Nonconvulsive partial status epilepticus mimicking recurrent infarction revealed by diffusion-weighted and arterial spin labeling perfusion magnetic resonance images

Arterial spin labeling perfusion in acute Wernicke encephalopathy: a case series discussion

Wernicke's encephalopathy (WE) is a life-threatening neurologic disorder resulting from thiamine (vitamin B1) deficiency that can be secondary to chronic alcohol abuse, gastrointestinal surgery, systemic infectious and non-infectious diseases, and chemotherapy. WE is classically characterized on MRI by reduced diffusion and T2 prolongation along the mammillothalamic tracts, periaqueductal gray and tectal plate. We present two patients with acute WE who had baseline arterial spin labeling (ASL) perfusion at the time of presentation, demonstrating increase in cerebral blood flow (CBF) within the classically involved brain regions and concurrent global cerebral cortical hypoperfusion. Both patients were successfully treated with intravenous thiamine infusion. Post-treatment MRI demonstrated improvement of reduced diffusion and normalization of CBF within the involved structures. Prior histopathological studies have documented prominent undulation and luminal dilatation of arteries and arterioles in acute WE lesions, likely explaining the increased perfusion shown by imaging. The root of this pathophysiologic process may trace back to thiamine's biochemical role in maintaining osmotic gradients and glucose metabolism, that if failed can lead to arterial hyper-perfusion. Our findings show that ASL-CBF can highlight the underlying pathophysiology in patients with acute WE by demonstrating increased CBF in involved central structures. This luxury perfusion may be a compensatory or protective mechanism by which increased metabolic demand is met in the acute setting and which, if treated timely, will show normalization of CBF on ASL imaging.

[Sequential arterial spin labeling findings of status epilepticus showing generalized periodic discharges on EEG following acute infarction in the right occipital lobe]

In addition to electroencephalogram (EEG), arterial spin labeling (ASL) perfusion images with the dual postlabeling delay (PLD) method are useful for evaluating the hemodynamic state of status epilepticus (SE). A 72-year-old man suffered from an acute infarction in the right occipital lobe, resulting in SE with general periodic discharges on EEG with a higher amplitude on the right side. On ASL, blood flow was increased at a wide area of the right hemisphere centered on this infarct. With improvement of SE, sequential ASL with dual PLD method clearly demonstrated not only the reduction of the signal both in intensity and area but also the decrease of the blood flow velocity.

Detection of ictal and periictal hyperperfusion with subtraction of ictal-interictal 1.5-Tesla pulsed arterial spin labeling images co-registered to conventional magnetic resonance images (SIACOM)

Background

Our recent report showed that 1.5-T pulsed arterial spin labeling (ASL) magnetic resonance (MR) perfusion imaging (1.5-T Pulsed ASL [PASL]), which is widely available in the field of neuroemergency, is useful for detecting ictal hyperperfusion. However, the visualization of intravascular ASL signals, namely, arterial transit artifact (ATA), is more remarkable than that of 3-T pseudocontinuous ASL and is easily confused with focal hyperperfusion. To eliminate ATA and enhance the detectability of (peri) ictal hyperperfusion, we developed the subtraction of ictal-interictal 1.5-T PASL images co-registered to conventional MR images (SIACOM).

Methods

We retrospectively analyzed the SIACOM findings in four patients who underwent ASL during both (peri) ictal and interictal states and examined the detectability for (peri) ictal hyperperfusion.

Results

In all patients, the ATA of the major arteries was almost eliminated from the subtraction image of the ictal-interictal ASL. In patients 1 and 2 with focal epilepsy, SIACOM revealed a tight anatomical relationship between the epileptogenic lesion and the hyperperfusion area compared with the original ASL image. In patient 3 with situation-related seizures, SIACOM detected minute hyperperfusion at the site coinciding with the abnormal electroencephalogram area. SIACOM of patient 4 with generalized epilepsy diagnosed ATA of the right middle cerebral artery, which was initially thought to be focal hyperperfusion on the original ASL image.

Conclusion

Although it is necessary to examine several patients, SIACOM can eliminate most of the depiction of ATA and clearly demonstrate the pathophysiology of each epileptic seizure.

