Functional MRI to study brain plasticity in clinical neurology

Functional magnetic resonance imaging (fMRI) is being widely used to study recovery of function in patients with several neurological conditions, including multiple sclerosis, stroke and Alzheimer's disease. The application of this MR technique has shown that plastic cortical changes do occur after central nervous system (CNS) injury of different aetiology, that such changes are related to the extent of CNS damage and that they can contribute in limiting the clinical consequences of brain damage. Conversely, the failure or exhaustion of the adaptive properties of the cerebral cortex might be among the factors responsible for the accumulation of 'fixed' neurological deficits. New studies aimed at investigating the effect of therapies devoted to promote brain plasticity are now warranted.

Deep brain stimulation

Deep brain stimulation (DBS) has provided remarkable benefits for people with a variety of neurologic conditions. Stimulation of the ventral intermediate nucleus of the thalamus can dramatically relieve tremor associated with essential tremor or Parkinson disease (PD). Similarly, stimulation of the subthalamic nucleus or the internal segment of the globus pallidus can substantially reduce bradykinesia, rigidity, tremor, and gait difficulties in people with PD. Multiple groups are attempting to extend this mode of treatment to other conditions. Yet, the precise mechanism of action of DBS remains uncertain. Such studies have importance that extends beyond clinical therapeutics. Investigations of the mechanisms of action of DBS have the potential to clarify fundamental issues such as the functional anatomy of selected brain circuits and the relationship between activity in those circuits and behavior. Although we review relevant clinical issues, we emphasize the importance of current and future investigations on these topics.

Incidental findings in magnetic resonance imaging of the brains of healthy young men

BACKGROUND AND PURPOSE

To determine the frequency of serious intracranial abnormalities in a healthy young male population.

METHODS

Cranial MRI of 2,536 healthy young males, mean age 20.5 years, all applicants for military flying duties in the German Air Force.

RESULTS

The authors report a variety of morphological abnormalities in the brains of a large population of healthy young males, providing data on disease prevalence. Arachnoid cysts were found in 1.7% (95% CI 1.2 to 2.3%), vascular abnormalities in 0.51% (95% CI 0.29 to 0.9%), and intracranial tumors in 0.47% (95% CI 0.26 to 0.85%) of the applicants. No cerebral aneurysms were found.

CONCLUSION

The prevalence of primary brain tumors seems to be higher, whereas the prevalence of intracranial aneurysms is lower than expected. Only a small percentage of the detected abnormalities require urgent medical attention.

The p75 neurotrophin receptor in human development and disease

The functional effects of nerve growth factor (NGF) and its precursor, pro-NGF, are thought to be mediated through binding of these ligands to one or both of their receptors, TrkA and p75NTR. While the signaling pathways and downstream effects of NGF binding to TrkA are reasonably well known, those related to the binding of NGF and pro-NGF to p75NTR are less well understood. Furthermore, p75NTR appears to play functional roles that are unrelated to its ability to bind NGF and pro-NGF, some of which are ligand-independent and others of which are dependent upon binding to other neurotrophins. As these functional roles and their biochemical mechanisms become better known, the importance of p75NTR, related receptors, and both extracellular ligands and intracellular interactors and effectors for human development and health has become increasingly apparent. A complete understanding of p75NTR and its cellular partners is best served by approaching the remaining questions from both sides, with studies of function in normal states and studies of dysfunction in aberrant states mutually informing one another.

Adult neurogenesis in the mammalian central nervous system

Forty years since the initial discovery of neurogenesis in the postnatal rat hippocampus, investigators have now firmly established that active neurogenesis from neural progenitors continues throughout life in discrete regions of the central nervous systems (CNS) of all mammals, including humans. Significant progress has been made over the past few years in understanding the developmental process and regulation of adult neurogenesis, including proliferation, fate specification, neuronal maturation, targeting, and synaptic integration of the newborn neurons. The function of this evolutionarily conserved phenomenon, however, remains elusive in mammals. Adult neurogenesis represents a striking example of structural plasticity in the mature CNS environment. Advances in our understanding of adult neurogenesis will not only shed light on the basic principles of adult plasticity, but also may lead to strategies for cell replacement therapy after injury or degenerative neurological diseases.

