The term naevus refers to a hamartomatous malformation of the skin. Naevi may be principally composed of dermal elements, such as connective tissue naevus, melanocytes (naevocellular naevus), vascular elements, or epidermal elements (epidermal naevi). Epidermal naevi are verrucous or wart-like and are frequently present at birth although may develop later in childhood or (rarely) in adult life. They may be small, resembling true viral warts, but more typically they form large linear plaques or linear arrays of warty papules. Rarely, large areas of the body surface may be covered by linear or swirling arrays of these lesions. Epidermal naevi are typically asymptomatic, although large linear naevi may become spontaneously inflamed, with the development of pruritus and erythema of the lesions and surrounding skin.

Epidermal naevi are generally of little consequence to the general health of the patient. Very rarely, they may be associated with congenital malformations of underlying osseous and soft tissue structures, particularly when lesions occur on the head and neck. Malignant transformation within epidermal naevi is exceedingly rare, except in the case of a naevus sebaceus (see below).

Histologically, epidermal naevi are characterized by acanthosis and hyperkeratosis. Cytological atypism is not seen. They are most commonly removed for cosmetic reasons. Such treatment may involve excision with primary closure, electrodesiccation, carbon dioxide laser ablation, or cryosurgery.

Naevus sebaceus is a type of epidermal naevus that occurs exclusively on the scalp or face. Histologically, naevus sebaceus is characterized by the same type of epidermal proliferation seen in other epidermal naevi, but large mature sebaceus glands and apocrine glands are also present. Before puberty, naevus sebaceus is typically a smooth-surfaced flat plaque with slightly yellowish or yellow-orange colour. When it occurs on the scalp, which is the most common site, the absence of hair within the lesion may bring it to attention. At puberty, the sebaceous element within the naevus begin to hypertrophy and the surface becomes more verrucous. Unlike other epidermal naevi, naevus sebaceus may occasionally undergo malignant transformation, with the formation of basal cell carcinoma within the lesion. Since such transformation occurs in only about 5 per cent of patients with naevus sebaceus, the common practice of excising these lesions prophylactically is controversial. Benign tumours such as syringocystadenoma papilliferum may also occur within these naevi.

Connective tissue naevi are generally present at birth. They consist of firm, flesh-coloured papules and plaques and are usually solitary. The hair follicle orifices may be prominent within lesions, giving them the appearance of pig skin. Connective tissue naevi are usually idiopathic and are not associated with any other disease, with the exception of the shagreen patch that occurs in tuberous sclerosis. Histologically, connective tissue naevi are composed of dense aggregations of dermal elements, usually collagen fibres or elastic fibres, or both. Connective tissue naevi are harmless, although they may be excised for cosmetic or functional reasons.

Haemangiomas are proliferations of mature vascular elements (Fig. 1) 1501. These endothelium-lined vascular spaces are most commonly capillary sized, but larger ‘cavernous’ spaces also are found, especially in large lesions. Three clinical types of haemangiomas are commonly recognized.

Strawberry haemangiomas may be present at birth but, more typically, develop during the first few weeks of life. They are seen in approximately 3 per cent of newborn infants, and 80 per cent are solitary, although multiple haemangiomas also occur. Strawberry haemangiomas range in size from 1 mm to many centimetres. The lesions are well-demarcated, lobular, bright red nodules with a spongy consistency. The surface of the lesion is studded with small capillary tufts, which produce the resemblance to a strawberry.

Strawberry haemangiomas seldom require treatment, since the vast majority involute spontaneously by the age of 6 or 7 years. Treatment may be required, however, for lesions situated on the eyelids, nares, or lips, where they may cause functional impairment. Rarely, giant strawberry haemangiomas, particularly those with a cavernous component, may be associated with thrombocytopenia, presumably due to platelet sequestration with the lesion. This phenomenon, known as the Kasabach-Merritt syndrome, may require surgical treatment if other measures fail.

Administration of corticosteroids, which may stimulate gradual involution of lesions is often used as first-line treatment for rapidly growing strawberry haemangiomas. Surgical excision and carbon dioxide laser ablation are often successful, but may produce unacceptable scarring. The efficacy of dye laser treatment is currently being evaluated and promises to be effective.

