Mild influenza-associated encephalopathy/encephalitis with a reversible splenial lesion in a Caucasian child with additional cerebellar features

Usefulness of arterial spin labeling imaging, which contributed to the early detection of cerebellitis complicated by clinically mild encephalitis/encephalopathy with a reversible splenial lesion: Lessons from three cases

BACKGROUND

Cerebellitis is a rare complication of clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS); however, MERS with cerebellitis is associated with a higher risk of neurological sequelae in comparison to MERS alone. Although the disease is difficult to diagnose by conventional MRI in the early disease phase, arterial spin labeling (ASL), a noninvasive MRI perfusion technique using magnetically-labeled arterial blood water protons, is considered promising.

CASE REPORT

We experienced three cases of MERS with cerebellitis. Diffusion-weighted imaging showed a high-intensity lesion at the splenium of the corpus callosum. ASL showed increased blood flow in the cerebellum in all three cases, despite cerebellar symptoms being inapparent or difficult to notice in the early phase of disease in all cases. Patients received methylprednisolone pulse therapy and intravenous immunoglobulin from the early phase of the disease and recovered without neurological sequelae.

DISCUSSION

ASL magnetic response imaging simultaneously showed an area of hyperperfusion in the cerebellum. At the same time, the apparent diffusion coefficient of the splenial lesion was decreased in all three cases. The successful diagnosis of cerebellitis in the acute phase led to early therapeutic intervention, which may be important for this condition. We report the usefulness of ASL and review the relevant literature on MERS with cerebellitis.

Cerebellar mutism syndrome of non-tumour surgical aetiology-a case report and literature review

Cerebellar mutism syndrome (CMS) is a well-known complication of posterior fossa (PF) tumour surgery. CMS has previously been reported in cases of non-tumour surgical aetiology in a limited number of publications. We report a case of a 10-year-old girl who suffered a cerebellar haemorrhage and subsequent CMS following surgical treatment of a ruptured arteriovenous malformation (AVM) in the cerebellar vermis. The AVM was removed acutely through a transvermian access, and hydrocephalus was treated with temporary external drainage. In the postoperative period, she suffered diffuse vasospasms of the anterior cerebral circulation and had a permanent shunt placed for hydrocephalus. Her mutism resolved after 45 days but severe ataxia persisted. To our knowledge, this is the first reported case of CMS related to a vermian haemorrhagic stroke with postoperative diffuse vasospasms. Based on this case, we present a literature review on CMS of non-tumour surgical origin in children.

Mild Encephalopathy With Partial Reversible Splenium Lesion Associated With SARS-CoV-2 Infection

Viral-associated encephalitis/encephalopathy includes a wide spectrum of syndromes reported often in children. A rare form presents with mild encephalitis/encephalopathy and reversible splenial lesion(s). This report describes a case of this rare presentation associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in a 68-year-old woman. The patient presented to the hospital with altered mental status. Examination revealed mild encephalopathy with disorientation to date and time. Initial laboratory workup was significant for mild hypernatremia and acute kidney injury, and a polymerase chain reaction (PCR) test for SARS-CoV-2 was positive. MRI of the brain revealed an area of hyperintensity and water restriction in the corpus callosum. The patient was treated with tocilizumab, dexamethasone, and remdesivir. MRI of the brain five weeks later revealed partial resolution of the hyperintensity, and complete resolution of the restricted diffusion previously seen in the corpus callosum, which confirmed the diagnosis of mild encephalitis/encephalopathy with a reversible splenial lesion. We highlight the importance of recognizing this phenomenon in association with SARS-CoV-2 infection.

