Epilepsy

Epilepsy Andy HuCassie VuSophie JonesYvonne LaTrixie Kong TSGQ (2011)AnatomyPrimary GeneralisedOriginate deep within the brain (Paur, 2007)Affecting the whole bodyspreads to both hemishphereassociated with grand mal Seizures (Ubach, 2013)

Partial/FocalSmall and unchanging (ubach, 2013)Always identical in origin locationcan be multipleeffects are specific.

Mesial Temporal SclerosisA common cause of TLE (Hopkins University, 2013)Often leads to intractable epileptic syndromes.

Birmingham City University, 2013Bote et al. 2008Epilepsy exists in many different forms but can be categorised into partial or focal seizures or primary generalised seizures. (Paur, 2007) The location of the lesion has direct correlation with the type of seizure and the body part it affects. Primary generalised epilepsy originates deep within the brain and rapidly expands into both hemispheres, though not necessarily in a symmetrical fashion. It can affects the entire brain and therefore the entire body are are usually associated with grand mal seizures(Ubach, 2013)Focal epileptic lesions are so called because they have one focal point from which the seizure generates which is always the same, this reflects their specific effect on the body. the lesions are usually small but there can be more than one, and though they can develop into secondary generalised seizures if neuron pathways are continuously damaged they usually do not change throughout the course of a persons life. according to Ubach 2013 Focal seizures can be confused for generalised seizures when the lesions are located in silent brain areas such as the pre-frontal or occipital regions.

Temporal Lobe epilepsy is the most common form of Epileptic seizure. It is often caused by medial temporal sclerosis which is a scarring of a region of the temporal lobe, specifically in the hippocampal folds which are highlighted with the arrows. Epileptic syndromes that are caused by this scarring have a high propensity to become intractable, meaning that the patient will have a serious time Clinical indicationsOnset of seizures at any age with evidence of focal onset or EEGOnset of unclassified or apparently generalised in the first year of life or in adulthoodEvidence of a focal fixed deficit on neurological or neuropsychological examinationDifficulty in obtaining control of seizures with first-line anti epileptic drug treatmentLoss of control of a change in seizure patterns occur(Panayiotopoulos, 2005).

Imaging is not required for patients with a definite diagnosis of generalised epilepsy. (Smith, 2001, p103)

Sequences Standard scanning protocol is insufficient in detecting the majority of lesions in epilepsy patients with refractory epilepsy (Von Oertzen et al, 2002). Focal-lesion sensitivity for standard MRI was 50%, compared with a sensitivity of 91% for epilepsy protocol MRI.The International League Against Epilepsy (1997), recommends an MRI protocol for these patients.

PROTOCOL: Images the entire brain from nasion to inion. T1-weighted magnetization prepared rapid gradient echo (MPRAGE) or spoiled gradient recalled (SPGR) images 1.5mm slice thickness with no intervening gap obtained in the coronal oblique plane. Coronal and axial fluid-attenuated inversion recovery (FLAIR) sequences with a 2-3mm slice thickness and a 0-1 mm interslice gap.

MPRAGE - MR measurement technique. 3D extension of the turbo flash technique with prepared inversion pulses. Only one segment or partition of a 3D data record is obtained per preparatory pulse.

The spoiled gradient recalled (SPGR) - acquisition in steady state uses semi-random changes in the phase of the radio frequency (RF) pulses to produce a spatially independent phase shift.

FLAIR - longer effective echo time and longer inversion time for suppressing fluids. Lesions that are normally covered by bright fluid signals using conventional T2 contrast are made visible by Dark Fluid Technique. the inversion pulse is applied such that the T1 relaxation of the fluid reaches zero crossing at time point T1, resulting in the signal being erased. Sequences Conventional thin-slice (3mm), T2 weighted, axial and coronal sequence (Deblaere&Achten, 2008).

BENEFITS: T1-weighted images enhance gray/white matter differentiation, which is crucial to the analysis of cortical architecture. Images acquired in a coronal oblique plane perpendicular to the long axis of the hippocampus, important in evaluating temporal lobe epilepsy (TLE).

