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DNB Otorhinolaryngology ENT Paper 4 - Model Answers

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QUESTION 1 [10 marks]

a) Factors Affecting Wound Healing and Ways to Improve It [5 marks]

1. Nutritional optimization - Proteins (1.5-2 g/kg/day), Vitamin C 500 mg, Zinc supplementation, Vitamin A
2. Glucose control - Target HbA1c < 7% in diabetics pre-operatively
3. Smoking cessation - At least 4 weeks before elective surgery
4. Wound bed preparation - TIME principle: Tissue debridement, Infection control, Moisture balance, Edge of wound
5. Moist wound environment - Use of hydrocolloid, hydrogel, foam dressings
6. Negative pressure wound therapy (NPWT/VAC) - Increases perfusion, removes exudate, promotes granulation
7. Growth factors - Platelet-rich plasma (PRP), recombinant PDGF (becaplermin)
8. Hyperbaric oxygen therapy - In radiation-induced wounds and refractory ischemic wounds
9. Adequate hemostasis and tissue handling - Minimize dead space, gentle technique
10. Treat underlying systemic disease - Correct anemia, hypothyroidism, etc.

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b) Surgical Cricothyrotomy [5 marks]

• Lies between thyroid cartilage (superior) and cricoid cartilage (inferior)
• Dimensions: ~9 mm height x 30 mm width
• Avascular zone in the central lower third is the safe zone
• Superior cricothyroid vessels run in the upper third - AVOID
• Covered by subcutaneous tissue and platysma

• Failed intubation - cannot intubate, cannot oxygenate
• Severe maxillofacial trauma
• Laryngeal edema (anaphylaxis, burns, angioedema)
• Massive oropharyngeal hemorrhage
• Foreign body obstruction at/above glottis

• Early: hemorrhage, false passage, esophageal placement, posterior tracheal wall perforation
• Late: subglottic stenosis (most feared - due to cricoid damage), voice change, swallowing difficulty

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QUESTION 2 [10 marks]

Nuclear Medicine Scans in Head and Neck Diseases - Scan for Paraganglioma and Parathyroid Adenoma [4+3+3]

• Thyroid scan (cold vs hot nodule assessment)
• Salivary gland scintigraphy (Sjogren's, obstruction)

• Thyroid cancer staging and post-ablation surveillance
• Assessment of ectopic thyroid tissue and metastases
• I-123: diagnostic; I-131: therapeutic

• Primary hyperparathyroidism - preoperative localization
• Thyroid nodule vascularity assessment

• Paragangliomas, pheochromocytomas, neuroblastomas

• Paragangliomas (especially head and neck)
• Neuroendocrine tumors

• Staging head and neck squamous cell carcinoma
• Unknown primary workup
• Post-treatment surveillance

• Most sensitive for paragangliomas (somatostatin receptor positive)
• Replacing Octreotide scan due to better resolution

• Tc-99m sulfur colloid - used in cutaneous malignancies of head and neck

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• Most sensitive (>95%) and specific modality currently
• Somatostatin receptor type 2 (SSTR2) over-expressed on paraganglioma cells
• Advantages: whole body scan, identifies multifocal disease, detects hereditary SDH-mutation related tumors, superior to MIBG

• Based on uptake by catecholamine-secreting cells
• Sensitivity ~70-80% for paragangliomas
• Used when Ga-68 DOTATATE unavailable
• Positive in functional (secretory) tumors

• I-111 Octreotide scan (Octreoscan) - older modality, lower resolution
• FDG-PET: useful for malignant/metastatic paragangliomas (especially SDH-B mutations)
• MRI neck with contrast - anatomical delineation (salt and pepper appearance on T1/T2)
• CT angiography - demonstrates blood supply

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• Mechanism: MIBI (sestamibi) concentrates in mitochondria-rich cells. Parathyroid adenomas have abundant oxyphil cells with high mitochondrial density - retain MIBI longer than thyroid tissue
• Protocol:
  • Double phase (early & delayed): Early scan at 15-20 min; Delayed scan at 2-3 hours
  • Thyroid washes out early; adenoma retains tracer (persistent "hot spot")
  • Sensitivity: ~80-90% for single adenoma

