Serial diffusion-weighted imaging in a patient with MELAS and presumed cytotoxic oedema

Clinicoradiologic Criteria for the Diagnosis of Stroke-like Episodes in MELAS

Background and Objectives

Stroke-like episodes (SLEs) in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome are often misdiagnosed as acute ischemic stroke (AIS). We aimed to determine unique clinical and neuroimaging features for SLEs and formulate diagnostic criteria.

Methods

We retrospectively identified patients with MELAS admitted for SLEs between January 2012 and December 2021. Clinical features and imaging findings were compared with a cohort of patients who presented with AIS and similar lesion topography. A set of criteria was formulated and then tested by a blinded rater to evaluate diagnostic performance.

Results

Eleven MELAS patients with 17 SLE and 21 AISs were included. Patients with SLEs were younger (median 45 [37-60] vs 77 [68-82] years, p < 0.01) and had a lower body mass index (18 ± 2.6 vs 29 ± 4, p < 0.01), more commonly reported hearing loss (91% vs 5%, p < 0.01), and more commonly presented with headache and/or seizures (41% vs 0%, p < 0.01). The earliest neuroimaging test performed at presentation was uniformly a noncontrast CT. Two main patterns of lesion topography with a stereotypical spatiotemporal evolution were identified-an anterior pattern (7/21, 41%) starting at the temporal operculum and spreading to the peripheral frontal cortex and a posterior pattern (10/21, 59%) starting at the cuneus/precuneus and spreading to the lateral occipital and parietal cortex. Other distinguishing features for SLEs vs AIS were cerebellar atrophy (91% vs 19%, p < 0.01), previous cortical lesions with typical SLE distribution (46% vs 9%, p = 0.03), acute lesion tissue hyperemia and venous engorgement on CT angiography (CTA) (45% vs 0%, p < 0.01), and no large vessel occlusion on CTA (0% vs 100%, p < 0.01). Based on these clinicoradiologic features, a set of diagnostic criteria were constructed for possible SLE (sensitivity 100%, specificity 81%, AUC 0.905) and probable SLE (sensitivity 88%, specificity 95%, AUC 0.917).

Discussion

Clinicoradiologic criteria based on simple anamnesis and a CT scan at presentation can accurately diagnose SLE and lead to early administration of appropriate therapy.

Classification of Evidence

This study provides Class III evidence that an algorithm using clinical and imaging features can differentiate stroke-like episodes due to MELAS from acute ischemic strokes.

Clinical score for early diagnosis and treatment of stroke-like episodes in MELAS syndrome

BACKGROUND AND OBJECTIVES

Stroke-like episodes (SLEs) in patients with MELAS syndrome are often initially misdiagnosed as acute ischemic stroke (AIS), resulting in treatment delay. We aimed to determine clinical features that may distinguish SLEs from AISs and explore the benefit of early L-arginine treatment on patient outcomes.

METHODS

We looked retrospectively for MELAS patients admitted between January 2005 and January 2022 and compared them to an AIS cohort with similar lesion topography. MELAS patients who received L-arginine within 40 days of their first SLE were defined as the early treatment group and the remaining as late or no treatment group.

RESULTS

Twenty-three SLEs in 10 MELAS patients and 21 AISs were included. SLE patients had significantly different features: they were younger, more commonly reported hearing loss, lower body mass index, had more commonly a combination of headache and/or seizures at presentation, serum lactate was higher, and hemiparesis was less common. An SLE Early Clinical Score (SLEECS) was constructed by designating one point to each above features. SLEECS ≥ 4 had 80% sensitivity and 100% specificity for SLE diagnosis. Compared to late or no treatment, early treatment group patients (n = 5) had less recurrent SLEs (total 2 vs. 11), less seizures (14% vs. 25%, p = 0.048), lower degree of disability at first and last follow-up (modified ranking scale, mRS 2 ± 0.7 vs. 4.2 ± 1, p = 0.005; 2 ± 0.7 vs. 5.8 ± 0.5, p < 0.001, respectively), and a lower mortality (0% vs. 80% p = 0.048).

CONCLUSIONS

The SLEECS model may aid in the early diagnosis and treatment of SLEs and lead to improved clinical outcomes.