Mild Encephalopathy/Encephalitis With a Reversible Splenial Lesion (MERS) and Longitudinally Extensive Transverse Myelitis (LETM) in Influenza B: Neurotropic Mechanisms and Diagnostic Challenges

Mild encephalopathy/encephalitis with a reversible splenial lesion (MERS) and longitudinally extensive transverse myelitis (LETM) are neuroinflammatory conditions related to the brain and spinal cord, respectively. Most cases of MERS and LETM are related to a secondary autoimmune process in response to an initial insult (i.e., infection, immunization, etc.). The case of an 18-year-old female who developed a three-day history of fever, quadriplegia, cough, and mild encephalopathy is reported here. The patient tested positive for influenza B by nasopharyngeal swab with polymerase chain reaction (PCR). Initial magnetic resonance imaging (MRI) revealed the presence of a diffusion-restricted non-enhancing lesion confined to the splenium of the corpus callosum (MERS type I) and longitudinally extensive non-enhancing T2 hyperintensities from C1 to C5. The patient was managed with a five-day course of 1,000 mg of intravenous methylprednisolone (IVMP). Additionally, five days of therapeutic plasmapheresis (PLEX) was completed. The patient showed significant improvement with medical management and physical therapy. At the one-year follow-up, her motor symptoms had resolved and endorsed only mild paresthesia in the upper extremities. A repeat MRI revealed a reversal of the splenium lesion and moderate improvement in T2 hyperintensities of the cervical cord. Assessing neuroinvasion of the influenza virus is difficult, and diagnostic challenges arise in determining primary infectious versus autoimmune-mediated neuroinflammation. A review of the literature on influenza infection with radiographic findings of MERS and LETM is included.

Multisystem Inflammatory-like Syndrome in a Child Following COVID-19 mRNA Vaccination

A 12-year-old male was presented to the hospital with acute encephalopathy, headache, vomiting, diarrhea, and elevated troponin after recent COVID-19 vaccination. Two days prior to admission and before symptom onset, he received the second dose of the Pfizer-BioNTech COVID-19 vaccine. Symptoms developed within 24 h with worsening neurologic symptoms, necessitating admission to the pediatric intensive care unit. Brain magnetic resonance imaging within 16 h of admission revealed a cytotoxic splenial lesion of the corpus callosum (CLOCC). Nineteen days prior to admission, he developed erythema migrans, and completed an amoxicillin treatment course for clinical Lyme disease. However, Lyme antibody titers were negative on admission and nine days later, making active Lyme disease an unlikely explanation for his presentation to hospital. An extensive workup for other etiologies on cerebrospinal fluid and blood samples was negative, including infectious and autoimmune causes and known immune deficiencies. Three weeks after hospital discharge, all of his symptoms had dissipated, and he had a normal neurologic exam. Our report highlights a potential role of mRNA vaccine-induced immunity leading to MIS-C-like symptoms with cardiac involvement and a CLOCC in a recently vaccinated child and the complexity of establishing a causal association with vaccination. The child recovered without receipt of immune modulatory treatment.

Clinical analysis of reversible splenial lesion syndrome in Chinese adults: A retrospective study of 11 cases

Reversible splenial lesion syndrome (RESLES) is a clinico-radiological entity that defines a reversible lesion in the splenium of the corpus callosum (SCC) on magnetic resonance imaging (MRI). The clinical and radiological characteristics of RESLES are poorly defined and most RESLES literature is in the form of case reports. We reviewed the clinical and radiological data from 11 RESLES patients in order to more clearly describe the characteristics of this disorder in adults.Patients included in this study were diagnosed with RESLES from May 2012 to March 2018. We collected clinical, imaging, and laboratory data of 11 adult patients from Neurology Department of the Affliated Yantai Yuhuangding Hospital of Qingdao University. After analyzing various clinico-radiological features and laboratory parameters, including serum sodium, pathogen testing, cerebrospinal fluid (CSF) studies, electroencephalography (EEG), and MRI findings, we made a diagnosis of RESLES based on the criteria proposed previously by Garcia-Monco et al.Of the 11 patients, 7 (63.63%) were male and 4 (36.36%) were female, ranging in age from 24 to 62 years with an average age of 31.48 ± 11.47 years. Seven cases occurred in the months of winter and spring (December-March). The primary clinical symptoms were headache, seizure, disturbance of consciousness, mental abnormality, and dizziness. All 11 patients had lesions in the SCC and all the lesions disappeared or significantly improved on follow-up imaging that was done within a month of symptom resolution.We found 5 (45.45%) patients had a CSF opening pressure >180 mmH2O, in addition to elevated protein and(or) leukocytes levels in 3 (27.27%) patients. The serum sodium concentration in 6 (54.55%) patients was low (<137 mmol/L) and EEG showed nonspecific slowing in waves 4 (36.36%) patients.When we encounter clinical manifestations such as headache accompanied with mental symptoms, disturbance of consciousness or epilepsy, and brain MRI finds lesions of the corpus callosum, we should consider whether it is RESLES. In order to find out the possible cause of the disease, we should carefully inquire about the history of the disease, complete etiology examination, and CSF tests. Of course, it is one of the necessary conditions for the diagnosis that the lesions in the corpus callosum are obviously relieved or disappeared.

