The eagle-wing finding in FP-CIT SPECT, as a characteristic finding in patients with DESH- type iNPH

Although dopamine transporter (DAT) imaging has been reported to be useful for differentiating idiopathic Normal Pressure Hydrocephalus (iNPH) from its mimics, the radiological findings of DAT imaging in iNPH have not been established. We investigated [¹²³I] N-ω-fluoropropyl-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (FP-CIT) single photon emission computed tomography (SPECT) images from patients with disproportionately enlarged subarachnoid-space hydrocephalus (DESH)-type iNPH to understand the characteristics of DAT images of iNPH.

We retrospectively collected 11 DESH-type iNPH patients without comorbidities who underwent FP-CIT SPECT imaging. The patients' FP-CIT SPECT were examined using both visual and quantitative evaluations. Visual assessment used Kahraman et al.'s five-step grading, and quantitative assessment used DaTView and MIM software to calculate specific binding ratios (SBRs) for four volumes of interest (VOIs): the entire striatum, caudate nucleus, anterior putamen, and posterior putamen. Intergroup comparisons were made between the DESH group and a normal control (NC) group adjusted for age and sex.

The visual assessment classified 91% of DESH patients as showing grade 4 'eagle-wing' on FP-CIT SPECT, with a Kappa coefficient of 0.601. The median SBR was lower in the DESH group than in the NC group for all four VOIs, and significantly lower in the anterior and posterior putamen (p < 0.05).

In DESH-type iNPH, FP-CIT SPECT imaging typically shows the 'eagle-wing' finding due to decreased DAT concentration in the putamen. Our results enhance the utility of FP-CIT SPECT in diagnosing iNPH and distinguishing it from mimics.