Malignancy of the External Auditory Canal (EAC)

A Comprehensive Essay for 50 Marks | RGUHS ENT

INTRODUCTION

"SCC is the most common primary malignancy of the temporal bone." — K.J. Lee's Essential Otolaryngology, p. 491

ANATOMY RELEVANT TO EAC MALIGNANCY

┌─────────────────────────────────────────────────────────────┐
│               EXTERNAL AUDITORY CANAL                        │
│                                                              │
│  Outer 1/3: Cartilaginous (fibrocartilage)                  │
│             - Ceruminous glands, hair follicles              │
│             - Fissures of Santorini → parotid spread        │
│                                                              │
│  Inner 2/3: Osseous (tympanic bone)                         │
│             - Thin skin, no adnexa                          │
│             - Close to: TM, middle ear, mastoid, facial n.  │
│                                                              │
│  LENGTH: ~25 mm  |  Lined by squamous epithelium            │
└─────────────────────────────────────────────────────────────┘
         ↓ Anteriorly          ↓ Superiorly    ↓ Posteriorly
    Parotid / TMJ          Tegmen / Middle    Mastoid
                           cranial fossa      cortex

• Anterior canal wall / lateral pinna → Pre-auricular (parotid) nodes
• Posterior canal wall / upper pinna → Post-auricular nodes
• Floor of EAC / lobule → Superficial and deep cervical nodes (levels II–III)
• Nodes → ultimately drain into deep cervical chain (K.J. Lee's Essential Otolaryngology, p. 471)

AETIOPATHOGENESIS & RISK FACTORS

PATHOLOGY

Histological Types

EAC MALIGNANCIES
│
├── Squamous Cell Carcinoma (SCC) ─────── MOST COMMON (~60-70%)
│       └── Well / moderately / poorly differentiated
│
├── Basal Cell Carcinoma (BCC) ──────────── ~45% of all ear skin cancers
│       └── Serpiginous ulceration, lacks pearly edges in canal
│
├── Adenoid Cystic Carcinoma (AdCC) ─────── Perineural spread ++
│       └── Appears as small pimple; severe pain; slow growing
│
├── Ceruminous Adenocarcinoma ───────────── Arises from ceruminous glands
│
├── Mucoepidermoid Carcinoma
│
├── Malignant Melanoma ──────────────────── 7% of H&N sites involve ear
│
└── Sarcoma / Rhabdomyosarcoma (children)

CLINICAL FEATURES

Symptoms (in decreasing order of frequency)

"Persistence of otitis externa despite adequate management by routine treatment measures should increase suspicion for carcinoma." — Cummings Otolaryngology, p. [Ch. 178]

Signs on Examination

• Polypoid / meaty / granular lesion in EAC
• Foul-smelling or blood-stained discharge
• BCC: serpiginous ulceration (no pearly rolled edges — thin canal skin)
• AdCC: epithelium-covered, nodular, intensely painful lesion
• Hard, fixed parotid mass / pre-auricular or cervical lymphadenopathy
• Facial nerve palsy (LMN type)
• Cranial nerve involvement in advanced stages (V, IX, X, XI, XII)

DIFFERENTIAL DIAGNOSIS

Malignant EAC Lesion (Blood-stained discharge + otalgia)
        │
        ├── Malignant Otitis Externa (MOE / Skull base osteomyelitis)
        │       - Pseudomonas; diabetic/elderly; granulation at BCC junction
        │       - Radiologically indistinguishable → BIOPSY mandatory
        │
        ├── Keratosis Obturans (EAC cholesteatoma)
        │
        ├── Chronic Otitis Externa
        │
        └── Necrotising (Malignant) Otitis Externa

"CT and MRI alone cannot differentiate MOE from malignancy — biopsy of any unusual EAC tissue is mandatory." — Cummings Otolaryngology

INVESTIGATIONS

1. Biopsy

• Mandatory — punch biopsy of granular tissue
• Beware pseudoepitheliomatous hyperplasia (benign mimic requiring expert histopathological review)

2. Audiological Assessment

• Pure tone audiometry: conductive vs sensorineural loss
• Tuning fork tests

3. Imaging

HRCT Temporal Bone (First-line)

• Demonstrates bony destruction of EAC walls
• Extent to middle ear, mastoid, otic capsule, carotid canal
• Heterogeneously enhancing mass with aggressive bone destruction

Fig 1. Coronal HRCT of the right EAC showing aggressive bony destruction of the canal floor (SCC) — Cummings Otolaryngology (Fig. 135.16)

MRI Temporal Bone + Neck

• T1WI: Low signal mass with peripheral enhancement
• T2WI: Heterogeneous high signal
• Superior to CT for: dural, intracranial, perineural (AdCC), and soft tissue involvement

CT Neck with Contrast

• Parotid/pre-auricular and cervical lymphadenopathy
• Necrotic nodes = established metastatic disease

Fig 2. Axial post-contrast CT showing necrotic parotid node (arrow) from EAC SCC primary — Cummings Otolaryngology (Fig. 135.17)

CT Chest / PET-CT

• Distant metastasis (lung most common)
• PET-CT increasingly used for staging and post-treatment surveillance

