Atelencephalic microcephaly in a 21-week human fetus

Presence of congenital anomalies in three dog litters

This report describes multiple congenital malformations found in three dog litters delivered by emergency caesarean section. In all of the litters, some puppies were born alive but were euthanized because of the seriousness of their malformations and low probability of survival. In two litters, gastroschisis was associated with amelia of the right anterior limb. Other malformations such as anencephaly were also found in three puppies among the different litters. This report describes the morphological findings of the affected puppies, discusses the most appropriate terminologies for each case and highlights the importance of an epidemiological survey to identify potential factors associated with the cases.

Prenatal diagnosis of holoprosencephaly

Holoprosencephaly is a spectrum of congenital defects of forebrain development characterized by incomplete separation of the cerebral hemispheres. In vivo diagnosis can be established with prenatal brain imaging and disease severity correlates with extent of abnormally developed brain tissue. Advances in magnetic resonance imaging (MRI) over the past 25 years and their application to the fetus have enabled diagnosis of holoprosencephaly in utero. Here, we report on the prenatal diagnosis of holoprosencephaly using MRI as part of a diagnostic and management evaluation at a tertiary and quaternary referral center. Using an advanced MRI protocol and a 1.5-Tesla magnet, we show radiographic data diagnostic for the holoprosencephaly spectrum, including alobar, semilobar, lobar, middle interhemispheric, and septopreoptic variant. Accurate prenatal evaluation is important because the severity of imaging findings correlates with postnatal morbidity and mortality in holoprosencephaly. Therefore, this work has implications for the evaluation, diagnosis, management, and genetic counseling that families can receive during a pregnancy.

Prenatal evaluation of atelencephaly

Atelencephaly is a rare lethal congenital brain malformation characterized by underdevelopment of the prosencephalon and is often accompanied by the facial features seen in some cases of holoprosencephaly, such as cyclopia. We report a case of atelencephaly in the fetus with characteristic ultrasound findings. In addition, we report the findings on fetal MRI, which have not been previously described in the literature.

Holoprosencephaly-polydactyly (pseudotrisomy 13) syndrome: case report and diagnostic criteria

We report a new case of a fetus with holoprosencephaly-polydactyly syndrome, also known as pseudo-trisomy 13 syndrome, and no other apparent abnormalities except for septal agenesis of the left lung. The fetal karyotype was normal. Mutational analysis of five genes (SHH, SIX3, TGIF, ZIC2, and GLI3), which are major genes associated with holoprosencephaly, did not disclose any mutational findings. We therefore propose that the abnormalities of our fetus support the demarcation of this syndrome as an autonomous phenotype. Specific diagnostic criteria for holoprosencephaly-polydactyly syndrome need to be complemented by the absence of mutations in the major holoprosencephaly genes.

Cyclopia, aprosencephaly, and acardiac twinning: Is hypoxia-ischemia a unifying mechanism?

In a recent case of monochorionic diamniotic twinning we observed one twin with acardia, cyclopia, and aprosencephaly, an association not reported previously. In most cases of acardia, the development of tissues in superior regions of the body is disrupted severely, while inferior structures develop more normally. A common explanation for this disruption is hypoxia-ischemia due to twin reversed arterial perfusion (TRAP). In this condition, arterial-arterial and venous-venous anastomoses in the placenta permit twin-twin transfusion and reversal of blood flow in the umbilical vessels and aorta of the recipient twin. The heart is absent or severely deficient, either by secondary atrophy or possibly a more primary, though currently unknown, mechanism. As a result, cranial tissues are less likely to be perfused with oxygenated blood than caudal tissues. A host of craniocerebral anomalies are observed in acardia, including total absence of the head and brain, rudimentary brain, anencephaly, holoprosencephaly, neuronal migration defects, and near-normal brain. Hypoxia-ischemia could be an important factor in the disruption of tissues in the present case, although a more generalized process affecting heart, head, and brain cannot be excluded. The findings suggest that hypoxia-ischemia may play a role in the pathogenesis of some cases of holoprosencephaly and aprosencephaly. This mechanism has been underreported and requires additional investigation.

