Idiopathic normal pressure hydrocephalus (INPH) was first reported by Hakim and Adam in 1965 (1). It is a sympathetic treatable and reversible dementia by ventriculo-peritoneal (V-P) shunt (2, 3). The current diagnosis of INPH is primarily based on clinical symptoms and brain fluid-attenuated inversion recovery (FLAIR)-magnetic resonance (MR) imaging. To distinguish INPH from other neurodegenerative diseases and vascular dementia (VD), in adults over 60, had been a considerable challenge. That is why many INPH patients have a poor response to V-P shunt surgery. Leukoaraiosis (LA) and cerebral amyloid angiopathy (CAA) are fairly specific to older people and often co-exist with INPH. Since they share the same clinical symptoms and MR imaging, accurate diagnosis of INPH has become essential to prediction of patient reaction and monitoring patient responsiveness to V-P shunt operations.

The development of functional magnetic resonance imaging (fMRI) makes it possible for us to concretely identify VDs. As SWI has become practical, cerebral microbleeds (CMBs), defined as hemorrhagic microvascular lesions or microangiopathy in the brain, are commonly observed in patients with LA and CAA, respectively (4–6). Here, we demonstrated three typical cases who received a standard scanning including T1-weighted MR, T2-weighted MR, and FLAIR-MR imaging to show the similarities and difference of the MRI and VD symptoms among INPH, LA, and CAA, to provide the best clinical reference for neurosurgical decisions.

All three cases met the diagnostic standard of promising INPH according to either the guidelines of international version or the Japanese second edition: (1) Individuals were older than 60 years; (2) Each had more than one of the clinical triad: gait disturbance, urinary incontinence, or cognitive impairment; (3) Brain imaging showed ventricular dilation (Evan index >0.3) and periventricular and deep white matter changes; (4) CSF pressure was <200 mmH₂O, and the CSF content were normal; and (5) Secondary hydrocephalus had been excluded (3, 7, 8).

Scanning by T1-weighted MR, T2-weighted MR and FLAIR-MR imaging showed exactly the same clinical brain images among INPH, LA, and CAA patients (Figure 1) (Supplementary Figure 1). If we applied SWI, those three persons then varied from one another mostly in the presence and distribution of CMBs (Figure 2). Case I showed multiple vascular risk factors, but with no CMBs in the brain, as indicated by MR-SWI scanning, and he was considered suitable for V-P shunt treatment. Case II showed multiple CMBs predominantly located in deep brain structures, and these were considered to be associated with hypertensive arteriopathy (9–11). Case III also showed multiple CMBs, but they were apparently distributed in the cerebral lobars and cortical subarachnoid hemorrhage, which was supposed to be the feature of CAA (12). Although case 3 presented with cerebral atrophy in MRI, indicating that INPH occurred primarily in the elderly, it was not an exclusion criterion for definition of INPH, based upon the guidelines of Japanese second edition (3). Therefore, among these cases, only Case I underwent V-P shunt surgery. Indeed, the symptoms of that patient with typical INPH were considerably improved after the surgery. Given the information about potential outcomes of Case II and III after V-P shunt, for whom surgical intervention was not recommended, we recommend MR-SWI as a prerequisite for V-P shunt operation to thoroughly distinguish INPH from VDs and to efficiently ensure the surgical effectiveness and safety of V-P shunt operation.

Our study perspective could be supported by one previous study showing that INPH patients with cerebrovascular disease (CVD), such as LA or stroke, had poorer short- and long-term treatment outcome than those patients without CVD (13). Moreover, both studies also showed normal pressure hydrocephalus (NPH) with LA could not obtain a favorable outcome after V-P shunt surgery and they considered LA as a negative factor in decisions regarding V-P shunt treatment (14, 15), although several studies found that patients with severe LA could also benefit from the shunt surgery (16, 17). In addition, Alzheimer's disease (AD) has been shown to frequently coexist with INPH, and patients presenting with AD are less likely to obtain a fully favorable long-term outcome of shunt surgery than in those persons without AD (18). Currently, experts do not recommend against shunting in INPH patients with AD because of pathological features of AD in INPH patients, which predict a worse cognitive outcome of shunt surgery (18). Recently, Elias Johansson et al found that among 14 INPH patients, two INPH patients with extensive CMB showed serious adverse events and died within 30 days after V-P shunt (19). These evidences indicate that poor outcomes could be associated with those potential comorbidities in INPH patients (20), and it is necessary to exclude them to improve the success rate of surgery for INPH through advanced MR imaging. In order to decrease misdiagnosed events and avoid the poor outcome from shunt surgery, we therefore recommend SWI as a regular MR procedure to distinguish independent INPH without CMB from LA and CAA before V-P shunt treatment.

INPH, LA, and CAA might co-exist together and also share the same clinical symptoms in elders. MR-SWI was showed to precisely distinguish independent INPH from vascular dementia including LA and CAA. Therefore, we fully recommend that SWI should be incorporated into the international identification criteria, Japanese 3rd version of INPH identification, and strongly suggested it as a routine pre-operative examination to identify independent INPH before V-P shunt treatment.

This study was approved by Xiamen ethical committee. Written informed consent was obtained from the patients for the publication of this case report. They have consented to the submission of the case report for publication in the journal.

W-QH and H-NL contributed to collection of the study data, drafting of the manuscript, and critical revision of the article. QL and C-MT contributed to the study concept and design, image analysis, and interpretation of the data.