Our objective was to assess the impact of hydrocephalus on SPM analysis, particularly focusing on the cingulate gyrus.

The evaluation of cortical glucose metabolism in dementia diagnosis is commonly conducted using [18F]fluorodeoxyglucose (FDG) PET scans. Statistical parametric mapping (SPM) is a method employed to compare standardized uptake values (SUVs) in specific brain regions across individuals. Region-specific Z-scores, generated by SPM, quantitatively indicate the deviation of SUVs from an age-matched reference database of cognitively normal subjects allowing for a more objective and sensitive assessment. Accurate measurement of cingulate metabolism is vital for neurodegenerative disorder assessments. In the context of cognitive impairment, communicating hydrocephalus is a crucial consideration.  We hypothesize that ventricular enlargement and associated lack of FDG avidity can affect the accuracy of SPM analysis of circumventricular structures.  

We reviewed brain FDG-PET scans conducted between 2014-2022. Inclusion criteria encompassed FDG-PET scans for dementia evaluation and indications of hydrocephalus on MRI. Our analysis targeted the anterior, middle, and posterior cingulate gyrus (ACG, MCG, PCG) and used the cerebellum as a reference region due to its minimal susceptibility to hydrocephalus. Non-parametric t-tests were employed to compare each cingulate region with the reference area, utilizing GraphPad Prism software.

49 patients were evaluated (22/49, 45% female; mean age 78), the cerebellum, ACG, MCG, and PCG displayed Z-score means of -1.2 (-6 to -5), -4.3 (-13.8 to 7.7), -6.9 (-21.6 to 1.8), -3.2 (-7.9 to 1.8), respectively. Z-scores in the ACG, MCG, and PCG were markedly lower than cerebellar Z-scores (p <0.0001 in each analysis). Interestingly, this disparity was not evident in qualitative assessments.

In the evaluation of dementia using FDG-PET SPM analysis, hydrocephalus can act as a confounding factor, especially when examining the cingulate gyrus. It is imperative to conduct meticulous qualitative reviews to prevent misinterpretation of SPM data.