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DNB Otorhinolaryngology ENT Paper 1 — Model Answers

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QUESTION 1 (10 Marks)

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a) Cochlear Microphonics [3 marks]

• They are AC (alternating current) potentials that mimic the waveform and frequency of the stimulus
• Generated by the stereocilia mechanotransduction of OHCs — movement of stereocilia opens ion channels, generating receptor potentials
• Best recorded at the round window or via electrocochleography (ECochG)
• They persist even after death of the spiral ganglion neurons (unlike ABR)
• No neural component — purely a hair cell response

• Preserved CMs with absent ABR = pathognomonic of Auditory Neuropathy Spectrum Disorder (ANSD)
• When using ABR, CMs must be distinguished from stimulus artifact (by reversing stimulus polarity — true CM reverses, artifact does not)
• Absent CMs suggest OHC dysfunction (sensory hearing loss)

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b) Role of Otoacoustic Emissions (OAE) in Neonatal Hearing Screening [3 marks]

1. Transient Evoked OAEs (TEOAEs): Elicited by click stimuli; test frequencies 500–4000 Hz — most widely used in neonatal screening
2. Distortion Product OAEs (DPOAEs): Elicited by two pure tones (f1 and f2); frequency-specific, faster — used in second-tier screening

• Quick (< 2 minutes), objective, non-invasive, no sedation required
• Easy to administer by trained technicians
• Sensitive indicator of OHC function
• Can detect ≥ 30–35 dB HL hearing loss
• Suitable for mass screening

• Does not detect retrocochlear pathology (e.g., ANSD)
• Affected by vernix, amniotic fluid in the EAC in first 24–48 hours (false fail)
• Middle ear pathology can cause failure (false positive)
• For this reason, AABR (Automated ABR) is used as second tier — especially in NICU babies to identify ANSD

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c) High-Risk vs Universal Neonatal Hearing Screening & NPPCD [5 marks]

• Family history of congenital hearing loss
• NICU stay > 48 hours
• Craniofacial anomalies (e.g., cleft palate, ear malformations)
• In-utero infections (TORCH — especially CMV)
• Ototoxic drug exposure (aminoglycosides, loop diuretics)
• Hyperbilirubinemia requiring exchange transfusion
• Birth asphyxia, low Apgar score
• Syndromes associated with hearing loss (Treacher Collins, Down syndrome)

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• Prevalence of congenital hearing loss: 1–3 per 1000 live births (most common congenital sensory disability)
• Critical period of auditory brain development: 0–3 years (maximal neural plasticity)
• Identification by UNHS achieves mean age of diagnosis = 2–3 months; without screening = 24–30 months
• Early intervention (hearing aids, cochlear implants) within 6 months → normal speech/language development
• UNHS passes the Wilson-Jungner criteria for a screening program (common, serious, treatable early, reliable test available)

1. High disease burden: India has ~1 million children born with/acquiring hearing loss each year
2. Currently NPPCD focuses on school-age children — pre-lingual deafness missed
3. UNHS enables identification before language development begins, maximizing benefit of amplification/CI
4. Without early identification, these children require special education, increasing economic burden
5. OAE-based UNHS is cost-effective and feasible even in primary health care settings
6. JCIH 1-3-6 guideline: Screen by 1 month → Diagnose by 3 months → Intervene by 6 months
7. Integrating UNHS into NPPCD aligns with WHO's WHA70.13 resolution on deafness prevention

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QUESTION 2 (10 Marks)

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a) Indications for Intraoperative Facial Nerve Monitoring [3 marks]

1. Acoustic neuroma (vestibular schwannoma) surgery — cerebellopontine angle tumors
2. Parotid gland surgery (especially revision, malignant, or large tumors)
3. Revision mastoid/middle ear surgery (altered anatomy, obliterated landmarks)
4. Facial nerve decompression surgery
5. Glomus jugulare/tympanicum tumors

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b) Anaesthesia Modifications [3 marks]

1. Neuromuscular blockade:
   • Short-acting NMBA (e.g., succinylcholine) only for intubation
   • NO long-acting NMBAs (vecuronium, rocuronium, pancuronium) intraoperatively
   • If needed, sugammadex can reverse rocuronium rapidly for reversal
   • Train-of-four (TOF) monitoring must show 3/4 or 4/4 twitches before meaningful monitoring
2. Depth of anaesthesia:
   • Total intravenous anaesthesia (TIVA) with propofol + remifentanil is preferred — does NOT affect EMG monitoring
   • Volatile agents (isoflurane, sevoflurane) are acceptable but high doses may reduce EMG response amplitude
   • Avoid deep anaesthesia that blunts EMG responses
3. Communication with anaesthesiologist:
   • Surgeon must inform anaesthesiologist BEFORE incision
   • Any planned NMBA top-up must be communicated to monitoring team
   • Alarm thresholds must be set before surgical draping
4. Patient positioning:
   • Facial muscles must be fully accessible to recording electrodes
   • Ground electrode placed remote from surgical field

