Cranium, Ventricles, and Meninges

by

CRANIAL VAULT AND MENINGES

Foramina

Holes allowing cranial nerves, spinal cord, blood vessels to enter and leave cranial cavity

  • Foramen magnum– largest; at base of skull
  • Cervicomedullary junction – occurs at the level of foramen magnum; point where spinal cord meets medulla

Fossae

Compartments of the cranial cavity divided by ridges of bone

  • Anterior fossa – contains frontal lobe; divided from middle fossa by lesser wing of sphenoid bone
  • Middle fossa – contains temporal lobe; divided from posterior fossa by petrous ridge of temporal bone, as well as sheet of meninges
  • Posterior fossa – contains cerebellum and brainstem

Meninges

Final layers within skull are meninges and CSF

From inside to outside (PAD):

  • Pia– thin layer of cells
    • adheres to brain surface closely and follows gyri and depths of sulci
    • surrounds initial portion of each blood vessel as it enters brain surface, , then fuses with blood wall
  • Arachnoid– “spidery”
    • adheres to inner surface of dura
  • within arachnoid, CSF “percolates” over surface of brain
  • Dura– “hard”; 2 fibrous layers, which are fused with each other and adhere to the inner surface of skull except in two places (where one layer dips inward):
    • falx cerebri – flat sheet of dura suspended from roof of cranium; separates R and L hemisphere
    • tentorium cerebelli – tentlike sheet of dura covering upper surface of cerebellum; tentorium cerebelli and petrous portions of temporal bones divide posterior fossa from rest of cranial vault:
      • supratentorial: cavity above tentorium
      • infratentorial: cavity below tentorium

Spaces

Potential spaces formed by meninges; blood vessels within spaces can cause hemorrhage

  • Epidural space: b/w inner surface of skull and dura
    • Middle meningeal artery: branch of external carotid artery; supplies the dura
  • Subdural space: b/w dura and arachnoid
    • Bridging veins and dural venous sinuses—provide venous drainage from brain and meninges
  • Subarachnoid space: b/w arachnoid and pia
    • CSF and Major arteries (then penetrate into brain)
  • Spinal cord- enveloped by same 3 meningeal layers as exits through foramen of magnum; only difference is a layer of epidural fat in the spinal canal

VENTRICLES AND CEREBROSPINAL FLUID

Basic facts

  • Contain CSF
  • Two lateral ventricles, one in each hemisphere
  • Third within diencephalon
  • Fourth surrounded by pons, medulla, and cerebellum
  • Choroid plexus: inside ventricles; vascular structure that produces CSF; lined with epithelial cells
  • Ependymal cells: line inner walls of ventricles

Lateral Ventricles

  • Horns- extensions named after lobes or directions they extend
    • Frontal (Anterior) Horn- extends anteriorly from body of lateral ventricle into frontal lobe
    • Occipital (Posterior) Horn- extends back to occipital lobe
    • Temporal (Inferior) Horn- extends inferiorly and anteriorly into temporal lobe
  • Body- posterior to interventricular foramen of Monro, within frontal and parietal lobes
    • Atrium (Trigone): connects the body with the occipital and temporal horns
  • “C” shaped structures- follow curve of vent; caudate nucleus; corpus callosum, fornix, stria terminalis
  • Communicates with third ventricle via interventricular foramen of Monro

Third Ventricle

  • Walls formed by thalamus and hypothalamus
  • Communicates with fourth vent via cerebral aqueduct (aqueduct of Sylvius) which travels through midbrain

Fourth Ventricle

  • Roof formed by cerebellum
  • Floor formed by pons and medulla

Cerebrospinal Fluid

  • leaves fourth ventricle via: lateral foramina of Luschka and midline foramen of Magendie
  • Travels around brain and spinal cord in subarachnoid space
  • Reabsorbed by arachnoid granulations into dural venous sinuses (back into bloodstream)
  • Cisterns- widening of subarachnoid space to form large CSF collections

BLOOD-BRAIN BARRIER

Capillary endothelial cells

  • Brain capillary- tight junctures; cell transport required for passage of water soluble substances
  • Systemic capillary- capillary wall separated by clefts allowing passage of fluids and molecules
  • Choroid epithelial cells: form blood-CSF barrier; barrier between capillaries and CSF

Blood-brain and blood-CSF barriers separate arterial blood from brain parenchyma

  • Lipid soluble substances cross both (O2 and CO2)
  • Other substances conveyed in both directions through transport systems

Primary role of blood-brain barrier is to protect brain function from fluctuations in blood chemistry

  • Circumventricular organs: areas where blood-brain barrier is interrupted, allowing brain to respond to changes and secrete neuropeptides into system

