External Auditory Canal Exostoses: Otoscopic Appearance
On otoscopic examination, external auditory canal exostoses appear as firm, sessile, multinodular bony masses arising from the tympanic ring in the bony portion of the external auditory canal, typically presenting as broad-based elevations of bone that are usually multiple and bilaterally symmetric.
Key Visual Characteristics
Exostoses have distinct otoscopic features that differentiate them from other ear canal pathology:
- Location: Arise specifically from the tympanic ring of the bony external auditory canal 1, 2
- Morphology: Broad-based, sessile (not pedunculated), multinodular bony elevations 1, 2
- Distribution: Typically multiple lesions and bilaterally symmetric 2
- Appearance: Smooth, bony protrusions covered by normal canal skin
Clinical Context
The guidelines identify exostoses as an anatomic abnormality that can predispose to acute otitis externa by narrowing the canal 3. These are "irritation nodules" that develop painlessly over years, most commonly from prolonged cold water exposure 1.
Severity grading is based on canal obstruction:
- Mild: <25% occlusion
- Moderate: 25-75% occlusion
- Severe: >75% occlusion 4
Symptoms typically don't appear until approximately 10 years of aquatic exposure, when obstruction becomes significant enough to trap cerumen or cause recurrent external otitis 1.
Critical Distinction: Exostoses vs. Osteomas
You must differentiate exostoses from osteomas on examination 2:
- Exostoses: Broad-based, multiple, bilateral, symmetric, arising from tympanic bone
- Osteomas: Discrete, pedunculated (on a stalk), usually solitary, arising along the tympanosquamous suture line 2
This distinction matters because the etiology and clinical behavior differ, though both are benign bony lesions.
Associated Findings
When exostoses become symptomatic, you may observe:
- Impacted cerumen trapped behind the bony narrowing 1
- Signs of acute external otitis (edema, erythema, debris) 3
- Conductive hearing loss secondary to canal occlusion 1, 5
The hearing loss is mechanical from obstruction, not from the exostoses themselves affecting the tympanic membrane or ossicular chain.