[Vascular middle ear structure. Ectopic course of the internal carotid artery]

Development of the protympanum

The protympanum, the only opening of the tympanic cavity, has enormous significance in the pathogenesis of middle ear inflammation. In our study, we analyzed 70 macerated temporal bones stereomicroscopically to understand the development of the protympanum. Details of this embryonic process were attained using histological sections made in frontal and horizontal planes. In contrast to recent descriptions, the present work reveals that almost the entire protympanum develops from different processes of the petrous bone. The tympanic bone takes part in forming only the posterior border of the lateral wall of the protympanum. Consequently the tympanic plate, which forms the inferior half of the mandibular fossa, is formed by two anlages. The anterosuperior quarter is formed by the petrous bone and the remainder by the tympanic bone. The main structures of the medial wall of the protympanum are the carotid canal with the internal carotid artery (ICA). The carotid canal starts to develop as two laminae of the petrous bone in the 18th fetal week. In cases of incomplete closure of these laminae the carotid canal occupies dehiscences increasing the danger of injury to the ICA. The presence of the ICA is necessary for the development of the carotid canal. If the artery takes an aberrant pathway in the tympanic cavity, or is absent, there is no sign of the carotid canal.

Aberrant internal carotid artery in the middle ear

This study was undertaken to evaluate the incidence, typical clinical signs, and proper management of patients with an aberrant internal carotid artery in the middle ear as presented in a case report and review of the relevant literature. A total of 86 cases were reviewed concerning gender, affected side, presenting symptoms, findings on clinical and radiologic examination, and further treatment. About two thirds of the patients (68.6%) were female. The right side was affected in 40 patients, and both sides were affected in 13 patients. Hearing loss (41 patients) and pulsatile tinnitus (26 patients) were the most common symptoms. Preponderances of affected side and gender seem to be reduced by the increasing number of reports. Bilateral findings are not unusual, indicating meticulous examination of both sides. Glomus tumors often mimic an aberrant internal carotid artery. If vascular malformations in the middle ear are suspected, high-resolution computed tomography or magnetic resonance angiography is required before any surgical intervention to exclude vascular malformations. Brisk bleeding, hemiparesis, aphasia, deafness, Horner's syndrome, and intractable vertigo may result if the lesion is injured unintentionally. Once the disorder is correctly diagnosed, yearly follow-up is advisable.