Chiari’s Network as a Cause of Fetal and Neonatal Pathology

Chiari’s network is a remnant of the eustachian valve located in the right atrium. Incomplete involution of the fetal sinus venosus valves results in “redundant” Chiari’s network, which may compromise cardiovascular function. This report describes a case with the novel finding of prenatal compromise due to redundant Chiari’s network and an uncommon case with significant postnatal symptoms. In both cases, the symptoms (fetal hydrops and postnatal cyanosis) resolved spontaneously. The variety of cardiovascular pathologies described in the literature is believed to be associated with persistence of a Chiari network. Knowledge about this not always harmless structure is important for perinatologists, pediatricians, and pediatric cardiologists alike. The clinical importance of this rare pathology is that prenatal counseling may anticipate a generally positive outcome and that surgical intervention generally should be avoided

Structural Characteristics and Stellar Composition of Low Surface Brightness Disk Galaxies

We present UBVI surface photometry of a sample of low surface brightness (LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential disks with no preferred value for either scale length, central surface brightness, or rotational velocity. Indeed, the distribution of scale lengths is indistinguishable from that of high surface brightness spirals, indicating that dynamically similar galaxies (e.g., those with comparable Rv^2) exist over a large range in surface density. These LSB galaxies are strikingly blue. The complete lack of correlation between central surface brightness and color rules out any fading scenario. Similarly, the oxygen abundances inferred from HII region spectra are uncorrelated with color so the low metallicities are not the primary cause of the blue colors. While these are difficult to interpret in the absence of significant star formation, the most plausible scenario is a stellar population with a young mean age stemming from late formation and subsequent slow evolution. These properties suggest that LSB disks formed from low initial overdensities with correspondingly late collapse times.Comment: Astronomical Journal, in press 45 pages uuencoded postscript (368K) including 9 multipart figures also available by anonymous ftp @ ftp.ast.cam.ac.uk /pub/ssm/phot.uu CAP-30-210442962983742937