JC M PRAC ANATOMY 1

JC M PRAC ANATOMY 1

EAR, CRANIAL FOSSAE, MENINGES
Prof Lucas

Prof Sham

Mon 21-10-2002
EAR

Equilibrium + hearing

EXTERNAL EAR

Auricle - collects sound

External acoustic meatus (EAM) - conducts sound to tympanic membrane

Auricle

Concha - deepest depression

Lobule - no cartilage (only fibrous tissm fat, BV)

A - posterior auricular, superficial temporal

N - (skin) great auricular (sup, lat inf to EAM), auriculotemporal (br CN V₃, sup to EAM)

L - superficial parotid (lat sup 1/2), mastoid (retroauricular) + deep cervical (med sup 1/2), superficial cervical (remainder)

External Auditory Meatus

Thru temporal bone (tympanic part)

2-3 cm long (adult)

Lat 1/3 - cartilage, skin continuous with auricle, glands (ceruminous, sebaceous) ® cerumen

Med 2/3 - bony, thin skin continuous with ext tympanic membrane

Tympanic membrane - 1 cm Æ , ext thin skin, int mucous membr

Umbo - peak of central depression

Otoscope - cone of light radiates anteroinferiorly from umbo

Pars flaccida - superior to lateral process of malleus, no radial/ circular fibres, lat wall of superior recess of tympanic cavity

Pars tensa - inferior to lat process of malleus

N - auriculotemporal (br CN V₃) (external surface), aurical br vagus (some), glossopharyngeal (internal surface)

MIDDLE EAR

Petrous part temporal bone

Contents - auditory ossicles (malleus, incus, stapes), stapedius + tensor tymani m's, chorda tympani (br CN VII), tympanic plexus of n

N (mucosa) - tympanic br glossopharyngeal n

Walls

Tegmental roof - tegmen tympani (bone), sep from dura mater of floor of middle cranial fossa

Floor (jugular wall) - bone, sep from superior bulb IJV

Lateral (membranous wall) - lat by tympanic mem, sup by bony epitympanic recess

Medial (labyrinthine wall) - promontory of cochlea (intiial basal part)

Anterior (carotid wall) - sep from carotid a, sup is opening of auditory tube + canal for tensor tympani

Posterior (mastoid wall) - aditus (opening) to mastoid antrym, cana for facial n descends bet posterior wall + antrum (medal to aditus)

Mastoid Antrum

Cavity in mastoid process of temporal bone

Antrum and mastoid cells lined by mucous membrane continous with ME lining

Eustachian (Pharyngotympanic) Tube

Connects tympanic cav to nasopharyn (opens posterior to inferior meatus of nasal cavity)

Posterolateral 1/2 bony (remainder cartilage)

Function - equalise pressure in ME with atmosphere (free movt tympanic mem)

Opened by levator veli palati pushing one side while tensor veli palati pulls other side

A - br ascending pharyngeal, br ext carotid, br maxillary (middle meningeal, a of pterygoid canal)

V - into pterygoid venous plexus

N - tympanic plexus (facial + glossopharyngeal) + pterygopalatine ganglion

Auditory Ossicles

Chain from tympanic mem to oval window (fenestra vestibuli)

Oval window - medial wall tympanic cav - to vestibule of IE (bony labyrinth)

1^st to ossify - mature at birth

Malleus (tympanic mem) ® Incus ® Stapes (oval window)

Malleus - head lies in epitympanic recess, neck against pars flaccida, head embedded in tympanic mem, functions as level

Chorda tympani n crosses medial surface of neck of malleus

Incus - body lies in epitympanic recess (articulates with head of malleus)

Long limb process parallel to handle of malleus, articulates with stapes w/ lenticular process

Short limb connected by lig to posterior wall tympanic cav

Stapes - smalles, head articulates with incus, base (footplate) fits in oval window

Base smaller than head \ vibration 10x > tympanic mem

\ Auditory ossicles force but ¯ amplitude of vibrations from tympanic mem

Muscles Assoc with Ossicles

Tensor tympani - from sup surface cartilage part Eustachian tube, greater wing sphenoid, petrous part temporal

Inserts handle of malleus (pulls medially) - tenses tympanic mem + ¯ oscillations

Function - prevent damage to IE w/ loud sound

N - mandibular

Stapedius - smalles striated m, inside pyramidal eminence, inserts on stapes neck