• Dual tracer technique: I-123 (thyroid only) subtracted from Tc-99m MIBI (both thyroid + parathyroid) = net parathyroid image
• Useful in thyroid pathology where standard MIBI scan ambiguous

• Non-nuclear but important adjunct
• 4 phases: pre-contrast, arterial, venous, delayed
• Adenomas show early arterial enhancement and washout
• Excellent for ectopic glands; sensitivity ~88%

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QUESTION 3 [10 marks]

Hemorrhagic Shock - Definition, Classification, Management, Packed Red Cells and FFP [3+3+2+2]

• A - Airway with C-spine protection
• B - Breathing - O2 supplementation; intubate if GCS < 8
• C - Circulation - IV access (2 large bore IVs), blood samples (CBC, coagulation, crossmatch, ABG)
• D - Disability - GCS, pupils
• E - Exposure and environment

• Direct pressure, tourniquet (extremity), wound packing with hemostatic gauze (QuikClot, Celox)
• Pelvic binder for pelvic fractures
• REBOA (Resuscitative Endovascular Balloon Occlusion of Aorta) in non-compressible hemorrhage
• Damage control surgery

• Permissive hypotension: Target MAP 50-65 mmHg (SBP 80-90) in penetrating trauma until surgical hemorrhage control
• Avoid crystalloid overload (>1.5L may worsen coagulopathy and hypothermia)
• Damage Control Resuscitation (DCR): 1:1:1 ratio of pRBC:FFP:Platelets
• Tranexamic acid (TXA): 1g IV within 3 hours of injury (CRASH-2 trial)
• Massive Transfusion Protocol (MTP) - activated for Class III-IV

• Prepared by removing ~200-250 mL plasma from whole blood; each unit ~250-350 mL with HCT ~55-65%
• Contains RBCs, residual WBCs (unless leukoreduced), minimal plasma
• Indications:
  • Hemoglobin < 7 g/dL in stable patients (restrictive threshold)
  • Hemoglobin < 8-10 g/dL in cardiac patients or acute hemorrhage
  • Acute Class III-IV hemorrhage regardless of Hb
• 1 unit pRBC raises Hb by ~1 g/dL and HCT by ~3%
• Storage: 2-6°C; shelf life 35-42 days (additive solutions)
• Complications: Transfusion reactions (febrile, hemolytic, allergic, TRALI, TACO), hypothermia, hypocalcemia, hyperkalemia, infection, iron overload

• Prepared from whole blood or apheresis; frozen within 8 hours to preserve labile factors (V and VIII); volume ~200-250 mL
• Contains all clotting factors, fibrinogen, anticoagulants (protein C, S, antithrombin)
• Indications:
  • Coagulopathy due to multiple factor deficiency (PT/INR > 1.5x normal)
  • Massive transfusion (1:1:1 protocol with pRBC and platelets)
  • DIC with active bleeding
  • Warfarin reversal (emergent, when PCC unavailable)
  • TTP (Thrombotic Thrombocytopenic Purpura) - plasma exchange
  • Factor V or XI deficiency (no specific concentrate available)
• Dose: 15-20 mL/kg (usually 4 units)
• Must be ABO compatible; thaw at 37°C; use within 24 hours once thawed
• Complications: Allergic reactions, TRALI (most serious transfusion-related death), TACO, infection

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QUESTION 4 [10 marks]

a) Cystic Hygroma - Neck, Chest, Mediastinum [5 marks]

• Neck (75-80%): Most common; posterior triangle > anterior triangle; left > right
• Axilla (5%): Second most common
• Mediastinum (1-2%): Anterior > posterior; may cause SVC syndrome, respiratory distress
• Chest: May be extension of cervical hygroma
• Retroperitoneum, groin, tongue, orbit: Less common

• Present at birth (50-65%) or within first 2 years of life (90%)
• Soft, compressible, brilliantly transilluminant mass
• Painless unless infected; tense and tender during infection or hemorrhage
• Can cause respiratory distress (large cervico-mediastinal hygroma), dysphagia
• Cervical hygroma: Posterior triangle swelling, fluctuant, crosses midline
• Mediastinal involvement: May present as superior mediastinal mass on CXR; causes SVC syndrome, stridor, cough
• Associations: Turner syndrome (45XO), Trisomy 13, 18, 21; Noonan syndrome; hydrops fetalis

