CLIPPERS results in lesions with a characteristic appearance, both in terms of where they are and what they look like, on brain MRI. Pittock et al describe them as "a characteristic pattern of punctuate and curvilinear enhancement peppering the pons and extending variably into the medulla, brachim pontis and mid-brain". The lesions are thought to result from some underlying inflammatory process which has yet to be identified. The exact number and location of lesions is different amongst different patients, presumably contributing to the variability in symptoms seen.
MRI is a key part of diagnosis in most brain conditions today. There are many different kinds of MRI scan possible, each designed to show some different properties of the brain tissue and highlight differences between normal and abnormal tissue. Below are some images from my pre-treatment brain MRIs.
Standard Structural ("T1-weighted") MRI
The panel shows some slices through my brain at different positions from the back (top-left) to the front (bottom-right) of my head. The scan is designed to highlight differences in a tissue property called T1 - different tissues have different T1s and so appear with different brightness in the scan. The view is as if you are standing facing me and have removed my face (!) so you can see sections through my brain. You can see the brain, inside the scalp, with dark fluid surrounding it. The dark holes in the middle of the brain are also filled with fluid and are called ventricles; this is the same fluid which is sampled from the spine during a lumbar puncture. As the slices are taken from further forward (bottom-right) you can start to see the eye-sockets. From a CLIPPERS perspective these scans don't show very much that's unusual. A slightly different procedure is required.
Contrast-Enhanced MRI
The panel shows slices which superficially look very similar to standard structurals. However these ones were collected after I had an injection of Gadolinium contrast agent. This substance changes the local magnetic properties of tissue so that damaged areas appear bighter than normal. In particular in this case it causes bright signal in places where the blood-brain barrier has been disrupted because of CLIPPERS lesions. This is most obvious in the slices in the top-right and middle-left of the panel especially when compared with the same slices in the first panel.
"T2-Weighted Inversion Recovery" MRI
This panel shows a different scan which highlights differences in a tissue property called T2. Again you can see evidence of CLIPPERS lesions in the slices towards the right of the top row and the left of the middle row. These and other scans collected during a 30 minute scanning session were used to diagnose CLIPPERS but they don't tell the whole story. One of the diagnostic problems is that several brain conditions result in similar symptoms and potentially have a similar pattern of lesions in MR even though the underlying cause may be different. The level of detail in an MRI scan is around a mm so it can detect the damage resulting from microscopic processes but it can't see them directly. So MRI provides powerful supporting evidence for CLIPPERS but other more direct measurements, like lumbar puncture or brain biopsy, may be required to exclude other conditions.
"T2-Weighted" Axial MRI
Finally, this panel shows a different view of a different kind of T2-weighted scan. Here the view is as if you are standing behind and above me and looking down through my head towards my feet. The slices go from the base of the brain (near the neck) on the top-left to the top of the head on the bottom-right. The back of the head is at the bottom of each slice and my eyes and nose can be seen at the top of some slices. In these scans fluid-filled areas are bright which can make spotting pathology easier. Not much unusual here as far as I can see (with the usual caveat that I am not a medical professional and certainly not qualified to read clinical scans).
There are many other kinds of MRI scan. Contrast-Enhanced scans are very important for seeing the effects of CLIPPERS but the best combination of scans to distinguish CLIPPERS from other conditions hasn't been established. A way of unequivocally identifying CLIPPERS purely from some combination of MRI scans would be a major step forward in diagnosis.
Read other articles in this series at Living With CLIPPERS. 
Living With CLIPPERS by Bill Crum is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.