Monogenic Causes of Strokes

Strokes are the main cause of death and long-term disability worldwide. A stroke is a heterogeneous multi-factorial condition, caused by a combination of environmental and genetic factors. Monogenic disorders account for about 1% to 5% of all stroke cases. The most common single-gene diseases connected with strokes are cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) Fabry disease, mitochondrial myopathy, encephalopathy, lactacidosis, and stroke (MELAS) and a lot of single-gene diseases associated particularly with cerebral small-vessel disease, such as COL4A1 syndrome, cerebral autosomal recessive arteriopathy with subcortical infarcts and leukoencephalopathy (CARASIL), and Hereditary endotheliopathy with retinopathy, nephropathy, and stroke (HERNS). In this article the clinical phenotype for the most important single-gene disorders associated with strokes are presented. The monogenic causes of a stroke are rare, but early diagnosis is important in order to provide appropriate therapy when available.

Acute Cortical Lesions in MELAS Syndrome: Anatomic Distribution, Symmetry, and Evolution

BACKGROUND AND PURPOSE

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a rare mitochondrial disorder affecting children and young adults. Stroke-like episodes are often associated with acute cortical lesions in the posterior cerebral cortex and are classically described as asymmetric and transient. In this study we assessed the anatomic distribution of acute cortical lesions, the incidence of symmetry, and the temporal evolution of lesions.

MATERIALS AND METHODS

This was a retrospective cohort study of patients who had a confirmed genetic diagnosis of a pathogenic variant associated with MELAS and MR imaging performed at our center (2006-2018). Each MR imaging study was assessed for new lesions using T1, T2, FLAIR, DWI, ADC, and SWI. The anatomic location, symmetry, and temporal evolution of lesions were analyzed.

RESULTS

Eight patients with the same pathogenic variant of MELAS (MT-TL1 m.3243A>G) with 31 MR imaging studies were included. Forty-one new lesions were identified in 17 of the studies (5 deep, 36 cortical). Cortical lesions most commonly affected the primary visual cortex, the middle-third of the primary somatosensory cortex, and the primary auditory cortex. Thirty of 36 cortical lesions had acute cortical diffusion restriction, of which 21 developed cortical laminar necrosis on subacute imaging. Six of 11 studies with multiple lesions showed symmetric cortical involvement.

CONCLUSIONS

Acute cortical lesions in MELAS most commonly affect the primary visual, somatosensory, and auditory cortices, all regions of high neuronal density and metabolic demand. The most common pattern of temporal evolution is acute cortical diffusion restriction with subacute cortical laminar necrosis and chronic volume loss. Symmetric involvement is more common than previously described.

Diagnosis of adult-onset MELAS syndrome in a 63-year-old patient with suspected recurrent strokes - a case report

BACKGROUND

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) is a mitochondrial cytopathy caused by mutations in mitochondrial DNA. Clinical manifestation is typically before the age of 40.

CASE PRESENTATION

We present the case of a 63-year-old female in whom the symptoms of MELAS were initially misdiagnosed as episodes of recurrent ischemic strokes. Brain imaging including MRI, clinical and laboratory findings that lent cues to the diagnosis of MELAS are discussed. In addition, MRI findings in MELAS in comparison to imaging mimics of MELAS are presented.

CONCLUSIONS

This case underscores the importance of considering MELAS as a potential cause of recurrent stroke-like events if imaging findings are untypical for cerebral infarction, even among middle-aged patients with vascular risk factors.

Cerebral imaging in paediatric mitochondrial disorders

OBJECTIVES

Because the central nervous system (CNS) is the second most frequently affected organ in mitochondrial disorders (MIDs) and since paediatric MIDs are increasingly recognised, it is important to know about the morphological CNS abnormalities on imaging in these patients. This review aims at summarising and discussing current knowledge and recent advances concerning CNS imaging abnormalities in paediatric MIDs.

METHODS

A systematic literature review was conducted.

RESULTS

The most relevant CNS abnormalities in paediatric MIDs on imaging include white and grey matter lesions, stroke-like lesions as the morphological equivalent of stroke-like episodes, cerebral atrophy, calcifications, optic atrophy, and lactacidosis. Because these CNS lesions may be seen with or without clinical manifestations, it is important to screen all MID patients for cerebral involvement. Some of these lesions may remain unchanged for years whereas others may be dynamic, either in the sense of progression or regression. Typical dynamic lesions are stroke-like lesions and grey matter lesions. Clinically relevant imaging techniques for visualisation of CNS abnormalities in paediatric MIDs are computed tomography, magnetic resonance (MR) imaging, MR spectroscopy, single-photon emission computed tomography, positron-emission tomography, and angiography.

CONCLUSIONS

CNS imaging in paediatric MIDs is important for diagnosing and monitoring CNS involvement. It also contributes to the understanding of the underlying pathomechanisms that lead to CNS involvement in MIDs.