For the detection of hemosiderin depositions, small cavernomas or vascular anomalies, a gradient echo T2 image or a newer susceptibility weighted image is advised (Urbach, 2013).

http://emedicine.medscape.com/article/1155295-overview#aw2aab6b3

SequencesTemporal Lobe EpilepsyMost common focal epilepsy.The hippocampus is the most vulnerable and affected structure in patients (Van Paesschen, 2004).

SEQUENCES: Axial T2 high resolution (2mm)Diffusion weighted imaging Coronal oblique T2 Turbo Gradient Spin-Echo (TGSE)Sagittal T1 FLAIR (DLA & Castillo, 2007). Inversion Recovery (IR) - SPACE 0.9mm volume and T2 SPACE FLAIR sequences are highly sensitive in locating temporal lobe abnormalities, which includes coronal oblique planes aligned to the hippocampus and axial planes at 2mm (Hakyemaz, 2003).

Turbo GSE - measurement technique. additional gradient echoes are generated before and after each spin echo. the spin echoes are allocated to the center of the raw data matrix to give pure T2 contrast. the gradient echoes primarily determine the image resolution. faster, fat is darker, more sensitive to susceptibility effects (e.g.bleeding with hemosiderin)

IR - measurement technique. method for creating a signal dependent primarily on T1. the longitudinal magnetization is inverted in the opposite direction by a 180 degree pulse. transverse magnetization remains equal to zero. during the subsequent recovery, the negative longitudinal magnetization decays to zero and then begins to rise. because transverse magnetization is not possible, no signal is measured. to generate an MR signal, the longitudinal magnetization must be converted to transverse magnetization through application of a 90 degree pulse. SequencesMesial Temporal Lobe Sclerosis (MTLE) It is the most common pathological abnormality in TLE. In a study performed by Berkovic and colleagues in 1995, sensitivity of MRI for mesial temporal sclerosis was as high as 97%, and specificity was 83%.Classic MRI FINDINGS: Decreased volume and an abnormally increased T2 signal of the hippocampus. (Urbach, 2013).

SequencesSEQUENCES: Oblique coronal thin sections perpendicular to the plane of the hippocampus have high sensitivity and specificity for mesial temporal sclerosis. Plane is perpendicular to the long axis. Thin section T2-weighted spin-echo and FLAIR.

BENEFITS:T2-weighted spin-echo imaging is better for demonstrating the internal architecture of the hippocampus. Degree of signal abnormality is more obvious FLAIR imaging.

The advantage of FLAIR imaging is derived from the decreased background signal intensity that originates in extrahippocampal structures. This difference occurred because the hippocampal structures are relatively flat and lie predominantly in the axial plane (in which most routine sequences are performed); therefore, subtle lesions of the hippocampus may be missedPathologyHIPPOCAMPAL SCLEROSISlinked to temporal lobe epilepsylesion featuring neuronal loss, gliosis and sclerosisMRI findings:Atrophy and abnormal T2-weighted signal. This is associated with reduced hippocampal volume. Increased signal intensity on T2 weighted and volume loss represent gliosis and cell loss. (Bote, 2008)On heavily T1-weighted coronal inversion recovery images, decreased T1-weighted signal demonstrates loss of internal architecture. (Duncan, 1997)Loss of grey-white matter interface in the anterior temporal lobe

(Bote, 2008)

(ACNR, 2008)temporal lobe epilepsy: recurrent or unprovoked seizures originating from the medial or lateral temporal lobe.Artefacts

Susceptibility ArtefactsDental implants and orthodontics (Costa et al 2009) Post electrode implant surgery (Pozdin et al 2005)

Truncation ArtefactsGibbs rings (Erasmus 2004)

Motion ArtefactsMinute lesionsSeizure

Erasmus (2004)Costa et al. (2009)There are many different artefacts that may affect imaging for epilepsy, two of the main ones are susceptibility and truncation artefacts. Susceptibility artefacts are due to magnetic susceptibility differences between tissues. A study on imaging the brain in patients with dental implants and orthodontics Costa et al (2009) found that they could cause quite serious susceptibility artefacts in most planes (as shown in pictures A&B) he stated that in patients with full orthodontic braces it was quite common for the artefacts to be so severe as to be detrimental to their diagnosis. Another situation in epilepsy imaging where susceptibility artefacts occur is in post electrode implantation surgery imaging which can make it difficult to assess to the success of the surgery. Gibbs rings whilst not specific to epilepsy are common artefacts in brain imaging, this is quite similar to reverberation artefacts in ultrasound where hard anatomical lines are repeated. In MR this is due to a lack of high frequency sampling but can easily be overcome with computer algorithms applied during post processing whereas susceptibility artefacts cant always be resolved.