Mild encephalitis/encephalopathy with reversible splenial lesion (MERS) in twin sisters with two CD36 frameshift mutations

Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is a clinical radiological syndrome with good prognosis that affects mainly children or young adults. We describe two cases of MERS, associated with echovirus 6 and influenza A infection, in two twin sisters, at the age of 4 years. Genetic analysis was performed; next exome sequencing was performed on twins to disclose the eventual causative gene. Two different frameshift mutations in the CD36 gene [NM_000072] were found in both twins and confirmed by Sanger sequencing. To best of our knowledge, we report an association between CD36 mutation and MERS. We think that this relation between CD36 and inflammation has had a crucial role in the same callosal alteration during viral disease in the twin sister with the same gene mutation.

Clinical applications of diffusion weighted imaging in neuroradiology

Abstract

Diffusion-weighted imaging (DWI) has revolutionised stroke imaging since its introduction in the mid-1980s, and it has also become a pillar of current neuroimaging. Diffusion abnormalities represent alterations in the random movement of water molecules in tissues, revealing their microarchitecture, and occur in many neurological conditions. DWI provides useful information, increasing the sensitivity of MRI as a diagnostic tool, narrowing the differential diagnosis, providing prognostic information, aiding in treatment planning and evaluating response to treatment. Recently, there have been several technical improvements in DWI, leading to reduced acquisition time and artefacts and enabling the development of diffusion tensor imaging (DTI) as a tool for assessing white matter. We aim to review the main clinical uses of DWI, focusing on the physiological mechanisms that lead to diffusion abnormalities. Common pitfalls will also be addressed.

Teaching Points

• DWI includes EPI, TSE, RESOLVE or EPI combined with reduced volume excitation.

• DWI is the most sensitive sequence in stroke diagnosis and provides information about prognosis.

• DWI helps in the detection of intramural haematomas (arterial dissection).

• In diffusion imaging, ADC is inversely proportional to tumour cellularity.

• DWI and DTI derived parameters can be used as biomarkers in different pathologies.

[Syndrome of mild encephalopathy with a reversible splenial corpus callosum lesion]

Mild encephalopathy with a reversible splenial lesion (MERS) is a clinico-radiological syndrome that has been associated with a variety of underlying etiologies including viral and bacterial infections, epilepsy and antiepileptic drug cessation, hypoglycemia and electrolyte imbalance. We report a case of a 24-year-old woman who had an isolated splenial lesion in the corpus callosum on neuroimaging associated with MERS.

Reversible splenial lesion syndrome associated with lobar pneumonia: Case report and review of literature

BACKGROUND

Reversible splenial lesion syndrome (RESLES) is a rare clinico-radiological disorder with unclear pathophysiology. Clinically, RESLES is defined as reversible isolated splenial lesions in the corpus callosum, which can be readily identified by magnetic resonance imaging (MRI) and usually resolve completely over a period of time. RESLES could be typically triggered by infection, antiepileptic drugs (AEDs), poisoning, etc. More factors are increasingly recognized.

