Fetal head biometry assessed by fetal magnetic resonance imaging following in utero myelomeningocele repair.

OBJECTIVE: To examine the impact of fetal myelomeningocele (MMC) repair on fetal head biometry and cerebrospinal fluid (CSF) spaces assessed by magnetic resonance imaging (MR) studies. STUDY DESIGN: Axial measurements of intracranial structures were taken at defined anatomical landmarks. Pre- and postnatal head biometry data and CSF spaces obtained from in utero repaired MMC fetuses (n = 22) were compared to the pre- and postnatal measurements of MMC patients that underwent standard neurosurgical MMC repair after birth (n = 16) and a cohort of age-matched control patients (prenatal, n = 52; postnatal, n = 9). RESULTS: In fetuses with MMC, initial MR scans showed an almost complete absence of supratentorial and posterior fossa CSF spaces. No differences in postnatal CSF spaces were found between controls and prenatally repaired MMC newborns. In fetuses with postnatal MMC repair, CSF spaces remained significantly reduced (p < 0.0001). The mean ventricular diameter (VD) increase in the postnatal repaired MMC group was significantly higher compared to the mean percentage of VD increase in the fetal repaired MMC group (6.4 vs. 4.2 mm; p = 0.02). Pre- and postnatal brain thickness measurements were significantly reduced in both MMC populations compared to age-matched normal values (p < 0.0001). In contrast to postnatally repaired patients, in utero repair fetuses showed significant reversal of hindbrain herniation and normalization of the posterior fossa CSF spaces. CONCLUSION: Mid-gestational repair of MMC promotes normalization of extra-axial CSF spaces. Due to progressive ventriculomegaly, brain thickness remains decreased in both prenatal repaired and age-matched non-repaired MMC patients when compared to age-matched normal values. Restoration of CSF volume in the posterior fossa after in utero repair is indicative of reversal of hindbrain herniation.

Evolution of subarachnoid space in normal fetuses using magnetic resonance imaging.

OBJECTIVE: The purpose of this study was to measure the fetal subarachnoid spaces at different sites of the brain using magnetic resonance (MR) images and analyze them in relation to gestational age. METHODS: Fetal MR images were obtained from 158 fetuses between 18 and 39 weeks of gestation who later showed no neurological problems. We bilaterally measured the distance between the superoanterior gyrus and the cranium as the frontal subarachnoid space (FSS) and the distance between the cortex in the parieto-occipital sulcus and the cranium as the parietal subarachnoid space (PSS). We also measured the cisterna magna between the cerebellar vermis and the cranium. Each of these was analyzed in relation to gestational age. RESULTS: The width of the FSS began to decrease significantly at 32 weeks of gestation (P < 0.05). The width of the PSS started to decrease significantly at 34 weeks of gestation (P < 0.05). There was no difference between the right and left sides (P < 0.05). The size of the cisterna magna showed a positive correlation with gestational age (P < 0.05). CONCLUSION: Measurement of the subarachnoid space is potentially useful for evaluating fetal development.

Embryology of the internal carotid artery dural crossing: apropos of a continuous series of 48 specimens.

The aim of this study was to describe the embryologic and foetal development of the anterior paraclinoid region and more precisely the relationship of the internal carotid artery to the dura mater. This has been done by examining a collection of histological sections, representing a continuous series of 48 embryologic and foetal specimens, covering the period of the first 6 months of intra-uterine life. Neurological and vascular elements develop during the embryologic period; the internal carotid artery is recognizable in the various sections of its course and acquires a histological adult parietal constitution. The foetal period corresponds to the development of the meningeal structures. The superior, medial and lateral walls appear on the fifteenth week of amenorrhoea and do not change after that. The internal carotid artery enters subarachnoid space accompanied by a sleeve of mesenchymatous cells, which fixes it to the anterior clinoid process. The constitution of this sleeve, arising from the superior wall of the lateral sellar compartment, remained independent of the principle vascular part, which allows the formation of a plan of cleavage. The foetal relations of the dura mater and the internal carotid artery were seen to be different from those of adult subjects described in the literature, suggesting an existence of period of maturation postnatally.

The subarachnoid space develops early in the human embryonic period.

The anlage of the subarachnoid space is seen in embryos at stage 14 (33 days) in the innermost zone of the primary meninx as irregular spaces on the ventral surface of the spinal cord. At first this space is only on the ventral surface of the spinal cord. From stage 18 (44 days) on, when the dura mater proper is formed, the reticular tissue of the primary meninx and spaces are around the circumference of the spinal cord. These spaces gradually coalesce and contain many blood vessels.

