INTRODUCTION

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Background

Several different terms have been used to describe epidermal cysts. Epidermal inclusion cyst refers to those cysts that are the result of the implantation of epidermal elements in the dermis. However, many cysts originate from the infundibular portion of the hair follicle, and the more general term, epidermoid cyst, is favored. Milia merely represent miniature epidermoid cysts. The term wen should be reserved for trichilemmal or pilar cysts. Sebaceous cyst is a misnomer, and the term should not be used at all because these cysts are not of sebaceous origin.

Pathophysiology

Epidermoid cysts result from the proliferation of epidermal cells within a circumscribed space of the dermis. They have been shown to not be of sebaceous origin based on the analysis of their lipid pattern, which demonstrates similarities to the epidermis. In addition, epidermoid cysts express cytokeratins 1 and 10, which are constituents of the suprabasilar layers of the epidermis. The source of this epidermis is often the infundibulum of the hair follicle, as evidenced by the observation that the lining of the 2 structures is identical.

Inflammation is in part mediated by the horny material contained in epidermoid cysts. Extracts of this material have been shown to be chemotactic for polymorphonucleocytes.

The manner in which carcinomas may rarely arise within epidermoid cysts is unknown. In a series of epidermoid cysts with carcinoma, immunohistochemical results for human papillomavirus (HPV) were negative, leading the authors to conclude that HPV is not likely to be the cause of squamous cell carcinomas (SCCs) in these cysts. Some have proposed that repetitive trauma and inflammation may play a role.

Mortality/Morbidity

• Epidermoid cysts grow slowly and usually do not cause symptoms, but they may become inflamed or secondarily infected, resulting in pain and tenderness.
• Rarely, malignancies, including basal cell carcinoma, Bowen disease, SCC, and even mycosis fungoides, have developed in epidermoid cysts.

Sex

In one study, epidermoid cysts were approximately twice as common in men as in women.

Age

Epidermoid cysts may occur at any time in life, but they are most common in the third and fourth decades of life. Gardner syndrome is an exception; the average patient age at onset is 13 years.

CLINICAL

Section 3 of 11  

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History

• Discharge of a foul-smelling cheeselike material is a common complaint.
• Less frequently, the cysts can become inflamed or infected, resulting in pain and tenderness.
• In the uncommon event of malignancy, rapid growth, friability, and bleeding have been reported.
• When located orally, the cysts can cause difficulty in breathing, swallowing, or even speaking.
• Lesion of the genitals can be especially painful during intercourse and cause problems with walking or wearing underwear. They can also interfere with urination.
• Subungual lesions have also been associated with pain, as have plantar lesions, causing difficulty with walking or other activities.

Physical

Epidermoid cysts appear as firm, round, mobile, flesh-colored to yellow or white subcutaneous nodules of variable size. A central pore or punctum is an inconsistent finding that may tether the cyst to the overlying epidermis and from which a thick cheesy material can sometimes be expressed. In individuals with dark pigmentation, epidermoid cysts may also be pigmented. In a study of Indian patients with epidermoid cysts, 63% of the cysts contained melanin pigment.

• In one study, epidermoid cysts were most common (in descending order of frequency) on the face, the trunk, the neck, the extremities, and the scalp. While facial involvement is also frequent in Gardner syndrome, the extremities tend to be affected more than the trunk. The Ibos of Nigerian and other cultures who practice female circumcision represent special groups of patients in whom the vulva is the most common site.
• Epidermoid cysts of the genitals are also common in the general population and may appear as a mass in the breast, the vulva, the clitoris, the penis, the scrotum, or the perineum. For one woman, a clitoral cyst present from age 12 years resulted in ambiguous genitalia. 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.
• Epidermoid cysts manifest in various ways on the extremities. When the cysts occur subungually, they can cause changes in the nails, such as onycholysis and subungual hyperkeratosis, which may be mistaken for psoriasis or onychomycosis. Furthermore, epidermoid cysts on the distal portions of the digits may extend into the terminal phalanx. These cysts also produce changes in the nails, such as pincer nails, in addition to erythema, edema, tenderness, and pain. Sometimes, these findings can mimic arthritis. Palmoplantar lesions represent a unique subset of epidermoid cysts.
• The anterior fontanelle, umbilicus, and popliteal fossa are unusual locations where epidermoid cysts have been found.

Causes

Epidermoid cysts likely form by several mechanisms. They may result from the sequestration of epidermal rests during embryonic life, occlusion of the pilosebaceous unit, or traumatic or surgical implantation of epithelial elements. HPV infection and eccrine duct occlusion may be additional factors in the development of palmoplantar epidermoid cysts. HPV has also been identified in nonpalmoplantar epidermoid cysts.

