Intravenous contrast is almost never necessary for the indications. Images presented in an algorithm that highlights bone detail are most useful for assessment. In the temporal bone region, MRI is useful for assessing for a mass in the internal auditory canal (IAC) abnormal cranial nerve caliber or enhancement the fluid-filled spaces of the labyrinthine structures for characterizing masses in the middle ear, for example to distinguish a cholesteatoma from an encephelocele and for assessing marrow, for example in the setting of skull base osteomyelitis.ĬT of the temporal bone must be performed at high-resolution and small field of view with thin imaging slices (0.5 mm), in order to be able to visualize the small, fine structures of the temporal bone to maximal detail. But since MRI is not dependent on material density, but rather on spin properties of material at the subatomic particle level, they can behave quite differently within a magnetic field and produce quite different signal on various MR imaging sequences, allowing much better visual distinction. normal muscle and an adjacent sarcoma), they can be difficult to distinguish or demarcate from each other. On CT, if two soft tissue structures are similar in density (e.g. MRI, on the other hand, offers much better, more specific, and more distinctive soft tissue characterization than CT. In the temporal bone region, therefore, CT is useful for assessing the margin and patency of the external auditory canal (EAC) thickness of the tympanic membrane, as it is bordered on either side by air, and whether there may be myringosclerosis, perforation, or retraction margins, aeration, and opacities of the middle ear and bony and calcified structures such as the ossicles, mastoid septations, otic capsule, morphology and margins of the cochlea and semicircular canals, vestibular aqueduct, and facial nerve canal. CT allows excellent delineation of calcifications, cortical bone, air, and fat. The patient’s presenting symptoms and suspected diagnoses help guide the choice of modality.ĬT offers better spatial resolution compared to MRI. Each modality has its strengths and limitations. Imaging evaluation of the ear and temporal bone is primarily accomplished by computed tomography (CT) or magnetic resonance imaging (MRI).
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