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. However, the lateralization of olfactory processes is known to depend on the task and nature of stimuli. It still remains unclear whether olfactory system projections in humans also correspond to functional pathways during olfactory tasks without any trigeminal, perceptual or cognitive-motor components. Twenty young healthy subjects with a normal sense of smell took part in an olfactory functional magnetic resonance imaging (fMRI) study. We used two types of nostril specific stimulation, passive (no sniffing) and active (with sniffing), with phenyl ethyl alcohol, a pure olfactory stimulant, to investigate fMRI activity patterns in primary and secondary olfactory-related brain structures. Irrespective of the stimulated nostril and the type of stimulation, we detected symmetrical activity in primary and secondary olfactory-related brain structures such as the primary olfactory cortex, entorhinal cortex, and orbitofrontal cortex. In the absence of perceptual or cognitive-motor task demands, the perception of monorhinally presented pure odors is processed bilaterally in the brain.

Imaging of Neurologic Conditions in Pregnant Patients.

A number of physiologic, hormonal, immunologic, and hemodynamic changes take place in the maternal body during pregnancy. The majority of these changes are essential for maintaining the normal course of pregnancy. However, these changes may also cause acute or chronic conditions that affect various biologic systems in the mother. In addition, conditions of the central and peripheral nervous systems can cause a variety of neurologic symptoms and complications. Neurologic signs and symptoms in pregnant and postpartum women may be due to the exacerbation of a preexisting medical condition, the initial manifestation of a primary central nervous system-related problem, or a neurologic problem unique to pregnancy and the postpartum period. Because the symptoms of these conditions are either nonspecific or overlapping, it can be challenging to pinpoint the diagnosis clinically. These conditions can be classified into more commonly seen conditions such as headache, venous thrombosis, preeclampsia, subarachnoid hemorrhage, posterior reversible encephalopathy syndrome, and certain pituitary disorders; and less commonly seen entities such as aneurysm, arteriovenous malformation, primary or secondary neoplasm, Sheehan syndrome, and Wernicke encephalopathy. Imaging has an important role in the differentiation and exclusion of various neurologic conditions, and most of the time, imaging findings can point the clinician to a specific diagnosis. The imaging appearances of common and uncommon neurologic conditions that can occur during pregnancy and the early postpartum period are highlighted in this article. ©RSNA, 2016.

Hippocampal Changes in Febrile Infection-Related Epilepsy Syndrome (FIRES).

BACKGROUND: Febrile seizures are the most common seizure disorder in childhood, associated with a significant rise in body temperature. However, post-infectious refractory afebrile form of seizures in previously healthy children is being increasingly recognized in around the world, which evolves into a chronic refractory form of epilepsy. The term 'Febrile infection-related epilepsy syndrome' (FIRES) has been proposed for these conditions and represents a refractory severe post-infectious epileptic condition in previously normal children. CASE REPORT: We report the initial and follow-up MR imaging findings in a 5year-old with refractory epilepsy post-febrile seizures. CONCLUSIONS: In summary, acute post-infectious seizures are increasingly being recognized across the globe with the newly coined term 'Febrile infection-related epilepsy syndrome'(FIRES) for this group of immune-mediated epileptic encephalopathy in previously healthy children. This has three phases: episode of simple febrile infection, followed by acute refractory seizures and lastly the chronic phase of neuropsychological impairments and seizures.

Spontaneous thrombosis of developmental venous anomaly (DVA) with venous infarct and acute cerebellar ataxia.

Developmental venous anomaly (DVA), formally known as venous angioma, is a congenital anatomic variant of the venous drainage of the brain. Although they typically have a benign clinical course and a low symptomatic rate, thrombosis of a drainage vein may occur, leading to potentially debilitating complications. We report a unique case of spontaneous thrombosis of a posterior fossa developmental venous anomaly with cerebellar infarct in a 61-year-old man who presented with acute onset cerebellar ataxia. DVA thrombosis was well-depicted on CT and MR studies. Patient was put on anticoagulant therapy and complete recanalization was seen on follow-up imaging.

