Histopathologic studies of benign infantile hemangioendothelioma of the parotid gland.

Five hundred and eighty-four cases of primary parotid gland tumors and tumor-like conditions were examined. Primary benign hemangiomas of the parotid gland were relatively rare, comprising 29 cases (4.9%) of 584 tumors. These could be divided into either cavernous hemangioma or so-called benign hemangioendothelioma. In our series, the incidence of the latter was 1.5% (nine cases), or 31.0% of the total number of hemangiomas. The so-called benign hemangioendotheliomas were found in patients under the age of 12 months, during the infantile period, and occurred predominantly in females and on the right side. Histologically, this tumor showed a uniform growth pattern so that each lobular portion exhibited a strikingly identical appearance. The vascular lumina of the tumor were lined by flattened endothelial cells that were occasionally mixed with some plump cells showing mild atypism. Electron microscopy revealed that the tumor consisted of two distinct components, one being definite endothelial cells lining the vascular channels and the other pericytes located outside of the endothelium embracing the vascular channels. The tumor cells can be interchangeable with one another. It seems that this tumor is derived from the intralobular vascular system of the parotid gland. This tumor is benign in nature and found almost exclusively during the infantile period. Hence, from the clinicopathologic aspect, "benign infantile hemangioendothelioma" seems to be a more suitably descriptive term than simply "benign hemangioendothelioma".