Parosteal lipoma: MR imaging characteristics

The purpose of this study was to determine the characteristics of parosteal lipomas on MR imaging.

We retrospectively reviewed the images and medical records of eight patients with surgically and pathologically confirmed parosteal lipomas. Radiologic studies performed included conventional radiography and MR imaging (n = 8), CT (n = 7), conventional tomography (n = 2), and scintigraphy (n = 5).

Osseous reaction was present in all cases, manifesting as either mild cortical thickening best seen on magnification radiographs or larger osseous excrescences seen on all radiologic images. These osseous reactions were surrounded by the lipomatous component of the neoplasm and created a firm attachment of the neoplasm to the underlying bone. The lipomatous component showed typical features of adipose tissue on all images and was usually seen on radiographs (n = 7). However, CT or MR imaging was needed to determine the anatomic location and relationship to surrounding structures before surgery. MR imaging was considered superior to CT for preoperative assessment, primarily because of its multiplanar imaging capability. In addition, cartilage and fibrous tissue (n = 3) were identified adjacent to larger osseous excrescences. Associated muscle atrophy in three cases was caused by nerve impingement. These manifestations of parosteal lipoma were also better assessed with MR images because of improved contrast resolution. The distribution of muscle atrophy could be used to determine the site of nerve involvement preoperatively.

We conclude that MR imaging is the most useful adjunct to conventional radiography in the presurgical evaluation of parosteal lipomas because of its multiplanar imaging capabilities and improved contrast resolution for detecting muscle atrophy and site of nerve involvement when present. These factors are important for preoperative assessment to help guide surgical intervention.