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Biomedical subjects

J R Siebert

Publications and source records attributed to J R Siebert.

46 records · Page 3Linked to original sources
PubMed1982

The ethmoid bone: implications for normal and abnormal facial development.

Deficiencies of the ethmoid and embryologically related bones of the anterior cranium have been observed in patients with abnormalities in development or placement of the orbits and eyes, nose, upper lip, mouth, and palate. Although these facial anomalies are commonly associated with holoprosencephaly, they may occur in other syndromes or as isolated cases with normocephaly. Such facial alterations represent the consequences of aberrant migration of tissues into the region normally occupied by the ethmoid bone, beginning early in the sixth week of gestation. The subtle interplay of forces involved in the normal development of the median face appears to be mediated by the ethmoid bone. This interaction may be perceived by dividing the ethmoid bone into three functional components which correspond to and operate in each of the major anatomic planes.

Cell Differentiation↗
PubMed1981

The facial features of holoprosencephaly in anencephalic human specimens. I. Historical review and associated malformations.

At least 19 human anencephalic specimens have been published which have the facial features of holoprosencephaly. All categories of holoprosencephaly are represented except ethmocephaly, the rarest form. Because of current scientific and clinical interest in both neural tube defects and holoprosencephaly it seems important to establish whether or not this association occurs by chance alone. The study of human embryos with holoprosencephaly by Matsunaga and Shiota ('78) and the anencephalic collection of Lemire et al ('78) suggests the association may be real.

Abnormalities, Severe Teratoid↗
PubMed1981

The facial features of holoprosencephaly in anencephalic human specimens. II. Craniofacial anatomy.

The craniofacial anatomy of two anencephalic human specimens with the facial features of holoprosencephaly is reported. Many of the malformations have distinctly holoprosencephalic or anencephalic features. Absence of the entire ethmoid complex, observed in both specimens of the present study, has rarely been described and, to our knowledge, has never been confirmed histologically. The significance of agenesis of the ethmoid bone in the development of normal and holoprosencephalic facial features has not been considered previously. On the basis of several morphological variations in the two specimens described, it is evident that the ethmoid bone provides integral support in multiple planes for tissues of the median face. It is postulated that the spatial relationships of the bony and soft tissue components of the median face are guided and maintained by the ethmoid complex during morphogenesis. Specifically, hypotelorism and superiorly displaced structures of the nose and upper lip may well represent migration of embryonic tissues into areas normally occupied by the ethmoid bone. Absence of the sella turcica and pituitary gland is ascribed to the holoprosencephalic process. A variant of choanal atresia, due to collapse of the pterygoid plates, is described.

Anencephaly↗
PubMed1980

Small-intestine length in infants and children.

Small-intestine length from ligament of Treitz to ileocecal valve was measured in 183 infants and children ranging up to 15 years of age. Elongation of the intestine was rapid until crown-heel length was 60 cm and remained constant from 100 to 140 cm of body length. When patients were placed into three general diagnostic categories (congenital heart disease, abdominal lesions, and miscellaneous) no significant differences were found. However, several striking instances of abnormally long or short small intestines were encountered.

Adolescent↗
PubMed1977

Observations on trichinosis in the rhesus monkey.

Monkeys infected with 2.0 larvae/g body weight died 31-41 days post-infection (PI): two of three monkeys infected with 1.0 larva/g body weight became moribund and were sacrificed at 50 days, but six of six monkeys infected with 1.0 larva/g body weight were healthy 225 days PI. Periorbital and facial edema and eosinophilia were observed in all groups during the second week PI, and myalgia and stiffening of joints was observed during the third week. High numbers of encyse, biceps brachii and deltoideus. Adult worms were recovered from the intestine 49 days PI. The morphological changes were essentially similar to those seen in humans and a generalized lymphoid hyperplasia was not observed. Thus, rhesus monkeys develop trichinosis which show similarities clinically, pathologically and morphologically to human disease.

Animals↗
PubMedDate not supplied

Cyclopamine-induced holoprosencephaly and associated craniofacial malformations in the golden hamster: anatomic and molecular events.

Holoprosencephaly is a complex congenital malformation of the brain and is often associated with a spectrum of facial anomalies ranging from normocephaly or nondiagnostic changes to cleft lip/palate (premaxillary dysgenesis), cebocephaly, ethmocephaly, and cyclopia. The primary insult is thought to occur during gastrulation, when prechordal mesenchyme and overlying anterior neural plate undergo complex developmental interactions. Exposure to cyclopamine, a steroid isolated from the desert plant Veratrum californicum, causes holoprosencephaly in mammalian embryos. We have begun to study the pathogenesis of cyclopamine-induced holoprosencephaly and associated craniofacial anomalies in Syrian golden hamsters (Mesocricetus auratus). Embryos were exposed to a single maternal dose of cyclopamine during gastrulation on embryonic day (E) 7.0. By E13.0, 62% of fetuses showed craniofacial malformations, including premaxillary dysgenesis, ocular hypotelorism, and cebocephaly. Facial anomalies were associated with absence of the premaxilla and abnormalities of the midline cranial base, particularly the ethmoid and sphenoid bones. Histological sections from cyclopamine-treated embryos at earlier stages showed marked deficiency of cranial mesenchyme derived from the rostral neural crest. Expression of two transcription factors, HNF-3 beta and Hox-b5, which have been implicated in specification of rostral and caudal neural crest cells, respectively, were examined immunohistochemically. Treatment with cyclopamine caused a transient loss of HNF-3 beta immunoreactivity in prechordal mesenchyme, but had no effect on Hox-b5 expression. The findings suggest that an early event in the pathogenesis of cyclopamine-induced holoprosencephaly may be altered expression of selected proteins in the prechordal mesenchyme and floor plate with secondary impaired development of the adjacent neural plate and cranial neural crest.