Other cerebrovascular occlusive disease

In this chapter we review the optimal imaging modalities for subacute and chronic stroke. We discuss the utility of computed tomography (CT) and multimodal CT imaging. Further, we analyze the importance of specific magnetic resonance imaging sequences, such as diffusion-weighted imaging for acute ischemic stroke, T2/fluid-attenuated inversion recovery for subacute and chronic stroke, and susceptibility imaging for detection of intracranial hemorrhages. Different ischemic stroke mechanisms are reviewed, and how these imaging modalities may aid in the determination of such. Further, we analyze how topographic patterns in ischemic stroke may provide important clues to the diagnosis, in addition to the temporal evolution of the stroke. Lastly, specific cerebrovascular occlusive diseases are reviewed, with emphasis on the optimal imaging modalities and their findings in each condition.

Review: Central nervous system involvement in mitochondrial disease

Mitochondrial respiratory chain defects are an important cause of inherited disorders affecting approximately 1 in 5000 people in the UK population. Collectively these disorders are termed ‘mitochondrial diseases’ and they result from either mitochondrial DNA mutations or defects in nuclear DNA. Although they are frequently multisystem disorders, neurological deficits are particularly common, wide‐ranging and disabling for patients. This review details the manifold neurological impairments associated with mitochondrial disease, and describes the efforts to understand how they arise and progressively worsen in patients with mitochondrial disease. We describe advances in our understanding of disease pathogenesis through detailed neuropathological studies and how this has spurred the development of cellular and animal models of disease. We underscore the importance of continued clinical, molecular genetic, neuropathological and animal model studies to fully characterize mitochondrial diseases and understand mechanisms of neurodegeneration. These studies are instrumental for the next phase of mitochondrial research that has a particular emphasis on finding novel ways to treat mitochondrial disease to improve patient care and quality of life.

Central Nervous System Imaging in Mitochondrial Disorders

Imaging of central-nervous-system (CNS) abnormalities is important in patients with mitochondrial disorders (MCDs) since the CNS is the organ second most frequently affected in MCDs and some of them are potentially treatable. Clinically relevant imaging techniques for visualization of CNS abnormalities in MCDs are computed tomography, magnetic resonance imaging, and MR-spectroscopy. The CNS abnormalities in MCDs visualized by imaging techniques include stroke-like lesions with cytotoxic or vasogenic edema, laminar cortical necrosis, basal ganglia necrosis, focal or diffuse white matter lesions, focal or diffuse atrophy, intra-cerebral calcifications, cysts, lacunas, hypometabolisation, lactacidosis, hemorrhages, cerebral hypo- or hyperperfusion, intra-cerebral artery stenoses, or moyamoya syndrome. The CNS lesions may proceed with or without clinical manifestations, why neuroimaging should be routinely carried out in all MCDs to assess the degree of CNS involvement. Some of these lesions may remain unchanged for years, some may show contiguous spread and progression, but some may even disappear, spontaneously or in response to medication. Dynamics of Stroke-like lesions may be positively influenced by L-arginine, dichloracetate, steroids, edavarone, or antiepileptics. Symptomatic treatment of CNS abnormalities in MCD patients may positively influence their outcome.

Quantitative measurement of cerebral oxygen extraction fraction using MRI in patients with MELAS

OBJECTIVE

To quantify the cerebral OEF at different phases of stroke-like episodes in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) by using MRI.

METHODS

We recruited 32 patients with MELAS confirmed by gene analysis. Conventional MRI scanning, as well as functional MRI including arterial spin labeling and oxygen extraction fraction imaging, was undertaken to obtain the pathological and metabolic information of the brains at different stages of stroke-like episodes in patients. A total of 16 MRI examinations at the acute and subacute phase and 19 examinations at the interictal phase were performed. In addition, 24 healthy volunteers were recruited for control subjects. Six regions of interest were placed in the anterior, middle, and posterior parts of the bilateral hemispheres to measure the OEF of the brain or the lesions.

RESULTS

OEF was reduced significantly in brains of patients at both the acute and subacute phase (0.266 ± 0.026) and at the interictal phase (0.295 ± 0.009), compared with normal controls (0.316 ± 0.025). In the brains at the acute and subacute phase of the episode, 13 ROIs were prescribed on the stroke-like lesions, which showed decreased OEF compared with the contralateral spared brain regions. Increased blood flow was revealed in the stroke-like lesions at the acute and subacute phase, which was confined to the lesions.

