Applied Radiology

Prepared by John F. Healy, MD of the Veterans Administration Medical Center in San Diego, CA.

CASE SUMMARY

This 51-year-old woman was found in her automobile in an apparent post-ictal state. No focal deficits were noted, but the patient had signs of frontal lobe release. She had a long history of lupus and the diagnosis of lupus vasculitis was entertained. Cytoxan therapy was contemplated. The patient had severe renal disease.

DIAGNOSIS

Meningioma

DISCUSSION

Low contrast dose digital selective angiography with careful renal mon-itoring was advised. However, the clinicians opted for magnetic res-onance angiography (MRA) at another institution. At that institution, a diagnosis of proximal left middle cerebral arteritis was made solely on the basis of the maximum intensity projected algorithm images (figure 1). The sagittal localizer and the MRA source images were not viewed by the radiologist. Most experts recommend that MRA never be performed without an accompanying MRI and that source images always be examined. These dictums were not followed in this case.

When the patient returned to our hospital, we did not feel that the above study was adequate. An MRI was performed and an MRA was repeated with filming and complete evaluation of the source images.

The sagittal localizer, done but not viewed at the outside MRI facility, clearly showed an isodense mass with edema in the left frontal lobe (figure 2). The edema and mass effect were also noted on the MRA source images (figure 3). No evidence of vasculitis was noted (figure 4). Contrast-enhanced MRI scan revealed a left frontal meningioma (figure 5).

When the MRA examination was done properly (with viewing of source images and localizer images and accompanied by an MRI examination), this patient was spared unnecessary treatment (cytoxan therapy) for a disease that she did not have (lupus vasculitis). In addition, the poorly performed incomplete examination did not diagnose her real disease (meningioma), although adequate MRI data (source images and sagittal localizer) had been acquired from and billed to the patient.

Magnetic resonance angiography has proven to be a helpful screening test in neuroradiology. Generally, a normal MRA study precludes significant disease in the carotid arteries. Subtle intracranial disease may be missed by MRA; however, clinical practice has borne out the expectation that false positives are a more significant problem with MRA than false negatives. ^1-3

Cost cutting efforts and managed care often encourage incomplete and thus less costly imaging evaluation of sick patients. When an MRA is done improperly and incompletely, the chances for error are magnified.

Intracerebral magnetic resonance angiography examinations should be performed in conjunction with an MR examination of the brain. Source images should always be examined. It is poor practice to rely solely on maximum intensity projected images. This case dramatically emphasizes the need to adhere to these basic tenets of MRA; when they were violated, a misdiagnosis was made. This was rectified by a properly performed examination a few days later.

REFERENCES

1. Heiserman JE : The role of magnetic resonance angiography in the evaluation of cerebrovascular ischemic disease. Neuroimaging Clin North Am 2:753-769,1992.

2. Crosby DL, Turski PA, Davis WL : Magnetic resonance angiography and stroke: Techniques, applications, and limitations. Neuroimaging Clin North Am 2:509-539, 1992.

3. Masaryk AM, Ross JS, DiCello MC, et al : 3DFT MR Angiography of the carotid bifurcation: Potential and limitation as a screening examination. Radiology 179:797-804, 1991.