4. Tumors of Connective-tissue Type.
Lipoma.
—Lipomas, or tumors composed of fat, are the most common of the neoplasms. Their normal type is the ordinary adipose tissue of the body, and may be divided into the encapsulated and the diffuse, the former of which are surrounded by fibrous tissue. The diffuse lipomas are those which have no capsule, and where the pathological collection of fat merges into that normally present—in other words, they are not circumscribed.
Subcutaneous Lipomas.
—Subcutaneous lipomas are perhaps the most common of all, and are usually irregularly lobulated and encapsulated, adherent rather to the skin than to the deeper tissues. Usually but one is found in an individual, though instances of multiple lipomas are not rare. They develop sometimes to enormous size, cases being on record where the tumor has even weighed one hundred pounds. They may be met with at any point on the surface of the body. The lobules often burrow between the muscles, and those found in the palm of the hand penetrate even beneath the palmar fasciæ. They are sometimes markedly pedunculated, and often hang by a small stem. The diffuse subcutaneous lipoma is most common about the neck, in the groin, and in the axilla.
Subserous Lipomas.
—Subserous lipomas are mostly retroperitoneal, and large tumors of this character, mistaken for ovarian, have been successfully removed by operation. They also occur in the hernial canals and spaces. They develop beneath the peritoneum covering the intestines, and in this location give rise occasionally to intussusception. Here in their pathological development they have the general form and significance of appendices epiploicæ.
Subsynovial Lipomas.
—Subsynovial lipomas occur about various joints and tendon sheaths; within the knee they assume a distinctive type which has been called lipoma arborescens, where they take on a dendritic appearance and arrangement. Submucous lipomas are rare. Intermuscular fatty tumors are occasionally met with, an interesting variety being that which develops between the masseter and buccinator muscles. Intramuscular forms rarely occur, as well as a variety known as parosteal, which arises in connection with the periosteum. Fatty tumors also occur within the spinal dura, as well as outside of it within the spinal canal, and more or less lipomatous alterations are common in connection with spina bifida.
Lipomas are ordinarily easy of recognition, save when deeply located. The subcutaneous forms are intimately related with the overlying skin, and have a dough-like consistence which is usually pathognomonic. Tumors, suspected to be fatty, in the middle line of the back or cranium are always to be viewed with suspicion, as they are often connected with congenital meningeal protrusions.