R.N. Sener

Diffusion MRI: apparent diffusion coefficient (ADC) values in the normal brain and a classification of brain disorders based on ADC values

Diffusion-weighted imaging, dependent on motion of water molecules, provides information regarding tissue integrity. Apparent diffusion coefficient (ADC) values in the normal brain parenchyma, and those in a variety of lesions were studied by echo-planar diffusion MRI in 310 cases. Brain disorders were classified based on their ADC values, taking the ADC values of the normal brain white matter as the principal category. In the normal white matter ADC ranges were 0.60-1.05x10(-3)mm(2)/s, and the mean ADC value was 0.84+/-0.11x10(-3)mm(2)/s. It was possible to distribute brain disorders, as well as artefacts on diffusion MRI to five major categories: category 1, ADC similar to normal white matter; category 2, ADC lower than normal white matter; category 3, ADC higher than normal white matter; category 4, ADC similar to CSF; and category 5, markedly low or high ADC. Further studies can provide addition of different lesions as well as refinements of these categories.

Herpes simplex encephalitis: diffusion MR imaging findings

We studied five patients with herpes simplex encephalitis type 1 with diffusion-weighted MR imaging, as this sequence provides information regarding tissue integrity. Diffusion-weighted imaging was obtained using the echo-planar sequence. True diffusion images (i.e. b=1000s/mm(2) images), and the ADC (apparent diffusion coefficient) values were studied. In addition, diffusion imaging of 12 normal cases, 46 patients with acute ischemia (cytotoxic edema), and 12 patients with vasogenic edema were studied for comparison. In patients with herpes encephalitis, two distinct types of diffusion imaging findings (on b=1000s/mm(2) images, and ADC maps) were noted: lesions similar to cytotoxic edema, and lesions similar to vasogenic edema. The patients with the former type of lesions had fulminating disease, and were in severe clinical condition. Those with the latter represented early cases, and they were in fairly good clinical condition with a good outcome by prompt therapy. Diffusion imaging appears to be a promising sequence to monitor the changes in the brain tissue in herpes encephalitis, and in other infections as well with respect to restriction of movement (cytotoxic edema) or relatively high-motion (vasogenic edema) of water molecules, providing data on the severity of the disease.

Association of persistent falcine sinus with different clinicoradiologic conditions: MR imaging and MR angiography

Nine pediatric patients are reported with persistent falcine sinuses associated with a variety of clinicoradiologic conditions and disorders. Besides MR imaging studies four patients had MR angiography examinations. Persistent falcine sinus was associated with arteriovenous malformations in three patients. In two cases persistent falcine sinus was an incidental finding. In the remaining four patients persistent falcine sinus was associated with total absence of the corpus callosum, acrocephalosyndactyly (Aperts syndrome), osteogenesis imperfecta, Chiari II malformation. The straight sinuses were either absent or rudimentary or entirely normal in these cases. It can be concluded that a mesenchymal disorder can be the primary cause for an open falcine sinus either in isolation or in association with variable changes in the straight sinus.

Diffusion MRI in Rasmussen's encephalitis, herpes simplex encephalitis, and bacterial meningoencephalitis

Three patients with Rasmussens encephalitis, herpes simplex type 1 encephalitis, and bacterial meningoencephalitis are included in this study. Echo-planar diffusion MRI was acquired with the trace protocol at 1.5 T. b= 1000 s/mm(2) images, and apparent diffusion coefficient (ADC) maps were studied with respect to lesion identification. ADC values were also studied, and compared to those of 25 normals. In Rasmussens encephalitis b= 1000 s/mm(2) images were uninformative while ADC maps had superior information. In herpes simplex type 1 encephalitis both b= 1000 s/mm(2) images, and ADC maps had diagnostic information. In meningoencephalitis b= 1000 s/mm(2) images had superior information, especially with respect to early cerebritis while ADC maps were negative. In conclusion, diffusion MRI provided useful imaging data on different types of encephalitis, either on b= 1000 s/mm(2) images or on ADC maps, or on both.

Unusual MRI findings in rhombencephalosynapsis

Rhombencephalosynapsis is mainly characterized by fusion of the cerebellar hemispheres and vermian agenesis. We report severe cerebellar hypoplasia, pachygyria of the cerebrum, an isolated (trapped) fourth ventricle, and facial hemangioma in association with this condition. Our findings suggested that the frequency of rhombencephalosynapsis appears to be higher than previously thought (approximately 0.13%), and it should not be misinterpreted as Chiari II malformation.

Diffusion MRI findings in Wilson's disease.