Quantitative Analysis of Diffusion-Restricted Lesions in a Differential Diagnosis of Status Epilepticus and Acute Ischemic Stroke

Background and Purpose

Distinction between acute ischemic stroke (AIS) and status epilepticus (SE) on MRI can be challenging as restricted diffusion may occur in both conditions. In this study, we aimed to test a tool, which could help in differentiating AIS from SE when restricted diffusion was present on MRI.

Materials and Methods

In diffusion weighted imaging (DWI) with a b-value of 1,000 and apparent diffusion coefficient (ADC) maps, we compared the ratios of intensities of gray values of diffusion-restricted lesions to the healthy mirror side in patients with AIS and SE. Patients were recruited prospectively between February 2019 and October 2021. All patients underwent MRI and EEG within the first 48 h of symptom onset.

Results

We identified 26 patients with SE and 164 patients with AIS. All patients had diffusion-restricted lesions with a hyperintensity in DWI and ADC signal decrease. Diffusion restriction was significantly more intense in patients with AIS as compared to patients with SE. The median ratios of intensities of gray values of diffusion-restricted lesions to the healthy mirror side for DWI were 1.42 (interquartile range [IQR] 1.32–1.47) in SE and 1.67 (IQR 1.49–1.90) in AIS (p < 0.001). ADC decrease was more significant in AIS as compared to SE with median ratios of 0.80 (IQR 0.72–0.89) vs. 0.61 (IQR 0.50–0.71), respectively (p < 0.001). A cutoff value for ratios of DWI signal was 1.495 with a sensitivity of 75% and a specificity of 85%. Values lower than 1.495 were more likely to be associated with SE and higher values were with AIS. A cutoff value for ADC ratios was 0.735 with a sensitivity of 73% and a specificity of 84%. Values lower than 0.735 were more likely to be associated with AIS and higher values were with SE.

Conclusion

Diffusion restriction and ADC decrease were significantly more intense in patients with AIS as compared to SE. Therefore, quantitative analysis of diffusion restriction may be a helpful tool for differentiating between AIS and SE when restricted diffusion is present on MRI.

Nonconvulsive status epilepticus due to pneumocephalus after suprasellar arachnoid cyst fenestration with transsphenoidal surgery: illustrative case

BACKGROUND

Nonconvulsive status epilepticus (NCSE) requires prompt diagnosis and treatment, particularly after neurosurgical procedures for cerebral damage. Here, the authors reported an extremely rare case of suprasellar arachnoid cyst presenting with NCSE after cyst fenestration with transsphenoidal surgery, which was associated with pneumocephalus.

OBSERVATIONS

A 61-year-old man presented with visual impairment and was diagnosed with a suprasellar arachnoid cyst on magnetic resonance imaging (MRI). The patient received cyst fenestration with endonasal transsphenoidal surgery. His visual symptoms improved immediately after the operation; however, on postoperative day 3, semicoma appeared and was prolonged. The patient was diagnosed with NCSE due to pneumocephalus based on MRI and electroencephalography (EEG) findings. The administration of antiepileptic drugs (AEDs) improved his clinical symptoms and the abnormal findings on MRI and EEG.

LESSONS

This is the first case of NCSE with pneumocephalus after transsphenoidal surgery for a suprasellar arachnoid cyst. Pneumocephalus due to cerebrospinal fluid leakage can cause NCSE. Arterial spin labeling perfusion imaging and diffusion-weighted imaging are as useful for differentially diagnosing NCSE as EEG and AED tests.

Implications and limitations of magnetic resonance perfusion imaging with 1.5-Tesla pulsed arterial spin labeling in detecting ictal hyperperfusion during non-convulsive status epileptics

Background:

Recent our reports showed that 3-T pseudocontinuous arterial spin labeling (3-T pCASL) magnetic resonance perfusion imaging with dual post labeling delay (PLD) of 1.5 and 2.5 s clearly demonstrated the hemodynamics of ictal hyperperfusion associated with non-convulsive status epilepticus (NCSE). We aimed to examine the utility of 1.5-T pulsed arterial spin labeling (1.5-T PASL), which is more widely available for daily clinical use, for detecting ictal hyperperfusion.

