Reliability and Interobserver Variability of Evans' Index and Disproportionately Enlarged Subarachnoid Space Hydrocephalus as Diagnostic Criteria for Idiopathic Normal Pressure Hydrocephalus

Kiyoshi Takagi; Ryota Watahiki; Toru Machida; Kenji Onouchi; Kazuyoshi Kato; Marie Oshima

doi:10.4103/ajns.AJNS_354_19

Reliability and Interobserver Variability of Evans' Index and Disproportionately Enlarged Subarachnoid Space Hydrocephalus as Diagnostic Criteria for Idiopathic Normal Pressure Hydrocephalus

Asian J Neurosurg. 2020 Feb 25;15(1):107-112. doi: 10.4103/ajns.AJNS_354_19. eCollection 2020 Jan-Mar.

Authors

Kiyoshi Takagi^{1

2}, Ryota Watahiki³, Toru Machida⁴, Kenji Onouchi⁵, Kazuyoshi Kato⁶, Marie Oshima²

Affiliations

¹ Normal Pressure Hydrocephalus Center, Kashiwatanaka Hospital, Kashiwa (Current institute: Normal Pressure Hydrocephalus Center, Nagareyama Central Hospital, Nagareyama), Tsukuba, Japan.
² Department of Mechanical and Biofunctional Systems, Institute of Industrial Science, The University of Tokyo, Tsukuba, Japan.
³ Department of Rehabilitation, Tsukuba Medical Center Hospital, Tsukuba, Japan.
⁴ Center for Diagnostic Radiology, International University of Health and Welfare Mita Hospital, Tokyo, Japan.
⁵ Department of Neurology, Tsukuba Hospital, Tsukuba, Japan.
⁶ Department of Surgery, Abiko Seijinkai Hospital, Abiko, Japan.

Abstract

Background: The image diagnosis of idiopathic normal-pressure hydrocephalus (iNPH) is based on the ventriculomegaly, whose criterion is an Evans' Index (EI) >0.3. Recently, disproportionately enlarged subarachnoid space hydrocephalus (DESH) has been proposed as a morphological characteristic to iNPH. Several studies cast doubt on the reliability of these criteria in the diagnosis of iNPH. Furthermore, interobserver differences of these criteria have not yet been investigated. The objective of this study was to assess the diagnostic reliability and interobserver variability of EI and DESH.

Materials and methods: The preoperative magnetic resonance (MR) images of 84 definite iNPH patients were retrospectively evaluated by a neuroradiologist (NR) and physical therapist (PT). They independently assessed the EI and DESH. The MR images were evaluated preoperatively by a neurosurgeon (NS). The results were showed in mean (standard deviation).

Results: The mean age was 78.4 (6.3) years (male:female = 49:35). The mean EI was 0.33 (0.04), 0.32 (0.04), and 0.31 (0.03) for NS, NR, and PT, respectively (P < 0.0001). The rate of accurate diagnosis of iNPH with EI >0.3 was 74%, 66%, and 61% for NS, NR, and PT, respectively, and there was a moderate level of agreement. By contrast, there was a substantial lower level of accuracy in assessment with DESH for all three evaluators as 50%, 44%, and 27% for NS, NR, and PT, respectively, again with a moderate level of agreement. However, the rates of patients fulfilling both EI >0.3 and DESH were remarkably lower than either of the two parameters individually at a mere 37%, 30%, and 16% for NS, NR, and PT, respectively, with a low level of agreement between the rates.

Conclusion: This study suggests that DESH cannot be a diagnostic criterion for iNPH. If EI >0.3 and DESH were both necessary to diagnose iNPH, then more than 70% of patients would have been misdiagnosed and would have been deprived of the chance of treatment and its benefits. These results request a paradigm shift in the concepts of iNPH.

Keywords: Disproportionately enlarged subarachnoid space hydrocephalus; Evans' Index; idiopathic normal pressure hydrocephalus; interobserver variability; ventriculoatrial shunt.