Cherry haemangiomas are generally smaller than strawberry haemangiomas, and tend to be round and bright red. They begin to appear during childhood, and continue to develop throughout adult life. The tendency to develop cherry haemangiomas appears to be transmitted within families as an autosomal dominant trait. Cherry haemangiomas seldom require treatment other than for cosmetic reasons: they are easily excised with a scalpel or biopsy punch. Occasionally, cherry haemangiomas thrombose, changing in colour from bright red to purplish black. This colour change may alarm patient and physician alike, since the apparent sudden appearance of a black papule raises the spectre of nodular malignant melanoma. Biopsy is indicated in such cases.

Cavernous haemangiomas, like strawberry haemangiomas, may be present at birth and grow rapidly during the first few months of life. They also involute spontaneously. Cavernous haemangiomas are primarily situated beneath the skin, and clinically appear as soft, bluish masses that distend the surrounding features. A typical strawberry haemangioma may form the cutaneous component of a cavernous haemangioma. Both strawberry and cavernous haemangiomas, when multiple, may be the presenting sign of diffuse neonatal haemangiomatosis, in which multiple haemangiomas occur not only in the skin and subcutaneous tissue, but also in the liver and other organs.

Port wine stains, unlike haemangiomas, do not represent the proliferation of excessive numbers of vascular elements, but are caused by ectasia of normal numbers of vessels within the skin. The dermal vessels that comprise port wine stains are capillary size or slightly larger. Port wine stains are generally present at birth, and occur in 0.3 per cent of neonates. Early in life, port wine stains are generally pink or purplish-pink in colour, and macular. With time, the vascular channels become more and more ectatic, imparting a lumpy appearance to the skin. Mature port wine stains are frequently dark purple. Port wine stains are most commonly found on the head and neck, but may also be seen on the trunk, particularly in the pectoral area, and on the extremities, usually the arms. Port wine stains of the orbital region may be associated with unilateral glaucoma.

The Sturge–Weber syndrome is characterized by the presence of a port wine stain in the distribution of the first branch of the trigeminal nerve, associated with a similar vascular malformation of the underlying cerebral cortex and meninges (Fig. 2) 1502. Seizures, mental retardation, and motor cortical deficits are seen in many patients. The Klippel–Trenaunay–Weber syndrome is an association of port wine stain of an extremity or the trunk with arteriovenous malformations and hemihypertrophy.

Until recently, the treatment for port wine stains was unsatisfactory and produced unacceptable scarring: cryosurgery, carbon dioxide and argon laser surgery, excision and grafting, and tattooing with skin-coloured pigments were all used with variable degrees of success. The development of tuneable dye lasers has revolutionized the treatment of port wine stains, making it possible to remove these lesions partially or completely without excessive scarring.

Pyogenic granuloma is a common vascular lesion that presents as a rapidly-growing papule or nodule which is friable and bleeds easily after minor trauma. Pyogenic granuloma is a misnomer: it is actually an eruptive capillary haemangioma. Treatment with electrofulguration, carbon dioxide laser ablation, or simple excision is usually curative, although lesions may recur. Since the differential diagnosis of a rapidly growing and bleeding nodule also includes nodular malignant melanoma, biopsy should be performed if there is any doubt about the diagnosis.

Lymphangiomas may be composed of capillary sized lymphatic vessels, or they may consist of larger cavernous spaces. Lymphangioma circumscriptum is a common type of lymphangioma. Lesions consist of a superficial proliferation of capillary sized lymphatic vessels, which produces the appearance of multiple vesicles on the cutaneous surface, and a deeper component consisting of large ‘cisternae’ within adjacent muscle tissue. The appearance of the superficial portion of lymphangioma circumscriptum has been likened to frog eggs. Small precipitates of red blood cells can often be seen at the bottom of the lymphatic vesicles.

Treatment of lymphangioma circumscriptum may be attempted for cosmetic reasons. Both excision and carbon dioxide laser ablation have been successfully employed, but the connection of the skin to the deeper cisternae means that recurrences are common.

Cavernous lymphangiomas and cystic hygromas are proliferations of lymphatic vascular tissue consisting of larger vascular spaces than those seen in lymphangioma circumscriptum. Cystic hygroma is the more common of the two; it most frequently occurs in the neck, although it may be seen on the head or inguinal regions. Cystic hygroma behaves like a benign tumour and grows slowly in size. Large lesions may cause functional impairment, particularly in the neck. Surgical excision is difficult, but highly successful in cystic hygroma. Excision of cavernous lymphangiomas is less likely to be curative; recurrence is common.

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