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Medical Forum / General / General / October 2004Variations in Brain Structure
I am used to seeing the textbook illustrations of a typical human brain. I am wondering how much variation from those illustrations is normal? Is it normal, for example, for one hemisphere of the brain to be obviously larger than the other? And, in an MRI photograph, what would bright regions in the brain represent? Higher nerve density? pooua@aol.com (Richard Alexander) wrote in part: >I am used to seeing the textbook illustrations of a typical human >brain. I am wondering how much variation from those illustrations is >normal? Is it normal, for example, for one hemisphere of the brain to >be obviously larger than the other? And, in an MRI photograph, what >would bright regions in the brain represent? Higher nerve density? There are definitely fairly large individual differences. In fact, people who appear quite normal can deviate markedly from the "typical." One hemisphere may be larger than another, but at some point the suspicion arises that some kind of atrophy is at work. Bright regions in an MRI indicate water. In a disease such as MS, water replaces the fatty myelin sheath that surrounds nerves, and these areas are abnormally bright. -- Jim Chinnis Warrenton, Virginia, USA jchinnis@alum.mit.edu : pooua@aol.com (Richard Alexander) wrote in part: : >I am used to seeing the textbook illustrations of a typical human : >brain. I am wondering how much variation from those illustrations is : >normal? Is it normal, for example, for one hemisphere of the brain to : >be obviously larger than the other? And, in an MRI photograph, what : >would bright regions in the brain represent? Higher nerve density? : There are definitely fairly large individual differences. In fact, people who : appear quite normal can deviate markedly from the "typical." : One hemisphere may be larger than another, but at some point the suspicion : arises that some kind of atrophy is at work. : Bright regions in an MRI indicate water. In a disease such as MS, water : replaces the fatty myelin sheath that surrounds nerves, and these areas are : abnormally bright. Water? Isn't it uptake? They use radioisotopes in fMRIs, no? Emma > : pooua@aol.com (Richard Alexander) wrote in part: > [quoted text clipped - 20 lines] > > Emma Mr Alexander never mentioned fMRI. Funcional MRI just means that you try to correlate an observed activity with a supposed function. Emma, I know of PET scans using isotopes, but not fMRI's. I might be wrong though. MRI maps the distribution and the molecular enviroment of water molecules. A T2 weighted image (the "Pathologic image") will show water as white, while a T1 weighted image will show fat and white brain matter(which is more fatty than gray matter) as white. [snip] > > : Bright regions in an MRI indicate water. In a disease such as MS, water > > : replaces the fatty myelin sheath that surrounds nerves, and these areas [quoted text clipped - 6 lines] > Emma, I know of PET scans using isotopes, but not fMRI's. I might be wrong > though. I know that no radioisotopes were used in this particular MRI. There was absolutely no special preparation prior to the MRI, apart from the patient emptying all his pockets. I noticed on one of the pictures (I want to say, "slides") in particular that there were symmetric, bright crescents, one in each hemisphere. I would expect that kind of symmetry is too regular to be disease or damage, so must be part of the design of the brain. They were located deep inside the brain mass, with the concave side faced anterior. Apparently, the brain structures are all normal. > MRI maps the distribution and the molecular enviroment of water molecules. > A T2 weighted image (the "Pathologic image") will show water as white, while > a T1 weighted image will show fat and white brain matter(which is more fatty > than gray matter) as white. That is interesting, and thank you for providing that information. I would like to add something subjective. I just had my first brain MRI (my second MRI procedure), and it went smoothly. The procedure took about 20 minutes. During the procedure, I tried to rest with my eyes closed, but my eyes kept opening. Sometimes, my right eye felt like it was throbbing a little (I've had intermittent pain in that eye for months). After the procedure, I began to feel a little dizzy. That might have been because I was lying on my back for so long or because I wasn't used to being awake so early. But, I suspect there might have been extra blood flow in my brain, perhaps because of the MRI itself. The dizziness wore off (my eye still bothers me--the MRI found polyps in my sinuses). I might be thinking a little more clearly than I had been prior to the procedure, maybe because there is something of interest to me, or maybe as a result of the procedure. I expect the effect will be temporary. I also expect to be told that there are no biological effects from an MRI. >I noticed on one of the pictures (I want to say, "slides") in >particular that there were symmetric, bright crescents, one in each [quoted text clipped - 4 lines] > >Apparently, the brain structures are all normal. The bright crescents are the ventricles, large structures in the brain that are filled with spinal fluid, i.e. mainly water. As you've guessed, they are an entirely normal part of brain anatomy. |
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