PBL - Schwannoma Of Vetsibulocochlear Nerve Flashcards
Define the term tinnitus.
Perception of sounds in the absense of external auditory stimulus
What three things cause tinnitus.
Hearing loss
Sounds produced by adjacent structures
Other disease processes
What sounds can be produced by tinnitus
Ringing of the ears Hissing Roaring Buzzing Humming sound
Which two ways can tinnitus be defined?
Objective tinnitus
Subjective tinnitus
What is objective tinnitus?
Sound is potentially detectable by another observer
What are the causes of objective tinnitus?
Vascular abnormalities or neuromuscular disorders
- sounds generated by turbulent blood flow conducted into auditory system
- pulsatile
What is subjective tinnitus
Noise perception when there is no noise stimulation in the cochlear
What can cause transient tinnitus in normal people?
Aspirin
Nicotine
Coffee
Name some conditions associated with more persistent subjective tinnitus.
Noise induced hearing loss Prebycusis - sensorineural hearing loss Hypertension Atherosclerosis Cochlear of labyrinthine infection Inflammation
What is the suggested pathophysiology of tinnitus?
Abnormal firing of auditory receptors
Dysfunction of cochlear neurotransmitters function or ionic balance
Alterations in central processing of the signal
Define vertigo.
Illusion of motion associated with disorders of vestibular function
Define objective and subjective vertigo?
Objective - person is in motion and environment is stationary
Subjective - person is stationary and environment is in motion
What are some differential diagnoses of vertigo?
Light-headedness
Syncope
Faintness
What can unstable gait be caused by?
Disorders of sensory input
Peripheral neuropathy
Gait problems
Vertigo can be caused by peripheral and central vestibular problems, what is the difference between them?
Peripheral - severe in intensity, and episodic
Central - mild and consistent
Describe motion sickness.
Normal physiological vertigo caused by repeated rhythmical stimulation of vestibular system
Symptoms of motion sickness
Vertigo Malaise Nausea Vomiting Autonomic symptoms - lowered BP - tachycardia - sweating Hyperventilation - can causes pooling of blood in lower extremities
What is the pathology of Ménière’s disease?
Occurs due to distension of the endolymph compartment of the inner ear
What is the ‘triad’ of Ménière’s disease?
Vertigo
Tinnitus
Hearing loss
What are the suggested mechanisms that may cause Ménière’s disease.
Increased endolymph production
Decreased production of perilymph accompanied by compensatory increase in endolymph sac
Decreased endolymph absorption
- caused by malfunction of endolymph sac or blockage of endolymphatic pathways
Name five things which are thought to cause Ménière’s disease.
Infection - syphilis Trauma Immunological Endocrine - adrenal-pituitary insufficiency and hypothyroidism Vascular disorders
What is Ménière’s disease characterised by?
Fluctuating episodes of tinnitus, feeling of ear fullness, violent rotatory vertigo
What happens to hearing loss as Ménière’s progresses?
Stops fluctuating and progressively worsens
Both ears become affected
What happens to the vertigo as the Ménière’s progresses?
Episodes of vertigo diminish and disappear although the person may be unsteady
List the differential diagnoses of Ménière’s disease
ENT causes - acoustic neuroma - otitis media - earwax - too toxic drugs Intracranial pathology - vertebrobasilar insufficiency - tumours - migraine Systemic illness - Anaemia - hypothyroidism - DM - autoimmune disease - syphilis
What is a schwanomma of the vestibulocochlear nerve?
Benign Schwann cell tumour affecting CN VIII
How does a schwanomma cause unilateral sensorineural hearing loss?
Compresses the cochlear nerve of interferes with the blood supply to the nerve and cochlear
What genetic problem is through to cause tumour growth?
Tumour suppressor gene abnormality on chromosome p22 (schwanomma protein)
How do patients with a schwannoma present?
Decreased hearing
Episodes of vertigo
What does unilateral hearing loss do to your hearing?
Leaves you unable to localise sound
Which other nerves are likely to become affected if the tumour grows to big - and what problems will that cause?
