Diagnostic performance and interobserver agreement of the callosal angle and Evans' index in idiopathic normal pressure hydrocephalus: a systematic review and meta-analysis

Automated Detection of Normal Pressure Hydrocephalus Using CT Imaging for Calculating the Ventricle-to-Subarachnoid Volume Ratio

BACKGROUND AND PURPOSE

Normal pressure hydrocephalus (NPH) is a diagnostic challenge because its clinical symptoms and imaging appearance resemble normal aging and other forms of dementia. Identifying NPH is essential so that patients can receive timely treatment to improve gait distortion and quality of life. An automated marker of NPH was developed and evaluated on clinical CT images, and its utility was assessed in a large patient cohort.

MATERIALS AND METHODS

A retrospective review was conducted of CT images from 306 tap test-responsive patients with NPH between January 2015 and January 2022. Control CT images were obtained from patients in the emergency department who were evaluated for headache and had unremarkable CT findings between June 2021 and August 2022. The ventricle-to-subarachnoid volume ratio (VSR) was automatically calculated by the imaging software and used as a predictor of NPH in linear regression modeling with adjustment for age and sex. The correlations of VSR with age, sex, and the receiver operating characteristic were computed.

RESULTS

VSR was significantly greater in patients with NPH than controls (P < .001). Importantly, VSR was not significantly correlated with age (P = .56, R2 = 0.001). VSR identifies NPH with a sensitivity and specificity of 94.1% and 92.5%, respectively, with an area under the receiver operating characteristic curve of 0.99 (95% CI 0.975-0.995).

CONCLUSIONS

Automated assessment of the VSR on head CT images identified probable NPH with 93% accuracy. The assessment of a large cohort of patients with NPH supports the generalizability of clinical screening of CT images. Moreover, the results support the utility of ventricle-to-sulcal concordance often used by radiologists but not currently a part of the accepted guidelines for imaging markers of NPH.

Automated Idiopathic Normal Pressure Hydrocephalus Diagnosis via Artificial Intelligence-Based 3D T1 MRI Volumetric Analysis

BACKGROUND AND PURPOSE

Idiopathic normal pressure hydrocephalus (iNPH) is reversible dementia that is underdiagnosed. The purpose of this study was to develop an automated diagnostic method for iNPH using artificial intelligence techniques with a T1-weighted MRI scan.

MATERIALS AND METHODS

We quantified iNPH, Parkinson disease, Alzheimer disease, and healthy controls on T1-weighted 3D brain MRI scans using 452 scans for training and 110 scans for testing. Automatic component measurement algorithms were developed for the Evans index, Sylvian fissure enlargement, high-convexity tightness, callosal angle, and normalized lateral ventricle volume. XGBoost models were trained for both automated measurements and manual labels for iNPH prediction.

RESULTS

A total of 452 patients (200 men; mean age, 73.2 [SD, 6.5] years) were included in the training set. Of the 452 patients, 111 (24.6%) had iNPH. We obtained area under the curve (AUC) values of 0.956 for automatically measured high-convexity tightness and 0.830 for Sylvian fissure enlargement. Intraclass correlation values of 0.824 for the callosal angle and 0.924 for the Evans index were measured. By means of the decision tree of the XGBoost model, the model trained on manual labels obtained an average cross-validation AUC of 0.988 on the training set and 0.938 on the unseen test set, while the fully automated model obtained a cross-validation AUC of 0.983 and an unseen test AUC of 0.936.

CONCLUSIONS

We demonstrated a machine learning algorithm capable of diagnosing iNPH from a 3D T1-weighted MRI that is robust to the failure. We propose a method to scan large numbers of 3D T1-weighted MRIs with minimal human intervention, making possible large-scale iNPH screening.

The benefits of ventriculoperitoneal shunting in normal pressure hydrocephalus patients-a follow-up of three years

OBJECTIVE

The ventriculoperitoneal shunt (VPS) is an established approach in treating normal pressure hydrocephalus (NPH). This study aims to examine the long-term effects of VPS regarding clinical and radiological outcomes, to explore interdependencies with comorbidities and medication, and to determine a suitable opening pressure of the programmable valve.

