Spontaneous Ectopic Sebaceous Glands (Fordyce's Granules) in the Oral Mucosa of Sprague-Dawley Rats

Abstract

Although Sprague-Dawley rats are most frequently used in numerous toxicological studies, there are only few reports dealing with the spontaneous occurrence of ectopic sebaceous glands in the oral tissue (Fordyce's granules) so far. Hence, to clarify the morphological characteristics of Fordyce's granules with their incidence in this strain, 110 male and 110 female CD(SD)IGS rats aged 19 to 112 weeks were examined microscopically. Fordyce's granules were identified in the upper molar gingiva, and most of them were located around the first and third molars. The granules consisted of one or more sebaceous glands without hairs and hair follicles, and had some lobules comprising acini with adipose vacuoles. The short excretory duct was lined with stratified squamous cells and drained to the gingival surface. The sebum constituting disintegrated acinar cells in the duct was also noted. In some cases, the granules were accompanied by cystic dilatation in the ducts and/or inflammatory reactions, without neoplastic or pre-neoplastic lesions. The overall incidence (9.1%) of Fordyce's granules in males was higher than that (0.9%) in females, and it somewhat increased with ascending ages, demonstrating sex- or age-specific difference. Based on the above findings, the nature of Fordyce's granules seen in CD(SD)IGS rats was similar to those of other strains and humans.