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Biomedical subjects

M S Dias

Publications and source records attributed to M S Dias.

14 recordsLinked to original sources
PubMed1995

Split cord malformations.

Previous classifications of split cord malformations (SCM's), including such terms as diastematomyelia and diplomyelia, have done little to foster a true understanding of these disorders. The authors instead propose a unifying classification in which all SCM's share a common embryogenesis. SCM's are divided into two types, based upon the composition of the dural coverings and intervening mesenchymal tissue. Type I malformations are composed of two dural sacs and a bony or fibrocartilaginous spur; Type II malformations are composed of a single dural sac and intradural fibrous bands. In either case, the intervening mesenchymal elements contribute to progressive neurologic, urologic, and orthopedic deterioration from spinal cord tethering. The natural history of these lesions supports an early and aggressive operative approach to untether the spinal cord before clinical deterioration begins.

Adolescent↗
PubMed1992

Mesoderm movement and fate during avian gastrulation and neurulation.

Quail/chick transplantation chimeras were constructed during stages of gastrulation and neurulation to follow the subsequent movement and fate of cells of the primitive streak. All grafts were placed solely within the confines of the primitive streak to prevent confusion between cells that had not yet ingressed and those that had already ingressed, and transplanted cells were distinguished from host cells on the basis of a naturally occurring cell marker. Pathways of movement of ingressing cells corresponded to their level of residence within the primitive streak. Cells residing within Hensen's node (the cranial end of the primitive streak) initially migrated mainly cranially, remaining on or near the midline, and then extended caudally along the midline as regression of Hensen's node occurred. Cells residing within the nodus posterior (the caudal end of the primitive streak) migrated caudally. Cells residing at levels of the primitive streak between Hensen's node and the nodus posterior typically migrated bilaterally, confirming that such cells had not already ingressed prior to their transplantation (in which case, they would have migrated unilaterally). Subsets of these cells residing at progressively more caudal levels of the primitive streak migrated incrementally more laterally. Hensen's node contributed cells to the gut endoderm, head mesenchyme, notochord, and median hinge-point (MHP) cells of the neural tube (future floor plate). At younger stages (i.e., stages 3a, 3b) Hensen's node contributed cells to principally the foregut endoderm and head mesenchyme, whereas at older stages (i.e., stages 3c, 3d, 4), it contributed cells to principally the notochord and MHP region. The remaining segments of the cranial half of the primitive streak contributed cells to the various mesodermal subdivisions of the embryo, and the lengths of the segments forming these subdivisions were estimated. The most cranial level of the streak (directly behind Hensen's node) contributed cells to the most medial mesodermal subdivisions (head mesenchyme, somites) and consecutively more caudal levels of the streak contributed cells to sequentially more lateral mesodermal subdivisions (intermediate mesoderm, lateral plate mesoderm). The caudal half of the primitive streak contributed cells to the extraembryonic mesoderm, with the nodus posterior contributing to the most caudal extraembryonic mesoderm, including the blood islands. Our results confirm and extend the previous avian prospective fate maps, increasing our understanding of the movement and fate of cells of the gastrula and neurula stages.

Animals↗
PubMed1992

Split cord malformation: Part I: A unified theory of embryogenesis for double spinal cord malformations.

Much confusion still exists concerning the pathological definitions and clinical significance of double spinal cord malformations. Traditional terms used to describe the two main forms of these rare malformations, diastematomyelia and diplomyelia, add to the confusion by their inconsistent usage, ambiguities, and implications of their dissimilar embryogenesis. Based on the detailed radiographic and surgical findings of 39 cases of double cord malformations and the autopsy data on two other cases, this study endorses a new classification for double cord malformations and proposes a unified theory of embryogenesis for all their variant forms and features. The new classification recommends the term split cord malformation (SCM) for all double spinal cords. A Type I SCM consists of two hemicords, each contained within its own dural tube and separated by a dura-sheathed rigid osseocartilaginous median septum. A Type II SCM consists of two hemicords housed in a single dural tube separated by a nonrigid, fibrous median septum. These two essential features necessary for typing, the state of the dural tube and the nature of the median septum, do not ever overlap between the two main forms and can always be demonstrated by imaging studies so that accurate preoperative typing is always possible. All other associated structures in SCM such as paramedian nerve roots, myelomeningoceles manqué, and centromedian vascular structures frequently do overlap between types and are not reliable typing criteria. The unified theory of embryogenesis proposes that all variant types of SCMs have a common embryogenetic mechanism. Basic to this mechanism is the formation of adhesions between ecto- and endoderm, leading to an accessory neurenteric canal around which condenses an endomesenchymal tract that bisects the developing notochord and causes formation of two hemineural plates. The altered state of the emerging split neural tube and the subsequent ontogenetic fates of the constituent components of the endomesenchymal tract ultimately determine the configuration and orientation of the hemicords, the nature of the median septum, the coexistence of various vascular, lipomatous, neural, and fibrous oddities within the median cleft, the high association with open myelodysplastic and cutaneous lesions, and the seemingly unlikely relationship with fore and midgut anomalies. The multiple facets of this theory are presented in increasing complexity against the background of known embryological facts and theories; the validity of each facet is tested by comparing structures and phenomena predicted by the facet with actual radiographic, surgical, and histopathological findings of these 41 cases of SCM.

