Epidermoid cyst
Other names: Epidermal cyst, epidermal inclusion cyst, keratin cyst, infundibular cyst[1]
Epidermoid cyst
Specialty	Dermatology
Symptoms	Painless, unless ruptured or infected, centralblackhead[2]
Complications	Cancer[3]
Usual onset	30s and 40s[3]
Duration	Long-term[3]
Causes	Random,Gardner syndrome,Gorlin syndrome,cyclosporine[3]
Diagnostic method	Based on symptoms and examination[1]
Differential diagnosis	Lipoma,dermoid cyst,acne,trichilemmal cyst,milia[1][3]
Treatment	None,incision and drainage, surgical removal[1]
Frequency	Relatively common[3]

Epidermoid cysts are generallynon-serious skincysts.^[3] They typically do not result in pain, unless anabscess forms or they rupture internally.^[2] Adark pore may be present.^[3] They are most common on the face, neck, and trunk; though may form anywhere.^[3] They often gradually grow over years.^[3] Rare complications may includecancer.^[3]

Generally they occur randomly; though are associated withGardner syndrome,Gorlin syndrome, and the medicationcyclosporine.^[3] They occur under theepidermis and are filled withkeratin.^[3] Diagnosis is generally based on symptoms and examination.^[1]

Specific treatment is not required in those without symptoms.^[1] Larger cysts may be removed surgically, with efforts to also remove the capsule.^[1] If infected,incision and drainage together withantibiotics may be indicated.^[1]

They are the most common type of cyst.^[3] Most often they occur in peoples 30s and 40s.^[3] They effect males twice as often as females.^[3] They have incorrectly been referred to as a "sebaceous cyst", as they do not containsebum.^[1]

Signs and symptoms

The epidermoid cyst may have no symptoms, or it may be painful when touched. It can release maceratedkeratin (cheesy material). In contrast topilar cysts, epidermoid cysts are usually present on parts of the body with relatively little hair.^[4] An epidermoid cyst can occur as avaginal cysts.^[5]

Although they are notmalignant, there are rare cases of malignant tumors arising from an epidermoid cyst.^[6] Epidermal inclusion cysts account for approximately 85–95% of all excised cysts, malignant transformation is exceedingly rare. The incidence of squamous cell carcinoma developing from an epidermal inclusion cyst has been estimated to range from 0.011 to 0.045%.^[7]

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  Epidermal cyst with a central poor

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  Epidermal cyst on the neck, inflamed

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  Epidermal cyst in theearlobe

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  Discharge from the cyst with palpation

Causes

Epidermoid cysts commonly result from implantation of epidermis into the dermis, as intrauma or surgery. They can also be caused by a blocked pore adjacent to abody piercing. They are also seen inGardner's syndrome andNevoid basal-cell carcinoma syndrome on the head and neck. They can be infected bybacteria and form apimple-like shape.

Diagnosis

Epidermoid cysts are usually diagnosed when a person notices a bump on their skin and seeks medical attention. The definitive diagnosis is made after excision by apathologist based onmicroscopic appearance of a cystic lesion lined by cornifiedepithelium containing lamellated keratin withoutcalcifications. They can also be seen as isointense lesions onMRI or hyperintensities onFLAIR.

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  CT scan, showing a homogenous hypodense volume (unspecificcyst-like)

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  Epidermoid cyst in a testicle on ultrasound, with lamellated ("onion skin") appearance

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  Macroscopic appearance of a resected (surgically removed) intracranial cyst, with pearl appearance

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  Histopathology, showing a keratinizing stratified squamous epithelium, and a lumen containing keratin flakes

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  Histopathology showing epithelium and lamellated keratin (left)

Treatment

Cysts can be removed by excision.^[8]

In case of fronto-ethmoidal epidermoid cysts, surgical resection appears to be the mainstay of treatment; however, the extent of resection is dictated by adherence of the tumor capsule to the surrounding vital structures.^[9]

Hydrogen peroxide gel (H₂O₂) was previously recommended for cyst treatment, particularly those on body piercings. However the gel cannot adequately permeate the cyst and was not found to be effective.^[10] Hydrogen peroxide is no longer recommended for wound care by doctors as it can damage the healing tissues.^[11]

On body piercings, self treatment with a hot saline soak to help drain the cyst and the use of an antibacterial or medicatedtalcum powder to help dry out the bump and reduce bacterial proliferation is generally recommended until medical advice can be obtained.^[12] (Use of talc is no longer recommended due to recently discovered associations with multiple cancers.)^{[citation needed]} Piercings, however, are more likely to be victims ofhypertrophic scarring than a cyst. Cheek piercings seem to be the piercing most prone to cysts due to the possible interruption of saliva ducts.

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  Surgery of a suprasternal epidermoid cyst, showing a smooth surface

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  a) Giant earlobe epidermoid cyst b) cyst resection and content

Terminology

Several synonyms exist for epidermoid cysts, including epidermal cyst, infundibular cyst, keratin cyst and epidermal inclusion cyst^{[13][14]: 778 [15]}Epidermal inclusion cyst more specifically refers to implantation ofepidermal elements into thedermis. The terminfundibular cyst refers to the site of origin of the cyst: theinfundibular portion of thehair follicle. The majority of epidermal inclusion cysts originate from the infundibular portion of the hair follicle, thus explaining the interchangeable,^[16] yet inaccurate, use of these two terms.

Epidermoid cyst may be classified as asebaceous cyst,^[17] although technically speaking it is not sebaceous.^[18] "True" sebaceous cysts, cysts which originate fromsebaceous glands and which contain sebum, are relatively rare and are known assteatocystoma simplex or, if multiple, assteatocystoma multiplex. Medical professionals have suggested that the termsebaceous cyst be avoided since it can be misleading.^[19]: 31 In practice, however, the term is still often used for epidermoid and pilar cysts.

See also

• Intracranial epidermoid cyst
• List of cutaneous neoplasms associated with systemic syndromes
• Proliferating epidermoid cyst
• Verrucous cyst

References

External links

• DermNetlesions/cysts

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