Disruption of blood-brain barrier- caused by tumor, infection

  • Results in extravasation of fluids into interstitial space
  • Vasogenic edema- excessive extracellular fluid
  • Cytotoxic edema- excessive intracellular fluid within brain cells caused by cellular damage

HEADACHE

  • No pain receptors in parenchyma- pain caused by mechanical traction, inflammation, or irritation of other structures in the head that are innervated, such as blood vessels, meninges, scalp, and skull.
  • Side of headache often corresponds to side of pathology (but not always)

Vascular headache

Migraine (term also used to mean cluster headache)

  • Pathophysiology thought to involve inflammatory, autonomic, serotonergic, neuroendocrine, and other influences on blood vessel caliber in the head
  • 75% have + family history
  • Sx provoked by foods, stress, eye strain, menstrual cycle, changes in sleep
  • Aura: warning sx; visual blurring, shimmering, scintillating distortions, fortification scotoma (region of visual loss bordered by zigzagging lines resembling walls of a fort)
  • Often unilateral; if bilateral, warrants MRI to exclude vascular malformation or lesion
  • Pain is throbbing; exacerbated by light (photophobia), sound (phonophobia), or sudden movement
  • Nausea, vomiting, tender scalp may occur
  • 30 minutes to 24 hours duration; relief often after sleeping
  • Occur once every few years, to several times a week

Complicated migraine

  • Accompanied by transient focal neurologic deficits: sensory phenomena, motor deficits, visual loss
  • Migraine should be diagnosis of exclusion only after other causes (e.g., post-ictal headaches or cerebrovascular disease) have been ruled out

Treatment of migraine

  • Acute attacks: nonsteroidal anti-inflammatories, anti-emetics, serotonin agonists, ergot derivatives, rest in dark.
  • Preventive measures: avoid triggers, treatment with meds, hydration

Cluster headache

  • Less than 1/10 as common as migraine
  • Clusters occur once to several time per day over a few weeks then vanish for months
  • Pain is severe, described as boring sensation over one eye; lasts 30-90 minutes
  • Accompanied by unilateral autonomic sx (tearing, eye redness); Horner’s syndrome (ptosis, miosis, anhidrosis- covered in Ch. 13), unilateral flushing, sweating, nasal congestion
  • Treatment similar to migraine; inhaled oxygen effective in stopping attack

Tension headache (renamed tension-type headache)

  • Steady dull ache, described as band-like sensation
  • May be related to excessive contraction of scalp and neck muscles
  • Pathophysiological distinction between tension h/a and migraine has been questioned
  • Mild to mod h/a lasting few hours, but there is a chronic form
  • Treatment- muscle relaxation techniques; nonsteroidal anti-inflammatory; analgesics; TCAs

SEE TABLE 5.2 FOR OTHER CAUSES OF HEADACHE

Other causes

  • Any “explosive” onset of severe h/a should have CT – to rule out subarachnoid hemorrhage
  • Cerebral ischemia and infarction
  • Post-ictal period
  • Low CSF- from lumbar puncture or spontaneously; worse while standing, better when lying down
  • Increase CSF- neoplasms; worse when lying down
  • Meningitis-accompanied by fever, signs of meningeal irritation (stiff neck, light sensitivity)
  • Pseudotumor cerebri- elevated ICP with no mass lesion; common in adolescent females; tx w/ acetazolamide or shunt
  • Temporal arteritis (giant cell arteritis)- seen in elderly; vasculitis affects temporal arteries, including those supplying eyes; artery enlarged and firm; may lose vision

INTRACRANIAL MASS LESIONS

Mass– anything abnormal that occupies volume within the cranial vault (e.g., tumor, hemorrhage, abscess) Neurologic symptoms caused by:

  • compression and destruction of adjacent brain regions
    • local tissue damage (ex- lesion in primary motor cortex cause contralateral weakness)
    • distorts or irritates blood vessels, can cause headache
    • compression of blood vessels can cause ischemic infarction
    • erosion through blood vessel walls can cause hemorrhage
  • increased intracranial pressure
  • herniation: mass displaces structures so that they are shifted from one compartment to another
    • Mass effect- distortion of normal brain geometry due to mass lesion
    • Effacement- mild flattening of sulci next to lesion; seen on MRI but no symptoms
  • Other effects:
    • Disruption of blood-brain barrier leads to vasogenic edema
    • Compression of ventricular system obstructs CSF flow resulting in hydrocephalus
    • lesions produce abnormal electrical activity, causing seizures
    • Midline shift- shift in brain structures away from lesion
    • pineal calcification used to measure extent of shift at level of upper brainstem
    • displacement and stretching of upper brainstem impairs RAS

