Cerebral microbleeds: Causes, clinical relevance, and imaging approach - A narrative review.

With advances in magnetic resonance imaging (MRI) sequences, there has been increased identification of microbleed/microhemorrhage across different population ages, but more commonly in the older age group. These are defined as focal areas of signal loss on gradient echo MRI sequences (T2* and susceptibility-weighted images), which are usually <5 mm in size representing hemosiderin deposition with wide ranges of etiologies. Susceptibility-weighted imaging (SWI) has become a routine MRI sequence for practices across the globe resulting in better identification of these entities. Over the past decade, there has been a better understanding of the clinical significance of microbleeds including their prognostic value in ischemic and hemorrhagic stroke. Cerebral amyloid angiopathy and hypertension are the two most common causes of microbleeds following peripheral and central pattern, respectively. In the younger age group, microbleeds are more common due to familial conditions or a wide range of hypercoagulable states. This review outlines the pathophysiology, prevalence, and clinical implications of cerebral microhemorrhage along with a brief discussion about the technical considerations of SWI.

Monorhinal and Birhinal Odor Processing in Humans: an fMRI investigation.

The olfactory nerve, also known as cranial nerve I, is known to have exclusive ipsilateral projections to primary olfactory cortical structures. It is still unclear whether these projections also correspond to functional pathways of odor processing. In an olfactory functional magnetic resonance imaging (fMRI) study of twenty young healthy subjects with a normal sense of smell, we tested whether nostril specific stimulation with phenyl ethyl alcohol (PEA), a pure olfactory stimulant, asymmetrically activates primary or secondary olfactory-related brain structures such as primary olfactory cortex, entorhinal cortex, and orbitofrontal cortex. The results indicated that without a challenging olfactory task, passive (no sniffing) and active (with sniffing) nostril-specific PEA stimulation did not produce asymmetrical fMRI activation in olfactory cortical structures.

Value of quantitative apparent diffusion coefficients in differentiating low-grade gliomas from mixed neuronal-glial tumors.

Purpose: To retrospectively assess if diffusion-weighted MR imaging (DWI) and quantitative apparent-diffusion coefficient (ADC) maps could be used to differentiate between low-grade gliomas (LGGs) and mixed neuronal-glial tumors (MNGTs including Dysembryoplastic Neuroepithelial Tumor and Ganglioglioma). Materials and methods: We retrospectively searched the clinical, pathological, and radiological databases for a span of 9 years and identified 24 patients with biopsy proven LGG. This included WHO (fourth edition) grade I and II tumors including astrocytoma, oligoastrocytoma and oligodendrogliomas. We also identified 22 patients with MNGTs (WHO grade I) including 13 patients with DNET and 9 patients with Ganglioglioma. All patients with pathologically confirmed tumors who had MRI including DWI sequence were included in the study. Regions of interest (ROIs) of 0.1-0.15 cm2 were manually positioned on the ADC maps and multiple values (10-6 mm2/s) were obtained including the ADCmean. Optimal thresholds of ADC values and ADC ratios for distinguishing low-grade gliomas from mixed neuronal-glial tumors were determined by receiver operating characteristic (ROC) curve analysis. Results: All the four ADC measurement variables, including the minimum (ADC min), the (ADC max) maximum, the mean of ADC values (ADC mean) and the ADC ratios (ADC mean/ADCnormal) showed significant difference between the MNGTs and LGGs. The most significant difference was seen with the maximum ADC value (ADC max) of the tumor where the values for LGGs were 1317 ± 314 whereas the values for MNGTs were 2134 ± 438. In both subsets of patients with MNGTs (DNET and Ganglioglioma), this difference was statistically significant (P = .015 and P = .0066, respectively). However, there was no significant difference between the ADC values of these subtypes of MNGTs. Conclusion: The ADC values of MNGTs are significantly higher compared to LGGs and can be helpful in radiological demarcation of these two conditions. The high ADC of MNGTs may be attributable to the presence of large extracellular spaces and their cellularity, which is much lower than that of pure glial neoplasms.

Congenital Malformations of Cerebellum.

Advances in pre and postnatal neuroimaging techniques, and molecular genetics have increased our understanding of the congenital malformation of the brain. Correct diagnosis of these malformations in regards to embryology, and molecular neurogenetics is of paramount importance to understand the inheritance pattern and risk of recurrence. Lesions detected on prenatal imaging require confirmation either with postnatal ultrasound and/or with MR imaging. With the advent of the faster (rapid) MRI techniques, which can be conducted without sedation, MRI is commonly used in the evaluation of congenital malformation of the brain. Based on neuroimaging pattern, the congenital malformations of the posterior fossa are classified into 4 main categories: (a) predominantly cerebellar, (b) cerebellar and brainstem, (c) predominantly brainstem, and (d) predominantly midbrain malformations.

Imaging of Premature Infants.

