RADIOLOGY: HEAD: Case# 33045: INTRAPAROTID LIPOMA. Patient is a 78 year old male who noted a "fullness" involving the left side of his face while shaving approximately three weeks ago. A 3 x 3cm prominently homogeneous low attenuation mass is seen within the left parotid gland, superficial and posterior to the ramus of the mandible. Attenuation of this lesion measures -95 hounsfield units consistent with fat. A few linear densities are seen within the fatty tissue consistent with fibrous bands. The mass is well circumscribed with definitive borders. There is no evidence of adenopathy within the neck. Although lipomas are the most common soft-tissue tumor type of adulthood, they account for only 2-3% of tumors of the parotid gland. Lipomas are of mesenchymal cell origin and arise from fatty tissue. Most of these neoplasms are benign, subcutaneous in nature, and consist of a thinly encapsulated aggregate of mature adipocytes. Although the adipocytes are histologically similar to normal fat cells they are not available for normal fat metabolism. Radiographic methods are effective for diagnosing both subcutaneous and deep lipomas. On CT and MR lipomas are characterized as being homogeneous and similar in attenuation or signal intensity to subcutaneous fat. Structures adjacent to lipomas are usually displaced or compressed, but rarely infiltrated. Although typical lipomas do not exhibit neovascularity, early venous filling, or hypervascularity on angiograms, there are certain variants that do display these phenomena. The fibrous capsule separating the lipoma from the surrounding tissue may be visualized on CT, but does not enhance on post-contrast scans. If the mass under investigation is inhomogeneous, contains areas of soft-tissue density, or is poorly defined, a liposarcoma should be suspected.