METHODS

127 patients with VPS were retrospectively evaluated. The Hakim triad along with Evans index (EI) and callosal angle (CA) were examined preoperatively and postoperatively at various time points up to over thirty-six months. Preexisting comorbidities and medication were considered. Adjustments to valve settings were documented along with symptom development and complications. Wilcoxon and paired-sample t-tests were used to analyze postoperative change. Chi-square, Eta-squared, and Pearson coefficients were used in correlation analyses.

RESULTS

Relief from individual symptoms was most prominent within the first 6 months (p < 0.01). EI and CA significantly decreased and increased, respectively (p < 0.05). Postoperative clinical and radiological improvement was largely maintained over the follow-up period. Diabetes mellitus and apoplexy correlated with surgical outcomes (p < 0.05). The median opening pressure as a function of overall symptom management was determined to be 120 mmH2O for women and 140 mmH2O for men.

CONCLUSION

VPS is effective in treating NPH with respect to both clinical and radiological outcomes, although these two components are independent of each other. Improvement is most pronounced in short-term and maintained in the long-term. Comorbidities have significant influence on the course of NPH. The valve setting does not forecast change in radiological findings; consequently, priority should be placed on the patient's clinical condition.

Brain and Ventricle Volume Alterations in Idiopathic Normal Pressure Hydrocephalus Determined by Artificial Intelligence-Based MRI Volumetry

The aim of this study was to employ artificial intelligence (AI)-based magnetic resonance imaging (MRI) brain volumetry to potentially distinguish between idiopathic normal pressure hydrocephalus (iNPH), Alzheimer's disease (AD), and age- and sex-matched healthy controls (CG) by evaluating cortical, subcortical, and ventricular volumes. Additionally, correlations between the measured brain and ventricle volumes and two established semi-quantitative radiologic markers for iNPH were examined. An IRB-approved retrospective analysis was conducted on 123 age- and sex-matched subjects (41 iNPH, 41 AD, and 41 controls), with all of the iNPH patients undergoing routine clinical brain MRI prior to ventriculoperitoneal shunt implantation. Automated AI-based determination of different cortical and subcortical brain and ventricular volumes in mL, as well as calculation of population-based normalized percentiles according to an embedded database, was performed; the CE-certified software mdbrain v4.4.1 or above was used with a standardized T1-weighted 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence. Measured brain volumes and percentiles were analyzed for between-group differences and correlated with semi-quantitative measurements of the Evans' index and corpus callosal angle: iNPH patients exhibited ventricular enlargement and changes in gray and white matter compared to AD patients and controls, with the most significant differences observed in total ventricular volume (+67%) and the lateral (+68%), third (+38%), and fourth (+31%) ventricles compared to controls. Global ventriculomegaly and marked white matter reduction with concomitant preservation of gray matter compared to AD and CG were characteristic of iNPH, whereas global and frontoparietally accentuated gray matter reductions were characteristic of AD. Evans' index and corpus callosal angle differed significantly between the three groups and moderately correlated with the lateral ventricular volumes in iNPH patients [Evans' index (r > 0.83, p ≤ 0.001), corpus callosal angle (r < -0.74, p ≤ 0.001)]. AI-based MRI volumetry in iNPH patients revealed global ventricular enlargement and focal brain atrophy, which, in contrast to healthy controls and AD patients, primarily involved the supratentorial white matter and was marked temporomesially and in the midbrain, while largely preserving gray matter. Integrating AI volumetry in conjunction with traditional radiologic measures could enhance iNPH identification and differentiation, potentially improving patient management and therapy response assessment.

Efficacy and safety of shunt surgery in patients with idiopathic normal-pressure hydrocephalus: can we predict shunt response by preoperative magnetic resonance imaging (MRI)?

AIM

The aim of this study was to identify preoperative magnetic resonance imaging (MRI) findings that can predict the shunt responsiveness in idiopathic normal-pressure hydrocephalus (iNPH) patients and to investigate postoperative outcome and complications.

MATERIALS AND METHODS

A total of 192 patients with iNPH who underwent shunt at our hospital between 2000 and 2021 were included to investigate complications. Of these, after exclusion, 127 (1-month postoperative follow-up) and 77 (1-year postoperative follow-up) patients were evaluated. The preoperative MRI features (the presence of tightness of the high-convexity subarachnoid space, Sylvian fissure enlargement, Evans' index, and callosal angle) of the shunt-response and nonresponse groups were compared, and a systematic review was conducted to evaluate whether preoperative MRI findings could predict shunt response.

