Magnetic Resonance Imaging of Mesial Temporal Sclerosis (MTS): What radiologists ought to know?

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1 Magnetic Resonance Imaging of Mesial Temporal Sclerosis (MTS): What radiologists ought to know? Poster No.: C-0856 Congress: ECR 2012 Type: Educational Exhibit Authors: P. Singh, G. Mittal, R. Kaur, K. Saggar ; Ludhiana/IN, Haryana/IN Keywords: Diagnostic procedure, Comparative studies, MR-Functional imaging, MR, Image manipulation / Reconstruction, Education, Anatomy, Neuroradiology brain, Imaging sequences, Seizure disorders, Congenital, Neoplasia DOI: /ecr2012/C-0856 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 20

2 Learning objectives To review the MR anatomy of the temporal lobe, especially medial region. To discuss optimal MRI temporal lobe protocol. To describe primary as well as secondary magnetic resonance features of MTS. To discuss the role of quantitative volumetric MRI, T2 relaxometry, MR spectroscopy and functional imaging methods in the presurgical workup of temporal lobe epilepsy (TLE). Background Approximately 30% of patients with epilepsy do not respond to adequate medical treatment. They are then said to have medically refractory or intractable epilepsy. In these patients, the opinion of surgical treatment needs to be considered. Hippocampal sclerosis is the most common pathology in patients undergoing temporal lobe surgery. Identifiable pathology,such as Hippocampal sclerosis, is associated with a good outcome from surgery and its reliable preoperative diagnosis is important for the assessment and management of patients with intractable partial epilepsy. Imaging findings OR Procedure details MR anatomy of Medial Temporal Lobe NORMAL ANATOMY Because of its different functions and organization, the temporal lobe may be divided into lateral and medial parts. The neural structures that constitute the mesial temporal lobe are the parahippocampal gyrus, uncus, hippocampus, fimbria, dentate gyrus, and amygdala. Page 2 of 20

3 The hippocampus is a curved structure on the medial aspect of temporal lobe consisting of complex U-shaped layers of the dentate gyrus and cornu ammonis, which are interlocked together. The cornu ammonis blends into the subiculum, which forms the transition to the neocortex of parahippocampal gyrus. Fig. 1: Coronal TSE T2-weighted scan through the body of the hippocampal formation Green :Nucleus dentatus Pink: Ammon's horn (most of it forms the floor of the lateral ventricle) Brown: Subiculum, which continues with the gray substance of the parahippocampal gyrus (thick arrow). Thin arrow indicates ambiens cistern. Page 3 of 20

4 Fig. 2: Coronal turbo spin echo (TSE) T2-weighted depicts the sulci and convolution of the temporal lobe. 1st (first or superior temporal sulcus); 2nd (second or middle temporal sulcus); 3rd (third or inferior temporal sulcus) and SF (Sylvian fissure) Page 4 of 20

5 Fig. 3: Coronal TSE T2-weighted MR scan through the head of the hippocampus. The folds (thick arrow) of the pes hippocampi (head of hippocampus), which form the floor or the temporal horn, characterize it. Amygdala (thin arrow) is located above and forms the roof of the temporal horn. The convex ventricular surface of hippocampus is covered with ependyma, underneath which tangential white-matter tracts, called alveus, pass medially to converge to form the fimbria, which projects into the ventricular cavity and continues as fornix. Fig. 4 on page 17 Page 5 of 20

6 Fig. 4: Coronal IR 1.5-T imaging through the body of thehippocampus depicts the thin white matter tract (alveus) over convex ventricular surface of hippocampus(thick arrow) and choroidal plexus in the ventricle (thin arrow). METHODS OF DETECTING HIPPOCAMPAL PATHOLOGY USING MAGNETIC RESONANCE IMAGING Page 6 of 20