Adolescent↗
PubMed1991

Neurenteric cysts of the posterior fossa: recognition, management, and embryogenesis.

Neurenteric cysts are endothelium-lined structures most commonly encountered in the lower cervical or upper thoracic spinal cord. The occurrence of neurenteric cysts within the cranial vault is unusual. We present three patients with neurenteric cysts located within the posterior fossa: one near the jugular foramen deforming the 4th ventricle, a second in the cerebellopontine angle, and a third in the prepontine cistern. Several different theories have been advanced to explain the embryogenesis of neurenteric cysts. We review these theories and conclude that cranial neurenteric cysts may arise from a disturbance of early gastrulation, shortly after the onset of primitive streak regression.

Adult↗
PubMed1991

Juvenile intervertebral disc calcification: recognition, management, and pathogenesis.

Juvenile intervertebral disc calcification is an uncommon disorder of childhood, characterized by calcification of the nucleus pulposus of one or more intervertebral discs. Calcification may remain dormant or subsequently become symptomatic. The symptoms include fever, malaise, and neck pain and are associated with an elevated erythrocyte sedimentation rate and, occasionally, leukocytosis. Although disc protrusion occurs in 38% of patients, neurological signs are distinctly uncommon. We report the case of a patient with a herniated T2-T3 calcified intervertebral disc and compressive myelopathy. Juvenile intervertebral disc calcification is generally a self-limiting disease that seldom requires an operation. The symptoms are transient, and resorption of the disc calcification is the rule once symptoms occur. Neither the cause of the disc calcification nor the trigger for the onset of symptoms is known. An inflammatory response within the disc appears to give rise to clinical symptoms and is associated with eventual resorption of the disc calcification.

Calcinosis↗
PubMed1990

Formation of ectopic neurepithelium in chick blastoderms: age-related capacities for induction and self-differentiation following transplantation of quail Hensen's nodes.

Hensen's node, regarded as the avian and mammalian homologue of Spemann's neural inducer (i.e., the amphibian dorsal blastoporal lip), has been transplanted in many previous studies to the germinal crescent of avian blastoderms to examine ectopic neural induction. All these studies have suffered from one or more major shortcomings, the most significant of which has been the lack of a reliable cell marker to determine the contributions of graft cells to ectopic embryos. In the absence of such marker, induced (i.e., derived from the host) and self-differentiated (i.e., derived from the graft) neurepithelium cannot be distinguished from one another with certainty. We have transplanted quail Hensen's nodes to chick host blastoderms and have subsequently used the quail nucleolar heterochromatin marker to identify graft cells unequivocally. We systematically varied both donor and host ages (i.e., stages 3-8 and 3-5, respectively) to examine the effects of age on ectopic neural induction and self-differentiation. Our results demonstrate that the age of the donor is more critical than that of the host over the stages examined. With advancing donor age, the frequency of host induction decreases, while the frequency of graft self-differentiation increases. Previous studies not using cell markers have concluded that the craniocaudal level of the induced neuraxis is determined by the age of the donor, that is, young donors induce cranial neuraxial levels, whereas old donors induce caudal levels. By contrast, we found that with grafts from older donors, neurepithelium was more commonly self-differentiated rather than induced and that progressively more caudal levels of the neuraxis self-differentiated with advancing donor age. Induction of caudal neuraxial levels never occurred in the absence of induced cranial levels. The frequency of neural induction was inversely correlated with the age of the donor and directly correlated with the quantity of graft endodermal cells contributed to the ectopic embryo, supporting a previous assertion that in avian embryos, the earliest and principal source of neural inducer lies within the endoderm rather than mesoderm. From our results, we propose that the role of neural induction is to produce neurepithelium of unspecified regional character, and that the formation of regional character depends on subsequent morphogenetic events.