RESULTS

Postoperative complications within one month after surgery were observed in 6.8% (13/192), and the most common complication was hemorrhage. Changes in corpus callosum were observed in 4.2% (8/192). The shunt-response rates were 83.5% (106/127) in the 1-month follow-up group and 70.1% (54/77) in 1-year follow-up group. In the logistic regression analysis, only Evans' index measuring >0.4 had a significant negative relationship with shunt response at 1-month follow-up; however, no significant relationship was observed at 1-year follow-up. According to our systematic review, it is still controversial whether preoperative MRI findings could predict shunt response.

CONCLUSION

Evans' index measure of >0.4 had a significant relationship with the shunt response in the 1-month follow-up group. In systematic reviews, there is ongoing debate about whether preoperative MRI findings can accurately predict responses to shunt surgery. Postoperative corpus callosal change was observed in 4.2% of iNPH patients.

A Male Patient with Hydrocephalus via Multimodality Diagnostic Approaches: A Case Report

Introduction: Idiopathic normal pressure hydrocephalus (iNPH) is a kind of hydrocephalus that is easily to be misdiagnosed with brain atrophy due to the similarity of ventricular dilation and cognitive impairment. In this case, we present an old male patient who was diagnosed with iNPH by multimodality approaches. Outcomes: A 68-year-old male patient, with deteriorated gait, declined cognitive function for at least 3 years and urinary incontinence for 3 months. The doctors suspected him a patient with hydrocephalus or Alzheimer's disease based on his symptoms. We used multimodality diagnostic approaches including brain imaging, cerebrospinal fluid tap test, continuous intracranial pressure monitoring, and infusion study to make the final diagnosis of iNPH. He underwent ventriculoperitoneal shunt surgery and was well recovered. Conclusion: This case demonstrates the efficacy of using multimodality approaches for iNPH diagnosis, which saves patient time and clinical cost, worthy of further promotion.

Improve the diagnosis of idiopathic normal pressure hydrocephalus by combining abnormal cortical thickness and ventricular morphometry

Background

The primary imaging markers for idiopathic Normal Pressure Hydrocephalus (iNPH) emphasize morphological measurements within the ventricular system, with no attention given to alterations in brain parenchyma. This study aimed to investigate the potential effectiveness of combining ventricular morphometry and cortical structural measurements as diagnostic biomarkers for iNPH.

Methods

A total of 57 iNPH patients and 55 age-matched healthy controls (HC) were recruited in this study. Firstly, manual measurements of ventricular morphology, including Evans Index (EI), z-Evans Index (z-EI), Cella Media Width (CMW), Callosal Angle (CA), and Callosal Height (CH), were conducted based on MRI scans. Cortical thickness measurements were obtained, and statistical analyses were performed using surface-based morphometric analysis. Secondly, three distinct models were developed using machine learning algorithms, each based on a different input feature: a ventricular morphology model (LVM), a cortical thickness model (CT), and a fusion model (All) incorporating both features. Model performances were assessed using 10-fold cross validation and tested on an independent dataset. Model interpretation utilized Shapley Additive Interpretation (SHAP), providing a visualization of the contribution of each variable in the predictive model. Finally, Spearman correlation coefficients were calculated to evaluate the relationship between imaging biomarkers and clinical symptoms.

Results

iNPH patients exhibited notable differences in cortical thickness compared to HC. This included reduced thickness in the frontal, temporal, and cingulate cortices, along with increased thickness in the supracentral gyrus. The diagnostic performance of the fusion model (All) for iNPH surpassed that of the single-feature models, achieving an average accuracy of 90.43%, sensitivity of 90.00%, specificity of 90.91%, and Matthews correlation coefficient (MCC) of 81.03%. This improvement in accuracy (6.09%), sensitivity (11.67%), and MCC (11.25%) compared to the LVM strategy was significant. Shap analysis revealed the crucial role of cortical thickness in the right isthmus cingulate cortex, emerging as the most influential factor in distinguishing iNPH from HC. Additionally, significant correlations were observed between the typical triad symptoms of iNPH patients and cortical structural alterations.

Conclusion

This study emphasizes the significant role of cortical structure changes in the diagnosis of iNPH, providing a novel insights for assisting clinicians in improving the identification and detection of iNPH.

