A 28-year-old woman with a 3-year history of left ear discharge and conductive hearing loss attends the ENT clinic. Otoscopy shows a large central perforation with granulation tissue at the margins. Audiometry confirms 30 dB air-bone gap. CT temporal bone shows ossicular erosion and a small area of bone erosion in the posterosuperior canal wall. What is the most appropriate next step in management?

Explanation

## Clinical Interpretation **Key Point:** The combination of **granulation tissue at perforation margins** + **posterosuperior canal wall bone erosion on CT** raises suspicion for **occult cholesteatoma**, even though the CT does not show a definitive mass. ## Differential Diagnosis: CSOM vs. Cholesteatoma | Feature | Tubotympanic CSOM | Atticoantral CSOM/Cholesteatoma | |---------|-------------------|----------------------------------| | Perforation site | Central | Marginal (posterosuperior) | | Discharge | Mucoid, foul | Foul, scanty, blood-stained | | Granulation tissue | Absent | Present at margins | | Ossicular erosion | Incus > stapes | Malleus handle, all ossicles | | Canal wall erosion | Absent | **Posterosuperior canal wall** | | Conductive loss | 20–30 dB | Often mixed (bone loss if erosion severe) | | Imaging: CT findings | Ossicular erosion only | Ossicular erosion + **canal wall defect** | | Imaging: MRI role | Not needed | **Essential to detect cholesteatoma matrix** | **High-Yield:** MRI (diffusion-weighted imaging / DWI) is the **gold standard** for detecting cholesteatoma matrix when CT shows suspicious bone erosion but no definite mass. ## Why MRI Before Surgery? ```mermaid flowchart TD A[CSOM with posterosuperior canal wall erosion on CT]:::outcome --> B{MRI DWI performed?}:::decision B -->|No cholesteatoma detected| C[Canal wall up ossiculoplasty + tympanoplasty]:::action B -->|Cholesteatoma confirmed| D[Canal wall down mastoidectomy]:::urgent C --> E[Single-stage surgery]:::action D --> F[Staged approach if needed]:::action ``` **Clinical Pearl:** Posterosuperior canal wall erosion is a **red flag** for atticoantral disease. Even if CT shows no obvious mass, MRI DWI must be obtained to exclude cholesteatoma before planning canal wall up surgery. Missed cholesteatoma leads to residual/recurrent disease in 20–40% of cases. **Mnemonic: CSOM Red Flags for Cholesteatoma — GRACE** - **G**ranulation tissue at perforation margin - **R**ecurrent/resistant discharge despite treatment - **A**ttic/posterosuperior involvement - **C**anal wall erosion on imaging - **E**rosion of ossicles (malleus handle, all bones) **Tip:** If MRI shows cholesteatoma, canal wall down (CWD) mastoidectomy is safer than canal wall up (CWU) surgery, even though CWU preserves hearing better. CWD has lower recurrence (5–10%) vs. CWU (20–40%). [cite:Hazarika ENT 5e Ch 15; Dhingra ENT 8e Ch 10]