Pulls stapes posterior + tilts base in oval window, tightens anular ligment

Function - ¯ oscillatory range, prevent XS movt of stapes

N - n to stapedius (br facial)

Paralysis - hyperacusis/ hyperacusia (eg. facial n lesion)

Course of facial n (see Lucas' diagram)

Enter medial wall - geniculate ganglion - cannot travel further (promontory)

Turn 90 deg to post wall

Travel inferior past pyramid (m for stapes) - stylomastoid foramen - VII - motor to facial m

Other br - turn 90 deg to ant wall (greater petrosal n)

INTERNAL EAR

Vestibulocochlear organ ® sound reception, balance

Petrous part temporal bone

Membranous labyrinth (endolymph) suspended within Body labyrinth (perilymph)

Bony Labyrinth

Cochlea, Vestibule, Semicircular canals

Optic capsule - denser bone than rest of petrous temporal bone (¹ bony labyrinth, which is fluid-filled space)

Cochlea - shell-shaped, spiral canal begins at vestibule, 2.5x around bony modiolus, basal turn produces promontory (medial wall tympanic cav)

Vestibule - contains utricle + saccule, oval window on lat wall, cont with cochlea ant + semicirc canals post + posterior cranial fossa by aqueduct of the vestibule (opens posterolat to int acoustic meatus, transmits endolymphatic duct + 2 BV)

Semicirc canals - ant/post/lat, ^ to each other, ampulla at one end, 5 openings into vestibule of bony labyrinth (ant + post have share a limb), semicircu ducts within

Membranous Labyrinth

Contains endolymph

Vestibular labyrinth

Utricle + saccule (in vestibule of bony labyrinth) - connect via utrosaccular duct (macula of utricle horizontal + macula of saccule vertical, hair cells innervated by vestibular br CN VIII, primary sensory n in vestibular ganglion/ int acoustic meatus). Endolymphatic duct traverses vestibular acqueduct of bony labyrinth - through bone of post cranial fossa - expands into endolymphatic sac (stores XS endolymph)
3 semicircular ducts (in semicir canals) - ampulla (sensory) + ampullary crest (sense endolymph movt from hear rotation) - hair cells (+) 1^o sensory neurones (cell body in vestibular ganglia)

Cochlear labyrinth - cochlear duct secured to spiral canal of cochlea (spiral lig) and osseous spiral lamina of modiulus - communicates at cochlear apex (helicotrema). Hydraulic press waves in perilymph of vestibule to apex of cochlea by scaala vestibuli, descend back down to basal turn by scala tympani, vibrates secondary tympanic mem (occupies round window). Roof = vestibular membrane. Floor = basilar membrane + outer osseous spiral lamina. Spiral organ (of Corti) on basilar membrane with hair cells (their tips in tectorial membrane) - receives auditory stimuli

Internal Acoustic Meatus

Opens in posteromedial petrous part temporal bone

Closed laterally by thin/ perforated bone (sep it from IE) - facial n, br CN VIII, BV pass through

Divides - vestibular n + cochlear n

CRANIAL FOSSAE (Moore, p.842)

Anterior cranial fossa

Foramen cecum - nasal emissary vein (1% pop)

Foramina in cribiform plate - axons of olfactor cells in olfactor epitheliu, that form olfactory n

Ant + post ethmoidal foramina - BV + n (same name)

Middle cranial fossa

Optic canal - CN II + opthlamic a's

Superior orbital fissures - opthlamic v + n (CN V₁), III, IV, VI, SNS fibres

Foramen rotundum - maxillary n (CN V₂)

Foramen ovale - mandibular n (CN V₃) + accessory meningeal a

Foramen lacerum - int carotid a (accompanying SNS + v plexuses)

Groove/ Hiatus of greater petrosal n - great petrosal n + petrosal br middle meningeal a

Posterior cranial fossa

Foramen magnum - medulla, meninges, vertebral a, spinal root CN IX, dural vein, ant + post spiral a's

Jugular foramen - CN IX, X, XI, superior bulb IJV, inferior petrosal + sigmoidal sinuses, meningeal br ascending pharyngeal + occipital a's

Hypoglossal canal - hypoglossal n (CN XII)

Condylar canal - emissary v (from sigmoid sinus to vertebral v in neck)

Mastoid foramen - mastoid emissary v (from sigmoid sinus) + meningeal br occipital a

MENINGES

Function

Protect brain
Framwork - a, v, venous sinuses
Enclose subarachnoid (leptomeningeal) space