Methods:

We retrospectively analyzed the findings of 1.5-T PASL with dual PLD of 1.5 s and 2.0 s in six patients and compared the findings with ictal electroencephalographic (EEG) findings.

Results:

In patients 1 and 2, we observed the repeated occurrence of ictal discharges (RID) on EEG. In patient 1, with PLDs of 1.5 s and 2.0 s, ictal ASL hyperperfusion was observed at the site that matched the RID localization. In patient 2, the RID amplitude was extremely low, with no ictal ASL hyperperfusion. In patient 3 with lateralized periodic discharges (LPD), we observed ictal ASL hyperperfusion at the site of maximal LPD amplitude, which was apparent at a PLD of 2.0 s but not 1.5 sec. Among three patients with rhythmic delta activity (RDA) of frequencies <2.5 Hz (Patients 4–6), we observed obvious and slight increases in ASL signals in patients 4 and 5 with NCSE, respectively. However, there was no apparent change in ASL signals in patient 6 with possible NCSE.

Conclusion:

The detection of ictal hyperperfusion on 1.5-T PASL might depend on the electrophysiological intensity of the epileptic ictus, which seemed to be more prominent on 1.5-T PASL than on 3-T pCASL. The 1.5-T PASL with dual PLDs showed the hemodynamics of ictal hyperperfusion in patients with RID and LPD. However, it may not be visualized in patients with extremely low amplitude RID or RDA (frequencies <2.5 Hz).

Arterial spin labeling hyperperfusion in seizures associated with non-ketotic hyperglycaemia: is it merely a post-ictal phenomenon?

A 53-year-old chronic uncontrolled diabetic patient presented with one episode of generalized seizures followed by drowsiness and post-ictal confusion. MR imaging at admission revealed left temporal subcortical T2/FLAIR hypointensities with overlying cortical T2/FLAIR hyperintensities and increased perfusion on arterial spin labeling (ASL). Follow-up imaging at 4- and 8-week interval revealed persistent ASL hyperperfusion with significant resolution of conventional MR imaging findings. Delayed persistent ASL hyperperfusion suggests that hyperglycemia-induced increased blood-brain barrier permeability rather than a mere post-ictal phenomenon in non-ketotic hyperglycemia (NKH) and may result in long-term cognitive disturbances.

Comparison of pseudocontinuous arterial spin labeling perfusion MR images and time-of-flight MR angiography in the detection of periictal hyperperfusion

Background

Magnetic resonance imaging (MRI), including perfusion MRI with three-dimensional pseudocontinuous arterial spin labeling (ASL) and diffusion-weighted imaging (DWI), are applied in the periictal (including ictal and postictal) detection of circulatory and metabolic consequences associated with epilepsy. Our previous report revealed that periictal hyperperfusion can firstly be detected on ASL, and cortical hyperintensity of cytotoxic edema secondarily obtained on DWI from an epileptically activated cortex. Although magnetic resonance angiography (MRA) using three-dimensional time-of-flight is widely used to evaluate arterial circulation, few MRA studies have investigated the detection of periictal hyperperfusion.

Methods

To compare the ability of ASL and MRA to detect the periictal hyperperfusion on visual inspection, we retrospectively selected 23 patients who underwent ASL and MRA examination on both periictal and interictal periods. Patients were divided into the following three groups according to periictal ASL/DWI findings: positive ASL and DWI findings (n = 13, ASL+/DWI+ group), positive ASL and negative DWI findings (n = 5, ASL+/DWI- group), and negative ASL and DWI findings (n = 5, ASL-/DWI- group).

Results

Periictal hyperperfusion on MRA was detected in 6 out of 13 patients (46.2%) in the ASL+/DWI+ group, but not in all patients in the ASL+/DWI- and ASL-/DWI- groups. Furthermore, in 5 out of these 6 patients, the diagnosis of periictal MRA hyperperfusion could not be made without referring to interictal MRA and/or periictal ASL findings, because the periictal MRA findings were so minute.

Conclusion

The minimum requirement for the development of periictal MRA hyperperfusion is that its epileptic event is intense enough to induce the uncoupling between metabolism and circulation, with the induction of glutamate excitotoxity, and severe cytotoxic edema on DWI. ASL is vastly superior to MRA in the detection of periictal hyperperfusion.