• USG: First-line; multiseptate, multilocular cystic lesion; no flow on Doppler
• MRI: Best for extent mapping - "infiltrative" nature through tissue planes; T1 low, T2 high signal
• CT chest/neck: For mediastinal extension; demonstrates relationship to great vessels
• Prenatal USG/amniocentesis: Detects fetal hygroma + karyotyping

• OK-432 (Picibanil) - most effective; derived from Streptococcus pyogenes group A; causes intense inflammatory response
• Bleomycin - 1-2 mg/kg intralesional; effective; risk of pulmonary fibrosis with overdose
• Doxycycline/STS - used for macrocystic lesions
• Multiple sessions usually required

• Definitive treatment; complete excision preferred
• Challenging due to infiltration into vital structures (brachial plexus, carotid sheath, vagus nerve)
• Risk of recurrence with incomplete excision (50-100%)
• Indicated: large lesions, failure of sclerotherapy, airway compromise
• Stage approach for extensive disease

• Sirolimus (mTOR inhibitor): increasingly used for complex/refractory lymphatic malformations; inhibits lymphangiogenesis via PI3K/AKT/mTOR pathway

• Ex-utero intrapartum therapy (EXIT procedure) for massive fetal cervical hygroma compromising airway at birth

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b) Role of CBNAAT in Diagnosis of Extrapulmonary TB of Head and Neck [5 marks]

• Real-time PCR (polymerase chain reaction) based automated molecular test
• Simultaneously detects:
  1. Mycobacterium tuberculosis complex (MTBC) - by targeting 81 bp region of rpoB gene
  2. Rifampicin resistance - by detecting mutations in rpoB gene (surrogate marker for MDR-TB)
• Closed cartridge system - minimizes biosafety risk
• Result in 2 hours (vs 6-8 weeks for culture)

• Faster than culture (gold standard)
• More sensitive than smear microscopy (AFB smear)
• Detects RIF resistance simultaneously
• Minimal biosafety requirements (Category 2 lab sufficient)
• Reduced operator skill requirement
• Approved by WHO (2010) and RNTCP/NTEP India

• Sensitivity for culture-confirmed lymph node TB: ~80-90% (FNA specimen)
• Specificity: >98%
• Better on biopsy material (caseous tissue) > FNA alone
• Sensitivity lower in paucibacillary extrapulmonary sites

• Cannot distinguish live from dead bacilli (remains positive post-treatment)
• Cannot detect all drug resistances (only RIF/INH in Xpert Ultra)
• Does not replace histopathology (granuloma with Langhans giant cells remains gold standard)
• Cannot do drug sensitivity for second-line drugs
• False negatives in paucibacillary samples

• Positive MTB + RIF sensitive: Start standard first-line ATT (2HRZE + 4HR)
• Positive MTB + RIF resistant: Suspect MDR-TB; escalate to second-line; send for DST
• Negative result: Does NOT rule out TB in extrapulmonary sites - clinical judgment + histopathology required

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QUESTION 5 [10 marks]

a) Aetiopathogenesis of Various Branchial Anomalies [4 marks]

• Branchial clefts (external/ectoderm-lined)
• Pharyngeal pouches (internal/endoderm-lined)
• Branchial plates (closing membrane between cleft and pouch)

• Normally branchial clefts 2-5 are covered by the 2nd arch (operculum of His) forming the cervical sinus of His, which subsequently obliterates
• Incomplete fusion or obliteration leaves remnants as cysts, sinuses, or fistulae

• Sequestration of ectodermal rests within lymph nodes gives rise to cysts (explains late presentation in adults)

• Failure of obliteration of 1st branchial cleft (between 1st and 2nd arch)
• Tract runs parallel to external auditory canal
• Work Classification:
  • Type I - Duplication of membranous EAC; ectoderm only; superficial to facial nerve
  • Type II - Contains ectoderm + mesoderm (cartilage, skin); runs deep to, through, or superficial to facial nerve; opens near angle of mandible
• Closely related to facial nerve (VII)
• Presents as preauricular/periauricular cyst, sinus, or fistula

