In planning the restorative surgery, HRCT is aimed at answering questions important to otosurgeons, i.e. those concerning the condition of the external and middle ear. Of no less importance, regardless the different origin in the embryonic period, is assessing the condition of the otic capsule, internal ear structures, course of facial nerve canal and temporo-mandibular joint, since the combination of such anomalies determines the indications and contraindications for surgical treatment, and makes hearing restoration in the postoperative period more difficult. Table 1 shows the sequence of studying the anatomic structures when evaluating the series of tomograms in patients with external ear anomalies.

Table 1.

Sequence of evaluating anatomic structures in external ear canal and middle ear anomalies

Atretic or stenosal plate. In our study we used the classification system that divides all anomalies of the external auditory canal into complete (atresia) and incomplete (stenosis), with further division, according to dysplasia expression, into the membranous (cartilaginous), osseous and mixed. Patients division in accordance with the types of external auditory canal defects revealed is shown in Table 2.

Table 2.

Revealed developmental defects of external auditory canal

Stenoses of the external auditory canals were observed in 3 temporal bones with normally developed and formed auricles as the narrowing of their osseous segments (Fig. 1a), as well as the continuation of the scutum, which is the superior medial margin of the external auditory canal (Fig. 1b).

Membranous and mixed atresias were rare. In these cases the osseous segment of the external auditory canal was formed but was found to be a soft-tissue component in the first case (Fig. 2) and a soft-tissue component with cartilaginous and osseous inclusions in the second case.

Most frequently dysplasia was present in the form of the osseous atresia of the external auditory canal (36 temporal bones). In these cases the osseous segment of the external auditory canal was absent, and instead of it there was a thick osseous mass of cellular or sclerotic composition, functioning as the non-existing lateral wall of the tympanic cavity (Fig. 3).

Mastoid process and tympanic cavity. According to the literature, the degree of mastoid process pneumatization and the size of tympanic cavity are inversely proportional to the thickness of the atretic plate. Normally developed pneumatized mastoid process with differentiated cells and antrum was observed in 23 temporal bones; the mastoid process reduced in size and impoverished in the number of cells was seen in 11 temporal bones. Drastically impoverished cellular system or its absence was found in 9 temporal bones, the mastoid process presented the osseous mass undifferentiated into the antrum and cells.

When studying the tympanic cavity in the majority of temporal bones the tympanic cavity was of a normal size, and its pneumatization was intact. In some cases tympanic cavity hypoplasia with intact pneumatization was noted , in 7 cases the tympanic cavity hypoplasia was combined with reduced pneumatization. In 5 temporal bones the tympanic cavity was either absent or present as a narrow non-pneumatized fissure (Fig. 4). Literature suggests that the tympanic cavity width less than 3 mm (measured from promontorium to the atretic plate lateral margin) is an unfavorable prognostication factor for surgery. In 34 cases the tympanic cavity was located typically, in 9 temporal bones it was severely displaced anteriorly and located just over the temporo-mandibular joint, as determined during coronal scans assessment.

Condition of ossicles. Assessed were the malleus and incus shape as well as the condition of incudomallear joint. The malleus and incus fusion took place most frequently due to the disturbed relationships in the incudomallear joint (Fig.5). In all cases of the osseous atresia the mallear handle was absent and its head was hypoplastic. In 8 temporal bones there were no changes in the ossicle shape. In 6 cases the change of the incus shape and the absence or deformity of its processes were seen. Undifferentiated conglomerate of ossicles was found in 8 patients (Fig.6). Complete tympatic cavity obliteration and the absence of ossicless were observed in 5 patients (see Fig.4).

The stapes and the oval window were studied separately. Stapes identification is one of the important SCT tasks, since the stapes base is anchored in the vestibular oval window, this being a significant link of sound conduction. These structures were best visualized in the axial scan. In some cases for better visualization we used photographic inversion [4]. In the cases where the tympanic cavity pneumatization or size were severely reduced, the stapes and oval window visualization was hindered (Fig.8). . In 32 cases the oval window was unchanged; in 6 cases there were the areas of reduced density and in 5 cases the oval window was closed (Fig.7). The round window was unchanged in 36 cases and was closed in 7 temporal bones.

Internal ear and internal auditory canal. In the majority of cases the internal ear structures were unchanged. In one child there was bilateral hypoplasia of lateral semicircle canal (Fig. 9). In one case there was unilateral Mondini deformity.

Facial nerve course. Identification of the facial nerve course is important for surgical planning. Unchanged facial nerve course was seen in 16 cases. In 21 cases the anterolateral displacement of the mastoid aspect of the facial nerve was observed alongside with the anterolateral displacement of the extracranial segment of the facial nerve in the stylomastoid foramen. In 6 cases there was an anomalous location of the facial nerve tympanic segment contiguous to the oval window.

Vessels. The condition of jugular vein, sigmoid sinus and internal carotid artery was assessed. The jugular vein course and the sigmoid sinus location were normal in 22 cases. In 13 cases a superior location of the jugular vein was observed, and in 8 cases the sigmoid sinus adjacent position was noted. There were no changes in the internal carotid artery canal.

Condition of the temporo-mandibular joint. In 15 cases the reduced in size and deformed articular mandibular process and the temporal bone articular surface were seen (Fig. 10 a,b). In 28 cases the temporo-mandibular joint was developed normally and was analogous to the intact opposite side (Fig.10c).