ELEVATED INTRACRANIAL PRESSURE

Elevated ICP can cause decreased cerebral blood flow and ischemia, though autoregulation of vessels compensates for modest increases in ICP

Symptoms/ signs of increased ICP

  • Headache- worse in morning because brain edema rises overnight from lying down
  • Altered mental status- *** most important indicator; irritability and depressed level of alertness and attention
  • Nausea and projectile vomiting
  • Papilledema- engorgement and elevation of optic disc; sometimes also see retinal hemorrhage
  • Visual loss caused by transient or permanent optic nerve damage
  • Diplopia caused by traction on CN VI, causing unilateral or bilateral abducens nerve palsies
  • Cushing’s triad- hypertension, bradycardia, irregular respirations

Treatment Goals

  • Reduce to safe level, giving time to treat underlying disorder
  • Measure through LP – BUT do not perform if severely elevated ICP because of risk of precipitating a herniation

BRAIN HERNIATION SYNDROMES

Herniation- mass effect severe enough to push structures into another compartment

 

Transtentorial Herniation-

herniation of medial temporal lobe, especially uncus, inferiorly through tentorial notch

  • uncal herniation– clinical triad:
    • blown pupil- compression of CNIII; dilated, unresponsive pupil; ipsilateral to lesion in 85% of cases
    • hemiplegia- compression of cerebral peduncles; can be ipsilateral or contralateral to lesion.
    • coma- distortion of midbrain reticular formation

Central Herniation

  • downward displacement of brainstem or cerebellar tonsils through foramen magnum
  • associated with any lesion causing increased ICP

Subfalcine Herniation

  • cingulate gyrus and other brain structures herniated under falx cerebri to other side of cranium
  • no clinical signs; may cause occlusion of anterior cerebral arteries

HEAD TRAUMA

Mild Head Trauma

Concussion – LOC; headache; dizziness; nausea; vomiting

Recovery usually complete, but can see postconcussive syndrome:

  • headaches
  • lethargy
  • mental dullness
  • lasts months after accident

Severe Head Trauma

Cause permanent injury to brain through:

  • Diffuse axonal shearing- damage to white matter and cranial nerves
  • Petechial hemorrhages- small spots of blood in white matter
  • Intracranial hemorrhage- symptoms can occur after delay of several hours after event
  • Cerebral contusion
  • Tissue injury from penetrating trauma
  • Cerebral edema, contributing to increased ICP

INTRACRANIAL HEMORRHAGE

Epidural Hematoma

Location

  • space between dura and skull

Cause

  • rupture of middle meningeal artery from fracture of temporal bone

Clinical features

  • increased ICP; pt may have lucid interval lasting hrs before lapsing into unconsciousness

Subdural Hematoma

Location

  • between dura and arachnoid

Cause

  • rupture of bridging veins

Clinical features

  • Two types
    • Chronic- slowly oozing blood collects; headache, cognitive impairment, unsteady gait, focal signs
    • Acute- high velocity impact injury

Subarachnoid Hemorrhage

Location Between arachnoid and pia

Cause

  • Two causes
    • Nontraumatic (spontaneous)- onset with severe headache; result of arterial aneurysm or bleed from AVM
      • Risk factors- hypertension, smoking, alcohol, sudden increase in BP
      • Clinical symptoms- headache, meningeal irritation, nuchal rigidity, cranial nerve, neuro deficits
      • Cerebral vasospasm- seen 1 week post; can lead to infarction
    • Traumatic: bleeding into CSF from damaged blood vessels due to contusions/ traumatic injury

Intracerebral or Intraparenchymal Hemorrhage

Location Within parenchyma in cerebral hemispheres, brainstem, cerebellum, spinal cord

Cause

  • Two types
    • Traumatic: contusions from skull ridgesl; coup/contrecoup injury; commonly frontal or temporal poles
    • Nontraumatic: caused by hypertension, brain tumor, vascular malformation
      • Most common- small penetrating blood vessels in basal ganglia; thalamus; cerebellum; pons

Intraventricular extension– extends from parenchyma to involve ventricles Intraventricular hemorrhage– arise from blood vessels in vents

Vascular malformations

  • Arteriovenous malformations: congenital abnormalities causing direct connection b/w artery and vein; tangle of abnormal blood vessels; hemorrhage is usually intraparenchymal; present with headache, seizure
  • Cavernous malformation: abnormally dilated vascular cavity lined by only one layer of vascular endothelium
  • Capillary telangiectasias- small regions of abnormally dilated capillaries; rarely give rise to hemorrhage
  • Venous angiomas- dilated veins; no clinical symptoms but associated with cavernous malformations