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c) Management of Intraoperative Facial Nerve Injury with Loss of Signal [4 marks]

• Check electrode impedance and placement
• Verify no NMBA administered recently (check TOF)
• Repeat stimulation at known facial nerve point proximal to surgical site
• Rule out technical failure (loose electrodes, amplifier issue)

• If signal loss is sudden → likely mechanical transection or thermal injury
• If gradual progressive decline → traction, stretch, devascularization
• Stimulate proximal and distal to the suspected injury site with a handheld nerve stimulator

• Remove retractors immediately
• Irrigate with warm saline
• Wait 15–20 minutes — signal may recover
• If no recovery → assess for hematoma or bone fragment compressing the nerve

• Immediate copious irrigation with cold saline
• Avoid further thermal exposure
• If irreversible → consider decompression

• Identify nerve stumps clearly
• If < 1 cm gap → primary epineural end-to-end repair (gold standard)
• If > 1 cm gap → cable grafting using:
  • Greater auricular nerve (most accessible — same surgical field)
  • Sural nerve (longest graft available)
  • Lateral femoral cutaneous nerve
• Approximate tension-free; epineural sutures with 8-0 or 9-0 nylon under microscope

• If nerve runs through tumor that cannot be preserved → sacrifice + immediate cable graft

• Document intraoperative findings
• Counsel patient regarding expected House-Brackmann grade
• Protective eye care: methylcellulose drops, moisture chamber, taping — prevent exposure keratopathy
• Re-exploration if no recovery at 6 months — consider XII-VII anastomosis (hypoglossal-facial reinnervation) if proximal stump unavailable

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QUESTION 3 (10 Marks)

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a) Keratosis Obturans Presenting with Facial Nerve Palsy [4 marks]

• A condition characterized by accumulation of desquamated epithelial debris (keratin plug) in the external auditory canal
• Results from abnormal epithelial migration and desquamation
• Associated with bronchiectasis and sinusitis (in ~25% of cases)

• Severe otalgia (characteristically intense, episodic)
• Conductive hearing loss
• White/creamy keratin plug filling the canal
• Bilateral in ~50% of cases

1. As keratin mass expands, it erodes the anterior/inferior bony canal wall
2. Pressure resorption can extend to the tympanic portion of the facial nerve canal (dehiscent in ~55% of people)
3. Inflammation, edema, and direct pressure → neuropraxia of the facial nerve
4. Cholesteatoma of EAC (a related/advanced condition) can erode the mastoid segment of the facial nerve
5. Secondary infection can spread to surrounding structures

• Regular microsuction debridement under microscopy (often requires GA due to pain)
• Topical antiseptics (aluminium acetate, acetic acid drops)
• Treat any secondary infection (topical ± systemic antibiotics)
• Meatoplasty if recurrent — widens the canal to allow better self-cleaning
• Facial nerve palsy: IV steroids (dexamethasone), protective eye care; if progressive → imaging (CT temporal bone) to assess extent of erosion; surgical decompression of facial nerve if no response
• Follow-up: Regular debridement every 3–6 months

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b) Recurrent Pre-auricular Sinus Infection After Surgery [3 marks]

• Congenital pit/tract anterior to tragus, due to incomplete fusion of auricular hillocks of His (1st and 2nd branchial arch derivatives)
• Lined by stratified squamous epithelium; contains desquamated material
• Incidence 0.1–0.9%; may be bilateral (25–50%), familial

1. Incomplete excision — most common cause; failure to remove the entire epithelium-lined tract
2. Branching tracts — sinus has multiple ramifications, not all identified
3. Supra-auricular extension — tract may extend to the auricular cartilage; not excised
4. Previous incision and drainage — creates scar tissue, obscures planes, makes re-excision difficult
5. Wound breakdown — infection of suture line seeding remnant epithelium

• Sinectomy — complete surgical excision; performed in quiescent, infection-free interval (ideally 3 months after last infection)
• Inject methylene blue into the pit to delineate the tract fully
• Supra-auricular approach (Lü's technique) gives wider exposure and lower recurrence rates than standard technique
• Excise a cuff of perichondrium with the sinus if it adheres to cartilage
• Use loupe magnification for complete tract visualization
• Recurrence rate: Standard technique 5–40%; Supra-auricular technique 1–5%

• Treat with antibiotics (S. aureus most common organism)
• Incision & drainage only if abscess present
• Wait until inflammation subsides → formal re-excision

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c) Tympanosclerosis of the Middle Ear [3 marks]

• Results from repeated episodes of otitis media
• Cascade: Inflammation → Subepithelial fibrous tissue → Hyalinization (loss of collagen organization) → Dystrophic calcification (hydroxyapatite crystal deposition)
• Also occurs after myringotomy and tympanostomy tube insertion

1. Tympanic membrane (myringosclerosis) — most common; white plaques in TM
2. Ossicular chain — fixation of the stapes (most functionally significant), incus, malleus
3. Round window niche obliteration
4. Epitympanum and aditus

