 It's a complex case, a 52-year-old man who carries a diagnosis of multiple sclerosis. And yes, he does have extraordinary atrophy and signal throughout the colosal and the colosal septal interface. As you go off to the side, you can see some areas of right angle demyelination. But he presents now with episodes of falling down. And while it's true, you can get extensive atrophy. We see that in the cingulate sulcus and super marginal sulcus going up. You wouldn't get this severity posterior fossa atrophy from MS alone. I mean, look at the size of his pons. It is extremely small. His cerebellar vermis, with the individual vermian lobes, are also small. You can see the prominence of the patient's primary fissure right here, the postural lateral fissure. Then we go down to the medulla. We see the medullary clava as a landmark. And then go to the pons and the midbrain. And of the two, the pons look a bit smaller than the midbrain. But one of the differential diagnostic considerations here would be progressive super nuclear palsy. And you look at the inferior colliculus, you see it's got a pretty good bump. And as you go off to the side, the superior colliculus also has a pretty good bump. They're almost equal. So PSP or progressive super nuclear palsy, which, by the way, is associated with gait disturbance and paralysis of gays, which this patient doesn't have, wouldn't be a favored diagnosis. The severe pontine atrophy, though, in the absence of postural lateral plaque formation, which is where you would get MS in the pons, is a tip off to the diagnosis. And if we go down a little bit lower at the level of the brachium conjunctivum or superior cerebellar peduncle, it is very atrophic, with this T-shaped area of vertical high signal in the median pontine raffae and a cross going from side to side from medial lateral, producing what's known as the hot cross bun sign of this disorder, multi-system atrophy. This patient does have atrophy, and it's hard to tell what component of the atrophy is related to chronic, long-standing MS and which component is related to this patient's MSA. Now MSA can be subdivided into three types. The three types are MSAC, which affects the cerebellum and the pons, also falling into the category of olivopontos cerebellar atrophy. It's one of the olivopontos cerebellar atrophies. There are hereto-familial ones as well. So it's a subset of OPC disorders. And these patients have severe ataxia and falling down as their major manifestation. The other types of multi-system atrophy are MSA, multi-system atrophy, A, which stands for autonomic failure. When they stand up, they get hypotension. Sometimes when they stand, they simply get tremors in their legs. They can't stand in one place. But they can walk, which is very different than classic Parkinson's disease, where walking is challenging due to the rigidity. So when they stand still in shy Drager syndrome, which is basically the autonomic type of MSA, they have trouble staying in one place. Then you've got the Parkinsonian variation, MSAP, also known as striatoneigral variant of multi-system atrophy. And this one may be very difficult to differentiate from Parkinson's disease, and doesn't respond very well to the typical cinnamon and Parkinsonian preparations. These patients often have a fair amount of disturbance in their speech and laryngeal parises. Patients with MSA often have involvement of the pyramids. So there may be a combination of motor dysfunction with some of these others. This patient's pyramids look pretty good. Death is often related to bulbar dysfunction and dysphagia. The patients often die from aspiration pneumonia or apnea. This patient manifests the hot cross bun sign seen down low at the level of the ponds of MSAC with associated cerebellar atrophy, atrophy of the brachium conjunctivum, or superior cerebellar peduncle, and the cerebellar and pontine atrophy conspicuous in the sagittal projection in a patient who has concomitant MS.