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ASL is superior to MRA in the detection of periictal hyperperfusion.

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Marked DWI hyperintensity is required to develop the MRA hyperperfusion.

Arterial Spin Labeling Magnetic Resonance Imaging for Differentiating Acute Ischemic Stroke from Epileptic Disorders

BACKGROUND

Differential diagnosis between acute ischemic stroke (AIS) and epilepsy-related stroke mimics is sometimes difficult in the emergency department. We investigated whether a combination of diffusion-weighted imaging (DWI) and arterial spin labeling imaging (ASL) is useful in distinguishing AIS from epileptic disorders.

METHODS

The study included suspected AIS patients who underwent emergency MRI including both DWI and ASL, and who exhibited DWI high-intensity lesions corresponding to neurological symptoms. We investigated the relationship between the ASL results from within and/or around DWI lesions and the final clinical diagnosis.

RESULTS

Eighty-five cases were included (mean age, 71 ± 13 years; 47 men). The time from onset to the MRI examination was 493 ± 536 minutes. ASL showed hyperintensity in 13 patients, isointensity in 43, and hypointensity in 29. All ASL hyperintensities were observed in the cortex, with 4 patients (31%) presenting with AIS and 9 (69%) with an epileptic disorder. All of the AIS patients with ASL hyperintensity were diagnosed with cardioembolic stroke (4/4, 100%), with magnetic resonance angiography demonstrating recanalization of the occluded artery in all cases (4/4, 100%). In the 9 patients with an epileptic disorder, the area of ASL hyperintensity typically extended beyond the vascular territory (7/9, 78%) and involved the ipsilateral thalamus (7/9, 78%). All patients with ASL isointensity and hypointensity were diagnosed with AIS; none had epileptic disorders.

CONCLUSIONS

Although cortical ASL hyperintensity can indicate cardioembolic stroke with recanalization, hyperintensity beyond the vascular territory may alternatively suggest an epileptic disorder in suspected AIS patients with DWI lesions.

What to Look for on Post-stroke Neuroimaging

The most feared complication after acute ischemic stroke is symptomatic or asymptomatic hemorrhagic conversion. Neuroimaging and clinical criteria are used to predict development of hemorrhage. Seizures after acute ischemic stroke or stroke-like symptoms from seizures are not common but may lead to confusion in the peristroke period, especially if seizures are repetitive or evolve into status epilepticus, which could affect neuroimaging findings. Malignant infarction develops when cytotoxic edema is large enough to lead to herniation and death. Post-stroke neuroimaging prognosticators have been described and should be assessed early so that appropriate treatment is offered before herniation leads to additional tissue injury.

Neuroimaging of status epilepticus

In the past 2 decades we have observed an extensive use of different neuroimaging techniques to evaluate patients with status epilepticus. Magnetic resonance imaging (MRI) in particular may show a broad spectrum of abnormalities that are either the causes or the consequences of sustained epileptic activity. Neuroimaging techniques can offer a contribution both in the clinical management of individual patients, identifying hemodynamic patterns that support the diagnosis, and also in the recognition of periictal reversible or irreversible alterations. For the future it is necessary to develop larger and prospective studies in which imaging techniques and electroencephalography (EEG) recordings are acquired closely to understand which EEG patterns are related to imaging biomarkers of neuronal damage.

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

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.

Arterial spin labeling: Clinical applications

Arterial spin labeling (ASL) is a magnetic resonance imaging perfusion technique that enables quantification of cerebral blood flow (CBF) without the use of intravenous gadolinium contrast. An understanding of the technical basis of ASL and physiologic variations in perfusion are important for recognizing normal variants and artifacts. Pathologic variations in perfusion can be seen in a number of disorders including acute and chronic ischemia, vasculopathy, vascular malformations, tumors, trauma, infection/inflammation, epilepsy and dementia.

