Are You Confident of the Diagnosis?
What you should be alert for in the history
Patients typically will have a prior history of an noninflamed cyst that had appeared as a firm mobile intradermal or subcutaneous nodule.
Patients may report that pressure to the previously noninflamed cyst had produced a discharge of thick cheesy keratinous material through a central punctum. The previously noninflamed cyst may suddenly develop inflammation, redness, and tenderness. The cyst may feel softer, or more fluctuant when compared to the previously noninflamed cyst. Pressure may lead to the discharge of purulent material, in addition to keratin debris. By contrast to the noninflamed cyst, the inflamed cyst typically emits a less viscous discharge. The cause of cyst rupture is usually unclear.
Characteristic findings on physical examination
In the acute phase, the cyst presents as a fluctuant, soft, subcutaneous nodule or cyst. Inflammation and redness, with or without tenderness, are usually present. Pressure may lead to discharge of a purulent and keratinous material. If the inflammation is severe, the ruptured cyst may cause an ulcer, through which the cyst contents may drain (Figure 1).
In the chronic phase, the ruptured cyst presents as a firm, often deep-seated, subcutaneous nodule. The ruptured cyst may feel fixed to the underlying fascia. Tenderness, inflammation, and drainage are typically absent, but recurrence of inflammation may occur.
Epidermal inclusion cysts can arise anywhere on the surface of the skin.
Expected results of diagnostic studies
Diagnosis is often apparent from history and clinical examination.
Biopsy will confirm the clinical impression (Figure 2). The biopsy technique must reach the pathology within the dermis and possibly the subcutaneous fat. Punch, incisional, or excisional biopsy techniques are preferred.
Bacterial culture of the drainage will confirm whether or not a bacterial pathogen is contributing to the inflammation.
Abscess from bacterial infection is the main differential diagnosis for an inflamed cyst. Patient history can help to distinguish a keratin granuloma/inflamed cyst from a bacterial abscess. The inflamed cyst will have a history of a previously noninflamed subcutaneous nodule, whereas the bacterial abscess will not.
Bacterial culture may or may not distinguish between an abscess and inflamed cyst. It is possible that the inflamed cyst is infected with bacteria, but previous studies have shown no difference in the culture results between inflamed and uninflamed cysts. Extrusion of keratin, rather than infection from bacteria, appears to be the primary cause of inflammation in the keratin granuloma.
Who is at Risk for Developing this Disease?
Any person with an uninflamed epidermal inclusion cyst is at risk for rupture of the cyst wall and formation of a keratin granuloma.
Patients with Gardner syndrome, nevoid basal cell carcinoma syndrome, and Favre-Racouchot syndrome are at risk to develop multiple epidermal inclusion cysts.
Men who smoke may also be at increased risk to form epidermal inclusion cysts.
What is the Cause of the Disease?
Epidermal inclusion cysts are dermal-based proliferations of surface epidermal cells that continue to produce keratin. The lack of communication with the surface of the skin leads to the formation of a dermal-based epithelial-lined sac filled with keratin. The initial cause of formation of epidermal inclusion cysts is uncertain. Proposed mechanisms for epidermal inclusion cyst formation include occlusion of pilosebaceous follicles and implantation of epidermal cells into the dermis after penetration injury.
The proposed mechanism of implantation of epidermal cells in the dermis after penetration injury is supported by multiple reports of epidermal inclusion cyst formation after surgery or traumatic injury.
The onset of inflammation of the cyst results from rupture to the cyst wall and extrusion of the keratinous contents of the cyst into the dermis. The extruded keratin elicits an inflammatory response, hence the name “keratin granuloma.”
The cause of cyst rupture remains uncertain. Bacterial infection may or may not contribute to cyst rupture. Some authors argue that bacterial infection does not cause cyst rupture. Others argue that anaerobic bacteria play a role in the inflammatory process.
Systemic Implications and Complications
Most inflamed cysts/keratin granulomas arise spontaneously and are not associated with any systemic disorders. For patients presenting with multiple epidermal inclusion cysts, one may consider work-up for Gardner syndrome or nevoid basal cell carcinoma syndrome.
Nonsurgical treatment options aim to decrease the inflammation and discomfort associated with the keratin granuloma. These methods do not remove the cyst wall, therefore the patient remains at risk for recurrence of inflammation. Subsequent definitive surgical therapy will be necessary if the patient desires complete removal.
Intralesional kenalog can be given, but the concentration should be modified according to the depth, firmness, and age of the scarred cyst. Mature keratin granulomas are typically firmer and thicker and will benefit from injection of a higher concentration (e.g. 40mg/cc of triamcinolone acetonide injectable suspension). Recently developed keratin granulomas frequently have a soft and attenuated cyst wall. Incision and drainage is usually preferred in the acute phase, but injection with a lower concentration of intralesional kenalog (e.g. 10mg/cc of triamcinolone acetonide injectable suspension) may help to reduce inflammation.