Holoprosencephaly: clinical, anatomic, and molecular dimensions

Holoprosencephaly is addressed under the following headings: alobar, semilobar, and lobar holoprosencephaly; arrhinencephaly; agenesis of the corpus callosum; pituitary abnormalities; hindbrain abnormalities; syntelencephaly; aprosencephaly/atelencephaly; neural tube defects; facial anomalies; median cleft lip; minor facial anomalies; single maxillary central incisor; holoprosencephaly-like phenotype; epidemiology; genetic causes of holoprosencephaly; teratogenic causes of holoprosencephaly; SHH mutations; ZIC2 mutations; SIX3 mutations; TGIF mutations; PTCH mutations; GLI2 mutations; FAST1 mutations; TDGF1 mutations; and DHCR7 mutations.

Holoprosencephaly and limb reduction defects: a consideration of Steinfeld syndrome and related conditions

Individuals with holoprosencephaly (HPE) and limb reduction defects have been ascribed historically to a variety of syndromes with overlapping phenotypic features. As such, these patients are challenges for clinicians and researchers alike. In an effort to better understand this association, we reviewed our autopsy records and identified five cases of HPE with reduction defects of the limbs and other anomalies. One case appears to be the third reported instance of Steinfeld syndrome, while others represent microgastria-limb reduction sequence, VATER/VACTERL association, and an additional unique condition characterized by HPE, rhombencephalosynapsis, absent left radius, first metacarpal, and thumb, and congenital heart disease. The phenotypic heterogeneity inherent in these patients continues to complicate diagnosis, which will hopefully be simplified by continuing delineation at morphologic and especially genetic levels.

XK-aprosencephaly and related entities

We offer further biological characterization of the XK atelen/aprosencephaly syndrome in two infants, one with prolonged survival, the other presenting prenatally with apparent hydranencephaly and an orbital tumor (OS). Familial occurrence in the former born to presumably nonconsanguineous Lybian parents may represent parental germinal mosaicism or autosomal recessive inheritance. Both had apparently normal chromosomes; however, the Lybian infant had slightly increased induced chromosome breakage suggesting that this rare multiple congenital anomalies syndrome may involve a DNA repair defect. Virtual absence of atelen/aprosencephalic structures may lead to an arthrogryposis-like prenatal movement disorder. The orbital tumor in the Utah infant consisted of dystopic neural tissue compressing a rudimentary globe and was connected by a thin bridge of neural tissue to the small mass of disorganized brain tissue usually found in atelen/aprosencephalic infants and fetuses. No evidence of an encephaloclastic process was found in the autopsied Utah infant.

Microcephaly with plate-like cortical calcification

Congenital malformations of the central nervous system have varied presentations depending on the stage of embryological development when the insult occurred. We report a neonate with microcephaly associated with plate-like cortical calcification, probably secondary to an unidentified insult at around 11-12 weeks post-conceptional age causing an arrest of the proliferative phase. The associated vasculopathy probably caused diffuse cortical calcification.

Aprosencephaly and cerebellar dysgenesis in sibs

Aprosencephaly is a rare, lethal malformation sequence of the central nervous system that has been attributed to a postneuralation encephaloclastic process. We describe autopsy findings consistent with aprosencephaly in 2 fetuses conceived from a consanguineous mating (first cousins). Both showed anencephalic manifestations; however, the crania were intact, with fused sutures. The neuropathologic findings were essentially identical. Each fetus had complete absence of the telecephalon and pyramidal tracts, rudimentary diencephalic and mesencephalic structures, primitive cerebellar hemispheres, posterolateral clusters of primitive neural cells in the medullas suggesting an abnormality of neural migration, a normally-formed spinal cord, and retinal dysplasia within normally-formed globes. In addition, both fetuses manifested a peculiar perivascular mesenchymal proliferation seen only within the central nervous system. The similarity of these cases, coupled with parental consanguinity, suggests a primary malformation in brain development due to the homozygous representation of a mutant allele. We hypothesize that these patients may represent a defect in a gene important in brain development, the nature of which has yet to be elucidated.

