Sialolipoma: a report of seven cases of a new variant of salivary gland lipoma

Aims: We propose the designation 'sialolipoma' to establish and characteriz e a new category of benign lipomatous tumour occurring in salivary glands. Until now, these tumours have not been regarded as a distinct entity in the salivary glands. Methods and results: We evaluated the clinicopathological and immunohistoch emical features of seven sialolipomas among 2051 surgically resected primar y salivary gland tumours deposited in our files. The seven patients with si alolipoma were five men and two women, aged 20-75 years (mean: 54.4 years). Five tumours had arisen in the parotid gland, one in the soft palate, and one in the hard palate. The tumours ranged from 10 to 60 mm (mean: 38 mm) i n maximum diameter. Histologically, the tumours were characterized by a wel l circumscribed mass composed of glandular tissue and mature adipose elemen ts. The adipose elements in the tumours arising in the parotid gland were m ore abundant than those arising in the minor salivary gland. The glandular components consisted of ductal, acinar, basal and myoepithelial cells, and closely resembled the cellular and structural compositions of normal saliva ry gland tissues. These findings were confirmed by immunohistochemical and ultrastructural studies. These components had no atypia, except for the pre sence of some minor variations, e.g. ductal ectasia with fibrosis and focal oncocytic metaplasia. In all cases, cell proliferative activity as assesse d by Ki67 (MIBI) immunostaining, was low. From these findings, it is likely that our cases were lipomas with secondary entrapment of the salivary glan d elements. No recurrence was seen in all cases after superficial. parotide ctomy, or after surgical excision in the patients with palatal tumours. Conclusions: We regard sialolipoma as a distinct variant of salivary gland lipoma that can occur in both the major and minor salivary glands. Superfic ial parotidectomy, or surgical resection in the case of palatal tumours, is an appropriate treatment for this benign tumour.