Apparent Wall Thickening In Fluid Filled Versus Air Filled Tympanic Bulla In Computed Tomography

Barthez PY, Koblik PD, Hornof WJ, et al.

Veterinary Radiology & Ultrasound 1996;37:95-98.

A series of CT imaging experiments was performed to test the hypothesis that when the tympanic bulla is filled with fluid there would be a false impression of bulla wall thickening. CT images were obtained before and after introduction of water in the tympanic bulla of a fresh canine cadaver. Images were acquired using different mA settings, slice thicknesses, reconstruction algorithms, and displayed at different window widths. The wall of the fluid filled bulla appeared thicker than that of the air filled bulla. This artifact was also demonstrated on a phantom composed of a thin (0.5 mm) and a thick (5 mm) piece of aluminum imaged in air and water. The effect was more apparent when images were acquired as thick slices ( > 5 mm), reconstructed with a soft tissue algorithm, or displayed with a narrow window ( < 250 CT numbers). The radiologist must be aware of this artifact when interpreting CT images of the tympanic bullae.