Sebaceous (Epidermoid) Cysts

Synonyms: epidermal cysts and epidermoid cysts

It is said that sebaceous cyst is a misnomer as these cysts are not of sebaceous origin and some would argue that the term should be dropped. Analysis of the pattern of lipids has shown that they do not originate from the sebaceous glands but from proliferation of epidermal cells within the dermis.¹ The source of the epidermal cells is often the infundibulum of the hair follicles.

There are several different types of cysts. An epidermal inclusion cyst is the result of the implantation of epidermal elements in the dermis. Milia are miniature epidermoid cysts. The aetiology of these cysts remains unclear.

They are extremely common and probably most of us will have a few over the course of our lives but they resolve spontaneously. They are said to be twice as common in men as in women and most frequent in the 20s and 30s.

• Most often they are a painless lump
• They may present with discharge of a foul cheese-like material
• If they become infected they are red, inflamed and painful
• Lesions of the genitals can be painful during intercourse and cause problems with walking or wearing underwear. They can also interfere with micturition.
• Sebaceous or epidermoid cysts appear as firm, round, mobile, flesh-coloured to yellow or white subcutaneous nodules of variable size.
• A central pore or punctum may tether the cyst to the overlying epidermis and a thick cheesy material can sometimes be expressed.
• In people with dark skin, the cysts may also be pigmented.

Sites affected

• The sites most commonly affected are, in descending order of frequency, the face, the trunk, the neck, the extremities, and the scalp.
• Sebaceous cysts of the genitals are less common and may appear as a mass in the breast, the vulva, the clitoris, the penis, the scrotum, or the perineum. In cultures that practice female circumcision, more correctly referred to as female genital mutilation, cysts on the vulva are common.²
• The ocular and oral mucosae can also be affected, and cysts have been reported on the palpebral conjunctivae, on the lips, on the buccal mucosa, on and under the tongue, and even on the uvula. These are not sites with hair follicles.
• Epidermoid cysts may occur on the extremities. They can cause changes in the nails, such as onycholysis and subungual hyperkeratosis, which may be mistaken for psoriasis or onychomycosis when there is really a subungual cyst. These cysts also produce changes in the nails, such as pincer nails, in addition to erythema, oedema, tenderness, and pain. Palmoplantar lesions represent a unique subset of epidermoid cysts.

• Lipoma tends to be larger and is very soft
• A neurofibroma is hard and may be multiple
• An abscess is hot and red and may resemble an infected sebaceous cyst. Even the discharging contents of an infected boil do not smell quite as bad as a sebaceous cyst
• Multiple cysts in a teenager may suggest Gardiner's syndrome.

Usually the diagnosis is clear and no investigations are required for this indolent condition. In exceptional cases where malignancy may be suspected then excision and histology are required.

Sebaceous cysts are a feature of Gardiner' syndrome. Gardiner's syndrome is an autosomal dominant of familial polyposis coli, cutaneous cysts, osteomas or other soft-tissue tumours. The sebaceous cysts tend to occur at an earlier age than usual, presenting most often in early teens. The face may be involved but the extremities tend to be affected more than the trunk. If the syndrome is confirmed, only total colectomy will prevent malignancy from developing in the bowel.³Simple sebaceous cysts often tend to run in families too.

• Most people with a sebaceous cyst never seek medical attention and it resolves spontaneously.
• If a cyst is uncomplicated then masterly inactivity should be advised. Tell the patient that the cyst will probably disappear spontaneously leaving no trace but even the most skilful excision will leave a permanent scar. As always, should the situation change the patient may return.
• If the cyst is red and hot it is probably infected. Flucloxacillin or another antibiotic effective against staphylococci should be chosen. The contents of a cyst smell foul, even if not infected. Infection may be mixed and in lesions of the scalp and ano-genital area anaerobic flora are more likely.⁴
• If the cyst has ruptured the foul contents can be expressed. This should be done but the cyst may well re-form.
• An inflamed but uninfected cyst may respond to intralesional injection of steroid but it is not easy to tell if an inflamed cyst is infected or not.
• If the cyst is troublesome or if the patient, after counselling, is eager to have it removed, then it may be excised as a surgical procedure under the enhanced service of minor surgery. There is no place for simple incision as the cyst will re-form. The entire cyst wall must be removed.

Excision of a sebaceous cyst

• The usual preliminaries of informed consent are assumed. Information includes the warning that the cyst may recur if all the wall is not removed.
• The venue is an appropriate place to perform minor surgery. The area is swabbed with an antiseptic and paper towels are draped.
• Local anaesthetic such as 1% lignocaine with adrenaline is used, with the usual caveats about areas to avoid using adrenaline. The area is infiltrated with local anaesthetic, being careful not to puncture the cyst. It may be best to infiltrate all round it instead. Give a few minutes for it to take effect.
• Make a careful and superficial incision over the cyst, trying to keep so superficial that the cyst is not incised. It is best if it can be removed intact but if not, this is not a disaster, provided that all the wall is taken.
• Use toothed forceps to grip the skin and carefully cut the adhesions that bind the cyst wall to the skin and underlying tissues so as to shell it out. If it can be removed intact, it looks rather like a small pickled onion. If it is not intact, care must still be taken to dissect out all the cyst wall.
• If the cyst is ruptured, either before or during operation, grasp it with a firm instrument such as mosquito forceps and dissect out all the cyst wall. Some people may elect to rupture the cyst to permit a smaller scar. To remove the cyst intact requires an incision that is slightly longer than the diameter of the cyst whilst a ruptured cyst may be removed through an incision that is slightly shorter.
• Haemostasis is not usually a problem but if there is bleeding it should be secured. If the cyst is large and leaves a significant defect then a resorbable subcutaneous suture should be used to restore anatomy and to close a potential space for haematoma to form.
• Silk sutures may used to close the skin although vicryl is said to give less scarring. For a small incision, simple sutures give the neatest result but over a larger wound mattress sutures may be preferable.
• The diagnosis of a sebaceous or epidermal cyst is usually clear and many would argue that to send it for histology is a waste of resources. Others argue that anything that is surgically excised should be submitted for histology.

• Usually they are no problem but they may cause anxiety or cosmetic embarrassment. Sometimes they become infected. They may discharge spontaneously and the contents are extremely unpleasant.
• In the uncommon event of malignancy (e.g. squamous cell carcinoma, rapid growth, friability, and bleeding have been reported. This really is very rare and the literature tends to be case reports rather than series.⁵

They will usually grow slowly and only need removal if causing symptoms.⁶ If incised rather than excised, recurrence is to be expected.

• The vast majority of sebaceous cysts are of no great consequence but some in certain places are a cause for concern:
• Genital and umbilical lesions sometimes extend into the pelvis or below the midline fascia. This may not be apparent until they are being removed.
• Lesions over the skull can have an intracranial or intraosseous connection and should be referred to a neurosurgeon. Inappropriate management may result in cerebrospinal fluid leakage and potentially introduce infection leading to fatal meningitis. Preliminary x-ray or ultrasound may be of value.⁷Features suggestive of intracranial or intraosseous extension include the following:
  • Present since birth or appearance in early childhood although some lesions, especially small ones, can occasionally remain unnoticed until adulthood.
  • Bruits, pulsation or fluctuation in size with straining or crying
  • Fixation to underlying tissue, fluid-filled consistency, or ability to transilluminate
  • Location along the nasal, forehead, or scalp midline, or along cranial suture lines
  • Dimple or unusual overlying hair growth pattern
  • History of cranial trauma or surgery
  • Family history of neural developmental anomalies, neurological symptoms or history of meningitis