The structure and development of avian lumbosacral specializations of the vertebral canal and the spinal cord with special reference to a possible function as a sense organ of equilibrium.

The avian lumbosacral vertebral column and spinal cord show a number of specializations which have recently been interpreted as a sense organ of equilibrium. This sense organ is thought to support balanced walking on the ground. Although most of the peculiar structures have been described previously, there was a need to reevaluate the specializations with regard to the possible function as a sense organ. Specializations were studied in detail in the adult pigeon. The development of the system was studied both in the pigeon (semiprecocial at hatching) and in the chicken (precocial). Specializations in the vertebral canal consist of a considerable enlargement, which is not due to an increase in the size of the spinal nervous tissue, but to a large glycogen body embedded in a dorsal rhomboid sinus. The dorsal wall of the vertebral canal shows segmented bilateral dorsal grooves, which are covered by the meninges towards the lumen of the vertebral canal leaving openings in the midline and laterally. This results in a system of lumbosacral canals which look and may function similar to the semicircular canals in the inner ear. Laterally these canals open above ventrolateral protrusions or accessory lobes of the spinal cord which contain neurons. There are large subarachnoidal cerebrospinal fluid spaces, lateral and ventral to the accessory lobes. Movement of this fluid is thought to stimulate the lobes mechanically. As to the development of avian lumbosacral specializations, main attention was given to the organization of the lobes and the adjacent fluid spaces including the dorsal canals. In the pigeon the system is far from being adult-like at hatching but maturates rapidly after hatching. In the chicken the system looks already adult-like at hatching. The implications derived from the structural findings are discussed with regard to a possible function of the lumbosacral specializations as a sense organ of equilibrium. The adult-like organization in the newly hatched chickens, which walk around immediately after hatching, supports the assumed function as a sense organ involved in the control of locomotion on the ground.

[Lipomatous hamartomas of the brain--malformations of the subarachnoid space]. / Lipomatózní hamartomy mozku--malformace subarachnoidálního prostoru.

Lipomatous hamartomas are rare disorders affecting the central nervous system. In our report, two observations of this disorder are presented. Both are interhemispheric in location and are associated with a complete agenesis of the corpus callosum, while having different histological structures. In our first patient, the intracranial formation caused refractory seizures, was partially surgically removed, and a biopsy was performed. Light microscopic examination disclosed the presence of a highly vascularized mature adipose tissue with numerous calcifications. The second case was an incidental finding at autopsy. Microscopically, we found adipose tissue together with numerous foci of hemopoiesis and structures of lamelar bone. In both cases, the indistinct demarcation of the collagenous capsule from the surrounding brain tissue and the continuity of the hamartoma with the leptomeninges were striking. In recent findings about the development of meninges and brain commissures, the origin of this disorder is explained as a defective resorption of the embryonic meninx primitiva. This disorder then causes other developmental aberrations of the brain, which are often found in association. The varying microscopic pattern of these disorders can also be satisfactorily explained by their origin in the primitive meninx, which is formed from both mesenchyme and neuroectoderm.

The subarachnoid space: normal fetal development as demonstrated by transvaginal ultrasound.

Enlargement of the subarachnoid spaces can be seen in the following conditions: communicating hydrocephalus, brain atrophy and benign enlargement of the subarachnoid spaces. These disorders may begin in utero. There are no established normograms for the fetal subarachnoid spaces. This study was conducted in order to determine its normal development. Transvaginal sonography was used to examine the subarachnoid space in 80 fetuses between 16 and 40 weeks' gestation. The sinocortical width (SCW) and craniocortical width (CCW) were measured in a coronal plane at the level of the foramen of Monro. The SCW remained relatively constant during the gestational period. The CCW increased in size from the 20th to the 28th week of pregnancy, with a subsequent gradual decrease until term. Determination of fetal subarachnoid space normograms may potentially help in the diagnosis of pathological conditions affecting this space and allow prenatal counselling.

Normal fetal brain development: MR imaging with a half-Fourier rapid acquisition with relaxation enhancement sequence.

