Pleomorphic lipoma or giant-cell lipoma is a recently recognized entity affecting predominantly elderly and middle-aged men. The neck, shoulder region and back are the sites of predilection. The clinical setting is similar to that seen with spindle-cell lipoma. The lesion is characterized by an intricate mixture of mature fibrous tissue, adipose tissue and myxoid tissue interspersed with cellular foci. Most characteristic of the latter are a variety of giant cells and especially the 'floret' giant-cells, so named because of the arrangement of their nuclei which is reminiscent of the petals of a flower. The pleomorphism of the lesion frequently leads to misdiagnosis as liposarcoma. Criteria for the differentiation from the various types of liposarcoma are discussed. The possible relationship of pleomorphic lipoma to some of the 'atypical lipomas' described in the recent literature is analysed. The pleomorphic lipoma is a benign lesion of subcutaneous tissue which must be sharply differentiated from sarcomas. Some of the liposarcomas alleged in the literature to have originated within a pre-existing lipoma possibly represented pleomorphic lipomas. Pleomorphic lipoma is an entity which must be added to the growing number of pseudosarcomatous lesions of soft tissue.

Pleomorphic lipoma: a benign tumor simulating liposarcoma. A clinicopathologic analysis of 48 cases.Cancer. 1981 Jan 1;47(1):126-33.

A clinicopathologic study of 48 cases of pleomorphic lipoma from the files of the Armed Forces Institute of Pathology reveals that this tumor occurs principally in males (83%) in the fifth to seventh decades (mean 57 years) and shows a predilection for the posterior neck, shoulder, and back. Typically, the lesion appears as a painless, circumscribed subcutaneous mass that, on gross examination, resembles an ordinary lipoma. However, microscopically, in contrast to the uniform appearance of the mature adipose tissue cells of an ordinary lipoma, this neoplasm is characterized by an intimate admixture of variably-sized fat cells, and bizarre, pleomorphic, multinucleated giant cells. Many of the latter cells show a distinctive floret-like arrangement of the nuclei and are associated with interlacing bundles of dense birefringent collagen. Despite this pleomorphic picture, which not infrequently leads to a misdiagnosis of liposarcoma, follow-up data obtained for 34 patients (median follow-up period of three years) establish the invariably benign clinical behavior of this unusual tumor.

Fine-needle aspiration of a pleomorphic lipoma of the head and neck: a case report. Diagn Cytopathol. 2005 Feb;32(2):110-3.

Pleomorphic lipoma is a rare soft-tissue tumor, most commonly seen in the head and neck regions of middle-aged men. Fine-needle aspiration (FNA) of these lesions can present a diagnostic challenge. Its large, hyperchromatic cells and multinucleated forms (floret cells) can easily be mistaken for a malignancy. A patient with a round, well-circumscribed, painless, soft, subcutaneous posterior neck mass for 6 yr presented to our FNA clinic. Aspiration of the mass showed a hypocellular specimen with atypical large and floret cells with fragments of mature fibroadipose tissue in the background. Based on the clinical and cytomorphological findings, a diagnosis of pleomorphic lipoma was suggested, and it was confirmed on excision. This case highlights the need to be aware of unusual benign lesions that may arise in the head and neck region. Knowledge of these benign lesions will help in making the correct cytological diagnosis when these lesions are sampled by FNA.