• Conductive hearing loss — due to ossicular fixation
• The stapes fixation mimics otosclerosis clinically
• On audiometry: CHL with absent/reduced stapedial reflexes

• White chalky plaques visible on otoscopy (TM involvement)
• CHL proportional to extent of fixation
• On tympanometry: Type A or As pattern (reduced compliance)

• Myringosclerosis alone — does not require treatment; rarely affects hearing significantly
• Ossicular fixation:
  • Surgery: Tympanoplasty + ossiculoplasty
  • Release the fixed ossicle; if stapes superstructure fixed → stapedectomy/stapedotomy with prosthesis (TORP/PORP)
  • Round window obliteration: drill away calcification carefully
  • Hearing aid — if surgery not feasible or patient refuses
• Prognosis: Recurrence common; hearing gain limited if multiple sites involved

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QUESTION 4 (10 Marks)

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a) Neural Plasticity and Neural Scavenging [2 marks]

• Critical period: Birth to 3.5 years — maximal plasticity; auditory cortex is experience-dependent during this window
• Deprivation effects: Absence of auditory input → cortical areas normally subserving hearing are taken over by other sensory modalities (cross-modal plasticity) → reduced benefit from cochlear implantation if done late
• Use-dependent plasticity (positive): Early hearing intervention → strengthens auditory neural pathways → better speech and language outcomes
• Basis for benefit of early cochlear implantation and hearing aids in prelingual deafness

• OHC and IHC loss → reduction in neurotrophin (BDNF, NT-3) support → SGN apoptosis
• This process is called neural scavenging or auditory nerve degeneration
• Clinically relevant because: fewer viable SGNs → poorer cochlear implant outcomes
• Basis for early cochlear implantation — done before significant SGN loss
• Prevention: Intracochlear BDNF delivery and electrical stimulation can slow SGN degeneration

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b) Diagnosis and Management of Auditory Neuropathy Spectrum Disorder (ANSD) [2+6 marks]

Diagnosis [2 marks]:

• Disproportionately poor speech discrimination relative to pure tone thresholds
• Extreme difficulty in noisy environments
• Associated risk factors: prematurity, hyperbilirubinemia, hypoxia, neonatal NICU stay, family history

• Pre-synaptic: IHC or ribbon synapse pathology (e.g., OTOF gene mutation — most common genetic cause; otoferlin protein absent)
• Post-synaptic: Auditory nerve demyelination (e.g., Friedreich's ataxia, Charcot-Marie-Tooth)
• Central: Auditory brainstem abnormalities

Management [6 marks]:

• MRI brain and internal auditory meati — assess auditory nerve integrity, cochlear nerve hypoplasia, demyelinating lesions

• OTOF mutation screening — if positive, cochlear implant outcome is excellent (post-synaptic mechanism intact)

• 3–6 month trial of conventional hearing aids
• Many ANSD children benefit from amplification (those with pre-synaptic pathology)
• Monitor speech/language progress with Ling-6 sound test and MAIS/MUSS scales
• FM systems (frequency modulation) help bypass the noise-degraded neural synchrony

• Indicated if:
  • HA trial fails (no speech/language progress)
  • Behavioral thresholds ≥ 70 dB HL
  • Cochlear nerve present on MRI
• Cochlear implants bypass the dysfunctional IHC/ribbon synapse, delivering electrical stimulation directly to SGNs
• Outcomes: Excellent for OTOF-related ANSD; variable for central/demyelinating forms
• Bilateral CI preferred for bilateral ANSD

• Post-implant rehabilitation is critical
• Structured listening-based therapy to develop spoken language

• Serial audiological assessment (ABR, OAE, behavioral audiometry)
• Some cases of ANSD (especially neonatal hyperbilirubinemia-related) may resolve spontaneously by 12–18 months — observation period justified before CI decision

• Parents counselled about diagnosis, realistic expectations, communication options (oral vs total communication)
• School placement with FM systems and preferential seating

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QUESTION 5 (10 Marks)

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Hidden Areas of Middle Ear in Cholesteatoma [3 marks]

1. Sinus tympani (Posterior tympanum, medial to facial nerve ridge) — most important hidden area
2. Facial recess (posterior tympanum, lateral to facial nerve ridge, medial to chorda tympani)
3. Epitympanum (attic) — lateral attic recess, Prussak's space, anterior epitympanic recess
4. Supratubal recess (anterior to tensor tympani)
5. Hypotympanum — air cells below the level of the annulus
6. Retrofacial cells — posterior to the descending portion of the facial nerve
7. Perilabyrinthine cells — suprasemlaboratory and infralabyrinthine air cell tracts
8. Sinodural angle — between sigmoid sinus and tegmen
9. Apical cells — around the petrous apex
10. Protympanum — anterior to the tympanic orifice of the Eustachian tube

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Advantages of Canal Wall Down (CWD) Mastoidectomy for Hidden Areas [3 marks]