METHODS AND RESULTS

We reported herein an 18-year-old female patient with lobar pneumonia who developed mental abnormalities during hospitalization. An isolated splenial lesion in the corpus callosum was found by head MRI and the lesion disappeared 15 days later. Based on her clinical manifestations and radiological findings, she was diagnosed with lobar pneumonia associated RESLES. We further summarize the up-to-date knowledge about the etiology, possible pathogenesis, clinical manifestations, radiological features, treatment, and prognosis of RESLES.

CONCLUSION

This report contributes to the clinical understanding of RESLES which may present with mental abnormalities after infection. The characteristic imaging of reversible isolated splenial lesions in the corpus callosum was confirmed in this report. The clinical manifestations and lesions on MRI could disappear naturally after 1 month without special treatment.

Reversible splenial lesion syndrome associated with encephalitis/encephalopathy presenting with great clinical heterogeneity

BACKGROUND

Reversible splenial lesion syndrome (RESLES) is a disorder radiologically characterized by reversible lesion in the splenium of the corpus callosum (SCC). Most of patients with RESLES associated with encephalitis/encephalopathy were identified in Japanese population, but almost no Chinese patients were diagnosed as RESLES associated with encephalitis/encephalopathy.

METHODS

Possible patients with reversible isolated SCC lesions were retrieved from January 2012 to July 2015 using keyword "restricted diffusion and isolated SCC lesion" in MRI report system from a large academic center. The clinical, laboratory and radiological data were summarized.

RESULTS

A total of 15 encephalitis/encephalopathy patients (9 males and 6 females) were identified with a reversible isolated SCC lesion. Except for 13 patients with fever symptom, 8 patients also had cold symptoms before the onset of neurological symptoms. The neurological symptoms included headache, vertigo, seizure, disturbance of consciousness, and delirious behavior. Thirteen patients completely recovered within 1 month, but 2 patients who were subjected to mechanical ventilation had persistent neurological deficits. The initial MRI features showed isolated ovoid or extending SCC lesions with homogeneous hyperintense on diffusion weighted imaging (DWI) and decreased apparent diffusion coefficient (ADC) values. The follow-up MRI revealed that isolated SCC lesions with diffuse restriction disappeared at 10 to 32 days after the initial MRI study. Fractional anisotropy map revealed the decreased value of SCC lesion in a severe case with poor prognosis.

CONCLUSIONS

RESLES associated with encephalitis/encephalopathy is a reversible syndrome with an excellent prognosis in most patients, while a few patients required ventilator supporting at the early stage might have severe neurological sequelae. Reversible signal changes on DWI and ADC are identified in all patients, but fractional anisotropy values can be decreased in severe patient with neurological sequelae.

Mild encephalitis/encephalopathy with reversible splenial and cerebellar lesions (MERS type II) in a patient with hemolytic uremic syndrome (HUS)

The typical form of mild encephalitis/encephalopathy with a reversible splenial lesion— called MERS type I—is characterized by a singular, reversible lesion in the midline of the splenium. Very rarely, additional lesions with similar signal characteristics can occur in other brain areas, which is then referred to as MERS type II. We present the case of a patient with a reversible splenial lesion and concomitant reversible cerebellar lesions within the scope of an atypical hemolytic uremic syndrome (HUS).

Mild encephalopathy with reversible splenial lesion in a patient with influenza A infection--first report in an adult patient in the USA

We present a case of a 51-year-old man with panhypopituarism who developed clinically mild encephalopathy with a lesion in the splenium of the corpus callosum, in the setting of acute influenza A infection. The patient's initial presentation included hypernatraemia due to pre-existing iatrogenic central diabetes insipidus. Despite adequate treatment of hypernatraemia, his course was complicated by otherwise unexplained mild encephalopathy. Brain MRI revealed a diffusion restricted lesion in the splenium of the corpus callosum. This presentation was consistent with mild encephalopathy with reversible splenial lesion (MERS). The patient subsequently tested positive for influenza A. This is the first reported case of MERS syndrome due to influenza A infection in an adult patient in the USA. Mild encephalopathy associated with influenza A infection and a reversible splenial lesion of the corpus callosum has a favourable prognosis and resolves spontaneously.

