Radiographic classification of the vestibular and cochlear aqueducts: the paired correlation between normal and abnormal vestibular aqueduct and cochlear aqueduct anatomy.

Multidirectional tomography (MDT) can be useful in determining the caliber, shape, and course of the vestibular aqueduct (VA) and cochlear aqueduct (CA). Clinical decisions have been based on the findings from MDT. Unfortunately, the clinical utility of these observations has been confusing and controversial because similar MDT techniques were not used. This study will address some of the difficult questions and clinical controversies derived from MDT observations. This new perspective has evolved with the use of high resolution computed tomography (HRCT). An analysis of 750 petrous bones for the occurrence of the various types of VAs and CAs using Gado's classification, further vestibular aqueduct and a variation of Gado's classification for the cochlear classification is reported. The distribution of the possible paired types of VA and CA are evaluated. MDT results indicate that the paired analysis in patients with inner ear dysfunction is not useful, cost effective, diagnostic, or of prognostic value. MDT can provide clinically valid observations of periaqueductal and perilabyrinthine pneumatization which is helpful in anticipating the size and position of the endolymphatic sac at the time of surgery for those few patients who may benefit from endolymphatic system surgery. However, when a comparison is made between MDT and CT of 60 ears in those same patients, the clinical limitations of MDT for inner ear diagnosis and prognosis became apparent. The future for HRCT scanning with reformatting holds potential for clinically meaningful visualization of inner and middle ear structures previously expected from MDT imaging.