Canavan disease: diffusion magnetic resonance imaging findings

Brain Magnetic Resonance Imaging Findings in Poorly Controlled Homocystinuria

Homocystinuria is an inherited metabolic disorder most commonly caused by cystathionine β-synthase deficiency. Severe cases can cause white matter abnormalities that can mimic other vascular, toxic and metabolic disorders on computed tomography and magnetic resonance imaging. We present such a case which demonstrates not only extensive white matter abnormalities on magnetic resonance imaging, but also previously unreported basal ganglia signal abnormalities and imaging manifestations of increased intracranial pressure, likely caused by elevated methionine and betaine therapy. We also review the literature and discuss the potential underlying biologic mechanisms of these imaging findings.

Dentate Update: Imaging Features of Entities That Affect the Dentate Nucleus

The dentate nucleus is a cerebellar structure involved in voluntary motor function and cognition. There are relatively few entities that affect the dentate, and the clinical features of these conditions are often complex and nonspecific. Because these entities are rarely encountered, the formulation of a differential diagnosis can be difficult. Many of the conditions are reversible or treatable with early intervention. Therefore, it is important to recognize classic clinical presentations and their associated characteristic imaging findings. We provide a summary of entities that affect the dentate nucleus and a diagnostic workflow for approaching dentate nucleus imaging abnormalities.

Cytotoxic edema and diffusion restriction as an early pathoradiologic marker in canavan disease: case report and review of the literature

Background

Canavan disease is a devastating autosomal recessive leukodystrophy leading to spongiform degeneration of the white matter. There is no cure or treatment for Canavan disease, and disease progression is poorly understood.

Results

We report a new presentation of a patient found to have Canavan disease; brain magnetic resonance imaging (MRI) revealed white matter cytotoxic edema, indicative of an acute active destructive process. We performed a comprehensive review of published cases of Canavan disease reporting brain MRI findings, and found that cytotoxic brain edema is frequently reported in early Canavan disease.

Conclusions

Our results and the literature review support the notion of an acute phase in Canavan disease progression. These findings suggest that there is a window available for therapeutic intervention and support the need for early identification of patients with Canavan disease.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.

An atypical case of Canavan disease with stroke-like presentation

BACKGROUND

Canavan disease is an autosomal recessive leukodystrophy caused by a deficiency of aspartoacylase. The disease has a severe course, with death occurring in the first few years of life. Atypical patients with mild courses have been reported, but acute presentations similar to stroke have not been well described.

PATIENT DESCRIPTION

We present a boy who presented at 4 months of age with seizures after an episode of cardiopulmonary arrest is discussed.

RESULTS

He was initially thought to have an ischemic watershed stroke based on his initial clinical presentation and magnetic resonance imaging. However, biochemical and follow-up radiologic evaluation were consistent with mild Canavan disease. DNA sequencing of the ASPA gene indicated one known mutation (A305E) and a novel mutation, L30V. Follow-up magnetic resonance imaging did not reveal the atrophy which would have been expected with watershed ischemia. Magnetic resonance spectroscopy demonstrated elevated N-acetyl aspartate to creatinine and N-acetyl aspartate to choline ratios. At 4 years of age, he was normocephalic, with mild clumsiness, speech delay, and seizures.

CONCLUSIONS

This child's unusual acute presentation, along with his prolonged mild course, raises questions about the relationship between biochemical signs of abnormal aspartoacylase function and clinical findings. This patient highlights the need for long-term clinical follow-up of children with mild Canavan disease to clarify the significance of these biochemical abnormalities.

L-2 Hydroxyglutaric Aciduria: Magnetization Transfer Contrast and Diffusion Weighted Magnetic Resonance Imaging Findings

We describe the case of a 13-year-old male with ù aciduria. Conventional magnetic resonance imaging and diffusion weighted imaging disclosed some previously unreported findings. In particular, we observed an almost total sparing of early myelinated regions, and a restricted diffusion pattern in the dentate nuclei. Magnetization transfer contrast showed a normal range of values in early myelinated regions, and revealed abnormal values in the subcortical temporal white matter, internal capsule and globi palladi.

Genetic disorders associated with macrocephaly

Macrocephaly is associated with many genetic disorders and is a frequent cause of referral to the clinical geneticist. In this review we classify the commonly encountered macrocephaly disorders into useful categories and summarize recent genetic advances. Conditions where macrocephaly is a predominant aspect of the clinical presentation are discussed and a diagnostic approach to the common macrocephaly disorders is provided. Some emphasis is placed on familial macrocephaly (sometimes referred to as benign external hydrocephalus) and on the macrocephaly associated with autism spectrum disorders. The more recent conditions associated with the leukodystrophies and the organic acidurias are reviewed, but the well known conditions involving storage disorders and bone dysplasias are mentioned but not discussed. The genetic macrocephaly conditions cover a broad spectrum of gene disorders and their related proteins have diverse biological functions. As of yet it is not clear what precise biological pathways lead to generalized brain overgrowth.

Restricted diffusion in Canavan disease

INTRODUCTION

Canavan disease is a megalencephalic leukodystrophy due to deficiency of the enzyme aspartoacylase. Proton MR spectroscopy finding of elevated N-acetyl-L: -aspartate is considered diagnostic of Canavan disease.

CASE REPORT

We report a case of Canavan disease, which showed restricted diffusion in diffusion-weighted imaging and discuss the cause of it.

