Introduction

Epidermoid cyst, also known as a sebaceous cyst, is a benign encapsulated, subepidermal nodule filled with keratin material.  Although most commonly located on the face, neck, and trunk, epidermoid cysts can be found anywhere, including the scrotum, genitalia, fingers, and cases within the buccal mucosa. Cysts may progress slowly and remain present for years. The term sebaceous cyst is commonly used; however, it is a misnomer, as it does not involve the sebaceous gland. Epidermoid cysts develop within the infundibulum. Other common synonyms include infundibular cyst, epidermal cyst, and epidermal inclusion cyst. Although these cysts are recognized as benign lesions, a rare malignancy can arise.[1][2][3]

Etiology

The majority of epidermoid cyst cases are sporadic. Although epidermoid cysts can be found in autosomal dominant (AD) Gardner syndrome (familial adenomatous polyposis) and Gorlin syndrome (basal cell nevus syndrome). Epidermoid cysts occurring before puberty in unusual locations and numbers raise the suspicion of a syndrome. In elderly patients with Favre-Racouchot syndrome (nodular elastosis with cysts and comedones), epidermoid cysts may result from chronic sun damage. Patients on BRAF inhibitors can develop epidermoid cysts of the face. Lately, imiquimod and cyclosporine have been associated with epidermal inclusion cysts.[4][5][6]

Epidemiology

Epidermoid cysts are the most common cutaneous cysts and typically occur in the third and fourth decades of life. It is rare to find these cysts before puberty. They are predominantly found in males versus females (ratio 2:1). In the neonatal period, small epidermal cysts, referred to as milia, are common. Approximately 1% of epidermoid cysts have been noted to have a malignant transformation to squamous cell carcinoma (SCC) and basal cell carcinoma (BCC).

Pathophysiology

Epidermoid cysts are derived from the follicular infundibulum. Generally, these cysts are the result of the plugging of the follicular orifice. The cyst communicates with the surface of the skin through a keratin-filled orifice. Disruption of the follicle is important in the pathogenesis, as those with acne vulgaris may have multiple epidermoid cysts originating from comedones. Additionally, they can also occur from traumatic and penetrating injuries leading to the implantation of the epithelium. Epidermoid cysts are lined with stratified squamous epithelium that leads to an accumulation of keratin within the subepidermal layer or dermis. Generally, the cysts are asymptomatic until they rupture. When the cysts rupture, an inflammatory reaction occurs due to the displacement of soft, yellow keratin into the dermis and surrounding tissue. Recently, ultraviolet (UV) light and human papillomavirus (HPV) infection have been implicated in the development of epidermoid cysts.

Histopathology

Stratified squamous epithelium lines the cyst. Histological examination reveals an epithelial-lined cyst filled with laminated keratin located within the dermis. The lining of the cyst is similar to the surface epithelium but differs in lacking rete ridges.  A granular layer is present, filled with keratohyalin granules.

History and Physical

Physical examination generally reveals a non-fluctuant, compressible mass measuring 0.5 cm to several centimeters. A central, dark comedone opening (punctum) is often described. Epidermoid cysts are usually asymptomatic; however, if ruptured, they may closely resemble a furuncle with tenderness to palpation, erythema, and swelling. A foul-smelling, yellowish, cheese-like material discharged from the skin may be described. Some patients may describe an event of a fall on their back or someone slapping their back, causing painful swelling and the resulting cystic rupture. Epidermoid cysts can occur anywhere, but are most common on the face, neck, chest, upper back, scrotum, and genitals. They can also be found on the buttocks, palms, and plantar side of feet due to penetrating trauma. If occurring on the distal portion of the fingers, changes to the nail plate may occur. Taking a good history can help determine whether the cyst is an isolated case, medication-related, or part of a genetic syndrome.

Evaluation

Evaluation of epidermoid cysts is based largely on history and physical examination. The need for histological examination of the excised mass is often debated. Laboratory examination is not necessary. Radiographic tests are not commonly utilized in the evaluation of epidermoid cysts.