Hemodynamic state of periictal hyperperfusion revealed by arterial spin-labeling perfusion MR images with dual postlabeling delay

Background

Magnetic resonance imaging (MRI), including perfusion MRI with arterial spin labeling (ASL) and diffusion-weighted imaging (DWI), are applied in the periictal detection of circulatory and metabolic consequences associated with epilepsy. Although previous report revealed that prolonged ictal hyperperfusion on ASL can be firstly detected and cortical hyperintensity of cytotoxic edema on DWI secondarily obtained from an epileptically activated cortex, the hemodynamic state of the periictal hyperperfusion has not been fully demonstrated.

Methods study-1

We retrospectively analyzed the relationship between seizure manifestations and the development of periictal MRI findings, in Case 1 with symptomatic partial epilepsy, who underwent repeated periictal ASL/DWI examination for three epileptic ictuses (one examination for each ictus). Study-2: We evaluated the hemodynamic state of periictal hyperperfusion with the ASL technique using a dual postlabeling delay (PLD) of 1.5 and 2.5 s in nine patients, according to the presence or absence of the localized epileptogenic lesion (EL) on conventional 3 T-MRI, who were divided into Group EL+ (six patients) and Group EL- (three patients).

Results

Study-1 confirmed that the stratified representation of the periictal MRI findings depends on the time interval between the ictal cessation and MRI examination in addition to the magnitude and duration of the epileptic activity. In Study-2, two types of periictal hyperperfusion were noted. In all six Group EL+ patients, periictal ASL findings showed "fast flow type". Markedly increased ASL signals were noted at the epileptically activated cortex, having a tight topographical relationship with EL, on ASL with a PLD of 1.5 s, which is decreased on ASL with a PLD of 2.5 s. In all three Group EL- patients, periictal ASL findings showed "gradual flow type", which is characterized by gradual signal increase of the epileptically activated cortex on ASL with a PLD of 1.5 and 2.5 s.

Conclusion

We confirmed that ASL hyperperfusion is superior to DWI in the periictal detection of epileptic events. ASL with dual PLD offers the ability to document two types of hemodynamics of periictal hyperperfusion.

Arterial spin labeling hyperperfusion in Rasmussen's encephalitis: Is it due to focal brain inflammation or a postictal phenomenon?

BACKGROUND AND PURPOSE

The study evaluated the utility of arterial spin labeling (ASL) perfusion imaging in Rasmussen's encephalitis (RE).

MATERIAL AND METHODS

The hospital electronic database was searched using the search words "encephalitis," "autoimmune encephalitis" and "Rasmussen's encephalitis" for the period of 1 Jan 2015 to 31 Jan 2017. Clinically diagnosed cases of RE for which epilepsy protocol magnetic resonance imaging (MRI) with perfusion imaging (ASL) performed on a 3T scanner were retrieved. The diagnosis of RE was based on Bien's criteria (Bien et al., 2005). We obtained patient's demographic details, clinical features, electrophysiological studies, and follow-up data from electronic hospital records.

RESULTS

We included nine patients with RE of whom seven patients showed increased perfusion, and two patients decreased perfusion. Among these patients, MRI changes of gyral hyperintensity without volume loss corresponded to regional ASL hyperperfusion in six patients and ASL hypoperfusion in one patient. Two patients who showed ASL hypoperfusion had corresponding atrophy on MRI. Eight patients of RE had epilepsia partialis continua (EPC) or daily seizures, and one patient was seizure-free post-surgery. Five patients showed a concordance of ASL hyperperfusion with clinical ictal onset zone. Among the seven patients with ASL hyperperfusion, the finding was concordant (complete or partial) with the electroencephalogram (EEG) ictal onset zone in six patients and with interictal epileptiform discharges (IED) in seven patients.

CONCLUSION

Increased perfusion in ASL of the involved brain parenchyma in RE is a common MRI finding and may be due to either active inflammation of the brain involved or a seizure-related finding.

Sequential changes of arterial spin-labeling perfusion MR images with dual postlabeling delay following reconstructive surgery for giant internal carotid artery aneurysm

BACKGROUND

Arterial spin-labeling magnetic resonance perfusion imaging (ASL-MRI) allows noninvasive measurement of cerebral blood flow (CBF) but depends on arterial transit time (ATT). To overcome this problem, we developed a simple ASL technique with dual postlabeling delay (PLD) settings. In addition to the routinely used PLD of 1.5 seconds, we selected another PLD of 2.5 seconds to assess slowly streaming blood flow and detect arterial transit artifacts (ATAs) resulting from stagnant intravascular magnetically labeled spins.

