We have followed the classification adopted by Alexis Thomson in his work On Neuroma, and Neuro-fibromatosis (Edinburgh: 1900).
Neuroma is a clinical term applied to all tumours, irrespective of their structure, which have their seat in nerves.
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.
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.
The treatment is conducted on the same lines as sarcoma in other situations; the insertion of a tube of radium after removal of the tumour diminishes the tendency to recurrence; a portion of the nerve-trunk being sacrificed, means must be taken to bridge the gap. In inoperable cases it may be possible to relieve pain by excising a portion of the nerve above the tumour, or, when this is impracticable, by resecting the posterior nerve roots and their ganglia within the vertebral canal.
The so-called amputation neuroma has already been referred to (p. 344).
Diffuse or Generalised Neuro-Fibromatosis—Recklinghausen's Disease.—These terms are now used to include what were formerly known as “multiple neuromata,” as well as certain other overgrowths related to nerves. The essential lesion is an overgrowth of the endoneural connective tissue throughout the nerves of both the cerebro-spinal and sympathetic systems. The nerves are diffusely and unequally thickened, so that small twigs may become enlarged to the size of the median, while at irregular intervals along their course the connective-tissue overgrowth is exaggerated so as to form tumour-like swellings similar to the trunk-neuroma already described. The tumours, which vary greatly in size and number—as many as a thousand have been counted in one case—are enclosed in a capsule derived from the perineurium. The fibromatosis may also affect the cranial nerves, the ganglia on the posterior nerve roots, the nerves within the vertebral canal, and the sympathetic nerves and ganglia, as well as the continuations of the motor nerves within the muscles. The nerve fibres, although mechanically displaced and dissociated by the overgrown endoneurium, undergo no structural change except when compressed in passing through a bony canal.
The disease probably originates before birth, although it may not make its appearance till adolescence or even till adult life. It is sometimes met with in several members of one family. It is recognised clinically by the presence of multiple tumours in the course of the nerves, and sometimes by palpable enlargement of the superficial nerve-trunks (Fig. 86). The tumours resemble the solitary trunk-neuroma, are usually quite insensitive, and many of them are unknown to the patient. As a result of injury or other exciting cause, however, one or other tumour may increase in size and become extremely sensitive; the pain is then agonising; it is increased by handling, and interferes with sleep. In these conditions, a malignant transformation of the fibroma into sarcoma is to be suspected. Motor disturbances are exceptional, unless in the case of tumours within the vertebral canal, which press on the spinal medulla and cause paraplegia.
Neuro-fibromatosis is frequently accompanied by pigmentation of the skin in the form of brown spots or patches scattered over the trunk.
The disease is often stationary for long periods. In progressive cases the patient becomes exhausted, and usually dies of some intercurrent affection, particularly phthisis. The treatment is restricted to relieving symptoms and complications; removal of one of the tumours is to be strongly deprecated.
In a considerable proportion of cases one of the multiple tumours takes on the characters of a malignant growth (“secondary malignant neuroma,” Garrè). This malignant transformation may follow upon injury, or on an unsuccessful attempt to remove the tumour. The features are those of a rapidly growing sarcoma involving a nerve-trunk, with agonising pain and muscular cramps, followed by paralysis from destruction of the nerve fibres. The removal of the tumour is usually followed by recurrence, so that high amputation is the only treatment to be recommended. Metastasis to internal organs is exceptional.
There are other types of neuro-fibromatosis which require brief mention.
The plexiform neuroma (Fig. 87) is a fibromatosis confined to the distribution of one or more contiguous nerves or of a plexus of nerves, and it may occur either by itself or along with multiple tumours of the nerve-trunks and with pigmentation of the skin. The clinical features are those of an ill-defined swelling composed of a number of tortuous, convoluted cords, lying in a loose areolar tissue and freely movable on one another. It is rarely the seat of pain or tenderness. It most often appears in the early years of life, sometimes in relation to a pigmented or hairy mole. It is of slow growth, may remain stationary for long periods, and has little or no tendency to become malignant. It is usually subcutaneous, and is frequently situated on the head or neck in the distribution of the trigeminal or superficial cervical nerves. There is no necessity for its removal, but this may be indicated because of disfigurement, especially on the face or scalp or because its bulk interferes with function. When involving the ophthalmic division of the trigeminus, for example, it may cause enlargement of the upper lid and proptosis, with danger to the function of the globe. The results of excision are usually satisfactory, even if the removal is not complete.
The cutaneous neuro-fibroma or molluscum fibrosum has been shown by Recklinghausen to be a soft fibroma related to the terminal filaments of one of the cutaneous nerves (Fig. 88). The disease appears in the form of multiple, soft, projecting tumours, scattered all over the body, except the palms of the hands and soles of the feet. The tumours are of all sizes, some being no larger than a pin's head, whilst many are as big as a filbert and a few even larger. Many are sessile and others are distinctly pedunculated, but all are covered with skin. They are mobile, soft to the touch, and of the consistence of firm fat. In exceptional cases one of the skin tumours may attain an enormous size and cause a hideous deformity, hanging down by its own weight in lobulated or folded masses (pachy-dermatocele). The treatment consists in removing the larger swellings. In some cases molluscum fibrosum is associated with pigmentation of the skin and with multiple tumours of the nerve-trunks. The small multiple tumours rarely call for interference.
Elephantiasis neuromatosa is the name applied by Virchow to a condition in which a limb is swollen and misshapen as a result of the extension of a neuro-fibromatosis to the skin and subcutaneous cellular tissue of the extremity as a whole (Fig. 89). It usually begins in early life without apparent cause, and it may be associated with multiple tumours of the nerve-trunks. The inconvenience caused by the bulk and weight of the limb may justify its removal.