1. Wide en bloc exposure — removal of the canal wall eliminates the blind angle posterior to the canal, allowing direct visualization of the facial ridge, facial recess, and posterior mesotympanum
2. Retrofacial cells — become directly accessible once canal wall removed; disease in the infrafacial compartment can be fully removed
3. Infralabyrinthine and hypotympanic cells — exposed by drilling the inferior mastoid cortex and lowering the facial ridge
4. Epitympanum — complete exenteration possible with meatoplasty
5. Lower residual/recurrence rates for extensive cholesteatoma compared to CWU (residual disease in CWU: 20–40%; in CWD: 5–10%)
6. Self-cleaning cavity — post-CWD cavity accessible for long-term office surveillance and cleaning; squamous debris does not collect silently as in CWU
7. Exteriorization — disease brought to the surface, eliminating the risk of silent, expanding residual cholesteatoma

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Management of Sinus Tympani Cholesteatoma Extending Beyond the Vertical Part of the Facial Nerve [4 marks]

• Medially: Cochlear promontory
• Laterally: Vertical (mastoid) segment of the facial nerve
• Superiorly: Ponticulus
• Inferiorly: Subiculum
• Posteriorly: Mastoid air cells

• HRCT temporal bone (0.5 mm cuts): assess extent of disease, facial canal integrity, labyrinthine involvement, sigmoid sinus/jugular bulb relationship
• MRI with DWI (diffusion-weighted): non-echo planar DWI (HASTE/BLADE sequences) to confirm cholesteatoma and residual disease
• Assess hearing (audiometry) — residual cochlear function

• Standard CWD mastoidectomy performed first
• Facial ridge (buttress of bone over descending facial nerve) is lowered to within 1 mm of the nerve sheath using diamond burr
• This exposes the sinus tympani directly from above/laterally
• Cholesteatoma matrix carefully peeled from the promontory medially

• In CWU setting, posterior tympanotomy opens the facial recess
• However, if disease is truly behind the vertical facial nerve, the facial recess alone is insufficient
• Endoscope-assisted surgery (30° or 45° endoscope) passed through posterior tympanotomy or via trans-canal route can visualize and remove disease in sinus tympani behind the nerve

• For disease medial to the facial nerve eroding the promontory
• Requires careful drilling medial to the facial nerve
• Profound SNHL is a risk if cochlea entered

• If nerve is eroded/dehiscent due to cholesteatoma: peeling matrix off the exposed nerve using blunt micro-instruments under high magnification
• Do NOT strip epineurium if nerve is intact — leave matrix if risk of nerve injury is high; second-look surgery in 9–12 months
• If nerve is transected: primary repair or cable graft (greater auricular nerve) as described in Q2

• A retrofacial/infralabyrinthine approach may be required
• Disease can be approached by: drilling between the posterior semicircular canal and sigmoid sinus (retrofacial corridor)
• Extreme disease: Transcochlear approach sacrificing cochlear function to access petrous apex/infralabyrinthine cells

• Planned at 9–12 months in all CWU cases and when matrix left behind
• DWI MRI (non-EPI) at 12–18 months to identify residual before second look

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QUESTION 6 (10 Marks)

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a) Auditory Effects of Noise Pollution [4 marks]

• Reversible elevation of hearing threshold after noise exposure
• Metabolic exhaustion of OHCs, reduced blood flow to stria vascularis
• Recovers within 16–48 hours after cessation of noise
• Repeated TTS → permanent damage

• Irreversible SNHL due to:
  • OHC stereocilia damage (mechanical shearing)
  • Metabolic exhaustion of OHCs (glutamate excitotoxicity, free radical generation)
  • Strial atrophy with chronic exposure
  • SGN degeneration (secondary)
• Predominantly affects the 4 kHz (3–6 kHz) region — notch on audiogram; 4 kHz notch is pathognomonic
• Later spreads to adjacent frequencies (3, 6 kHz) then 2 and 8 kHz

• Single intense noise exposure (explosion, gunshot, blast) → immediate PTS
• Mechanical rupture of Reissner's membrane, basilar membrane, perilymph fistula
• May be associated with tympanic membrane perforation

• Common accompaniment of NIHL
• High-pitched tinnitus (4–8 kHz) correlating with zone of cochlear damage
• May be permanent

• Noise damages IHC-ribbon synapses even when OHCs and PTA are normal
• Results in poor speech-in-noise discrimination despite normal audiogram
• Detectable by DPOAE/ABR mismatch or electrocochleography

• Cardiovascular: Hypertension, tachycardia, increased cortisol
• Sleep disturbance, irritability, reduced cognitive performance
• Increased accident risk (communication masking)

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b) Hearing Conservation Program (HCP) for Occupational NIHL [4 marks]

• Measure noise levels in the workplace (sound level meter, dosimeter)
• OSHA action level: 85 dB(A) TWA (Time-Weighted Average over 8 hours)
• OSHA permissible exposure limit (PEL): 90 dB(A) TWA
• NIOSH recommended exposure limit: 85 dB(A) with 3 dB exchange rate

