Cysts

A cyst is a sac containing semisolid or liquid material. The sac contains keratin and lipid-rich debris and has an epithelial lining that produces keratin.
Cysts tend to be hereditary, arise in adulthood, and may occur as multiple lesions.
Epidermoid cysts (Fig. 30.26), are commonly, but erroneously, termed “sebaceous cysts” are the most common type. They are derived from the epithelium of the hair follicle and connect to the surface of the skin with a keratin-filled central pore that looks like a blackhead.
Pilar cysts (Fig. 30.27), the second most common type, have a thicker wall that develops from a stratified epithelium. Pilar cysts lack a central pore.
Scrotal (Fig. 30.28) and vulvar cysts are also commonly seen.

Clinical Manifestations ⬆ ⬇

Cysts are usually asymptomatic, unless inflamed or infected; consequently, they may become tender and painful (Fig. 30.29).
More often, they are of cosmetic concern to the patient.
Lesions appear as smooth, discrete, freely movable, dome-shaped nodules.
Cysts that have previously been infected, ruptured, drained, or scarred may be firmer to palpation and less freely movable.
Lesions range from 0.5 to 5.0 cm in diameter.
A cheesy-white, malodorous keratin material can be expressed from the central pore.
Pilar cysts are generally devoid of overlying scalp hair.
Scrotal and pilar cysts may calcify.

Clinical Variant ⬆ ⬇

Milia (see also in Chapter 2: Neonatal and Infantile Eruptions)

Milia (singular, milium) are extremely common epidermal cysts that contain keratin.
They can occur in people of any age. They may arise in traumatic scars or in association with certain scarring skin conditions, such as porphyria cutanea tarda.
Benign, asymptomatic.
1 to 2 mm in diameter and are white to yellow (Figs. 30.31 and 30.32).
Milia are most often noted on the face, especially around the eyes and on the cheeks and forehead.

Differential Diagnosis Cysts and Milia

Lipoma (see below)

Should be considered when cyst-like lesions are found on the trunk, the back of the neck, and extremities. However, the consistency of a lipoma is rubbery and somewhat softer when palpated than that of a cyst. Lipomas are also irregular in shape.

Closed Comedones

Point to Remember

Erythematous, tender, or draining epidermal and pilar cysts are often misdiagnosed as being infected rather than inflamed, and patients are often treated unnecessarily with oral antibiotics.

Management

Epidermoid and Pilar Cysts

Options

No treatment and reassure the patient of the benign nature of these lesions.
Total surgical excision that includes the cyst wall and its contents.
Incision and drainage: An alternative approach is to create a small aperture in the cyst by a punch biopsy tool or no. 11 blade followed by extrusion of the cyst contents, and, if possible, much or all of the cyst wall (see Chapter 35: Diagnostic and Therapeutic Techniques). The entire cyst wall does not have to be completely removed to prevent recurrence.
Incision and drainage of an inflamed tender or infected cyst may be performed with a no. 11 blade, followed by drainage and packing with iodoform gauze.
The contents of inflamed or so-called “infected” cysts are most often sterile or contain normal skin flora; thus pre- or postoperative antibiotics are probably unnecessary.

Milia

In contrast to closed comedones (which they resemble), milia must first be incised (usually with a no. 11 blade) before their contents can be expressed.
Alternatively, they can be destroyed with light electrodesiccation.