RD7.2 | Imaging in ASOM and CSOM — Summary & Reflection

KEY TAKEAWAYS

Imaging in ASOM and CSOM — Key Points

• ASOM is a clinical diagnosis; image only when a complication is suspected — acute (coalescent) mastoiditis, subperiosteal/neck abscess, facial palsy, labyrinthitis or intracranial spread. Routine scanning of uncomplicated otitis media is unjustified (ALARA).
• HRCT temporal bone is the workhorse for CSOM and complications: it maps disease extent, ossicular and scutum erosion, mastoid pneumatisation and the surgically critical tegmen, facial nerve canal and lateral semicircular canal — the surgical roadmap.
• CT cannot characterise soft tissue — cholesteatoma, granulation and cholesterol granuloma all look the same. Non-echo-planar (non-EPI) DWI MRI confirms cholesteatoma (restricts diffusion: bright DWI, low ADC; granulation does not) and detects recurrence; post-gadolinium MRI/MR venography shows intracranial complications and sigmoid sinus thrombosis.
• Cholesteatoma (unsafe CSOM) signs: non-dependent soft tissue in Prussak's space, scutum erosion, ossicular (incus long process/stapes) erosion, and the three dreaded erosions — tegmen, facial canal, lateral semicircular canal.
• Safe (mucosal/tubotympanic) CSOM: opacification/fluid without bone erosion.
• Management integration: complicated ASOM → cortical mastoidectomy ± abscess drainage / neurosurgical emergency; unsafe CSOM → choice and caution of mastoidectomy guided by HRCT erosions; ossiculoplasty for eroded ossicles; post-operative non-EPI DWI surveillance replaces routine second-look surgery.
• Plain mastoid X-ray is obsolete for this purpose; it cannot resolve the ossicles, scutum or critical canals.

REFLECT

On your next ENT or paediatric posting, watch how the team decides whether a discharging ear gets a scan. Notice the discipline of not imaging uncomplicated infection, and the speed with which a red flag — a boggy post-auricular swelling, a drooping face, a vertiginous patient — triggers an HRCT. When you next see a temporal-bone HRCT report, ask: did it comment on the tegmen, the facial canal and the lateral semicircular canal? Did the surgeon change the plan because of it? And if a cholesteatoma was uncertain, was DWI used to settle it? Consciously tracing the path from ear discharge to scan to operation — rather than treating imaging as a box to tick — is what turns radiological knowledge into clinical judgement.