Neuroradiology Objectives in the Neurology Clerkship

Review the normal anatomy and typical landmarks on CT and MRI scans of brain and spinal cord.
Understand that pathological lesions are usually asymmetrical, which “catches the eye” of the viewer. Having examined the patient, the clinician can “focus” on suspected anatomical lesion sites, with improved interpretation of the images.
Know the common appearance of certain pathology:
1. Acute hemorrhage appears bright on CT scan, whether in the brain itself, or outside (subarachnoid, subdural) the brain parenchyma. On T2 weighted MRI, the center of an acute hemorrhage is brighter, with a darker periphery, which changes as the hematoma ages.
2. Acute infarction is seen sooner with MRI (DWI earlier than T2 weighted or other images) than CT. This appears to be a bright lesion on MRI (DWI, T2 weighted or FLAIR) or a darker lesion on CT that occurs within a vascular territory. Very early infarcts on CT may only appear as subtle effacement of gray-white matter junction or sulci, or not appear until hours later.
3. Local mass effect or edema appears as a surrounding darkness (CT) or bright signal (T2 weighted or FLAIR series MRI) around the lesion itself. Contrast may help delineate the lesion within the surrounding edema. Greater mass effect may produce lateral shifts of cerebral hemispheres beneath the falx (across the midline) or down the foramen magnum.
4. Hydrocephalus, or ventricular enlargement, may involvement some or all of the ventricles, depending on whether there is a specific site of obstruction to CSF flow. The ventricles appear enlarged (ex vacuo) also if there is significant loss of brain tissue.
5. CNS infection includes abscesses (mass lesions with surrounding edema), encephalitis or myelitis (inflammation, often viral, of the brain or spinal cord, appearing bright on T2 weighted or FLAIR series MRI) or meningitis (which may be noted as contrast enhancement of leptomeninges on MRI).
6. Primary brain tumors are typically solitary lesions, which may be hemorrhagic or heterogeneous, with surrounding edema. Metastatic tumors are often multiple, with surrounding edema, usually found at the gray-white matter junction of the brain. Epidural spinal cord metastases often arise from vertebral bone, and expand toward the spinal cord.
7. Multiple sclerosis plaques occur in the white matter of the cerebral hemispheres, brain stem and spinal cord, seen as bright lesions on T2 weighted or FLAIR series MRI. Acute lesions may enhance. The bright MRI lesions of MS may be impossible to distinguish from subcortical infarctions, so clinical knowledge of the patient is crucial.
8. Degenerative spine disease (spondylosis, disc herniations) and its relation to the spinal cord and nerve roots are best seen with MRI. Intrathecal contrast may be necessary to better view these relationships with CT scanning (CT myelography).
MRI is the superior imaging modality of the brain and spinal cord. CT is used if there are contraindications for MRI, or if the patient is unstable and quickly deteriorating neurologically. In the latter case, a significant brain hemorrhage or midline shift should probably be detectable on CT scan.