Innate (inherent) control of brain infection, brain inflammation and brain repair: the role of microglia, astrocytes, "protective" glial stem cells and stromal ependymal cells

In invertebrates and primitive vertebrates, the brain contains large numbers of "professional" macrophages associated with neurones, ependymal tanycytes and radial glia to promote robust regenerative capacity. In higher vertebrates, hematogenous cells are largely excluded from the brain, and innate immune molecules and receptors produced by the resident "amateur" macrophages (microglia, astrocytes and ependymal cells) control pathogen infiltration and clearance of toxic cell debris. However, there is minimal capacity for regeneration. The transfer of function from hematogenous cells to macroglia and microglia is associated with the sophistication of a yet poorly-characterized neurone-glia network. This evolutionary pattern may have been necessary to reduce the risk of autoimmune attack while preserving the neuronal web but the ability to repair central nervous system damage may have been sacrificed in the process. We herein argue that it may be possible to re-educate and stimulate the resident phagocytes to promote clearance of pathogens (e.g., Prion), toxic cell debris (e.g., amyloid fibrils and myelin) and apoptotic cells. Moreover, as part of this greater division of labour between cell types in vertebrate brains, it may be possible to harness the newly described properties of glial stem cells in neuronal protection (revitalization) rather than replacement, and to control brain inflammation. We will also highlight the emerging roles of stromal ependymal cells in controlling stem cell production and migration into areas of brain damage. Understanding the mechanisms involved in the nurturing of damaged neurons by protective glial stem cells with the safe clearance of cell debris could lead to remedial strategies for chronic brain diseases.

[Neuronal heterotopy]

The diagnosis of most volumetric processes of the brain presents no difficulty today; however, there are a number of brain diseases whose clinical manifestations are similar to those of tumors. Despite the development of neurovisualization techniques (application of currently available computer and magnetic resonance tomographs and special programs, such as MR imaging and CT spectroscopy, diffusion and perfusion, etc.), some of these processes are difficult to differentiate from neoplasms noninvasively. It is evident that treatment policy should be quite different in these or those cases. Neuronal nodular heterotopy (ectopy) may be considered as one of such pseudotumorous processes. This case illustrates the rare abnormality that has the clinical and X-ray picture similar to that of neoplasms of the brain. Current noninvasive method do not always allow one to significantly verify the nature of brain tissue changes, which shows it necessary to use CT-stereotactic biopsy in some cases.

Spectrum of malformations of the hindbrain (cerebellum, pons, and medulla) in a cohort of children with high rate of parental consanguinity

We review 25 patients with a spectrum of hindbrain (cerebellum, pons, and medulla) malformations from a cohort of children with high parental consanguinity rate. Twenty-three of the 25 patients were born to consanguineous parents. The patients were classified in four groups. Eleven patients of 6 families had malformation of the hindbrain and midbrain with molar tooth sign (10 patients of 5 families with typical Joubert syndrome), 5 patients showed severe supratentorial anomalies in addition to the hindbrain malformations, 5 patients had pontocerebellar or cerebellar hypoplasia with anterior horn cell disease in the spinal cord (spinal muscular atrophy), and 4 patients showed malformations affecting predominantly the hindbrain without substantial involvement of other systems. A locus for Joubert syndrome was previously identified on chromosome 9q34.3 in two families, and a second locus on chromosome 11p12-q13.3 in another family. A third Joubert syndrome locus has been mapped at 6q23 and a mutation in the AHI1 gene at this site has been found recently in a further family from this cohort. Delineation of homogeneous subgroups of patients with hindbrain malformations and molecular genetic analysis of these groups may lead to identification of further loci, genes and mutations responsible for the malformations.

