CT findings of parosteal lipoma with hyperostosis

Objective: To determine the characteristics of parosteal lipomas with hyperostosis (osteochondromas or osseous protuberances) on CT images and to improve the knowledge of diagnosis and differential diagnosis of the disease. Methods: CT images and clinical history of 6 patients with pathologically confirmed parosteal lipomas with hyperostosis were retrospectively reviewed. All of the 6 patients underwent plain CT scans. Results: CT images clearly show lipomas and osseous projections or osteochondroma in the 6 cases. Parosteal lipomas were found with osteochondromas in 2 cases (1 at the ischium, and the other 1 at the femoral trochanter) and with osseous protuberances in 4 cases (2 at the diaphysis of femurs, 1 at the diaphysis of tibia and the other 1 at the sternum). These osteochondromas and osseous protuberances were surrounded by the adipose component of the neoplasm and had a firm attachment of the neoplasm to the underlying bone. The size of the osseous projections varied from 0.3 cm x 1.2 cm to 6.0 cm x 4.0 cm. The shape of the osseous projections was various. Osteochondromas found in 2 cases showed cortical continuity with the adjacent bone together with marrow continuity with the adjacent bone marrow. In the 4 cases of parosteal lipoma with osseous protuberances, 2 to 4 osseous protuberances were found in 2 cases and solitary osseous protuberance were found in the other 2 cases. The lipomatous component showed typical features of adipose tissue on all images. The size of the lipomas varied from 3.0 cm x 2.0 cm to 11.0 cm x 10.0 cm with clear border. Fibrous septa of different thickness were found within the adipose tissue. There was ossification and (or) calcification in 1 case and muscle atrophy in 2 cases. Conclusions: CT scan is useful in the presurgical evaluation of parosteal lipomas with osteochondromas or osseous protuberances because it can demonstrates the morphology, location and extent of the lesions, and it can show their relationship to the surrounding structures. It is important for differential diagnosis and preoperative assessment of the lesion. (authors)