Dura-skull interface

Extradural/ Epidural space

Potential space

Real space path - eg. blood from torn meningeal BV accumulates bet periosteum + skull

Dura mater - dense fibrous, sensation, ext periosteal + int meningeal layers, dural border cell layer (int meningeal layer, weakness), reflections/ dural infoldings (meningeal pulls away from periosteal) - eg. falx cerebri (bet R + L hemispheres), tentorium cerebelli (bet occipital + cerebellum), diaphragma sellae (covers pituitary), falx cerebelli (bet cerebellar hemispheres)

A - middle meningeal a (thry foramen spinosum) - ant br (vertex) + post br (posterior skull)

V - middle meningeal v (foramen ovale/ spinosum) - pterygoid venous plexus

V - ant cranial fossa (V1 ehtmoidal, meningeal br V₂ + V₃), middle cranial fossa (br V₂, V₃), posterior cranial fossa (tenotorial br opthalmic n, sensory br C1-3, CN X) - sensation along superior saggital sinus + tentorium cerebelli (cf cranium floor)

Dural venous sinuses

Endothelium-lined spaces betwene periosteal + meningeal layers of dura

Where the dural septa attach

Empty blood from brain v's - IJV

Superior saggital - bet sup cerebral hemispheres

Confluence of sinses - in cavernous sinus (superior saggital, straight, occipital, transverse meet)

Arachnoid granulations - tufted prolongations of arachoid, protrude into dural venous sinuses (transport CSF from subarachnoid space to venous system)

Inferior saggital - bet inf cereberal hemispheres

Straight sinus - along falx cerebri where it tacched to tentorium cerebelli (inferior saggital sinus + great cerebral v)

Transverse sinus - lateral from confluence - along posterolateral margins of tentorium cerebelli - become signmoid sinuses

Sigmoid sinuses - S-hspaed, deep grooves in temporal + occipital bones, turns anterior, crosses jugular foramen, continues inferiorly as IJV

Occipital sinus - cerebellar falx, along occipital lobe, communicates inferiorly with internal vertebral venous system

Cavernous sinus - aka lateral sellar compartment, bilat either side of sella turcica (rec from sup + inf opthlamic v, superficial middle cereberal v, sphenoparietal sinus - via intercaverous sinuses. Cavernous sinuses drain into sup/ inf petrosal sinuses + emissary v ® pterygoid plexuses. Lat wall cavernous sinus (sup to inf): oculomotor n, CN IV, V₁ (rarely V₂). Internal carotid a + abducens (lateral to a)

Emissary veins - connect dural venous sinuses with veins outside cranium (valveless, usu away from brain)

Dura-arachnoid interface

Subdural space

Potential

Arachnoid mater - delicate

Fibroblasts, collagen fibres, elastic fibres

Avascular arachnoid held against inner surface of dura by CSL pressure (not attached to dura)

Subarachnoid space

Actual space - CSF, trabecular cells, a, v

Pia mater - delicate vascular

Follows contours of brain

Follows cerebral arteries for a short distance - pial cost + periarterial space

CSF

Cf blood - less protein, different ions

Formed: choroid plexuses, circulates subarachnoid space

JC M PRAC ANATOMY 1 (PATH)

EAR, CRANIAL FOSSAE, MENINGES

Skull base meningioma

Gradual onset of generalised headache (worse am, severity over 2m) - typical of gradual ICP (eg. enlarging brain tumour, hydrocephalus). Acute onset: IC haemorrhage, migraine

O/E - VF defect, bilat papilloedema, impaired abduction left eye

MRI - tumour over left medial sphenoidal ridge nr the orbital (expect L eye blindness - nasal + temporal fields)

If tumour compressing optic chiasm: bitemporal hemianopia

If tumour compressing left optic tract posterior to optic chiasm: L nasal + R temporal field loss

CN palsy - impaired (1) Left eye abduction - VI (2) Left eye adduction - III

CN III palsy assoc. also assoc.: impaired pupil response to light + accomm

CN palsy causing diplopia while looking ‘down and in’ - IV

Vascular struc on medial side of this tumour - internal carotid a, opthlamic a, cavernous sinus

Ventricular dilatation - occlusion of foramen of Monro (\ CSF flow) due to upward compression by the tumour onto left frontal lobe

Meningioma: well-encap, attached to meninges, often calcified, 15-20% all brain tumours, mostly middle age (rare in children)

Cell type: mesodermal tissues making up the meninges (eg. fibroblasts, pial cells, arachnoid cells)

