An epidermoid cyst or epidermal inclusion cyst is a

benign Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malign ...

cyst A cyst is a closed sac, having a distinct envelope and cell division, division compared with the nearby Biological tissue, tissue. Hence, it is a cluster of Cell (biology), cells that have grouped together to form a sac (like the manner in which ...

usually found on the skin. The cyst develops out of

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...

al tissue.

Histologically Histology, also known as microscopic anatomy or microanatomy, is the branch of biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single ...

, it is made of a thin layer of

squamous epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

Signs and symptoms

The epidermoid cyst may have no symptoms, or it may be painful when touched. It can release macerated

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

. In contrast to

pilar cyst A trichilemmal cyst (or pilar cyst) is a common cyst that forms from a hair follicle, most often on the scalp, and is smooth, mobile, and filled with keratin, a protein component found in hair, nails, skin, and horns. Trichilemmal cysts are cl ...

s, epidermoid cysts are usually present on parts of the body with relatively little hair. An epidermoid cyst is one type of

vaginal cysts Vaginal cysts are uncommon benign cysts that develop in the vaginal wall. The type of epithelial tissue lining a cyst is used to classify these growths. They can be congenital. They can present in childhood and adulthood. The most common type is ...

. Although they are not

malignant Malignancy () is the tendency of a medical condition to become progressively worse. Malignancy is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous ''benign'' tumor in that a malignancy is not s ...

, there are rare cases of malignant tumors arising from an epidermoid cyst. 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%.

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 a

pathologist Pathology is the study of the causal, causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when us ...

based on

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...

appearance of a cystic lesion lined by cornified

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

containing lamellated keratin without

calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...

s. They can also be seen as isointense lesions on

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

or hyperintensities on FLAIR.

Treatment

Cysts can be removed by excision. 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.

Hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

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. Hydrogen peroxide is no longer recommended for wound care by doctors as it can damage the healing tissues. On body piercings, self treatment with a hot saline soak to help drain the cyst and the use of an antibacterial or medicated

talcum powder Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening age ...

to help dry out the bump and reduce bacterial proliferation is generally recommended until medical advice can be obtained. (Use of talc is no longer recommended due to recently discovered associations with multiple cancers.) Piercings, however, are more likely to be victims of

hypertrophic scar A hypertrophic scar is a cutaneous condition characterized by deposits of excessive amounts of collagen which gives rise to a raised scar, but not to the degree observed with keloids. Like keloids, they form most often at the sites of pimples, b ...

ring than a cyst. Cheek piercings seem to be the piercing most prone to cysts due to the possible interruption of saliva ducts.

Terminology

Several synonyms exist for epidermoid cysts, including epidermal cyst, infundibular cyst, keratin cyst and epidermal inclusion cystFreedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. .James, William; Berger, Timothy; Elston, Dirk (2005). ''Andrews' Diseases of the Skin: Clinical Dermatology''. (10th ed.). Saunders. . ''Epidermal inclusion cyst'' more specifically refers to implantation of

epidermal The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...

elements into the

dermis The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...

. The term ''infundibular cyst'' refers to the site of origin of the cyst: the

infundibular An infundibulum (Latin for ''funnel''; plural, ''infundibula'') is a funnel-shaped cavity or organ. Anatomy * Brain: the pituitary stalk, also known as the ''infundibulum'' and ''infundibular stalk'', is the connection between the hypothalamus and ...

portion of the

hair follicle The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between h ...

. The majority of epidermal inclusion cysts originate from the infundibular portion of the hair follicle, thus explaining the interchangeable, yet inaccurate, use of these two terms. Epidermoid cyst may be classified as a

sebaceous cyst A sebaceous cyst is a term commonly used to refer to either: * Epidermoid cysts (also termed epidermal cysts, infundibular cyst) * Pilar cysts (also termed trichelemmal cysts, isthmus-catagen cysts) Both of the above types of cysts contain kera ...

, although technically speaking it is not sebaceous. "True" sebaceous cysts, cysts which originate from

sebaceous gland A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest number ...

s and which contain sebum, are relatively rare and are known as steatocystoma simplex or, if multiple, as

steatocystoma multiplex Steatocystoma multiplex, is a benign, autosomal dominant congenital condition resulting in multiple cysts on a person's body. Steatocystoma simplex is the solitary counterpart to steatocystoma multiplex. In steatocystoma multiplex, the tendency to ...

. Medical professionals have suggested that the term ''sebaceous cyst'' be avoided since it can be misleading. In practice, however, the term is still often used for epidermoid and pilar cysts.

Additional images

File:Epidermal Inclusion Cyst.jpg, Epidermal inclusion cyst on the nape of a person's neck File:Epidermal Cyst ear.JPG, Epidermal cyst in the

earlobe The human earlobe (''lobulus auriculae''), the lower portion of the outer ear, is composed of tough areolar and adipose connective tissues, lacking the firmness and elasticity of the rest of the auricle (the external structure of the ear). In ...

File:CT scan of epidermoid cyst.jpg, CT scan, showing a homogenous hypodense volume (unspecific

-like) File:Epidermoid cyst testicle.jpg, Epidermoid cyst in a testicle on ultrasound, with lamellated ("onion skin") appearance File:Epidermoid cyst macro.jpg, Macroscopic appearance of a resected (surgically removed) intracranial cyst, with pearl appearance File:Surgery of suprasternal epidermoid cyst.jpg, Surgery of a suprasternal epidermoid cyst, showing a smooth surface File:Histopathology of epidermoid cyst.jpg, Histopathology, showing a keratinizing stratified squamous epithelium, and a lumen containing keratin flakes File:Dermoid cyst intracranial.jpg, Histopathology showing epithelium and lamellated keratin (left)

References

External links

* {{Disorders of skin appendages Epidermal nevi, neoplasms, and cysts Conditions of the skin appendages