Excerpt from Liposarcoma, Soft Tissue

Synonyms, Key Words, and Related Terms: soft tissue liposarcoma, soft tissue tumors, soft tissue neoplasms, soft tissue lesions, mesenchymal malignancy, mesenchymal tumor, adipose tissue tumor, soft tissue mass, tumors of large connective tissue spaces, retroperitoneal tumors, myxoid tumors, round cell tumors, well-differentiated tumors, pleomorphic tumors

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Background: Liposarcoma is a malignant tumor of mesenchymal origin in which the bulk of the tumor differentiates into adipose tissue. Liposarcoma is a common neoplasm of the soft tissues, and it affects middle-aged patients. Commonly affected sites include the thigh, gluteal region, retroperitoneum, leg, and shoulder area. Liposarcomas rarely arise from a preexisting lipoma. The clinical presentation depends on the site of the tumors, most of which are palpable masses.

On radiographs, findings in the soft tissue mass are nonspecific. Frequently, fat is not detectable radiologically. In general, the more aggressive tumors demonstrate more radiopacity, whereas well-differentiated tumors have a greater fat content. Liposarcoma tumors are the most radiosensitive soft tissue tumors.

Pathophysiology:

Location and appearance

Liposarcoma is regarded as a tumor in adults, and it is only rarely found in areas in which most of the body fat is usually stored. Liposarcoma should be regarded as a tumor of the large connective tissue spaces in which cells have retained a potential for lipogenesis. The principal sites of involvement are the intermuscular gliding spaces and the perivascular and subcoelomic regions. Most tumors occur in the lower limbs, particularly in the popliteal fossa, with a special preference for the adductor canal; the medial thigh; the shoulder area; and the retroperitoneal, perirenal, and mesenteric regions.

The most common intra-abdominal location is the posterior perirenal site, in which the tumor usually displaces the kidney medially and anteriorly. The tumor demonstrates a close relationship to the psoas muscle and the renal capsule to which it usually adheres. Renal invasion is usually not seen, but the tumor commonly compresses the renal pelvis, and it may compress and obstruct the ureter. Occasionally, the tumor may infiltrate the mesentery or grow beneath the parietal peritoneum, invading the anterior or lateral abdominal wall.

Multiple apparently independent tumors have been described in the retroperitoneum, mesentery, and omentum. Rarely, the site of origin may be in the pelvis; occasionally, a pelvic tumor may arise in the buttock with subsequent pelvic invasion. For reasons that remain unclear, the left side of the retroperitoneum is involved more frequently, whereas in the lower limbs, the right leg is preferred. Almost all tumors are deep seated, and most tumors arise from large connective-tissue spaces between muscles and along vessels and nerves.

An origin in the subcutaneous tissues is unusual, and tumors typically reach a considerable size before they invade the subcutaneous tissues occurs. The only exception to this rule occurs in the neck, face, and shoulders in which smaller tumors may invade the subcutaneous fat.

Retroperitoneal tumors may reach an enormous size; the largest tumor reported weighed 275 lb. The mean weight reported was 7800 g, with a mean diameter of 22 cm. The mean weight of a lower-limb liposarcoma reported was 1640 g, with a mean diameter of 11.2 cm.

The gross appearance of the tumor depends on the histologic type, degree of vascularity, presence of necrosis, and amount of mature fat and fibrous tissue. The tumor appears as smooth, lobulated, or nodular mass, and in most instances, it is well encapsulated. However, the appearance of an encapsulated tumor may be misleading because daughter nodules are often present around the main mass. Recurrent tumors are not as well encapsulated. Complete excision is not always possible because of the close association of the tumor with vital structures; therefore, the recurrence rate is high.

Histologic features

Histologically, liposarcomas are classified in distinct groups.

The myxoid type with intermediate differentiation is the most common histologic form of liposarcoma. Histologically, the tumors exhibit moderate-sized .....