Types of human wax and definition of keratosis obturans
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Human Earwax (Cerumen) — Types and Composition
Definition
Cerumen (earwax) is a normal substance present in the external auditory canal (EAC). It is formed by a combination of:
- Glandular secretions from the sebaceous and apocrine glands located in the cartilaginous (outer one-third) portion of the EAC
- Desquamated (sloughed) squamous epithelial cells
- As it migrates laterally, it may also mix with hair and other particulate matter
It is composed of lipids, complex proteins, and simple sugars, and serves important protective functions:
- Hydrophobic — repels water, keeping the canal dry
- Acidic (pH 6.0–6.5) — creates an antimicrobial environment that protects the underlying epithelium and prevents infection
- Acts as a self-cleaning mechanism — cerumen slowly migrates laterally toward the external meatus through normal jaw movement and epithelial migration
— Cummings Otolaryngology Head and Neck Surgery, p. 2655; Textbook of Family Medicine 9e, p. 402; Roberts and Hedges' Clinical Procedures in Emergency Medicine
Types of Cerumen
There are two main genetic types of human cerumen:
| Feature | Wet (Moist) Type | Dry (Flaky) Type |
|---|---|---|
| Appearance | Yellow-brown, sticky, honey-like | Gray-white, dry, flaky |
| Consistency | Soft and adhesive | Hard and brittle |
| Genetics | Autosomal dominant; common in Europeans and Africans | Autosomal recessive; common in East Asians and Native Americans |
| Gene | ABCC11 (wild-type allele) | ABCC11 (single nucleotide polymorphism: 538G>A) |
| Lipid content | Higher | Lower |
| Body odor association | Higher (linked to axillary odor) | Lower |
The distinction is genetically determined by a single-nucleotide polymorphism in the ABCC11 gene on chromosome 16, which encodes an ATP-binding cassette transporter expressed in the apocrine glands of the EAC. The dry type results from reduced secretory activity of these glands.
(Note: The genetic detail of ABCC11 is well-established scientific knowledge; the textbooks in this library cover the clinical aspects of cerumen rather than its molecular genetics.)
Cerumen Impaction
A clinically significant finding occurs when cerumen accumulates and becomes impacted. This is present in approximately:
- 10% of children
- 5% of healthy adults
- 57% of older patients in nursing homes
- 36% of patients with intellectual disability
Risk factors include cotton-tip applicator use, narrow external canals, hearing aid or earplug use, and hair in the lateral canal.
— Cummings Otolaryngology Head and Neck Surgery
Keratosis Obturans
Definition
Keratosis obturans is an abnormal, diffuse disorder of the circumferential skin of the medial external auditory canal characterized by the accumulation of a dense plug of desquamating (hyperplastic) keratin that can completely occlude the auditory canal.
Key distinguishing features:
- It is a diffuse, circumferential process (involving the entire canal circumference) — contrasting with EAC cholesteatoma, which is focal and localized
- There is no erosive bony change (bony walls may be widened by pressure, but osteonecrosis is absent) — contrasting with EAC cholesteatoma, which causes bony erosion/scalloping
- The tympanic membrane is typically intact
Pathophysiology
Two theories exist:
- Faulty epithelial migration — abnormal migration patterns of the epithelial layer of the tympanic membrane and EAC skin
- Excessive epithelial cell production — overproduction of keratinocytes as the primary defect
The exact underlying trigger is unknown.
Clinical Features
- Age: Primarily adults aged 30–60 years
- Symptoms: Severe otalgia (from aggressive secondary external otitis), conductive hearing loss
- Bilateral involvement is common, though asymmetric
- If neglected, the pressure of the keratin plug can cause widening of the bony EAC ("automatousectomy" cavity)
- Thickening/mucosal change of the tympanic membrane and blunting of periannular canal skin may occur
- Rare complications: tegmen dehiscence, facial palsy, lateral semicircular canal erosion
Imaging (CT)
HRCT shows soft tissue mass filling the EAC without bony scalloping or erosive change. The bony edges may be enlarged but not destroyed.
Treatment
- Atraumatic removal of the epithelial/keratin debris (occasionally with prior softening using otic drops or under general anesthesia)
- Regular scheduled follow-up for prophylactic cleaning before infection/inflammation develops
- Acetic acid irrigations (helps with pH maintenance)
- Lifelong debridements may be necessary
- Surgical removal in refractory cases
Comparison: Keratosis Obturans vs. EAC Cholesteatoma
| Feature | Keratosis Obturans | EAC Cholesteatoma |
|---|---|---|
| Distribution | Diffuse, circumferential | Focal (inferoposterior) |
| Bone | No osteonecrosis; canal widens | Osteonecrosis, bony erosion |
| Bilaterality | Frequent | Rare |
| TM | Thickened but intact | May be involved |
| CT | Soft tissue filling EAC, no erosion | Scalloping, bony flecks in ~50% |
| Treatment | Debridement ± cerumenolytic | Debridement ± surgery with fascial graft |
— Cummings Otolaryngology Head and Neck Surgery, p. 2655–2656; K.J. Lee's Essential Otolaryngology, p. 992; Grainger & Allison's Diagnostic Radiology
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