MRI of the brain shows classic cerebral volume loss (atrophy) especially visible in the temporal and parietal lobes. Multiple white matter T2 hyperintense lesions suggest a coexisting component of chronic small vessel ischemic change. Findings: MRI is consistent with the presenting symptoms of Alzheimer’s disease in this elderly patient.
Atrophy is a wasting away process (or shrinkage) of certain areas of the brain due to nerve cell death and tissue loss. In the case of ‘white matter T2 hyperintense lesions’ this is not as complicated as it sounds; the T2 weighted MRI refers to specific settings for echo time and repetition in the MRI process. The hyperintense lesions (clearly seen in Image 1 above) are bright white glowing patches that suggest damaged cell tissues. These white lesions show areas whereby the tissue contains more fluid inside than is normal for that specific tissue type. In MRI this type of setting to highlight fluid within the tissues is known as a ‘flair’ sequence. These bright white lesions are important in early diagnosis because sometimes they can be seen on MRI before significant symptoms have developed and are therefore an early indicator of cerebral changes. They can also be helpful in confirmation of a known diagnosis of Alzheimer’s.
MRI in Alzheimer’s Disease
MRI (Magnetic Resonance Imaging) plays an important role in establishing physiological changes of the brain to aid in the diagnosis of Alzheimer’s disease. A CT (Computerised Tomography) scan is able to demonstrate typical patterns of neurological atrophy in Alzheimer’s disease, but MRI is more sensitive to early changes and better equipped to exclude other causes of dementia such as brain tumours, hydrocephalus, multiple infarctions and subdural hematoma. One of the major roles of MRI in the diagnosis of Alzheimer’s disease is the accurate assessment of volume loss (demonstrating atrophy) in certain regions of the brain, especially the hippocampus and related regions. Volume changes, as depicted in the MRI above, can have a diagnostic accuracy of up to 87% (1).
The hallmark characteristics of Alzheimer’s disease are the accumulation within the brain of senile plaques, neurofibrillary tangles and progressive loss of neurons(1). Senile plaque can be defined as, “a microscopic mass of fragmented and decaying nerve terminals around an amyloid core”(2). Neurofibrillary tangles are twisted protein fibres that are found within nerve cells. The fibres are made up of a protein called ‘tau’ which is found inside brain cells and plays an essential role in the normal functioning and structure of the cells. Senile plaques and neurofibrillary tangles together are the two most significant findings in the brain cells of patients with Alzheimer’s disease. The typical progression process of Alzheimer’s disease initially involves the entorhinal region, (which is located in the temporal lobe and has connections with the hippocampus and other cortical and subcortical structures, and therfore is an integral part of the medial temporal lobe memory system),(3) and after spreads to the hippocampal complex and mesial temporal lobe structures, and eventually, the temporal lobes and basal forebrain(4)
1. Norfray JF, Provenzale JM. Alzheimer’s disease: neuropathologic findings and recent advances in imaging. AJR Am J Roentgenol. 2004;182 (1): 3-13. AJR Am J Roentgenol (full text) – Pubmed citation.
2. Oxford Medical Dictionary
3. MIKKONEN, MIA. THE HUMAN ENTORHINAL CORTEX: Anatomic organization and its alteration in Alzheimer’s disease and temporal lobe epilepsy. Series of Reports, No 50, Department of Neurology, University of Kuopio. 1999.
4. Galton CJ, Patterson K, Xuereb JH et-al. Atypical and typical presentations of Alzheimer’s disease: a clinical, neuropsychological, neuroimaging and pathological study of 13 cases. Brain. 2000;123 Pt 3 : 484-98.doi:10.1093/brain/123.3.484 – Pubmed citation