Transcript the olfactory nerve

Introduction to Upper
Airway and Olfaction
Lecture by: Matthew Bromwich, MD FRCSC
Slides by: Kristian Macdonald MD FRCSC
Otolaryngology—Head and Neck Surgery
University of Ottawa
Feb. 15th, 2016
WHAT IS OTOLARYNGOLOGY—
HEAD AND NECK SURGERY?
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Surgical specialty with significant medical component
– Head and neck excluding eye and brain
– E.g. acute airway emergencies, ear surgery, sinus surgery, neck surgery,
microsurgery, short cases, long cases, neonates to geriatrics, cancer and
benign disease, hearing
5 year residency +/- fellowship
Approximately 25 residency positions
600 practicing Otolaryngologists in Canada
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Informal survey 2012: 20% > 65
Significant collaboration with: neurosurgery, thoracic surgery, plastic surgery,
ophthalmology, respirology, allergy, endocrinology, anesthesia, audiology, speech
language pathology
Underserviced in many communities
Global Health Opportunities available
WHERE IS OTOHNS IN YOUR
CURRICULUM?
• UNIT 1
– AIRWAY
– NOSE AND PARANASAL SINUS
– VOICE
• UNIT 2
– ORAL CAVITY/OROPHARYNX/NECK
– SWALLOWING AND SALIVARY GLANDS
– THYROID AND PARATHYROID
• INTEGRATION UNIT
– EAR
OBJECTIVES
• Recognize the pathway of air travel from the environment
through the nose to the lung
• Describe the vascular and nerve supply to the nose
• List and briefly describe the four main physiological functions
of the nose including filtration and protection, humidification
and warming, olfaction, vocal resonance
• Define anosmia and hyposmia and create a short differential
diagnosis (2 per category) for anosmia based on the following:
neural etiology, obstructive etiology
• Recognize how a loss of olfaction may lead to a loss of sense
of taste
• Recognize otolaryngology as a specialty
PATHWAY OF AIR TO LUNGS
•
https://www.das.uk.com/content/patient_info/what_is_airway_mana
gement
FUNCTIONS OF THE NASAL
CAVITY
1. WARM THE AIR
– Highly vascular
– Vessels superficial
2. HUMIDIFY THE AIR
– Mucous glands
3. OLFACTION
– CN I and CN V
4. FILTER THE AIR
– Hair and cilia
NASAL CAVITY
Vascular Supply to the nose
VASCULAR SUPPLY TO THE
NOSE
Moore KL. Clinically Oriented Anatomy.
NOSE AND PARANASAL
SINUSES
OLFACTION
WHY DO YOU SMELL?
• So that I can taste my food
• It can help me avoid harmful situations (e.g.
fire)
• It can warn me if food shouldn’t be eaten
• It helps me decide if I’m attracted to someone
• All of the above
• None of the above
REASONS FOR OLFACTION
• SAFETY
– ASSESS QUALITY OF AIR
• AVOID DANGEROUS
ENVIROMENTS
• AVOID DANGEROUS
FOODS
• PLEASURE
– DETERMINES FLAVOUR
OF FOOD AND
BEVERAGES
– OTHER AESTHETICS
OLFACTION
• Definition:
– Sense of smell
• Other terminology:
– Anosmia: loss of sense of smell
– Hyposmia: reduced sense of smell
– Dysosmia: olfactory distortion
– Presbyosmia: olfactory loss, sensorineural in
nature, related to aging
INTRANASAL CHEMOSENSATION
• CN I (OLFACTORY)
– Mediates “smell”—provides
flavour
– Aggregate of 40 nerve bundles that
course from olfactory epithelium
through cribiform plate to brain
– Large number of receptor cells
(second only to vision)
• CN V (TRIGEMINAL)
– Dispersed throughout nasal
mucosa
– Mediate:
• chemical and non chemical stimuli
• Somatosensory sensations (irritation,
burning, cooling, tickling)
– Induces reflexes (e.g. mucous
secretion, inhalation cessation) to
prevent /minimize injury to
nose/lungs
http://www.ehponline.org/members/1993/1013/meggsfig1.GIF
THE OLFACTORY NERVE
Neuroepithelium is located on the cribiform plate, superior septum and
superior and middle turbinates
THE OLFACTORY NERVE
•Neuroepithelium:
•Pseudostratified columnar epithelium
•Comprised of 6 different cell types
including the receptor cell (Bipolar Cell)
•First cell (Bipolar cell):
•Bipolar receptor cell
•Projects from nasal cavity into brain
without an intervening synapse
•Cilia have transmembrane receptors
that interact with odorant ligands
•Provides major route of viral, fungal and
bacterial invasion into CNS
•22 cm2 in human; 7m2 in german
shepherd
•1000 types of receptors are present
within the epithelium
•Glomerulus
•Decreased number with age
•Location of synapse between bipolar
cells and second order neurons (mitral
and tufted cells)
•Olfactory bulbOlfactory
tractolfactory cortex (primary and
secondary)
http://www.leffingwell.com/olf2.gif
OLFACTORY CORTEX—JUST REMEMBER
THAT IT’S COMPLEX
http://www.nature.com/nature/journal/v444/n7117/images/nature05405-f2.2.jpg
CAUSES OF OLFACTORY LOSS
• CONDUCTIVE
– Airflow to olfactory
receptor cells is blocked
– Usually treatable
• SENSORINEURAL
– Damage to olfactory
receptors or to central
neural structures
– Usually untreatable
• MIXED
– Combination of conductive
and sensorineural
http://upload.wikimedia.org/wikipedia/commons/3/3a/Head_olfactory_nerve.jpg
DIFFERENTIAL DIAGNOSIS OF
ANOSMIA/HYPOSMIA
• List is very very long!
