Alexander disease: An important mimicker of focal brainstem glioma

A Case Report of Adult-Onset Alexander Disease with a Tumor-Like Lesion in the Lateral Ventricle

Adult-onset Alexander disease (AOAD) is an autosomal dominant progressive astrogliopathy caused by pathogenic variants in glial fibrillary acidic protein (GFAP). Individuals with this disorder often present with a typical neuroradiologic pattern, including frontal white matter abnormality with contrast enhancement, atrophy and signal intensity changes of the medulla oblongata and upper cervical cord on MRI. Focal lesions are rarely seen in AOAD, which causes concern for primary malignancies. This study aimed to present the case of a 37-year-old male patient initially diagnosed with an astrocytoma in the lateral ventricle that was later identified as GFAP mutation-confirmed AOAD. GFAP sequencing revealed a heterogeneous missense mutation point c.236G>A. Hence, AOAD should be considered in patients with tumor-like lesion brain lesion in association with atrophy of medulla oblongata and upper cervical spinal cord, and frontal white matter abnormality with contrast enhancement.

Imaging pitfalls in paediatric posterior fossa neoplastic and non-neoplastic lesions

Paediatric posterior fossa lesions can have much overlap in their clinical and radiological presentation. There are, however, a number of key imaging features that can help the reading radiologist to distinguish tumours from important tumour mimics which are often inflammatory or metabolic entities. This pictorial review provides a number of important cases that proved challenging on imaging and illustrates some common pitfalls when interpreting lesions in the posterior fossa in children. Not everything that is abnormal will be a tumour, but often other causes are overlooked and misinterpreted as tumours, leading to great morbidity for that child. This article highlights some lesions that were mistaken as tumours and will introduce the reader to less commonly seen pathologies which are important to consider on a differential list for this location.

Alexander disease: an astrocytopathy that produces a leukodystrophy

Alexander Disease (AxD) is a degenerative disorder caused by mutations in the GFAP gene, which encodes the major intermediate filament of astrocytes. As other cells in the CNS do not express GFAP, AxD is a primary astrocyte disease. Astrocytes acquire a large number of pathological features, including changes in morphology, the loss or diminution of a number of critical astrocyte functions and the activation of cell stress and inflammatory pathways. AxD is also characterized by white matter degeneration, a pathology that has led it to be included in the "leukodystrophies." Furthermore, variable degrees of neuronal loss take place. Thus, the astrocyte pathology triggers alterations in other cell types. Here, we will review the neuropathology of AxD and discuss how a disease of astrocytes can lead to severe pathologies in non-astrocytic cells. Our knowledge of the pathophysiology of AxD will also lead to a better understanding of how astrocytes interact with other CNS cells and how astrocytes in the gliosis that accompanies many neurological disorders can damage the function and survival of other cells.

Pediatric brainstem gliomas: new understanding leads to potential new treatments for two very different tumors

Pediatric brainstem gliomas include low-grade focal brainstem gliomas (FBSG) and high-grade diffuse intrinsic pontine gliomas (DIPG). These tumors share a crucial and eloquent area of the brain as their location, which carries common challenges for treatment. Otherwise, though, these two diseases are very different in terms of presentation, biology, treatment, and prognosis. FBSG usually present with greater than 3 months of symptoms, while DIPG are usually diagnosed within 3 months of symptom onset. Surgery remains the preferred initial treatment for FBSG, with chemotherapy used for persistent, recurrent, or inoperable disease; conversely, radiation is the only known effective treatment for DIPG. Recent developments in biological understanding of both tumors have led to new treatment possibilities. In FBSG, two genetic changes related to BRAF characterize the majority of tumors, and key differences in their biological effects are informing strategies for targeted chemotherapy use. In DIPG, widespread histone H3 and ACVR1 mutations have led to new hope for effective targeted treatments. FBSG has an excellent prognosis, while the long-term survival rate of DIPG tragically remains near zero. In this review, we cover the epidemiology, biology, presentation, imaging characteristics, multimodality treatment, and prognosis of FBSG and DIPG, with a focus on recent biological discoveries.

Aquaporin-4 autoimmunity masquerading as a brainstem tumor

Brainstem glioma is a highly devastating disease, and any mass-like lesion in the brainstem can raise suspicion of this diagnosis. However, other inflammatory, demyelinating, or degenerative diseases can mimic brainstem glioma in clinical presentation and imaging features. Therefore, diagnosis based solely on imaging is often insufficient for brainstem lesions and may lead to incorrect diagnosis and treatment. This case report is the first description of central nervous system aquaporin-4 (AQP4) autoimmunity confined mainly to the brainstem. It demonstrates the wide spectrum of neuroinflammatory diseases in children and highlights the utility of surgical biopsy for suspicious brainstem lesions with atypical imaging features for glioma.

Alexander's disease: reassessment of a neonatal form

INTRODUCTION

Alexander disease is a disorder caused by a mutation and accumulation of the glial fibrillary acidic protein. Currently, three subtypes are acknowledged: an infantile, a juvenile, and an adult form. However, onset early in infancy or in the prenatal period has been shown to present with a uniform pattern of symptoms-suggesting the presence of a distinct neonatal form of the disease.

RESULTS AND DISCUSSION

Though the neonatal form of Alexander disease is not well acknowledged, a uniform and distinct presentation of the disease in neonates has been observed, suggesting the need for a different course of identification and treatment. Clinical presentation of the neonatal form is distinguished by leukodystrophy and generalized, frequent, and intractable seizures. While the infantile form presents with ataxia, hyperreflexia, and other upper motor neuron symptoms, none of these has been observed in the neonatal form. In the diagnosis of neonatal Alexander disease, it is essential to rule out other causes of leukodystrophy and the presence of neoplasms.

Magnetic resonance spectroscopy in the diagnostic evaluation of brainstem lesions in Alexander disease

Alexander disease is a progressive neurodegenerative disease, which can present with brainstem lesions with imaging characteristics similar to multifocal low-grade glioma, thus presenting a diagnostic dilemma. The authors report a 6-year-old child presenting with multifocal brainstem lesions subsequently diagnosed to have Alexander disease. In vivo magnetic resonance spectroscopy generated a metabolite profile of the lesion allowing differentiation from low-grade glioma. Magnetic resonance spectroscopy is a powerful tool in the assessment of brainstem lesions and is a useful adjunct to conventional magnetic resonance imaging in the assessment and diagnosis of atypical brain lesions.

[Metabolic disorders with typical alterations in MRI]

The classification of metabolic disorders according to the etiology is not practical for neuroradiological purposes because the underlying defect does not uniformly transform into morphological characteristics. Therefore typical MR and clinical features of some easily identifiable metabolic disorders are presented. Canavan disease, Pelizaeus-Merzbacher disease, Alexander disease, X-chromosomal adrenoleukodystrophy and adrenomyeloneuropathy, mitochondrial disorders, such as MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes) and Leigh syndrome as well as L-2-hydroxyglutaric aciduria are presented.