Contents
Inflammatory process in external auditory canal (EAC) associated with ectopic proliferation of squamous tissue causing osteolysis.
- Very rare disease, representing 0.1–0.5% of otologic disease
Aetiology
Whatever the inciting factor/factors, EACC presents as extensive bony erosion due to a wide-mouthed sac lined by keratinizing stratified squamous epithelium with focal periosteitis and osteonecrosis.
Primary EACC:
Due to slowing of normal process of expulsion of keratin debris from external surface of tympanum and external auditory canal outward
- Other risk factors: Repeated microtrauma and persistence of first branchial cleft epithelium.
Secondary EACC:
Entrapment/isolation of pockets of keratin debris within the canal due to secondary causes. Secondary cases are usually less extensive than primary or less prominent symptoms
- Iatrogenic injuries: Surgery, trauma, radiation to EAC
- Stenosis following osteoma
- Exostosis
- Nevus
Clinical features
The clinical presentation of EACC is that of an elderly male with otorrhea and chronic dull earache.
- Otalgia and otorrhea (M/C features)
- Other features: External ear canal occlusion, hearing loss, itching
More extensive disease may present with labyrinthine fistula and facial nerve dysfunction
Diagnosis
Imaging is essential for diagnosis.
High-resolution computed tomography (HRCT):
Imaging modality of choice as it has a high spatial resolution and thus a very high sensitivity to delineate any soft tissue lesion in the petrous temporal bone. The interface between cholesteatoma and EAC is erosive; however, in the absence of osteolysis, HRCT findings are quite nonspecific because the soft tissue cannot be further characterized. Thus, the specificity of imaging diagnosis can be enhanced by addition of diffusion weighted imaging (DWI)
- Stage I: EACC limited to external auditory canal
- Stage II: EACC invades TM and middle ear
- Stage III: EACC creates defect of EAC and involves air cells in mastoid
- Stage IV: EACC beyond temporal bone
MRI:
MRI findings in cholesteatoma are nonspecific.
Diffusion weighted imaging (DWI):
Application of DWI was a breakthrough with cholesteatomas depicting high signal intensity due to T2 shine through and partly because of diffusion restriction.
Differential diagnosis:
Presence of soft tissue plug within the EAC without bone erosion is seen in keratosis obturans and post-inflammatory medial canal fibrosis whereas EACC, malignant otitis externa, and squamous cell carcinoma (SCC) of the EAC do show osteolysis.
- Keratosis obturans: Closest differential of EACC, presents with smooth widening of EAC. The clinical picture includes acute severe otalgia with conductive hearing loss whereas otorrhea is rare. There is a predilection for young age and bilateral involvement. Keratosis obturans bears a definite relationship with sinusitis and bronchiectasis. EACC is typically unilateral; however, occasionally it can involve bilateral EACs but in an asymmetric manner. Differentiation between the two entities is clinically important because management of keratosis obturans is medical.
- Post-inflammatory medial canal fibrosis: Fibrosis of medial canal of EAC (visualized on otoscopy) following an inflammatory event (chronic otitis externa and/or media)
- Malignant otitis externa (necrotizing external otitis): Diagnosis based on clinical presentation of elderly diabetic with rapidly progressive fulminant otitis externa diffusely involving adjacent soft tissues and skull base, presence of severe otalgia & otorrhea, isolation of pseudomonas aeruginosa as the offending microbe, presence of granulation tissue along the floor of EAC, and imaging findings of an enhancing soft tissue EAC lesion with infratemporal extension, which lacks diffusion restriction.
- Squamous cell carcinoma (SCC) of EAC: SCC arising in adjacent regions may secondarily involve canal rather than primary affliction of EAC. It is seen in elderly and presents with irregular erosion, but may be indistinguishable from EACC on imaging alone.
Management
Treatment of EACC depends on the extent of involvement. For smaller lesions localized to EAC, conservative management with frequent debridement is offered. For lesions beyond the EAC, surgery is the treatment of choice. Prognosis depends on the time when the lesion is detected. Higher rates of recurrence are seen in cases of larger lesions and bony erosions.
