Korean J Radiol.  2018 Oct;19(5):965-977. 10.3348/kjr.2018.19.5.965.

The Imaging of Localization Related Symptomatic Epilepsies: The Value of Arterial Spin Labelling Based Magnetic Resonance Perfusion

• Nagesh C
• Kumar S
• Menon R
• Thomas B
• Radhakrishnan A
• Kesavadas

• KMID: 2418561
• DOI: http://doi.org/10.3348/kjr.2018.19.5.965

Abstract

Accurate identification of the epileptogenic zone is an important prerequisite in presurgical evaluation of refractory epilepsy since it affects seizure-free outcomes. Apart from structural magnetic resonance imaging (sMRI), delineation has been traditionally done with electroencephalography and nuclear imaging modalities. Arterial spin labelling (ASL) sequence is a non-contrast magnetic resonance perfusion technique capable of providing similar information. Similar to single-photon emission computed tomography, its utility in epilepsy is based on alterations in perfusion linked to seizure activity by neurovascular coupling. In this article, we discuss complementary value that ASL can provide in the evaluation and characterization of some basic substrates underlying epilepsy. We also discuss the role that ASL may play in sMRI negative epilepsy and acute scenarios such as status epilepticus.

Keyword

Epilepsy; Seizures; Neuroimaging; Arterial spin labelling; MR perfusion; Non-contrast

MeSH Terms

Electroencephalography
Epilepsy*
Magnetic Resonance Imaging
Neuroimaging
Neurovascular Coupling
Perfusion*
Seizures
Status Epilepticus
Tomography, Emission-Computed

Figure

• 

  Fig. 1 Various zones around epileptogenic lesion. Successful surgical outcome is dependent on resection of EZ. EZ = epileptogenic zone

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  Fig. 2 Hippocampal sclerosis. Peri-ictal imaging in 14-year-old female child who presented with new-onset hypomotor complex partial seizures showing swelling and T2 hyperintensity of right hippocampus (arrow, A) with hyperperfusion on ASL fusion images (arrow, B). Unlike this particular case, chronic hippocampal sclerosis with secondary atrophy commonly show hypoperfusion on ASL. ASL = arterial spin lebelling

• 

  Fig. 3 Focal cortical dysplasia. Interictal imaging in 24-year-old female with occasional breakthrough seizures showing right frontal Type II FCD on FLAIR (arrow, A) with hypoperfusion on corresponding ASL fusion images (arrow, B). In another case of 11-year-old female child with refractory extratemporal complex partial seizures, peri-ictal imaging showing right parietal FCD on T1 SPGR (arrow, C) and focal hyperperfusion on ASL grey-scale source images (arrow, D) consistent with active seizure focus. FCD = focal cortical dysplasia, FLAIR = fluid attenuation inversion recovery, SPGR = spoiled gradient recalled acquisition

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  Fig. 4 Hemimegalencephaly. Note subtle enlargement of left cerebral hemisphere on FLAIR (most obvious in regions between arrows in A) in 16-year-old male with global developmental delay and refractory seizures. Interictal ASL fusion images (B) showing areas of cortical hypoperfusion that allow more clear delineation of extent of involvement (between arrows in B).

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  Fig. 5 Polymicrogyria. Left perisylvian polymicrogyria seen on T1 SPGR (arrows, A) in 25-year-old male with extratemporal complex partial seizures. Focal areas of hyperperfusion are seen on ASL fusion images of polymicrogyric cortex (arrows, B) compared to normal perfusion pattern of contralateral side (C) in this peri-ictal scan.

• 

  Fig. 6 Dysembryoplastic neuroepithelial tumor. T2-weighted images (A) showing dysembryoplastic neuroepithelial tumor involving right peri-Rolandic region in 24-year-old male. While lesion per se is hypoperfused, adjacent hyperperfusion involves lateral right sensorimotor cortex (arrow, B) on this peri-ictal scan despite sMRI showing lack of perilesional changes, concordant with presentation of simple partial seizures of left hand despite lesion was located in foot region. sMRI = structural magnetic resonance imaging

• 

  Fig. 7 Arteriovenous malformation. Unruptured AVM involving left frontal lobe as seen on MR angiography (black arrow, A) in 34-year-old male with secondary generalized seizures. Shunting as depicted by intravascular signal within AVM nidus (black arrow, B) and draining superior sagittal sinus (black arrow, C) is seen on ASL color cerebral blood flow maps. Note hypoperfusion involving rest of left middle cerebral artery territory (best seen at white arrows in B, C). Catheter angiography confirmed high flow shunting with attenuation of ipsilateral parenchymal capillary blush (D) compared to contralateral normal side (E). Steal phenomena like these are known causes of seizures in AVMs. AVM = arteriovenous malformation

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  Fig. 8 Rasmussen's syndrome. Left hemispheric involvement in 15-year-old girl post-callosotomy. FLAIR (A), shows burnt-out disease in atrophied left frontal region (black arrow, A) which shows corresponding low perfusion on ASL (black arrow, B). Persistent marked hyperperfusion along left parieto-occipital cortex (white arrows, B) despite seizure-free post-surgical outcome suggests concomitant ongoing inflammation.

• 

  Fig. 9 Tubercular meningitis. Biopsy-proven case in 44-year-old female with secondary generalized seizures and depressed sensorium. Enhancing dura-based granulomatous lesion is seen on T1-weighetd image (black arrow, A) with adjacent cortex showing significant hypoperfusion on ASL (white arrows, B) in this peri-ictal scan.

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  Fig. 10 Sequelae of periventricular hemorrhagic infarction. 12-year-old boy with daily seizures and stormy perinatal history. Ulegyria diffusely involves entire right cerebral hemisphere on T1 (A). Peri-ictal ASL fusion images (B) show significant hyperperfusion involving posterior regions (arrows, B), allowing localization of seizure focus concordant with electroencephalography findings.

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  Fig. 11 sMRI negative temporal epilepsy. 15-year-old boy with temporal neocortical epilepsy. Hippocampi appeared normal on T2-weighted image (A). Right temporal hypoperfusion on ASL (arrows, B) suggested right temporal EZ. Confirmatory positron emission tomography showing excellent concordance with ASL (arrows, C).

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  Fig. 12 Epilepsia partialis continua. 13-year-old boy presented with continuous right hemispheric partial seizures. FLAIR showed right frontal FCD (arrow, A) lacking significant changes in rest of ipsilateral hemisphere (not shown). Ictal ASL showed intense hyperperfusion of FCD along with secondary hyperperfusion in rest of ipsilateral cerebrum (B, C). This likely represents spread of seizure activity to symptomatogenic zone.

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