The cavernous lymphangioma appears as an ill-defined, soft swelling, presenting many of the characters of a subcutaneous haemangioma, but it is not capable of being emptied by pressure, it does not become tense when the blood pressure is raised, as in crying, and if the tumour is punctured, it yields lymph instead of blood.  It also resembles a lipoma, especially the congenital variety which grows from the periosteum, and the differential diagnosis between these is rarely completed until the swelling is punctured or explored by operation.  If treatment is called for, it is carried out on the same lines as for haemangioma, by means of electrolysis, igni-puncture, or excision.  Complete excision is rarely possible because of the want of definition and encapsulation, but it is not necessary for cure, as the parts that remain undergo cicatrisation.

[Illustration:  FIG. 76.—­Congenital Cystic Tumour or Hygroma of Axilla.

(From a photograph lent by Dr. Lediard.)]

The cystic lymphangioma, lymphatic cyst, or congenital cystic hygroma is most often met with in the neck—­hydrocele of the neck; it is situated beneath the deep fascia, and projects either in front of or behind the sterno-mastoid muscle.  It may attain a large size, the overlying skin and cyst wall may be so thin as to be translucent, and it has been known to cause serious impairment of respiration through pressing on the trachea.  In the axilla also the cystic tumour may attain a considerable size (Fig. 76); less frequent situations are the groin, and the floor of the mouth, where it constitutes one form of ranula.

The nature of these swellings is to be recognised by their situation, by their having existed from infancy, and, if necessary, by drawing off some of the contents of the cyst through a fine needle.  They are usually remarkably indolent, persisting often for a long term of years without change, and, like the haemangioma, they sometimes undergo spontaneous cicatrisation and cure.  Sometimes the cystic tumour becomes infected and forms an abscess—­another, although less desirable, method of cure.  Those situated in the neck are most liable to suppurate, probably because of pyogenic organisms being brought to them by the lymphatics taking origin in the scalp, ear, or throat.

If operative interference is called for, the cysts may be tapped and injected with iodine, or excised; the operation for removal may entail a considerable dissection amongst the deeper structures at the root of the neck, and should not be lightly undertaken; parts left behind may be induced to cicatrise by inserting a tube of radium and leaving it for a few days.

Lymphangiomas are met with in the abdomen in the form of omental cysts.

DISEASES OF LYMPH GLANDS

#Lymphadenitis.#—­Inflammation of lymph glands results from the advent of an irritant, usually bacterial or toxic, brought to the glands by the afferent lymph vessels.  These vessels may share in the inflammation and be the seat of lymphangitis, or they may show no evidence of the passage of the noxa.  It is exceptional for the irritant to reach the gland through the blood-stream.