Ultrastructure of a bronchial mucoepidermoid tumour of a seven-year-old boy.

A bronchial mucoepidermoid tumour of a 7-year-old boy was histopathologically and electronmicroscopically studied. The light microscopy revealed an epidermoid structure in whose cells an intracellular and extracellular accumulation of acid mucopolysaccharides occurred. The origin of this transformation seems to be located within the cells of a glandular duct. Electron microscopy pointed out the main characteristics of epidermoid cells (tonofibrils, cellular junctions of desmosomal type) and the secretory transformation by the large development of polyribosomes, of the rough endoplasmic reticulum and of dilated cisternae filled with the secretory product. The prolonged evolution with repeated obstructive pneumonitides, the proliferation after partial endoscopic resection, the absence of mitoses and invasion, as well as the late evolution of the case, suggested the semi-malignancy of this tumour and the impossibility of its consideration as a mucoepidermoid carcinoma. The hypothesis of a unique class of tumours with different secretory possibility including carcinoids, cylindromas (adenocystic tumours) and mucoepidermoid tumours is sustainable.