Radionuclide Diagnosis of Arteriovenous Malformations with Rapid Sequence Brain Scans

THERE HAVE BEEN discussions in the literature on what is the appropriate length of time to wait between administration of a radiopharmaceutical and scanning of the brain in order best to portray an arteriovenous malformation. It is generally conceded that there is a higher frequency of detection with early scanning because it is primarily the blood pool that is being visualized and not radioactive material diffusing across a disrupted bloodbrain barrier (1–4). The appearance of the arteriovenous malformation on the scan, however, is not definitive and may simulate a neoplasm, infarct, intracerebral hematoma, or other less common causes of positive results. It has been our experience that a characteristically high concentration of radioactivity can be observed passing through the malformation when serial five-second-exposure scintiphotos are taken with the gamma-ray scintillation camera immediately after an intravenous injection of radiopertechnetate (5). The concentration observed in the malformation with the initial bolus is considerably higher than that on the conventional scan obtained fifteen minutes afterward or later. This distinguishing feature has been encountered in five consecutive cases of arteriovenous malformations studied during the last year. Technic The gamma camera detector is positioned over the head in a frontovertex attitude—or occipitovertex if the lesion is suspected to be posterior in location—and 15 mCi of radiopertechnetate is rapidly injected into an antecubital vein. Serial five-second-exposure scintiphotos are obtained, beginning ten seconds after the injection. Conventional scans are procured at fifteen minutes and one hour. Cases I–III are described and illustrated in Figures 1–3, respectively. Case IV: Cerebral angiography demonstrated a small arteriovenous malformation at the vertex of the left hemisphere. The radiopertechnetate blood flow study was obtained in the occipitovertex position, and it showed a high concentration of the test agent in the lesion with the first bolus (Fig. 4, A). A conventional scan was procured fifteen minutes after injection (Fig. 4, C and D), and although it demonstrated the malformation there was a much lower concentration of radioactivity in the lesion. A left carotid injection of radioiodinated macroaggregates of human serum albumin revealed some interesting facets of this arteriovenous malformation. The defect caused by the lesion was discernible in the left lateral (Figure 4, E) and vertex (Figure 4, G) projections (single arrow), but there was a segment of brain substance dependent upon the left anterior cerebral artery which showed a relatively reduced perfusion (double arrows). Presumably its blood supply and that of other portions of the brain were being shunted through the malformation. The degree of shunting is quite large in spite of the smallness of the lesion, and this can be assessed by scanning the lungs.