According to the World Health Organization (WHO), 15 million babies are born preterm each year. Preterm infants are those born at less than 37 weeks, while extremely and very preterm neonates include those born at 22 to less than 32 weeks gestational age. Infants that fail to make it to term are missing a key part in neurodevelopment, as weeks 24 to 40 are a critical period of brain development. Neonatal brain injury is a crucial predictor for mortality and morbidity in premature and low birth weight (<1500 g) infants. Although the complications associated with preterm birth continue to be the number one cause of death in children under 5, the survival rates are increasing (Volpe, 2019). Despite this, the incidence of comorbidities, such as learning disabilities and visual and hearing problems, is still high. The functional deficits seen in these infants can be contributed to the white matter abnormalities (WMA) that have been found in 50% to 80% of extremely and very preterm neonates. While numerous, the etiology of the neonatal brain injury is essential for determining the mortality and morbidities of the infant, as there is an increased risk for both intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL), which can be attributed to their lack of cerebrovascular autoregulation and hypoxic events. Neuroimaging plays a key role in detecting and assessing these neurologic injuries that preterm infants are at risk for. It is essential to diagnose these events early on to assess neurologic damage, minimize disease progression, and provide supportive care. Brain MRI and cranial ultrasound (CUS) are both extensively used neuroimaging techniques to assess WMA, and it has become ever more important to determine the best imaging techniques and modalities with the increasing survival rates and high incidence of comorbidities among these infants.

Imaging of Microcephaly.

One of the most common definitions of microcephaly cited is that of an occipitofrontal circumference (OFC) of the head that is less than two standard deviations below the average for age (or gestational age, if identified prenatally) and sex. Similarly, severe microcephaly is defined as an OFC that is less than three standard deviations below the average. Microcephaly is not a diagnosis, but rather, a finding that is secondary to a multitude of etiologies that can be categorized as prenatal versus postnatal, genetic versus environmental, and congenital versus acquired.

Imaging of Congenital Craniofacial Anomalies and Syndromes.

Craniofacial malformation is one of the most commonly encountered birth defects in the prenatal and postnatal periods. Higher-resolution and 3D antenatal ultrasonography and multidetector computed tomographic scan with 3D reformatted images have improved the definition of the soft tissue and bone structures of the craniofacial anatomy and its malformations. Early diagnosis of these conditions is important to make the clinical decisions and more so in understanding the possibility of malformation recurring in the next pregnancy, which is one of the major concerns for the parents and the treating physicians.

Imaging of Headaches due to Intracranial Pressure Disorders.

Changes in intracranial pressure are a potentially serious etiology of headache. Headache secondary to changes in intracranial pressure frequently present with characteristic clinical features. Imaging plays a key role in the diagnosis and management of this category of headache. In this article, we will review the physiology, clinical presentation, and key imaging findings of major etiologies of changes in intracranial pressure resulting in headache including obstructive and nonobstructive hydrocephalous, idiopathic intracranial hypertension (IIH), and cerebrospinal fluid (CSF) leak.

Imaging of Cranial Neuralgias.

Cranial neuralgia (CN) can cause significant debilitating pain within a nerve dermatome. Accurate diagnosis requires detailed clinical history and examination, understanding of pathophysiology and appropriate neuroimaging to develop an optimal treatment plan. The objective of this article is to review and discuss some of the more common CNs including trigeminal neuralgia and its associated painful neuropathies, occipital neuralgia, and less common glossopharyngeal neuralgia (GPN). The neuroanatomy, pathophysiology, diagnostic imaging, and treatment of each of these pathologies are reviewed with emphasis on the role of CT and MR imaging findings in guiding diagnosis. Although CT is often used to initially identify an underlying cause such as neoplasm, infection, or vascular malformation, MRI is optimal. Clinical history and examination findings along with MRI constructive interference steady state/fast imaging employing steady-state acquisition sequences and MRA of the brain can be used to distinguish between primary and secondary cranial neuropathies and to discern the best treatment option. Pharmacologic and noninvasive therapy is the first-line of treatment of these cranial and cervical neuralgias. If symptoms persist, stereotactic radiosurgery is an option for some patients, although microvascular decompression surgery is the most curative option for both trigeminal and GPN. Refractory occipital neuralgia can be treated with a nerve block, an ablative procedure such as neurectomy or ganglionectomy, or more recently occipital nerve stimulation.

Headache Attributed to Disorder of the Cranium and Base of the Skull.

The article describes the approach to imaging that clinicians should adopt in cases of headaches suspected to be secondary to cranial vault or skull-base disorder. As a rule, computed tomography (CT) is superior to MRI for most of the osseous lesions, and lesions of the middle and external ear. MRI provides a complimentary role to CT and is the modality of choice in a few conditions such as extraosseous neoplasms of the skull base.

Neuroimaging in Pediatric Headache.

Headache represents one of the most common disorders in childhood and leads to nearly half a million visits to the physician's office or emergency department every year. Although the estimated prevalence is around 58.4%, the actual incidence of headache in the pediatric population might be underestimated, given only a percentage of cases seek medical attention. The first step in the evaluation of pediatric headache is a detailed clinical history and relevant clinical examinations. AAN and ACR do not recommend neuroimaging for patients with primary headache. However, neuroimaging becomes mandatory in presence of red flags to rule out the underlying cause.