• Bailey classification (I-IV) based on depth:
  • Type I - Superficial to SCM
  • Type II - Deep to SCM, against carotid sheath (most common)
  • Type III - Between ECA and ICA passing toward skull base
  • Type IV - Medial to carotid sheath, against pharyngeal wall
• Sinus opens at anterior border of lower 1/3 SCM
• Fistula passes between ECA and ICA, over CN IX and XII, to open at tonsillar fossa

• Passes posterior to CCA/ICA, anterior to CN X (vagus)
• Internal opening into piriform sinus (apex)
• Closely associated with recurrent suppurative thyroiditis (usually left-sided)

• Loop around subclavian artery (right) or arch of aorta (left)
• Opens into apex of piriform sinus or esophagus
• Presents as deep neck infection, thyroid abscess, suppurative thyroiditis

• Cyst: Fluctuant swelling, may enlarge with URTI
• Sinus: External opening on skin - intermittent discharge
• Fistula: Complete tract with both internal and external openings

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b) Clinical Features and Management of Type 1 Branchial Cleft Anomaly [3+3 marks]

• Intermittent pre-auricular or periauricular swelling
• Purulent discharge from sinus near EAC or angle of mandible
• Recurrent infections misdiagnosed as otitis externa or parotid abscess
• Post-auricular or pre-auricular pit or sinus opening
• May present as a fluctuant swelling at angle of mandible
• CHL (conductive hearing loss) if cyst compresses EAC

• Type I: Opening in or near EAC (often at floor or posterior wall); cyst parallels EAC; superficial to facial nerve
• Type II: Sinus opening below and anterior to ear, near angle of mandible; deep to / through / superficial to facial nerve; contains skin appendages and cartilage
• Both types may present as parotid region mass

• CT scan with contrast: Defines tract, relationship to facial nerve, parotid gland
• MRI: Better soft tissue delineation; preferred preoperatively
• Fistulogram: Injecting contrast into sinus to outline tract (less commonly used now)
• Probe sinogram
• Fine needle aspiration if cystic

• Treat active infection first (antibiotics, incision & drainage)
• Never operate in acute infection phase
• Complete workup: CT/MRI for tract delineation
• Facial nerve monitoring - mandatory (electrodes placed in orbicularis oculi and oris)

• Elliptical incision around the sinus opening
• Separate incision in parotid region (modified Blair's incision or pre-auricular incision)
• Identify and preserve facial nerve branches throughout
• Trace tract to EAC (Type I) or deeper parotid structures (Type II)
• Complete excision of tract including EAC cartilage if adherent (Type I may require sleeve resection of EAC)
• Post-auricular skin excision if cyst involves it

• Drain placement
• Facial nerve function assessment
• Recurrence rate low with complete excision

• Facial nerve injury (most serious - especially with Type II)
• Recurrence (common with incomplete excision or if operated during acute infection)
• Salivary fistula (parotid involvement)
• Hematoma, infection, scar

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QUESTION 6 [10 marks]

a) Thyroid Ophthalmopathy and its Management [5 marks]

• Autoantibodies against TSH receptor (TSHR) and IGF-1 receptor expressed on orbital fibroblasts
• Fibroblast activation leads to:
  • Glycosaminoglycan (hyaluronic acid) accumulation in orbital fat and extraocular muscles
  • Adipogenesis (fat expansion)
  • Extraocular muscle enlargement (especially inferior > medial > superior > lateral rectus - mnemonic: I'M SLow)
• Results in proptosis, diplopia, compressive optic neuropathy

• N - No signs/symptoms
• O - Only signs (lid retraction, stare, lid lag)
• S - Soft tissue involvement (periorbital edema, chemosis, conjunctival injection)
• P - Proptosis (>20 mm = abnormal; >25 mm = severe)
• E - Extraocular muscle involvement (diplopia, restriction of gaze)
• C - Corneal involvement (exposure keratopathy, ulceration)
• S - Sight loss (compressive optic neuropathy - MOST SERIOUS)