Idiopathic Normal Pressure Hydrocephalus: The Real Social and Economic Burden of a Possibly Enormous Underdiagnosis Problem

Normal Pressure Hydrocephalus (iNPH) typically affects the elderly and can cause cognitive decline, resulting in its differential diagnosis with other neurodegenerative conditions. Moreover, it is probably underdiagnosed; such under- and misdiagnosis prevents the patient from receiving the right treatment and significantly affects the quality of life and life expectancy. This investigation is an in-depth analysis of the actual incidence of iNPH in the population of the province served by our hospital (circa 580,000 individuals). The first phase of this study was conducted by visualizing a total of 1232 brain CT scans performed in the Emergency Departments of the four hospitals of our network on patients who were admitted for different complaints yet screened as suspicious for iNPH. Subsequently, corresponding Emergency Department medical records were investigated to understand the medical history of each patient in search of elements attributable to an alteration of CSF dynamics. The cohort of positive CT scans, according to the radiological and clinical inclusion criteria, included 192 patients. Among the reasons to require acute medical care, "Fall" was the most common. The cumulative incidence of CT scans suggestive of iNPH among the patients undergoing CT scans was as high as 15.58%, and the period prevalence calculated for the total amount of patients accessing the Emergency Departments was 1.084%. The real incidence of iNPH in the population may be underestimated, and the social burden linked to the assistance of patients suffering from such untreated conditions could be significantly relieved.

Brain linear measurements for differentiating normal pressure hydrocephalus from Alzheimer's disease: an exploratory study

BACKGROUND AND PURPOSE

Easy and reliable tools for the differential diagnosis between idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) are needed.

MATERIALS AND METHODS

In this cross-sectional study iNPH and AD patients referred to the Neurology Unit of the University of Catania from 1 January 2020 to 1 December 2022 were enrolled. The following brain linear measurements (BLMs) were calculated: Evan's index (EI), the parieto-occipital ratio (POR) and the temporal ratio (TR). For each index, sensitivity, specificity and the area under the curve (AUC) were calculated. Moreover, a cumulative index, the BLM index, was also considered.

RESULTS

Fifty patients (25 iNPH and 25 AD) were enrolled. In differentiating iNPH from AD, EI had the highest AUC (0.956), POR had the highest specificity (100%) whilst TR had the highest sensitivity (92%). The BLM index differentiated iNPH and AD with a sensitivity of 96%, a specificity of 92% and an AUC of 0.963 with an optimal cut-off value of 0.303.

CONCLUSION

Evan's index, POR and TR may be useful in the differential diagnosis between iNPH and AD. At an individual level, the BLM index represents a valid and reliable tool to achieve an accurate differentiation between these two conditions.

Risk estimation for idiopathic normal-pressure hydrocephalus: development and validation of a brain morphometry-based nomogram

OBJECTIVES

To develop and validate a nomogram based on MRI features for predicting iNPH.

METHODS

Patients aged  ≥ 60 years (clinically diagnosed with iNPH, Parkinson's disease, or Alzheimer's disease or healthy controls) who underwent MRI including three-dimensional T1-weighted volumetric MRI were retrospectively identified from two tertiary referral hospitals (one hospital for derivation set and the other for validation set). Clinical and imaging features for iNPH were assessed. Deep learning-based brain segmentation software was used for 3D volumetry. A prediction model was developed using logistic regression and transformed into a nomogram. The performance of the nomogram was assessed with respect to discrimination and calibration abilities. The nomogram was internally and externally validated.

RESULTS

A total of 452 patients (mean age ± SD, 73.2 ± 6.5 years; 200 men) were evaluated as the derivation set. One hundred eleven and 341 patients were categorized into the iNPH and non-iNPH groups, respectively. In multivariable analysis, high-convexity tightness (odds ratio [OR], 35.1; 95% CI: 4.5, 275.5), callosal angle  < 90° (OR, 12.5; 95% CI: 3.1, 50.0), and normalized lateral ventricle volume (OR, 4.2; 95% CI: 2.7, 6.7) were associated with iNPH. The nomogram combining these three variables showed an area under the curve of 0.995 (95% CI: 0.991, 0.999) in the study sample, 0.994 (95% CI: 0.990, 0.998) in the internal validation sample, and 0.969 (95% CI: 0.940, 0.997) in the external validation sample.