Mild encephalopathy with reversible splenial lesion: an important differential of encephalitis

Mild encephalopathy with a reversible splenial lesion (MERS) is a clinico-radiological syndrome characterized by a transient mild encephalopathy and a reversible lesion in the splenium of the corpus callosum on MRI. This syndrome has almost universally been described in children from Japan and East Asia. Here we describe seven cases of MERS occurring in Caucasian Australian children from one centre seen over a 3 year period. All patients had a fever-associated encephalopathy (n = 7), which presented with confusion (n = 4), irritability (n = 3), lethargy (n = 3), slurred speech (n = 3), drowsiness (n = 2) and hallucinations (n = 2). Other neurological symptoms included ataxia (n = 5) and seizures (n = 1). These symptoms resolved rapidly over 4-6 days followed by complete neurological recovery. In all patients, MRI performed within 1-3 days of onset of encephalopathy demonstrated a symmetrical diffusion-restricted lesion in the splenium of the corpus callosum. Three patients had additional lesions involving other parts of the corpus callosum and adjacent periventricular white matter. These same three patients had mild persisting white matter changes evident at followup MRI, while the other patients had complete resolution of radiological changes. A potential trigger was present in five of the seven cases: Kawasaki disease, Salmonella, cytomegalovirus, influenza B and adenovirus (all n = 1). Elevated white cell count (n = 4), elevated C reactive protein (n = 5) and hyponatremia (n = 6) were commonly observed. CSF was performed in four patients, which showed no pleocytosis. This case series of MERS demonstrates this condition occurs outside of East Asia and is an important differential to consider in children presenting with acute encephalopathy.

Clinicoradiological spectrum of reversible splenial lesion syndrome (RESLES) in adults: a retrospective study of a rare entity

The presence of reversible lesions that involve the splenium of the corpus callosum (SCC) has been reported in patients with a broad spectrum of diseases and conditions and is referred to as reversible splenial lesion syndrome (RESLES).To describe the clinicoradiological features and establish a clinical position for this disease, we retrospectively examined the clinicoradiological features of adult RESLES patients, as well as discuss the potential pathophysiological mechanisms of this disease.The clinical and MRI findings of patients who presented with RESLES accompanied by symptoms of neurological disorders were retrospectively reviewed. The patients were classified into 2 subgroups (favorable and poor outcome subgroups), which corresponded to the severity of the disability using the Modified Oxford Handicap Scale. In addition, we compared the clinical and neuroimaging features between the 2 outcome subgroups.Eight patients with RESLES associated with various diseases and conditions were included. The clinical presentation was nonspecific; however, MRI exhibited consistent lesions in the SCC with a hypointensity on apparent diffusion coefficient maps and a hyperintensity via diffusion-weighted imaging, which disappeared after a variable lapse. The number of patients with a severe disturbance of consciousness, extracallosal lesions, or diffuse slow waves in the poor outcome subgroup was significantly increased compared with the favorable outcome subgroup (P < 0.05). Thus, the clinicoradiological spectrum of RESLES could be classified into 2 principal categories according to differential outcomes.RESLES is a rare entity with a broad clinicoradiological spectrum because of the various diseases and conditions. Although the overall symptoms of RESLES patients tend to be alleviated, the prognosis of patients with a severe disturbance of consciousness, extracallosal lesions, or diffuse slow waves is likely unfavorable.

Neurologic complications of influenza

We report on a child with mild encephalopathy with reversible splenial lesion (MERS) associated with influenza infection and present a case series of neurological complications associated with influenza infections in children who presented to a tertiary children's hospital in Australia over a period of one year.