• Thyroid function control (euthyroid state reduces activity)
• Smoking cessation - MOST IMPORTANT modifiable risk factor (smoking x5 risk; worsens RAI-induced GO)
• Lubricating eye drops for exposure
• Sunglasses, head elevation at night, selenium supplementation (mild active disease - 200 mcg/day x 6 months)

• Selenium 200 mcg/day orally x 6 months (reduces progression)
• Artificial tears, lubricating ointments
• Prism glasses for diplopia

• IV methylprednisolone (pulsed steroids): 500 mg IV weekly x 6 weeks, then 250 mg x 6 weeks (total cumulative dose < 8g to avoid hepatotoxicity); more effective and better tolerated than oral steroids
• Orbital radiation: 2 Gy x 10 fractions; synergistic with steroids; especially for myopathy/diplopia
• Teprotumumab (IGF-1R inhibitor): FDA approved 2020; highly effective in reducing proptosis and CAS; game-changer for moderate-severe TED
• Rituximab (anti-CD20) for refractory cases
• Mycophenolate mofetil as steroid-sparing agent

• Emergency treatment
• IV methylprednisolone 1g/day x 3 days
• If no response in 2 weeks → URGENT ORBITAL DECOMPRESSION SURGERY

• Orbital decompression: Removal of orbital walls/fat; reduces proptosis; indicated for compressive optic neuropathy, severe proptosis, corneal exposure. Usually performed first.
• Strabismus surgery: Muscle recession for diplopia correction; after decompression and stability
• Eyelid surgery: Lid retraction correction (levator recession, Muller's muscle recession); LAST step

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b) Role of Central Neck Dissection in Differentiated Thyroid Cancers [5 marks]

• Central compartment is the primary drainage of the thyroid
• 20-80% of papillary thyroid cancers (PTC) have nodal metastases; subclinical (microscopic) central nodal disease is common
• Central recurrence is difficult to manage (proximity to RLN, parathyroids, great vessels)
• CND improves staging (pN status), guides adjuvant RAI dosing, reduces biochemical recurrence

1. Therapeutic CND (T-CND): Performed when clinically/radiologically evident (N1a) nodal disease; universally agreed upon
2. Prophylactic/Elective CND (P-CND): Performed in clinically node-negative (cN0) central compartment; controversial

• Absolute (Therapeutic): Clinically positive central nodes (N1a); imaging evidence of central nodal disease
• Relative (Prophylactic):
  • T3 or T4 tumors
  • Extrathyroidal extension
  • Multifocal PTC
  • High-risk features (tall cell, columnar, diffuse sclerosing variant)
  • Elevated postoperative Tg suggesting residual disease

• Recurrent Laryngeal Nerve (RLN): Risk of injury 1-11%; transient or permanent voice change (hoarseness)
• Parathyroid glands: Bilateral CND carries high risk of hypoparathyroidism - transient (10-40%), permanent (1-10%)
• Chyle leak (left-sided dissection)
• Hematoma, infection, scar

• Meticulous identification of bilateral RLNs before central dissection
• Parathyroid identification and autotransplantation of devascularized parathyroids to sternocleidomastoid muscle (bivalve, confirm on frozen section)
• En bloc dissection with thyroid when performing total thyroidectomy
• Use of nerve integrity monitoring (NIM) for RLN
• Intraoperative PTH monitoring where available

• P-CND reduces central compartment recurrence in PTC from ~10-15% to ~2-5%
• No proven OS benefit in low-risk disease
• Higher complication rates offset the benefit in cN0 low-risk tumors

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QUESTION 7 [10 marks]

a) Principles of Stereotactic Radiation [3 marks]

• Single high dose (12-25 Gy) delivered in one session
• Platforms: Gamma Knife (201 Co-60 sources), CyberKnife (robotic LINAC), LINAC-based SRS
• Used for small lesions < 3-4 cm

• Multiple fractions (2-5 sessions) of high dose
• Takes advantage of normal tissue repair between fractions (radiobiological rationale)
• Better for larger lesions or lesions near critical structures (brainstem, optic apparatus)

