Fetal posterior fossa dimensions: normal and anomalous development assessed in mid-sagittal cranial plane by three-dimensional multiplanar sonography

OBJECTIVES

To construct nomograms of the dimensions of the fetal posterior fossa (PF), assessed in the mid-sagittal plane in the second and third trimesters, and to assess how measurements from fetuses with PF abnormalities deviate from our normal ranges.

METHODS

This was a prospective cross-sectional study of 378 healthy fetuses in low-risk singleton pregnancies between 15 and 35 weeks. PF size was evaluated in the mid-sagittal plane of the fetal head using three-dimensional multiplanar reconstruction (3D-MPR). The borders of the PF were defined from the clivus to the tentorium (clivotentorial distance, CTD) and from the occipital bone to the level of the upper mesencephalic edge (tecto-occipital distance, TOD), and the posterior fossa area (PFA) and perimeter (PFP) were assessed. Growth charts were produced. Thirty-nine fetuses diagnosed with PF malformations were analyzed by calculating the z-scores of PFA, PFP, TOD and CTD, relative to the developed nomograms.

RESULTS

Of the 378 healthy fetuses initially included, there were 281 with adequate visualization of the PF borders; i.e. PF mid-sagittal plane morphometry was feasible in 74.3% of cases. There was a linear relationship between each of PFA, PFP, TOD and CTD, and gestational age, with Pearson correlation coefficients of 0.97, 0.97, 0.96 and 0.95, respectively (P < 0.001 for each). Chiari II malformation (CM-II) and Dandy-Walker malformation (DWM) were associated with the greatest difference in PF size compared with normal; PFA z-scores exceeded 2.6 in all five DWM cases and were below -2.66 in all 11 CM-II cases.

CONCLUSIONS

Sonographic evaluation of fetal PF size in the mid-sagittal plane is feasible. Our constructed nomograms provide reference data that may be helpful when evaluating PF congenital malformations.

Function of Rieger syndrome gene in left-right asymmetry and craniofacial development

Rieger syndrome, an autosomal dominant disorder, includes ocular, craniofacial and umbilical abnormalities. The pitx2 homeobox gene, which is mutated in Rieger syndrome, has been proposed to be the effector molecule interpreting left-right axial information from the early embryonic trunk to each organ. Here we have used gene targeting in mice to generate a loss-of-function allele that would be predicted to result in organ randomization or isomerization. Although pitx2-/- embryos had abnormal cardiac morphogenesis, mutant hearts looped in the normal direction. Pitx2-/- embryos had correctly oriented, but arrested, embryonic rotation and right pulmonary isomerism. They also had defective development of the mandibular and maxillary facial prominences, regression of the stomodeum and arrested tooth development. Fgf8 expression was absent, and Bmp4 expression was expanded in the branchial-arch ectoderm. These data reveal a critical role for pitx2 in left-right asymmetry but indicate that pitx2 may function at an intermediate step in cardiac morphogenesis and embryonic rotation.

Pulsed-field gel electrophoresis and FISH mapping of chromosome 9q22: placement of a novel zinc finger gene within the NBCCS and ESS1 region

Chromosome 9q22 is a gene-rich region to which several human disease loci have been mapped. Pulsed field gel electrophoresis (PFGE) and FISH were used to determine the order of and distance between 12 chromosome 9q22 markers flanked by D9S196 and D9S180. D9S780 and XPA were within 190 kb of each other and hybridized to the same 460-kb NotI fragment as D9S180. ZNF169, a novel kruppel-type gene, and D9S280 shared several PFGE fragments indicating that they are not more than 300 kb apart. Interphase FISH showed that COL15A1 lies distal to the region bounded by D9S180 and D9S196 and that ZNF169 is adjacent to D9S196. Based on the restriction fragment lengths in this region and estimates from FISH, the distance from D9S180 to D9S196 is not less than 2 Mb.

The role of the human homologue of Drosophila patched in sporadic basal cell carcinomas

Basal cell carcinoma (BCC) is the most common cancer in humans. The majority of sporadic BCCs have allele loss on chromosome 9q22 implying that inactivation of a tumour suppressor in this region is an important step in BCC formation. The gene for nevoid basal cell carcinoma syndrome (NBCCS), an autosomal dominant disorder characterized by multiple BCCs, maps to the same region and is presumed to be the tumour suppressor inactivated at this site. NBCCS has been identified recently and encodes a protein with strong homology to the Drosophila segment polarity gene, patched. Analysis of Drosophila mutants indicates that patched interacts with the hedgehog signalling pathway, repressing the expression of various hedgehog target genes including wingless, decapentaplegic and patched itself. Using single strand conformational polymorphism (SSCP) to screen human patched in 37 sporadic BCCs, we detected mutations in one-third of the tumours. Direct sequencing of two BCCs without SSCP variants revealed mutations in those tumours as well suggesting that inactivation of patched is probably a necessary step in BCC development. Northern blots and RNA in situ hybridization showed that patched is expressed at high levels in tumour cells but not normal skin suggesting that mutational inactivation of the gene leads to overexpression of mutant transcript owing to failure of a negative feedback mechanism.

Mutations of the human homolog of Drosophila patched in the nevoid basal cell carcinoma syndrome

The nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by multiple basal cell carcinomas (BCCs), pits of the palms and soles, jaw keratocysts, a variety of other tumors, and developmental abnormalities. NBCCS maps to chromosome 9q22.3. Familial and sporadic BCCs display loss of heterozygosity in this region, consistent with the gene being a tumor suppressor. A human sequence (PTC) with strong homology to the Drosophila segment polarity gene, patched, was isolated from a YAC and cosmid contig of the NBCCS region. Mutation analysis revealed alterations of PTC in NBCCS patients and in related tumors. We propose that a reduction in expression of the patched gene can lead to the developmental abnormalities observed in the syndrome and that complete loss of patched function contributes to transformation of certain cell types.