Pediatric epilepsy surgery: lessons and challenges

Pediatric epilepsy surgery has come of age, from being considered as a last resort in medically refractory focal epilepsy, after failure of numerous antiepileptic drug trials spanning many years, to a preferred treatment option in carefully selected candidates. There have been certain key developments that have catalyzed this change. First, we are able to predict medical intractability earlier during the course of epilepsy. Second, improved understanding of how the maturing brain recovers from neurologic insults has led to earlier consideration of surgical intervention during a window of developmental plasticity. Finally, improved diagnostic and surgical capabilities now enable us to identify more candidates suitable for surgery. At the same time, as the surgical frontier has been rapidly pushed to new horizons, we have also unearthed new challenges. In this review, several pediatric epilepsy syndromes are discussed to highlight these important developments.

Operative indications and neuroendoscopic management of symptomatic cysts of the septum pellucidum

OBJECTIVE

Since there is no current consensus on the diagnostic standards or surgical indications for symptomatic cysts of the septum pellucidum (CSP), we presented our experience treating such cases with neuroendoscopic surgery in order to possibly make a contribution to the attainment of such a consensus.

METHODS

In the last 5 years, we effectively treated 5 patients (4 males and 1 female) with CSP by neuroendoscopic surgery. The 3 congenital cases were young: 9, 14, and 29 years old. The 2 secondary cases were adults aged 51 and 65 years old. We were able to fenestrate, and biopsy for pathological analysis, the cyst walls of symptomatic CSP using a minimally invasive neuroendoscopic technique, with postoperative improvement in compression of adjacent structures, as well as clinical signs.

CONCLUSIONS

It is necessary to consider the overall picture including clinical signs, progress of the condition, intracranial pressure, and cerebral circulation, in deciding whether surgery is indicated. Neuroendoscopic surgery is an effective, optimal, and convenient therapeutic modality for symptomatic CSP.

[A case of encephalitis-type encephalopathy related to Pleurocybella porrigens (Sugihiratake)]

A 65-year-old man who had been on hemodialysis for chronic renal failure was well until 7 days after ingestion of Pleurocybella porrigens (Sugihiratake) when he developed a loss of consciousness and status epilepticus of generalized tonic and clonic seizures. High fever and high CRP were followed and cerebrospinal fluids showed marked pleocytosis with polynuclear cell predominance. Brain MRI showed diffuse lesions in the basal ganglia and multiple ringed lesions in cerebral cortex. Glucocorticoid therapy was effective for clinical improvement. This case showed the presence of encephalitis-type of encephalopathy related to Pleurocybella porrigens (Sugihiratake).

Use of a compact intraoperative low-field magnetic imager in pediatric neurosurgery

OBJECT

The majority of investigations on the utility of and indications for intraoperative magnetic resonance imaging (iMRI) have been in adult patients. We report our initial experience utilizing low-field iMRI in pediatric patients.

METHODS

We performed 21 procedures on 20 patients aged 2 months to 18 years (mean 8.9 years) utilizing the PoleStar -10 iMRI system. The procedures included 15 craniotomies, 2 shunts, and 1 each of the following surgeries: transsphenoidal, craniotomy/transsphenoidal, cranioplasty, and endoscopic biopsy and fenestration. Treated lesions included low-grade astrocytoma (5), craniopharyngioma (3), cortical dysplasia (3), hydrocephalus (2), and others (8). The number of scans ranged from 2 to 5 with a mean of 3.2. Intraoperative imaging and navigation provided valuable information on the extent of resection and catheter placement. In eight procedures it influenced the surgical strategy. No untoward events attributable to the system occurred.

CONCLUSIONS

The low-field PoleStar -10 iMRI system can safely assist pediatric neurosurgeons treating a variety of diseases. In addition to neuronavigation it provides information on extent of resection, real-time guided catheter placement, and avoidance of complications.