• Congenital epidermoid cysts of the anterior fontanelle or those that are orogenital in location presumably result from sequestration or trapping of epidermal rests along embryonic fusion planes during development. Lip and lingual lesions may be related to aberrant fusion of the branchial arches, and genital lesions could result from improper closure of the genital folds.
• Any benign or malignant process affecting or growing near the pilosebaceous unit may lead to occlusion or impingement of the follicular ostia and subsequent formation of a cyst. Many cysts with an acneiform distribution are probably the result of follicular occlusion. In elderly persons, accumulated sun damage can injure the pilosebaceous unit, thus causing abnormalities, such as comedonal plugging and hypercornification, both of which can eventuate in cyst formation. Alternatively, cases of mycosis fungoides, Bowen disease, molluscum contagiosum, seborrheic keratoses, and nevi have all been reported in association with epidermoid cysts. In each case, the process was growing in and around the hair follicle.
• True epidermal inclusion cysts result from the implantation of epithelial elements in the dermis.
• • Injuries, especially of the crushing type, such as the slamming of a car door on a finger, are frequently reported in association with subungual or terminal phalanx epidermoid cysts.
  • As previously mentioned, female circumcision is associated with the formation of epidermoid cysts, perhaps from instruments that are not sharp or from imprecise cutting.
  • Theoretically, any surgical procedure may result in epidermoid cysts, and it is surprising that they are not a more common occurrence. Unusual examples of this mechanism include the formation of multiple epidermoid cysts after rhinoplasty and reduction mammoplasty. The use of dermal grafts, presumably because of the inclusion of epithelial elements, has also resulted in the formation of epidermoid cysts. A similar situation has been observed with the use of myocutaneous flaps where the cutaneous portion is buried. Even seemingly minor procedures, such as needle biopsy of the breast, have reportedly induced epidermoid cysts.
• The origin of palmoplantar cysts is especially controversial, and their etiology may be unique. This idea is based on the discovery of HPV and eccrine structures within these cysts. In addition, the palms and the soles lack the pilosebaceous units present in other parts of the body. Some have also questioned the role of daily minor foot trauma, while others implicate all 3 factors.
• • Numerous reports have documented HPV types 57 and 60 antigens, as well as histologic changes characteristic of wart infection, in epidermoid cysts. These findings have been found more consistently in plantar cysts than in palmar cysts, and HPV type 60 has been identified more frequently than type 57. Although most patients deny a history of trauma, many of these cysts are located over pressure points, and mechanical pressure or minor trauma may be a contributing factor. In one study of 25 plantar epidermoid cysts, all were located on weight-bearing areas. The theory is that trauma introduces wart virus into the epidermis and that mechanical pressure forces the wart and the epidermis to descend into the dermis. Subsequently, the wart induces epithelial proliferation that may result in the formation of cysts. On the other hand, the presence of HPV in epidermoid cysts may merely represent superinfection.
  • Carcinoembryonic antigen–positive ductal structures in conjunction with HPV have been found in plantar epidermoid cysts. Some authors speculate that HPV may preferentially infect acrosyringeal epithelium and then invade dermal eccrine ducts, inducing the formation of cysts.

    In fact, connections between the eccrine dermal duct and epidermoid cysts have been characterized with 3-dimensional reconstruction analysis. Others dispute the notion that epidermoid cysts (at least palmar ones) are of eccrine origin in light of a study in which palmar epidermoid cysts failed to react with antibodies specific to luminal and secretory cells of lesions in eccrine glands. Instead, immunoreactivity to differentiation-specific cytokeratins (1 and 10) identical to those of the suprabasal layers of the epidermis and follicular infundibulum occurred. The authors of this study concluded that palmar epidermal cysts with HPV infection are not of eccrine origin, but that they are the result of epidermal implantation or trauma. Another explanation that has been proposed, however, is that these findings reflect metaplasia of the eccrine duct epithelium.

• Certain hereditary syndromes have epidermoid cysts as part of their features. Examples include Gardner syndrome, basal cell nevus syndrome, and pachyonychia congenita. In addition, idiopathic scrotal calcinosis may actually represent an end stage of dystrophic calcification of epidermoid cysts in that area of the body.
• • In a study of 39 patients with Gardner syndrome, 13 (33%) had at least 1 epidermoid cyst. The number of lesions varied from 1 to 20, and the average was 4. Of significance, in another study, epidermoid cysts occurred before polyps were detectable in 39 (53%) of 74 patients with Gardner syndrome. Pilomatrical differentiation may be present in portions of the cysts in these patients. A distinct syndrome with colonic polyps and epidermoid cysts has also been described, where patients had malignant brain tumors and lacked the soft-tissue abnormalities seen in Gardner syndrome.
  • An epidermoid cyst may be a feature of pachyonychia congenita. In addition, a syndrome of leukonychia totalis, multiple epidermoid cysts, and renal calculi has been reported.
  • As the name implies, the etiology of idiopathic scrotal calcification is unknown. However, some authors view this condition as an end stage of dystrophic calcification of scrotal epidermoid cysts. This hypothesis is based on the histologic observation of squamous linings surrounding calcified masses. The lining or wall is not always seen because biopsy specimens are often from older lesions where inflammation has destroyed it.