CONCLUSION

A brain morphometry-based nomogram including high-convexity tightness, callosal angle  < 90°, and normalized lateral ventricle volume can help accurately estimate the probability of iNPH.

KEY POINTS

• The nomogram with MRI findings (high-convexity tightness, callosal angle, and normalized lateral ventricle volume) helped in predicting the probability of idiopathic normal-pressure hydrocephalus. • The nomogram may facilitate the prediction of idiopathic normal-pressure hydrocephalus and consequently avoid unnecessary invasive procedures such as the cerebrospinal fluid tap test, drainage test, and cerebrospinal fluid shunt surgery.

Higher prevalence of idiopathic normal pressure hydrocephalus-like MRI features in progressive supranuclear palsy: An imaging reminder of atypical parkinsonism

OBJECTIVES

The classic triad of idiopathic normal pressure hydrocephalus (NPH) encompass gait disturbance, cognitive impairment, and urinary incontinence. These symptoms overlap with parkinsonism but with distinct treatment. Lacking applicable differentiation also hampers the prediction to therapeutic response. Here, we try to clarify this issue among different Parkinsonian syndromes and propose some innovative thinking while approaching a patient with parkinsonism and hydrocephalus concomitantly.

METHODS

Twenty-four patients with clinical probable multiple system atrophy (MSA), 34 with probable progressive supranuclear palsy (PSP), and 58 with sex- and age-matched Parkinson's disease (PD) were enrolled. Evans' index (EI), callosal angle (CA), antero-posterior (AP) diameter of the midbrain, length of the midbrain tegmentum diameter (MB^Tegm ), and disproportionately enlarged subarachnoid space hydrocephalus (DESH) were evaluated using the conventional MRI. Logistic regression was applied to identify the independent variables in hydrocephalus.

RESULTS

Patients with PSP had higher mean EI than those with MSA and PD. Around 38.2% of patients with PSP had accompanied hydrocephalus (EI > 0.3). Parkinsonism subtypes (PD, MSA, or PSP), AP diameter of the midbrain, and MB^Tegm were significantly different among patients with and without hydrocephalus. After regression analysis, parkinsonism subtype stood out to be the most key risk factor of hydrocephalus. The comparison between patients with PSP with and without hydrocephalus did not disclose specific clinical characteristics or risk factors.

CONCLUSIONS

This study demonstrates that the presence of NPH-like MRI features is much higher in PSP patients, and this tendency is decided upon the determination of parkinsonism subtype. Sharing pathophysiological characteristics in these two diseases is implied. More diagnostic tools are needed to better differentiate the two diseases and decide the treatment. To closely observe hydrocephalic parkinsonism patients and well inform the possible limited shunting benefits if PSP core features appear, will be more pivotal and practical at present clinical practice.

SV, Borchert R, Russo S, Eide PK. Radiological predictors of shunt response in the diagnosis and treatment of idiopathic normal pressure hydrocephalus: a systematic review and meta-analysis

BACKGROUND

Patients with the dementia subtype idiopathic normal pressure hydrocephalus (iNPH) may improve clinically following cerebrospinal fluid (CSF) diversion (shunt) surgery, though the predictors of shunt response remain debated. Currently, radiological features play an important role in the diagnosis of iNPH, but it is not well established which radiological markers most precisely predict shunt responsive iNPH.

OBJECTIVE

To conduct a systematic review and meta-analysis to identify radiological predictors of shunt responsiveness, evaluate their diagnostic effectiveness, and recommend the most predictive radiological features.

METHODS

Embase, MEDLINE, Scopus, PubMed, Google Scholar, and JSTOR were searched for original studies investigating radiological predictors of shunt response in iNPH patients. Included studies were assessed using the ROBINS-1 tool, and eligible studies were evaluated using a univariate meta-analysis.

RESULTS

Overall, 301 full-text papers were screened, of which 28 studies were included, and 26 different radiological features were identified, 5 of these met the inclusion criteria for the meta-analysis: disproportionately enlarged subarachnoid space (DESH), callosal angle, periventricular white matter changes, cerebral blood flow (CBF), and computerized tomography cisternography. The meta-analysis showed that only callosal angle and periventricular white matter changes significantly differentiated iNPH shunt responders from non-responders, though both markers had a low diagnostic odds ratio (DOR) of 1.88 and 1.01 respectively. None of the other radiological markers differentiated shunt responsive from shunt non-responsive iNPH.

