Measurement of apparent diffusion coefficient in pediatric mitochondrial encephalopathy patients and the comparison of the follow-up measurements of diffusion coefficient with the parenchymal changes due to the disease course

PURPOSE: Although the sensitivity of magnetic resonance imaging (MRI) in detecting white matter lesions is high, its specificity in the identification of the underlying pathology is limited. Diffusion weighted imaging (DWI) is a functional imaging method that has recently been introduced into clinical use. It visualizes the random microscopic motion of water molecules and thereby provides an image contrast. Methods such as DWI, which are based on measurement, offer more detailed information about the underlying pathologic alterations. The aim of the present study was to demonstrate the contribution of DWI and MRI to the diagnosis of metabolic encephalopathy in pediatric patients and evaluate the patients? apparent diffusion coefficient (ADC) values measured in the 20 predetermined regions by comparing them with those of the individuals in the control group. Additionally, another purpose of the study was to evaluate the superiority of the ADC measurement over conventional imaging sequences or the extent of its contribution to those sequences, using control group comparison.MATERIAL AND METHOD: Ten patients who underwent MRI and DWI examinations with the preliminary diagnosis of neurometabolic disease in the magnetic resonance imaging unit of our department and were diagnosed with mitochondrial encephalopathy after clinical, laboratory and/or genetic examinations between 2004 and 2008 were included in the study. Of the 10 patients included in the study, 6 underwent MRI-DWI examinations 1 to 4 years after their first examinations. Since three of the patients died, their control examinations could not be performed. The brain MR examinations of all patients were performed via 1.5 Tesla MR and standard head coil. All conventional and diffusion MR images were evaluated by two radiologists, one of who was a veteran resident. The evaluation included parenchymal signal intensity changes, localization and number of lesions, the investigation of whether additional lesions could be detected via DWI and the diffusion of lesions. The signal characteristics on DWI were evaluated visually and the ADC values of all patients in the control and patient groups were measured in the predetermined regions using standard ROI. The findings were compared with those of the patients of similar age and gender in the control group. The ADC values obtained from the control and patient groups were compared by the Mann Whitney U test.RESULTS: Since 3 of the 10 patients diagnosed with mitochondrial encephalopathy had died, their control examinations could not be performed. In those three patients, an increase in diffusion and ADC values was determined using DWI. In one of the 3 patients in whom diffusion restriction on DWI scans and a decrease in ADC values were observed at the first examination, an increase in ADC values was determined at the control examination performed four years after the first one. Although a slight increase was observed in the ADC values of the remaining two patients at their control examination performed 1 year after the first one, the values were still low, compared to the control group. Although the ADC values of one patient was within the normal range at the first examination, they were found to be decreased at the second examination performed four years after the first one. In three patients, an increase in diffusion and ADC values was observed between the first examination and the control examination. The number of lesions and the size of the lesions were found to be increased in two and one patients, respectively, at the control examination. Involvement was determined in similar locations in two pairs of siblings.DISCUSSION AND CONCLUSION: In the present study, we concluded that DWI offered additional diagnostic contribution in routine examinations by detecting additional lesions, demarking lesions with clearer boundaries and determining the varying diffusion characteristics in homogeneous hyperintense lesions. As the results of the measurements performed on the ADC map were compared with those of the normal control group, a statistically significant difference was not determined because increases or decreases in ADC values associated with the acute or chronic stages of the disease were already present. Since the disease is rare and a small number of patients were included in the study, homogeneous groups involving a sufficient number of patients could not be performed and consequently, the statistical analysis could not be performed appropriately. Thus, the patients were compared individually with the patients of similar age and gender in the control group.However, DWI and ADC measurement play an important role in the determination of the involvement, diffusion and stage of the disease in regions where signal intensity alterations cannot be detected via conventional sequence imaging. We believe that this result is particularly important for patients with white matter disease. Because it is important to determine whether the white matter, which appears normal on conventional MRI in white matter diseases, is affected or not.Diffusion weighted MRI offers information that complements the findings obtained by conventional MR sequences in mitochondrial encephalopathy and make great contributions to the determination of lesion stage, extent of lesion-induced degeneration and progression of lesions. Given this aspect of the imaging method, it should be evaluated as a sequence that needs to be integrated into routine brain MR examinations.