DIFFERENTIALS

Section 4 of 11  

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Other Problems to be Considered

Nasal glioma
Rheumatoid nodule

WORKUP

Section 5 of 11  

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Lab Studies

• The contents of epidermoid cysts suspected of being infected can be sent for bacterial culture.

Imaging Studies

• Features of epidermoid cysts have been well characterized on sonograms.
• • Most cysts appear as spherical or ovoid hypoechoic masses containing variable echogenic foci and lacking color Doppler signals.
  • Ruptured cysts may have more lobulated contours and show color Doppler signals.
  • Calcified cysts appear as solid hypoechoic masses with multiple calcific foci associated with dense digital acoustic shadowing.
• Epidermoid cysts have also been characterized by MRI.
• • Margins appear well circumscribed, without enhancement of the inside.
  • Compared to muscle, iso- to slightly high-signal intensity is observed on T1-weighted images.
  • T2-weighted images show high-signal intensity.
  • Both T1- and T2-weighted images may also have irregular low-signal intensity areas.
• Radiographs of epidermoid cysts on the distal phalanges may show well-defined osteolytic lesions outlined by a fine rim of bone.
• Lesions with features suggestive of intracranial or intraosseous extension are best evaluated with computed tomography and plain radiography.

Other Tests

• Fine needle aspiration has been used to help diagnose epidermoid cysts. Smears of aspirated material can be stained with Wright-Giemsa, and they demonstrate nucleated squames and wavy keratin material.

Histologic Findings

The typical epidermoid cyst is lined with stratified squamous epithelium that contains a granular layer and is filled with keratinous material that is often in a laminated arrangement. Hybrid cysts can also occur where part of the lining has features of an apocrine hidrocystoma or trichilemmal cyst. Older cysts may exhibit calcification or a foreign body reaction to the contents of the cyst that has ruptured into the dermis.

An important finding is the occasional presence of malignancy in an epidermoid cyst. The most common malignancies are SCC and basal cell carcinoma, respectively, but Bowen disease, metastatic carcinoma, Merkel cell carcinoma, and mycosis fungoides have all been reported. In addition, benign processes, such as bowenoid papulosis, Darier disease, molluscum contagiosum, pilomatricomas, psoriasis, pyogenic granulomas, and seborrheic keratoses, can also grow in the wall of an epidermoid cyst.

Pigmented epidermoid cysts may demonstrate melanin pigment in the wall and a keratin mass. A surrounding infiltrate of melanocytes and melanophages may also be observed.

Palmoplantar epidermoid cysts that are infected with HPV show characteristic histologic changes. The findings include intracytoplasmic eosinophilic inclusion bodies in the cyst wall, vacuolated cells and cells with condensed keratohyalin granules in the granular layer, elongated rete ridges, and vacuolated structures and parakeratotic nuclei in the keratinous mass. Structures resembling eccrine ducts are also observed in some lesions.

TREATMENT

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Medical Care

Asymptomatic epidermoid cysts do not need to be treated.

• Uninfected, inflamed cysts may respond to an intralesional injection of triamcinolone.
• For cysts considered to be infected, incision and drainage followed by treatment with antistaphylococcal oral antibiotics is recommended.

Surgical Care

Various surgical techniques, including lasers, have been used in the treatment of epidermoid cysts. Popular approaches include incision and drainage, traditional or mini excision, and trephination.

• Incision and drainage is a fast and simple manner of dealing with epidermoid cysts. However, recurrences are frequent because the keratin producing lining of the cyst is not removed.
• Excision in toto represents a more definitive treatment and may by the surest way to prevent recurrence and avoid missing malignant changes. It is also preferable in the face of fibrosed cysts. If the punctum is visible, the excision should be designed around it. Wounds can be sutured immediately, or they can be allowed to drain prior to closure, especially if secondary infection is suspected. Some consider the Desmarres clamp to be a useful instrument in the removal of cysts on the earlobe. The main drawbacks of excising epidermoid cysts are the increased wound length and the risk of scarring.
• Combinations of the above procedures have been used to address their individual deficiencies.
• • Mini-incisions or microincisions, which allow drainage of epidermoid cysts, are followed by removal of the lining through the opening. Sometimes, the application of a chemical, such as phenol or Solcoderm (a copper ion and acid solution), to dehydrate the wall can facilitate its removal. However, phenol has been noted to depigment skin around the incision in individuals with dark pigmentation.
  • Trephination with punch biopsy essentially serves the same purpose as the microincision. The authors of one study reported a recurrence rate of 3.6-8.9% with this technique. Greater than half of these recurrences were within the first year, and they occurred most frequently on the back and ear.
  • Alternatively, a diathermy needle can be inserted in the cyst to decompress it, after which the lining can be accessed if desired.
  • Because of their small size, the wounds from mini-incisions or microincisions, trephination, or decompression with a diathermy needle are often allowed to heal secondarily.
• The treatment of epidermoid cysts on the terminal phalanx is more complicated and may consist of curettage or chemical cautery followed by packing with bone chips.
• A woman with multiple facial epidermoid cysts was successfully treated with a carbon dioxide laser.

