The pathology of incipient polymicrogyria

Hydrocortisone Attenuates the Development of Malformations of the Polymicrogyria Spectrum

Most of the malformations of the polymicrogyria spectrum are caused by destructive lesions of the neocortex during the third trimester of pregnancy, triggered by hypoxic-ischemic, hemorrhagic or infectious events, with neuroinflammation as a common pathophysiological mechanism. Our study investigated hydrocortisone treatment in attenuating inflammation, malformations development and seizures predisposition in mice subjected to neonatal transcranial freeze lesion. Our results show attenuation of malformation and predisposition to febrile seizures, with concomitant reduction of macrophages/microglia after neonatal freeze lesion, polarizing them towards an anti-inflammatory profile. Thus, we have identified a promising treatment to minimize the development of cortical developmental malformations.

Skeletal Growth Arrest Lines in Fetal Remains: Histopathology and Correlative Placental Pathology

INTRODUCTION

Skeletal growth arrest lines (GAL) are transverse lines of metaphyseal radiodensity accompanying episodic severe physiological stress. They are poorly described in fetal remains.

MATERIALS AND METHODS

We searched our autopsy practice for instances of fetal GAL in post mortem radiology, and correlated them with long bone histology and placental pathology. We describe the appearance, distribution, and pathology of GAL in a cohort of fetal autopsies, and compare the placental pathology accompanying GAL to the placental pathology of asymmetrical growth restriction (AGR) in the same time period.

RESULTS

In 2108 consecutive fetal post mortems, we found 20 cases with GAL. About 16 were in singletons with AGR. In these 16, the distribution of placental pathologies was similar to a contemporaneous cohort of 113 cases with AGR. Of the remaining 4, two twins out of 9 sets of monochorionic twins with AGR demonstrated GAL. One case of GAL had symmetrical growth restriction with cytomegalovirus infection, and one case had no AGR and an old, unexplained retroplacental hemorrhage. On histology, GAL are characterized by a region of mineralized chondroid, which is variably incorporated into irregular trabecular bone.

DISCUSSION

GALs accompany a variety of placental pathologies and twin-twin transfusion, suggesting episodic disease progression.

Altered excitatory and inhibitory neocortical circuitry leads to increased convulsive severity after pentylenetetrazol injection in an animal model of schizencephaly, but not of microgyria

OBJECTIVE

Malformations of the polymicrogyria spectrum can be mimicked in rodents through neonatal transcranial focal cortical freeze lesions. The animals presenting the malformations present both altered synaptic events and epileptiform activity in the vicinity of the microgyrus, but the comprehension of their contribution to increased predisposition or severity of seizures require further studies.

METHODS

In order to investigate these issues, we induced both microgyria and schizencephaly in 57 mice and evaluated: their convulsive susceptibility and severity after pentyleneterazol (PTZ) treatment, the quantification of their symmetric and asymmetric synapses, the morphology of their dendritic arbors, and the content of modulators of synaptogenesis, such as SPARC, gephyrin and GAP-43 within the adjacent visual cortex.

RESULTS

Our results have shown that only schizencephalic animals present increased convulsive severity. Nevertheless, both microgyric and schizencephalic cortices present increased synapse number and dendritic complexity of layer IV and layer V-located neurons. Specifically, the microgyric cortex presented reduced inhibitory synapses, while the schizencephalic cortex presented increased excitatory synapses. This altered synapse number is correlated with decreased content of both the anti-synaptogenic factor SPARC and the inhibitory postsynaptic organizer gephyrin in both malformed groups. Besides, GAP-43 content and dendritic spines number are enhanced exclusively in schizencephalic cortices.

SIGNIFICANCE

In conclusion, our study supports the hypothesis that the sum of synaptic alterations drives to convulsive aggravation in animals with schizencephaly, but not microgyria after PTZ treatment. These findings reveal that different malformations of cortical development should trigger epilepsy via different mechanisms, requiring further studies for development of specific therapeutic interventions.

Roots of the Malformations of Cortical Development in the Cell Biology of Neural Progenitor Cells

The cerebral cortex is a structure that underlies various brain functions, including cognition and language. Mammalian cerebral cortex starts developing during the embryonic period with the neural progenitor cells generating neurons. Newborn neurons migrate along progenitors’ radial processes from the site of their origin in the germinal zones to the cortical plate, where they mature and integrate in the forming circuitry. Cell biological features of neural progenitors, such as the location and timing of their mitoses, together with their characteristic morphologies, can directly or indirectly regulate the abundance and the identity of their neuronal progeny. Alterations in the complex and delicate process of cerebral cortex development can lead to malformations of cortical development (MCDs). They include various structural abnormalities that affect the size, thickness and/or folding pattern of the developing cortex. Their clinical manifestations can entail a neurodevelopmental disorder, such as epilepsy, developmental delay, intellectual disability, or autism spectrum disorder. The recent advancements of molecular and neuroimaging techniques, along with the development of appropriate in vitro and in vivo model systems, have enabled the assessment of the genetic and environmental causes of MCDs. Here we broadly review the cell biological characteristics of neural progenitor cells and focus on those features whose perturbations have been linked to MCDs.

