FACTS & HINTS

High-Yield Facts

Clinical Points

Otitis externa

Defined as an inflammation or infection of the external ear

Also called swimmer's ear

Usuallybacterial in origin

Pathogens include pseudomonas aeruginosa and staphylococcus aureus

Patient maypresent with itchiness, a sensation of having the ear blocked, and pain

Ear on examination is painful, erythematous, and maybe discharging pus

Treatment is with topical antibiotics (eardrops)

Clinical Points

Otitis media

Defined as an inflammation of the middle ear Also known as glue ear

Most common in children between the ages of 6 months and 2 years

Symptoms include: pulling or rubbing the ears because of ear pain, fever, fussiness, or irritability, fluid leaking from the ear, changes in appetite or sleeping patterns, trouble hearing

Usuallyto the result of bacterial infection

On examination with an otoscope, the ear drum looks dull with loss of the cone of light Commonlytreated with antibiotics

With frequent reoccurring infections and evidence of hearing loss or speech delay, small tubes called tympanostomytubes are placed in the eardrums to ventilate the area behind the eardrum and keep the pressure equalized to atmospheric pressure in the middle ear.

Clinical Points

Weber Test and Rinne Test for Hearing

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Weber Test

With a Weber test of hearing, a tuning fork is struck and placed on the patient's forehead The patient is asked to report in which ear the sound is heard louder

This test cannot confirm normal hearing, because hearing defects affecting both ears equallywill produce an apparentlynormal test result ARinne test should be done at the same time

Rinne Test

ARinne test compares perception of sounds, as transmitted byair or bysound conduction through the mastoid

This is achieved byplacing a vibrating tuning fork (512 Hz) initiallyon the mastoid, then next to the ear and asking which sound is loudest Apatient with normal hearing with a positive Rinne on both sides would hear the sound equallyin both ears or maynot even hear it at all if the room is noisyenough to mask the subtle sound of the tuning fork

Apatient with a unilateral (one-sided) conductive hearing loss would hear the tuning fork loudest in the affected ear (conduction through bone is more effective that the normal route through the outer and middle ear)

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11 Meninges and Brain

STUDYAIMS

At the end of your study, you should be able to:

Outline the gross structure of the brain

State the lobes of the cerebral hemispheres and their function

Describe the layers of the meninges

Outline the venous drainage of the brain and the keyvenous sinuses

Describe the formation of cerebrospinal fluid

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GUIDE

Head and Neck: Meninges and Brain

Brain

[Plate 104, Cerebrum: Lateral Views]

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[Plate 105, Cerebrum: Medial Views]

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Is composed of sixregions for purposes of description

(1)Cerebral hemispheres (cerebrum)

Largest part of brain

Occupyanterior and middle cranial fossae

Two, separated bylongitudinal cerebral fissure

Connected bytransverse fiber bundle at base of longitudinal fissure: corpus callosum

Cavityin each hemisphere = ventricle

Composed of four lobes:

Frontal lobe:

Involved in higher mental function Contains speech and language centers

Parietal lobe: Initiates movement Involved in perception

Temporal lobe:

Involved in memory, hearing, and speech Occipital lobe:

Contains visual cortex

Each lobe marked byfolds (gyri) and grooves (sulci)

(2) Diencephalon

Composed of

Epithalamus

Thalamus

Hypothalamus

Surrounds third ventricle of brain between right and left halves

(3) Midbrain (mesencephalon)

At junction of middle and posterior cranial fossae

Contains narrow canal: cerebral aqueduct

(4) Pons

Found in anterior region of posterior cranial cavity

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Contains cavitythat contributes to fourth ventricle

(5) Medulla oblongata

Lies in posterior cranial fossa

Continuous with spinal cord

Contains inferior portion of fourth ventricle

(6) Cerebellum

Dorsal to pons and medulla

Beneath posterior cerebrum

Composed of two lateral hemispheres connected byvermis in midline

Important in

Maintenance of balance, posture and coordination Timing and strength of contraction of muscles