Animals↗
PubMedDate not supplied

Cerebral mantle thickness: a measurement useful in anatomic diagnosis of fetal ventriculomegaly.

The ultrasonographic diagnosis of cerebral ventriculomegaly carries grave implications, in that affected fetuses may suffer abnormal postnatal development or therapeutic abortion. It is important for pathologists to corroborate the clinical diagnosis, but because diagnostic methodologies and criteria differ so radically, this can be problematic. The clinical diagnosis is made primarily by serial ultrasound examinations of the cerebral ventricles, spaces that can be altered postmortem, particularly when the brain is autolysed or deformed artifactually. We therefore sought to learn if examination of tissue, rather than spaces, can identify accurately those fetuses diagnosed with cerebral ventriculomegaly by prenatal ultrasound. The thickness of the cerebral mantle was obtained in 100 control fetuses aged 14 to 26 postmenstrual weeks. Statistical analysis revealed significant correlation of cerebral mantle thickness with crown-rump length, foot length, and head circumference. Twenty fetuses diagnosed with ventriculomegaly showed mantle thicknesses that were less than the control mean. In a few cases, mantle thickness fell between the mean and -1 SD; in several others, thickness was diminished by -1 SD to -2 SD; in one-half of cases, mantle thickness was 2 SDs or more below the expected mean. Head circumference was within 2 SDs of the control mean in most cases, and increased beyond 2 SDs in only two cases. Head circumference is an unreliable indicator of ventriculomegaly in the midgestational fetus. By contrast, cerebral mantle thickness is a simple and useful way of corroborating ultrasonographic diagnoses at autopsy and may also prove useful in clinical settings.

Case-Control Studies↗
PubMedDate not supplied

Enlargement of the tongue in sudden infant death syndrome.

Anatomic details of the infantile oropharynx and relationships to possible airway obstruction in sudden infant death syndrome (SIDS) are understood incompletely. Tonkin recognized this in 1975, suggesting that enlargement of the tongue might be important in SIDS, within the context of other anatomic and physiologic factors unique to early life. We therefore conducted a morphometric study of the tongue in 100 victims of SIDS and 36 control infants; the latter group consisted of infants with the same range in age and body size who had grown normally and died acutely. Highly significant differences in tongue weight, width, and thickness were demonstrated between the two groups by linear regression and analysis of covariance. Two multivariate techniques, stepwise discriminant analysis and factor analysis, identified marked discordance between somatic and lingual size in SIDS and a statistical uniqueness in tongue thickness. Certain explanations for lingual enlargement in SIDS were ruled out: redistribution of fluid and other effects of death, postmortem interval, duration and mode of feeding, and smallness of control tongues. At present, the functional significance of these observations is unclear. The effects of both normal and increased tongue size on airway patency are, however, widely recognized. Further studies of the enlarged tongue, addressing such topics as in situ anatomy and developmental mechanisms, are necessary to establish the potential for pathophysiologic consequences in SIDS.

Analysis of Variance↗
PubMedDate not supplied

Organ weights in sudden infant death syndrome.

This comprehensive study of organ weights in sudden infant death syndrome (SIDS) should be of use to those studying postmortem data in SIDS and may have application to issues of growth and development. Analysis of data from 500 autopsies, performed over 15 years by one individual, revealed mean body weights generally below the 50th percentile for living infants. The weights of the thymus, lungs, liver, and brain were significantly greater than published norms. Thymic weights in SIDS probably represent the normal state more closely than those reported in several other series; elevated lung weights are presumably due to the intense pulmonary congestion and edema commonly encountered in SIDS; the liver edge routinely extends below the costal margins at SIDS autopsies, but the reason for increased weight is unknown, although a hemodynamic alteration seems likely; elevated brain weight has been described previously in SIDS. Other organs showed trends differing from "normal"--heart weights showed a marginally significant increase above published norms; for the adrenal glands, a uniform decrease was apparent, but slopes of linear regressions were low, hampering statistical analysis. Organ weights correlated more closely with body weight than with age. When victims were classified as "possible SIDS," "probable SIDS," or "classic SIDS," differences in organ weights were rarely significant. Analysis of organ weights using Z scores and their standard deviations (sigma-Z, or "pattern variability index") revealed increased variability in SIDS victims. Explanations for these findings include the possibility that some weights previously published as normal are low due to confounding variables. Changes could also be genuine, resulting from disturbances in growth or physiology, or artifactual, possibly the result of agonal or postmortem changes. A database on carefully selected, previously healthy infants who died suddenly and unexpectedly of known causes (i.e., trauma) is much needed.

Body Weight↗