Bacterial Culture and Sensitivities
Bacterial culture and sensitivities can be conducted, followed by the administration of appropriate systemic antibiotics, if an infection is found.
Surgical treatment options aim to relieve pressure (by draining cyst contents) andprevent recurrence (by removing the entire cyst wall and its contents). The timing of the surgery may vary depending on the suspicion of infection and degree of inflammation. Delaying surgery may be prudent if the ruptured cyst is infected.
Incision and Drainage
While incision and drainage can relieve pressure and inflammation, it does not remove the cyst wall. Subsequent excision will be necessary if the patient desires cyst removal. Nevertheless, culture of the cyst contents can detect the presence of bacteria and guide antibiotic choice, if the cyst is infected.
Minimal Excision Techniques
Multiple authors have published articles that describe satisfactory outcomes that resulted from extruding the uninflamed cyst and its contents through small incisions. Minimal excision techniques are frequently not possible for keratin granulomas, however. The ruptured cyst wall lacks integrity and is often dispersed throughout the dermis. Therefore, the surgeon loses his or her ability to visualize the cyst wall. In addition, the inflammation around the ruptured cyst leads to scarring. The scarred tissue cannot be extracted through a small incision.
Wide Excision Techniques
Wide excision is typically necessary to cure ruptured cysts. Excision during the acute inflammatory phase may lead to increased complications with infection and difficulty suturing, because of the loss of integrity of the dermis immediately around the inflamed cyst. Incision and drainage during the acute inflammatory phase can relieve pain and inflammation. Antibiotics can be prescribed, pending the results of cultures and sensitivities.
After approximately 6 weeks, the drained cyst will usually have scarred down and the inflammation will have subsided. Excision of all palpable components of the keratin granuloma can then be performed.
Optimal Therapeutic Approach for this Disease
Loss of integrity of the cyst wall and formation of scar tissue usually precludes excision of keratin granulomas through a small excision. Complete excision around all palpable components of the ruptured cyst is usually a practical necessity to achieve a cure. Avoid excision in the acute inflammatory phase. Incise and drain in the acute phase and prescribe antibiotics according to culture and sensitivities. Perform a complete excision when a scar has formed and/or inflammation has subsided.
After complete excision, patients have low risk for recurrence and rarely require monitoring or follow-up.
Patients treated with conservative therapies (i.e. intralesional steroid, antibiotics), incision and drainage alone, or minimal incision techniques should be counseled regarding the risk for recurrent episodes of inflammation and the potential need for subsequent excision.
Unusual Clinical Scenarios to Consider in Patient Management
The scarring and inflammation from a ruptured cyst frequently extends through the subcutaneous fat. When performing a wide excision, the surgeon will benefit from taking the deep plane of the excision to the level of the fascia.
What is the Evidence?
Diven, DG, Dozier, SE, Meyer, DJ, Smith, EB. “Bacteriology of inflamed and uninflamed epidermal inclusion cysts”. Arch Dermatol. vol. 134. 1998. pp. 49-51. (Brief summary—comparison of the aerobic and anaerobic bacterial culture results from twenty-five inflamed and twenty-five uninflamed epidermoid cysts)
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. vol. 36. 2010. pp. 894-8. (Brief summary—retrospective survey of 301 patients with epidermal inclusion cysts. A higher percentage of men with facial cysts were smokers than those in the control group [p<.01].)
Kuniyuki, S, Yoshida, Y, Meakawa, N, Yamanaka, K. “Bacteriology study of epidermal cysts”. Acta Derm Venereol. vol. 88. 2008. pp. 22-5. (Brief summary—comparison of isolates of aerobic and anaerobic bacterial cultures obtained from 115 cases inflamed and 37 uninflamed epidermal cysts. The rate of bacterial growth and the recovered anaerobes were significantly greater in the inflamed than the uninflamed epidermal cysts.)
Zuber, TJ. “Minimal excision technique for epidermoid (sebaceous) cysts”. Am Fam Physician. vol. 65. 2002. pp. 1409-12. (Brief summary—description of minimal excision technique for epidermoid cyst removal.)
Mehrabi, D, Leonhardt, JM, Brodell, RT. “Removal of keratinous and pilar cysts with the punch incision technique: analysis of surgical outcomes”. Dermatol Surg. vol. 28. 2002. pp. 673-7. (Brief summary—retrospective chart review evaluating the overall recurrence rates of keratinous and pilar cysts removed by the punch incision technique, and rates of recurrence by location and using other cyst characteristics. The punch incision technique had a recurrence rate of less than 10%.)
Smoot, EC. “Removal of large inclusion cysts with minimal incisional scar”. Plast Reconstr Surg. vol. 119. 2007. pp. 1395(Brief summary—description of staged technique to remove large cysts with minimal scarring.)
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