Are You Confident of the Diagnosis?

Epidermal inclusion cysts (EIC) are benign neoplasms of the skin that are also known by the following synonyms: epidermal cyst, infundibular cyst, keratinous cyst, epidermoid cyst and sebaceous cyst. They can occur anywhere on the cutaneous surface, with the face, chest, and back being the most common locations.

Characteristic findings on physical examination

Clinically, they appear as a slow growing yellow or white papule or nodule anywhere from a few millimeters to multiple centimeters in diameter. Characteristically, they have a smooth surface and a small opening to the surface of the skin, known as a punctum. Most uninflamed EIC are soft and mobile. However, if the cyst rutures or becomes inflamed, the patient presents with a tender erythematous nonmobile nodule. With repeated inflammation, scarring develops in association with the cyst.

Expected results of diagnostic studies

The vast majority of EIC can be diagnosed by clinical examination. Upon removal of an EIC, the diagnosis is confirmed by submitting the excised tissue for routine histopathology.

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Microscopically, one sees a cystic space in the dermis with an epithelial lining wall. The cyst wall is contiguous with the surface epidermis, creating the “pore” that is seen clinically. The wall of the cyst is characterized by epithelium that mimics normal epidermis, including basal, spinous, and granular cell layers. The contents of the cyst are composed of laminated orthokeratin which has a “flaky” appearance in contrast to the dense pink keratin of a pilar cyst.

Ruptured cysts show discontinuity of the cyst wall associated with mixed inflammation including neutrophils, eosinophils, lymphocytes, histiocytes and muntinucleated giant cells. Previously ruptured cysts will show surrounding scar tissue.

Radiological techniques are generally not required for diagnosis of an EIC. However if the diagnosis is in question for a large or deep-seated lesion, ultrasound may be able to distinguish a cystic lesion from a solid tumor.

Diagnosis confirmation

The clinical differential diagnosis of EIC includes other benign and malignant tumors of the skin. Atypical clinical presentations, including a history of rapid or continued growth, should prompt consideration of biopsy and/or removal. The differential diagnosis of an inflamed EIC includes a bacterial furuncle which is often caused by Stapylococcus aureus. In the latter entity, there is a history of acute onset in contrast to a history of a long-standing lesion that became red and/or painful. Bacterial culture is important in this clinical scenario.

Milia are small white superficial keratinizing cysts. While milia typically appear in and of themselves in adults, they can occur in the setting of acne vulgaris, chronic actinic damage, following trauma or subepidermal blistering disorders. They may also be congenital as they are seen in about 40% of newborns, as well a feature of multiple genodermatoses. Histologically, they are identical to EIC except for their small size and location in the superficial dermis, just beneath the epidermis (Figure 4).

Figure 1.

Epidermal inclusion cyst: note central punctum (Courtesy of Joseph Sobanko, MD)

Figure 2.

Low-power view of an epidermal cyst showing a cystic invagination of epithelium that connects with the overlying epidermis.

Figure 3.

The wall of the cyst shows a granular cell layer. The contents of the cyst are laminated keratin.

Figure 4.

Milium: a small epidermal cyst in the superficial dermis.

Who is at Risk for Developing this Disease?

Epidermal inclusion cysts are the most common type of cutaneous cyst. While they are usually seen in patients in their third to fourth decade of life, they may occur in persons of at any age, including infants and the elderly. They are seen more commonly in males than females. A history of acne, exposure to ultraviolet light, and human papillomavirus infection have all been proposed as possible etiological agents, however, in most patients, they appear to occur sporadically.

What is the Cause of the Disease?

Most EIC are thought to originate from the infundibular portion of a hair follicle. A slow-growing outpouching of the follicular epithelium expands into the dermis and/or the subcutaneous fat and produces keratin within the cystic space. Traumatic EIC can be found in non-hairbearing locations such as the palms and soles, as well as in other areas of trauma or significant blistering. In this latter scenario, a portion of epidermis is introduced into the dermis and subsequently develops into a cystic lesion. Rarely, EIC have been associated with human papillomavirus infection, many of which have been located on the sole of the foot. Inflammation of EIC may occur secondary to local trauma or without an inciting external event.

Systemic Implications and Complications

The vast majority of EIC do not have systemic associations. However, multiple EIC have been associated with Gardner’s syndrome. In addition, multiple EIC can be seen in basal cell nevus syndrome (Gorlin syndrome).

The most common complication of EIC is rupture and inflammation, which can cause significant pain and discomfort for patients. Although the cyst becomes tender, erythematous, and warm, the majority are not truly infected. In some instances, however, secondary bacterial infection can occur, producing cellulitis with fever and elevated white blood cell count.

Treatment Options

Asymptomatic EIC do not necessarily need any treatment. Uninflamed EIC are often removed under the following circumstances: (1) If the diagnosis is in question, the lesion should be removed and sent for histopathology; (2) cosmetic concern to the patient; or (3) prophylactic removal to prevent rupture and inflammation.