CASE DESCRIPTION

We validated the dual PLD method with digital subtraction angiography (DSA) findings in a patient with an unruptured right giant internal carotid artery (ICA) aneurysm who underwent proximal ligation of the right cervical ICA followed by right superficial temporal artery-middle cerebral artery anastomosis. The giant aneurysm was detected as a strongly hyperintense signal area of ATA using both values of PLD. Decreased signal in the right hemisphere at PLD 1.5 seconds was somewhat improved at PLD 2.5 seconds. DSA revealed that this laterality resulted from the different ATT values between hemispheres due to stagnation of the labeled spin within the aneurysm. Postoperatively, with gradual but complete thrombosis and regression of the aneurysm, the size of the ASL hyperintense signal area decreased markedly. At postoperative 2 years, the aneurysm was not demonstrated as an ATA; furthermore, the decreased signals in the right hemisphere at PLD 1.5 seconds had mostly improved.

CONCLUSION

Serial ASL-MRI with dual PLDs could show dynamic changes of giant aneurysms and the associated hemodynamic state following the surgery.

Identification of cerebral perfusion using arterial spin labeling in patients with seizures in acute settings

This study aimed to explore the utility of arterial spin labeling perfusion-weighted imaging (ASL-PWI) in patients with suspected seizures in acute settings. A total of 164 patients who underwent ASL-PWI for suspected seizures in acute settings (with final diagnoses of seizure [n = 129], poststroke seizure [n = 18], and seizure mimickers [n = 17]), were included in this retrospective study. Perfusion abnormality was analyzed for: (1) pattern, (2) multifocality, and (3) atypical distribution against vascular territories. Perfusion abnormality was detected in 39% (50/129) of the seizure patients, most (94%, 47/50) being the hyperperfusion pattern. Of the patients with perfusion abnormality, multifocality or hemispheric involvement and atypical distribution against vascular territory were revealed in 46% (23/50) and 98% (49/50), respectively. In addition, seizures showed characteristic features including hyperperfusion (with or without non-territorial distribution) on ASL-PWI, thus differentiating them from poststroke seizures or seizure mimickers. In patients in whom seizure focus could be localized on both EEG and ASL-PWI, the concordance rate was 77%. The present study demonstrates that ASL-PWI can provide information regarding cerebral perfusion status in patients with seizures in acute settings and has the potential to be used as a non-invasive imaging tool to identify the cerebral perfusion in patients with seizures.

The initial use of arterial spin labeling perfusion and diffusion-weighted magnetic resonance images in the diagnosis of nonconvulsive partial status epileptics

BACKGROUND

In the diagnosis of nonconvulsive status epilepticus (NCSE), capture of ongoing ictal electroencephalographic (EEG) findings is the gold standard; however, this is practically difficult without continuous EEG monitoring facilities. Magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI) and perfusion MRI with arterial spin labeling (ASL), have been applied mainly in emergency situations. Recent reports have described that ictal MRI findings, including ictal hyperperfusion on ASL and cortical hyperintensity of cytotoxic edema on DWI, can be obtained from epileptically activated cortex. We demonstrate the characteristics and clinical value of ictal MRI findings.

METHODS

Fifteen patients diagnosed as having NCSE (eight had complex partial status epilepticus (SE) and seven subtle SE) who underwent an initial MRI and subsequent EEG confrmation, participated in this study. Follow-up MRI and repeated routine EEG were performed.

RESULTS

In 11 patients (73%), ictal MRI findings were obtained on both DWI and ASL, while in four (27%) patients, ictal hyperperfusion was found on ASL without any DWI findings being obtained. In all 10 patients with an epileptogenic lesion, there was a tight topographical relationship between the lesion and the localization of ictal MRI findings. In the other five patients, ictal MRI findings were useful to demonstrate the pathophysiological mechanism of NCSE of non-lesional elderly epilepsy, or 'de novo' NCSE of frontal origin as situation-related NCSE. Ictal MRI findings are generally transient; however, in three cases they still persisted, even though ictal EEG findings had completely improved.

