A 28-year-old woman presents with a 3-year history of recurrent ear discharge and progressive hearing loss in the right ear. She reports a history of ear infection at age 8 following measles. On examination, there is a small perforation in the posterosuperior quadrant with a white, gritty mass visible. Audiometry shows a 40 dB air-bone gap. She is counselled about surgical management. Which of the following is the MOST important preoperative investigation to determine the surgical approach?

Explanation

## Preoperative Assessment of Cholesteatoma **Key Point:** HRCT temporal bone is the gold standard preoperative imaging for cholesteatoma, essential for surgical planning and assessing complications. ### Why HRCT is Critical for Surgical Planning | Imaging Modality | Role in Cholesteatoma | Limitation | |------------------|----------------------|------------| | **HRCT** | Defines extent, ossicular erosion, canal wall status, SCC/labyrinth/facial nerve involvement | Cannot differentiate residual from recurrent disease | | **MRI (DWI)** | Detects residual/recurrent disease, differentiates from granulation | Not for initial surgical planning; used postoperatively | | **Tympanometry** | Assesses middle ear compliance (type B = flat) | Non-specific; does not guide surgical approach | | **VEMP** | Detects labyrinthine fistula if symptomatic | Not routine; only if vertigo present | **High-Yield:** HRCT is **mandatory** before any cholesteatoma surgery to: 1. Assess **ossicular chain integrity** (malleus, incus, stapes erosion) 2. Determine **canal wall status** (intact vs. eroded) → guides canal wall-up vs. canal wall-down approach 3. Detect **labyrinthine fistula** (SCC erosion) 4. Evaluate **facial nerve canal** for erosion 5. Assess **mastoid pneumatization** and extent of disease ### Surgical Decision Tree ```mermaid flowchart TD A[Cholesteatoma diagnosis confirmed]:::outcome --> B[HRCT Temporal Bone]:::action B --> C{Canal wall status?}:::decision C -->|Intact| D[Canal wall-up mastoidectomy]:::action C -->|Eroded| E[Canal wall-down mastoidectomy]:::action B --> F{Ossicular erosion?}:::decision F -->|Yes| G[Plan ossiculoplasty]:::action F -->|No| H[Ossicular chain preserved]:::action B --> I{SCC fistula?}:::decision I -->|Yes| J[Intraoperative precautions]:::urgent I -->|No| K[Standard approach]:::action ``` **Clinical Pearl:** **Canal wall-up (CWU) vs. Canal wall-down (CWD):** - **CWU:** Preserves canal integrity; lower morbidity but higher recurrence risk (10–40%) - **CWD:** Higher recurrence control but results in chronic drainage, hearing loss, water precautions - **HRCT findings guide choice:** Extensive disease with SCC erosion favours CWD ### Ossicular Erosion Patterns **Mnemonic — Order of Ossicular Erosion (MIST):** - **M**alleus (least commonly eroded) - **I**ncus (most commonly eroded; long process vulnerable) - **S**tapes (eroded in advanced disease) - **T**ympanic membrane (perforation) **High-Yield:** Incus long process erosion is the **most common** ossicular finding in cholesteatoma, leading to conductive hearing loss. ### Why Other Options Are Incorrect - **Tympanometry:** Shows type B (flat) tracing in any middle ear disease with perforation; non-specific and does not guide surgical approach - **MRI with DWI:** Useful **postoperatively** to detect residual/recurrent disease; not needed for initial surgical planning - **VEMP:** Only indicated if patient has vertigo; not routine preoperative assessment **High-Yield:** MRI is increasingly used **post-surgery** (6–12 months) to detect residual disease, but HRCT is the **preoperative standard** for surgical planning.