SKULL BASE OSTEOMYELITIS (MALIGNANT/NECROTIZING OTITIS EXTERNA)

A Comprehensive 50-Mark Answer — RGUHS Pattern

DEFINITION

The term "malignant" was coined by Chandler (1968) — not implying neoplasm but reflecting the malignant course. Meltzer & Kelemen later popularized the term "Skull Base Osteomyelitis" as more anatomically precise. (Cummings Otolaryngology, 7th ed.)

EPIDEMIOLOGY

ETIOLOGY AND PREDISPOSING FACTORS

Primary Causative Organism

• Pseudomonas aeruginosa — responsible for ~95% of cases
  • Produces exotoxins, proteases, elastases
  • Has inherent resistance to multiple antibiotics
  • Thrives in moist, earwax-deficient canals

Alternate Organisms (Rare but Important)

• Aspergillus fumigatus / flavus — second most common; seen in immunocompromised, HIV, post-COVID patients
• Staphylococcus aureus (including MRSA)
• Klebsiella pneumoniae, Proteus mirabilis
• Polymicrobial infections in severely immunocompromised hosts

Predisposing Conditions

1. Diabetes mellitus — impaired neutrophil function, microangiopathy, reduced tissue perfusion
2. HIV/AIDS and other immunodeficiency states
3. Haematological malignancies (leukemia, lymphoma)
4. Long-term corticosteroid/immunosuppressant therapy
5. Old age (immunosenescence)
6. Post-COVID-19 mucormycosis/immunosuppression
7. Radiotherapy to head and neck (osteoradionecrosis predisposes)
8. Malnutrition

SURGICAL ANATOMY — RELEVANT TO SKULL BASE OSTEOMYELITIS

External Auditory Canal (EAC)
        ↓  (Santorini's Fissures / Huschke's foramen)
Periparotid / Retrocondylar Space
        ↓
Stylomastoid Foramen (CN VII — Facial nerve)
        ↓
Jugular Foramen (CN IX, X, XI)  ←→  Internal Jugular Vein Thrombosis
        ↓
Hypoglossal Canal (CN XII)
        ↓
Petrous Apex / Clivus
        ↓
Intracranial: Meningitis / Sigmoid Sinus Thrombosis / Brain Abscess

• Infection begins at the bony-cartilaginous junction of the EAC
• Spreads via Santorini's fissures (defects in the cartilaginous EAC floor) into the periparotid fat
• Then to the stylomastoid foramen → facial nerve palsy
• Medially to the jugular foramen → multiple cranial nerve palsies (IX, X, XI)
• Anteriorly → temporomandibular joint → trismus
• Medially → clivus, petrous apex → CN VI palsy (Gradenigo's syndrome variant)
• Intracranially → meningitis, epidural abscess, dural sinus thrombosis

PATHOGENESIS

┌─────────────────────────────────────────────────────────────┐
│                  PATHOGENESIS FLOWCHART                      │
└─────────────────────────────────────────────────────────────┘

 Immunocompromised Host (DM, HIV, etc.)
             ↓
 Trauma / Instrumentation / Water exposure → Pseudomonas colonization of EAC
             ↓
 Breach in epithelium of EAC (bony-cartilaginous junction)
             ↓
 Bacterial invasion → Periostitis → Osteitis
             ↓
 Impaired host defense + Pseudomonal virulence factors
 (exotoxin A, elastase, alkaline protease, phospholipase C)
             ↓
 Endarteritis obliterans of small vessels → Tissue ischemia
             ↓
 Necrosis and progressive osteomyelitis of skull base
             ↓
 Spread along fascial planes and foramina
             ↓
 Cranial Nerve Involvement → Intracranial Extension

CLINICAL FEATURES

Classic Triad (Meltzer & Kelemen)

1. Severe otalgia — disproportionate, deep, boring, worse at night
2. Otorrhoea — purulent, foul-smelling
3. Immunocompromised host (usually elderly diabetic)

Symptoms (in order of progression)

Signs

• Granulation tissue at bony-cartilaginous junction of EAC (pathognomonic)
• Tenderness over mastoid and periauricular region
• Periauricular cellulitis, induration
• Tragal tenderness
• Tympanic membrane usually intact (differentiates from CSOM)

CHANDLER'S CLASSIFICATION (1968)

