4. Anatomy and physiology of the inner ear. Methods of examination. Otosclerosis. Clinical complications.

Question 1

Describe the Inner Ear

Answer 1

• Located in PETROUS PART of TEMPORAL BONE
• Consists of MULTIPLE INTERCONNECTED DUCTS aka THE LABYRINTH
• BONY Labyrinth = Accommodates the MEMBRANOUS Labyrinth

Question 2

What are the 3 Parts of the BONY LABYRINTH?

Answer 2

• Semi-circular Canals
• Vestibule
• Cochlea

Question 3

Describe the COCHLEA (Bony Labyrinth)

Answer 3

Consists of:
1) MODIOLUS = The Axis

2) BONY Cochlear Canal = Turns 2.5x AROUND Axis (3 - 3.5cm)

3) SPIRAL LAMINA = Projects FROM MODIOLUS to the LATERAL WALL of Cochlear Canal

4) BASILAR MEMBRANE
a. Extends FROM Axis TO LATERAL WALL of Cochlear Canal
b. It’s Base is MARKEDLY STIFFER

5) REISSNER’S MEMBRANE = Seals the Cochlear Duct

Question 4

Describe THE ORGAN OF CORTI

Answer 4

• Lies on BASILAR MEMBRANE
• Consists of Sensory / Hair Cells AND Supporting Cells
  a. MECHANORECEPTORS = Transform Mechanical Energy (ME) into ELECTRICAL Potential

b. COCHLEAR AMPLIFIER = Contracts OUTER Hair Cells and INCREASES LOW Intensities

• Has a TECTORIAL and RETICULAR MEMBRANE

Question 5

What are the 3 Parts of the MEMBRANOUS LABYRINTH?

Answer 5

• Membranous SCC
• Utricule AND Saccule
• Scala Media

Question 6

What are the 4 PRE-FORMED PATHWAYS for INTRACRANIAL EXTENSION of Temporal Bone Infections?

Answer 6

1) Endo-lymphatic Duct

2) Peri-lymphatic Duct = Establishes communication BTW Peri-lymph Space AND Subarachnoid Space

3) Fallopian Canal
4) Internal Acoustic Meatus

Question 7

What is the BLOOD SUPPLY of the INNER EAR?

Answer 7

• From LABYRINTHINE ARTERY = Arises from ANTERIOR INFERIOR Cerebellar Artery / Basilar Artery
• Running via VESTIBULOCOCHLEAR NERVE via INTERNAL Auditory Canal, DIVIDING INTO:
  a. Vestibular Artery
  b. Cochlear Artery
• These Vessels ANASTOMOSE with MIDDLE EAR Vessels
• Blood is drained FROM the Inner Ear TO the SUPERIOR BULB of JUGULAR VEIN / INFERIOR PETROSAL SINUS

Question 8

Describe the PHYSIOLOGY of the INNER EAR

Answer 8

1) COCHLEA
- Decodes the TONE of Frequency (f) and the LOUDNESS

2) INTERNAL ACOUSTIC MEAUS
- Vestibulocochlear Nerve (CN 8) leaves the Brainstem as trunk and FORMS Vestibular GANGLION in FUNDUS of Internal Canal

• Has Cochlear Nerve which FORMS the Cochlear GANGLION in MODIOLUS of Cochlea

** SENSORINEURAL HL is due to DAMAGE of
- Cochlea
- Retrocochlear Structures = Acoustic Nerve / Central Structures

Question 9

What are the METHODS OF EXAMINATION?

Answer 9

1) HISTORY
- Have Former / Current noise exposure during work

• Previous Acute Noise Trauma / Cranial Trauma
• Direct Contusion of Cochlea
• Previous Chronic OM = Indirectly damage Cochlea
• ## Family Hx of Hearing Disorders2) CLINICAL EXAM
• Inspection / Otoscopy s shows NO ABNORMALITIES
• Tuning Fork test = NORMAL
• Rinne Test = NORMAL
• ## Whispered-Speech Test = shows SIGNIFICANT IMPAIRMENT in ability to REPEAT whispered N.O3) AUDIOMETRY
• Findings are of SENSORINEURAL HL
• Hearing Threshold in PURE-TONE AUDIOGRAM = INCREASED for Air / Bone Conduction
• ABSENT Oto-acoustic Emissions, DUE to IMPAIRED FUNCTION of Cochlear Amplifier
• ## ABNORMAL Speech Recognition4) IMAGING TESTS
  a. CT = Temporal Bone scan to detect changes in BONY Labyrinth, DUE to Malformations / Trauma / Osteogenesis Imperfecta / Paget Disease / Advanced Otosclerosis

b. MRI = Examining the AUDITORY NERVE and Diagnosing RETROCOCHLEAR LESION and Detect changes in Auditory Nerve / Brainstem

Question 10

What is OTOSCLEROSIS?

Answer 10

• Disease of the BONY OTIC CAPSULE, leading to STAPE FIXATION, causing Conductive HL
• Due to LOCAL INFX = E.g. Measles
• Otic Capsule undergoes LOCALISED RESOPRTION with SPONGIOTIC Structural Change, leading to a SCLEROTIC Bone
• SYMPTOMS = Slow, Progressive HL in 1 / both ears; Cochlear Ear Impairment; Tinnitus
• DIAGNOSIS
  a) Weber Test LATERALISED TO AFFECTED Ear
  b) Rinne Test = NEGATIVE

c) Pure-Tone Audiometry = Air Conduction tH is HIGHER than Bone Conduction

d) CT = Shows otosclerotic Foci in Otic Capsule aka CIRCUMSCRIBED SITES of DECALCIFICATION

• DDx = Conductive HL with INTACT TM
  a) Middle Ear Anomalies
  b) Ossicular Chain Disruption DUE to Aseptic Necrosis of LONG PROCESS of Incus // Traumatic Dislocation of Ossicular Chain
• TREATMENT = Unknown; Sodium Fluoride can stop progression of inner ear changes IF taken Orally for Several Months

Question 11

What are the CLINICAL COMPLICATIONS of the INNER EAR?

Answer 11

1) Hearing IMPAIRMENT = With a COCHLEAR CAUSE involves DIMINISHED Hearing Ability

2) Tinnitus = ABSENCE of External Acoustic / Electrical Stimulus

3) Retro-cochlear Disorders = TUMORS of Internal Auditory Canal AND Cerebellopontine Angle // COMPRESSION of Auditory Nerve via Vascular Loops

4) Hereditary Sensorineural HL = SYMMETRICAL in Both Ears

5) Labyrinthitis = INFECTION affecting Labryrinth or Surroundings

Question 12

What are the 6 FORMS of LABYRINTHITIS?

Answer 12

a) TYMPANOGENIC = Infx of Middle Ear via Round / Oval Window

b) SEROUS = Inflammation VIA Substances RELEASED INTO Middle Ear

c) ACUTE SUPPURATIVE = Bacterial Infx of Middle Ear, spreading to Labyrinth

d) CHRONIC

e) MENINGEAL = Bilateral Infx FROM Intracranial Space VIA S.PNEUMONIAE, leading to COMPLETE Deafness & CALCIFICATION of Labyrinth

f) HEMATOGENOUS = Virus AND Bacterial Infx (Mumps, Measles, HIV and Syphillis)