Two-layer appearance on brain perfusion SPECT in idiopathic normal pressure hydrocephalus: a qualitative analysis by using easy Z-score imaging system, eZIS

Background/Aims: It is often difficult to distinguish idiopathic normal pressure hydrocephalus (iNPH) from other neurodegenerative disorders such as Alzheimer’s disease (AD). To understand the characteristic pattern of blood flow in iNPH, we performed brain perfusion SPECT and analyzed the results by using the easy Z-score imaging system (eZIS). Methods: Subjects were 12 patients with probable iNPH and 10 probable AD patients with prominent ventriculomegaly. They underwent brain perfusion SPECT using 99mTc-ethylcysteinate dimer as a tracer. Results: The two-tailed view display in eZIS demonstrated an obvious two-layer structure consisting of decreased blood flow around the corpus callosum and, in iNPH, enhanced perfusion in areas surrounding the cingulate gyrus in the sagittal view, while no AD cases showed these findings. Conclusion: Hypoperfusion around the corpus callosum in iNPH could be, at least partially, a false-positive finding due to an insufficient anatomical standardization of SPECT images caused by an abnormally enlarged ventricle. Increased blood perfusion in the external layer adjacent to the hypoperfused area might be caused by increased radioisotope count per volume resulting from exclusion of cerebral cortex by a dilated ventricle. Our results demonstrate that a two-layer appearance revealed by the two-tailed view analysis of brain perfusion SPECT using eZIS could be a means to detect iNPH.