Abbott Specimen 49

Abbott 49

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Specimen Card Nomenclature
Pulmonary stenosis with large defect of interventricular septum, deviation to right of aorta and patent foramen ovale.
International Classification of Diseases
Tetralogy of Fallot
Atlas Illustration
Dr. P.P. Smyth
Ten years
Front view shows an enlarged right ventricle (R) with a red rod extending through the tricuspid valve orifice. The pulmonary artery (long arrow) is markedly stenotic. The aortic valve (A) partly over-rides a large ventricular-septal defect (short arrows). The back view shows a normal left ventricle. A blue rod is present in an atrial septal defect.

Abbott 49 with letters

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The primitive heart consists of a straight tube whose proximal and distal ends are fixed within the pericardial cavity. Because the tube's growth is more rapid than that of the cavity, it is forced to bend, forming sulci and “segments” corresponding to future cardiac structures. The ascending limb of this bent structure (the bulbis cordis) differentiates into three components:

  • Proximal - the trabeculated portion of the right ventricle
  • middle (the conus cordis) - the outflow tracts of the ventricles
  • distal (the truncus arteriosus) - the proximal aorta and pulmonary arteries

Four tissue ridges−two each related to the truncus and the conus−develop on the inner aspect of the bulbis cordis. The truncus swellings enlarge and fuse to form the truncus septum, which grows in a spiral course to divide the truncus into distinct pulmonary and aortic channels. The conus swellings also grow and fuse with each other and with the endocardial cushions inferiorly, eventually contributing to the development of the superior portions of both ventricles (including the membranous portion of the interventricular septum). An abnormality of this complex process is believed to underly the structural components of Tetralogy of Fallot.

Tetralogy is the most frequent congenital anomaly of the conotruncal region, occurring in about 1 per 1000 births. The structural abnormalities which define it are:

  • stenosis of the pulmonary outflow tract
  • a ventricular septal defect
  • a partially displaced aorta that overrides the septal defect

The latter two abnormalities allow blood to flow from the venous to the systemic circulation. The fourth component of the anomaly−right ventricular hypertrophy−occurs as a consequence of elevated right ventricular pressure. The obligatory right to left shunt typically results in decreased systemic PO2 and cyanosis. Other clinical findings include dyspnea, digital clubbing, syncope (“tet spells”) and embolic stroke (as was likely the case in the boy whose heart is shown here).

Etienne-Louis Arthur Fallot was a French cardiologist who described the condition in detail in 1888. Despite the recognition given to him for this, the anomaly had been documented much earlier by the Danish anatomist Niels Stensen (Nicolas Steno) in 1672, as well as a variety of other physicians in the following years.

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