Sebaceous cyst is a term which was used in old days to denote presumably sebum containing cysts originating from sebaceous glands but which were actually one of the following
- Epidermoid cysts (epidermal cyst, epithelial cyst or infundibular cyst) – It is an intradermal or subcutaneous cyst.
- Pilar cysts (trichelemmal cysts, isthmus-catagen cysts) Pilar cysts originate from hair follicle and are clinically indistinguishable from epidermal cyst.
None of the above contains sebum. These contain keratin and do not originate from sebaceous glands. Epidermoid cysts originate in the epidermis and pilar cysts originate from hair follicles.
A cyst that originates from sebaceous glands and which contain sebum are quite rare. The term used for them is steatocystomas.
The term sebaceous cyst, therefore, should be dropped and epidermoid cyst and pilar cyst should be used. But these terms along with sebaceous cyst are interchangeably used in practice..
Epidermal or Epidermoid Cyst
It is a benign cyst usually found on the skin and develops from skin and related tissue. It contains a thin layer of stratified squamous epithelium. It occurs most often on the face, scalp, neck, back and scrotum.
Pilar cyst originates from hair follicle. About 90% of pilar cysts occur on the scalp. Rest occur on face, trunk and extremities. These are more common in females, and an autosomal dominant pattern has been observed.
Presentation of Sebaceous Cyst
A sebaceous cyst or pilar cyst most commonly presents as painless swelling. It may appear as firm, round, mobile nodule of variable size. The color may vary from flesh colored to yellow or white. It may show a central pore or punctum and sometimes thick cheesy material can be expressed from that.
Face, trunk, neck, extremities, and scalp are most common sites of occurrence. Vulva, clitoris, penis, scrotum, or perineum are less commonly affected. Cyst can also occur in the oral cavity, nails and palms.
The cyst itself may present with discharge of a foul cheese like material. A cyst can get infected and it may cause it to become painful and red.
The site of cyst may give rise to other problems, such as intercourse problems or urinating in case of genitals.
The cyst itself contains fibrous tissue, fluid and keratinous substance that resembles cottage cheese and emanates foul smell.
Common differentials are lipoma, neurofibroma, and abscess. Multiple cysts in a young patient point towards Gardner’s syndrome, an autosomal dominant condition comprising familial polyposis coli, cutaneous cysts and osteomas or other soft-tissue tumors.
Sometimes the cyst is intracranial though it is quite rare. This needs to be differentiated from a dermoid cyst, teratoma, cavernous angioma, glioma, craniopharyngioma and schwannoma.
The diagnosis is mainly clinical and investigations are generally not required. These however, may be required to rule out other differentials.
Most of the epidermoid or pilar or sebaceous cysts do not require treatment. In most cases, patients also do not seek medical advice. These cysts are known to disappear spontaneously.
In case of rupture of the cyst, the contents may be expressed but reformation may occur.
Antibiotics are prescribed for an infected cyst and excision of the cyst may be required. An inflamed cyst is difficult to distinguish from an infected one and the treatment is on the same line.
Excision of the Cyst
The cyst is removed under local anesthesia taking all aseptic precautions. It should be attempted to take the cyst out in toto and care should be taken to remove all the cyst wall if the cyst is ruptured.
An infected cyst may require oral antibiotics or other treatment before or after excision.
Prognosis and Complications
These cysts grow slowly and only need removal if causing symptoms. A cyst may sometimes cause cosmetic concern and it is better to excise it. Malignant change is very rare but infection may occur. A scalp cyst with intracranial connections may result in complications of CSF leakage and infection.
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