Implications of Hydrocephalus on [18F]-Fluorodeoxyglucose Positron Emission Tomography Statistical Parametric Mapping Analysis in Neurodegenerative Disease Evaluation

BACKGROUND AND PURPOSE: Brain [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) is critical in the diagnosis of neurodegenerative disease. Quantitative analysis with statistical parametric mapping (SPM) has been shown to improve diagnostic accuracy of FDG-PET and has been incorporated in clinical workflows. This study aimed to assess the effects of hydrocephalus on FDG PET SPM analysis accuracy, focusing on cingulate gyrus regions, which are of particular interest in dementia evaluation, and also are adjacent to the lateral ventricles.

MATERIALS AND METHODS: In this retrospective IRB-approved study, patients who underwent brain FDG-PET/CT or PET/MRI were evaluated. Inclusion criteria were clinical history of cognitive impairment/suspected neurodegenerative disease and MRI evidence of communicating hydrocephalus. Region-specific Z-scores for the anterior, middle, and posterior cingulate gyri (ACG, MCG, PCG), as well as for the cerebellum were generated using SPM analysis. Blinded expert qualitative assessment was performed for each anatomic region. Kappa coefficients were computed to evaluate agreement between quantitative and qualitative results. Paired nonparametric t-tests assessed Z-score differences between cingulate and cerebellar regions.

RESULTS: The study included 48 patients (17 females, mean age 76). SPM analysis found significantly lower cingulate Z-scores compared to the cerebellum [-4.3 (ACG), -6.9 (MCG), and -3.2 (PCG), -1.2 (CBL) p < 0.0001]. Similar results were observed in the signed rank tests comparing cingulate regions to cerebellum [ACG -3.2 (SD 2.1), MCG -5.7 (SD 3.6), PCG -1.9 (SD 2.4), p < 0.001 for all 3 cingulate regions]. Kappa coefficients indicated poor agreement between SPM and qualitative assessments (kappa 0.05-0.19, p-values 0.078-0.479).

CONCLUSIONS: Our study highlights hydrocephalus as an important pitfall of FDG-PET SPM, particularly when analyzing the cingulate regions, integral to the clinical evaluation of dementia. Awareness of this pitfall can improve diagnostic accuracy and thus improve clinical outcomes in this growing patient population.

ABBREVIATIONS: FDG= [18F]fluorodeoxyglucose, PET= Positron Emission Tomography, SPM:=Statistical Parametric Mapping, SUV:= Standardized Uptake Values, NPH= Normal Pressure Hydrocephalus, MRI= Magnetic Resonance Imaging, CT= Computed Tomography, ACG= Anterior Cingulate Gyrus, MCG= Middle Cingulate Gyrus, PCG= Posterior Cingulate Gyrus, CBL= Cerebellum.