Mild encephalopathy with splenial lesion and parainfluenza virus infection

Mild encephalopathy with reversible splenial lesions has mainly been associated with influenza A and B virus infection. Patients present with neurologic symptoms 1 to 3 days after a prodromal illness and recover completely within a few days. Magnetic resonance imaging typically shows reversible lesions with reduced diffusion in the corpus callosum, predominantly in the splenium. We report on a 5-year old Caucasian boy who was referred with recurrent seizures and decreased level of consciousness after a 2-day prodromal fever and cough. Magnetic resonance imaging showed cytotoxic edema of the entire corpus callosum and the adjacent periventricular white matter with diffusion restriction and faint T(2)-hyperintensity. Parainfluenza virus type 1-3 infection was documented by direct immunofluorescence in the initial nasopharyngeal swab, but polymerase chain reaction for parainfluenza virus type 1-4 in the cerebrospinal fluid remained negative. This is-to our knowledge-the first description of mild encephalopathy with reversible splenial lesions in association with parainfluenza virus infection. The pathogenesis of mild encephalopathy with reversible splenial lesions, however, still remains unclear, and further studies investigating detailed mechanisms that lead to the typical brain lesions are warranted.

Expanding the spectrum of MERS type 2 lesions, a particular form of encephalitis

We report on a 13-year-old boy who presented with signs suggestive of encephalitis and in whom magnetic resonance imaging revealed lesions in the genu and splenium of the corpus callosum and symmetrical lesions bilaterally in the center semiovale. This clinical-radiologic entity was previously reported in the literature and was given the acronym MERS type 2 (mild encephalitis with reversible splenial) lesion. The clinical, radiologic, and biochemical characteristics of the patient with MERS type 2 lesions presented in this article show some differences with those in previously reported patients. His clinical recovery was particularly slow, cerebrospinal fluid was abnormal, and on magnetic resonance imaging the typical time course of MERS type 2 lesions resolving through a phase of solitary lesions in the splenium of the corpus callosum, the so-called type 1 lesions, was not seen. He is also the first patient in whom mycoplasma pneumoniae was found to be associated with MERS type 2 lesions. These findings further expand the spectrum of MERS type 2 lesions. The question raises whether the MERS type 2 lesion represents a new type of encephalitis or a particular radiologically recognizable subtype of postinfectious encephalitis. In the article, previously reported patients with MERS type 2 lesions are reviewed.

Influenza-associated neurological complications

While mostly diagnosed in the pediatric population, neurological complications of pandemic influenza A infection may affect young and previously healthy adults, and may follow a fulminant, severe, and occasionally fatal course. We reviewed severe neurological complications secondary to influenza infection reported in the literature, in attempt to outline recurrent syndromes that may assist the clinician in making a timely diagnosis. Vigilance and awareness of these clinical entities are key in the neurologist and intensivist's role in surveillance and early recognition of pandemic influenza, and in ensuring improved survival for affected patients.

Mild Encephalopathy with Reversible Splenial Lesion in Children

Mild encephalopathy with reversible splenial lesion (MERS) is a recently described clinico-radiological syndrome. It is characterised by acute mild encephalopathy and changes in the splenium of the corpus callosum on brain magnetic resonance imaging (MRI). MERS has been described mainly in East Asian populations. Infection, particularly influenza, is the most common association. The prognosis is generally favourable with spontaneous resolution of clinical and radiological abnormalities. We report two cases of non-influenza MERS in children, one associated with varicella, and discuss their differing clinical presentations.

Post-marketing assessment of neuropsychiatric adverse events in influenza patients treated with oseltamivir: an updated review

