DDx
Differential Diagnoses
Media Gallery
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The structure and function of cilia is shown here. (A) Most motile cilia are organized with 9 microtubule doublets surrounding a core pair of doublets (9+2 configuration). Outer dynein arms (green) and inner dynein arms (blue) are shown. Cilia on the cells of the ventral node in the normal mouse embryo have no core doublet (a 9+0 configuration) and were initially thought to be nonmotile; however, upon closer scrutiny, node cilia were seen to have a rotatory motion (600 rpm). [Figure A is from Hirokawa N, Tanaka Y, Okada Y. Left-right determination: involvement of molecular motor KIF3, cilia, and nodal flow. Cold Spring Harb Perspect Biol. Jul 2009;1(1):a000802 and is reprinted with permission of Cold Spring Harbor Press.] (B) lrd (left-right dynein), the protein (green) mutated by the iv mutation, is also known as DNAH11, DNAHC11, and DLP11. [Figure B is from the United States Department of Energy Genomes to Life Program.] (C) The rotatory cone of each cilium is tilted posteriorly. Hence, the cilia make a leftward swing at the fluid surface and a rightward swing at the cellular surface. Because more viscous drag is present at the cellular surface, the rightward sweep is less effective at generating fluid movement than is the leftward sweep. [Figure C is from Hirokawa N, Tanaka Y, Okada Y, Takeda S. Nodal flow and the generation of left-right asymmetry. Cell 2006; 125:33-45 and is reproduced with permission from Cell Press.] A = anterior; L = left; P = posterior; r = Right.
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Three phases of elaboration of left-right (LR) asymmetry are shown. The first step consists of differentiating the left and right sides on the cellular level. This probably takes place by means of a chiral molecule. (A) A subset of the cells (yellow) of the fairly early embryo undergo this process. (B) Localized cellular asymmetry is propagated between cells to cause LR determinants to accumulate on one side of the embryonic midline, possibly by a process involving transport through gap junctions. These determinants would then induce cascades of factors in multicellular fields of the embryo. (C) Finally, the asymmetric presence of these factors induces or suppresses asymmetrically located organs such as the spleen and regulates asymmetric morphogenesis of other organs such as the heart tube. Courtesy of Levin M, Mercola M. The compulsion of chirality: toward an understanding of left-right asymmetry. Genes Dev. Mar 15 1998;12(6):763-9.
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Genes required for proper left-right asymmetry are shown. Genes are presented in five columns, according to the developmental phase in which they are currently thought to function. The leftmost column has the earliest functioning genes. The second column has genes required for the development of the node (or its equivalent). The third and fourth column have genes that are required for normal node cilia function. Genes in white, green, or blue denote those in which the proof came from studies of fruit fly (Drosophila melanogaster), zebrafish (Danio rerio), or frog (Xenopus laevis), respectively. Genes in brown are those studied in mice (Mus musculus), whereas those discovered in humans (Homo sapiens) are shown in red.
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Axial magnetic resonance image (MRI) of a case of heterotaxy with polysplenia. (A) The abdominal aorta (abd ao) is on the left side of the spine (S), as is the left-sided azygos (L Azy). Two right-sided spleens (spl) are visible. LHV = left hepatic vein; RHV = right hepatic vein. (B) A common atrioventricular valve (black unlabelled arrows) is markedly malaligned to the right ventricle (RV). A diminutive left atrium (LA) is represented by only an appendage. The patient had an extracardiac conduit (EC) type of Fontan operation. No fenestration is noted between the EC and the neo-left atrium (neoLA). (C) Because this patient had subaortic stenosis, a proximal pulmonary artery-to-ascending aortic anastomosis was performed early in life, along with augmentation of the aortic arch. The L Azy connects to the left superior vena cava (LSVC). LU DAo = left upper descending aorta; Prox = proximal. (D) The LSVC connected originally to the coronary sinus (CS) and then to the right atrium. Despite the fact that the LSVC has been disconnected from the heart and anastomosed end-to-side to the left pulmonary artery, the CS remains large. The narrowed left ventricular outflow tract (LVOT) is seen. Ao = aorta; PA = pulmonary root; RLL PV = right lower lobe pulmonary vein. (E) Because this patient had absence of the hepatic segment of the inferior vena cava, the left-sided SVC-to-left pulmonary artery (LPA) anastomosis is referred to a left-sided Kawashima (LK). The anastomosis of the right superior vena cava to the right pulmonary artery is a right-sided bidirectional Glenn (R BDG) shunt. (F) The left lower lobe pulmonary vein (LLL PV), as part of this patient's totally anomalous pulmonary venous connection, connects to the original right atrium, which is now the neoLA.
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Coronal magnetic resonance image (MRI) of the same patient as shown in the previous image. (A) Both superior vena cava (SVC)–to–pulmonary artery (PA) anastomoses can be seen. LCCA = left common carotid artery. (B) Three-dimensional surface rendering. RIA = right innominate artery. (C) Three-dimensional reconstruction of only the systemic venous pathway.
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Malrotation of the gut. This upper gastrointestinal (GI) barium study of the same heterotaxy patient as shown in the previous two images shows a right-sided stomach (St), opposite of the normal site. The duodenum heads to the left, the duodenal-jejunal junction is to the left of the spine (opposite to what would be expected for situs inversus totalis), and the jejunum (J) stays left-sided.
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