Canavan disease: A white matter disorder

Breakdown of oligodendrocyte-neuron interactions in white matter (WM), such as the loss of myelin, results in axonal dysfunction and hence a disruption of information processing between brain regions. The major feature of leukodystrophies is the lack of proper myelin formation during early development or the onset of myelin loss late in life. These early childhood WM diseases are described as hypomyelination or dysmyelination arising from a primary block in normal myelin synthesis because of a genetic mutation expressed in oligodendrocytes, or failure in myelination secondary to neuronal or astroglial dysfunctions (van der Knaap 2001 Dev. Med. Child Neurol. 43:705-712). Here, we describe the pathophysiological parameters of Canavan disease (CD), caused by genetic mutations of the aspartoacylase (ASPA) gene, a metabolic enzyme restricted in the central nervous system (CNS) to oligodendrocytes. CD presents pathophysiological dysfunctions similar to diseases caused by myelin gene mutations, such as Pelizaeus-Merzbacher disease (PMD) and several animal models, such as myelin deficient rat (md), jimpy (jp), shiverer (sh), and quaking (qk viable) mutant mice. These single gene mutations have pleiotropic effects, whereby the alteration of one myelin gene expression disrupts functional expression of other oligodendrocyte genes with an outcome of hypomyelination/dysmyelination. Among all of the known leukodystrophies, CD is the first disorder, which was approved and tested for the adeno-associated virus vector (AAV)-ASPA gene therapy (Leone et al. 2000 Ann. Neurol. 48:27-38; Janson et al. 2001 Trends Neurosci. 24:706-712) without much success following the first two attempts. ASPA gene delivery attempts in animal models have shown a lowering of N-acetyl L-aspartate and a change in motor functions, while sponginess of the WM, a characteristic of CD remained unchanged (Matalon et al. 2003 Mol. Ther. 7 (5, Part 1):580-587; McPhee et al. 2005 Brain Res. Mol. Brain Res. 135:112-121) even with better viral serotype and delivery of the gene during early phase of development (Klugmann et al. 2005 Mol. Ther. 11:745-753). While different approaches are being sought for the success of gene therapy, there are pivotal developmental questions to address regarding the specific regions of the CNS and cell lineages that become the target for the onset and progression of CD symptoms from early to late stages of development.

Diffusion-weighted MR imaging in leukodystrophies

Leukodystrophies are genetically determined metabolic diseases, in which the underlying biochemical abnormality interferes with the normal build-up and/or maintenance of myelin, which leads to hypo- (or arrested) myelination, or dysmyelination with resultant demyelination. Although conventional magnetic resonance imaging has significantly contributed to recent progress in the diagnostic work-up of these diseases, diffusion-weighted imaging has the potential to further improve our understanding of underlying pathological processes and their dynamics through the assessment of normal and abnormal diffusion properties of cerebral white matter. Evaluation of conventional diffusion-weighted and ADC map images allows the detection of major diffusion abnormalities and the identification of various edema types, of which the so-called myelin edema is particularly relevant to leukodystrophies. Depending on the nature of histopathological changes, stage and progression gradient of diseases, various diffusion-weighted imaging patterns may be seen in leukodystrophies. Absent or low-grade myelin edema is found in mucopolysaccharidoses, GM gangliosidoses, Zellweger disease, adrenomyeloneuropathy, L-2-hydroxyglutaric aciduria, non-ketotic hyperglycinemia, classical phenylketonuria, Van der Knaap disease and the vanishing white matter, medium grade myelin edema in metachromatic leukodystrophy, X-linked adrenoleukodystrophy and HMG coenzyme lyase deficiency and high grade edema in Krabbe disease, Canavan disease, hyperhomocystinemias, maple syrup urine disease and leukodystrophy with brainstem and spinal cord involvement and high lactate.

Diffusion-weighted MR imaging and MR spectroscopy in glutaric aciduria type 1

Although conventional magnetic resonance imaging (MRI) findings of glutaric aciduria type 1 (GA-1) have been well established, diffusion weighted MR imaging (DWI) and proton MR spectroscopy (MRS) findings are limited. We report widespread restricted diffusion in the white matter and increased diffusion in bilateral putamen in a case of GA-1. The MRS showed decreased N-acetyl-aspartate (NAA)/creatine (Cr) ratio compared with a sex and age-matched control with no significant change in choline (Cho)/Cr ratio. The presence of the lactate peak reflecting disturbed mitochondrial functions in this disease has never been reported.

Application of new MR techniques in pediatric patients

Pediatric neuroradiology is a fascinating and challenging field because there are normal changes associated with normal development and unique and unusual pathologies that occur in this population. The numerous new MR techniques first applied in the adult population are appropriate for use in the pediatric population, often with minimal modification of parameters. These new techniques will undoubtedly contribute significantly to use of pediatric neuroimaging, but the adult experience is not always directly transferable. The pediatric brain, particularly the immature brain is different in structure, has predilection for different types of disease processes, and may react differently to insults than the adult brain. As a result, the role of these techniques needs to be evaluated in the context of the pediatric brain and common pediatric disease processes.

L-2 hydroxyglutaric aciduria: proton magnetic resonance spectroscopy and diffusion magnetic resonance imaging findings

A 10-month-old boy was reported with the diagnosis of L-2 hydroxyglutaric aciduria. Amino acid chromatographic analysis revealed an 80-fold increase of hydroxyglutaric acid in the urine. Proton magnetic resonance (MR) spectroscopy of the brain obtained with the hybrid chemical shift imaging sequence (repetition time = 1,500 milliseconds, echo time = 40 milliseconds) revealed prominent peaks resonating at 2.50 ppm, which were attributable to L-2 hydroxyglutaric acid. Diffusion MR imaging was obtained using the echo-planar trace sequence (repetition time = 5,700 milliseconds, echo time = 139 milliseconds). Two different diffusion patterns were evident: a restricted diffusion pattern in the globi pallidi and an increased diffusion pattern in the white matter.