• Source control: Machine enclosures, damping vibrating surfaces, silencers on exhausts
• Path control: Acoustic barriers, sound-absorbing wall panels, increasing distance
• Receiver control: Isolating noisy machinery in separate soundproofed rooms

• Job rotation — limit duration of exposure for individual workers
• Scheduling noisy operations during off-peak hours with fewer workers present
• Limiting overtime in high-noise areas

• Ear plugs (foam, flanged, custom-molded): NRR 25–33 dB
• Ear muffs: NRR 20–30 dB
• Combined: NRR approximately 36 dB
• Adequate only if worn consistently and correctly

• Baseline audiogram: At commencement of employment (< 6 months of joining)
• Annual audiograms thereafter
• Comparison to baseline to detect standard threshold shift (STS): ≥ 10 dB shift at 2, 3, or 4 kHz averaged in either ear
• Workers with STS: Counselled, fitted with better PPE, re-evaluated

• Annual training on hazards of noise, proper use and maintenance of HPDs, audiogram results
• Signage in high-noise areas

• Maintain noise exposure records, audiogram records for duration of employment + 30 years

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c) The 60% Rule [2 marks]

• Listen at no more than 60% of maximum volume
• For no more than 60 minutes per day

• At 60% volume on typical personal music devices, output is approximately 70–80 dB(A)
• This keeps exposure below NIOSH recommended limit (85 dB TWA for 8 hours)
• Popularized by WHO's "Make Listening Safe" initiative (2015) addressing the growing epidemic of recreational NIHL among adolescents and young adults
• WHO estimates 1.1 billion young people are at risk globally from unsafe personal audio device use

• Maximum volume on devices should be capped at 85 dB
• Use noise-cancelling headphones (allows lower volume in noisy environments)
• Take listening breaks

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QUESTION 7 (10 Marks)

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a) Meniere's Disease vs Meniere's Syndrome [3 marks]

• Definite MD: 2+ spontaneous episodes of vertigo (20 min–12 hours) + SNHL confirmed on audiometry + tinnitus or aural fullness + not better explained by other diagnosis
• Probable MD: 2+ episodes of vertigo/dizziness + tinnitus/fullness + fluctuating hearing symptoms

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b) Aetiopathogenesis of Meniere's Disease [3 marks]

• Produced mainly by stria vascularis (Na⁺ pump, K⁺ secretion)
• Resorbed by the endolymphatic sac (in the posterior fossa dura)
• Unique composition: High K⁺ (150 mEq/L), low Na⁺ — essential for hair cell mechanoelectrical transduction

1. Decreased resorption by the endolymphatic sac:
   • Sac hypoplasia, fibrosis, or immune-mediated injury → reduced resorption capacity
   • Viral hypothesis: Prior HSV/EBV infection → immune-mediated sac damage
   • Autoimmune theory: Anti-endolymphatic sac antibodies (anti-68 kD heat shock protein, anti-type II collagen)
2. Increased production:
   • Increased strial secretory activity (less well-supported)
3. Ductal obstruction:
   • Narrow vestibular aqueduct predisposes to inadequate drainage

• Distension leads to periodic ruptures of Reissner's membrane
• K⁺-rich endolymph floods into perilymph → bathes the vestibular and cochlear neurons
• K⁺ → depolarization block of nerve endings → acute attack of vertigo and hearing loss
• Membrane heals → symptoms resolve (episodic nature explained)
• Repeated ruptures → permanent hair cell/neuronal damage → progressive SNHL and chronic disequilibrium

• Familial cases (~10–20%): mutations in aquaporin genes (AQP2, AQP3), collagen genes
• Aquaporin-2 in endolymphatic sac regulates water transport; dysfunction → hydrops

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c) Intratympanic Drug Therapy for Meniere's Disease [4 marks]

• Gentamicin is preferentially vestibulotoxic over cochleotoxic (type I hair cells of semicircular canals > cochlear OHCs)
• Chemical ablation of the diseased vestibular neuroepithelium → reduces abnormal firing → central compensation reduces vertigo

• Multiple injection protocols: Low-dose titration (single injection, repeat if vertigo recurs — preferred to minimize hearing loss risk) vs. Fixed-dose (4 weekly injections)
• Dose: 26.7 mg/mL (1 mL) injected through tympanic membrane via myringotomy or tuberculin syringe
• Patient supine, injected ear up for 30 minutes

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• Anti-inflammatory/immunosuppressive effect on inner ear
• Upregulates Na⁺-K⁺-ATPase in stria vascularis → reduces endolymph accumulation
• Reduces reactive oxygen species
• May modulate autoimmune-mediated endolymphatic sac damage

• Meniere's disease with serviceable hearing to preserve
• When gentamicin contraindicated (only hearing ear, bilateral disease)
• Acute attacks of SNHL in Meniere's

• Dexamethasone 4 mg/mL or methylprednisolone 40 mg/mL (higher concentration preferred)
• 3–4 weekly injections or as a course of daily injections
• Patient tilts head 45° to affected side, supine, for 30 minutes after injection