Age Factors↗
PubMed1990

Intracranial hemorrhage from aneurysms and arteriovenous malformations during pregnancy and the puerperium.

Intracranial hemorrhage (ICH) from an intracranial aneurysm or arteriovenous malformation is a grave complication of pregnancy and is responsible for 5 to 12% of all maternal deaths. We critically analyzed 154 cases of verified ICH during pregnancy from an identified intracranial lesion, including 2 patients treated at our institution and 152 cases previously reported in the literature in English. Aneurysms were responsible for ICH in 77% of patients, and arteriovenous malformations in 23%. Hemorrhage occurred antepartum in 92% of patients and postpartum in 8%. Women with angiomatous hemorrhage were younger than those with aneurysmal hemorrhage; however, in contrast to previous reports, we found no differences between angiomatous and aneurysmal hemorrhage with respect to parity or gestational age at the time of the initial hemorrhage. Hypertension and/or albuminuria were present at some time during the pregnancy in 34% of patients with documentation, which sometimes made it difficult to differentiate angiomatous or aneurysmal ICH from that associated with eclampsia. In a logistic regression analysis, surgical management of aneurysms, but not arteriovenous malformations, was associated with significantly lower maternal and fetal mortality, independent of other covariants. For those patients with a lesion not operated on, cesarean delivery afforded no better maternal or fetal outcome than did vaginal delivery. We conclude that the decision to operate after ICH during pregnancy should be based upon neurosurgical principles, whereas the method of delivery should be based upon obstetrical considerations. The perioperative and anesthetic management of the pregnant patient with a neurosurgical complication is discussed.

Adult↗
PubMed1989

Management of hydrocephalus complicating childhood posterior fossa tumors.

We examined the treatment of hydrocephalus in children with posterior fossa tumors to (1) compare the use of external ventricular drainage (EVD) with ventriculoperitoneal shunts (VPS), (2) determine the frequency of postoperative hydrocephalus requiring permanent shunts, and (3) determine which factors predict the need for a permanent shunt. The records of 58 children with posterior fossa tumors and associated hydrocephalus treated at our institution from 1979 to 1987 were retrospectively reviewed. Initial management of hydrocephalus included VPS in 25 patients, EVD in 17, and no treatment in 16. Patients in the 'VPS', 'EVD', and 'no treatment' groups differed only in the severity of hydrocephalus (less severe in the no treatment group than in the VPS and EVD groups) and in the method of dural closure following tumor resection (dura was left open more often in the EVD and no treatment groups). Of the 33 patients not initially shunted, only 9 (27%) subsequently required a shunt. These patients were compared with the remaining 24 patients who did not require a shunt. Two features predicted the need for a subsequent shunt: (1) resection of only a small volume of tumor and (2) the dura open following tumor resection. Complications of EVD were few; no patient deteriorated neurologically during or after ventricular catheter removal. We conclude that between two thirds and three quarters of patients with childhood posterior fossa tumors and associated hydrocephalus may be managed with perioperative EVD and will not require shunts. Patients in whom only a minimal tumor resection is performed and those in whom the dura is left open are more likely to need permanent VPS.

Brain Neoplasms↗
PubMedDate not supplied

Complications of myelomeningocele closure.

Closure of a myelomeningocele is a deceptively simple operation; however, attention to several subtle details can significantly reduce operative complications. Important preoperative concerns include social issues of dealing with a distraught and often overwhelmed family, the timing of surgery, and assessment of associated severe or life-threatening malformations. Operative intervention should be directed toward preserving neurological function and optimizing the subsequent repair of a tethered spine should this become necessary. Careful attention to the vascular supply to the placode, precise separation of neural from cutaneous tissues, a diligent search for associated tethering anomalies such as diastematomyelia and a thickened filum terminale, careful pia to pia reconstruction of the placode, and simple but meticulous wound closure all help in achieving these aims. The timely management of associated hydrocephalus will help to avoid cerebrospinal fluid leakage and wound breakdown. Close attention to these details will ameliorate many of the immediate and delayed complications of myelomeningocele closure.

Humans↗