Keratosis Obturans and Canal Cholesteatoma

Introduction

Keratosis obturans (KO) and external auditory canal cholesteatomas (CC) are uncommon diseases of the external auditory canal that share the common characteristic of a buildup of desquamated keratin in the ear canal. Since the 19th century, KO and CC have been considered variants of the same disease until 1980, when Piepergerdes et al. classified these diseases as separate entities, often requiring distinct management plans. Distinguishing between these two disease entities remains clinically challenging because of the overlap in disease presentation with involvement of the wall of the ear canal, which is commonly observed in both KO and CC.

CC may appear as a keratin “pearl” often on the floor of the ear canal. More extensive involvement causes deeper irregular erosion of the bony ear canal, which is usually restricted in the area lateral to the annulus. There is often thinning of the skin that exposes bone within the canal. KO is also lateral to the annulus but encompasses the circumference of the canal skin. There is diffuse failure of epithelial desquamation and migration creating a laminar keratin plug that widens the diameter of the ear canal. It can cause occlusion of the ear canal resulting in a conductive hearing loss.

Key Operative Learning Points

1.
High-resolution computed tomography (CT) scan can help to differentiate the two conditions by the presence of focal bony erosion, seen only in CC, versus a widened bony canal, seen typically in KO.
2.
External auditory CC should be distinguished from squamous cell carcinoma by histologic examination of the ulcerated skin edges.
3.
When performing canaloplasty for either disease condition, drilling of the medial posteroinferior canal wall may expose the mastoid segment of the facial nerve.
4.
Complete removal of unhealthy canal skin and devitalized bone, with the smooth contouring of the bony canal defect and relining the denuded bone with fascia or skin graft, is the definitive surgical management of external auditory CC.
5.
Exposed mastoid air cells need to be obliterated with fascia or adipose tissue to avoid persistent otorrhea or fistula formation resulting in recurrent cholesteatoma formation.

Preoperative Period

History

1.
History of present illness

Clinical difference between KO and CC can be distinguished by the following characteristics:
- a.
  KO
  - 1)
    Conductive hearing loss may be present.
  - 2)
    Otorrhea is rare.
  - 3)
    Bilateral pain can occur.
  - 4)
    It is often seen in young or middle-aged individuals.
- b.
  CC
  - 1)
    Unilateral chronic and dull ache
  - 2)
    Otorrhea is common.
  - 3)
    Bleeding from the ear canal
  - 4)
    Normal hearing
  - 5)
    Older individuals
2.
Past medical history
- a.
  KO
  - 1)
    Excessive cerumen accumulation
  - 2)
    Medical illness: There is an association with abnormal or immotile cilia conditions—chronic sinusitis and bronchiectasis, particularly in children.
- b.
  CC
  - 1)
    Idiopathic
  - 2)
    Secondary:
    - a)
      Congenital
      - i)
        Auditory atresia
    - b)
      Acquired
      - i)
        Recurrent infections in the ear canal
      - ii)
        Recurrent disruptions of external auditory canal skin
      - iii)
        External auditory canal/stenosis
      - iv)
        Posttraumatic or postoperative external auditory canal wall defects

Physical Examination

An examination of the ear using a microscope is the most important part of the physical examination for both conditions.

1.
KO
- a.
  Accumulation of large plugs of circumferential, desquamated, laminar keratin in the ear canal due to a defect in lateral epithelial migration ( Figs. 128.1 and 128.2 )
- b.
  Widening of the bone wall of the ear canal secondary to constant circumferential pressure induced by the keratin plug resulting in bony resorption, without focal erosion of the bone
- c.
  Canal epithelium typically remains intact but can become thickened or inflamed.
- d.
  Tympanic membrane is usually intact but may be involved
- e.
  Conductive type of hearing loss
2.
CC
- a.
  Invasion of squamous tissue into a localized area of the bony canal with localized osteitis, focal erosion, and bone sequestration
- b.
  Trapping and tunneling of epithelium may occur beneath the skin of the external auditory canal.
- c.
  The most commonly reported site is the posteroinferior aspect of the canal ( Fig. 128.3 ); however, it can extend into the middle ear and mastoid.
- d.
  Surrounding epithelium can appear ulcerated with bleeding and granulation tissue present at the site of bone erosion ( Fig. 128.4 ).

Imaging

A high-resolution CT scan of the temporal bone scan can help to differentiate the two conditions.

1.
KO
- a.
  Widening of the external auditory canal
- b.
  Intact bony contour of external auditory canal
- c.
  Possible disease progression into the middle ear space via a diseased or perforated tympanic membrane
2.
CC
- a.
  Focal bone erosion of the external auditory canal
- b.
  Identify the extent of disease invasion into the mastoid from the erosion and destruction of the posterior bony external auditory canal.
- c.
  Identify the potential for involvement of the facial nerve.

Indications

1.
Persistent “clogged” ear sensation with otalgia, otorrhea, and hearing loss
2.
Inflammatory granulation tissue in the external auditory canal that requires a biopsy to rule out other pathologies, including carcinoma of the auditory canal or malignant otitis externa. This is more commonly seen in cases of CC.
3.
CT of the temporal bone can identify tissue extension into middle ear and/ormastoid space, with or without facial nerve involvement.

Contraindications

1.
Medical comorbidities with increased risk for general anesthesia
2.
Greater risk when surgery is performed in the only hearing ear

Preoperative Preparation

1.
Audiogram to determine hearing threshold
2.
CT scan of the temporal bone to determine disease extension in relation to important anatomic landmarks and the integrity of the bony external auditory canal
3.
KO: emollients and lubricants to soften the keratin plug a few days in advance for ease of removal
4.
CC: topical antibiotic ear drops to minimize epithelial infection at the site of bony canal erosion

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