We have here a tumour composed of blood-vessels or lymphatics. The tumour varies in bulk according to the fulness of the vessels, hence some of them are occasionally designated Erectile tumours. The term Naevus, though really meaning nativus, or congenital mark of any kind, is almost synonymous in its use with angioma of the surface.'
The commonest form is (1) the Plexiform or Capillary angioma. This includes most of the vascular nsevi, and consists of capillary and intermediate vessels forming a rich plexus. It is mostly a growth of, the skin, and may be very small or cover a large area, forming a flat soft surface of dark or bright hue. It is nearly always congenital, although it may increase in size after birth. Minute capillary nsevi are very common, and are frequently multiple. These capillary nsevi graduate into (2) the Venous or Varicose naevi, or those consisting of dilated veins (Fig. 87). They have similar situations to the capillary form and similar appearances.
(3) The Cavernous angioma consists of tissue like that of the corpus cavernosum of the penis or clitoris, namely, a network with meshes which communicate freely and are filled with blood. When empty they are seen to be composed of a pale tissue, in its texture resembling a sponge, with variously thick trabecule and variously wide spaces. These trabecular are all accurately lined with endothelium, and consist of connective tissue with some muscular fibre-cells. These tumours are usually more or less prominent (noma prominent); they are erectile and sometimes pulsatile. Sometimes the tumour merges into the neighbouring vessels without distinct boundary, but sometimes it has a distinct connective-tissue capsule, which, however, appears to be of secondary formation. Sometimes also it is indurated in the centre, and the induration may gradually lead to the obliteration of the spaces and the destruction of the tumour. These tumours are not so usually congenital as the former kind, but they come on in childhood at latest, and they may develop out of the other form.
Fig. 87. - Section of skin in a case of diffuse venous mevus. The large sinuses (shaded) are seen to lie superficially between the hair-follicles and glands. (Virohow).
Fig. 88. - Cavernous angioma of liver. The fibrous septa are shown. The spaces between are occupied with blood, x about 50.
The skin is a frequent seat of the cavernous angioma, especially that of the face and head, but also sometimes of the trunk or limbs. They are also met with in the liver, not forming prominent tumours, but simply replacing a piece of liver tissue by cavernous tissue. (See Fig. 88).
(4) The Lymphangioma is a tumour composed of lymphatic vessels. Two forms have been distinguished here also, namely, the Plexiform and Cavernous. The former consists of a congeries of dilated lymphatics, while the latter forms a more definite tumour. Sometimes the spaces dilate so as to form complex cysts.
These tumours are mostly congenital, and they form a considerable proportion of the Congenital cystic tumours. The cavernous form seems to be the cause of the congenital enlargements of the tongue, to which the name Macroglossia is applied, as well as of similar enlargements of the lips and cheeks. In certain cases of elephantiasis there is a great dilatation of the lymphatics which some regard as forming angiomas.