A 2008 review by our group concluded that the risk of neuropsychiatric adverse events (NPAEs) in influenza patients was not increased by oseltamivir exposure, and did not identify any mechanism by which oseltamivir or its metabolites could cause or worsen such events. The current article reviews new information on this topic. Between September 16, 2007 and May 15, 2010, 1,805 spontaneously-reported NPAEs were identified in 1,330 patients receiving oseltamivir: 767 (42.5%) from Japan, 296 (16.4%) from the USA, and 742 (41.1%) from other countries. NPAEs were more common in children: 1,072 (59.4%) events were in those aged ≤16 years. NPAEs often occurred within 48 h of treatment initiation (953 events; 52.8%). Nearly half of the events were serious in nature (838; 46.4%). The three largest categories of events were abnormal behavior (457 events, 25.3%), miscellaneous psychiatric events (370; 20.5%), and delusions/perceptual disturbances (316 events, 17.5%). A total of 1,545 events (85.6%) in eight different categories were considered to be delirium or delirium-like. Twenty-eight suicide-related events were reported. A US healthcare claims database analysis showed that the risk of NPAEs in 7,798 oseltamivir-treated patients was no higher than that in 10,411 patients not on antivirals, but a study on oseltamivir and abnormal behavior in Japan was less conclusive. NPAE frequency in oseltamivir-exposed Japanese and Taiwanese children with influenza was the same as in unexposed children. New analysis of the UK General Practice Research Database showed that the relative adjusted risk of NPAEs in influenza patients was 2.18-times higher than in the general population. Other epidemiology studies report frequent occurrence of encephalitis and similar disorders in influenza patients independently of oseltamivir exposure. The new data support the findings of the original assessment. Evidence suggests that influenza-related encephalopathies are caused by influenza-induced inflammatory responses, but more work is needed to confirm the underlying mechanisms.

H1N1 encephalitis with malignant edema and review of neurologic complications from influenza

Background

Influenza virus infection of the respiratory tract is associated with a range of neurologic complications. The emergence of 2009 pandemic influenza A (H1N1) virus has been linked to neurological complications, including encephalopathy and encephalitis.

Methods

Case report and literature review.

Results

We reviewed case management of a 20-year old Hispanic male who developed febrile upper respiratory tract signs and symptoms followed by a confusional state. He had rapid neurologic decline and his clinical course was complicated by refractory seizures and malignant brain edema. He was managed with oseltamavir and peramavir, corticosteroids, intravenous gamma globulin treatment, anticonvulsants, intracranial pressure management with external ventricular drain placement, hyperosmolar therapy, sedation, and mechanical ventilation. Reverse transcriptase polymerase chain reaction analysis of nasal secretions confirmed 2009 H1N1 virus infection; cerebrospinal fluid (CSF) was negative for 2009 H1N1 viral RNA. Follow-up imaging demonstrated improvement in brain edema but restricted diffusion in the basal ganglia. We provide a review of the clinical spectrum of neurologic complications of seasonal influenza and 2009 H1N1, and current approaches towards managing these complications.

Conclusions

2009 H1N1-associated acute encephalitis and encephalopathy appear to be variable in severity, including a subset of patients with a malignant clinical course complicated by high morbidity and mortality. Since the H1N1 influenza virus has not been detected in the CSF or brain tissue in patients with this diagnosis, the emerging view is that the host immune response plays a key role in pathogenesis.

The corpus callosum: white matter or terra incognita

The corpus callosum is the largest white matter structure in the brain, consisting of 200-250 million contralateral axonal projections and the major commissural pathway connecting the hemispheres of the human brain. The pathology of the corpus callosum includes a wide variety of entities that arise from different causes such as congenital, inflammatory, tumoural, degenerative, infectious, metabolic, traumatic, vascular and toxic agents. The corpus callosum, or a specific part of it, can be affected selectively. Numerous pathologies of the corpus callosum are encountered during CT and MRI. The aim of this study is to facilitate a better understanding and thus treatment of the pathological entities of the corpus callosum by categorising them according to their causes and their manifestations in MR and CT imaging. Familiarity with its anatomy and pathology is important to the radiologist in order to recognise its disease at an early stage and help the clinician establish the optimal therapeutic approach.

Magnetic resonance imaging of infections of the white matter

Infections of the nervous system are a common and serious occurrence. Neuroimaging has allowed to improve early detection and thus to initiate treatment earlier. Magnetic resonance (MR) imaging has become the method of choice in investigating a patient with suspicion of an infection of the central nervous system. Newer modalities such as MR spectroscopy and MR diffusion and perfusion will further help to improve diagnostic accuracy of the technique. For the investigation of infections of white matter, techniques such as diffusion imaging are essential.