Treatment / Management

The most effective treatment involves complete surgical excision of the cyst with the cyst wall intact. The complete excision should be delayed if an active infection is present, as the planes of dissection will be difficult to identify. In these cases, an initial incision and drainage may be indicated, with a potential for recurrence. A local anesthetic with epinephrine is preferred to minimize bleeding. Anesthetic should be injected around the cyst, avoiding direct injection into the cyst. A small diameter elliptical incision with the inclusion of the central core, or punctum can be utilized. For optimal cosmetic results, it is important to maintain the incision along the minimal skin tension lines. A multiple-layered subcuticular and epidermal closure will yield an optimal outcome. An alternative surgical approach can also involve a punch biopsy, with expulsion of the intact cyst through the small defect, or standard excision. If there is surrounding inflammation, intralesional triamcinolone may be used to help reduce inflammation and delay surgical removal. If the cyst has ruptured and its lining has been destroyed, it will not recur. However, removing the entire cystic lining is important in decreasing recurrence.[7][8][9]

Differential Diagnosis

Depending on location, the differential diagnoses of epidermoid cysts include the following: lipoma, dermoid cyst, pilar cyst (isthmus-catagen cyst, trichilemmal, wen), furuncle, branchial cleft cyst, milia, pilonidal cyst, calcinosis cutis, Pachyonychia Congenita, steatocystoma, and cutaneous findings of Gardner syndrome.

Prognosis

Epidermal inclusion cysts are recognized as benign cysts. However, rare malignancy can occur. Squamous cell carcinoma (SCC) is the most common malignancy followed by basal cell carcinoma (BCC).  In developing malignancy, squamous cell carcinoma occurs approximately 70% of the time.

Complications

Complications of rupture include erythema, swelling, and pain. Complications of surgical removal include bleeding, infection, and scarring. Erythema and pain can be managed with intralesional triamcinolone. Infection following surgery can be prevented using proper aseptic techniques. While recognized as a benign cyst, a rare malignancy may occur.

Postoperative and Rehabilitation Care

Following surgical excision, it is appropriate to avoid contact sports and strenuous activity. Sutures may be removed within 7-10 days. Patients should be instructed that the surgical scar will generally take 8 weeks to reach a maximum tensile strength of 80% of the original skin strength. Scar revision, if necessary, should take place between 6 months and 1 year following excision, as the remodeling phase of wound healing occurs between 3 weeks and 1 year.

Consultations

Consultations are not necessary unless the cyst is large and in an unusual location, such as the mouth or face. In those circumstances, specialist consultation may be warranted. Adults with epidermoid cysts in rare locations, such as the fingers and toes, a history of multiple lipomas, and a family history of colon cancer should raise the suspicion of Gardner syndrome, with an appropriate specialist referral.

Pearls and Other Issues

Epidermoid cysts (sebaceous cysts) are common benign encapsulated cysts. Due to the inflammatory reaction from the release of keratin contents, many practitioners will mistake the cyst for an abscess and prescribe antibiotics.

Enhancing Healthcare Team Outcomes

Epidermal cysts are commonly encountered by the primary care provider, dermatologist, nurse practitioner, surgeon, and internist. While the majority of these cysts are benign, it is important to send the excised sample for evaluation to ensure that there is no malignancy.When completely excised, the outcomes are excellent. However, recurrences are common in patients with genetic syndromes.[10]

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References

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Ma J, Jia G, Jia W. Primary intradiploic epidermoid cyst: A case report with literature review. Clin Neuropathol. 2019 Jan/Feb;38(1):28-32. [PubMed: 30526818]

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Weir CB, St.Hilaire NJ. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 8, 2023. Epidermal Inclusion Cyst. [PubMed: 30335343]

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Prior A, Anania P, Pacetti M, Secci F, Ravegnani M, Pavanello M, Piatelli G, Cama A, Consales A. Dermoid and Epidermoid Cysts of Scalp: Case Series of 234 Consecutive Patients. World Neurosurg. 2018 Dec;120:119-124. [PubMed: 30189303]

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Frank E, Macias D, Hondorp B, Kerstetter J, Inman JC. Incidental Squamous Cell Carcinoma in an Epidermal Inclusion Cyst: A Case Report and Review of the Literature. Case Rep Dermatol. 2018 Jan-Apr;10(1):61-68. [PMC free article: PMC5903124] [PubMed: 29681810]

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Disclosure: Patrick Zito declares no relevant financial relationships with ineligible companies.

Disclosure: Richard Scharf declares no relevant financial relationships with ineligible companies.