Last revised by Fabio Macori on 2 Sep 2021

The precuneus is a part of the parietal lobe of the brain, lying on the medial surface of the cerebral hemisphere. It plays a role in visuospatial imagery, episodic memory retrieval and self-processing operations 1.

Posterior to the precuneus lies the cuneus, separated from it by the medial portion of the parieto-occipital sulcus 1,2.  

Anteriorly lies the paracentral lobule, separated from it by the pars marginalis (ascending branch of the cingulate sulcus1,2.  

Inferiorly is located the cingulate gyrus, separated from it by the subparietal sulcus 1,2.  

While highly variable, the main arterial supply arises from the posterior cerebral artery, predominantly the P2 segment. The precuneus derives blood supply from the occipito-parietal artery, a terminal branch of the internal occipital artery.

The parieto-occipital sulcus joins with the anterior end of the calcarine sulcus to form a 'lazy Y' configuration, sometimes referred to as the parieto-occipito-calcarine sign 2. The precuneus lies superior to the upper limb of the Y (parieto-occipital sulcus), whereas the cuneus lies in between the two limbs, and the lingual gyrus below the lower limb. 

Along with the posterior cingulate cortex and posterior temporoparietal areas, the precuneus is one of the key areas involved in Alzheimer disease. Characteristic hypometabolic patterns of FDG-PET maps involving precuneus and posterior cingulate gyrus (without occipital involvement) helps to distinguish Alzheimer disease from other kinds of dementia 3.

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