7 VISUAL ANALYSIS(QUALITATIVE ANALYSIS) QUANTITATIVE MEASUREMENTS OF HIPPOCAMPAL SCLEROSIS. 1. Hippocampal Volumetry 2. T2 Relaxometry MR SPECTROSCOPY FUNCTIONAL IMAGING Epilepsy Protocol MRI Routine MR imaging at our institution includes: T1w, T2w, FLAIR, Diffusion weighted and GRE sequences in axial plane with 5mm slice thickness and 30% interslice gap. Inversion recovery (IR) oblique coronal images (TE-51, TR-3500, FOV-250 mm, slice thickness 2 mm) and Oblique coronal T2 W images (TR- 4000, TE- 101, FOV - 230, Slice thickness - 2 mm) covering whole brain are acquired. Oblique coronal plane is perpendicular to the long axis of hippocampus or the parahippocampal convolution. For hippocampal volumetry, a Oblique coronal three dimensional gradient echo sequence (MP-RAGE: TR-2400, TE-3.75, FOV -250, Flip Angle-8, Matrix -192x192, slice thickness 0.85 mm, interslice gap 1.3mm) is obtained perpendicular to long axis of hippocampus or the parahippocampal convolution (only in selected cases). If indicated, T2 relaxation times of hippocampi (T2 relaxometry) are measured using 16echo Carr-Purcell-Meiboom-Gill sequence (TE,22-352). Page 7 of 20

8 Fig. 5 MAGNETIC RESONANCE FEATURES OF HIPPOCAMPAL SCLEROSIS THAT ALLOW A VISUAL DIAGNOSIS CHANGES IN MORPHOLOGY HIPPOCAMPAL ATROPHY Visual assessment of hippocampal atrophy is the first feature that many radiologists used to assess the hippocampus. CHANGES IN TISSUE SIGNAL Abnormal Hippocampal T2-Weighted signal. Increased T2-weighted signal intensity was the first method that demonstrated a correlation between hippocampal pathology and MR-detectable signal abnormality. Page 8 of 20

9 The atrophic hippocampus often demonstrates decrease signal on T1-weighted images with dark appearance and this correspond to high signal on T2-weighted sequences. The IR sequence (heavily T1-weighted sequence) can be thought of as doing the job of increasing sensitivity of T1 images for this feature of signal abnormality. Fig. 6: MR features of HIPPOCAMPAL SCLEROSIS Primary signs 1. A small atrophic unilateral hippocampus. 2. Hyperintensity on T2 W images. 3. Loss of the hippocampal internal architecture and that of normal digitations of the head. Page 9 of 20

10 Fig. 7: IR Image showing atrophy with hypointensity of the left Hippocampus (arrow). Secondary signs of Hippocampal Sclerosis Fig. 8 on page 17 Page 10 of 20

11 Fig. 8 QUANTIATIVE MEASUREMENTS OF HIPPOCAMPAL SCLEROSIS Hippocampal Volumetry Ipsilateral hippocampal volume loss is sensitive and specific indicator of hippocampal sclerosis in the clinical context of epilepsy. Because of relatively anisotropy of the hippocampus, slices 3-mm thick or less are necessary for accurate estimation of hippocampal volume. T2 Relaxometry Hippocampal T2 relaxation time increases in patient of hippocampal sclerosis. Page 11 of 20

12 T2 relaxation times are easy to acquire, and post acquisition processing to calculate T2 maps from these data takes only a few minutes. The necessary acquisition and processing software is available on most commercial imaging systems, and the measurement of T2 in the region of interest is then made. Fig. 9: QUANTITATIVE MEASUREMENTS OF HIPPOCAMPAL SCLEROSIS. 1. Hippocampal Volumetry 2. T2 Relaxometry: This quantative measurement is an objective means of determining the frequency and severity of T2 abnormality. Hippocampal T2 relaxation time increases in patient of hippocampal sclerosis. MR Spectroscopy 1.N-acetylaspartate occurs in neurons but not in mature glial cells. Thus, it is considered a marker of neuronal abundance or function. In comparison, creatine activity and choline activity are associated more with glial cells than with neurons. Page 12 of 20

13 2.N-acetylaspartate and creatine signals can be measured with 1H MRS to assess 2 major pathological features of MTS: decreased NAA for neuronal loss and slightly increased or unchanged creatine for astroglial proliferation. 3.The ratio between NAA and creatine signals is frequently used to detect temporal lobe abnormalities in candidates for epilepsy surgery. 4. The correspondence between the decreased NAA: creatine ratio and the side of MTS or EEG-detected seizure onset (EEG seizure onset) is as high as 90% in temporal lobe epilepsy. 5. Also, 1H MRS is especially helpful in patients who do not have Hippocampal atrophy. 6. Thus, 1H MRS is sensitive enough to detect mild cases of MTS, ie, MTS not severe enough to be identified as hippocampal atrophy on MRI. Fig. 10: Magnetic resonance spectroscopy 1H spectra measured in the temporal lobes of an 16-year-old patient with intractable epilepsy. The NAA/Cr ratio in the right(rt) temporal region is considerably lower than control values, whereas the ratio is normal on the left(lt) side. Since undergoing a right temporal lobectomy, the patient has been seizure free. Page 13 of 20

