On a standard lumbar spine MRI with axial and sagittal scans, the sacrum is not specifically imaged. So what can you do to find a sacral fracture which may be the cause of the patient’s back pain?
The key is to look at the lateral most scans on both sides of mid line and look for signal abnormality on the T1 scans. What you are looking for is reduced T1 marrow signal. On the T2 scans the oedema is not as obvious as often its not much brighter than adjacent fat. You will see this only on the lateral most scans as usually the oedema doesnt spread to the mid line scans.
Image Above: Red arrow lateral most scan right of mid line and blue arrow lateral most scan left of mid line. Reduced T1 marrow signal on right compared to left is the clue to a sacral abnormality. Central image with dashed yellow lines demonstrates level of lateral most scans.
Image above: Red Arrow reduced T1 signal on tight side lateral most scan. Compare with normal T1 signal on left ( blue arrow). Central image demonstrates the right sacral fracture dashed yellow line indicates location of scan on right.
Image Above: Right sacral ala fracture ( blue arrow) with surrounding oedema ( pink arrow). Adding a routine coronal PDFS or T2FS to the lumbar series makes the diagnosis much easier. But when you dont have it, look at the lateral most slices for reduced T1 marrow signal.