Diagnostic value of periodic complexes in Creutzfeldt-Jakob disease

In 1996, our group published objective electroencephalogram (EEG) criteria to define periodic sharp-wave complexes (PSWCs) suggestive for Creutzfeldt-Jakob disease (CJD). These criteria have since then been strictly applied in all cases reported to us as possible CJD in the course of the German CJD surveillance study. Furthermore, EEG analysis of the records was performed without any additional information on complementary clinical and laboratory data. In this study, we investigated sensitivity, specificity, and the predictive values of these EEG criteria exclusively in cases in which autopsy confirmed (n=150) or excluded (n=56) CJD. EEG criteria were positive in 64% (n=96) of the CJD cases and falsely positive in 9% (n=5) of other dementias. The resulting figures for sensitivity, specificity, and positive and negative predictive values were 64%, 91%, 95%, and 49%, respectively. In the falsely positive cases, Alzheimer's disease (n=4) and vascular dementia (n=1) were the underlying diseases. However, only in one of these five cases both clinical and EEG data would have led to the false-positive result to diagnose probable CJD. These data prove the high diagnostic value of our objective EEG criteria in CJD.

Distinct clinicopathologic subtypes of cortical dysplasia of Taylor

BACKGROUND

Two pathologic subtypes based on the presence or absence of balloon cells have been described in cortical dysplasia of Taylor (CDT).

OBJECTIVE

To determine whether the pathologic subtype has any distinct clinical or MRI features that are relevant to management.

METHODS

The histopathologic, clinical, and MRI features of 34 children with CDT who underwent epilepsy surgery at Miami Children's Hospital from 1990 to 2001 were investigated.

RESULTS

Bizarre neuronal cytomegaly was the primary pathologic feature of 15 patients with the dysplasia-only subtype, and 19 cases showed additional characteristics including balloon cells and marked white matter abnormalities. Both groups presented with severe intractable epilepsy of very-early-onset, multiple daily seizures, cognitive disability, and focal neurologic deficits. The dysplasia-only subtype had higher rates of neonatal onset, hemiparesis, and severe mental retardation (p < 0.05). The MRI features of focal cortical thickening with associated cortical T2 signal change showed excellent sensitivity (94%) and reasonable specificity (73%) for the diagnosis of the balloon cell subtype. The overall surgical outcome was 59% seizure freedom at 2 years.

CONCLUSIONS

Children with cortical dysplasia of Taylor type have in common a very-early-onset, severe epilepsy with neurologic co-morbidity. Patients with the non-balloon cell pathologic subtype have a more severe phenotype. A trend toward a better outcome in the balloon cell group suggests that preoperative identification of these subtypes may impact surgical planning.

Subdural EEG Patterns in Children With Taylor-Type Cortical Dysplasia: Comparison With Nondysplastic Lesions

The authors compared interictal and ictal abnormalities from chronic intracranial recordings in children with Taylor-type cortical dysplasia (TTCD) and nondysplastic lesions. Interictal epileptiform discharges and ictal patterns were retrospectively analyzed in 13 children with TTCD and 12 children with nondysplastic lesions (tumor, 4; gliosis, 8). Features analyzed and compared between groups included the morphologic and temporal characteristics and field distribution of ictal and interictal patterns and rapidity of ictal propagation. The frequency of runs of interictal continuous epileptiform discharges (CEDs) or bursts of fast activity did not differ significantly between dysplastic and nondysplastic tissue. Fast frequencies characterized the majority of seizure onsets (49/67) in dysplastic patients and repetitive spikes were more frequent at seizure onset (31/56) in nondysplastic patients (P < 0.002). Field of ictal onset was limited to adjacent cortex and independent of histology. The interval between seizure onset and spread to adjacent or nonadjacent cortex was significantly shorter in dysplastic than nondysplastic patients. Interictal EEG patterns are not specific markers of dysplastic cortex but the morphology of ictal onset differs significantly with dysplastic cortex showing significantly more rapid propagation than nondysplastic cortex. These findings suggest that markers other than CEDs physiologically characterize dysplastic cortex and that children with TTCD exhibit more widespread excitability of neural pathways.