CONCLUSION

MRI can quantitatively show changes in OEF at different phases of stroke-like episodes. The utilization of oxygen in the brain seems to be reduced more severely after the onset of episodes in MELAS, especially for those brain tissues involved in the episodes.

Neuroimaging of rapidly progressive dementias, part 2: prion, inflammatory, neoplastic, and other etiologies

Most dementias begin insidiously, developing slowly and generally occurring in the elderly age group. The so-called rapidly progressive dementias constitute a different, diverse collection of conditions, many of which are reversible or treatable. For this reason, accurate identification and assessment of acute and subacute forms of dementia are critical to effective treatment; neuroimaging aids greatly in narrowing the diagnosis of these conditions. This second installment of a 2-part review of rapidly progressive dementias examines the use of imaging in an assortment of other etiologies in the differential diagnosis, from prion disease and neoplastic-related conditions to rare metabolic and other conditions such as Wernicke encephalopathy. In these clinical conditions, MR imaging has the potential to narrow this broad differential diagnosis and, at times, can definitively aid in the diagnosis of certain conditions on the basis of typical imaging patterns.

Perfusion status of the stroke-like lesion at the hyperacute stage in MELAS

Hypoperfusion on single-photon emission computed tomography (SPECT) of the stroke-like lesion (SLL) at the hyperacute stage of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) is considered to be a supportive evidence of the mitochondrial angiopathy theory. Our objectives were to examine whether other neuroimages, especially transcranial color-coded sonography (TCCS), done at the hyperacute stage of stroke-like episode (SLE) is consistent with hypoperfusion of the SLL. We reviewed the magnetic resonance imaging (MRI), SPECT, cerebral angiography, and TCCS of a patient with MELAS syndrome, all of which were performed at the hyperacute stage of one SLE. MRI on the 1st day post SLE showed right temporoparietal lesion with vasogenic edema. SPECT on the 2nd day showed focal decreased uptake of technetium-99m hexamethylpropyleneamine oxime ((99m)Tc-HMPAO) in the same region, but cerebral angiography and TCCS on the 3rd day showed increased regional cerebral blood flow (rCBF) and distal arteriole dilation in the same region. TCCS can delineate increased rCBF of the SLL at the hyperacute stage of SLE. We propose that the discrepancy between the decreased (99m)Tc-HMPAO uptake and increased rCBF might be caused by mitochondrial dysfunction. The phenomenon of "hypoperfusion" on SPECT might be caused by cell dysfunction but not decreased rCBF. We suggest that SPECT can be complemented by angiography and TCCS in future studies to delineate the perfusion status of SLLs.

Acute mitochondrial encephalopathy reflects neuronal energy failure irrespective of which genome the genetic defect affects

Mitochondrial dysfunction and disease may arise as a result of mutations in either the mitochondrial genome itself or nuclear encoded genes involved in mitochondrial homeostasis and function. Irrespective of which genome is affected, mitochondrial encephalopathies share clinical and biochemical features suggesting common pathophysiological pathways. Two common paradigms of mitochondrial encephalopathy are mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes caused by maternally transmitted mutations of mitochondrial DNA and mitochondrial spinocerebellar ataxia and epilepsy caused by recessively inherited mutations of the nuclear-encoded DNA polymerase gamma, which replicates and repairs the mitochondrial genome. We studied and compared the disease mechanisms involved in these two syndromes. Despite having different genetic origins, their pathophysiological pathways converge on one critical event, damage to the respiratory chain leading to insufficient energy to maintain cellular homeostasis. In the central nervous system, this appears to cause selective neuronal damage leading to the development of lesions that mimic ischaemic damage, but which lack evidence of decreased tissue perfusion. Although these stroke-like lesions may expand or regress dynamically, the critical factor that dictates prognosis is the presence of epilepsy. Epileptic seizures increase the energy requirements of the metabolically already compromised neurons establishing a vicious cycle resulting in worsening energy failure and neuronal death. We believe that it is this cycle of events that determines outcome and which provides us with a mechanistic structure to understand the pathophysiology of acute mitochondrial encephalopathies and plan future treatments.

