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a closed sac that develops abnormally in some body structure

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/10/04 14:30:48」(JST)

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An epidermoid cyst is a benign cyst usually found on the skin. The cyst develops out of ectodermal tissue. Histologically, it is made of a thin layer of squamous epithelium.

Terminology

Several synonyms exist for epidermoid cysts, including epidermal cyst, epidermal inclusion cyst, infundibular cyst and keratin cyst.^[1]^:778^[2] "Epidermal inclusion cyst" more specifically refers to implantation of epidermal elements into the dermis. Infundibular cyst refers to the site of origin of the cyst: the infundibular portion of the hair follicle. In fact, the majority of epidermal inclusion cysts originate from the infundibular portion of the hair follicle thus explaining the interchangeable,^[3] yet technically incorrect, use of these two terms.

Causes

Epidermoid cysts commonly result from implantation of epidermis into the dermis, as in trauma or surgery. They can also be caused by a blocked pore adjacent to a body piercing. They are also seen in Gardner's syndrome on the head and neck. They can be infected by bacteria and form a pimple-like shape.

Presentation

The epidermoid cyst may be totally asymptomatic, or it may hurt when touched. It can release pus. It is very common for women on the major or minor labia. In contrast to pilar cysts, epidermoid cysts are usually present on parts of the body with relatively little hair.^[4]

Occasionally, an epidermoid cyst will present with trigeminal neuralgia.

Although they are not malignant, there are rare cases of malignant tumors arising from an epidermoid cyst.^[5]

Diagnosis

Macroscopic appearance of a resected cyst

Histology showing epithelium and lamellated keratin (left)

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 a pathologist based on microscopic appearance of a cystic lesion lined by cornified epithelium containing lamellated keratin without calcifications. They can also be seen as isointense lesions on MRI or hyperintensities on FLAIR.

Treatment

Cysts can be removed by excision.^[6]

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.^[7] In cases where pus and blood are excreted, (particularly in those caused by body piercings,) hydrogen peroxide gel can be used to dry out the cyst. Patients should be aware this will slow the healing process for a new piercing.

References

^ Freedberg, et al. (2003). Fitzpatrick's Dermatology in General Medicine. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.
^ James, William; Berger, Timothy; Elston, Dirk (2005). Andrews' Diseases of the Skin: Clinical Dermatology. (10th ed.). Saunders. ISBN 0-7216-2921-0.
^ "Epidermoid cyst". http://www.meddean.luc.edu/lumen/MEdEd/Medicine/dermatology/melton/cyst10.htm. Retrieved 2007-11-14.
^ "cysts - British Association of Dermatologists". http://www.bad.org.uk/patients/leaflets/cysts.asp. Retrieved 2007-11-14.
^ Jehle KS, Shakir AJ, Sayegh ME (2007). "Squamous cell carcinoma arising in an epidermoid cyst". British journal of hospital medicine (London, England : 2005) 68 (8): 446. PMID 17847698.
^ "Minimal excision technique for removal of an epidermoid cyst". Am Fam Physician 65 (7): 1423–4. 2002. PMID 11996427. http://www.aafp.org/afp/20020401/1423ph.html.
^ Epidermoid Cyst; Frontal Lobe; Case Series

External links

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Case of epidermal cyst on the glans penis.

Nobeyama Y, Nakagawa H.SourceDepartment of Dermatology, The Jikei University School of Medicine, Tokyo, Japan.
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