• Vertigo control comparable to gentamicin in some studies (~60–70%)
• No cochleotoxicity — safer for hearing
• May require repeated courses (effect may wane)

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QUESTION 8 (10 Marks)

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a) Superior Semicircular Canal Dehiscence Syndrome (SCDS) [5 marks]

• Prevalence of CT-confirmed dehiscence: ~0.5%
• Symptomatic SCDS: Rarer
• Often bilateral CT findings but unilateral symptoms
• Described by Lloyd Minor in 1998

• Normal inner ear: Sound energy divided between oval window (in) and round window (out)
• In SCDS: A third window at the dehiscent SSC allows energy to "leak" into the intracranial space
• Low-frequency sound energy → preferentially shunts through the third window → reduced oval window energy → low-frequency conductive hearing loss (CHL)
• Simultaneously, mechanical stimulation (pressure, Valsalva, loud sounds) → stimulates the dehiscent SSC → generates anomalous vestibular activation

1. Tullio phenomenon — vertigo/oscillopsia induced by loud sounds (low frequency, 100 Hz tuning fork)
2. Hennebert sign — vertigo with pressure changes (Valsalva, coughing, sneezing, nose blowing, tragal compression)
3. Chronic disequilibrium, oscillopsia

1. High-Resolution CT Temporal Bone (HRCT):
   • Reformatted in the Pöschl plane (parallel to SSC) and Stenvers plane (perpendicular to SSC)
   • Shows absent/thinned bone over SSC in middle fossa
   • Minimum slice thickness 0.5 mm required
2. Pure Tone Audiometry (PTA):
   • Low-frequency CHL (250–1000 Hz)
   • Negative bone conduction thresholds (below 0 dB HL) — pathognomonic of third window lesion
3. Tympanometry:
   • Type A — normal
4. Stapedial Reflexes:
   • Present (distinguishes from otosclerosis where reflexes absent)
5. Vestibular Evoked Myogenic Potentials (VEMPs):
   • cVEMP (cervical VEMP): Enhanced amplitude (lower threshold, > 100 µV) — highly sensitive
   • oVEMP (ocular VEMP): Elevated amplitude responses to bone-conducted vibration
   • Both reflect hypersensitivity of the saccule/utricle through the third window
6. Video-nystagmography: Torsional-vertical nystagmus in the plane of the SSC with sound/pressure stimulation

• Avoid triggers (loud sounds, straining, Valsalva)
• Adequate if symptoms mild

• Indicated for debilitating symptoms
• Middle fossa craniotomy approach (standard): Expose the middle fossa floor, identify dehiscence, repair by:
  • Resurfacing — lay fascia/bone wax/bone chips over the dehiscence
  • Canal plugging — plug the SSC lumen with fascia/bone dust (sacrifices SSC function but preserves cochlear function)
• Transmastoid approach: Less morbid; can resurface or plug from below via the arcuate eminence
• Outcomes: Resolution of autophony and Tullio phenomenon in >80%; hearing improvement in ~60%

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b) Tuberculosis of the Temporal Bone [5 marks]

1. Hematogenous spread (most common): Primary pulmonary TB → bacteremia → temporal bone
2. Direct extension from middle ear via Eustachian tube (nasopharyngeal TB, lymph node erosion)
3. Retrograde lymphatic spread from cervical nodes
4. Direct inoculation (rare)

• Granulomatous inflammation: Epithelioid granulomas + Langhans giant cells + caseation necrosis
• Extensive bone destruction (osteitis, osteomyelitis)
• Perineural invasion → facial nerve granulomas

1. Painless, profuse, thin, odorless otorrhea — thin, watery discharge (unlike mucopurulent COM)
2. Multiple tympanic membrane perforations (pathognomonic — Swiss cheese pattern; may coalesce into subtotal perforation)
3. Facial nerve palsy — early, often the presenting feature; granulomatous infiltration of the facial canal; can be complete (House-Brackmann VI) with relatively mild ear disease
4. Severe profound sensorineural hearing loss (labyrinthitis)
5. Pre-auricular lymphadenopathy (nodes may caseous, form cold abscess)
6. Postauricular swelling/fistula (subperiosteal abscess)

1. Ear swab for AFB: Ziehl-Neelsen stain (positive in ~50%)
2. Culture on LJ medium: Gold standard; takes 6–8 weeks; GeneXpert MTB/RIF for rapid diagnosis
3. HRCT temporal bone: Extensive bone destruction, loss of ossicular chain, labyrinthine involvement; often more extensive than expected clinically
4. MRI: Intracranial extension, meningeal enhancement
5. Biopsy of middle ear granulation tissue: Histology shows caseating granulomas with AFB
6. Chest X-ray/CT chest: Pulmonary TB (may be absent — extrapulmonary TB)
7. Mantoux test / IGRA (Quantiferon-Gold)
8. HIV testing

