neuro_paed_epilepsy.md

Epilepsy Imaging

1. Epilepsy Imaging
   1. Diagnosis 1
      1. Developmental & Epileptogenic Encephalopathy.
      2. Causes 2
   2. Imaging
      1. Indications 1
         1. Indications for Repeating MRI.
      2. Technical 3
      3. Reporting 3
         1. Analysis for Temporal Lobe Epilepsy.
         2. Analysis for Focal Cortical Dysplasia 4
      4. Complications & Weird Stuff.
         1. Medication Effects.

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Diagnosis ¹

Defined as "Recurrent, unprovoked seizures." Important to get diagnosis right clinically, as per the ILAE Guidelines.⁵
Important to get imaging right early to spot the lesions as per the ILAE guidelines.³
Important to operate early on those with lesions to prevent DEE & because success of surgery is better earlier than later.
DEE = Developmental and Epileptogenic encephalopathy.

Developmental & Epileptogenic Encephalopathy.

• Was known as Symptomatic Generalized Epilepsy Syndrome.
• Epileptic activity contributes to severe cognitive and behavioural impairment ABOVE & BEYOND that expected from the underlying path.
• 50% of this group have genetic cause and thus no surgical input but 40%+ have structural cause and thus need MRI.
• The structural group can start with one lesion then with increased seizures develop more and then develop seizure networks. Therefore, diagnose, treat early. This can reverse some cognitive regression.
• Lesions include strokes, megalencephaly and Sturge-Weber thus will benefit from hemispherectomy but also subtle FCDs which can lead to generalised epilepsy with cognitive regression.

Causes ²

Divided into:

1. Mesial Temporal Sclerosis / Hippocampal Sclerosis.
2. Congential Malformations.
   1. Focal Cortical Dysplasia.
   2. Grey-matter heterotopia.
   3. Hamartoma of Hypothalamus (=> Gelastic). Look at floor of III.
   4. Hemimegalencephaly.
3. Neoplasms.
   1. Ganglioglioma
   2. Dysembryoplastic Neuroepithelial Tumour (DNET)
   3. (Others less often associated but Pleomorphic Xanthoastrocytoma (PXA) )
4. Neurocutaneous Disorders.
   1. Tuberous Sclerosis Complex.(TSC) = due to tubers.
   2. Sturge-Weber Syndrome. (SWS) = gliosis from chronic venous ischaemia
   3. Hypomelanosis of Ito.
5. Inflammatory Conditions.
   1. Encephalitis esp HSV.
   2. Febrile Infection-related Epilepsy Syndrome (FIRES)
   3. Rasmussen Encephalitis.
6. Focal, non-inflammatory process.
   1. Gliosis - any cause inc Stroke, surgery, infection, trauma etc
   2. Haemosiderin - from bleeds is more epileptogenic.
      1. Cavernoma with haemosiderin are likely epileptogenic

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Imaging

Indications ¹

ILAE published Guidelines in 2009 which put in modern lingo are:

1. Focal seizures (except BECTS)
2. Focal neuro history or exam, focal EEG findings.
3. Developmental regression
4. < 2 ys old
5. DEE (was called Symptomatic generalised Epilepsy Syndrome)
6. Status Epilepticus
7. Atypical course in any childhood epilepsy syndrome decline, poorly controlled seizures, focal spike on generalized epilepsy.

BECTS = Benign Epilepsy with Centrotemporal Spikes

NOT indicated for:

• Childhood absence epilepsy.
• Juvenile absence epilepsy.
• Juvenile myoclonic epilepsy.
• BECTS but 25% of babies with infantile spasms have FCD.

Indications for Repeating MRI.

1. If not done using HARNESS-MRI previously, or if poor quality, or unavailable.
   • In drug-resistant epilepsy with prior N MRI, ~ 40% have lesions on HARNESS.
2. If significant clinical changes ~ rapid cognitive decline, Inc Seizure freq.

Do as soon as possible after epilepsy onset. FDG-PET-MRI can increase Sens for FCD further.

Technical ³

Use HARNESS-MRI for all patients.
This is:

1. Volume GE T1 whole brain. 1 x 1 x 1 mm
2. Volume FSE FLAIR whole brain 1 x 1 x 1 mm
3. Cor T2 FSE Perpendicular to long axis of hippocampus 0.4 x 0.4 x 2mm (No gap).

HARNESS = Harmonized Neuroimaging of Epilepsy Structural Sequences

Reporting ³

Should have the clincal details and EEG details before the scan. Inspect all the slices of the volumes on workstation using 1mm MPR.

Analysis for Temporal Lobe Epilepsy.

1. Mesiotemporal Sclerosis (MTS)
   1. Path: Cell loss and astrocytic gliosis in hippocampus AND amygdala, entorhinal cortex, temporopolar cortex and temporal lobe. 20% are bilateral = Tricky to diagnose. Mostly Adolescent / YP.
   2. Radiology:
      1. Mostly in hippocampus: Atrophy, loss of internal structure, decreased T1, increased T2.
      2. Also : Atrophy of ipsilateral fornix, mammillary body (Wallerian degeneration of Circuit of Papez) & temporal lobe esp pole.
      3. And occasionally Malrotation = vertical orientation and rounding of hippocampus, though this is of uncertain significance as can be developmental.
      4. 3T demonstrates more subtle atrophy in specific places. Mesotemporal volumetry - mostly automated is probably better than visual at demonstrating atrophy.
2. Encephalocele of Temporal lobe
3. Parahippocampal dysplasia
   1. WM signal lesions with normal cortical thickness.
   2. So, look at the white matter throughout the temporal lobe.
4. Nodular Heterotopia
   1. Especially around the ventricle, so look there carefully.

Analysis for Focal Cortical Dysplasia ⁴

1. Type I : Unclear MRI findings.
2. Type II :
   1. T1: Increased cortical thickness & blurring of grey-white interface (70%).
   2. T2: Grey matter hyperintensity esp on FLAIR (95%+)
      1. 'Transmantle sign' = Funnel of signal from Grey matter to ventricle.
   3. NB often SUBTLE. Always inspect the bottom of deep sulci for thickening, preferably on axial images to allow comparison with other side.
3. Type II : Have other things to spot. FCD II - if seizure locus found then 90%+ will get seizure-free on surgery.

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Complications & Weird Stuff.

Medication Effects.

Chronic Anti-Epileptic Therapy can =>

• Cerebellar volume loss

Vigabatrin => Myelinic Oedema

• High T2/DWI in Globi pallidi, hypothalamus, central tegmental tracts of pons.

Footnotes

1. Gill D, ILAE Update (Lecture) SPIN 2021. ↩ ↩² ↩³ ↩⁴

2. Choudri A, Pediatric Neuroradiology: Clinical Practice Essentials. Thieme. ↩ ↩²

3. Bernasconi A et al, Recommendations for the use of structural magnetic resonance imaging in the care of patients with epilepsy: A consensus report from ILAE Neuroimaging Task Force. Epilepsia. 2019;60:1054–1068.DOI: 10.1111/epi.15612 Papers+ ↩ ↩² ↩³ ↩⁴ ↩⁵

4. EBR/paed_neuro/neuro_paed_malformation.md ↩ ↩²

5. Scheffer I et al, ILAE classification of the epilepsies: Position paper of the ILAE Commission for Classification and Terminology. Epilepsia, 58(4):512–521, 2017 doi: 10.1111/epi.13709 ↩