Visualization of normal and abnormal inner ear with volume rendering technique using multislice spiral CT

Objective To evaluate the ability of the volume rendering technique to display the normal and abnormal inner ear structures.Methods Forty normal earand 61 abnormal inner ears(40 congenital inner ear malformations,7 labyrinthitis ossificans,and 14 inner ear erosion caused by cholesteatomas)were examined with a MSCT scanner.Axial imaging were performed using the following parameters:120 kV,100 mAs,0.75 mm slice thickness,a pitch factor of 1.The axial images of interested ears were reconstructed with 0.1 mm reconstruction increment and a FOV of 50mm.The 3D reconstructions were done with volume rendering technique on the workstation.Results In the subjects without ear disorders a high quality 3D visualization of the inner ear could be achieved.In the patients with inner ear disorders all inner ear malformations could be clearly displayed on 3D images as follows:(1)Michel deformity(one ear):There was complete absence of all cochlear and vestibular structures.(2)common cavity deformity(3 ears):The cochlea and vestibule were represented by a cystic cavity and couldn't be differentiated from each other.(3)incomplete partition type Ⅰ(3 ears):The cochlea lacked the entire modiolus and cribriform area,resulting in a cystic appearance.(4)incomplete partition type Ⅱ(Mondini deformity)(5 ears):The cochlea consisted of 1.5 turns,in which the middle and apical turns coalesced to form a cystic apex.(5)vestibular and semicircular canal malformations(14 ears):Cochlea was normal,vestibule dilated,semicircular canals were absent,hypoplastic or enlarged.(6)dilated vestibular aqueduct(14 ears):The vestibular aqueduct was bell-mouthed.In 7 patients with labyrinthitis ossificans,3D images failed to clearly show the completeinner ears in 4 ears because of too high ossifications in the membranous labyrinth.In the other 3 ears volume rendering could display the thin cochlea basal turn and the intermittent semicircular canals.In the patients with cholesteatomas 3D volume rendering images could identify the site of the bony labyrinth erosion and its surrounding structures.Conclusions Volume rendering technique can provide higher quality three-dimensional images of the bony labyrinth and serves as a useful tool for analysis of normal and anomalies of the inner ear.