14 Functional Neuroimaging in Epilepsy Presurgical planning in epilepsy involves identifying eloquent cortex close to the lesion, which if injured during surgery will manifest with neurologic deficit. The goal of presurgical functional imaging is to minimize damage to these functional areas by knowing the location of eloquent cortex. PET and SPECT Approximately 30% of the patients with temporal lobe epilepsy have a normal MRI scan. In this subgroup of patients, PET studies have shown temporal lobe hypometabolism ipsilateral to ictal onset zone in 87% of the patients. Ictal SPECT has been shown to have a higher success in lateralizing seizure onset in patients with well-established temporal lobe epilepsy. Thus, PET or ictal SPECT may be a complementary tool in the presurgical evaluation of patients with medically intractable epilepsy, particularly with negative MRI. Page 14 of 20

15 Fig. 11: Images of SPECT scan in a patient presenting with epilepsy showing hypoperfusion in right temporal region in both interictal and ictal phases. Blood oxygenation level-dependent (BOLD) functional MRI (fmri) Clinical fmri is based on blood oxygenation level-dependent (BOLD) contrast. BOLD signal response arises from localized hemodynamic changes induced by regionally increased neuronal activity associated with processing a stimulus or performing a cognitive task defined by the paradigm. BOLD fmri is a high spatial resolution technique without ionizing radiation that maps physiologic and metabolic consequences of altered electrical activity in the brain. fmri has the potential to predict the possible deficits in language, and in visual, motor, and sensory functions that would arise from the surgical intervention. Page 15 of 20

16 Fig. 12: A 16-year-old with cortical dysplasia (thick arrow) involving precentral gyrus on the left side. Real-time fmri obtained after right finger tapping vs rest shows activation of primary hand motor area (thin arrow) placed close to the lesion. If resection extends to primary hand motor area, the patient is likely to develop post procedure neurologic deficit. Page 16 of 20

17 Images for this section: Fig. 4: Coronal IR 1.5-T imaging through the body of thehippocampus depicts the thin white matter tract (alveus) over convex ventricular surface of hippocampus(thick arrow) and choroidal plexus in the ventricle (thin arrow). Page 17 of 20

18 Fig. 8 Page 18 of 20

19 Conclusion 1. MRI forms the mainstay for structural and functional neuroimaging in patients with epilepsy. 2. With increasing availability of newer techniques and MR sequences, the sensitivity and specificity of detecting epileptogenic lesion on MRI has increased. 3. The MRI demonstration of a lesion very much helps in further presurgical evaluation. In patients with negative MRI, PET and SPECT may be used as complimentary tools in the presurgical workup. 4. In the recent years, advances in neuroimaging have helped to understand the pathophysiology of epilepsy better and also to prognosticate the outcome of medical and surgical treatments. 5. The advancements in neuroimaging have also provided noninvasive tools to detect the epileptogenic focus. Personal Information Dr. Paramdeep Singh MD Department of Radio-diagnosis MM Institute of Medical Sciences and Research Maharashi Markandashwar University Mullana (Ambala) Haryana. Pin paramdeepdoctor@gmail.com References Page 19 of 20

20 Kuzniecky R, Jackson GD. Magnetic resonance in epilepsy. New York:Raven Press ;1995. Atlas SW. Magnetic resonance imaging of brain and spine. 3rd ed. Philadelphia: Lippincott Williams and Wilkins; Van Paesschen W, Connelly A, King MD, et al. The spectrum of hippocampal sclerosis: a quantitative magnetic resonance imaging study. Ann Neurol 1997; 41: Thulborn KR: A BOLD move for fmri. Nat Med 4: , Van den Hoff J: Principles of quantitative positron emission tomography. Amino Acids 29: , Page 20 of 20