Usefulness of the convexity apparent hyperperfusion sign in 123I-iodoamphetamine brain perfusion SPECT for the diagnosis of idiopathic normal pressure hydrocephalus

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The gold standard for the diagnosis of idiopathic normal pressure hydrocephalus (iNPH) is the CSF removal test. For elderly patients, however, a less invasive diagnostic method is required. On MRI, high-convexity tightness was reported to be an important finding for the diagnosis of iNPH. On SPECT, patients with iNPH often show hyperperfusion of the high-convexity area. The authors tested 2 hypotheses regarding the SPECT finding: 1) it is relative hyperperfusion reflecting the increased gray matter density of the convexity, and 2) it is useful for the diagnosis of iNPH. The authors termed the SPECT finding the convexity apparent hyperperfusion (CAPPAH) sign.


Two clinical studies were conducted. In study 1, SPECT was performed for 20 patients suspected of having iNPH, and regional cerebral blood flow (rCBF) of the high-convexity area was examined using quantitative analysis. Clinical differences between patients with the CAPPAH sign (CAP) and those without it (NCAP) were also compared. In study 2, the CAPPAH sign was retrospectively assessed in 30 patients with iNPH and 19 healthy controls using SPECT images and 3D stereotactic surface projection.


In study 1, rCBF of the high-convexity area of the CAP group was calculated as 35.2–43.7 ml/min/100 g, which is not higher than normal values of rCBF determined by SPECT. The NCAP group showed lower cognitive function and weaker responses to the removal of CSF than the CAP group. In study 2, the CAPPAH sign was positive only in patients with iNPH (24/30) and not in controls (sensitivity 80%, specificity 100%). The coincidence rate between tight high convexity on MRI and the CAPPAH sign was very high (28/30).


Patients with iNPH showed hyperperfusion of the high-convexity area on SPECT; however, the presence of the CAPPAH sign did not indicate real hyperperfusion of rCBF in the high-convexity area. The authors speculated that patients with iNPH without the CAPPAH sign, despite showing tight high convexity on MRI, might have comorbidities such as Alzheimer’s disease.

ABBREVIATIONS 123I-IMP = 123I-iodoamphetamine; ARG = autoradiography; CAP = patients with the CAPPAH sign; CAPPAH = convexity apparent hyperperfusion; CBF = cerebral blood flow; DESH = disproportionately enlarged subarachnoid space hydrocephalus; FAB = Frontal Assessment Battery; iNPH = idiopathic normal pressure hydrocephalus; iNPHGS = iNPH Grading Scale; MMSE = Mini–Mental State Examination; NCAP = patients without the CAPPAH sign; rCBF = regional CBF; ROI = region of interest; SEE = stereotactic extraction estimation; SSP = stereotactic surface projection; TMT-A = Trail Making Test A; TUG = Timed Up and Go.

Article Information

Correspondence Masaki Kondo: Kyoto Prefectural University of Medicine, Kyoto, Japan.

INCLUDE WHEN CITING Published online March 16, 2018; DOI: 10.3171/2017.9.JNS171100.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    A representative case with indistinct DESH and distinct CAPPAH signs. Coronal FLAIR MR image (A) and axial and sagittal CBF SPECT images (B) of an 81-year-old woman suffering from gait disturbance and urinary incontinence. In the MR images, the DESH finding is indistinct because the subarachnoid spaces in the high-convexity area are narrow but the sulci can still be seen. In contrast, the CBF SPECT images show distinct hyperperfusion in the high-convexity area (the CAPPAH sign). Axial and sagittal CBF SPECT images (C) of a 69-year-old man with no neurological symptoms or cognitive deficits are also shown.

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    Definition of the CAPPAH sign using axial and coronal CBF SPECT images in patients with iNPH. In coronal slices, the relative CBF of the high-convexity area and medial parietal lobe is increased. On axial slices, the relative CBF of the high-convexity area is increased in a circular (A) or linear (B) pattern along the superior sagittal sinus.

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    Three regions regarded as the high-convexity area at the gyrus level. In our study, the 3 areas of the paracentral lobule (green), superior parietal lobule (blue), and precuneus (red), the Talairach Daemon Level 3 regions used in the SEE method, are defined as the high-convexity area.

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    Definition of the CAPPAH sign using 3D-SSP images. On 3D-SSP images in a patient with iNPH, the high-convexity area is represented in red, which means that the relative CBF is increased. CBL = cerebellum as reference regions; GLB = global brain regions as reference regions; INF = inferior view; LT.LAT = left lateral view; LT.MED = left medial view; PNS = pons as reference regions; POST = posterior view; RT.LAT = right lateral view; RT.MED = right medial view; SUP = superior view; THL = thalamus as reference regions.



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