Six patients having Wilsons disease were studied with diffusion MRI in order to characterize cerebral lesions. Diffusion MRI was obtained using the spin-echo, echo-planar sequence with a gradient strength of 30 mT/m. The trace protocol was used in the axial imaging plane. Heavily diffusion-weighted (b=1000s/mm(2)) images, and the ADC (apparent diffusion coefficient) values from automatically generated ADC maps were studied. The ADC values of the normal brain parenchyma were available in 17 age-matched cases for comparison (ADC values, 0.85+/-0.11 x 10(-3)mm(2)/s). In Wilsons disease two distinct diffusion MRI patterns were observed by quantitative evaluations of the ADC maps; cytotoxic edema-like (ADC values, 0.52+/-0.03 x 10(-3)mm(2)/s), and vasogenic edema-like (ADC values, 1.42+/-0.17 x 10(-3)mm(2)/s) patterns. Diffusion imaging appears to be a promising sequence to evaluate the changes in the brain tissue in Wilsons disease at least by revealing two different patterns.

Astroblastoma: diffusion MRI, and proton MR spectroscopy

A patient with grade II astroblastoma is reported. The tumor revealed an inhomogenous enhancement pattern on T1-weighted images after contrast medium. It contained cyst-like structures with high signal in FLAIR images, consistent with presence of viscous material. In spectroscopy, NAA was decreased, and Cho was increased. Peaks belonging to lipids and a combined broad peak belonging to myoinositol and glycine were noticed. In diffusion MRI, the mean apparent diffusion coefficient (ADC) value of intratumoral cyst-like structures was 2.12 x 10(-3)mm(2)/s less than that of CSF. The matrix of the tumor had lower ADC values ranging from 1.19 to 1.25 x 10(-3)mm(2)/s, higher than that of normal cerebral parenchyma.

Proton MR spectroscopy in Rett syndrome

Seven patients (mean age 7.7yr) with Rett syndrome, a condition with progressive regression of psychomotor development are included in this study. Proton MR spectroscopy images were obtained with the multivoxel chemical-shift imaging mode (TR=1500ms, TE=40ms). Spectra from 224 voxels in the brain parenchyma were studied. N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), and myoinositol (mI) peaks were quantitatively evaluated, and NAA/Cr, NAA/Cho, and Cho/Cr, mI/Cr ratios were calculated. Five age-matched normal cases were available as controls. In three patients with Rett syndrome spectroscopy findings were normal, and the metabolite ratios were similar to control cases. In the remaining four patients with the syndrome prominent decrease of the NAA peak was the main finding resulting in decreases in NAA/Cr (1.14+/-17), and NAA/Cho (1.08+/-27) ratios (p<0.0001). Cho/Cr ratios (0.93+/-26), and mI/Cr ratios (0.88+/-36) were normal compared to controls. There was no correlation between spectroscopic changes and clinical status of the patients. The findings suggested that not only reduced neuronal-dendritic arborizations but also decreased neuronal function could contribute to spectroscopy changes in Rett syndrome.

Diffusion MRI in neurofibromatosis type 1: ADC evaluations of the optic pathways, and a comparison with normal individuals.

In a control group of 12 normal children (ages ranging from 9 months to 3 years; mean=1.6 years) the mean apparent diffusion coefficient (ADC) value of the normal white matter, obtained from automatically generated ADC maps, was 0.84 +/- 0.14 x 10(-3)mm(2)/s. A patient with neurofibromatosis type 1 with bilateral optic gliomas, and extensive optic pathway involvement was evaluated by diffusion MRI. Multiple measurements of ADC values throughout the involved optic radiations revealed a higher mean value: 1.16 +/- 0.06 x 10(-3)mm(2)/s than that of the normal white matter, suggesting relatively high molecular motion in these regions, probably representing myelin vacuolization. ADC evaluation of a thalamic hamartoma revealed a lower value (=1.06 x 10(-3)mm(2)/s) than this. The mean ADC value obtained from multiple measurements of the enlarged optic chiasm, and intraorbital portions of the nerve was similar (=0.81+/- 0.09 x 10(-3)mm(2)/s) to that of the normal cerebral white matter of the control cases. It appears that diffusion imaging can be useful in evaluation of optic pathway involvement in NF1, and might contribute to differentiating optic gliomas from hamartomas, and myelin vacuolization, however, further studies will be required for assessing the role of diffusion imaging in such lesions.

Proton MR spectroscopy of craniopharyngiomas

To date, only a few cases of craniopharyngiomas have been studied by magnetic resonance (MR) spectroscopy. We report our spectroscopy experiences with five patients having surgically proven craniopharyngiomas. Proton MR spectroscopy images were obtained using the single-voxel mode with spin-echo point resolved spectroscopy. Very prominent peaks centered at 1-1.5ppm were noted in spectroscopic analysis, which probably corresponded to lipid/cholesterol peaks, correlating with the histological findings revealing high amounts of cholesterol in the cyst fluids.