervous system (CNS) and protects it against con-cussive injury.

2. It transports hormones and hormone-releasing factors.

3. It removes metabolic waste products through absorption.

B. Formation and absorption. CSF is formed by the choroid plexus. Absorption is primarily through the arachnoid villi into the superior sagittal sinus.

C. The composition of CSF is clinically relevant (Table 2-1).

1. The normal number of mononuclear cells is less than 5/fxl.

2. Red blood cells in the CSF indicate subarachnoid hemorrhage (e.g., caused by trauma or a ruptured berry aneurysm).

3. CSF glucose levels are normally 50 to 75 mg/dl (66% of the blood glucose level). Glucose levels are normal in patients with viral meningitis and decreased in patients with bacterial meningitis.

4. Total protein levels are normally between 15 and 45 mg/dl in the lumbar cistern. Protein levels are increased in patients with bacterial meningitis and normal or slightly increased in patients with viral meningitis.

5. Normal CSF pressure in the lateral recumbent position ranges from 80 to 180 mm H20. Brain tumors and meningitis elevate CSF pressure.

Table 2-1

Cerebrospinal Fluid Profiles in Subarachnoid Hemorrhage, Bacterial Meningitis, and Viral Encephalitis

Table 2-1

Cerebrospinal Fluid Profiles in Subarachnoid Hemorrhage, Bacterial Meningitis, and Viral Encephalitis

Cerebrospinal

Subarachnoid

Bacterial

Viral

Fluid

Normal

Hemorrhage

Meningitis

Encephalitis

Color

Clear

Bloody

Cloudy

Clear, cloudy

Cell count/mm3

< 5 lymphocytes

Red blood cells present

> 1000 polymorphonuclear leukocytes

25-500 lymphocytes

Protein

< 45 mg/dl

Normal to slightly

Elevated > 100

Slightly elevated

elevated

mg/dl

< 100 mg/dl

Glucose ~ 66%

> 45 mg/dl

Normal

Reduced

Normal

of blood (80-

120 mg/dl)

Cell counts in infants < 10 cells/mm3; protein in infants = 20-170 mg/dl.

Cell counts in infants < 10 cells/mm3; protein in infants = 20-170 mg/dl.

IV. HERNIATION (Figures 2-2, 2-3, 2-4, 2-5, and 2-6)

A. Transtentorial (uncal) herniation is protrusion of the brain through the tentorial incisure.

B. Transforaminal (tonsillar) herniation is protrusion of the brain stem and cerebellum through the foramen magnum.

C. Subfalcial herniation is herniation below the falx cerebri.

Contralateral Crus Cerebri Herniation

Figure 2-2. Coronal section of a tumor in the supratentorial compartment. (1) Anterior cerebral artery; (2) subfalcial herniation; (3) shifting of ventricles; (4) posterior cerebral artery (compression results in contralateral hemianopia); (5) uncal (transtentorial) herniation; (6) Kernohan's notch, with damaged corticospinal and cor-ticobulbar fibers; (7) tentorium cerebelli; (8) pyramidal cells that give rise to the corticospinal tract; (9) tonsillar (transforaminal) herniation, which damages vital medullary centers. (Adapted with permission from Leech RW, Shuman RM: Neuropathology. New York, Harper & Row, 1982, p. 16.)

Figure 2-2. Coronal section of a tumor in the supratentorial compartment. (1) Anterior cerebral artery; (2) subfalcial herniation; (3) shifting of ventricles; (4) posterior cerebral artery (compression results in contralateral hemianopia); (5) uncal (transtentorial) herniation; (6) Kernohan's notch, with damaged corticospinal and cor-ticobulbar fibers; (7) tentorium cerebelli; (8) pyramidal cells that give rise to the corticospinal tract; (9) tonsillar (transforaminal) herniation, which damages vital medullary centers. (Adapted with permission from Leech RW, Shuman RM: Neuropathology. New York, Harper & Row, 1982, p. 16.)

Brain Herniation Oculomotor Nerve

Figure 2-3. Axial section through the midbrain and the herniating parahippocampal gyrus. The left oculomotor nerve is being stretched (dilated pupil). The left posterior cerebral artery is compressed, resulting in a contralateral hemianopia. The right crus cerebri is damaged (Kernohan's notch) by the free edge of the tentorial incisure, resulting in a contralateral hemiparesis. Kernohan's notch results in a false localizing sign. The caudal displacement of the brain stem causes rupture of the paramedian arteries of the basilar artery. Hemorrhage into the midbrain and rostral pontine tegmentum is usually 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; (7) free edge of tentorium; (8) Kernohan's notch. (Adapted with permission from Leech RW, Shuman RM: Neuropathology. New York, Harper «Sl Row, 1982, p. 19.)

Figure 2-3. Axial section through the midbrain and the herniating parahippocampal gyrus. The left oculomotor nerve is being stretched (dilated pupil). The left posterior cerebral artery is compressed, resulting in a contralateral hemianopia. The right crus cerebri is damaged (Kernohan's notch) by the free edge of the tentorial incisure, resulting in a contralateral hemiparesis. Kernohan's notch results in a false localizing sign. The caudal displacement of the brain stem causes rupture of the paramedian arteries of the basilar artery. Hemorrhage into the midbrain and rostral pontine tegmentum is usually 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; (7) free edge of tentorium; (8) Kernohan's notch. (Adapted with permission from Leech RW, Shuman RM: Neuropathology. New York, Harper «Sl Row, 1982, p. 19.)

Kernohan Notch

Figure 2-4. Magnetic resonance imaging scan showing brain trauma. (A) Internal capsule; (ß) subdural hematoma; (C) subdural hematoma; (D) thalamus; (E) epidural hematoma. Epidural hematomas may cross dural attachments. Subdural hematomas do not cross dural attachments. The hyperintense signals are caused by methemoglobin. This is a T1 -weighted image.

Figure 2-4. Magnetic resonance imaging scan showing brain trauma. (A) Internal capsule; (ß) subdural hematoma; (C) subdural hematoma; (D) thalamus; (E) epidural hematoma. Epidural hematomas may cross dural attachments. Subdural hematomas do not cross dural attachments. The hyperintense signals are caused by methemoglobin. This is a T1 -weighted image.

Internal Capsule Hemorrhage
Figure 2-5. Computed tomography scan axial section showing an intraparenchymal hemorrhage in the left frontal lobe. (A) Intraparenchymal hemorrhage; (B) lateral ventricle; (C) internal capsule; (D) calcified glomus in the trigone region of the lateral ventricle.
Epidural Hematoma Images

Figure 2-6. Computed tomography axial section showing an epidural hematoma und a skull fracture. (A) Epidural hematoma; (B) skull fracture; (C) calcified pineal gland; (D) calcified glomus in the trigone region of the lateral ventricle. The epidural hematoma is a classic biconvex, or lentiform, shape.

Figure 2-6. Computed tomography axial section showing an epidural hematoma und a skull fracture. (A) Epidural hematoma; (B) skull fracture; (C) calcified pineal gland; (D) calcified glomus in the trigone region of the lateral ventricle. The epidural hematoma is a classic biconvex, or lentiform, shape.

Essentials of Human Physiology

Essentials of Human Physiology

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Responses

  • sam hay
    What does kernohan's notch look like?
    6 years ago

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