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Epidermal Inclusion Cyst
(follicular cyst)
What is an epidermal inclusion
cyst?
An "epidermal" inclusion cyst is something of a misnomer
since it is located in the dermis. Its name reflects the fact that it is
derived from the epidermal cells that line the upper portion of the hair
follicle. For this reason it is also known as a follicular cyst. The contents of the cyst are keratin (not sebum). It is
flesh-colored and "dome-shaped" in appearance and firm but malleable (i.e. able
to be deformed) in consistency. It is benign with no potential for
malignant transformation. They are common and occur at all ages, often on
the face or trunk. They range from several millimeters to several centimeters in
diamter.
With what can an
epidermal inclusion
cyst
be confused?
A pilar cyst (trichilemmal cyst), derived from the middle third of the
follicle, occurs frequently on the scalp and less often in other locations. It, too, is benign. A
lipoma is a subcutaneous nodule derived from fat
cells. Its consistency is usually described as "rubbery" but not
"malleable". In other words, it is more firm than an epidermal inclusion
cyst. A steatocystoma is a true sebaceous cyst
and is filled with sebum. If there is any doubt about the identity of a firm lesion, a
malignant tumor must be ruled out.
How is an
epidermal inclusion
cyst
diagnosed?
Epidermal inclusion cysts are typically asymptomatic and
are usually discovered incidentally. Occasionally a cyst can become secondarily infected or rupture, leading to
inflammation and drainage. It is usually diagnosed clinically based on appearance and feel. The presence of a central
pore within the cyst, indicative of the opening of the follicular unit, is a
useful clue that the lesion originates from that structure. It is
sometimes possible to express material from the central pore, which will be
cheesy and foul smelling. Incision and drainage can also be performed; the
drainage of cheesy keratinaceous material is diagnostic. Biopsy is not
necessary unless the diagnosis is in doubt. Histologically, the cyst wall is
composed of stratified squamous epithelium with a granular layer and the cavity
is filled with laminated keratin.
How is an
epidermal inclusion
cyst treated?
Unless the cyst is troublesome, no treatment is required. If the cyst is to be removed, the entire cyst lining must be excised to prevent
recurrence.
What is the prognosis for an epidermal
inclusion
cyst?
Epidermal inclusion cysts have no malignant potential. They enlarge then reach a stable size of
up to several centimeters in diameter. They may become infected or rupture, necessitating treatment.
Inflamed lesions may require incision and drainage and possibly treatment with
antibiotics. Intralesional steroids may
help resolve the inflammation.
Date created 04/02/2007
Last updated
01/03/2009
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