HYDROCEPHALUS

Excess CSF in intracranial activity

Caused by

  • Excess CSF production – rare; but can be seen with certain tumors (choroid plexus papilloma)
  • obstruction of flow in vents or subarachnoid space – more common
    • usually occurs at narrow points (foramen of Monro, cerebral aqueduct, fourth vent)
  • decrease in reabsorption due to damage or clogging of arachnoid granulations

Two categories

  • Communicating hydrocephalus- impaired CSF reabsorption in arachnoid granulations, obstruction of flow in subarachnoid space, or excess CSF productions
  • Noncommunicating hydrocephalus- obstruction of flow within ventricular system

Symptoms

  • Like any other cause of increased ICP- headache, nausea, vomiting, cognitive impairment, decreased vision
  • Dilation of vents compresses descending white matter pathways from frontal lobes leading to magnetic gait (feet barely leave floor) and incontinence
  • Infants- skull expands, leading to increase head circumference; bulging anterior fontanelle
  • Eye movement abnormalities- mild results in sixth nerve palsy (incomplete or slow abduction of eye in horizontal direction); severe results in inward deviation of both eyes

Treatment

  • Extraventricular drain- (ventriculostomy) fluid from lateral vents drained to bag outside head
  • Ventriculoperitoneal shunt- shunt tube passed from lateral vent into peritoneal cavity of abdomen
  • Third ventriculostomy- via endoscopy, blunt instrument perforates floor of third vent to allow CSF to drain

Normal Pressure Hydrocephalus – chronically dilated vents; measurement of CSF pressure not elevated Clinical triad of gait difficulties; urinary incontinence; mental decline (3 Ws: wet, wobbly, and wacky) Some improve after lumbar puncture (briefly) or VP shunt

Hydrocephalus ex vacuo – excess CSF in region where brain tissue lost due to stroke, surgery, atrophy, etc.

Common Congenital Causes in Children:

  • Neural tube defect (e.g., spina bifida/myelomeningocele)
  • Dandy-Walker syndrome
  • Aquaductal stenosis
  • Intraventricular Hemorrhage

PRIMARY CNS TUMORS

Adults Most common- glioblastoma, brain metastases (arise from neoplasms elsewhere in body that spread to brain) 30% infratentorial; 70% supratentorial

Pediatric Most common- astrocytoma, medulloblastoma, ependymoma 70% posterior fossa; 30% supratentorial Since many in posterior fossa, tend to cause hydrocephalus through compression/obstruction of fourth vent

Symptoms

  • Depend on size, location, rate of growth
  • Headache, signs of elevated ICP common at presentation
  • Seizures or focal symptoms depend on location

Benign– do not infiltrate or disseminate through nervous system Malignant– potential to spread; rarely spread outside CNS

Treatment

  • Surgical removal- should be > 90% tumor removal to have positive effect on outcome
  • Radiation therapy
  • Chemotherapy
  • Steroids to reduce edema

Types of Tumors

  • Gliomas- subdivided into several types, arise from glial cells
  • Meningiomas- arise from arachnoid villus cells
  • Pituitary adenomas- cause endocrine disturbance; cause bitemporal visual field defect by compressing optic chiasm
  • Schwannomas- most common on CN VIII; discussed Ch. 12
  • Lymphoma- arise in regions adjacent to vents; more common with increase in HIV infection
  • Pineal region tumor- uncommon; obstruct cerebral aqueduct causing hydrocephalus; compress midbrain

Pediatric Tumors

  • Cerebellar astrocytoma: grade I/IV; often cured by surgery alone
  • Medulloblastoma and ependymoma worse outcome

BACTERIAL INFECTIONS

Bacteria gain access through bloodstream, originating from infection elsewhere

Infectious meningitis

– infection of CSF in subarachnoid space

Symptoms- meningeal irritation: headache, lethargy, photophobia, phonophobia, fever, nuchal rigidity (neck muscles contract involuntarily, resulting in neck pain and resistance to neck flexion)

Diagnosis- symptoms may progress over hours or weeks; sample of CSF by lumbar puncture; CT before LP because removing CSF if there is a mass can cause herniation

Treatment- antibacterial therapy

Complications- seizures, cranial neuropathies, edema, hydrocephalus, herniation, infarcts, death

Brain abscess

expanding intracranial mass lesion, like brain tumor, but with more rapid course

Symptoms- lethargy, headache, fever, nuchal rigidity, vomiting, seizures; focal signs

Treatment- if small, treat with antibiotics; if large or progressive, treat with needle aspiration and antibiotics

