General description

Alzheimer's disease (AD) is a progressive neurocognitive disorder characterized by cerebral cortical and subcortical gray matter pathology, including extracellular deposition of beta-amyloid and intracellular neurofibrillary tangle formation, which results in cognitive decline.

AD is the most prevalent cause of dementia, accounting for 60-80% of cases in the elderly population. The prevalence of AD increases with advancing age and is approximately twice as high in women compared to men, partly attributable to the longer life expectancy in females. As the elderly demographic continues to grow in developed nations, the prevalence of AD is projected to rise correspondingly.

The majority of AD cases are sporadic, with onset typically occurring later in life and an unknown underlying etiology. Advanced age represents the most significant risk factor for developing the disease. However, approximately 10% of AD cases exhibit a familial pattern of inheritance. Of these familial cases, approximately half manifest at an early age (<65 years) and are frequently associated with specific genetic mutations.

Radiographic features

Parietotemporal atrophy

Neuroimaging studies in the initial stages of Alzheimer's disease typically reveal no apparent abnormalities. However, as the disease progresses, atrophic changes become evident, primarily involving the medial temporal lobes and parietal lobes, eventually culminating in global cerebral atrophy.

Ventriculomegaly

Atrophic changes in the hippocampus and parahippocampal gyrus result in enlargement of the hippocampal sulcus and collateral sulcus. Consequently, the inferior horn of the lateral ventricle appears widened. Additionally, the angle formed between the hippocampal sulcus and the base of the brain increases.

Decreased cerebral blood flow

Cerebral blood flow single-photon emission computed tomography (CBF SPECT) imaging demonstrates initial hypoperfusion involving the posterior cingulate gyrus and precuneus regions in Alzheimer's disease. As the disease progresses, CBF deficits extend to involve the parieto-temporal lobes. Notably, SPECT exhibits higher sensitivity compared to MRI in the detection of AD, as it can reveal perfusion deficits prior to the manifestation of atrophic changes on structural MRI.