A 22-year-old white man notices a bump on his skin and seeks medical attention. He reports a 1-month history of an asymptomatic lesion on his upper arm. Aside from a diagnosis of acne vulgaris, his medical and family history is unremarkable. He does not smoke. On examination, the lesion measures approximately 3 mm in diameter and is freely moveable, with a visible central punctum. His scalp, neck, back, nails, hair, oral mucosa, and genitals are normal.
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Epidermal inclusion cysts — also known as epidermoid, infundibular, and keratin cysts — are the most commonly diagnosed cutaneous cysts.1,2 These cysts are freely moveable, slow-growing masses with a central punctum that may present as painful, inflamed, and fluctuant nodules if rupture of the cyst occurs.2 These lesions commonly present on the face and trunk of young to middle-aged men; however, any location or age group can be affected.1,2 Diagnosis is made clinically and removal is typically not necessary.2 Treatment options include surgical excision, triamcinolone injections, and cyst drainage. Prognosis is excellent, although recurrence of excised lesions is common.
Milia are tiny epidermal inclusion cysts that are commonly present in neonates but can occur throughout life.1 Although not genetically linked, epidermal inclusion cysts can present alongside rare genetic conditions like Gardner syndrome and Gorlin syndrome.1-3 These cysts are more prevalent in patients with chronic sun-damaged skin, those who smoke, and those receiving treatment with BRAF inhibitors such as imiquimod and cyclosporine.2,4,5 Most notably, epidermal inclusion cysts are associated with acne vulgaris and other conditions that result in inflamed or irritated hair follicles.2
Epidermal inclusion cysts are lined with stratified squamous epithelium and filled with distinct keratin debris.6 They occur anywhere on the body, including the face, scalp, neck, back, and genitals and are considered sporadic, benign, and noncontagious cutaneous lesions.1,2,4,7,8 These lesions can range in size from a few millimeters to several centimeters in diameter, but one cannot predict the size of the lesion upon onset.1,2 Epidermal inclusion cysts can be categorized as either primary or secondary lesions.2 Primary cysts arise directly from obstructions in the cavity underlying the hair follicle. Patients with acne vulgaris have a higher prevalence of disrupted hair follicles and obstructed pores, which results in higher rates of primary cysts. Secondary cysts arise from follicular epithelium that implants into the dermis and are most commonly due to trauma. Epidermal inclusion cysts are often infected by normal skin flora including Staphylococcusaureus and Staphylococcusepidermidis.2 Infected nodules are asymptomatic unless ruptured, in which case cyst contents leak into and infect surrounding tissue.1
Almost all cases of epidermal inclusion cysts can be diagnosed by conducting a thorough history and physical examination.2,6 If a genetic condition (ie, Gardner syndrome or Gorlin syndrome) is suspected, then additional radiographic and ultrasonographic examination may be indicated.1,2 Upon histologic analysis, these cysts are characterized by the presence of epidermal elements in the dermis.2 The cyst wall protrudes into the cavity underlying the hair follicle and is filled with keratin and keratohyalin granules. In some cases, the cyst wall is derived from the hair follicle infundibulum. In infected states and rupture, epidermal inclusion cysts are acutely inflamed and present with invasion of neutrophils or giant cells.2,6 Unlike sebaceous cysts, epidermal cysts do not originate from sebaceous glands and lack sebum, instead containing keratin that has a “cheesy” appearance.1,2
Depending on the cyst’s location, differential diagnoses can range from pilar cysts, ganglion cysts, and lipomas to neuromas and neurofibromas.1 Pilar cysts, unlike epidermal inclusion cysts, are characterized by trichilemmal keratinization. Ganglion cysts often occur at joints and are characterized by hyaluronic acid contents. Lipomas, on the other hand, are benign tumors made of fat tissue that present as soft, movable, and painless lumps.1 Approximately 1% of epidermal inclusion cysts undergo malignant transformation into basal cell carcinomas and squamous cell carcinomas.2,9 Whenever carcinoma is suspected, skin biopsy is recommended for further testing and confirmation.
In general, epidermal inclusion cysts are usually benign and surgical excision is often not required. However, since these lesions likely will not resolve on their own, 3 forms of treatment can be considered: definitive treatment, alternative treatment, and conservative treatment.2 Definitive treatment involves surgical excision or punch biopsy, making sure to remove the entire sac of the cyst to avoid recurrence.1,2 Alternative treatment involves triamcinolone injections (10 mg/mL for nodules on the trunk and 3 mg/mL for nodules on the face) into the cyst proper.2 Triamcinolone injections have been found to resolve ongoing inflammation and prevent recurrence of infected epidermoid cysts. Conservative treatment involves draining the cyst and administering oral antibiotics against normal skin flora; such treatment is employed when epidermoid cysts are acutely inflamed.2,10 However, some studies suggest that these inflamed cysts can be safely excised with lower recurrence rates when appropriate washing and wound care are implemented.1
Complete excision of accumulated keratin and the cystic wall within epidermal inclusion cysts has an excellent prognosis. Surgical complications include infection, scarring, and wound dehiscence.2 Additionally, incomplete excision can lead to recurrence.1,2,10 Rupture of the cyst prior to excision can result in cellulitis, swelling, and erythema.2
The patient in this case was told that he had a benign epidermal inclusion cyst; he opted for excision as he was self-conscious about the lesion. He was pleased with the outcome.
Venkata S. Jonnakuti, BS, is a medical student; McKenna E. Boyd, BS, is a medical student; and Christopher Rizk, MD, is a dermatology fellow at Baylor College of Medicine, in Houston, Texas.
- Pandya KA, Radke F. Benign skin lesions: lipomas, epidermal inclusion cysts, muscle and nerve biopsies. Surg Clin North Am. 2009;89(3):677-687.
- Weir CB, St. Hilaire NJ. Epidermal inclusion cyst. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2019.
- Morice-Picard F, Sévenet N, Bonnet F, Jouary T, Lancombe D, Taieb A. Cutaneous epidermal cysts as a presentation of Gorlin syndrome. Arch Dermatol. 2009;145(11):1341-1343.
- Lin S-H, Yang Y-C, Chen W, Wu W-M. Facial epidermal inclusion cysts are associated with smoking in men: a hospital-based case-control study. Dermatol Surg. 2010;36(6):894-898.
- Richter A, Beideck S, Bender W, Frosch PJ. [Epidermal cysts and folliculitis caused by cyclosporin A]. Hautarzt. 1993;44(8):521-523.
- Handa U, Chhabra S, Mohan H. Epidermal inclusion cyst: cytomorphological features and differential diagnosis. Diagn Cytopathol. 2008;36(12):861-863.
- Pehlivan M, Özbay PÖ, Temur M, Yilmaz Ö, Gümüş Z, Güzel A. Epidermal cyst in an unusual site: a case report. Int J Surg Case Rep. 2015;8C:114-116.
- Apollos JR, Ekatah GE, Ng GS, McFayden AK, Whitelaw SC. Routine histological examination of epidermoid cysts; to send or not to send? Ann Med Surg. 2016;13:24-28.
- Bajoghli A, Agarwal S, Goldberg L, Mirzabeigi M. Melanoma arising from an epidermal inclusion cyst. J Am Acad Dermatol. 2013;68(1):e6-e7.
- Zuber TJ. Minimal excision technique for epidermoid (sebaceous) cysts. Am Fam Physician. 2002;65(7):1409-1412.