Brainstem

Parts of brain hidden bycerebral hemispheres and cerebellum

Contains third and fourth ventricles and cerebral aqueduct

Composed of

Midbrain

Pons

Medulla oblongata

Contains masses of graymatter, manyof which are sensoryand motor nuclei of cranial nerves

Arterial supply to the brain

Internal carotid artery

Arises in neck

Enters cranial cavityvia carotid canals

Terminates as

Anterior cerebral artery-connected to opposite arterybyanterior communicating artery

Middle cerebral artery

Joined to posterior cerebral arterynear termination byposterior communicating artery

Vertebral arteries

Ascend through transverse foramina of C1-C6 cervical vertebrae

Perforate dura

Enter posterior cranial fossa via foramen magnum

Unite at posterior pons to form basilar artery

Ascends on clivus

Divides into two posterior cerebral arteries

Unite with internal carotid arteryvia posterior communicating arteries

Circle of Willis

Cerebral arterial circle

Composed of

Anterior communicating artery

Anterior cerebral arteries

Internal carotid arteries

Posterior communicating arteries

Posterior cerebral arteries

Areas supplied byanterior cerebral artery

Medial and superior brain

Frontal pole

Areas supplied bymiddle cerebral artery

Lateral brain

Temporal pole

Posterior cerebral artery

Inferior brain

Occipital pole

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Meninges

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[Plate 100, Meningeal Arteries]

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[Plate 101, Meninges and Superficial Cerebral Veins]

Surround and protect the brain

Are the support for arteries, veins, and venous sinuses

Enclose the subarachnoid space

Enclose cerebrospinal fluid (CSF)

Are similar in name, structure, and arrangement to those around the spinal cord

Dura mater

Thick fibrous layer

Consists of two layers (unlike the dura mater around the spinal cord)

Outer periosteal layer = periosteum on inner surface of calvaria

Inner meningeal layer

Tightlybound to the periosteal layer

Continuous with the dural of the spinal cord

Arachnoid mater

Thin, nonvascular membrane

Looselyattached to dura mater

Separated from pia mater bysubarachnoid space

Pia mater

Adherent to brain and spinal cord

Highlyvascular connective tissue

Subarachnoid space

Real space between arachnoid and pia mater

Contains cerebrospinal fluid from ventricular system-cushions brain

Subarachnoid cisterns

Areas where pia and arachnoid are widelyseparated

Collect large pools of CSF

Occur mainlyat base of brain

Venous drainage of brain

Cerebral veins

Superior and lateral surfaces of brain to superior sagittal sinus

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On posterior and inferior aspects of brain drain into straight, transverse, and superior petrosal sinuses

Thin-walled and valveless

Superior cerebellar veins to straight, transverse, and superior petrosal sinuses

From dural venous sinuses to internal jugular vein

Dural infoldings

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Created byinternal meningeal layer of dura mater

Form septa that separate regions of the brain from other regions

Falxcerebri

Largest of infoldings

Lies in longitudinal fissure

Tentorium cerebelli

Second largest infolding

Crescent-shaped fold separating cerebral hemispheres from cerebellum

Attaches to

Anteriorlyto clinoid processes of sphenoid

Laterallyto petrous part of temporal bone

Posteriorlyand laterallyto internal occipital and parietal bones

Falxcerebri, which suspends tentorium

Tentorial notch

Gap in anterior border

Allows for passage of brain stem

Diaphragma sellae

Circular sheet of dura

Suspended between anterior and posterior clinoid processes

Contains gap for passage of pituitarystalk and accompanying veins

Dural venous sinuses

Endothelium lined channels between periosteal and meningeal layers of the dura Thick-walled and valveless

Formed where dura attaches

Confluence of sinuses: where superior sagittal, straight, occipital, and transverse sinuses meet at internal occipital protuberance Superior sagittal sinus

From crista galli to confluence of sinuses

Communicates via slit-like openings with lateral venous lacunae Inferior sagittal sinus: from crista galli to straight sinus

