NMR imaging in the recognition of giant intracranial aneurysms.

Most giant aneurysms present clinically as intracranial mass lesions. Many contain an organized lamellated thrombus with only a small eccentric lumen remaining that can be opacified at angiography. Four patients with such aneurysms were studied using flow-dependent nuclear magnetic resonance scanning sequences. The aneurysms show a smooth rounded margin, and the thrombus within is clearly distinguishable from the blood flowing through the patent lumen, which gives a low signal. By using different scan sequences it is possible to prove that the area of low signal is indeed fluid in rapid motion, thus confirming the diagnosis.