Facial nerve - nystagmus - slowed blink - altered taste - altered tearing Trigeminal - facial numbness
What is the differential diagnosis for a schwannoma?
Meningioma
Epidermoid
Facial nerve schwannoma
Trigeminal schwannoma
Where does the vestibulocochlear nerve arise?
From between the pons and the medulla
Where does the vestibulocochlear nerve leave the cranium?
Through the internal acoustic meatus
Where do the two parts of the vestibulocochlear merge when travelling back to the brain?
Inside the petrous part of the temporal bone
What does the vestibular nerve (vestibular ganglion) supply?
Three semi-circular ducts
Utricle
Saccule
How does the cochlear nerve innervate the cochlear?
Enters the base of the cochlear and passes up through the modiolus
- branches pass through lamina of modiolus to innervate receptors on spiral organ
Describe what a neoplasm is
Abnormal mass of tissue with uncoordinated growth
- growth persists excessively after cessation of the initial stimuli
Describe the growth pattern of a benign tumour.
Expansive
Capsule
Localised
Slow
Describe the growth pattern of a malignant tumour.
Infiltrative
No capsule
Metastasis
Rapid
What effects can a slowly enlarging space occupying lesion have on the brain or spine
Atrophy of adjacent brain or spinal tissue
What effects can a rapidly enlarging space occupying lesion have on the brain or spine
Rise in pressure in affected compartment from the normal level of
What clinical signs can be seen when a space occupying lesion distorts the meninges and blood vessels?
Headache
What clinical signs can be seen when a space occupying lesion compresses the optic nerve
Papillodema
What clinical signs can be seen when a space occupying lesion distorts the medulla?
Vomiting
What clinical signs can be seen when a space occupying lesion compresses the oculomotor nerve
Pupillary constriction and then dilation
What clinical signs can be seen when a space occupying lesion causes traction of the abducens nerve?
Abducens palsy - false localising sign
What clinical signs can be seen when a space occupying lesion compresses the posterior cerebral artery?
Occipital infarction
What clinical signs can be seen when a space occupying lesion causes traction on brainstem arteries?
Fatal infarction of brainstem/heamorrhage
What are the two layers of the dura mater called?
Endocranial layer
Meningeal layer
Where is an intracranial venous sinus located?
In certain areas, the dura mater splits into its two layers to enclose venous channels
Where does venous drainage leave the skull?
Jugular foramen
What is the relation between the inferior sagittal sinus and the flax cerebri?
Located in the lower margin of the fall
Which two veins join to become the straight sinus - and where does this sinus run?
Inferior sagittal sinus and the great cerebral vein
Runs in the junction between the falx and the tentorium cerebelli
Which transverse sinus does the superior sagittal sinus drain to?
Right
Which transverse sinus does the inferior sagittal sinus drain to?
Left
Which sinus does the internal carotid artery, the three nerves that supply the eye muscles and V1 + V3 branches of the trigeminal nerve pass?
Cavernosa sinus
How can schwannoma removal surgery cause other nerve problems?
Vestibulocochlear and facial nerve share a common cause through the internal auditory canal.
This proximity means the facial nerve is easily damaged during surgery = facial palsy
How does facial palsy present?
Weakness of muscles of facial expression and eye closure
Face sags
Face drawn to opposite side when smiling
Corneal and conjunctiva damage because the eye is open all the time
Mild dysarthria
Difficulty eating
What can occur in very severe cases of facial palsy?
Loss of taste over anterior tongue
Intolerance to high-pitched or loud noises
How to distinguish between facial palsy and a lower motor neuron.
In lower motor neuron disease -
Patient can’t wrinkle forehead because the final common pathway to the muscles is destroyed
Lesion must be in pons or outside the brainstem
How to distinguish between facial palsy and an upper motor neuron.
In upper motor neuron disease
- upper facial muscle are partially spared (other pathways in brainstem)
- appear to be different pathways for voluntary and emotional movement
- face sagging is less obvious
