Cysts

Epidermoid cyst (syn. sebaceous cyst, wen)

These cysts contain keratin and its breakdown products, surrounded by a wall of stratified squamous keratinising epithelium (the commonly used term sebaceous cyst is incorrect — these cysts only rarely have associated sebaceous glands and do not contain sebum). Epidermoid cysts often have a punctum. They are inherited in an autosomal dominant fashion. The common sites are the face, neck, shoulders and chest, areas favoured by acne vulgaris. Lesions may be solitary but are commonly multiple. They enlarge slowly and may become inflamed and tender from time to time. Suppuration may occur. The contents of an infected cyst become semiliquid and usually very foetid. Recurrent infective episodes cause the cyst wall to become adherent to surrounding subcutaneous tissue, and consequently more difficult to remove. If ulceration occurs it can resemble squamous cell carcinoma to which the term ‘Cock’s peculiar tumour’ may be applied (Fig. 13.15). The contents of a cyst sometimes escape slowly from the duct orifice and dry in successive layers on the skin, forming a ‘sebaceous horn’ (Fig. 13.16). Treatment is by surgical excision (except if inflamed, when it is better incised and drained). This can be performed under local anaesthesia; an ellipse of skin including the punctum is removed with the cyst. Unless the wall is completely removed, recurrence is likely.

Pilar cysts

Pilar cysts are usually multiple and occur on the scalp, and they have no punctum. Histologically, their lining is similar to the external root sheath of the hair follicle.  

Implantation dermoids

Implantation dermoids may result from deep implantation of a fragment of epidermis by a penetrating injury. Traumatic inclusion cysts usually appear on the palmar or plantar surfaces of the hands, or on the buttocks or knees.

Callosities, corns and warts

Callosity (French: ‘callosite’) is a localised thickened or hardened part of skin which is an acquired, superficial, circumscribed, yellow—white, flat, thickened patch of hyperkeratotic material. They occur at the regions of pressure or friction on the hands and feet and they are usually not painful. They are commonly occupational, occurring, for instance, on a gardener’s hands. There is no need for treatment, although paring may be necessary and should be carried out by a fully trained chiropodist.

Corn (Old French: corn = grain) is a horny induration of the cuticle with a hard centre, caused by undue pressure, chiefly affecting toes and feet. They are circumscribed, horny thickenings, cone-like in shape with their apex pointing inwards and their base on the surface. They occur at sites of frictional pressure and usually will spontaneously disappear when the aetiological factor is removed. Skilled treatment is important in patients with diabetes or with a poor peripheral circulation when a secondary infection may precipitate gangrene.

Wart (Old English: wearte) is a dry, rough excrescence on the skin (Fig. 13.17). It is a virus-induced tumour that undergoes spontaneous resolution. Transmission is by direct or intimate contact, the virus material usually being inoculated through an abrasion. It is well recognised that patients with immune deficiencies develop widespread resistant warts. They tend to occur on sites of trauma, such as the beard area, hands, genital region and feet. All warts first appear as small, smooth nodules often more easily palpable than seen. Warts are more common in children and young adults, but can be present at any age, causing pain and even difficulty in mobility. Plantar warts occur on the sole and are usually multiple. They may be so tender as to render standing or walking exceedingly uncomfortable. Treatment ranges from folk remedies to sophisticated modern techniques, but the important factor remains that there is no 100 per cent cure. Surgical removal is contraindicated as it leads to scarring and recurrences are frequent. Curettage and diathermy give excellent results, as does cryotherapy, but the latter is often accompanied by pain. The irritant 50 per cent podophyllin in liquid paraffin gives good results. Use of liquid nitrogen is probably easier and is more effective. Recalcitrant lesions may respond to 585-nm pulsed dye laser irradiation.

Venereal warts and moist warts (papillomata acuminata) occur in the genital region.

Herpes simplex is a viral skin infection that is recurrent in about I per cent of the population. An immunosuppressed patient may show dissemination with viraemia and may become seriously ill, requiring treatment with acyclovir infusions. Topical or oral acyclovir is available for the treatment of localised disease.

Orf is caused by the virus that produces pustular dermatitis in sheep. Those infected will have been in contact with sheep in one form or another. The lesions are usually single but may be multiple. The initial lesion is a dusky red papule that enlarges to 1—2 cm in diameter and then resembles a large domed pustule. This is a self-limiting condition that resolves in 5—8 weeks.