Transitory and Vestigial Structures of the Developing Human Nervous System

As with many body organs, the human central nervous system contains many structures and cavities that may have had functions in embryonic and fetal life but are vestigial or atrophic at maturity. Examples are the septum pellucidum, remnants of the lamina terminalis, Cajal-Retzius neurons, induseum griseum, habenula, and accessory olfactory bulb. Other structures are transitory in fetal or early postnatal life, disappearing from the mature brain. Examples are the neural crest, subpial granular glial layer of Brun over cerebral cortex, radial glial cells, and subplate zone of cerebral cortex. At times persistent fetal structures that do not regress may cause neurological problems or indicate a pathologic condition, such as Blake pouch cyst. Transitory structures thus can become vestigial. Examples are an excessively wide cavum septi pellucidi, suprapineal recess of the third ventricle, trigeminal artery of the posterior fossa circulation, and hyaloid ocular artery. Arrested maturation might be considered another aspect of vestigial structure. An example is the persistent microcolumnar cortical architecture in focal cortical dysplasia type Ia, in cortical zones of chronic fetal ischemia, and in some metabolic/genetic congenital encephalopathies. Some transitory structures in human brain are normal adult structures in lower vertebrates. Recognition of transitory and vestigial structures by fetal or postnatal neuroimaging and neuropathologically enables better understanding of cerebral ontogenesis and avoids misinterpretations.

Focal cortical dysplasia type 1

The ILAE classification of Focal Cortical Dysplasia (FCD) from 2011 has quickly gained acceptance in clinical practice and research and is now widely used around the world. This histopathology‐based classification scheme proposed three subtypes, that is, FCD Type 1 (with architectural abnormalities of the neocortex), FCD Type 2 (with cytoarchitectural abnormalities of the neocortex) and FCD Type 3 (architectural abnormalities of the neocortex associated with another principle lesion acquired during early life). Valuable knowledge was gathered during the last decade validating the clinical, pathological and genetic classification of FCD Type 2. This is in contrast to FCD subtype 1 and 3 with only few robust or new insights. Herein, we provide an overview about current knowledge about FCD Type 1 and its three subtypes. Available data strengthened, however, FCD Type 1A in particular, whereas a comprehensive clinico‐pathological specification for FCD Type 1B and 1C subtypes remain to be shown. The lack of a valid animal model for FCD Type 1 further supports our call and the ongoing need for systematic research studies based on a careful clinico‐pathological and genetic stratification of patients and human brain tissues.

Hypoxia: A teratogen underlying a range of congenital disruptions, dysplasias, and malformations

In this review, we explore evidence that hypoxia in the developing human fetus can lead not only to the more commonly accepted disruptive-type defects, but also patterns of anomalies that suggest that hypoxia can exert a more classic teratogenic effect, using the brain as one example. We review neuropathology in the context of intrauterine hypoxia, particularly as it relates to carbon monoxide poisoning, in utero strokes, and homozygous alpha-thalassemia. In general, the associated brain injuries resemble those seen with other causes of hypoxic-ischemic injury. Fetal strokes during development usually lead to loss of brain tissue in areas that do not follow a typical embryologic pattern, and therefore are considered disruptions. However, there is also evidence that fetal brain ischemia can cause more classically recognized patterns of abnormal embryonic neuronal migration and organization such as polymicrogyria, cortical dysplasia, or dysgenesis, including select types of focal cortical dysplasia. This study summarizes available literature and evidence to raise clinicians' awareness regarding the association between hypoxia and congenital anomalies, including brain malformations.

Brain and Placental Pathology in Fetal COL4A1 Related Disease

INTRODUCTION

Although fetal brain injury due to COL4A1 gene mutation is well documented, fetal central nervous system (CNS) and placental histopathology lack description. We report CNS and placental pathology in fetal cases with symptomatic COL4A1 mutation.

METHODS

We retrieved four autopsy cases of COL4A1 related disease, confirmed by genetic sequencing after fetal brain injury was detected.

RESULTS

One case was a midgestation fetus with residua of ventricular zone hemorrhage and normal placental villi. Three cases were 30-32 week gestation fetuses: two demonstrated CNS small vessel thrombosis, with CNS injury. Both demonstrated high grade placental fetal vascular malperfusion (FVM). One additionally showed villous dysmorphism, the other demonstrated mild villous immaturity. The fetus whose placenta demonstrated high grade FVM was growth restricted. A fourth fetus demonstrated schizencephaly with a CNS arteriopathy with smooth muscle cell degeneration and cerebral infarcts; the placenta demonstrated severe villous dysmorphism and low grade FVM.