• Immobilization: Rigid head frame (Leksell for Gamma Knife) or frameless mask system
• Imaging: High-resolution MRI/CT fusion for target delineation
• Treatment planning: Inverse planning; isodose curves; maximum dose to GTV, rapid falloff
• Multiple beams/arcs: Many non-coplanar beams intersect at target; low individual beam dose, high confluent dose at isocenter
• Conformality index: Ratio of prescription isodose volume to target volume (ideal = 1.0)
• Gradient index: Measures steepness of dose falloff outside target

• 4 Rs of Radiobiology: Repair, Reassortment, Repopulation, Reoxygenation
• SRS bypasses conventional radiobiology; relies on direct DNA double-strand breaks
• Vascular damage and thrombosis at high doses
• Radioresistant tumors (e.g., schwannomas, meningiomas) can be effectively controlled

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b) Stereotactic Radiation for Management of Vestibular Schwannoma [4 marks]

• Benign WHO Grade I tumor of Schwann cells arising from vestibular division of CN VIII
• Most commonly at cerebellopontine angle cistern and internal auditory canal
• Slow growing (2-3 mm/year average)

• Small to medium sized tumors (< 3 cm diameter)
• Elderly or medically unfit patients
• Residual or recurrent tumor post-surgery
• Patient preference
• Bilateral NF2-associated schwannomas (hearing preservation crucial)
• Growing tumor on observation

• Prescription dose: 12-13 Gy to the 50% isodose line (treating edge of tumor)
• Single session (1-3 hours treatment)
• Frame-based immobilization
• MRI-guided targeting; isocenter at tumor margin

• Tumor control rate: 93-97% at 10 years (local control = no progression)
• Hearing preservation: 50-70% at 2 years
• Facial nerve preservation: >97% (better than surgery)
• Complete resolution uncommon; most tumors stabilize or shrink slowly
• Pseudoprogression: Transient swelling 6-18 months post-SRS in ~30% - does NOT mean failure

• 25 Gy in 5 fractions or 54 Gy in 30 fractions
• Used for tumors > 3 cm or those involving brainstem
• Better hearing preservation data
• Longer treatment time; repeat immobilization required

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c) Complications of Stereotactic Surgery [3 marks]

• Pseudo-progression/tumor swelling: Transient expansion seen on MRI in ~30%; can cause increased symptoms (tinnitus, vertigo, headache); usually resolves without intervention
• Trigeminal neuropathy: Facial numbness/pain in ~3-5% (facial numbness, tingling)
• Hearing deterioration: Acute sensorineural hearing loss within weeks-months
• Vertigo/balance disturbance: Transient worsening

• Hearing loss (most common): Progressive SNHL in 25-50%; correlates with cochlear dose
• Facial nerve palsy: < 1-3% with modern techniques (12-13 Gy)
• Trigeminal dysfunction: Facial numbness/dysaesthesia, 3-5%
• Hydrocephalus: Rare; communicating hydrocephalus due to CSF protein elevation
• Malignant transformation: Extremely rare (<0.1%); SRS-induced sarcoma; long latency
• Brain necrosis: Radionecrosis at high doses; rare with doses < 14 Gy
• Tinnitus: Worsening in some patients
• Brainstem injury: Rare with appropriate dose selection; risk with tumors > 3 cm

• Prescription dose > 14 Gy
• Tumor volume > 15 cm3
• Prior surgery / irradiation
• Cochlear dose > 4-5 Gy correlates with hearing loss

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QUESTION 8 [10 marks]

a) What is a Vibrant Sound Bridge and How is it Different from a Bone Anchored Hearing Aid? [2+2 marks]

• An active middle ear implant (AMEI) that directly drives the ossicles or inner ear windows using electromagnetic vibration
• Manufactured by MED-EL
• Semi-implantable device

• External part: Audio processor worn on skin surface
• Internal part: Receiver coil + demodulator + Floating Mass Transducer (FMT)
• FMT (key component): A tiny titanium capsule containing a magnet and coil, surgically attached to the ossicular chain (typically round window, stapes head, or incus)

• Microphone in audio processor captures sound → converts to FM signal → transmitted transcutaneously to receiver coil → demodulated → FMT vibrates at sound frequency → drives ossicular chain or round window → mechanical vibration of perilymph → cochlear stimulation

