Nodal flow and situs inversus: A review of the literature

Abstract

Variations of situs solitus totalis, the normal organ disposition pattern, involve dextrocardia, situs inversus, situs inversus totalis and situs ambiguous. These laterality defects have been documented for more than 400 years, and a connection to ciliary abnormalities has been elucidated by observing cilia from the primitive node, which can promote “nodal flow”, possibly necessary for the development of left-right asymmetry. The aim of this work was to perform a literature review, showing variations in the usual anatomy and the connection between nodal flow and normal asymmetric pattern. A narrative review was carried out with articles from the MEDLINE/PubMed, SciELO and LILACS databases and with books relevant to the theme. The initial embryonic development comprises the formation of the organizing structure, a primitive node, and its cilia are responsible for the nodal flow, determinant in many vertebrates in the breaking of the embryonic bilateral symmetry. The formation of asymmetry is associated with morphogenic gradients to the left of the node, the model of two cilia and the mechanism of nodal vesicular plots, until it results in organogenesis. Ciliary abnormalities configure clinical manifestations in disorders such as Primary Ciliary Dyskinesia and Kartagener syndrome. The nodal flow, in fact, is important in normal anatomical standardization, and the cilia are necessary for the configuration of situs solitus totalis.