PURPOSE: To analyze normal maturation of the fetal brain with half-Fourier rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: The normal brains of 25 fetuses of 12-38 weeks gestational age were examined in utero with half-Fourier RARE imaging. Gyrus maturation, gray and white matter differentiation, ventricle-to-brain diameter ratio, and subarachnoid space size were evaluated with respect to gestational age. RESULTS: At 12-23 weeks, the brain had a smooth surface, and two or three layers were differentiated in the cerebral cortex. At 24-26 weeks, only a few shallow grooves were seen in the central sulcus, and three layers, including the immature cortex, intermediate zone, and germinal matrix, were differentiated in all fetuses. At 27-29 weeks, sulcus formation was observed in various regions of the brain parenchyma, and the germinal matrix became invisible. Sulcation was seen in the whole cerebral cortex from 30 weeks on. However, the cortex did not undergo infolding, and opercular formation was not seen before 33 weeks. At 23 weeks and earlier, the cerebral ventricles were large; thereafter, they gradually became smaller. The subarachnoid space overlying the cortical convexities was slightly dilated at all gestational ages, most markedly at 21-26 weeks. CONCLUSION: Changes in brain maturation proceed through stages in an orderly and predictable fashion and can be evaluated reliably with half-Fourier RARE MR imaging.

Meningioma with extensive vacuolization--a contribution to the pathogenesis of intratumoral cyst formation.

Seven cases of meningioma with extensive vacuolization are reported. Upon plain CT, two cases appeared as diffuse hypodense masses, while two cases were mixed-density masses consisting of iso-dense and low-density components. A diffuse marked enhancement effect was seen in three cases and a thin ring enhancement effect appeared in one case. In four of these cases, macroscopic cysts were observed. It is suggested that the formation of macroscopic cysts or microscopic vacuoles mimics the developmental process of the subarachnoid space in the embryo. A review of the literature on this phenomenon is presented.

The meninges in human development.

The brain and cranial meninges were studied in 61 serially sectioned embryos of stages 8-23. Much earlier stages than those examined by previous authors provided a more comprehensive view of meningeal development. As a result, the possible and probable sources of the cranial and spinal meninges are believed to be: (a) prechordal plate, (b) unsegmented paraxial (parachordal) mesoderm, (c) segmented paraxial (somitic) mesoderm, (d) mesectoderm (neural crest), (e) neurilemmal cells (neural crest), and (f) neural tube. Some of these sources (a, b, d) pertain to the cranial meninges, others (c, d, e) to the spinal coverings. The first of the future dural processes to develop is the tentorium cerebelli, which, at the end of the embryonic period proper, differs considerably in shape and composition from the later fetal and postnatal tentorium. The embryonic dural limiting layer (Duragrenzschicht) probably corresponds to the interface layer of the adult meninges. The appropriate literature was reviewed and summarized.

[Ultrastructure of the hyaloid canal and its retraction during gestation (author's transl)]. / Ultrastruktur des Canalis hyaloideus (Cloquet) und seine Rückbildung während der fetalen Wachstumsperiode.

1. The cells of the hyaloid canal originate from the primitive meningeal cells; 2. The lumen of the hyaloid canal can be observed through the optic nerve up to the subarachnoid space around the optic nerve; 3. Injections of tracer substances into the subarachnoid space of the optic nerve have shown that a communication between the subarachnoidal space and the lumen of the hyaloid canal is formed up to the capsula of the lens during the first 14 weeks of gestation. It may be assumed that in vivo cerebrospinal fluid reaches the lens because of the hyperplastic differentiation of the choroid plexus in the sixth week of gestation; 4. The distal two-thirds of the hyaloid canal retract between the 17th and 22nd week of gestation; 5. From the beginning of the 22nd week of gestation there exists an open communication between the subarachnoid space and the corpus vitreum.

The subarachnoid space: a review.

A historical review of our knowledge of the subarachnoid space dates from the ancients through the modern electron microscope era. Conflicting observation resulted from various methods of tissue preservation and species variability. A comparative submicroscopic study shows striking similarities in the ultrastructure and distribution of the subarachnoid space in mice, cats, monkeys and man. Development of the pia-arachnoid membranes in the mouse occurs in four stages: the first follows closure of the neural tube and is a period of initial vascularization of the developing telencephalon; the second is a period of delineation during which the limits of the subarachnoid space are defined; the third is a period of ensheathment of pia-arachnoidal blood vessels; and the fourth includes addition of smooth muscle to larger vessels, the appearance of macrophages in the subarachnoid space, and a general increase in extracellular collagenous and elastic fibers. The subarachnoid space over the telencephalic surface in the 10-day fetus exists prior to the secretion of cerebrospinal fluid as the typically large extracellular space of mesenchyme. By the 13th fetal day cerebrospinal fluid begins to seep into and replace the ground substance of the mesenchyme. The mesenchymal extracellular compartment is reduced peripherally, resulting in a compacted pia-arachnoidal tissue which limits the peripheral extent of the subarachnoid space. By the 21st postnatal day a subarachnoid space typical of the adult animal has been established. The developmental sequence occurring in the tissues surrounding the central nervous system is important to our understanding of the pathogenesis of hydrocephalus and congenital anomalies.

