The hyaline cartilage composing the tumour frequently undergoes myxomatous degeneration, resulting in the formation of a glairy, semi-fluid jelly, and if this change takes place throughout the tumour it comes to resemble a cyst.  On the other hand, the cartilage may undergo calcification or ossification.  The most important transition of all is that into sarcoma, the so-called malignant chondroma or chondro-sarcoma, which is associated with rapid increase in size, and parts of the tumour may be carried off in the blood-stream and give rise to secondary growths, especially in the lungs.

Cases have been met with in which certain parts of the skeleton—­only those developed in cartilage—­were so uniformly permeated with cartilage that the condition has been described as a “chondromatosis” and is regarded as dating from an early period of foetal life.  Unlike the condition known as multiple cartilaginous exostoses, it is a malignant disease.

[Illustration:  FIG. 142.—­Multiple Chondromas of Phalanges and Metacarpals in a boy aet. 10 (cf.  Fig. 143).]

The chondroma is met with as a slowly growing tumour which is specially common in the bones of the hand, often in a multiple form (Figs. 142 and 144).  The surface is smooth or lobulated, and in consistence the tumour may be dense and elastic like normal cartilage, or may present areas of softening, or of bony hardness.  The skin moves freely over it, except in relation to the bones of the fingers, where it may become adherent and ulcerate, simulating the appearance of a malignant tumour.  Large tumours growing from the bones of the extremities may implicate the main vessels and nerves, either surrounding them or pressing on them.

Portions of a chondroma, which have undergone calcification or ossification, throw a dark shadow with the X-rays; unaltered cartilage and myxomatous tissue appear as clear areas.

[Illustration:  FIG. 143.—­Skiagram of Multiple Chondromas shown in Fig. 142.]

Treatment.—­It is necessary to remove the whole tumour, and in chondromas growing from the surface of the bone, especially if they are pedunculated, this is comparatively easy.  When a bone, such as the scapula or mandible, is involved, it is better to excise the bone, or at least the part of it which bears the tumour.  In the case of central tumours the shell of bone is removed over an area sufficient to allow of the enucleation of the tumour, or the affected portion of bone is resected.  Should there be evidence of malignancy, such as increased rate of growth, a tube of radium should be inserted, and in advanced cases with destruction of tissue, amputation may be called for.

[Illustration:  FIG. 144.—­Multiple Chondromas in Hand of boy aet. 8]

In multiple chondromas of the hand in young subjects, it was formerly the custom to amputate the limb; an attempt should be made to avoid this by shelling out the larger tumours individually, and persevering with the application of the X-rays or of radium to inhibit the growth of the smaller ones.