A 32-year-old man presents with a 10-year history of foul-smelling otorrhoea from the left ear, conductive hearing loss, and recurrent ear discharge despite topical antibiotics. On otoscopy, a large perforation is seen with granulation tissue and polyps in the external auditory canal. Which investigation is most appropriate to assess the extent of bone erosion and guide surgical planning?

Question

Accepted Answer

A. High-resolution computed tomography (HRCT) of the temporal bone. ## Investigation of Choice in CSOM with Suspected Bone Erosion

**Key Point:** HRCT temporal bone is the gold standard imaging modality for assessing ossicular erosion, mastoid pneumatization, and bony erosion in chronic suppurative otitis media (CSOM), especially when surgical intervention is being considered.

### Why HRCT is Superior

**High-Yield:** HRCT provides:
- Excellent bony detail with sub-millimeter resolution
- Clear visualization of ossicular chain integrity (malleus, incus, stapes)
- Assessment of mastoid pneumatization and sclerosis
- Detection of tegmental dehiscence or sinus plate erosion
- Evaluation of facial nerve canal integrity
- Identification of cholesteatoma (if present) with high sensitivity

**Clinical Pearl:** In this patient with 10 years of active discharge, granulation tissue, and polyps, there is high risk of ossicular erosion and possible mastoid bone involvement. HRCT guides the surgeon on the extent of disease and helps plan the surgical approach (canal wall-up vs. canal wall-down mastoidectomy).

### Comparison with Other Modalities

| Investigation | Role in CSOM | Limitation |
|---|---|---|
| **HRCT temporal bone** | **Gold standard for bone erosion, ossicular status** | **Cannot assess soft tissue detail as well as MRI** |
| MRI brain/IAC | Soft tissue detail, intracranial complications | Poor bone resolution; not first-line for ossicular assessment |
| Pure tone audiometry | Quantifies hearing loss; documents conductive component | Functional test only; does not show anatomical erosion |
| Otoacoustic emissions | Cochlear function assessment | No role in assessing middle ear bone disease |

**Mnemonic:** **HRCT-CSOM** = **H**igh-**R**esolution **C**T for **T**emporal bone in **C**hronic **S**uppurative **O**titis **M**edia

### Clinical Context

Given the presence of:
- Long-standing disease (10 years)
- Active granulation and polyps (suggest aggressive disease)
- Planned surgical intervention (likely needed)

...HRCT is essential to:
1. Confirm ossicular erosion (especially incus long process)
2. Assess mastoid pneumatization
3. Rule out tegmental or sinus plate erosion
4. Plan surgical approach and extent of mastoidectomy

![Chronic Suppurative Otitis Media diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3653.webp)

Answer

B. Magnetic resonance imaging (MRI) of the brain and internal auditory canal

Answer

C. Otoacoustic emissions testing

Answer

D. Pure tone audiometry and tympanometry

Explanation

Investigation of Choice in CSOM with Suspected Bone Erosion

Why HRCT is Superior

Comparison with Other Modalities

Clinical Context

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Investigation	Role in CSOM	Limitation
HRCT temporal bone	Gold standard for bone erosion, ossicular status	Cannot assess soft tissue detail as well as MRI
MRI brain/IAC	Soft tissue detail, intracranial complications	Poor bone resolution; not first-line for ossicular assessment
Pure tone audiometry	Quantifies hearing loss; documents conductive component	Functional test only; does not show anatomical erosion
Otoacoustic emissions	Cochlear function assessment	No role in assessing middle ear bone disease