A tumour composed of newly formed nerve tissue is spoken of as a true neuroma; when ganglionic cells are present in addition to nerve fibres, the name ganglionic neuroma is applied. These tumours are rare, and are chiefly met with in the main cords or abdominal plexuses of the sympathetic system of children or young adults. They are quite insensitive, and their removal is only called for if they cause pain or show signs of malignancy.
A false neuroma is an overgrowth of the sheath of a nerve. This overgrowth may result in the formation of a circumscribed tumour, or may take the form of a diffuse fibromatosis.
The circumscribed or solitary tumour grows from the sheath of a nerve which is otherwise healthy, and it may be innocent or malignant.
The innocent form is usually fibrous or myxomatous, and is definitely encapsulated. It may become cystic as a result of hæmorrhage or of myxomatous degeneration. It grows very slowly, is usually elliptical in shape, and the solid form is rarely larger than a hazel-nut. The nerve fibres may be spread out all round the tumour, or may run only on one side of it. When subcutaneous and related to the smaller unnamed cutaneous nerves, it is known as a painful subcutaneous nodule or tubercle. It is chiefly met with about the ankle, and most often in women. It is remarkably sensitive, even gentle handling causing intense pain, which usually radiates to the periphery of the nerve affected. When related to a deeper, named nerve-trunk, it is known as a trunk-neuroma. It is usually less sensitive than the “subcutaneous nodule,” and rarely gives rise to motor symptoms unless it involves the nerve roots where they pass through bony canals.
A trunk-neuroma is recognised clinically by its position in the line of a nerve, by the fact that it is movable in the transverse axis of the nerve but not in its long axis, and by being unduly painful and sensitive.
Fig. 85.—Amputation Stump of Upper Arm, showing bulbous thickening of the ends of the nerves, embedded in scar tissue at the apex of the stamp.
Treatment.—If the tumour causes suffering it should be removed, preferably by shelling it out from the investing nerve sheath or capsule. In the subcutaneous nodule the nerve is rarely recognisable, and is usually sacrificed. When removal of the tumour is incomplete, a tube of radium should be inserted into the cavity, to prevent recurrence of the tumour in a malignant form.
The malignant neuroma is a sarcoma growing from the sheath of a nerve. It has the same characters and clinical features as the innocent variety, only it grows more rapidly, and by destroying the nerve fibres causes motor symptoms—jerkings followed by paralysis. The sarcoma tends to spread along the lymph spaces in the long axis of the nerve, as well as to implicate the surrounding tissues, and it is liable to give rise to secondary growths. The malignant neuroma is met with chiefly in the sciatic and other large nerves of the limbs.