DIFFERENTIAL DIAGNOSIS

INVESTIGATIONS

Laboratory Investigations

Imaging Investigations

1. High-Resolution CT (HRCT) Temporal Bone

• Best for cortical bone destruction (Bailey & Love, 28th ed., p. 625)
• Findings:
  • Soft tissue density in EAC
  • Erosion of bony EAC and adjacent skull base
  • Involvement of temporomandibular joint
  • Petrous apex erosion
• Limitation: Cannot assess soft tissue extent or marrow involvement early

2. MRI with Gadolinium Contrast (Investigation of Choice)

• Superior for soft tissue and marrow involvement
• T1: Low signal in marrow (replacing normal fat signal)
• T1 with Gad + fat saturation: Enhancement of infected areas
• T2: High signal oedema; "ink smudge" pattern in parapharyngeal abscess (pathognomonic on T2)
• Assesses: parapharyngeal spread, jugular vein/sigmoid sinus thrombosis, intracranial extension
• Best for monitoring treatment response

3. Radionuclide Scanning

4. Biopsy

• Granulation tissue biopsy from EAC: mandatory to exclude carcinoma of EAC
• Culture and histology
• Guides antibiotic selection
• Note: Negative biopsy does not rule out SBO

DIAGNOSTIC CRITERIA

1. Refractory otitis externa (>1 month)
2. Severe otalgia
3. Granulation tissue in EAC
4. Positive culture for Pseudomonas
5. Evidence of bone erosion on imaging
6. Positive bone scan
7. Immunocompromised host (usually DM)
8. Failure to respond to topical treatment

MRI/CT IMAGING

TREATMENT

Principles of Management

┌──────────────────────────────────────────────────────────────────┐
│              MANAGEMENT ALGORITHM — SBO / MOE                    │
└──────────────────────────────────────────────────────────────────┘

DIAGNOSIS CONFIRMED
        ↓
┌───────────────────────────────┐
│  1. Control Predisposing      │
│     Condition                 │
│  (Tight glycaemic control;    │
│   HbA1c target <7%)           │
└──────────────┬────────────────┘
               ↓
┌───────────────────────────────┐
│  2. Culture-Guided Antibiotic │
│     Therapy                   │
│  (Anti-Pseudomonal regimen)   │
└──────────────┬────────────────┘
               ↓
┌───────────────────────────────┐
│  3. Local Aural Toilet        │
│  Meticulous debridement of EAC│
│  Topical antibiotic drops     │
└──────────────┬────────────────┘
               ↓
┌───────────────────────────────┐
│  4. Monitor Response          │
│  ESR / CRP / Gallium scan /   │
│  FDG-PET CT / MRI             │
└──────────────┬────────────────┘
               ↓
    ┌──────────┴──────────┐
    ↓                     ↓
IMPROVING              NOT IMPROVING
Continue              ↓
antibiotics        Surgical debridement
(min. 6–8 wks)     ± Hyperbaric O₂ therapy
                   Review culture sensitivities

A. Medical Management

1. Control of Predisposing Factors

• Strict glycaemic control — most critical step; without this, no antibiotic will work
• Insulin therapy preferred in acute phase
• Treatment of underlying immunosuppression

2. Antibiotic Therapy

• Oral bioavailability equivalent to IV (~80%)
• Excellent bone penetration
• Drug of choice for oral outpatient management after initial IV stabilisation
• Resistance emerging — culture and sensitivity mandatory

• Voriconazole — drug of choice (6 mg/kg loading, then 4 mg/kg BD IV)
• Liposomal Amphotericin B (alternative)
• Duration: minimum 12 weeks or until clinical/radiological resolution

3. Topical Treatment

• Aural toilet under microscope — essential
• Topical ciprofloxacin drops (0.3%)
• Removal of granulation tissue under microscopy
• No water entry — strict ear precautions

4. Hyperbaric Oxygen Therapy (HBO)

• Adjunctive therapy — especially in refractory/relapsing cases
• Mechanism: increases tissue pO₂ → enhances neutrophil bactericidal activity, promotes angiogenesis, inhibits anaerobes
• Protocol: 2–2.5 atmospheres, 100% O₂, 90 min sessions, 20–40 sessions
• Shown to reduce recurrence rates
• (Scott-Brown's 8th ed.; Hazarika)

5. Pain Management

• NSAIDs, opioid analgesics for severe nocturnal pain
• Neuropathic pain — Gabapentin/Pregabalin for CN involvement