• SNHL: Mild to severe (FMT at round window - RW application)
• Conductive HL: FMT at stapes/oval window
• Mixed HL: Combined approach
• Patients who cannot tolerate conventional hearing aids (canal atresia, chronic otitis externa, discomfort)
• Patients who need occlusion-free fitting

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• A bone-conduction hearing device that uses an osseointegrated titanium implant to transmit sound vibrations through bone directly to the cochlea
• Bypasses the outer and middle ear entirely

• Titanium fixture implanted in mastoid bone
• External sound processor attached via snap-fit abutment (percutaneous) OR magnetic transcutaneous connection (Baha Attract, Osia)

• Sound processor vibrates → vibrations transmitted through abutment → titanium fixture → skull bone → vibrates cochlea directly (bone conduction)

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b) Indications and Surgical Procedure of Vibrant Sound Bridge [3+3 marks]

• Sensorineural hearing loss (30-65 dB HL): Moderate to moderately-severe; traditional hearing aids unsatisfactory or poorly tolerated
• Conductive hearing loss: Ossicular chain discontinuity, congenital aural atresia
• Mixed hearing loss: Combined conductive and sensorineural component
• Single-sided deafness (SSD): Cross-hearing configuration
• Chronic otitis externa / canal atresia: Precluding conventional HA use
• Otosclerosis: Post-stapedectomy with residual hearing loss
• Microtia (external ear malformation)

• PTA (pure tone average) 30-65 dB HL for SNHL
• WRS (word recognition score) > 50%
• Bone conduction thresholds within candidacy range
• Trial with acoustic hearing aid must show inadequate benefit

• Audiometric evaluation (PTA, speech tests, bone conduction)
• CT temporal bone - ossicular anatomy assessment
• Counseling regarding expectations, surgery

• Classic (long process of incus coupling): FMT crimped onto long process of incus using clip; used for SNHL with intact ossicular chain
• Round window (RW) application): FMT placed on or against round window membrane; used for SNHL, conductive HL with poor ossicular chain, or atresia; FMT vibrates RW directly
• Oval window coupling: FMT placed on stapes head or over oval window
• FMT must be secure without touching bony walls (feedback risk)

• Significant improvement in speech discrimination and quality of life
• Durable results; no occlusion; cosmetically superior
• Revision rate ~5-10% (FMT dislodgement, feedback)

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QUESTION 9 [10 marks]

a) Milan System for Reporting Salivary Gland Cytopathology [5 marks]

• Standardize FNA reporting terminology
• Provide risk of malignancy (ROM) for each category
• Guide clinical management decisions

• Category I (non-diagnostic) has a relatively HIGH ROM (~25%) compared to Bethesda system - emphasizes need for repeat biopsy
• Pleomorphic adenoma - most common benign neoplasm (Category IVa)
• Warthin tumor - second most common benign (Category IVa); bilateral in 10%
• Mucoepidermoid carcinoma - most common malignant salivary tumor
• FNA with ROSE (rapid on-site evaluation) improves adequacy rates
• Cell block for immunohistochemistry can upgrade category

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b) Surgical Landmarks for Facial Nerve Identification During Parotid Surgery [5 marks]

• The cartilaginous "pointer" at the inferior apex of the tragus
• Main trunk of facial nerve lies 1 cm deep, inferior and medial to the tip of the tragal pointer
• Most consistently used landmark in parotid surgery
• Reliability: ~90%

• The main trunk of facial nerve lies just anterior and superior to the point where the posterior belly of digastric crosses the posterior edge of the SCM
• The nerve crosses lateral to the styloid process at this level
• Very reliable landmark especially in revision or complex cases

• Facial nerve main trunk lies 6-8 mm inferior to the inferior end of the tympanomastoid fissure/cartilaginous EAC
• Good surface marking when stylomastoid foramen region is accessible

• Nerve exits skull at stylomastoid foramen - posterior to styloid process, anterior to mastoid
• Located between styloid process (anteromedially) and mastoid tip (posterolaterally)
• Direct visualization of foramen and nerve emerging

