Epidermal inclusion cyst of the external auditory canal

Case contributed by Ashesh Ishwarlal Ranchod
Diagnosis certain


The patient presented with a visible, pearly white, soft tissue mass occluding the left external auditory canal.

Patient Data

Age: 40 years
Gender: Female

There is an encapsulated, circumscribed, cystic mass within the left external auditory canal with an intracanalicular and extra canalicular component specifically it straddles both the cartilaginous and bony external auditory canal. The lesion measured 16.9x12.7x10.7 mm (width x anteroposterior x craniocaudal) and approximately 10 Hounsfield units. There is no calcification, no fatty components, and a homogeneous appearance on CT imaging. There is no bony erosion, no infiltration, and minimal expansion of the distal external auditory canal. The scutum specifically is normal within an intact tympanic membrane. Temporal bone imaging is otherwise normal bilaterally.

The lesion does not enhance post-contrast CT brain imaging.

Incidental empty sella and bilateral choroid plexus xanthogranulomata 

Histology confirmed an epidermal inclusion cyst.

EAC cholesteatoma was considered less likely based on the high-resolution temporal bone CT imaging.

Case Discussion

Epidermal inclusion cysts are sometimes called epidermal cysts, epidermoid cysts, infundibular cysts, or keratin cysts. They represent the proliferation of squamous epithelium and are usually dermal or subdermal within a confined space.

On MRI, they can restrict on diffusion imaging and occasionally demonstrate shine through artifacts. They usually demonstrate peripheral enhancement rather than central enhancement.

The differential diagnosis of external auditory canal masses includes:

  • debris: usually partially fill the external auditory canal with air foci
  • keratosis obturans: soft tissue keratin plug which usually enlarges the canal with no bony erosion
  • cholesteatoma: usually have bony erosions
  • carcinoma: irregular mass with or without bony erosions

In this instance, the patient underwent surgical excision and histology confirmed an epidermal inclusion cyst.

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