STAGING

Modified University of Pittsburgh Staging System (Arriaga & Janecka, modified by Moody et al. 2000)

┌──────────────────────────────────────────────────────────────────────────┐
│        MODIFIED UNIVERSITY OF PITTSBURGH TNM STAGING (EAC / Temporal Bone) │
├─────────┬──────────────────────────────────────────────────────────────── ┤
│ T Stage │ Extent of Disease                                               │
├─────────┼────────────────────────────────────────────────────────────────┤
│   T1    │ Tumor limited to EAC — no bony erosion, no soft tissue         │
│         │ extension                                                       │
├─────────┼────────────────────────────────────────────────────────────────┤
│   T2    │ Limited bony EAC erosion (not full-thickness) OR               │
│         │ < 0.5 cm soft tissue involvement                               │
├─────────┼────────────────────────────────────────────────────────────────┤
│   T3    │ Full-thickness bony EAC erosion with < 0.5 cm soft tissue      │
│         │ involvement OR involves middle ear AND/OR mastoid              │
├─────────┼────────────────────────────────────────────────────────────────┤
│   T4    │ Erodes medial wall of middle ear to involve:                   │
│         │ cochlea, labyrinth, petrous apex, jugular foramen,             │
│         │ carotid canal, dura; OR > 0.5 cm soft tissue (TMJ,            │
│         │ styloid, parotid); OR facial nerve palsy                      │
└─────────┴────────────────────────────────────────────────────────────────┘

NODAL STATUS:
  N0 — No regional lymph node metastasis
  N+ — Regional lymph node metastasis (→ automatically Stage III/IV)

METASTATIC STATUS:
  M0 — No distant metastasis
  M1 — Distant metastasis (→ automatically Stage IV)

Overall Stage Grouping (University of Pittsburgh)

"Involvement of lymph nodes is a poor prognostic finding and automatically places the patient in an advanced stage." — Cummings Otolaryngology (Box 178.2)

Pittsburgh vs. Other Staging Systems

MANAGEMENT

Management Algorithm

                     SUSPECTED EAC MALIGNANCY
                              │
                     Biopsy (Histopathology)
                              │
             ┌────────────────┴────────────────┐
         BENIGN                            MALIGNANT
             │                                 │
        Follow up              HRCT + MRI Temporal Bone
                                      CT Neck + Chest
                                      PET-CT (if T3/T4)
                                      Audiogram
                                              │
                              STAGING (University of Pittsburgh)
                                              │
              ┌──────────┬──────────┬─────────┴──────────┐
             T1          T2         T3                    T4
              │           │          │                     │
          Sleeve      Lateral    Sub-total          Total/near-total
         Resection    TBR (LTBR) TBR (STBR)         TBR ± parotidectomy
              │           │          │               ± neck dissection
              │           └──────────┴─────────────────────┤
                          Parotidectomy if parotid involved  │
                          Neck dissection if N+ (or T3/T4)  │
                                              │
                                   POST-OPERATIVE XRT
                                (T2 and above — all cases)
                                ± Concurrent chemotherapy
                                  (T4, +ve margins, N+)

Surgical Options

1. Sleeve Resection (Canaloplasty)

• Indication: T1 — tumour limited to skin of EAC, no bone invasion
• Technique: Skin of bony EAC + cartilaginous EAC portion ± tympanic membrane excised; bony canal left intact
• Margin: Must be histologically negative

2. Lateral Temporal Bone Resection (LTBR)

• Indication: T2 (limited bony erosion) and early T3
• Removes: EAC en bloc — bony EAC + tympanic membrane + malleus + incus + cartilaginous canal
• Facial nerve preserved if not involved
• Technique:
  • C-shaped post-auricular incision into cervical crease
  • Intra-canal incision in cartilaginous EAC encompassing the lesion
  • Flap elevated anteriorly to zygomatic root
  • Subperiosteal mastoidectomy
  • Canal sectioned at bony-cartilaginous junction → closed in layers
  • Temporalis muscle / TPF flap preserved for reconstruction

3. Subtotal Temporal Bone Resection (STBR)

• Indication: T3 (middle ear and/or mastoid involvement)
• Removes: LTBR specimen + petrous apex, otic capsule drilling to negative margins
• Petrous ICA and dura preserved if uninvolved
• Parotidectomy + neck dissection frequently required

4. Total Temporal Bone Resection (TTBR)

• Indication: T4 — extension to cochlea, carotid canal, jugular foramen, dura
• Includes: STBR + sigmoid sinus ± petrous carotid artery
• No proven survival benefit over STBR + adjuvant therapy in most series
• Very few centres offer this procedure
• Sacrifice of facial nerve almost inevitable → immediate cable graft reconstruction

Fig 3. Diagram illustrating Lateral Temporal Bone Resection, Subtotal Temporal Bone Resection, and Total Temporal Bone Resection — Schwartz's Principles of Surgery (Fig. 18-35)