Consultations

Signs or symptoms suggestive of intracranial or intraosseous extension, especially in children, warrant consultation with a neurosurgeon.

MEDICATION

Section 7 of 11  

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The goals of pharmacotherapy are to reduce morbidity and to prevent complications.

Drug Category: Corticosteroids

These agents have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body's immune response to diverse stimuli.

FOLLOW-UP

Section 8 of 11  

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Deterrence/Prevention

• When the cutaneous portion of a myocutaneous flap is to be buried, a dermatome should be used to remove the epidermis.

Complications

• The role of bacteria in epidermoid cysts is controversial; many cysts considered to be infected are likely just inflamed. However, noninflammed cysts grow skin commensals, such as Staphylococcus epidermidis and Propionibacterium acnes. Presumably, these cysts are colonized because of the connection with the overlying skin either directly or via a hair follicle or an eccrine duct. Therefore, epidermoid cysts should be susceptible to infection with pathogenic bacteria, and this observation has been demonstrated in a study of cyst abscesses. Most bacteria observed were either aerobic or facultative. S epidermis was the most common organism recovered, followed by group A streptococci organisms and Escherichia coli. These cysts were more common in the perirectal, vulvovaginal, and cranial areas than in the extremities. A case of Staphylococcus septicemia infection after the removal of an epidermoid cyst suspected of being infected has been reported.
• As mentioned, malignancies have been identified in epidermoid cysts. In one study, 473 specimens submitted as benign cysts were examined, and malignant tumors were found in 19 (4%). In a similar study of 553 cysts, 5 (0.9%) cases of malignancy were identified. A more comprehensive study found the incidence of carcinomas arising in excised cysts to be only 0.011%. These cysts were located on the face, the neck, and the trunk of patients aged 21-80 years. After a mean follow-up of 2.6 years, no recurrences or metastases had occurred. Separate analyses of cases of SCC and BCC found that these cysts had been present anywhere from 45 days to 56 years, that they were predominantly located on the head, and that patients were aged 30-80 years.
• An unusual complication reported from an oral epidermoid cyst was sialadenitis due to pressure on the submandibular salivary duct.

MISCELLANEOUS

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Medical/Legal Pitfalls

• The major pitfall in managing epidermoid cysts is failure to diagnose an associated malignancy. Therefore, removal is recommended for any cyst behaving in an unusual way (eg, rapid growth). In turn, all excised cysts should be sent for pathologic analysis.
• Genital and umbilical lesions should be approached with caution because they sometimes extend into the pelvis or below the midline fascia.
• Patients with lesions that are suspected of having an intracranial or intraosseous connection should be referred for neurosurgical evaluation. Inappropriate management of these lesions may result in cerebrospinal fluid leakage and potentially introduce infection leading to fatal meningitis. Features suggestive of intracranial or intraosseous extension include the following:
• • Presence since birth or appearance in early childhood (Some lesions, especially small ones, can occasionally remain unnoticed until adulthood.)
  • Bruits, or 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
  • Neurologic symptoms or history of meningitis

MULTIMEDIA

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Media file 1:  Unusually large epidermoid cyst with a prominent punctum on the back of a patient. (Ruler is in centimeters.)
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Media file 2:  Multiple epidermoid cysts on the forehead of a patient with Gardner syndrome.
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Media file 3:  Cyst containing keratinous material (hematoxylin and eosin, original magnification X1.6).
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Media file 4:  Higher-magnification view of the cyst wall of the cyst in Image 3 demonstrates a true epidermis with a granular layer and adjacent laminated keratinous material (hematoxylin and eosin, original magnification X20).
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Media type:  Photo

REFERENCES

Section 11 of 11

• Authors and Editors
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• Differentials
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• Fellner MJ, Osowsky MJ. Molluscum contagiosum in an epidermal inclusion cyst on the eyelid. Int J Dermatol. Mar 1979;18(2):160-1. [Medline].
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