Last Updated on September 13, 2023
A sebaceous cyst is a term that has been used conventionally to denote cutaneous cysts that occur most frequently on the face, scalp, neck, and trunk that contain pultaceous material and are presumed to be sebum-like. So the cyst was thought to contain sebum and originate from sebaceous glands.
A sebaceous cyst is more of a clinical term that may be used for
- Epidermoid cysts or epidermal inclusion cysts
- Pilar cysts
A cyst that originates from sebaceous glands and contains sebum is quite rare. Such cysts are called 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. Because these can hardly be differentiated on a clinical basis.
Epidermal Inclusion Cyst or Epidermoid Cyst
Epidermoid cysts have also been called follicular infundibular cysts [because they develop from the infundibular part, see parts of hair diagram], epidermal cysts, and epidermal inclusion cysts. The term epidermal inclusion cyst refers specifically to an epidermal cyst that is the result of the implantation of epidermal elements in the dermis.
As most lesions originate from the follicular infundibulum, the more general term epidermoid cyst is favored
It is a benign cyst that structurally has a thin layer of stratified squamous epithelium and contains a keratin substance. These re most common in hord and fourth decades.
The main sites of occurrence are
- Face
- Scalp
- Neck and back
- Scrotum
Causes
- Congenital
- Sequestration of epidermal rests during embryonic life
- Occlusion of the pilosebaceous unit
- Any benign or malignant process affecting or growing near the pilosebaceous unit may lead to occlusion or impingement of the follicular ostia with subsequent formation of a cyst. Cysts with an acneiform distribution are likely the result of follicular occlusion.
- Traumatic or surgical implantation of epithelial elements.
- Human papillomavirus infection
- Exposure to ultraviolet rays
- Eccrine duct occlusion
- Injury causing implantation of epithelial elements in the dermis [True epidermal inclusion cyst]
- Crush injury
- Needle piercing
- Needle biopsy
- Cosmetic surgery
- Skin graft
Pilar cyst or Trichilemmal Cyst
The pilar cyst originates from the hair follicle. About 90% of pilar cysts occur on the scalp. Other important sites are
- Face
- Trunk
- Limbs
These can occur sporadically or can be hereditary.
Presentation of Sebaceous Cyst
A sebaceous cyst most commonly presents as a painless swelling. It may appear as a firm, round, mobile nodule of variable size. The color may vary from flesh-colored to yellow or white and it may show a central pore or punctum.
Sometimes cheesy material can be expressed.
This cheesy material was thought to be sebum initially and therefore the term sebaceous cyst was used. Actually, that oily-looking substance is made of keratin, a protein in epidermal layer of skin and hair.
Though it is a misnomer, it is still used in clinical practice for epidermoid and pilar cysts. In fact, it may sometimes be wrongly used for other cutaneous cysts because of difficulty in distinguishing them.
Sites of sebaceous cysts [epidermoid and pilar cysts ] can be
- Face
- Trunk
- Neck
- Limbs
- Scalp [ninety percent of pilar cysts are in the scalp]
- Genital and perineal region
- Vulva
- Clitoris
- Penis
- Scrotum,
- Mouth
- Nails
- Palms.
Presentation of the sebaceous cyst as a ruptured cyst can also occur, presenting with a discharge or a foul-smelling cheese-like material.
Infection of the cyst may cause it to become painful and red.
In addition to this, cysts can lead to local symptoms depending on the sites of occurrence. For example, in the case of the genital region intercourse may be painful or there might be difficulty in urination.
Differential Diagnosis
- Lipoma
- Neurofibroma
- Abscess
- Dermoid cyst
- Other cutaneous cysts
- Hydrocystoma
- Vellus hair cyst
- Pigmented follicular cyst
Lab Studies
The diagnosis is mainly clinical and investigations are generally not required. These, however, may be required to rule out other differentials.
- Fine Needle Aspiration Cytology (FNAC) – It is an outdoor procedure. It is quick, involves minimal discomfort, and is economical. A thin needle is inserted into the swelling and the material aspirated is spread on a glass slide and studied under the microscope after appropriate staining. It is the investigation of choice and quickly allays the patient’s fear regarding the swelling as the results are obtained within a few hours.
- Biopsy – A preoperative biopsy is generally not required. However, excision of the cyst material is often followed by this procedure to confirm the diagnosis. Biopsy also can provide a definitive diagnosis. The entire cyst is removed and submitted for microscopic examination. The results usually take a few days.
Treatment
Most of the sebaceous cysts do not require treatment. In most cases, patients also do not seek medical advice. These cysts are also known to disappear spontaneously in some cases.
In the 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 lines.
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.
Laser-aided excision can also be done.
Prognosis and Complications
These cysts grow slowly and only need removal if they cause 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.
References
- Linda J Fromm, MD, MA, FAAD. Epidermal Inclusion Cyst. Accessed on 13 Sept 2023. https://emedicine.medscape.com/article/1061582-overview
- Venus MR, Eltigani EA, Fagan JM. Just Another Sebaceous Cyst? Ann R Coll Surg Engl. 2007;89(6):W19-W20.
- Zito PM, Scharf R. Cyst, Epidermoid (Sebaceous Cyst). Treasure Island (FL): StatPearls Publishing; 2020. Accessed 13 Sept 2023