Fukuyama Congenital Muscular Dystrophy.

Congenital muscular dystrophy (CMD) is a heterogeneous group of neurological disorders presenting at birth with weakness and hypotonia. Although the diagnosis is finally made through patterns of inheritance and muscle biopsy, the final imaging can be very characteristic in some of the variants, particularly the Fukuyama type of CMD (FCMD). We described the classic imaging findings in a child with this rare condition.

Management of Internal Carotid Artery and Intracranial Anterior Circulation Tandem Occlusion with Stenting versus No Stenting: A Multicenter Study.

BACKGROUND: Tandem occlusion (TO) describes not only occlusion of the middle cerebral artery but a contemporaneous occlusion of the cervical internal carotid artery. There is a paucity of data over whether mechanical thrombectomy (MT) alone, MT with angioplasty, or MT with carotid artery stent placement is superior. We aim to address a gap in the literature comparing carotid stenting with mechanical thrombectomy (CSMT) and carotid angioplasty with mechanical thrombectomy (CAMT) in patients presenting with acute anterior circulation TOs. METHODS: This is a multicenter, retrospective study from 2012 to 2020 comparing CSMT and CAMT presenting with acute anterior circulation TOs. Primary outcomes of interest were functional status, perioperative stroke, mortality, and symptomatic intracranial hemorrhage (sICH). A total of 92 patients (66 vs. 26 in CSMT and CAMT, respectively) met inclusion criteria for analysis. RESULTS: There was no statistically significant difference in functional outcomes at 90-day follow-up (adjusted odds ratio [aOR] 0.82; 95% confidence interval [CI] 0.20-3.5; P = 0.46). In addition, there was no statistically significant difference in 90-day mortality (aOR 0.361; 95% CI 0.016-2.92; P = 0.532) and perioperative stroke rate (aOR 1.76; 95% CI 0.160-15.6; P = 0.613). However, sICH risk was significantly greater in the stent-treated cohort (aOR 3.94; 95% CI 0.529-37.4; P = 0.003). CONCLUSIONS: Functional outcomes, mortality, and perioperative stroke rates do not significantly differ in CSMT and CAMT procedures in the acute setting. However, CSMT-treated patients do appear to have an increased risk of sICH, potentially due to the use of additional antiplatelet agents following stent placement.

Imaging Findings of New Entities and Patterns in Brain Tumor: Isocitrate Dehydrogenase Mutant, Isocitrate Dehydrogenase Wild-Type, Codeletion, and MGMT Methylation.

Molecular features are now essential in distinguishing between glioma histologic subtypes. Currently, isocitrate dehydrogenase mutation, 1p19q codeletion, and MGMT methylation status play significant roles in optimizing medical and surgical treatment. Noninvasive pretreatment and post-treatment determination of glioma subtype is of great interest. Although imaging cannot replace the genetic panel at present, image findings have shown promising signs to identify and diagnose the types and subtypes of gliomas. This article details key imaging findings in the most common molecular glioma subtypes and highlights recent advances in imaging technologies to differentiate these lesions noninvasively.

Neoplastic Meningitis and Paraneoplastic Syndromes.

Neoplastic meningitis (NM) and paraneoplastic syndromes (PNSs) are a rare group of disorders present in patients with cancer. Clinical diagnosis of these conditions is challenging, and imaging and laboratory analysis play a significant role in diagnosing. Diagnosis of NM largely depends on documenting circulating tumor cells in the cerebrospinal fluid (CSF) and/or leptomeningeal and nodular enhancement on contrast-enhanced MR imaging of the brain or axial spine. PNSs encompass a variety of symptoms or syndromes. Paraneoplastic neuronal disorder diagnosis requires a multidimensional approach, high clinical suspicion, CSF and serum examination, and imaging. Neuroimaging is an integral part in the evaluation.

Imaging of Neurologic Injury following Oncologic Therapy.

Neurologic injury arises from treatment of central nervous system malignancies as result of direct toxic effects or indirect vascular, autoimmune, or infectious effects. Multimodality treatment may potentiate both therapeutic and toxic effects. Symptoms range from mild to severe and permanent. Injuries can be immediate or delayed. Many early complications are nonspecific. Other early and delayed neurologic injuries, such as posterior reversible encephalopathy syndrome, dural sinus thrombosis, infarctions, myelopathy, leukoencephalopathy, and hypophysitis, have unique imaging features. This article reviews treatment options for neurologic malignancies and common and uncommon neurologic injuries that can result from treatment, focusing on radiologic features.

Radiogenomics of Gliomas.

The 2016 World Health Organization brain tumor classification is based on genomic and molecular profile of tumor tissue. These characteristics have improved understanding of the brain tumor and played an important role in treatment planning and prognostication. There is an ongoing effort to develop noninvasive imaging techniques that provide insight into tissue characteristics at the cellular and molecular levels. This article focuses on the molecular characteristics of gliomas, transcriptomic subtypes, and radiogenomic studies using semantic and radiomic features. The limitations and future directions of radiogenomics as a standalone diagnostic tool also are discussed.