5. Parotidectomy and Neck Dissection

• Parotidectomy: when tumour reaches parotid via fissures of Santorini or direct extension
• Prophylactic parotidectomy ± neck dissection: recommended for T3 and T4 disease even when N0 (occult nodal rate ~10–20%)
• Therapeutic neck dissection: for N+ disease
• Regional failure after surgery is the most common cause of death

Summary: Surgery by Stage

ADJUVANT THERAPY

Radiotherapy

• Standard recommendation: post-operative radiation for T2 and above
• Dose: 60–66 Gy (conventional fractionation) to temporal bone ± bilateral neck
• May include contralateral neck and parotid nodal basins in advanced cases
• Positive margins + RT → still almost uniformly fatal in carcinomas of the EAC
• SCC and BCC: radiosensitive
• AdCC: Intermediate; post-op RT reduces local recurrence

Chemotherapy

• Concomitant chemoradiotherapy (cisplatin-based) considered for:
  • T4 tumours
  • Positive/close surgical margins
  • Nodal disease (N+)
  • Perineural invasion (especially AdCC)
• Not established as primary therapy

Palliative Radiation

• For T4 patients where en bloc resection would be excessively deforming or futile
• Acceptable alternatives: lateral TBR + subtotal petrosectomy or total petrosectomy with chemoradiotherapy

SPECIAL HISTOLOGICAL TYPES

Adenoid Cystic Carcinoma (AdCC) of EAC

• Arises from ceruminous glands
• Perineural spread — hallmark feature; extensive skip lesions along nerve sheaths
• Clinically: intense otalgia, small pimple-like lesion
• Imaging: MRI essential to delineate perineural extension
• Treatment: wide surgery + post-op radiotherapy
• Proton beam / carbon ion therapy: 5-year local control >70% (K.J. Lee's, p. 491)
• Prognosis: late metastases (lung) even after apparent cure; 10-year survival better than expected

Basal Cell Carcinoma (BCC) of EAC

• Most common malignancy of the ear overall (~45%)
• Presents as erythematous lesion with raised margins
• Serpiginous ulceration in the canal (no pearly edges — thin adherent skin)
• Treatment: wide local excision; may require cartilage excision, skin graft, or local flaps
• Post-op RT in advanced or recurrent cases

RECONSTRUCTION

• Meatoplasty / split-skin graft: T1–T2 after sleeve resection
• Temporalis muscle flap / TPF flap: obliteration of cavity after LTBR
• Rectus abdominis free flap or pectoralis major flap: large defects after auriculectomy + STBR/TTBR
• Facial nerve grafting: cable graft (sural / great auricular nerve) at time of resection

PROGNOSIS AND OUTCOMES

1. Facial nerve palsy (T4 automatic → poor)
2. Positive surgical margins
3. Lymph node metastasis
4. Dural invasion
5. Delayed diagnosis

RECENT ADVANCES

FLOWCHART SUMMARY

CLINICAL PRESENTATION
Otalgia + Blood-stained discharge + Granular EAC polyp
                    │
         ┌──────────▼──────────┐
         │   CLINICAL EXAM     │
         │ + Audiometry         │
         └──────────┬──────────┘
                    │
         ┌──────────▼──────────┐
         │  BIOPSY (Mandatory) │
         │  Histopathology     │
         └──────────┬──────────┘
                    │
       ┌────────────▼────────────┐
       │  RADIOLOGICAL STAGING   │
       │  HRCT Temporal bone     │
       │  MRI + CT Neck/Chest   │
       │  PET-CT (T3/T4)        │
       └────────────┬────────────┘
                    │
       ┌────────────▼────────────────────────────────┐
       │   MODIFIED PITTSBURGH STAGING SYSTEM         │
       └─────┬──────┬──────┬────────────────┬────────┘
             │      │      │                │
            T1     T2     T3               T4
             │      │      │                │
          Sleeve   LTBR   STBR        STBR/TTBR
         Resect.        +Parotid     +Parotid+ND
                        ±ND          +Flap recon
             │      │      │                │
             └──────┴──────┴────────────────┘
                          │
               PORT-OP RADIOTHERAPY (T2+)
               ± CONCURRENT CHEMOTHERAPY
               (T4, N+, +ve margins)
                          │
              SURVEILLANCE (6-monthly imaging)
                          │
              RECURRENCE? → Salvage surgery
                           or Palliation

KEY POINTS FOR EXAMINATION (RGUHS)

1. Most common malignancy of EAC = SCC (followed by BCC, AdCC)
2. Commonest presenting symptom = Otalgia + blood-stained otorrhoea
3. Facial palsy = T4 (poor prognosis) — automatic upstaging
4. Staging system used = Modified University of Pittsburgh (Arriaga & Janecka, modified by Moody 2000)
5. T1 → sleeve resection; T2 → LTBR; T3 → STBR; T4 → STBR/TTBR
6. Positive margins = near universally fatal even with post-op RT
7. MOE vs carcinoma — biopsy mandatory to differentiate
8. AdCC = perineural spread; intense pain; proton beam therapy
9. BCC = most common ear skin malignancy (45%); serpiginous ulceration
10. Post-op RT mandatory for T2 and above

REFERENCES / TEXTBOOK CITATIONS