The commonest subcutaneous cysts encountered are epider-moid, often called sebaceous cysts. They are most frequently seen on the scalp, face and scrotum and are sometimes infected. The only indication for operation on an infected epidermoid cyst is if it forms an abscess that needs draining; otherwise the infection should be treated first. True dermoid cysts are seen at the outer end of the eyebrows or in the mid-line. Implantation dermoids occur where skin has been driven deeply as occurs in the fingers of seamstresses.
Before excising a simple, uninfected epidermoid cyst, written, informed consent must be obtained and all the required materials and instruments and good light secured. If hair interferes with the procedure, it should be shaved or trimmed. The skin is cleaned. A short distance from the normal skin near the cyst, 0.5% or weaker lignocaine is injected through a fine needle, raising a wheal extending to and over the cyst. The crown of the cyst where the punctum lies should be avoided in order not to penetrate the cyst and burst it. The injection is then extended around and under the cyst. The hydrostatic pressure should separate the cyst from all its attachments except at the punctum.
Five minutes is allowed for the local anaesthetic action of lig-nocaine to take effect. An incision is then made over the cyst, to one side of the crown, and extended a few millimetres at each end beyond the cyst, taking care to avoid opening the cyst. Control of bleeding is achieved by simple pressure. The two sides of the incision are separated with the tips of haemostatic forceps and the white cyst is now visible, free of attachments. Using the forceps blades as levers, the cyst is gently mobilized and freed until it is attached only at the punctum. Once free, the intact cyst is removed by cutting its attachment to the skin. If the cyst is ruptured, sebaceous material should be carefully removed, the cyst wall identified and dissected free.
Simple pressure is applied or persistent bleeding vessels picked up and tied. The wound is carefully sutured using fine metric 1. 5 or 1 (4/0 or 5/0) black monofilament polyamide or similar material. The wound usually requires only a plastic spray seal. The sutures can be removed after 4-5 days.
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