Skin nonmelanocytic tumor
Cysts
Epidermal (epidermoid) type

Senior Author: Joshua Wisell, M.D.
Editor-in-Chief: Debra Zynger, M.D.

Topic Completed: 9 May 2019

Revised: 9 May 2019

Copyright: 2002-2019, PathologyOutlines.com, Inc.

PubMed Search: Epidermal cyst[TI] OR epidermoid cyst[TI] pathology[TIAB]
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Cite this page: Vaughan VC, Wisell J. Epidermal (epidermoid) type. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/skintumornonmelanocytickeratinouscystepidermal.html. Accessed May 24th, 2019.
Definition / general
  • Benign skin tumor
  • Cystic mass containing keratin
Essential features
  • Cystic mass with soft white keratin contents
  • Histologically cystic mass with squamous epithelium and keratin flakes
Terminology
  • Epidermoid cyst, epidermal cyst, epidermal inclusion cyst, infundibular cyst
ICD coding
  • ICD-10: L72.0 - epidermal cyst
Epidemiology
Sites
  • Face, neck, trunk, perineal area, cerebellopontine angle
  • Less commonly spine, intrapancreatic accessory spleen
Pathophysiology
  • Follicular orifice becomes plugged with bacteria and keratin, leading to cystic dilation and entrapment of keratin debris 
  • Presence of multiple epidermal inclusion cysts has been documented in Gardner syndrome, a variant of familial adenomatous polyposis with benign osteomas and intestinal fibromatoses
  • Less frequently, patients may have lipomas, pilomatrixomas (including epidermoid cysts with pilomatrical lining) or leiomyomas
  • Multiple and large epidermoid cysts may occur with the use immunosuppressants in the posttransplantation setting, for example, with cyclosporine or tacrolimus (Cutis 1992;50:36Ann Dermatol 2011;23:S182)
  • May complicate penetrating trauma to skin, such as a sewing needle, with resultant implantation of squamous epithelium into the dermis (Turk J Pediatr 2011;53:108)
Diagrams / tables

Images hosted on other servers:

Age distribution

Site distribution

Clinical features
  • Present as smooth dome shaped swellings varying in size from a few millimeters to a few centimeters (Ann Dermatol 2017;29:33)
  • Usually occur on the face, neck or trunk but can occur anywhere
  • Overlying skin may be taut with the pressure of the cyst and have a central punctum
  • Generally occurs in postpubertal individuals
  • Freely mobile unless ruptured, in which case a foreign body giant cell reaction may make them more adherent to surrounding connective tissue
  • May become painful and inflamed with external manipulation
  • Cyst contents white, cheesy macerated keratin that may have an odor
Diagnosis
  • Often based on clinical examination
  • Pathological diagnosis relies on recognizing the cyst wall and contents
  • In cases of extensive foreign body giant cell reaction or fibrosis, the classic features may not be visualized as readily and a diligent search for keratin flakes may lead to diagnosis
Laboratory
  • No specific laboratory findings
Radiology description
  • Ultrasound:
    • Subcutaneous rounded structure that is mostly anechoic or hypoechoic with focal present inner echoes (pseudotestis appearance) representing cystic debris
  • MRI:
    • Fluid-like enhancement
    • High intensity of cyst contents on T2 weighted images and peripheral cyst wall enhancement with T1 gadolinium enhancement
    • Cyst rupture results in irregular enhancement (AJR Am J Roentgenol 2006;186:961)
Radiology images

Images hosted on other servers:

Lumbar spine epidermoid cyst

Abdominal epidermal inclusion cyst

Case reports
Treatment
  • Complete excision of the cyst is curative
Clinical images

Contributed by Jeremy Hugh, M.D.

White subcutaneous nodule

White nodule in hair bearing area



Images hosted on other servers:

Cheesy contents of
cystectomy in
mastoid region after
penetrating trauma

Gross description
  • Pearly glistening cyst with creamy contents
Gross images

Contributed by the University of Colorado Department of Pathology

Disrupted cyst wall and adjacent soft tissue



Images hosted on other servers:

Thin cyst with grumous contents

Intact pearly glistening cyst

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by the University of Colorado Department of Pathology

Loose keratin flakes

Stratified squamous epithelium lining

Ruptured epidermoid cyst

Giant cells, cholesterol clefts, mixed inflammation


Foreign body giant cell reaction

Epidermal inclusion cyst in cerebellopontine angle

Lamellated
keratin flakes in
cranial epidermal
inclusion cyst

Cytology description
  • Anucleate keratinizing squamous cells with some nucleated squamous cells
  • Frequent erythrocytes, leukocytes, multinucleated giant cells and cholesterol crystals (J Nat Sci Biol Med 2014;5:460)
Cytology images

Contributed by the University of Colorado Department of Pathology

Anucleate squamous cells

Keratinizing squamous cells

Anucleate squames and inflammatory cells

Sample pathology report
  • Skin, neck, excision:
    • Epidermal inclusion cyst
    • Microscopic description: Cyst lined by squamous epithelium with granular layer containing lamellated keratin.
Differential diagnosis
  • Proliferating epidermoid cyst:
    • May show carcinomatous changes, invasion and be locally aggressive
  • Trichilemmal (pilar) cyst:
    • Lack a granular layer in the cyst lining
    • Dense lamellated keratin cyst contents
    • More likely to occur on the scalp
  • Pilomatricoma:
    • Eosinophilic cellular outlines of squamous cells ("ghost cells") in addition to the more basophilic matrical cells
    • More likely to occur in a pediatric population
  • Hybrid cyst:
  • Dermoid cyst:
    • Similar in appearance
    • Has adnexal structures (ie. sebaceous glands) in cyst wall
    • Arises at sites of embryonic closure such as the lateral eyebrow
  • Pilonidal sinus:
    • Sinus tract surrounded by epithelium and mixed inflammation
    • Characteristically contains broken hair shafts
  • Steatocystoma:
    • Compressed sebaceous gland within the cyst wall
    • Characteristic wavy eosinophilic crenulated cuticle of the lining
  • Odontogenic keratocyst:
    • Attenuated squamous epithelium with parakeratosis
    • Retraction of epithelium with basal palisade can be a helpful finding
    • Often filled with keratin debris like epidermoid cyst
Board review question #1
An elderly man has a soft, round subcutaneous mass on the back of the neck with a central punctum. Which of the following is the most likely diagnosis?

  1. Angiosarcoma
  2. Epidermoid cyst
  3. Lymphadenitis
  4. Pilar cyst
  5. Spindle cell lipoma
Board review answer #1
B. Epidermoid cyst

Reference: Epidermal (epidermoid) cyst

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Board review question #2
The following is a section of a subcutaneous mass removed from the axilla of a 40 year old woman. What is the most likely diagnosis?



  1. Dermoid cyst
  2. Dilated pore of Weiner
  3. Epidermoid cyst
  4. Hailey-Hailey
  5. Trichilemmal cyst
Board review answer #2
C. Epidermoid cyst

Reference: Epidermal (epidermoid) cyst

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