Common locations: parasagittal region, sphenoid ridge, near the sella turcica and the cerebello-pontine angle (less common)

Near bone: tendency to excite osteoblastic reaction (bone formation)

Amenable to surgical removal (radiation no role)

18% of all primary intracranial + 25% of intraspinal tumours

Cut surface: greyish or pinkish-grey, faintly lobular pattern, tissue is firm + hard (necrosis rare)

Microscopically: variable - meningiotheliomatous, fibroblastic, transitional, psammomatous, angioblastic and sarcaomatous

Slow growing + benign, do not invade brain may infiltrate mesodermal supporting tiss (eg. bone) but usu. no tendency to metastasise

Acoustic neuroma

Hx: 6m gradual onset of left-sided hearing loss and tinnitus

O/E: no focal neuro deficit (apart from deafness)

Ix: MRI + CT: tumour at left cerebello-pontine angle, widening of internal acoustic meatus

2 CN transversing internal acoustic meatus: VII + VIII

2 other struc compressed by tumour ant + med: V + BS

Compressed by tumour inferiorly: lower CN - eg. IX, X, XI

2 kinds of deafness: conductive + sensorineural (tuning fork tests: Rinne’s + Weber’s)

This Pt likely: sensorineural deafness (Rinne’s test – air > bone for both ears b/c pattern of air > bone preserved for sensorineural; pattern reversed for conductive) (Weber’s: lateralised to R)

Other causes sensorineural deafness: Trauma, Infection, Congenital, LT noise exposure

This tumour = Schwannoma arising from vestibular nerve (VIII) - aka acoustic neuroma (misnomer) - tumour does not arise from the cochlear part VIII, not a neuroma \ correctly termed vestibular Schwannoma. Note: aka neurilemmoma of CN VIII

Neurilemmoma: tumours of nerve sheath, originate from Schwann cells

Acoustic neuroma (CN VIII) = 5% of intracranial neoplasms.

Aneurysm of Circle of Willis

Hx: 48/M sudden onset severe headache (also L frontal headache 10d) (also sudden excruciating headache, "burst")

O/E: fully conscious, severe neck stiffness, photophobia, left oculomotor nerve palsy

Ix: CT - subarachnoid haemorrhage; Angiography - aneurysm nr origin of left posterior communicating artery (PCoA). Aneurysm ruptured ® subarachnoid haemorrhage. LP - blood-stained CSF = subarachnoid haemorrhage

Demonstrate neck stiffness clinically (1) Pt turn head side to side (2) Pt touch his/her chest with chin (3) Passive flexion of Pts neck

Conditions causing neck stiffness: Neck injury, Meningeal irritation (meningitis), Subarachnoid haemorrhage

Conditions causing photophobia: Subarachnoid haemorrhage, Migraine, Meningitis, Acute glaucoma, Keratitis

Anatomical relation bet PcoA + CN III: CN III runs inf to PCoA along free edge of tentorium cerebelli \ PCoA aneurysm may present w/ ipsilateral CN III palsy (also meningeal irritation)

Tx aneurysm: clipping (complicated by spasm left internal carotid artery at operation)

Pouch-like evagination of the wall of an artery of the Circle of Willis ® dev defect (aplasia/ hypoplasia of muscle coat) of cerebral a

Defect exists at birth but intravascular pressure requires time + further degradation - exceeds restraining capacity of artery \ usu adulthood

> 90% of berry aneurysms within the carotid supply (1) Junction ant cerebral + ant communicating a (2) Middle cerebral a at 1^st/2^nd branching in Sylvian fissure (3) Junction of terminal portion int carotid a + its br (PcoA, ant + mid cerebral a)

Size 2mm - 2-3cm

10-20%: multiple aneurysms

1/3 die at first rupture, usu 5^th decade of life (blood: subarachnoid space (commonly), dissect brain + reach ventricles, subdural space)

Ruptured berry aneurysm is the most common cause of subarachnoid haemorrhage.

