MASSIVE LOCALIZED LYMPHEDEMA IN THE MORBIDLY OBESE - A HISTOLOGICALLYDISTINCT REACTIVE LESION SIMULATING LIPOSARCOMA

We report 14 cases of a soft tissue lesion in the limbs of morbidly ob ese adults that presents as a large mass and histologically simulates well-differentiated liposarcoma (WDL). Based on its distinctive clinic al setting and morphologic identity to diffuse lymphedema we have term ed this process massive localized lymphedema (MLL). All cases occurred in morbidly obese adults (mean weight 372 Ibs; mean age 47 years). Wo men predominated (9 women; 5 men). The lesions affected the proximal m edial aspect of the extremities (12 thigh; 2 arm) and were unilateral in all but two patients. Etiologically significant antecedent events i nclude ipsilateral axillary lymphadenectomy in both patients with arm lesions, chronic lymphedema resulting from vein-stripping 10 years pri or in one patient, inguinal lymphadenectomy for anal carcinoma in anot her patient, and significant blunt trauma to the inner thigh during a motor vehicle accident in a third patient. The tumors were long standi ng (1-10 years) and extremely large (mean size 33.4 cm, 7408 g). Clini cally, they were diffuse, ill-defined masses that histologically consi sted of lobules of mature fat interrupted by expanded connective tissu e septa. The constituents of the septa were fine, fibrillary collagen, edema fluid, and uniformly distributed fibroblasts. Clusters of capil laries were frequently found at the interface between fat and connecti ve tissue. The widened septa simulated the fibrous bands of sclerosing WDL, but MLL lacks the degree of nuclear atypia seen in the former. T he consistent clustering of reactive vessels at the interface between the fat and fibrous tissue also contrasted with WDL. Six patients expe rienced persistent or recurrent lesions within 10 months to 10 years. No aggressive growth or histologic progression was observed during thi s time, however. Awareness of the features of MLL is important to avoi d misclassification of this reactive lesion with WDL.