Memory span on the Wechsler Scales

This study had two goals. One was to assess whether the WMS-III Spatial Span subtest operates as a visual analogue of Digit Span while the second was to determine whether backward span is a more sensitive measure of working memory than the forward span condition. Analyses based on the WAIS-III-WMS-III standardization and clinical group data revealed some important distinctions between Digit and Spatial Span. The two tasks exhibited differences in patterns of performance on the forward versus backward conditions, in their relationships with age, and in their methodology. Moreover, the backward conditions of both Digit and Spatial Span did not appear more affected by risk factors such as aging or pathology than the forward scores. This runs contrary to the widespread notion that backward span provides differential sensitivity regarding working memory processing.

Cystic tuberculomas of the brain--two case reports

A 19-year-old male presented with raised intracranial pressure and a peripherally enhanced multinodular lesion with a large subjacent cyst in the right medial frontal lobe. Surgery revealed a solid tuberculoma and an underlying cyst lined with normal brain tissue. A 22-year-old male with a history of tuberculous meningitis and hydrocephalus presented with an exophytic brain stem and a left temporal tuberculoma, which were excised in two stages. The temporal tuberculoma had a peripherally located cyst that was lined with tuberculous tissue. Intracranial tuberculomas are an important part of the differential diagnosis where tuberculosis is endemic and in immunocompromised patients. Cystic tuberculomas are uncommon. The cysts may be centrally or peripherally intralesional, or either subdural and extralesional, or occur between the lesion and the brain. The type of cyst is important to recognize preoperatively, so that adequate precautions can be taken during the excision of these lesions.

[Cerebral vasculitis]

Cerebral vasculitides are infrequent in neurological practice but important for the differential diagnosis of multifocal CNS symptoms. The clinical presentation is typically a combination of chronic headache, multiple strokes and encephalopathy. In systemic vasculitis, a combination of CNS symptoms with inflammatory signs and with peripheral nervous system symptoms (painful multiplex polyneuropathy) or other organ manifestations (skin, joints, kidney, heart, lungs, eye) are frequent. In isolated CNS angiitis, CSF examinations are of particular value. Besides MRI, angiography, CSF and serum examinations, the verification of the diagnosis by biopsy is mandatory.

Neuroendoscopic surgery of intracranial cysts in adults

OBJECTS

The purpose of this study was to describe the indications, surgical techniques and postoperative outcome of neuroendoscopic interventions in a heterogeneous group of intracranial cystic pathologies.

PATIENTS AND METHODS

Between 1992 and 2003, 127 patients with symptomatic intracranial cysts and cystic tumours underwent neuroendoscopic treatment in our department. In 22 patients indication for surgery was colloid cysts, in 9 patients pineal cysts and in 3 patients cavum vergae cysts. Twelve arachnoid cysts, 10 cystic craniopharyngiomas, 2 Rathke's cleft cysts and 69 malignant cystic tumours were operated on. The patients' mean age was 45 years and their clinical presentations varied from typical signs of increased intracranial pressure to focal neurological deficits.

RESULTS

One hundred and twenty-seven patients with intracerebral cystic space-occupying lesions were operated on using stereotactic frameless or frame-based endoscopic techniques. There was no operative mortality. The operative morbidity was 3.1% including 1 memory deficit due to fornix injury, 1 hemiparesis due to postoperative haematoma after lesion biopsy, 1 aseptic meningitis and 1 subdural fluid collection.

CONCLUSIONS

Endoscopic interventions enable neurosurgeons to manage intracranial cystic lesions. Via the same approach, the obstructed CSF pathways may be restored and consequently the increased intracranial pressure diminishes. With the aid of stereotactic guidance or a neuronavigation system, access to the lesion can be gained rapidly and with high accuracy.