Motion artefacts as you all know can be quite common in MRI due to the length of the scans. When imaging for brain epileptogenic lesions which can often be minute, motion artefacts are a serious issue. If a seizure occurs that involves the patient physically moving it is likely any pictures obtained will not be of great use, and that the scan will have to be endedSafety IssuesFerromagnetic metal objects Limits patients with cardiac pacemakers, deep brain stimulators, intraocular metal, intracranial aneurysm clips, stents, prosthesis, implants, neurostimulators, or implantable pumpsstructural damage or dislodgementloss or distortion of signal impact the image quality

Gadoliniumreduced likelihood of contrast-related allergic reactions history of kidney disease, failure, transplant, or any other pathologyNephrogenic Systemic Fibrosis (NSF)The exact etiology of the disease is unclear but most of the reported cases of NSF have been documented in patients who received intravenous gadolinium and have severe acute or chronic renal failure, with a GFR < 30 (University of California San Francisco(UCSF), 2011)

There are a vast amount of potential hazards which can impact the degree of safety of an MRI procedure. The majority of these hazards are primarily related to the powerful magnetic field, which forms the functional basis of MRI.The presence of ferromagnetic metal objects is an absolute contraindication. Due to the strong magnetic forces within the MRI machine, metal objects can suddenly and forcefully become airborne as they are attracted towards the machine, acting as projectiles, causing potential danger to anyone or thing in its path. This therefore limits certain patients.The high radiofrequency energy used can cause metal to heat up, resulting in structural damage or dislodgement. The presence of these metallic objects may also cause a loss or distortion of signal and impact on image quality. Despite the reduced likelihood of contrast-related allergic reactions due to the lack of iodine in Gadolinium (Gad), there are certain contraindications to its use. Gad is not recommended for patients with a history of kidney disease, failure, transplant, or any other pathology. Contrast competes with the normal excretion process and may overwork the affected organ, resulting in potential organ failure. Special attention must be given to patients with Nephrogenic Systemic Fibrosis (NSF), a rare but serious systemic condition, which may be triggered and worsened with the use of gad-based contrast agents. The exact etiology of the disease is unclear but most of the reported cases of NSF have been documented in patients who received intravenous gadolinium and have severe acute or chronic renal failure, with a GFR < 30 (University of California San Francisco(UCSF), 2011)

Safety IssuesPregnancyThere is at present insufficient knowledge to establish unequivocal guidance for the use of MRI procedures on pregnant patients. (Medicines and Healthcare products Regulatory Agency (MHRA) 2007)Potential complications in the first trimester:TeratogenesisAcoustic damage to the foetus and motherTissue Heating

What happens when a patient has a seizure whilst having an MR scan?stop the scanstop injectionsroll into recovery positionperform first aid - not CPR.

There is at present insufficient knowledge to establish unequivocal guidance for the use of MRI procedures on pregnant patients. A risk/benefit analysis should be carried out, and informed consent obtained, as there are potential complications which affect the foetus, especially during the first trimester, where organ development is most fragile. These include the possibility of teratogenesis, defined as the prenatal toxicity characterised by structural or functional defects in the developing embryo, and the possibility of acoustic damage to the foetus, as well as the mother, which results from the high level of noise caused by the vibration of the gradient coils. Ear protection is always provided for the adult, but what about the fetus? Temperature of tissue increases with field strength. Although there are no proven adverse effects, heating may potentially damage the foetus, especially in the early stages of pregnancy. The scan should be halted immediately, contrast injections stopped (if used), and first aid should be performed, primarily rolling the patient into recovery position to prevent aspiration.The above shows the first-aid guide. As a bystander, we should remain calm, stay with the patient, observe and monitor breathing, and time the seizure. We should never restrain the patient while they are having an episode, or apply CPR.If a seizure continues for more than 30 minutes, it becomes a status epilepticus, a medical emergency which requires immediate treatment with emergency medication.Hence it is vital that MR technicians must closely monitor patients whilst they are within the bore, and have emergency protocols in place.

