The protympanum, or bony portion of the eustachian tube (ET), is a middle ear space that lies anterior to the mesotympanum. The space is also confluent with the epitym- panum superiorly, hypotympanum inferiorly, and the cartilaginous ET anteriorly.
The protympanum has been infrequently examined in the past due to its difficulty to view using the operating microscope.1 However, the area is now gaining relevance with endoscopic ear surgery because it can easily be seen with angled scopes. With surgery moving toward evaluation and restoration of ventilation pathways,2 the protympanum serves as the final common pathway between the tympanic cavity and external environment, drawing comparisons to the ventilatory function of the larynx in the airway.
True ossification of the protympanum only commences at the 18th fetal week because of its dependence on the bone growth of the otic capsule.4 Earlier studies reported a contribution to protympanum development from the tympanic part of the temporal bone,5 while more recent studies point to development solely from the petrous part of the temporal bone.