• When normal anatomy is distorted (large tumor, revision surgery, post-radiation)
• Identify marginal mandibular branch at lower border of mandible
• Identify zygomatic branches near the zygomatic arch
• Trace proximally to bifurcation and then to main trunk
• Technically more challenging; useful as adjunct

• The facial nerve lies in a plane between the superficial and deep lobes of the parotid gland
• Bifurcation occurs within 1-2 cm of the stylomastoid foramen
• In infants: mastoid is not yet developed; facial nerve more superficial - higher risk of injury

• Always achieve hemostasis before dissection in parotid area
• Use blunt dissection in the direction of expected nerve branches
• Never cut a structure without first confirming it is not the facial nerve
• Use of sharp dissection with mosquito/Allis clamp - "see-through" principle
• Maintain traction on the parotid tissue (not the nerve) during dissection
• If uncertain - stimulate electrically before cutting

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QUESTION 10 [10 marks]

Genes Responsible for Congenital Hearing Loss and Role of Gene Therapy [4+4 marks]

• 1 in 500-1000 newborns has significant hearing loss
• 50-60% of congenital hearing loss is genetic
• Of genetic HL: 70% nonsyndromic, 30% syndromic
• Of nonsyndromic HL: 75-80% autosomal recessive, 15-20% autosomal dominant, 1-2% X-linked, <1% mitochondrial

• 110 genes identified for nonsyndromic HL; > 400 syndromic HL conditions

• DFNA (autosomal dominant) - DFNA1, DFNA2, etc.
• DFNB (autosomal recessive) - DFNB1, DFNB2, etc.
• DFNX (X-linked)

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• Most genetic HL involves loss of function of a specific gene in a defined cell population (hair cells, spiral ganglion neurons, supporting cells)
• Cochlea is surgically accessible (round window injection)
• Cochlea is immune-privileged (blood-labyrinthine barrier)
• Hair cells are post-mitotic; gene delivery can be long-lasting

• Deliver functional copy of defective gene via viral vector
• Most advanced strategy; proof of concept in humans (2024)

• RNA interference (siRNA, shRNA) to knock down toxic mutant protein
• Antisense oligonucleotides (ASOs)

• CRISPR-Cas9: Correct specific point mutations; still experimental in hearing research
• Base editing, prime editing: More precise, lower off-target effects

• Atoh1/Math1 gene transfer: Drives supporting cells toward hair cell fate (hair cell regeneration)
• Still in preclinical stages for inner ear

• Adeno-associated virus (AAV): Most widely used; AAV1, AAV2, AAV8, Anc80L65 (highly efficient for cochlear transduction); low immunogenicity; long-term expression; cannot integrate (non-integrating)
• Adenovirus: High efficiency but immunogenic
• Lipid nanoparticles: Non-viral; emerging

• Round window membrane (RWM) injection: Most accessible, least traumatic
• Posterior semicircular canal injection: Better apex distribution
• Cochleostomy

• 2024: First successful gene therapy for hearing loss in humans
• OTOF gene (encoding otoferlin) delivered via AAV vector (dual-AAV approach due to large gene size)
• Children with DFNB9 (auditory neuropathy due to OTOF mutations)
• Results: Significant hearing improvement in treated ears; several patients developed functional hearing from profound deafness
• Trials: CGAC (China), CHORD trial (USA/Europe)
• This represents a landmark proof-of-concept for inner ear gene therapy

• GJB2 (connexin 26) gene therapy - preclinical success in mouse models
• TMPRSS3, LHFPL5 mutations - AAV trials ongoing
• VGLUT3 (SLC17A8) - successfully restored hearing in mouse models

• Large gene size (e.g., OTOF ~6kb exceeds single AAV capacity - requires dual-AAV)
• Efficient transduction of basal turn hair cells (key for high-frequency hearing)
• Immune response to viral vector
• Long-term durability of gene expression
• Off-target editing effects with CRISPR
• Ethical considerations (germline editing)

• GJB2 gene therapy (largest patient population) - phase I trials anticipated
• Combination with cochlear implant
• Preventive gene therapy for progressive HL (e.g., DFNA2/KCNQ4)

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