Visualization of anatomy in normal and pathologic middle ears by cone beam CT

Cone beam computed tomography (CBCT, syn. digital volume tomography = DVT) was introduced into ENT imaging more than 10 years ago. The main focus was on imaging of the paranasal sinuses and traumatology of the mid face. In recent years, it has also been used in imaging of chronic ear diseases (especially in visualizing middle and inner ear implants), but an exact description of the advantages and limitations of visualizing precise anatomy in a relevant number of patients is still missing. The data sets of CBCT imaging of the middle and inner ear of 204 patients were analyzed regarding the visualization of 18 different anatomic structures. A three-step scale (excellent visible, partial visible, not visible) was taken. All analyses were performed by two surgeons experienced in otology and imaging. The indications for imaging were chronic middle ear disease or conductive hearing loss. Previously operated patients were excluded to rule out possible confounders. In dependence of a radiological pathology/opacity of the middle ear, two groups (with and without pathology) were built. Regarding the possibility of excellent visualization, significant differences were only found for small bony structures: incu-stapedial joint (25.8 vs. 63.5 %), long process of incus (42.7 vs. 88.8 %), head of stapes (27.0 vs. 62.6 %), anterior crus of stapes (16.9 vs. 40.9 %) and posterior crus of stapes (19.1 vs. 42.6 %). The other structures (semicircular canals, skull base at mastoid and middle ear, jugular bulb, sinus sigmoideus, facial nerve) could be visualized well in both groups with rates around 85-100 %. Even CBCT shows little limitations in visualization of the small structures of the middle and inner ear. Big bony structures can be visualized in normal as well as in pathologic ears. Overall, due to pathology of middle ear, an additional limitation of evaluation of the ossicular chain exists. In future, studies should focus on comparative evaluation of different diseases and different radiological modalities and be performed by radiologists and otologists together to improve the quality of reports and to answer clinical questions more satisfactorily.