Straight sinus: formed byunion of inferior sagittal sinus and great cerebral vein (of Galen) Transverse sinus

Drains confluence of sinuses

Runs along posterolateral attachment of tentorium cerebelli

Becomes sigmoid sinus Sigmoid sinus

Traverses jugular foramen

Becomes internal jugular vein

Occipital sinus: at attached border of cerebellar falx Cavernous sinus

On either side of sella turcica

Is composed of a network of thin, valveless vein

Sinuses communicate with each other via intercavernous sinuses

Receives blood from

Superior and inferior ophthalmic veins

Superficial middle cerebral vein

Sphenoparietal sinus

Contains

Internal carotid artery

Oculomotor nerve (CN III)

Trochlear nerve (CN IV)

V1 division of trigeminal nerve (CN V)

Abducent nerve (CN VI)

Sympathetic plexus around artery

Superior petrosal sinus: from posterior ends of cavernous sinuses to transverse sinuses Inferior petrosal sinus: from posterior ends of cavernous sinuses to internal jugular vein Emissaryveins connect dural sinuses with veins outside the cranium

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[Plate 107, Ventricles of Brain]

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[Plate 109, Basal Nuclei (Ganglia)]

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Sinus	Location	Comment	Drains to
Superior	Upper border falxcerebri	1. Drains cerebral veins	Confluence of sinuses
sagittal sinus		2. Contains arachnoid villi and granulations for
		reabsorption CSF
Inferior sagittal	Lower free margin falxcerebri		Joins great cerebral vein
sinus			forming straight sinus
Straight sinus	Junction falxcerebri and	Formed byunion great cerebral vein with inferior sagittal	Confluence of sinuses
	tentorium cerebelli	sinus
Transverse	Lateral margin tentorium	1. Passes laterallyfrom confluence of sinuses	Sigmoid sinus
sinus	cerebelli	2. Left is usuallylarger
Sigmoid sinus	S-shaped course in temporal	Continuation transverse sinus	Internal jugular vein
	and occipital bones
Cavernous	Superior surface of bodyof	1. Receives superior and inferior ophthalmic and	Superior and inferior
sinus	sphenoid, lateral to sella	superficial middle cerebral veins and sphenoparietal	petrosal sinuses
	turcica	sinus
		2. Contains internal carotid arteryand CN III, IV, V1, and
		VI, sympathetic nerves
Intercavernous	Runs through sella turcica	Connects cavernous sinuses
sinus
Superior	Margin tentorium cerebelli	Connects cavernous sinus to transverse sinus	Transverse sinus
petrosal sinus	attached to petrous temporal
	bone
Inferior	Medial border petrous temporal	Connect cavernous sinus to internal jugular vein	Internal jugular vein
petrosal sinus	bone to jugular foramen

CSF

Maintains balance of extracellular fluid in the brain

Similar in content to blood

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Less protein

Different ion concentrations

Formed bychoroids plexuses in the four ventricles of the brain

Are plexuses of capillaries that project into the lateral, third and fourth ventricles Circulates through ventricular system

From lateral ventricles to interventricular foramina to third ventricle

From third ventricle through cerebral aqueduct to fourth ventricle

From fourth ventricle through paired lateral apertures and a single midline aperture in the roof into subarachnoid space Absorbed through arachnoid granulations into venous blood in dural venous sinuses

Arachnoid granulations are tufts of arachnoid villi protruding into the dural venous sinuses

Subarachnoid space with CSF extends into core of the tufts Approximately400 mL/dayof CSF → venous circulation

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Vasculature of dura

Primarilyprovides blood to calvaria

Middle meningeal artery

Branch of axillaryartery

Enters through foramen spinosum

Has anterior and posterior branches

Meningeal branches of

Ophthalmic arteries

Occipital arteries

Vertebral arteries

Venous drainage: meningeal veins

Accompanymeningeal arteries

Occur in pairs

Frequentlytorn in skull fractures

Middle meningeal veins drain to pterygoid venous plexus

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