Hippocampal volumetry with magnetic resonance imaging: a cost-effective validated solution

Normative hippocampal volumetric measurements using magnetic resonance imaging

Background/aim

A wide variety of neurological and psychiatric disorders have been shown to be closely related to changes in hippocampal volume (HV). It appears that hippocampal volumetry will be an indispensable part of clinical practice for a number of neuropsychiatric disorders in the near future. The aim of this study was to establish a normative data set for HV according to age and sex in the general population.

Materials and methods

Hippocampal magnetic resonance imaging scans of 302 healthy volunteers were obtained using a 1.5 T unit with a 20-channel head coil. The hippocampal volumetric assessment was conducted using the volBrain fully automated segmentation algorithm on coronal oblique T1-weighted magnetization prepared rapid gradient-echo (MP-RAGE) images obtained perpendicular to the long axis of the hippocampus. The mean values of HV of groups according to age and sex were calculated. The associations between HV and age and sex were analyzed.

Results

The mean HV of the study group was found to be 3.81 ± 0.46 cm3. We found that the mean HV of males (3.94 ± 0.49 cm3) was significantly higher than that of females (3.74 ± 0.42 cm3), and the mean right HV (3.86 ± 0.48 cm3) was significantly higher than that of the left HV (3.78 ± 0.49 cm3) (P = 0.001). Among both females and males, there were statistically significant but poor negative correlations between age and volumetric measurements of both the right and the left hippocampi (P < 0.05).

Conclusion

The normative hippocampal volumetric data obtained in this study may be beneficial in clinical applications for many neuropsychiatric diseases, especially for mesial temporal sclerosis and cognitive disorders.

Hippocampal volumetry: Normative data in the Indian population

BACKGROUND

Mesial temporal sclerosis (MTS) is the most common cause of temporal lobe epilepsy. Quantitative analysis of the hippocampus using volumetry is commonly being used in the diagnosis of MTS and is being used as a marker in prognostication of seizure control. Although normative data for hippocampal volume (HV) is available for the western population, no such data is available for the Indian population.

AIM

The aim of the study was to establish normative data for HV for the Indian population, which can aid in the accurate diagnosis of MTS.

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) scans of 200 healthy volunteers were acquired using a 3 Tesla (3T) MRI scanner. Manual segmentation and volumetry was done using Siemens Syngo software. The data was analyzed using two tailed t-test to detect associations between HV and age, gender, and education. The data so obtained was also correlated with the data available from the rest of the world.

RESULTS

A mean HV of 2.411 cm(3) (standard deviation -0.299) was found in the study, which was significantly smaller when compared to the data from the western population. The right hippocampus was larger than the left, with a mean volume of 2.424 cm(3) and 2.398 cm(3), respectively. HV was detected to be significantly higher in males. No association was found between HV and age and education.

CONCLUSION

The values obtained in this study may be adopted as a standard in the evaluation of patients with intractable epilepsy.

Comparison of two different measurement techniques of hippocampal resection length in temporal lobe epilepsy: results of a prospective study

BACKGROUND

Magnetic resonance imaging (MRI) volumetry has evolved to a highly sensitive method for presurgical detection of hippocampal sclerosis in temporal lobe epilepsy (TLE). Seizure resolution and neuropsychological sequelae are believed to correlate with extent of resection. Therefore an easy volumetric method to determine extent of resection is desirable. The purpose of this work is to evaluate and compare two different measurement techniques for hippocampal resection length.

METHODS

Sixty-one patients with a mean seizure history of 25.1 years and medically intractable TLE were included. They underwent MRI with sagittal acquired 3D T1-weighted spoiled gradient recalled echo sequence in 1 mm(3) isotropic voxel. Hippocampal resection length was calculated with two different methods. In the slice counting method (SCM) the number of consecutive 1-mm-thick slices containing resected hippocampus formation was counted. In the vector method (VM) the sum of the oblique and thus longer distances between the centre points of segmented hippocampal areas on each MRI slice were calculated.

RESULTS

Since the hippocampus is a curved body, the resection lengths measured with VM were always larger than measured with SCM. The comparison of resection length expressed in "percent of total length" showed good agreement between the two methods, because unlike the absolute values of resection length, the percentage values are unaffected by the three-dimensional shape of the hippocampus.

CONCLUSION

The easier and quicker method of "slice counting" may be used to determine resection length expressed in "percent of total length", giving reliable values for resection length but causing less volumetric work.