• Always think:
– CONDUCTIVE
• Is there anything blocking
airflow?
– SENSORINEURAL
• Could there be something
wrong with the nerve
conduction?
SOME EXAMPLES
•
INFECTIOUS/INFLAMMATORY
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URTI most common cause
Sinusitis
Rhinitis
Nasal polyps
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DEGENERATIVE
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ENVIRONMENTAL
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Intracranial—frontal lobe neoplasm
Intranasal--esthesioneuroblastoma
TRAUMA
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Long list…refer to CPS when required
NEOPLASTIC
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Air pollutants
Tobacco exposure
MEDICATIONS
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Sense of smell declines with age (>80yrs)
10% of pt with head trauma have olfactory
dysfunction
ENDOCRINE
–
E.g. hypothyroidism
RELATIONSHIP OF AGE AND
OLFACTION
CLINICAL ASSESSMENT OF
ANOSMIA
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HISTORY
– Onset
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Gradual suggests conductive
– Duration
•
– As per differential diagnosis
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Partial suggests better chance of
recovery
– Preceeding illness
•
E.g. URTI—most common reason
– Aggravating factors
– Relieving factors
•
E.g. Improved with warm day, exercise,
topical steroid suggests rhinitis
– Taste (sweet, sour, bitter, salty) vs
flavour
– Presence of nasal obstruction
– Presence of other nasal symptoms
Social History
– Smoking decreases olfactory ability
If present >6 months and sensorineural
is unlikely to return
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– Complete or partial
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PMHx:
Cumulative dose
Cessation can result in improvement
over time
– Allergies to the environment
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Medications
Review of systems
– Symptoms of intracranial lesion
(headaches, diplopia etc)
– Symptoms of acute/chronic sinusitis
(facial pain, postnasal drip, rhinorrhea)
CLINICAL ASSESSMENT OF ANOSMIA
PHYSICAL EXAMINATION FOCUS:
•NASAL EXAM
•Anterior rhinoscopy mandatory
•Endoscopy if concerned
•CRANIAL NERVE EXAM
•Olfactory Nerve
•CN II
•Papilledema
•Extra Ocular Movements (EOM)
•May be affected by
intranasal/intracranial tumour
•INVESTIGATIONS
•University of Pennsylvania Smell
Identification Test (UPSIT) if feasible
•40 scratch and sniff
•CT or MRI if suspect neoplasm
TREATMENT OF
ANOSMIA/HYPOSMIA
• TREAT THE CAUSE
• Good prognosis for conductive losses if treated
• Poor prognosis for sensorineural losses if complete and
>6 months
• Smoking—extent of recovery is directly related to
duration since cessation of smoking
• Reassurance
• Safety
– CO, smoke detectors
– Check food expiry dates
• Some evidence for a trial of prednisone if URTI/idiopathic
TEST YOUR KNOWLEDGE (1)
• 40 year old female presents
with 4 month history of
hyposmia and taste change
• Further questions:
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Onset after URTI
Smoker
No allergies
No other symptoms
• Examination:
– Anterior rhinoscopy: N
– CN: N
What is the most likely cause of
the hyposmia? (MCQ)
• Esthesioneuroblastoma
(conductive/sensorineural)
• Nasal polyps (conductive)
• Age (sensorineural)
• URTI (sensorineural)
• Tobacco use (sensorineural)
How would you manage this
patient?
• Choose all that apply:
– DC Tobacco
– Tell them it’s all in their head
– Explain the natural history of hyposmia (e.g.
statistics, likelihood for improvement)
– Urgent MRI
– Complete blood count (CBC)
TEST YOU KNOWLEDGE (2)
• 50 year old male
presents with anosmia
and nasal congestion of
3 years duration
• FURTHER HISTORY:
– Gradual onset
– Bilateral nasal
congestion
– Post nasal drip
– Occasional facial pain
– Rhinorrhea
– Allergies
TEST YOU KNOWLEDGE (2)
Anterior rhinoscopy
What is your diagnosis? (MCQ)
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Esthesioneuroblastoma
Nasal polyps (chronic sinusitis)
Foreign body in nose
Normal exam—this is likely because of an
URTI
• Presbyosmia
TEST YOU KNOWLEDGE (3)
• 89 year old male presents with
decreased taste (can’t taste
his wine anymore) and
decreased smell
• FURTHER HISTORY:
– 3 year progression
– No aggravating/relieving
factors
– No other associated symptoms
• Examination:
– Normal other than UPSIT
What is your diagnosis and
management strategy? (MCQ)
• Choose all that apply:
– URTI—Tell him to use Dristan
– Likely nasal tumor—inform him and discuss poor
prognosis
– Presbyosmia—discuss statistics with him and
reassure that this is a normal aging process
– Let him know that most of the time decreased
olfaction is because of chronic sinusitis/nasal
polyposis and treat him with antibiotics and
steroids
TEST YOUR KNOWLEDGE (4)
• 50 year old male presents
with 3 month history of
loss of sense of smell
• Further questions:
– Progressive
– Associated headaches,
nasal obstruction
– No relieving symptoms
– Non smoker
• Examination:
– Anterior rhinoscopy
normal
– CN: papilledema
– Limited extraocular gaze
Are you concerned about this
patient?
• No—most anosmia/hyposmia is related to age
or a previous URTI.
• Yes—he has some worrisome symptoms
TEST YOUR KNOWLEDGE (4)
• Since progressive this is
likely conductive
• Since associated with
headaches, papilledema
and change in EOM,
concern re neoplasm
• Radiology ordered
• Diagnosis:
Esthesioneuroblastoma
QUESTIONS?
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