CONCLUSION

The present study clearly demonstrates that the initial use of ASL and DWI could help to diagnose partial NCSE and also combined use of the MRI and EEG allows documentation of the pathophysiological mechanism in each patient.

Signal changes on magnetic resonance perfusion images with arterial spin labeling after carotid endarterectomy

BACKGROUND

Cerebral hyperperfusion after carotid endarterectomy (CEA) is defined as an increase in ipsilateral cerebral blood flow (CBF). Practically, however, prompt and precise assessment of cerebral hyperperfusion is difficult because of limitations in the methodology of CBF measurement during the perioperative period. Arterial spin labeling (ASL) is a completely noninvasive and repeatable magnetic resonance perfusion imaging technique that uses magnetically-labelled blood water as an endogenous tracer. To clarify the usefulness of ASL in the management of cerebral hyperperfusion, we investigated signal changes by ASL with a single 1.5-s post-labeling delay on visual inspection.

METHODS

Thirty-two consecutive patients who underwent CEA were enrolled in this retrospective study.

RESULTS

On postoperative day 1, 22 (68.8%) and 4 (12.5%) patients exhibited increased ASL signals bilaterally (Group A) and on the operated side (Group B), respectively. Follow-up ASL showed improvement in these findings. Six (18.8%) patients showed no change (Group C). There was no apparent correlation between ASL signals on postoperative day 1 and the preoperative hemodynamic state, including the cerebrovascular reserve (P = 0.2062). Three (9.4%) patients developed cerebral hyperperfusion syndrome (two in Group A and one in Group B). Coincidence in the localization of increased ASL signals and electroencephalographic abnormalities was noted in these patients.

CONCLUSION

Visual analysis of ASL with a single post-labeling delay overestimates CBF and cannot identify patients at risk of cerebral hyperperfusion syndrome probably because of the strong effect of the shortened arterial transit time immediately after CEA. However, ASL may be used as for screening.

Stroke mimic diagnoses presenting to a hyperacute stroke unit

Stroke services have been centralised in several countries in recent years. Diagnosing acute stroke is challenging and a high proportion of patients admitted to stroke units are diagnosed as a non-stroke condition (stroke mimics). This study aims to describe the stroke mimic patient group, including their impact on stroke services. We analysed routine clinical data from 2,305 consecutive admissions to a stroke unit at St George's Hospital, London. Mimic groupings were derived from 335 individual codes into 17 groupings. From 2,305 admissions, 555 stroke mimic diagnoses were identified (24.2%) and 72% of stroke mimics had at least one stroke risk factor. Common mimic diagnoses were headache, seizure and syncope. Medically unexplained symptoms and decompensation of underlying conditions were also common. Median length of stay was 1 day; a diagnosis of dementia (p=0.028) or needing MRI (p=0.006) was associated with a longer stay. Despite emergency department assessment by specialist clinicians and computed tomography brain, one in four suspected stroke patients admitted to hospital had a non-stroke diagnosis. Stroke mimics represent a heterogeneous patient group with significant impacts on stroke services. Co-location of stroke and acute neurology services may offer advantages where service reorganisation is being considered.

Arterial Spin-Labeling Magnetic Resonance Perfusion Imaging with Dual Postlabeling Delay in Internal Carotid Artery Steno-occlusion: Validation with Digital Subtraction Angiography

BACKGROUND

Arterial spin-labeling magnetic resonance perfusion imaging (ASL-MRI) allows noninvasive measurement of cerebral blood flow (CBF) but depends on the arterial transit time (ATT). With the commonly used single postlabeling delay (PLD) of 1.5 seconds, slow flow through collateral vessels may be underestimated. We used both 1.5 and 2.5 seconds to overcome this problem. We validated these PLD settings by measuring the ATT and identifying the angiographic circulation using digital subtraction angiography (DSA).

