#Varieties of Tumours.#—­In the following description, tumours are classified on an anatomical basis, taking in order first the connective-tissue group and subsequently those that originate in epithelium.

INNOCENT CONNECTIVE-TISSUE TUMOURS

#Lipoma.#—­A lipoma is composed of fat resembling that normally present in the body.  The commonest variety is the subcutaneous lipoma, which grows from the subcutaneous fat, and forms a soft, irregularly lobulated tumour (Fig. 45).  The fat is arranged in lobules separated by connective-tissue septa, which are continuous with the capsule surrounding the tumour and with the overlying skin, which becomes dimpled or puckered when an attempt is made to pinch it up.  As the fat is almost fluid at the body temperature, fluctuation can usually be detected.  These tumours vary greatly in size, occur at all ages, grow slowly, and, while generally solitary, are sometimes multiple.  They are most commonly met with on the shoulder, buttock, or back.  In certain situations, such as the thigh and perineum, they tend to become pedunculated (Fig. 46).

A fatty tumour is to be diagnosed from a cold abscess and from a cyst.  The distinguishing features of the lipoma are the tacking down and dimpling of the overlying skin, the lobulation of the tumour, which is recognised when it is pressed upon with the flat of the hand, and, more reliable than either of these, the mobility, the tumour slipping away when pressed upon at its margin.

[Illustration:  FIG. 45.—­Subcutaneous Lipoma showing lobulation.]

The prognosis is more favourable than in any other tumour as it never changes its characters; the only reasons for its removal by operation are its unsightliness and its probable increase in size in the course of years.  The operation consists in dividing the skin and capsule over the tumour and shelling it out.  Care must be taken that none of the outlying lobules are left behind.  If the overlying skin is damaged or closely adherent, it should be removed along with the tumour.

[Illustration:  FIG. 46.—­Pedunculated Lipoma of Buttock of forty years’ duration in a woman aet. 68.]

Multiple subcutaneous lipomas are frequently symmetrical, and in a certain group of cases, met with chiefly in women, pain is a prominent symptom, hence the term adiposis dolorosa (Dercum).  These multiple tumours show little or no tendency to increase in size, and the pain which attends their development does not persist.

In the neck, axilla, and pubes a diffuse overgrowth of the subcutaneous fat is sometimes met with, forming symmetrical tumour-like masses, known as diffuse lipoma.  As this is not, strictly speaking, a tumour, the term diffuse lipomatosis is to be preferred.  A similar condition was described by Jonathan Hutchinson as being met with in the domestic animals.  If causing disfigurement, the mass of fat may be removed by operation.