Benign fibrous lesions masquerading as sarcomas. Clinical and morphological pitfalls.

The "pseudosarcomas" have several features in common: rapid growth, pain and tenderness, infiltrative growth extending along fascial planes or subcutaneous septa or radiating into lobules of adipose tissue. Another common denominator is the pleomorphic pattern of proliferating fibroblasts and myofibroblasts, the presence of more or less ganglioncell-like large cells, uni-or binucleated with prominent nucleoli and a high mitotic rate. In order to avoid a false diagnosis of sarcoma several factors should be emphasized: 1. awareness of the existence of these lesions, 2. combined evaluation of clinical and morphological data, 3. rapid growth, often noted by the patients, is rare in sarcomas except in some cases of rhabdomyosarcoma. Like wise are the pain and tenderness not typical for sarcoma, 4. the appearance of the lesion at low power, 5. at high power in spite of the cellular pleomorphism, the nuclei are cytologically benign and atypical mitoses never seen. In doubtful cases immunohistochemistry may be of help as DNA-ploidy analysis. These lesions may be tetraploid but never aneuploid. Our present work-up of these lesions is primary FNA and when the clinical data and the cytologic features are typical for a "pseudosarcoma" we adopt an attitude of "wait and see" with clinical follow-up. As many of them regress or disappear after the needling there is no need for primary surgery.