Neuroimaging of stroke-like episodes in MELAS

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) shows sudden neurological deficits that are called 'stroke-like episodes'. With regard to the pathophysiology of stroke-like episodes, so-called mitochondrial angiopathy and cytopathy theories have been proposed, but the subject is still controversial. To clarify this matter and to contribute to the development of a treatment for MELAS, we review here current neuroimaging research and consider the pathophysiology of stroke-like lesions. With regard to diffusion-weighted imaging findings, early reports often showed an elevated apparent diffusion coefficient (ADC) in stroke-like lesions; this was considered to be mainly vasogenic edema in the acute phase and is a different pattern than that in stroke. However, there has recently been an increase in the number of reports of a decrease in ADC; these cases are considered to be cytotoxic edema in the acute phase, which is compatible with stroke. With regard to (1)H-magnetic resonance spectroscopy findings in stroke-like lesions, a decrease in N-acetylaspartate and an increase in lactate have been reported. With regard to single photon emission computed tomography findings for stroke-like lesions in MELAS, an overall trend is hyperperfusion in the acute stage (within 1 month) of stroke-like episodes and hypoperfusion in the chronic stage (several months later). With regard to positron emission tomography, nearly all of these reports are consistent with the mitochondrial cytopathy theory. With regard to neuropathology in MELAS, the most common findings during the chronic stage of stroke-like episodes include foci of necrosis and peculiar vascular changes (abnormalities of mitochondria in small arteries). Concerning the pathology of the acute stage of stroke-like episodes, extensive petechial hemorrhage along the gyri of the cortex corresponding to acute stroke-like lesions has been reported. To clarify the true pathophysiology of stroke-like episodes, we offer three suggestions. First, we must define the precise onset of stroke-like episodes. Second, current studies are limited by the difficulty of imaging just before and just after (within a few minutes) the onset of stroke-like episodes. Third, we hope to establish an experimental animal model. We should conduct a simultaneous multimodal imaging and histological study just before and just after (within a few minutes) the onset of stroke-like episodes in an experimental animal model.

Diffusion and perfusion characteristics of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) in thirteen patients

Objective

We analyzed the diffusion and perfusion characteristics of acute MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode) lesions in a large series to investigate the controversial changes of the apparent diffusion coefficient (ADC) that were reported in prior studies.

Materials and Methods

We analyzed 44 newly appearing lesions during 28 stroke-like episodes in 13 patients with MELAS. We performed a visual assessment of the MR images including the ADC and perfusion maps, comparison of the ADC between the normal and abnormal areas, comparison of % ADC between the 44 MELAS lesions and the 30 acute ischemic infarcts. In addition, the patterns of evolution on follow-up MR images were analyzed.

Results

Decreased, increased, and normal ADCs were noted in 16 (36%), 16 (36%), and 12 (27%) lesions, respectively. The mean % ADC was 102 ± 40.9% in the MELAS and 64 ± 17.8% in the acute vascular infarcts (p < 0.001), while perfusion imaging demonstrated hyper-perfusion in six acute MELAS lesions. On follow-up images, resolution, progression, and tissue loss were noted in 10, 4, and 17 lesions, respectively.

Conclusion

The cytotoxic edema gradually evolves following an acute stroke-like episode in patients with MELAS, and this may overlap with hyper-perfusion and vasogenic edema. The edematous swelling may be reversible or it may evolve to encephalomalacia, suggesting irreversible damage.

The appearance of ADCs in the non-affected areas of the patients with MELAS

INTRODUCTION

The exact mechanism of the mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) remain unclear. Diffusion-weighted imaging (DWI) is a magnetic resonance (MR) imaging technique for studying the pathophysiologic change of the MELAS. The purpose of the study is to see whether the apparent diffusion coefficient (ADC) of MELAS in the non-affected areas is different from the ADC of the normal subjects and to speculate the pathophysiological mechanisms of the MELAS.

METHODS

Sixteen cases of MELAS were retrospectively analyzed. Thirty healthy subjects were chosen to constitute the control group. All of them were performed on the 3.0T whole-body MR scanner with axial view T2 fluid attenuated inversion recovery (flair), T2-weighted imaging, T1flair, and DWI. An ADC map was reconstructed in the workstation. Two to five regions of interest were put in the non-affected frontal lobe and basal ganglia. All data took statistical analysis.

RESULTS

There were significant differences between the ADC of the patients with MELAS and the controls in the non-affected areas, including the superior frontal gyrus, precentral gyrus, corpus striatum, thalamus, and white matter of the semi-oval centrum.

CONCLUSION

ADCs in the non-affected areas of the patients with MELAS are higher than those of the normal subjects. Pathological changes take place in the non-affected areas of the patients with MELAS.