CONCLUSION

Callosal angle and periventricular changes are the only diagnostically effective radiological predictors of shunt responsive iNPH patients. However, due to the DORs approximating 1, they are insufficient as sole predictors and are advised to be used only in combination with other diagnostic tests of shunt response. Future research must evaluate the combined use of multiple radiological predictors, as it may yield beneficial additive effects that may allow for more robust radiological shunt response prediction.

Radiological biomarkers of idiopathic normal pressure hydrocephalus: new approaches for detecting concomitant Alzheimer's disease and predicting prognosis

Idiopathic normal pressure hydrocephalus (iNPH) is a clinical syndrome characterized by cognitive decline, gait disturbance, and urinary incontinence. As iNPH often occurs in elderly individuals prone to many types of comorbidity, a differential diagnosis with other neurodegenerative diseases is crucial, especially Alzheimer's disease (AD). A growing body of published work provides evidence of radiological methods, including multimodal magnetic resonance imaging and positron emission tomography, which may help noninvasively differentiate iNPH from AD or reveal concurrent AD pathology in vivo. Imaging methods detecting morphological changes, white matter microstructural changes, cerebrospinal fluid circulation, and molecular imaging have been widely applied in iNPH patients. Here, we review radiological biomarkers using different methods in evaluating iNPH pathophysiology and differentiating or detecting concomitant AD, to noninvasively predict the possible outcome postshunt and select candidates for shunt surgery.

Pleural effusion and respiratory compromise from spontaneous migration of a ventriculoperitoneal shunt catheter in a patient with normal-pressure hydrocephalus

Background:

Ventriculoperitoneal shunt (VPS) insertion is one of the most common neurosurgical procedures done around the world to treat hydrocephalus. The occurrence of spontaneous migration of the peritoneal shunt catheter into the thoracic cavity is a very rare complication; we report here case number 27 of respiratory complications of a VPS in a patient with normal-pressure hydrocephalus (NPH).

Case Description:

A 76-year-old woman with Alzheimer’s disease and anosognosia was diagnosed idiopathic NPH treated surgically with a VPS. Pleural effusion and pulmonary complications occurred 4 weeks after the insertion of the shunt due to the spontaneous migration of the peritoneal catheter of the VPS into the thoracic cavity. The hydrothorax of cerebrospinal fluid was drained and the distal catheter was removed and replaced. The patient made an uneventful recovery.

Conclusion:

Due to the rarity of this complication, there are no standard corrective procedures. Some of the methods used to diagnose and successfully treat this rare complication of the VPS are presented.

[Brain MRI-Based Artificial Intelligence Software in Patients with Neurodegenerative Diseases: Current Status]

The incidence of neurodegenerative diseases in the older population has increased in recent years. A considerable number of studies have been performed to characterize these diseases. Imaging analysis is an important biomarker for the diagnosis of neurodegenerative disease. Objective and reliable assessment and precise detection are important for the early diagnosis of neurodegenerative diseases. Artificial intelligence (AI) using brain MRI applied to the study of neurodegenerative diseases could promote early diagnosis and optimal decisions for treatment plans. MRI-based AI software have been developed and studied worldwide. Representatively, there are MRI-based volumetry and segmentation software. In this review, we present the development process of brain volumetry analysis software in neurodegenerative diseases, currently used and developed AI software for neurodegenerative disease in the Republic of Korea, probable uses of AI in the future, and AI software limitations.

Application of Evans Index in Normal Pressure Hydrocephalus Patients: A Mini Review

With an ever-growing aging population, the prevalence of normal pressure hydrocephalus (NPH) is increasing. Clinical symptoms of NPH include cognitive impairment, gait disturbance, and urinary incontinence. Surgery can improve symptoms, which leads to the disease's alternative name: treatable dementia. The Evans index (EI), defined as the ratio of the maximal width of the frontal horns to the maximum inner skull diameter, is the most commonly used index to indirectly assess the condition of the ventricles in NPH patients. EI measurement is simple, fast, and does not require any special software; in clinical practice, an EI >0.3 is the criterion for ventricular enlargement. However, EI's measurement methods, threshold setting, correlation with ventricle volume, and even its clinical value has been questioned. Based on the EI, the z-EI and anteroposterior diameter of the lateral ventricle index were derived and are discussed in this review.