• Standard regimen (2HRZE/4HR):
  • Intensive phase (2 months): Isoniazid (H) + Rifampicin (R) + Pyrazinamide (Z) + Ethambutol (E)
  • Continuation phase (4 months): Isoniazid + Rifampicin
  • Total duration: 6 months (9–12 months if extensive/bone involvement or immunocompromised)

• Not primarily surgical — ATT is the definitive treatment
• Surgery indicated for:
  1. Diagnostic biopsy if diagnosis uncertain
  2. Mastoidectomy if: intracranial complication (meningitis, abscess), failed ATT, sequestrum formation, subperiosteal abscess drainage
  3. Facial nerve decompression — if no recovery after 3–6 months of ATT; surgical decompression of the facial canal with excision of granulation tissue
  4. Tympanoplasty — deferred until ATT completed and disease quiescent (minimum 6 months post-ATT); success rates lower than for ordinary COM

• Meningitis, lateral sinus thrombosis, subdural empyema (intracranial spread)
• Permanent SNHL (labyrinthine TB)
• Permanent facial nerve palsy
• Cholesteatoma formation

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QUESTION 9 (10 Marks)

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a) Surgical Anatomy of the Petrous Apex [3 marks]

• Anterior: Greater wing of sphenoid, foramen lacerum, carotid canal
• Posterior: Posterior cranial fossa, inferior petrosal sinus
• Superior: Middle cranial fossa floor, Meckel's cave (trigeminal ganglion in Cavum Meckel)
• Inferior: Jugular foramen, carotid canal
• Medial: Clivus, basisphenoid
• Lateral: Internal auditory canal (IAC), cochlea, semicircular canals

• 30% of temporal bones have pneumatized petrous apex — susceptible to petrositis
• 70% are sclerotic (no air cells) — cholesteatoma can still occur (congenital)

Middle Cranial Fossa (Meckel's Cave - CN V)
        ↑
[GSPN] → [Carotid Canal ICA] → [Clivus/Medial]
        Petrous Apex
[IAC] ← [Cochlea] ← [Lateral]
        ↓
Posterior Cranial Fossa (IAC, CN VII/VIII)
Inferior: Jugular Bulb, CN IX/X/XI

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b) Clinical Features of Petrous Apex Cholesteatoma [3 marks]

1. Suppurative otitis media / otorrhea
2. Retro-orbital/periorbital pain (CN V — ophthalmic division, Meckel's cave involvement)
3. Abducens palsy (CN VI — Dorello's canal compression → lateral rectus palsy → diplopia)

1. Facial nerve palsy (CN VII — involvement of the petrous portion of the facial nerve)
2. Sensorineural hearing loss — labyrinthine extension, cochlear damage
3. Trigeminal neuralgia / facial numbness — Gasserian ganglion compression
4. Vertigo — semicircular canal involvement
5. Pulsatile tinnitus — if ICA involved or compressed
6. Trotter's triad (if spreading anteriorly): Unilateral deafness, palatal palsy (CN X), trigeminal neuralgia
7. Headache — dural involvement, meningitis
8. On imaging: Expansile, non-enhancing, T2-bright lesion; DWI shows restricted diffusion (hyperintense) — distinguishes cholesteatoma from other petrous apex lesions (cholesterol granuloma, mucocele)

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Surgical Approaches to Petrous Apex Cholesteatoma [4 marks]

• Indication: Petrous apex lesion in an ear with useful hearing; inferior to the labyrinth
• Route: Through mastoid → Infralabyrinthine corridor (between the labyrinth superiorly and jugular bulb inferiorly)
• Preserves cochlea, semicircular canals, facial nerve
• Limited access if jugular bulb is high-riding
• Drainage approach; marsupialization into mastoid

• Route: Through the hypotympanum → between the cochlea (superior) and jugular bulb (inferior) → enters the petrous apex
• More medial access than infralabyrinthine
• Hearing preserved if cochlea not disturbed
• Risk: Jugular bulb, ICA, cochlea

• Indication: Lesion superior to IAC / labyrinth; hearing present
• Craniotomy above the temporal bone → extradural dissection along middle fossa floor → identify cochlea, arcuate eminence, IAC → access petrous apex
• Risk: Temporal lobe retraction, CN V (trigeminal) injury, GSPN injury (dry eye)
• Excellent for apical lesions above the level of IAC

• Indication: No serviceable hearing; large cholesteatoma with labyrinthine involvement
• Drill through labyrinth (complete translabyrinthine), sacrificing all vestibular and cochlear function
• Wide access to petrous apex, IAC, posterior fossa
• Sacrifice: All remaining hearing; vertical canal, facial nerve at risk

• Indication: Extensive disease medial to ICA; no hearing
• Transmastoidal + translabyrinthine + cochlear removal → maximum medial exposure
• ICA mobilized anteriorly; widest petrous apex access
• Highest morbidity: Complete SNHL, facial nerve rerouting required

• Petrosal approach: Combined anterior transpetrosal + posterior retrosigmoid for giant lesions
• Kawase's approach: Anterior transpetrosal — remove bone medial to IAC, lateral to ICA → Meckel's cave, prepontine area accessed