Multiple sclerosis with initial stroke-like clinicoradiologic features: case report and literature review

A 17-year-old male presented with sudden onset of persistent focal neurological symptoms. Magnetic resonance imaging (MRI) demonstrated a nonenhancing white matter lesion that appeared hyperintense on fluid-attenuated inversion recovery sequence and diffusion-weighted imaging, while hypointense on apparent diffusion coefficient mapping corresponding to the patient's clinical features. A smaller subclinical lesion was also present. The patient's history, radiographic findings, and initial hospital course including response to treatment appeared supportive of a stroke diagnosis. However, a rapid recovery from his severe neurological deficits and results of subsequent serologic testing strongly indicated a demyelinating condition. The onset of adolescent multiple sclerosis can present diagnostic and therapeutic challenges, especially when the initial demyelinating event resembles an acute stroke in clinical and radiographic presentation. Every effort should be made to distinguish these diagnoses as early as possible to ensure timely and appropriate management.

MRI of sporadic Creutzfeldt-Jakob disease

The key MRI findings in five cases of sporadic Creutzfeldt-Jakob disease (CJD) are illustrated with four 'definite' and one 'probable' according to World Health Organization criteria. Close attention to fluid-attenuation inversion recovery and diffusion-weighted imaging sequences are important for diagnosis, noting especially restricted diffusion in cortical and deep grey matter. Our study and those of others show predominant cortical, caudate and thalamic involvement. This pattern is highly sensitive and specific for the diagnosis. Fluid-attenuation inversion recovery and diffusion-weighted imaging signal abnormality becomes progressively more extensive and bilateral as disease progresses, but may become less pronounced in end-stage disease because of atrophy.

Serial brain imaging analysis of stroke-like episodes in MELAS

We report 2 patients of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) and consider the pathophysiology of stroke-like lesions, using magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI) on MRI, perfusion imaging on MRI, and 1H magnetic resonance spectroscopy (1H-MRS). In Patient 1, T2-weighted imaging (T2-WI) on MRI at onset and even at 44 days after onset of the stroke-like episode showed high intensity in left parietal, temporal, and occipital lobe lesions. In the temporal lobe lesion, the apparent diffusion coefficient (ADC) at 44 days after onset was higher (average: 1.219x10(-3)mm2/s) than that in a normal region (average: 0.796x10(-3)mm2/s). (1)H-MRS of the left parietal lobe lesion at the same day showed a decrease in N-acetylaspartate/(creatine+phosphocreatine) (NAA/Cr) (0.43) and a peak in lactate. 1H-MRS of the contralateral side at the same day showed NAA/Cr (1.57) and no peak in lactate. Thereafter, ADC gradually decreased and NAA/Cr gradually increased, and the peak in lactate disappeared in the lesion. In Patient 2, T2-WI at onset showed high intensity in bilateral occipital lobe lesions. In the left occipital lobe lesion, ADC at the same day was higher (1.082x10(-3)mm2/s) than that in a normal region (average: 0.841x10(-3)mm2/s). (1)H-MRS of the left occipital lobe lesion at the same day showed a decrease of NAA (3.0mM) and a peak in lactate (13.1mM) (measured by LCModel). In 1H-MRS of the normal left parietooccipital lobe at 4 months before onset, NAA was 7.6mM and there was no peak in lactate (0mM). Perfusion imaging at onset showed high intensity in bilateral occipital lobes, which indicated hyperperfusion in stroke-like lesions. Thereafter, ADC gradually decreased and the peak in lactate partially decreased, and the low concentration of NAA persisted (regardless of the partial recovery) in the lesion. These results suggest that the stroke-like episodes is related to vasogenic edema, hyperperfusion, and neuronal damage. Acute oxidative phosphorylation defect may have a crucial role in the pathophysiology of stroke-like episodes.

Diffusion-weighted imaging of the brain in infants and children

During the last decade, diffusion-weighted imaging (DWI) has become an important tool in the evaluation of a variety of disorders of the central nervous system in children. DWI relies on variability in the diffusivity of water molecules in the presence of a supplemental diffusion-sensitizing gradient to produce image contrast. Pathologic states alter the diffusion characteristics of brain water in a reproducible fashion. In this review, the DWI appearances of a number of common abnormalities of the brain in infants and children are presented.

