Pneumatization and mesenchyme in the human middle ear

The normal pneumatization in human middle ears from Wittmaack's temporal bone collection (ENT Clinic, University of Hamburg Medical School) is investigated by means of light microscopy and compared with electron-microscopic findings in the rat. The fetal middle ear in man and rats is completely filled with mesenchyme. The compartmentalization of the middle ear by the associated mucosal folds of the ossicular chain and the middle ear pneumatization are results of the resorption of the mesenchyme present. Ultrastructural findings in the rat's middle ear reinforce light-microscopic studies and provide evidence of the fibrillogenesis which characterizes the transformation of the mesenchyme into the tunica propria of the middle ear mucosa. The microtopography of mesenchymal remnants in middle ears of neonates and in children during the first year of life, and their relevance as to the pathogenesis of the primary acquired keratoma (cholesteatoma) are discussed.