Surgical excision is standard therapy. Elliptial excision is generally curative. It should be noted that if the entire cyst wall is not removed, local recurrence is common. Because elliptical excision can result in a large surgical scar, other techniques have been suggested:

-A small fusiform ellipse of skin (smaller than the cyst) is cut, followed by extraction of the cyst via a small hole.

-Similar techniques using a punch or laser have been reported. These latter techniques result in a smaller surgical scar and faster postoperative recovery. However there may be a higher risk of local recurrence, especially with larger diameter (larger than 2 cm) cysts.

If an EIC is inflamed, several options are possible:

-Intralesional injection of corticosteroid as a single dose in the office. For lesions on the face, triamcinolone 5mg/cc is recommended. For larger lesions, especially on the back, 10mg/cc is more effective.

-Depending on the degree of inflammation, oral antibiotics (as an alternative or in addition to intralesional corticosteroid) can be utilized. Oral tetracycline, or one of its derivatives (doxycycline, minocycline both at a dose of up to 100mg orally twice a day in an adult), can be used for 1-2 weeks depending on the size of the lesion and the degree of inflammation. Alternatives to the tetracycline group include cephalexin, ciprofloxin, and erythromycin.

-In markedly inflamed cysts, especially those that are fluctuant, consider incision and drainage combined with temporarily packing the area with a gauze wick. This is done in conjunction with appropriate antibiotic therapy.

– Local warm compresses can provide some symptomatic relief.

-Surgical excision should be delayed until the lesion is no longer inflamed. Surgery on an inflamed EIC is more likely to cause fragmentation and incomplete removal of the cyst wall, resulting in recurrence.

Optimal Therapeutic Approach for this Disease

Decision-making for treating epidermal cysts often depends on the presence or absence of inflammation. Uninflamed cysts can be surgically removed or simply left untreated.

1. Asymptomatic uninflamed epidermal cyst: No treatment

2. Asymptomatic uninflamed epidermal cyst: Prophylactic excision

3. Inflamed epidermal cyst, mild or moderate: Intralesional triamcinolone

4. Infamed epidermal cyst, severe: add oral antibiotic and/or drainage

5. Epidermal cyst with history of inflammation: Surgical removal when no longer inflamed

There is minimal risk with these therapeutic options. With intralesional triamcinolone, the patient should be warned about the possibility of atrophy, especially if the lesion is in a cosmetically sensitive area such as the face. Surgical excision will result in a scar; as with all surgeries, there is a low risk of local infection.

Patient Management

No long-term follow up is necessary for patients with EIC. If the cyst is surgically removed, it should be sent for histopathological analysis to confirm the diagnosis.

Unusual Clinical Scenarios to Consider in Patient Management

Although rare, malignancies have been associated with EIC, including Bowen’s disease and squamous cell carcinoma, basal cell carcinoma, Merkel cell carcinoma, melanoma in situ, and Paget’s disease. These reports highlight the importance and submitting epidermal cysts for histopathologic examination. This is especially important if the lesion does not respond as one would expect after standard care, such as intralesional steroid injections and/or antibiotics – rather than continually repeat this approach, it may be prudent to excise the lesion with histopathologic analysis.

As noted above, bacterial furunculosis may clinically mimic an inflamed EIC. If the diagnosis is in question, culture and drainage should be considered.

What is the Evidence?

Jenkins, JR, Morgan, MB. “Dermal cysts: a dermatopathological perspective and histological reappraisal”. J Cutan Pathol. vol. 34. 2007. pp. 815-29. (This is a clinical and histopathological review and literature update of cutaneous dermal cysts.)

Ashida, M, Ueda, M, Kunisada, M. “Protean manifestations of human papillomavirus type 60 infection on the extremities”. Br J Dermatol. vol. 146. 2002. pp. 885(This is a case report and discussion of warts and cysts cause by human papillomavirus type 60.)

Lee, HE, Yang, CH, Chen, CH. “Comparison of the surgical outcomes of punch incision and elliptical excision in treating epidermal inclusion cysts: a prospective, randomized study”. Dermatol Surg. vol. 32. 2006. pp. 520-5. (A small study (n=60) comparing traditional wide excision with punch biopsy removal of cysts.)

Morice-Picard, F, Sevenet, N, Bonnet, F. “Cutaneous epidermal cysts as a presentation of Gorlin Syndrome”. Arch Dermatol. vol. 145. 2009. pp. 1341-3. (Two case reports of patients with Gorlin syndrome who presented with epidermal cysts.)

Berk, DR, Bayliss, SJ. “Milia: A review and classification”. J Am Acad Dermatol. vol. 59. 2008. pp. 1050-63. (This is a comprehensive reivew of milia in both pediatric and adult populations.)