B. Surgical Management

1. Failed medical management (>6 weeks)
2. Biopsy to exclude carcinoma
3. Intracranial complications
4. Sequestrum formation
5. Abscess drainage

• Debridement — most common; removal of necrotic bone and granulation tissue
• Mastoidectomy (modified radical) — if mastoid involvement
• Drainage of intracranial collections — if abscess/empyema
• Rarely: subtotal temporal bone resection (extensive disease)
• Facial nerve decompression — controversial; generally NOT done acutely

MONITORING TREATMENT RESPONSE

• Minimum 6–8 weeks of antibiotics
• Until: ESR normalises + Gallium scan normalises + clinical resolution
• In severe/fungal cases: 12–18 months may be required

COMPLICATIONS

Local Complications

• Mastoiditis
• Temporomandibular joint involvement → trismus
• Parotitis
• Soft tissue necrosis

Cranial Nerve Complications

• Facial nerve palsy (CN VII) — most common
• Multiple cranial nerve palsies (see table above)

Intracranial Complications

• Sigmoid sinus thrombosis / Internal jugular vein thrombosis
• Meningitis
• Epidural abscess
• Brain abscess
• Subdural empyema
• Temporal lobe abscess
• Leptomeningeal spread

Systemic Complications

• Septicaemia / Bacteraemia
• Death (mortality 10–20% with treatment; >50% untreated or with intracranial involvement)

PROGNOSIS

RECENT ADVANCES

1. Changing Epidemiology

• Increasing incidence of Aspergillus SBO in non-diabetic immunocompromised patients (HIV, post-transplant, haematological malignancies)
• Post-COVID-19 SBO — mucormycosis and Aspergillus-related SBO reported, linked to steroid use and immune dysregulation (Literature 2021–2023)
• MRSA-related SBO emerging in developed countries

2. Diagnostic Advances

• FDG-PET/CT now considered gold standard for:
  • Early diagnosis
  • Monitoring treatment response
  • Detecting subclinical recurrence
  • Superior to Gallium-67 in sensitivity and specificity (Bailey & Love, 28th ed., p. 625)
• High-resolution MRI 3T with DWI sequences for better delineation
• Whole-body MRI for multifocal SBO

3. Biomarkers

• Procalcitonin — emerging marker for bacterial SBO; guides antibiotic therapy
• Serum galactomannan / Beta-D-glucan — for fungal SBO diagnosis
• Cytokine panels (IL-6, TNF-α) — research stage

4. Fungal SBO Protocol

• WHO 2022 classification recognises fungal SBO as distinct entity requiring different treatment algorithm
• Endoscopic biopsy under image guidance (CT-guided transtympanic) for deep culture
• Combination antifungal therapy (Voriconazole + Caspofungin) in refractory Aspergillus SBO

5. Genetic and Immunological Profiling

• STAT3, DOCK8, MyD88 mutations predisposing to recurrent SBO in children
• Neutrophil functional studies in non-diabetic SBO

6. Drug-Eluting Implants

• Local ciprofloxacin-releasing biodegradable implants being trialled for EAC debridement
• Reduces systemic side effects and maintains local drug concentration

7. Surgical Navigation

• Intraoperative CT navigation for skull base debridement — improving surgical precision and reducing morbidity

8. Telemedicine and Outpatient IV Therapy

• Home IV ciprofloxacin via PICC line with telemedicine monitoring — reducing hospital stay without compromising outcomes (UK OPAT guidelines, 2022)

