Ultrastructural observations on luminal structures of pleomorphic adenoma of parotid and submandibular salivary glands of man

Summary Luminal structures found in salivary pleomorphic adenomas consisted of lumina surrounded by epithelial cells that varied from being packed together to being widely separated except at the luminal margin. Communication between lumina and the surrounding stroma was occasionally seen. Secretory material and cellular debris were seen in lumina, invaginations of the luminal surfaces of periluminal cells, associated vesicles, and vacuoles. Secretory granules, lysosomes and lipofuscin were seen in periluminal cells. Secretory material and debris from necrotic periluminal cells appear to accumulate in lumina, and to be endocytosed and degraded lysosomally by periluminal cells. The finding of communications between lumina and the surrounding stroma suggests that the stromalization of the epithelium includes the luminal structures. The present investigation supports the hypothesis that many of the cellular features of the pleomorphic adenoma relate to the microenvironment.