METHODS

We retrospectively selected 5 patients with unilateral occlusion or stenosis of the internal carotid artery (ICA) in whom ASL-MRI showed low CBF with 1.5-second PLD in the target area and improved CBF with 2.5-second PLD. We then compared the ASL-MRI findings visually with DSA findings at 1.5 and 2.5 seconds after injection of the contrast. When arterial transit artifacts (ATAs), attributed to stagnant intravascular spin-labeled blood, were observed, DSA findings were analyzed visually at 4.5 seconds.

RESULTS

DSA revealed that the hypovascular area seen at 1.5 seconds was improved via the primary and secondary collaterals and delayed anterograde flow at 2.5 seconds. Serpiginous or round-shaped ATAs, which appeared in nearly the same configuration on dual PLD ASL-MRI, were attributed to stagnant collaterals and flow in the M2 portion of the middle cerebral artery and ICA during the late venous phase.

CONCLUSIONS

Use of dual PLD times was validated by the DSA findings. ATA detection using the dual PLDs also differentiated well-developed and stagnant collateral vessels from focal hyperperfusion.

Epileptic Ictal Hyperperfusion on Arterial Spin Labeling Perfusion and Diffusion-Weighted Magnetic Resonance Images in Posterior Reversible Encephalopathy Syndrome

BACKGROUND

The hemodynamic state of the posterior dominant vasogenic edema in posterior reversible encephalopathy syndrome (PRES) is controversial. The aim of this retrospective study was to examine the contribution of epileptic ictal hyperperfusion in patients with PRES using combined magnetic resonance perfusion imaging with arterial spin labeling (ASL) and diffusion-weighted magnetic resonance imaging (MRI).

METHODS

A detailed review of chronological MRI findings in 2 patients, including diffusion-weighted imaging (DWI) and ASL, with special reference to clinical and electroencephalographic findings, was performed. At the onset of PRES, both patients developed secondary generalized seizures.

RESULTS

At the first PRES episode in Case 1, ASL and DWI clearly depicted "ictal hyperperfusion" and prolonged epilepsy-induced cytotoxic edema in the left parieto-occipital lobe cortex, located around the vasogenic edema of the PRES lesion in the left occipital lobe (hypoperfused area). At the second and third episodes (2 and 7 months after the first episode, respectively), although recurrent PRES was ruled out, ASL and DWI clearly demonstrated ictal hyperperfusion in the left posterior temporal and parieto-occipital lobes associated with partial nonconvulsive status epilepticus, which developed around the PRES-related old hematoma lesion. In Case 2, peri-ictal MRI findings of ictal ASL hyperperfusion and cortical hyperintensity on DWI were also noted in the left parieto-occipital lobe, but were mild compared with Case 1.

CONCLUSIONS

Combined use of DWI and ASL can provide information on hemodynamic state associated with epileptic ictal hyperperfusion in the various phases of PRES.

A neuroradiologist's guide to arterial spin labeling MRI in clinical practice

Arterial spin labeling (ASL) is a non-invasive MRI technique to measure cerebral blood flow (CBF). This review provides a practical guide and overview of the clinical applications of ASL of the brain, as well its potential pitfalls. The technical and physiological background is also addressed. At present, main areas of interest are cerebrovascular disease, dementia and neuro-oncology. In cerebrovascular disease, ASL is of particular interest owing to its quantitative nature and its capability to determine cerebral arterial territories. In acute stroke, the source of the collateral blood supply in the penumbra may be visualised. In chronic cerebrovascular disease, the extent and severity of compromised cerebral perfusion can be visualised, which may be used to guide therapeutic or preventative intervention. ASL has potential for the detection and follow-up of arteriovenous malformations. In the workup of dementia patients, ASL is proposed as a diagnostic alternative to PET. It can easily be added to the routinely performed structural MRI examination. In patients with established Alzheimer’s disease and frontotemporal dementia, hypoperfusion patterns are seen that are similar to hypometabolism patterns seen with PET. Studies on ASL in brain tumour imaging indicate a high correlation between areas of increased CBF as measured with ASL and increased cerebral blood volume as measured with dynamic susceptibility contrast-enhanced perfusion imaging. Major advantages of ASL for brain tumour imaging are the fact that CBF measurements are not influenced by breakdown of the blood–brain barrier, as well as its quantitative nature, facilitating multicentre and longitudinal studies.