Alternative ImagingMRI is often regarded as the absolute first preference due to its high soft tissue defining ability which allows clear visualization of the structural abnormalities of the brain such as hippocamal sclerosis and malformation of the cortical development.

However, CT is the main alternative modality for epilepsy evaluation but is inferior to MRI in terms of sensitivity and specificity, due to the lack of soft tissue resolution.CT- Inferior to MRI in terms of accuracy and radiation wise.- faster procedure- able to locate structural lesions (bleeding, tumours & cysts) but unable to determine site of seizure onset.- lower cost

Alternative ImagingNeuroimaging modalities:localize cerebral dysfunction through disturbances in ones metabolism and blood flow and mapping out the functional areas (Passaro, 2013)Functional MRI: investigates the cerebral blood flow and is able to detect epileptogenic regions

SPECT: During ictal period, the administration of the radiotracer enables increased perfusion at epileptic seizure onset (Passaro, 2013)

Positron Emission Tomography (PET): identifies interictal hypometabolism of the epileptogenic temporal lobe in more than 85% of the cases (Passaro, 2013). Correlating with MRI, it can yield a higher diagnostic result and enhance surgical seizure free outcomesSummaryWE NEED A SUMMARY References Berkovic SF, McIntosh AM, Kalnins RM, et al. Preoperative MRI predicts outcome of temporal lobectomy: an actuarial analysis. Neurology. Jul 1995;45(7):1358-63. [Medline].Birmingham City University. Epilepsy care and Management. 2013. Available at http://www.bcu.ac.uk/courses/epilepsy-care-and-managementBronen, R. (1992). Epilepsy: The role of mr imaging.American Roentgen Ray Society, (159), 1165-1174. Retrieved from Bote, R.P., Blazquez-Llorca, L., Fernandez-Gil,M., Alonso-Nanclares, L., Munoz, A., & De Felipe, J. (2008). Hippocampal sclerosis: Histopathology Substrate and Magnetic Resonance Imaging. Semin Ultrasound, CT MRI 29(1): 2-14Commission on Neuroimaging of the International League Against Epilepsy (1997) Recommendations for neuroimaging for patients with epilepsy. Epilepsia 38:1255-1256Costa.A., Appenzeller.S., Yasuda.C., Perieira.F., Zanardi.V., Cendes.F. (Jun 2009). Artifacts in brain magnetic resonance imaging due to metallic dental objects. Oral Medicine and Pathology.Deblaere K, Achten E, (2008). Structural magnetic resonance imaging in epilepsy, Neuro, European Radiology, Vol(18) p.119-129.DLA & Castillo, M (2007), MR Imaging of Temporal Lobe Epilepsy, Seminars is Ultrasound CT and MRI, vol. 28, pp. 424-436.Duncan, J.S. (1997). Imaging and Epilepsy. Brain 120: 339-377Encyclopaedia Britannica. (2013) Teratogenesis (biology). [Online] Available: http://www.britannica.com/EBchecked/topic/587782/teratogenesis[9 September 2013]Erasmus. L.J, Hurter. D., Nuade. M., Kritzinger. H.G., Acho. S., (August 2004) A short overview of MRI artefacts. SA Journal of Radiology.Helen Paur, Paul L. Chazot, The anatomy of epilepsy, Current Anaesthesia & Critical Care, Volume 18, Issue 1, 2007, Pages 3-7, ISSN 0953-7112, http://dx.doi.org/10.1016/j.cacc.2007.03.015.Passaro, E. (2013,July 11).). Medscape. Neuroimaging in Epilepsy - Evaluation of a first seizure. Retrieved from:

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