Brain Magnetic Resonance in the Diagnostic Evaluation of Mitochondrial Encephalopathies

Brain MR imaging techniques are important ancillary tests in the diagnosis of a suspected mitochondrial encephalopathy since they provide details on brain structural and metabolic abnormalities. This is particularly true in children where non-specific neurologic symptoms are common, biochemical findings can be marginal and genetic defects may be not discovered. MR imaging modalities include conventional, or structural, imaging (MRI) and functional, or ultrastructural, imaging (spectroscopy, MRS; diffusion, DWI-ADC; perfusion, DSCI—ASL). Among them MRI and MRS are the main tools for diagnosis and work up of MD, and this review will focus mainly on them. The MRI findings of MD are very heterogeneous, as they depend on the metabolic brain defects, age of the patient, stage and severity of the disease. No correlation has been found between genetic defects and neuroimaging picture; however, some relationships between MR findings and clinical phenotypes may be identified. Different combinations of MRI signal abnormalities are often encountered but the most common findings may be summarized into three main MR patterns: (i) non-specific; (ii) specific; (iii) leukodystrophic-like. Regarding the functional MR techniques, only proton MRS plays an important role in demonstrating an oxidative metabolism impairment in the brain since it can show the accumulation of lactate, present as a doublet peak at 1.33 ppm. Assessment of lactate should be always performed on brain tissue and on the ventricular cerebral spinal fluid. As for MRI, metabolic MRS abnormalities can be of different types, and two distinct patterns can be recognized: non-specific and specific. The specific metabolic profiles, although not frequent to find, are highly pathognomonic of MD. The un-specific metabolic profiles add value to structural images in allowing to define the lesion load and to monitor the response to therapy trials.

Diffusion weighted MR imaging in non-infarct lesions of the brain

Diffusion weighted imaging (DWI) is a relatively new method in which the images are formed by the contrast produced by the random microscopic motion of water molecules in different tissues. Although DWI has been tried for different organ systems, it has been found its primary use in the central nervous system. The most widely used clinical application is in the detection of hyperacute infarcts and the differentiation of acute or subacute infarction from chronic infarction. Recently DWI has been applied to various other cerebral diseases. In this pictorial paper the authors demonstrated different DWI patterns of non-infarct lesions of the brain which are hyperintense in the diffusion trace image, such as infectious, neoplastic and demyelinating diseases, encephalopathies - including hypoxic-ischemic, hypertensive, eclamptic, toxic, metabolic and mitochondrial encephalopathies - leukodystrophies, vasculitis and vasculopathies, hemorrhage and trauma.

Diffusion-weighted MR imaging of early-stage Creutzfeldt-Jakob disease: typical and atypical manifestations

Creutzfeldt-Jakob disease causes progressive dementia and, eventually, death. The infectious agent is thought to be proteinaceous scrapie particles. Prompt diagnosis is essential to prevent human-to-human transmission. Progressive brain atrophy and areas of high signal intensity in the cerebral cortex and basal ganglia are well-known features of Creutzfeldt-Jakob disease depicted on T2-weighted magnetic resonance (MR) images. However, in the early stage of disease, the appearance of the brain on T2-weighted MR images often is normal, and it may be impossible on that basis to reach a diagnosis. Diffusion-weighted imaging therefore has gained attention as a useful modality for the early diagnosis of Creutzfeldt-Jakob disease. Even before the appearance of the characteristic periodic synchronous discharges on the electroencephalogram, diffusion-weighted images in most cases of Creutzfeldt-Jakob disease depict areas of abnormal signal hyperintensity in the cortex and in the basal ganglia or thalamus. These imaging abnormalities are accompanied by decreased apparent diffusion coefficient values suggestive of restricted diffusion within the tissue. However, if diffusion-weighted imaging findings of abnormal high signal intensity are restricted to the cerebral cortex, it may be necessary to differentiate between Creutzfeldt-Jakob disease and other conditions that may produce progressive dementia (eg, venous hypertensive en-cephalopathy; chronic herpes encephalitis; and the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes).

Central nervous system manifestations of mitochondrial disorders

The central nervous system (CNS) is, after the peripheral nervous system, the second most frequently affected organ in mitochondrial disorders (MCDs). CNS involvement in MCDs is clinically heterogeneous, manifesting as epilepsy, stroke-like episodes, migraine, ataxia, spasticity, extrapyramidal abnormalities, bulbar dysfunction, psychiatric abnormalities, neuropsychological deficits, or hypophysial abnormalities. CNS involvement is found in syndromic and non-syndromic MCDs. Syndromic MCDs with CNS involvement include mitochondrial encephalomyopathy, lactacidosis, stroke-like episodes syndrome, myoclonic epilepsy and ragged red fibers syndrome, mitochondrial neuro-gastrointestinal encephalomyopathy syndrome, neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome, mitochondrial depletion syndrome, Kearns-Sayre syndrome, and Leigh syndrome, Leber's hereditary optic neuropathy, Friedreich's ataxia, and multiple systemic lipomatosis. As CNS involvement is often subclinical, the CNS including the spinal cord should be investigated even in the absence of overt clinical CNS manifestations. CNS investigations comprise the history, clinical neurological examination, neuropsychological tests, electroencephalogram, cerebral computed tomography scan, and magnetic resonance imaging. A spinal tap is indicated if there is episodic or permanent impaired consciousness or in case of cognitive decline. More sophisticated methods are required if the CNS is solely affected. Treatment of CNS manifestations in MCDs is symptomatic and focused on epilepsy, headache, lactacidosis, impaired consciousness, confusion, spasticity, extrapyramidal abnormalities, or depression. Valproate, carbamazepine, corticosteroids, acetyl salicylic acid, local and volatile anesthetics should be applied with caution. Avoiding certain drugs is often more beneficial than application of established, apparently indicated drugs.