SUMMARY FLOWCHART — COMPLETE MANAGEMENT

SUSPECTED SBO
(Elderly/Diabetic + Severe Otalgia + Granulation in EAC)
        ↓
INVESTIGATIONS:
• Blood: FBS, HbA1c, ESR, CRP, CBC
• Culture: EAC swab, blood culture
• Imaging: HRCT + MRI with Gadolinium
• Radionuclide: Gallium-67 scan / FDG-PET CT
• Biopsy: Exclude carcinoma
        ↓
DIAGNOSIS CONFIRMED
        ↓
        ┌─────────────────────────────────────────┐
        │  MEDICAL MANAGEMENT                     │
        │  1. Strict glycaemic control (insulin)  │
        │  2. IV Anti-Pseudomonal antibiotics      │
        │     (Pip-Taz / Ceftazidime + Tobramycin)│
        │  3. Step-down to oral Ciprofloxacin      │
        │  4. Topical Ciprofloxacin ear drops      │
        │  5. Aural toilet (microscopic)           │
        │  6. Pain management                      │
        └──────────────────────┬──────────────────┘
                               ↓
                    MONITOR RESPONSE
                  (ESR, CRP, Gallium scan)
                    ↓              ↓
               IMPROVING      NOT IMPROVING
               Continue      ↓
               (min 6–8 wk)  Consider:
                             • Repeat culture/biopsy
                             • Surgical debridement
                             • HBO therapy
                             • Antifungal (if fungal)
                               ↓
                    CURE = Normalised ESR +
                    Negative Gallium scan +
                    Clinical Resolution
                               ↓
                    FOLLOW-UP 12–18 months
                    (Watch for recurrence)

IMPORTANT POINTS FOR RGUHS EXAMINATION

1. Most common organism: Pseudomonas aeruginosa
2. Most common predisposing condition: Diabetes mellitus
3. Pathognomonic sign: Granulation tissue at bony-cartilaginous junction of EAC
4. Most common cranial nerve involved: CN VII (Facial nerve — stylomastoid foramen)
5. Granulation tissue must be biopsied to exclude squamous cell carcinoma of EAC
6. Investigation of choice for early diagnosis: Gallium-67 scan (or FDG-PET CT in modern practice)
7. Investigation of choice for soft tissue extent: MRI with gadolinium
8. Best monitoring scan: Gallium-67 (classic); FDG-PET CT (current gold standard)
9. Drug of choice: Ciprofloxacin (oral) — excellent bioavailability + bone penetration
10. Duration of treatment: Minimum 6–8 weeks; until Gallium scan normalises
11. Chandler coined the term "Malignant Otitis Externa" (1968)
12. TM is usually intact — differentiates from CSOM-related complications
13. Fungal SBO (Aspergillus) — increasing in post-COVID, HIV patients; treat with Voriconazole
14. Vernet's Syndrome = CN IX, X, XI (jugular foramen)
15. Multiple lower CN palsies = poor prognosis

REFERENCES

1. Scott-Brown's Otorhinolaryngology, Head & Neck Surgery — 8th Edition (Gleeson et al.) — External Ear, Vol. 3
2. Cummings Otolaryngology — Head and Neck Surgery — 7th Edition (Flint et al.) — Chapter on External Ear Diseases
3. Stell and Maran's Head and Neck Surgery — 4th Edition — Skull base infections
4. Diseases of Ear, Nose and Throat — P.L. Dhingra, 7th Edition — Chapter on Otitis Externa
5. ENT and Head & Neck Surgery — Hazarika P. — Chapter on Malignant Otitis Externa
6. Textbook of ENT — Zakir Hussain — External Ear disorders
7. Harrison's Principles of Internal Medicine — 21st Edition, p. 11393 — Invasive otitis externa in immunocompromised
8. Bailey & Love's Short Practice of Surgery — 28th Edition, p. 625 — Osteomyelitis: CT/MRI/FDG-PET
9. Chandler JR — Malignant external otitis. Laryngoscope. 1968;78(8):1257–1294
10. Meltzer PE, Kelemen G — Pyocyaneous osteomyelitis of the temporal bone, mandible and zygoma. Laryngoscope. 1959
11. Cohen D, Friedman P — The diagnostic criteria of malignant external otitis. J Laryngol Otol. 1987
12. Rubin J, Yu VL — Malignant external otitis: Insights into pathogenesis, clinical manifestations, diagnosis and therapy. Am J Med. 1988
13. Contrera KJ et al. — FDG-PET/CT for diagnosis and monitoring of skull base osteomyelitis. Laryngoscope, 2021
14. Stern Shavit S et al. — Defining the outcome of antibiotics for skull base osteomyelitis. Clin Otolaryngol. 2019
15. WHO Fungal Priority Pathogens List — 2022 — Aspergillus fumigatus, Mucor spp.

Word to the wise for RGUHS: This topic carries 50 marks and the examiner expects: definition + epidemiology + aetiology + pathogenesis flowchart + detailed clinical features with CN table + Chandler's classification + investigations with comparison table + management algorithm flowchart + recent advances. Diagrams of anatomical spread pathways and management flowcharts are essential for full marks.