Atherosclerosis: affects larger BV of brain (esp. vertebral, basilar, proximal BV portions from circle of Willis, internal carotid a

Complication of AS: aneurysm (rupture can be complication of HT)

Chronic subdural haematoma

Hx: 70/M 1w R-sided weakness, mental confusion

CT: haematoma over left fronto-parietal region bet skull and the brain (crescent-shaped, no extension into the cerebral sulci)

3 components of meninges: dura, arachnoid, pia mater

3 potential spaces between the skull and the brain: epidural, subdural, subarachnoid space

This haematoma in subdural space (epidural = lens-shaped; subarachnoid = extends into the cerebral sulci)

2 other conditions causing R-sided weakness + mental confusion: Left cerebral infarction / haemorrhage

Causing R-sided weakness alone w/out mental confusion: Left cerebral space-occupying lesion, Right-sided spinal cord compression

Source of bleeding: bridging veins between cerebral cortex and venous sinuses

Most likely cause of bleeding: minor head injury

Colour: greyish = early organisation; darker = recent extension

Subdural haematomas: acute or chronic

Acute form: head injury (50% skull #), BV torn in brain lacs, bridging veins between cortex and venous sinuses

Chronic: trivial/ no injury (eg. fall on buttocks)

Age: early symptoms in young adults, late in older (brain shrinkage, subarachnoid space)

Commonest site: superior saggital sinus

Fibroblasts from torn BV repair/ invest inner aspect of clot in 10d (dev fibroblastic capsule on deep aspect, arachnoid remains separate)

Slowly, fibroblasts sep outer layer of clot from dura

Liquefaction occurs within clot + fragile new BV can rupture and ooze \ clot grows

Enveloping mem may form within 2-3w

Fatal cases: herniation of parahippocampal gyrus through tentorial opening (compression of mid-brain + haemorrhage within)

Compression of one basis pedunculi - hemiplegia (false localising sign - confusion with cerebral infarct)

Present: increasing apathy + confusion® dementia

Tx: surgical.

Pituitary tumour

Hx: 40/F 6m gradual visual impairment

MRI: pituitary fossa tumour (no abn endo function)

Type of VF with pit tumour: bitemporal hemianopia

Clinical test to demonstrate VF defect: confrontation test

Ab w/pit tumour: endocrine disorder (hypopituitanism, acromegaly, galactorrhoea, Cushing’s disease, etc), hypothalamic dysfunction (sleep and eating disorders), ICP (hydrocephalus), epilepsy (rarely)

Other conditions causing gradual ¯ VA: ocular disease (cataract, retinal degeneration, glaucoma), optic nerve disease – neuritis, optic atrophy

Pit adenomas: chromophobe, eosinophil, basophil varieties (poor correl w/ spec cell types + H secr)

Now classified: functional and non-func (25%)

Most adenomas: single hormone (if two - GH + prolactin)

Occur: both sex, any age ( men)

Carcinomas extremely rare

Noticed: H effect, local effect (expanding)

Often small, discovered incidentally at post-mortem

Symptoms: hyperprolactinema (women = amenorrhoea, galactorrhoea; men = ¯ libido, infertility) (men: local > H effects)

XS GH: gigantism or acromegaly

Corticotropin secreting: 2^o adrenalcortical syndrome

Non-secretary adenomas may produce hypopituitarism

Metastatic CA to pituitary

Pit function: H function
Anatomical rel of pit: optic chiasm superiorly, sphenoid sinus inferiorly
S/S of metastatic tumour: headache, pit hypofunction, VF defect (bilateral temporal hemianopia)
Test VF clinically: confrontation test (covering one eye, ask Pt using his R eye to look into your L eye, move your hand on the plane midway bet Pt and you, ask Pt to say "yes" when you flick your finger (with your hand in different position of the plane)
Additional S/S if 1^o pit tumour: hypersecretion (esp. hyperprolactinemia: F: galactorrhoea + amenorrhoea, M: no H S/S), acromegaly
Spread from: 1^st = lung (bronchogenic carc), 2^nd = breast, Other tumours: kidney, melanomas (rare in HK), choriocarcinomas (common in HK)

Tuberculous meningitis

Early features: drowsiness, headache, fever, neck rigidity
Secondary path (+ S/S) from basal thick exudate

Obstructive hydrocephalus: ICP features (headache, vomit, drowsy, papilloedema)

Palsy of the lower cranial nerves (more commonly 7^th, 8^th,12^th)

CV VII - facial asym affecting lower and upper face (LMN lesion)
CN VIII - sensorineural hearing loss
CN VII - tongue wasting + fasciculation

Tuberculous meningitis is 2º to tuberculosis elsewhere (eg. lung)
Bacillus produces greatest involvement at base of the brain
Tuberculous meningitis may cause hydrocephalus (inflam stenosis of aqueduct of Sylvius or obliteration of subarachnoid pathways at base of the brain