Unlike the other forms of naevi, the cutaneous variety shows little tendency to disappear, and it is especially persistent when associated with overgrowth of the epidermis and of the hairs—­naevoid mole.

The treatment of the cutaneous naevus is unsatisfactory, owing to the difficulty of removing the naevus without leaving a scar which is even more disfiguring.  Very small naevi may be destroyed by a fine pointed Paquelin thermo-cautery, or by escharotics, such as nitric acid.  For larger naevi, radium and solidified carbon dioxide ("CO_2 snow”) may be used.  The extensive port-wine stains so often met with on the face are best left alone.

The subcutaneous naevus is comparatively rare.  It constitutes a well-defined, localised tumour, which may possess a distinct capsule, especially when it has ceased to grow or is retrogressing.  On section, it presents the appearance of a finely reticulated sponge.

Although it may be noticed at, or within a few days of, birth, a subcutaneous naevus is often overlooked, especially when on a covered part of the body, and may not be discovered till the patient is some years old.  It forms a rounded, lobulated swelling, seldom of large size and yielding a sensation like that of a sponge; the skin over it is normal, or may exhibit a bluish tinge, especially in cold weather.  In some cases the tumour is diminished by pressing the blood out of it, but slowly fills again when the pressure is relaxed, and it swells up when the child struggles or cries.  From a cold abscess it is diagnosed by the history and progress of the swelling and by the absence of fluctuation.  When situated over one of the hernial openings, it closely simulates a hernia; and when it occurs in the middle line of the face, head, or back, it may be mistaken for such other congenital conditions as meningocele or spina bifida.  When other means fail, the use of an exploring needle clears up the diagnosis.

Mixed Naevus.—­As its name indicates, the mixed naevus partakes of the characters of the other two varieties; that is, it is a subcutaneous naevus with involvement of the skin.

It is frequently met with on the face and head, but may occur on any part of the body.  It also affects parts covered by mucous membrane, such as the cheek, tongue, and soft palate.  The swelling is rounded or lobulated, and projects beyond the level of its surroundings.  Sometimes the skin is invaded by the naevoid tissue over the whole extent of the tumour, sometimes only over a limited area.  Frequently the margin only is of a bright-red colour, while the skin in the centre resembles a cicatrix.  The swelling is reduced by steady pressure, and increases in size and becomes tense when the child cries.

[Illustration:  FIG. 68.—­Mixed Naevus of Nose which was subsequently cured by Electrolysis.]