Epidural abscess

– occur in spinal canal

Symptoms- back pain, fever; headache; signs of nerve root or spinal cord compression

Treatment-surgical drainage; antibiotics

Subdural empyema

collection of pus in subdural space, resulting from infection of nasal sinus or inner ear

Treatment- surgical drainage and antibiotics

 

Tuberculous meningitis

– seen with resurgence of TB

Symptoms- headache, lethargy, meningeal signs over course of weeks; inflammatory response in basal cisterns affecting circle of Willis and causing infarcts; coma and death if untreated

Treatment- combination of drugs

Populations at risk- IV drug users; HIV +; people where TB is endemic

Infections Caused by Spirochetes

  • Neurosyphilis- recent resurgence due to HIV;
    • Primary – cancer sores
    • Secondary – diffuse skin lesions
    • Tertiary –diffuse white matter infarcts causing dementia, behavioral change, delusion, psychosis, upper motor neuron weakness; Tabes dorsalis (involvement of spinal cord dorsal roots)

 

Lyme Disease- deer tick

Symptoms– early rash; later neurologic manifestations after several weeks (meningeal signs, emotional changes, memory and concentration problems, cranial and peripheral neuropathies); arthritis, cardiac abnormalities

Diagnosis- clinical features, LP, blood test

Treatment- IV ceftriaxone

VIRAL INFECTIONS

Viral meningitis

Less intense, rapid than bacterial; recovery occurs spontaneously in 1-2 weeks

Symptoms- headache, fever, lethargy, nuchal rigidity, meningeal irritation (Table 5.5, p. 147)

Diagnosis- blood tests, LP, EEG

Viral encephalitis – involves brain parenchyma; more severe symptoms Meningoencephalitis– meninges involved

Causes

  • Herpes – psychotic symptoms; focal signs; causes necrosis of temporal and frontal structures
  • Postinfectious encephalitis- several days after viral infection, diffuse automimmune demyelination of CNS
  • Herpes zoster- shingles, chicken pox
  • Transverse myelitis- caused by viral infections of CNS (spinal cord)

HIV-Associated Disorders of Nervous System

  • Aseptic meningitis- caused at time of seroconversion; associated with cranial neuropathies involving facial nerve
  • AIDS dementia complex- most common neurologic manifestation of HIV; treat with AZT in combo therapy
  • Progressive multifocal leukoencephalopathy (PML)- gradual demyelination of brain, leading to death in 3-6 months
  • Opportunistic viral, bacterial, funga, and parasitic infections: herpes, varicella-zoster, cytomegalovirus, TB, neurosyphylis, cryptococcal meningitis, toxoplasmosis
  • Primary central nervous system lymphoma- B cell lymphoma; second most common cause of mass lesions

Parasitic Infections

Cysticercosis– ingestion of eggs of pork tapeworm

Symptoms- organism migrates through bloodstream, forming small cysts in muscles, eyes, CNS; causes seizures, headache, lymphocytic meningitis; hydrocephalus if cyst obstructs

Radiologic appearance- small cysts in parenchyma with surrounding edema

Course- organisms eventually die leaving calcifications throughout brain (“brain sand”)

Diagnosis- clinical history; radiologic appearance; antibody tests

Fungal Infections

Can involve brain parenchyma and cause inflammatory response and/or CN deficits

 

Prion-Related Illnesses

Prion– protein-based infectious agent; able to transit illness from one animal to another although no DNA or RNA

Symptoms- diffuse degeneration of brain and spinal cord, multiple vacuoles with spongiform appearance

Types- Creutzfeldt-Jakob; Gerstmann-Straussler-Scheinker; kuru; fatal familial insomnia

  • Creutzfeldt-Jakob
    • rapidly progressive dementia, exaggerated startle response, myoclonus, visual distortion, ataxia
    • EEG: period sharp wave complex
    • progressive deterioration and death within 6-12 months
    • incubation period 2-25 years
    • there does appear to be some genetic susceptibility in one strain

LUMBAR PUNCTURE

Access to subarachnoid space of lumbar cistern

  • obtain samples of CSF
  • measure CSF pressure
  • remove CSF in normal pressure hydrocephalus
  • give drugs

Perform CT first to evaluate for increased ICP and avoid herniation Red blood cells in CSF can indicate subarachnoid hemorrhage or traumatic tap (due to needle puncture)

LP used for diagnosing infection, hemorrhage, neoplasms, meningitis, and multiple sclerosis

 

CRANIOTOMY

Burr holes drilled through skull, then joined together with small saw to remove bone flap; dura folded back to provide access to brain