DISCUSSION

These cases confirm that small vessel disease is important in producing intracranial pathology in COL4A1mutation. We report an arteriopathy distinct from microvascular thrombosis and demonstrate that placental pathology is common in fetal COL4A1 related disease. This tentatively suggests that placental pathology may contribute to CNS abnormalities by affecting circulatory sufficiency.

Excitatory/Inhibitory Synaptic Ratios in Polymicrogyria and Down Syndrome Help Explain Epileptogenesis in Malformations

BACKGROUND

The ratio between excitatory (glutamatergic) and inhibitory (GABAergic) inputs into maturing individual cortical neurons influences their epileptic potential. Structural factors during development that alter synaptic inputs can be demonstrated neuropathologically. Increased mitochondrial activity identifies neurons with excessive discharge rates.

METHODS

This study focuses on the neuropathological examinaion of surgical resections for epilepsy and at autopsy, in fetuses, infants, and children, using immunocytochemical markers, and electron microscopy in selected cases. Polymicrogyria and Down syndrome are highlighted.

RESULTS

Factors influencing afferent synaptic ratios include the following: (1) synaptic short-circuitry in fused molecular zones of adjacent gyri (polymicrogyria); (2) impaired development of dendritic spines decreasing excitation (Down syndrome); (3) extracellular keratan sulfate proteoglycan binding to somatic membranes but not dendritic spines may be focally diminished (cerebral atrophy, schizencephaly, lissencephaly, polymicrogyria) or augmented, ensheathing individual axons (holoprosencephaly), or acting as a barrier to axonal passage in the U-fiber layer. If keratan is diminished, glutamate receptors on the neuronal soma enable ectopic axosomatic excitatory synapses to form; (4) dysplastic, megalocytic neurons and balloon cells in mammalian target of rapamycin disorders; (5) satellitosis of glial cells displacing axosomatic synapses; (6) peri-neuronal inflammation (tuberous sclerosis) and heat-shock proteins.

CONCLUSIONS

Synaptic ratio of excitatory/inhibitory afferents is a major fundamental basis of epileptogenesis at the neuronal level. Neuropathology can demonstrate subcellular changes that help explain either epilepsy or lack of seizures in immature brains. Synaptic ratios in malformations influence postnatal epileptogenesis. Single neurons can be hypermetabolic and potentially epileptogenic.

Fetal stroke and cerebrovascular disease: Advances in understanding from lenticulostriate and venous imaging, alloimmune thrombocytopaenia and monochorionic twins

Fetal stroke is an important cause of cerebral palsy but is difficult to diagnose unless imaging is undertaken in pregnancies at risk because of known maternal or fetal disorders. Fetal ultrasound or magnetic resonance imaging may show haemorrhage or ischaemic lesions including multicystic encephalomalacia and focal porencephaly. Serial imaging has shown the development of malformations including schizencephaly and polymicrogyra after ischaemic and haemorrhagic stroke. Recognised causes of haemorrhagic fetal stroke include alloimmune and autoimmune thrombocytopaenia, maternal and fetal clotting disorders and trauma but these are relatively rare. It is likely that a significant proportion of periventricular and intraventricular haemorrhages are of venous origin. Recent evidence highlights the importance of arterial endothelial dysfunction, rather than thrombocytopaenia, in the intraparenchymal haemorrhage of alloimmune thrombocytopaenia. In the context of placental anastomoses, monochorionic diamniotic twins are at risk of twin twin transfusion syndrome (TTTS), or partial forms including Twin Oligohydramnios Polyhydramnios Sequence (TOPS), differences in estimated weight (selective Intrauterine growth Retardation; sIUGR), or in fetal haemoglobin (Twin Anaemia Polycythaemia Sequence; TAPS). There is a very wide range of ischaemic and haemorrhagic injury in a focal as well as a global distribution. Acute twin twin transfusion may account for intraventricular haemorrhage in recipients and periventricular leukomalacia in donors but there are additional risk factors for focal embolism and cerebrovascular disease. The recipient has circulatory overload, with effects on systemic and pulmonary circulations which probably lead to systemic and pulmonary hypertension and even right ventricular outflow tract obstruction as well as the polycythaemia which is a risk factor for thrombosis and vasculopathy. The donor is hypovolaemic and has a reticulocytosis in response to the anaemia while maternal hypertension and diabetes may influence stroke risk. Understanding of the mechanisms, including the role of vasculopathy, in well studied conditions such as alloimmune thrombocytopaenia and monochorionic diamniotic twinning may lead to reduction of the burden of antenatally sustained cerebral palsy.