• For midline/bilateral petrous apex lesions accessible via the sphenoid sinus
• Less morbid but limited to well-pneumatized sinuses

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QUESTION 10 (10 Marks)

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a) Overall Survival Rate and its Calculation [3 marks]

• OS rate = (Number of patients alive at specified time / Total number of patients enrolled) × 100
• Most commonly reported as 1-year, 2-year, 5-year, and 10-year survival rates
• In oncology, the 5-year survival rate is the standard benchmark

• All patients followed for the full study period
• OS = Survivors at end of period / Total enrolled × 100
• Limitation: Requires long follow-up; patients lost to follow-up create bias

• Follow-up period divided into intervals (e.g., annual)
• For each interval: Effective number at risk = those alive at start − (½ × those withdrawn during interval)
• Conditional survival for each interval: P = (alive at end of interval) / (effective number at risk)
• Cumulative survival rate = Product of conditional survival probabilities for all intervals
• Handles withdrawals and losses

• Calculates survival at each event time point (when death occurs)
• S(t) = S(t−1) × [(n−d)/n] where n = at-risk individuals, d = deaths at time t
• Produces a step-function survival curve
• Accounts for censored observations (lost to follow-up, end of study)
• Groups compared using Log-rank test or Mantel-Haenszel test
• Results expressed as median survival (time when 50% of patients have died)

• Laryngeal cancer: 5-year OS ~60–70% for Stage III; ~30–40% for Stage IV
• Thyroid cancer (papillary): 5-year OS >95%
• Reporting survival improves understanding of prognosis and treatment outcomes

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b) Case-Control Study [3 marks]

• Cases: Individuals with the disease of interest
• Controls: Individuals without the disease, matched or sampled from the same source population

• Looks backward in time (retrospective) — from outcome to exposure
• Does NOT follow patients forward; historical exposure data collected

1. Define the disease (case definition)
2. Identify cases (hospital/registry-based)
3. Select appropriate controls (hospital-based or population-based)
4. Matching: Controls matched to cases for potential confounders (age, sex, socioeconomic status)
5. Collect exposure history from both groups (questionnaire, records)
6. Calculate Odds Ratio (OR) as measure of association

• OR > 1: Exposure associated with increased risk of disease
• OR = 1: No association
• OR < 1: Exposure protective

• Cases: 50 patients diagnosed with sinonasal adenocarcinoma at a tertiary hospital
• Controls: 200 patients without sinonasal cancer, matched for age and sex, attending the same hospital for unrelated conditions
• Exposure measured: History of occupational wood dust exposure (furniture makers, carpenters)
• Result: 40 of 50 cases had wood dust exposure vs. 30 of 200 controls
• OR = (40 × 170) / (10 × 30) = 6800/300 = 22.7
• Interpretation: Wood dust exposure is associated with 22.7 times higher odds of sinonasal adenocarcinoma

• Efficient for rare diseases (like sinonasal cancers)
• Relatively inexpensive and quick (retrospective)
• Can study multiple exposures simultaneously
• Suitable when long latency period exists

• Cannot calculate incidence or relative risk directly (only OR)
• Subject to recall bias (cases may remember exposure differently)
• Selection bias in choosing controls
• Cannot study rare exposures

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c) Incidence vs. Prevalence [4 marks]

1. Incidence Rate (Incidence Density):
   • = (Number of NEW cases during time period) / (Total person-time at risk)
   • Units: per 1000 person-years
   • Example: 50 new cases of laryngeal cancer per 100,000 person-years in males
2. Cumulative Incidence (Attack Rate):
   • = (Number of new cases during period) / (Population at risk at start of period)
   • Units: Proportion (no units); expressed per 1,000 or 100,000
   • Example: 5 new cases of sudden SNHL per 100,000 population per year

• Measures the risk of developing a disease
• Used to study aetiology and causation (cohort studies)
• Reflects disease occurrence rate

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1. Point Prevalence:
   • = (Number of existing cases at a given point in time) / (Total population at that time) × 100
   • Example: Prevalence of CSOM = 5% of school-age children in rural India
2. Period Prevalence:
   • = (Number of cases during a time period) / (Mid-period population) × 100
   • Includes old cases continuing + new cases developing during the period

• Measures disease burden at a point in time
• Used for planning health services and resource allocation
• Reflects disease frequency in a population at any moment

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Prevalence ≈ Incidence × Duration of disease

• A disease with high incidence but short duration (e.g., acute otitis media) → low prevalence
• A disease with low incidence but long duration (e.g., chronic tinnitus, progressive SNHL) → high prevalence
• Improved treatment that prolongs survival without cure → increases prevalence without increasing incidence

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Quick Reference — 10 Questions Answered

• Start with a definition/introduction sentence
• Use tables for comparisons — saves space and earns full marks
• Underline or bold key terms
• End each sub-part within the marks allocation (don't overwrite one part at cost of another)
• Diagrams (even schematic ones) earn bonus marks for Q9 petrous apex anatomy