Lipomatous salivary gland tumors: a series of 31 cases spanning their morphologic spectrum with emphasis on sialolipoma and oncocytic lipoadenoma.

Lipomatous neoplasms of the salivary glands are rare. Their wide histologic spectrum has not been sufficiently studied. We collected 31 fat-containing salivary gland lesions excluding pleomorphic adenoma and myoepithelioma with lipometaplasia. There were 19 male and 12 female patients aged 7 to 89 years (mean, 53 y). Tumors originated in the parotid (n=29) and the submandibular (n=2) gland. On the basis of the proportion and distribution of adipose tissue and the epithelial type, tumors could be categorized into 3 main groups: ordinary lipoma (n=20) identical to soft tissue lipoma but located within the salivary gland, oncocytic lipoadenoma (n=6) composed predominantly of oncocytes with variable fatty component, nononcocytic sialolipoma (n=4) composed of lobular fatty tissue (≥70%) with evenly distributed normal salivary tissue recapitulating the composition of normal salivary glands and microcystic lipoadenoma (n=1) composed of cystic ducts admixed with adipose tissue. The mean tumor size was 3.3, 3.8, and 2.9 cm for lipoma, oncocytic lipoadenoma, and nononcocytic sialolipoma, respectively. Associated diseases included Madelung disease with bilateral atypical lipomatous tumors of the neck and bilateral parotid lipoma (1), oncocytic lipoadenoma after irradiation for sinonasal adenocarcinoma (1), and periparotideal lipoma excised years before oncocytic lipoadenoma (1) and nononcocytic sialolipoma (1). No recurrence was recorded at a mean follow-up of 72 months (range, 6 to 184 mo). Sebaceous islands were seen in 5/6 oncocytic lipoadenomas and in 2/4 sialolipomas. Periductal inflammation/fibrosis was common in sialolipoma and oncocytic lipoadenoma. This study demonstrates the wide morphologic spectrum of fatty salivary gland lesions. Oncocytic lipoadenoma is an epithelial-predominant tumor that is distinct from the fat-dominated nononcocytic sialolipoma, but the 2 types seem to merge in some cases.