Pitfalls in the diagnosis of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes

We describe a patient with genetically- and biochemically-proven mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) who was initially misdiagnosed as having had multiple ischemic strokes in part because the clinical presentation appeared to be acute, the MRI of lesions showed restricted diffusion, and the brain biopsy showed features suggestive of stroke. This report emphasizes the pitfalls in the diagnosis of MELAS and points out the similarities and differences between MELAS and ischemic stroke.

Diffusion-weighted MR imaging: pediatric clinical applications

We have summarized the diffusion-weighed imaging (DWI) findings in a number of different cerebral disorders. In many cases, DWI with the accompanying apparent diffusion coefficient (ADC) map provides additional useful information to the standard imaging sequences. Pathophysiologic mechanisms resulting in baseline normal ADC values and changes with disease processes are not well understood; therefore, caution should be used when prognosticating the outcome of regions with abnormal ADCs. DWI should be used as an adjunct to routine imaging and interpreted in the context of the routine imaging findings and clinical scenario. As our understanding of ADC mechanisms increases and we begin to incorporate information about tissue organization from diffusion tensor imaging or diffusion spectrum imaging, the role of these methods in clinical diagnosis should continue to increase.

Diffusion-weighted MR imaging in patients with phenylketonuria: relationship between serum phenylalanine levels and ADC values in cerebral white matter

PURPOSE

To prospectively determine the relationship between serum phenylalanine levels and apparent diffusion coefficient (ADC) values in the cerebral white matter of patients with phenylketonuria (PKU).

MATERIALS AND METHODS

Institutional review board approval was obtained, and participants provided informed consent. Magnetic resonance (MR) imaging, which included T1- and T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and diffusion-weighted examinations, was performed in 21 patients with PKU (nine male and 12 female patients; age range, 3-44 years; mean age, 19.4 years). ADC values in deep cerebral white matter were calculated for each patient. Serum phenylalanine levels were obtained in all patients within 12 days after MR imaging. Serum phenylalanine levels were measured in 16 patients 1 year before MR imaging. ADC values in cerebral white matter and serum phenylalanine levels were compared. A total of 21 control subjects (12 male and nine female patients; age range, 3-33 years; mean age, 20.6 years) underwent MR imaging. ADC values in cerebral white matter were compared with serum phenylalanine levels by using the Pearson correlation.

RESULTS

Abnormal high signal intensity in white matter on T2-weighted and FLAIR MR images was noted in patients with PKU who had serum phenylalanine levels of more than 8.5 mg/dL (514.2 micromol/L). Diffusion in posterior deep cerebral white matter tended to be restricted in patients when increased serum phenylalanine levels were measured after MR imaging (r = -0.62). There was a correlation between ADC values in posterior cerebral white matter and serum phenylalanine levels measured 1 year before MR imaging (r = -0.77). ADCs of control subjects were significantly higher than ADCs of patients with PKU (P < .005).

CONCLUSION

Posterior deep white matter in patients with PKU and a serum phenylalanine level of more than 8.5 mg/dL showed high signal intensity in white matter on T2-weighted and FLAIR MR images and revealed decreased ADC. We suggest that to avoid brain-restricted diffusion due to hyperphenylalanemia, patients with PKU should maintain serum phenylalanine levels of less than 8.5 mg/dL (514.2 micromol/L).

A neuroimaging approach to inborn errors of metabolism

There are numerous neurodegenerative and neurometabolic disorders of childhood. Individually, however, they are quite rare. Some may be seen only once in a lifetime at a given medical center, even one devoted to the specialized care of children. This article presents the classic neuroimaging features of some of the more commonly seen entities and of some of the more recently described metabolic disorders.