Can a brain mri miss an avm?

Not likely: Hi. Every measurement has limits of resolution, so in theory, a small enough AVM below the limits of resolution on the MRI would be missed. But I would say that any meaningful brain AVM would be seen on brain MRI.

Not likely: depends on the quality of the scan and the size of the AVM but this is an excellent test to identify AVM in the brain

Yes: A vascular imaging study should be done if an AVM is suspected. CTAngiogram and MRAngiogram are less invasive studies, but the gold standard would be a cerebral angiogram, which does carry risks.

Rather unlikely: Any vascular lesion of significant size will be readily observed with MRI study with contrast injection.