Development of the cerebrospinal fluid pathway in the normal and abnormal human embryos.

The subarachnoid space, the chorioid plexus and the arachnoid villi are microscopically studied in 60 normal human embryos and in 3 abnormal human embryos with rhombencephaloschisis and cervical myeloschisis. The subarachnoid space has been generally considered to be developed by outflow of cerebrospinal fluid (CSF) of the choroid-plexus origin from the IVth ventricle. This generally accepted concept does not meet with our findings: (1) cavity formation in the meninx primitiva is seen before appearance of the choroid plexus; (2) the primitive subarachnoid space is developed earlier in the prepontine region than in the area dorsal to the rhombic roof, and (3) the primitive subarachnoid space is formed in the embryos with dysraphism where the perineural subarachnoid space is separated from the ventricles. Apparently the embryonic pattern of CSF circulation should be much different from the generally believed pattern of adult, since the arachnoid villi are absent in the embryos and the ability of production of CSF in the embryonic choroid plexus is questionable. It is suggested that such embryonic pattern of CSF production and absorption may partly persist in adult human being.

[The development of cerebro-spinal fluid pathway in human embryos (author's transl)].

The early development of the subarachnoid space, the choroid plexus, and the arachnoid villi was studied in 60 normal human embryos ranging from Carnegie stage 12 to 23. The embryos were fixed in Bouin's fluid, paraffin-embedded, serially sectioned and stained with hematoxylin-eosin and Azan. One abnormal human embryo with exencephaly and myeloschisis in the high cervical cord was added for the study. A primitive subarachnoid space (future subarachnoid space) is first distinguishable as cavity formation within the meninx primitiva in the areas ventral to the middle brain vesicle at stage 14. The development of the primitive subarachnoid space precedes the appearance of the choroid plexus. The primitive subarachnoid space appears earlier in the region ventral to the rhombencephalon than in the region posterior to the fourth ventricle. By stage 20, a primitive subarachnoid space almost completely surrounds the neural tube. A fairly-well developed primitive subarachnoid space was observed in the abnormal human embryo, in which the fourth ventricle was open to the amniotic cavity and the ventricular system was completely separated from the primitive subarachoid space. These findings imply that the extraventricular spread of fluid of choroid plexus origin is not an essential factors, and that probably it is not even an important factor, for the development of the subarachnoid space. The arachnoid villi dose not appear even at the end of the embryonal stage. Absorption of the cerebrospinal fluid in an embryo should be done by the way other than the arachnoid villi.

Developmental morphology of the subarachnoid space and contiguous structures in the mouse.

Development of pia-arachnoidal membranes in the mouse occurs in four stages: the first (prenatal days 10-13) follows closure of the neural tube and is a period of initial vascularization of the developing telencephalon; the second (prenatal days 14-16) is a period of delineation during which the limits of the subarachnoid space are defined; the third (prenatal day 17 to birth) is a period of ensheathment of pia-arachnoidal blood vessels; and the fourth (birth to postnatal day 21) includes addition of smooth muscle to larger vessels, the appearance of macrophages in the subarachnoid space, and a general increase in extracellular collagenous and elastic fibers. The mesenchyme over the telencephalic surface in the 10-day fetus has a typically large extracellular space. By the 13th fetal day cerebrospinal fluid begins to seep into and replace it. The mesenchymal extracellular compartment is reduced peripherally, resulting in a compacted pia-arachnoidal tissue which limits the peripheral extent of the subarachnoid space. By the 21st postnatal day a subarachnoid space typical of the adult animal has been established.

[Form and development of the human fetal subarachnoid cistern]. / Gestalt und Entwicklung der subarachnoidealen Zisternen beim menschlichen Feten

The development and form of the human fetal subarachnoid spaces have been elucidated by reconstruction (34 mm CRL fetus) and by plastic casts (several 20-30 cm CRL fetuses). Equivalents of adult cisterns are present in the young fetus. In older fetuses the cisternal shape is of adult type. It is suggested that pressure from the growing brain produces tension in the arachnoid mesenchyme and determines the initial orientation of the endo-ecto-meningeal limiting membrane. The fluid-filled subarachnoid spaces and the fetal brain together form a composite structural unit probably defining the configuration of the fetal head capsule. Prospective sutures develop over the inner ridges of the fetal dura. However, the lambda suture and the associated base of the tentorium eventually separate.