Magnetic resonance volumetric analysis of hippocampi in children in the age group of 6-to-12 years: a pilot study

Atrophy of the mesial temporal structures, especially the hippocampus, has been implicated in temporal lobe epilepsy. However, to date, there is very scant data regarding normal volumes of the hippocampus in the pediatric population. This is a pilot study to estimate the normal volumetric data for the Indian pediatric population between 6 and 12 years of age. We have also tried to understand whether age and gender have an effect on the hippocampal volumes in this age group. The study group comprised 20 children, 6-12-years old without history of epilepsy or other neurological deficits. There were nine boys and 11 girls. All scans were performed on a 1.5T GE echo speed scanner. 3D fast SPGR sequence was prescribed in the coronal plane. The images were post-processed on an Advantage Windows 3.1 workstation. Using an automated program, the same observer calculated the hippocampal area, in cubic centimeters, clockwise and anticlockwise. The clockwise/anticlockwise data were subjected to correlation analysis for detecting intra-observer agreement. The mean and SD for left and right hippocampal volumes were estimated. The lower and upper limits for normal hippocampal volumes were determined using 95% (+/- 2SD) limits on either side of the mean. In order to understand the effect of age on various hippocampal volumes we performed regression analysis. Mann-Whitney's test was used to test the significance of differences for gender variations. Correlation analysis established that there was intra-observer agreement. In the Indian pediatric population we have found the mean right hippocampal volume (RHV) to be 2.75 cm(3) and mean left hippocampal volume (LHV) to be 2.49 cm(3). Mean hippocampal volume was found to be 2.67 cm(3) (SD = 0.42). The upper and lower limits for hippocampal volumes were 3.51 cm(3) and 1.83 cm(3), respectively, based on 95% (+/- 2SD) limits on either side of the mean. There was no effect of age or gender on the hippocampal volumes. In the Indian pediatric population we determined hippocampal volumes in a small series of healthy children. We found that hippocampal volumes < or =1.83 cm(3) (< or =2SD) can be considered to be abnormal. These findings can be used as normative data to evaluate cases of hippocampal sclerosis in the Indian population.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

Lateralization of Temporal Lobe Epilepsy and Learning Disabilities, as Defined by Disability‐related Civil Rights Law

PURPOSE

Epilepsy research has identified higher rates of learning disorders in patients with temporal lobe epilepsy (TLE). However, most studies have not adequately assessed complex functional adult learning skills, such as reading comprehension and written language. We designed this study to evaluate our predictions that higher rates of reading comprehension, written language, and calculation disabilities would be associated with left TLE versus right TLE.

METHODS

Reading comprehension, written language, and calculation skills were assessed by using selected subtests from the Woodcock-Johnson Psycho-Educational Tests of Achievement-Revised in a consecutive series of 31 presurgical patients with TLE. Learning disabilities were defined by one essential criterion consistent with the Americans with Disabilities Act of 1990. Patients had left hemisphere language dominance based on Wada results, left or right TLE based on inpatient EEG monitoring, and negative magnetic resonance imaging (MRI), other than MRI correlates of mesial temporal sclerosis.

RESULTS

Higher rates of reading comprehension, written language, and calculation disabilities were associated with left TLE, as compared with right TLE. Nearly 75% of patients with left TLE, whereas fewer than 10% of those with right TLE, had at least one learning disability.

CONCLUSIONS

Seizure onset in the language-dominant hemisphere, as compared with the nondominant hemisphere, was associated with higher rates of specific learning disabilities and a history of poor literacy or career development or both. These results support the potential clinical benefits of using lateralization of seizure onset as a predictor of the risk of learning disabilities that, once evaluated, could be accommodated to increase the participation of patients with epilepsy in work and educational settings.

A reliable method for measurement and normalization of pediatric hippocampal volumes

A robust standardized method for segmentation, quantification, and normalization of pediatric hippocampal volumes using magnetic resonance imaging is presented. The method will find application in time course measurements of hippocampal volumes in pediatric patients who suffer from temporal lobe epilepsy and was tested prospectively on six control patients (13-60 mo of age). The un-normalized hippocampal volumes obtained using our segmentation method ranged from 3.85 to 6.38 mL, in agreement with previously published results. Inter- and intraobserver variability of the segmentation method was determined to be 13.3% and 2.8%, respectively. Four different methods of volume normalization were tested. Normalization is required to adjust for age-related increases in hippocampal volume. The normalization approach that seemed to compensate best for growth-related hippocampal volume changes was based on a simple estimation of intracranial volumes. This is the first report of a consistent and reliable method for segmentation and normalization of hippocampi from pediatric patients that can be used to study the progression of neurologic diseases in children.