Atelencephalic aprosencephaly

Absence of the telencephalon and diencephalon characterizes the syndrome of aprosencephaly, while in atelencephaly, only the telencephalon is absent. Atelencephalic aprosencephaly is characterized by the presence of at least a rudimentary diencephalon. Embryologically, aprosencephaly is thought to occur after the optic vesicles form but before the cerebral vesicles appear. The syndrome is quite rare, with only 10 cases previously reported. We describe two fetuses with atelencephalic aprosencephaly. A 25-week estimated gestational age fetus was born to first-cousin parents and had a prenatal ultrasonographic diagnosis of anencephaly. The second, a 19-week estimated gestational age fetus, was thought to have semilobar holoprosencephaly by prenatal ultrasound. At autopsy, neuropathologic examination in both cases showed virtual absence of the cerebral hemispheres with an incomplete diencephalon. Microscopic examination in one case revealed disorganized neuropil with a proliferative vasculopathy. The optic globes were completely formed and attached to hypoplastic optic nerves, but retinal dysplasia was apparent histologically in both cases, and bilateral colobomata were present in one case. The findings in these cases demonstrate a spectrum of congenital variations that lie between the syndromes of atelencephaly and aprosencephaly, underscoring the complexity of the congenital anomalies.

Mosaic r(13) in an infant with aprosencephaly

We report on a stillborn male infant with a mosaic ring 13 karyotype (45,XY,-13/46,XY,-13,+r(13)) with apparent aprosencephaly and clinical findings similar to those reported previously in the XK-aprosencephaly syndrome. Findings of patients with r(13) are often similar to those seen in individuals with del(13q). This case was unusual because of the presence of aprosencephaly, although brain malformations such as arhinencephaly and cerebellar hypoplasia are present in at least one-half of reported patients with 13q-. The overlap between these syndromes suggests a possible chromosomal model of the XK-aprosencephaly syndrome.

Aprosencephaly: review of the literature and report of a case with cerebellar hypoplasia, pigmented epithelial cyst and Rathke's cleft cyst

Aprosencephaly is a very rare brain malformation that occurs in isolated and sydromatic forms. The syndromatic form has been named "XK-aprosencephaly", and is characterized by near total absence of prosencephalon with a midline oculofacial defect similar to the most severe forms of holoprosencephaly, in association with limb and genital anomalies. We present a case of syndromatic aprosencephaly with absence of thumb and abnormal external genitalia. A previously undescribed finding was a Rathke's cleft cyst. Two other cystic structure were also identified--an ependymal cyst, which may represent a dorsal cyst as in holoprosencephaly, and a pigmented epithelial cyst, which may represent a rudimentary eye. Additional findings were extensive calcific vasculopathy in the rudimentary prosencephalon, absence of pituitary gland, forking of the aqueduct of Sylvius and marked cerebellar hypoplasia. Since calcific vasculopathy is a common accompaniment of other inflammatory diseases of the central nervous system, its presence in this case suggests that destructive processes may be involved in the genesis of some cases of aprosencephaly.

Perspectives on holoprosencephaly: Part III. Spectra, distinctions, continuities, and discontinuities

This paper attempts to balance our knowledge of holoprosencephalic spectra and continuities with important distinctions and discontinuities. Prevalence studies and syndrome delineation are briefly reviewed. The following topics receive detailed coverage: human teratogens, special aspects of forebrain and hindbrain malformations, aprosencephaly/atelencephaly, association with neural tube defects, current assessment of "facial principles," and endocrine abnormalities.

Atelencephalic microcephaly: craniofacial anatomy and morphologic comparisons with holoprosencephaly and anencephaly

This is the first detailed report of the craniofacial anatomy of atelencephaly. Comparisons were made with a control specimen and others with holoprosencephaly, anencephaly, and anencephaly with holoprosencephalic facial features. In the atelencephalic fetus, severe microcephaly, flattened calvaria, and partial synostosis of the metopic suture were apparent. The cranial fossae were much smaller than usual; lesser wings of the sphenoid were folded into a rounded basal mass. Facial features were pronounced, and orbits were hyperteloric, lowset, and rounded. Ethmoidal cartilages, nasal bones, and maxillary structures were distorted and elongated. The secondary palate was displaced inferiorly and cleft. Because major components of the craniofacial complex were generally present, although misshapen, changes in the atelencephalic skull seem to be deformations rather than malformations. Differences in the cranial morphology of associated disorders--holoprosencephaly and anencephaly--can be construed as aberrations of separate developmental fields. Relationships between atelencephaly and these fields are unclear.