CASE

An 8-year-old girl was brought to the clinic by her mother for evaluation of a lesion that had been on her face for more than a year. The lesion grew to its current size and had stabilized at that size a few months before our evaluation. The patient and her mother denied that there was any pain or discomfort in the area. Both parent and patient also denied that the patient had any history of previous trauma.

The child was otherwise healthy and very anxious to have the lesion removed from her face. There was no history of keloid formation.

The patient was Hispanic with type IV skin. Physical examination revealed a shallow, 7-mm, subcutaneous, round, bluish mass located on the left infraorbital cheek (see Figure 1). The lesion had no overlying skin changes such as a punctum. No inflammation was seen in the area of the cyst. The girl's youthful skin was otherwise flawless and free of any significant lesions.

WHICH FEATURE SUGGESTS THIS IS NOT AN EPIDERMAL CYST?

• The blue color
• The fact that it's on a child
• The abscence of a punctum
• The location

DISCUSSION

The correct answer is the lack of a punctum, or central comedone, through which the contents could be expressed. A punctum is a characteristic of epidermal cysts. The appearance of epidermal cysts usually coincides with the onset of puberty, when the skin produces far more oil than this child's skin demonstrates. Despite the absence of these features, however, our patient's cyst was an epidermal cyst.

Color is not helpful in ruling out epidermal cyst as a diagnosis because blue color is common, especially in children of color. This feature also is a common characteristic of pilomatricomas. Epidermal cysts commonly develop on facial and other sebaceous, or oily, skin. Therefore, location was of no help in ruling it this diagnosis.

COMMENT Cysts of all kinds are common on or in the skin. Types of cysts are differentiated by origin and histologic structure. The presence of a punctum is a major characteristic of the epidermal or sebaceous cyst, the most common type. Almost all other types of cysts have smooth surfaces and no opening. Other examples of smooth cysts are keratinous cysts, which are commonly seen on the trunk, and pilar cysts, which are commonly seen in the scalp (the so-called wen).

Fortunately, the cyst on this patient's face was far enough away from the eye to effectively rule out the most problematic skin cyst of all, the dermoid cyst. These cysts are more common around the eyes, such as on the brows and the eyelids. Dermoid cysts are much larger than other types of cysts, and much less discrete. Removal of a dermoid cyst can be a major surgical undertaking because the cyst can extend much deeper than is immediately evident on examination. CT scan will define the extent of the cyst, which can even be retro-orbital.

TREATMENT This patient's cyst was removed by simple excision, which produced a curved wound that matched the relaxed skin tension lines. Histologic examination confirmed that despite the absence of a connection to the surface, the cyst was of infundibular origin, had well-defined walls, and contained laminated keratin, as expected. JAAPA

Joe Monroe practices in the dermatology department of the Warren Clinic, Tulsa, Oklahoma, is the department editor for Dermatology Digest, and is the founder and past president of the Society of Dermatology Physician Assistants. He has indicated no relationships to disclose relating to the content of this article.