Postictal EEG suppression and hippocampal atrophy in temporal lobe epilepsy

Postictal EEG suppression and slowing recorded with scalp electrodes in patients with partial epilepsy is often maximal over the cortical area of ictal onset. The aim of this study was to determine whether a quantitative relationship exists between immediate postictal EEG suppression and hippocampal atrophy. Immediate postictal EEG was analyzed in 31 scalp-recorded seizures obtained from 8 patients who underwent temporal lobectomy with seizure-free outcomes (2 left, 6 right). Quantitative EEG analysis was performed using a temporal power asymmetry index for each frequency band. The hippocampal asymmetry (left-to-right ratio) based on T1- and T2-weighted MR images was determined by hippocampal volumetric analysis. The relationship between the average temporal power asymmetry index and either T1 or T2 hippocampal asymmetry ratio was assessed for each frequency band using Pearson's correlation coefficient. Only correlations of the temporal power asymmetry index with T1 hippocampal asymmetry were significant for the total bands (r = 0.768, P < 0.026) and 8-bands (r = 0.728, P < 0.041). The findings suggest that a quantitative relationship exists between postictal EEG suppression in the 6-frequency band and hippocampal atrophy in temporal lobe epilepsy.

Evidence of a smaller left hippocampus and left temporal horn in both patients with first episode schizophrenia and normal control subjects

Findings from cerebral magnetic resonance imaging (MRI) studies in schizophrenia indicating temporal lobe involvement have been inconsistent and controversial. In a prospective study, we quantified the volumes of temporal lobe structures in 20 male patients with first episode schizophrenia (FES; mean+/-S.D.=27.4+/-4. 8 years) and 20 healthy age-matched male control subjects (27.7+/-3. 1 years). Measurements were performed on contiguous 2.2-mm coronal MRI slices, which included, as well as the temporal lobe, the amygdala, the hippocampal formation, and the temporal horn of the lateral ventricle. The definition of the borders of the structures relied on measurement guidelines derived from mutual comparisons of MRI and histological data. The definition of the hippocampus-amygdala interface was also validated in a correlated triplanar display. We did not detect any significant volume reductions of the measured structures in the FES group, as compared with healthy control subjects, on either side. Comparisons within groups, however, revealed that in both the patients and the healthy volunteers the hippocampal formations showed a significant right-sided bias (+9%, P=0.004, in the FES group; +12%, P=0.0003 in the control subjects). A significant volume difference in favor of the right hemisphere was also observed in the temporal horns of the lateral ventricles (+17%, P=0.02 in the patients with FES; +34%, P=0. 003, in the control group). There was only a nonsignificant trend for a larger temporal horn on the left side in patients with schizophrenia as compared with the control subjects. Our findings do not indicate a loss or reversal of the normal volume asymmetry pattern in the FES group.

Geometric distortion correction in gradient-echo imaging by use of dynamic time warping

Distortion caused by local static field variations in magnetic resonance imaging can be corrected by using a method developed by Chang and Fitzpatrick (CF) that requires two acquisitions identical except for the polarity of the read gradient. This approach has previously been applied to spin-echo imaging. In this report, its role in correcting geometric distortion in gradient-echo imaging is investigated using a dynamic programming algorithm. This approach appears to successfully handle many of the edge artifacts otherwise inherent in the CF method. Once the correction has been made, it is then possible to extract the local magnetic field itself. Magn Reson Med 42:585-590, 1999.

The current state of epilepsy surgery

Epilepsy surgery is an effective therapy for many patients with refractory partial seizures. The results of epilepsy surgery have improved with advances in the evaluation of patients for surgery and the care of patients during and after surgery. This review looks at recent innovations in imaging modalities to identify the candidates for surgery who will benefit most, to identify subtle pathology, to resect the epileptogenic focus more precisely, and to preserve functionally important cortex in order to achieve the best possible outcome. Patient selection and the identification and removal of the epileptogenic focus, in a safe manner, are crucial for good outcome.