Looks like a stroke, acts like a stroke, but it's more than a stroke: a case of cerebral mucormycosis.

Mucormycosis is a fungus that exhibits angiocentric growth and can cause a thrombotic arteritis. Infection with this organism is uncommon and cerebral involvement is most often secondary to direct invasion through the paranasal sinuses. Here, we present a case of mucormycosis with cerebral involvement without sinus disease, which resulted in ischemic stroke with rapid progression resulting in death.

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.

A Review of the Role of Estrogens in Olfaction, Sleep and Glymphatic Functionality in Relation to Sex Disparity in Alzheimer's Disease.

Several risk factors contribute to the development of Alzheimer's disease (AD), including genetics, metabolic health, cardiovascular history, and diet. It has been observed that women appear to face a higher risk of developing AD. Among the various hypotheses surrounding the gender disparity in AD, one pertains to the potential neuroprotective properties of estrogen. Compared to men, women are believed to be more susceptible to neuropathology due to the significant decline in circulating estrogen levels following menopause. Studies have shown, however, that estrogen replacement therapies in post-menopausal women do not consistently reduce the risk of AD. While menopause and estrogen levels are potential factors in the elevated incidence rates of AD among women, this review highlights the possible roles estrogen has in other pathways that may also contribute to the sex disparity observed in AD such as olfaction, sleep, and glymphatic functionality.

Characteristic MRI findings in neonatal nonketotic hyperglycinemia due to sequence changes in GLDC gene encoding the enzyme glycine decarboxylase.

Neonatal metabolic encephalopathy may be related to electrolyte imbalances, endocrine dysfunction, or inborn errors of metabolism. The metabolic encephalopathies are always a diagnostic challenge to the neonatologist and pediatricians. This is more so because the signs and symptoms of are nonspecific and are often similar to those with other neonatal emergencies. Clinical suspicion of neonatal encephalopathy should be considered in any infant exhibiting an abnormal level of consciousness, seizures, tone and reflex abnormalities, apnea, aspiration, and feeding difficulties. A definitive diagnosis is frequently not possible during the neonatal care unit or emergency department. But the proper initial management based on the probable diagnosis can be life-saving or reduce neurologic sequelae. In the case of inborn errors of metabolism, imaging may play a vital role either in limiting the differential diagnosis or yet times pointing towards the specific diagnosis or error of metabolism. We report DWI-ADC changes on MRI in the acute stages of neonatal nonketotic hyperglycinemia (NKH) due to sequence changes in GLDC gene.

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.

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.

Imaging of stroke: Part 2, Pathophysiology at the molecular and cellular levels and corresponding imaging changes.

OBJECTIVE: Stroke is the third leading cause of death and the leading cause of severe disability. During the "decade of the brain" in the 1990s, the most promising development was the treatment of acute ischemic stroke. It is thought to result from a cascade of events from energy depletion to cell death. In the initial minutes to hour, clinical deficit does not necessarily reflect irreversible damage. The final outcome and residual deficit will be decided by how fast reperfusion is achieved, which in turn depends on how early the diagnosis is made. This article explains the pathophysiology of stroke at the molecular and cellular levels with corresponding changes on various imaging techniques. CONCLUSION: The pathophysiology of stroke has several complex mechanisms. Understanding these mechanisms is essential to derive neuroprotective agents that limit neuronal damage after ischemia. Imaging and clinical strategies aimed at extending the therapeutic window for reperfusion treatment with mechanical and pharmacologic thrombolysis will add value to existing treatment strategies. Acute ischemic stroke is defined as abrupt neurologic dysfunction due to focal brain ischemia resulting in persistent neurologic deficit accompanied by characteristic abnormalities on brain imaging. Knowledge of the pathophysiologic mechanisms of neuronal injury in stroke is essential to target treatment. Neuroprotective and thrombolytic agents have been shown to improve clinical outcome. Physiologic imaging with diffusion-weighted imaging (DWI) and perfusion CT and MRI provide a pathophysiologic substrate of evolving ischemic stroke.

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.

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.