MRI of the Head/Brain

MRI has essentially replaced CT for evaluation of all non-acute, non-traumatic brain imaging. This is because of MRI's superior soft tissue contrast. CT is still used as initial imaging in the work up of acute stroke and trauma; in both instances to evaluate for the presence of blood. In the evaluation of a stroke, MRI frequently follows because of its ability to detect hyper-acute stroke, not possible with CT.

MRI has long been the modality of choice for almost all non-traumatic brain imaging. This includes imaging of congenital abnormalities, cancer (including evaluation for metastatic disease), white matter disease, vascular malformations, and infectious disease (cerebritis and encephalitis as well as meningitis, though mainly for complications of meningitis). Regarding contrast use, the same rules apply to CT and MRI. When hemorrhage is possible (stroke, trauma, "the worst headache of my life"), no contrast should be used. Contrast should be used only when a mass or vascular malformation is suspected, or in the rare instance when an inflammatory condition is suspected (meningitis, encephalitis, cerebritis).

MRI of the Head/Pituitary Gland

MRI is the only way to adequately evaluate the pituitary gland. For all pituitary and supra-sellar lesions, MRI offers multiplanar capabilities and soft tissue contrast essential in detecting these lesions. The large tumors (meningiomas and macro-adenomas) pose no imaging problem. Microadenomas, small enough to exist within the substance of an otherwise normal gland without distorting its contour, pose an additional problem. In order to achieve contrast distinction between normal gland and adenoma, dynamic contrast imaging has proven effective. This relies on differential enhancement and washout patterns between most adenomas and normal pituitary tissue. Contrast is a must!

MRI of the IAC (Internal Auditory Canal)

Ordered in patients with hearing loss or vertigo. The two main categories of hearing loss are conductive and sensorineural. For the former, CT is the modality of choice. This will nicely assess the ossicular chain, as well as other conductive abnormalities in the external and middle ear (Paget disease, fibrous dysplasia).