Tetralogy of Fallot

Description: Depicted here is the normal anatomy of the conoventricular septum in the right ventricular outflow tract. The parietal band (PB) is inserted into the fork formed by the branching of the septal band (SB) to form its superior limb (SL) and inferior limb (IL). Note the proximity of the pulmonary valve (PV). Note on the inferior limb the insertion of a chorda from the anterior leaflet of the tricuspid valve onto the muscle of Lancisi. The portions of the SB and the PB interposed between the AV valve and the pulmonary valve compose the conus.

This is a photo of the right ventricular outflow tract in an adult with tetralogy of Fallot (ToF). The anatomical basis of ToF is an anterior malalignment of the parietal band (PB). As a result of this malalignment a conoventricular septal defect (VSD) is created and the right ventricular outflow tract (RVOT) is narrowed. The pulmonary valve may or may not also be stenotic or even atretic.

Clinical correlation: In addition to a VSD and narrowing of the RVOT the other features of tetralogy of Fallot (ToF) are right ventricular hypertrophy and overriding of the aorta. In the fetus, of course, “right ventricular hypertrophy” is the norm. The normal anatomy of the heart includes over-riding of the aorta. Overriding is exaggerated in ToF and in another anomaly closely resembling ToF, double outlet right ventricle (DORV).

ToF is often now discovered in utero. A newborn with ToF will quickly become cyanotic after birth when the ductus arteriosus closes. The amount of obstruction in the RVOT or pulmonary valve strongly correlates with the severity of symptoms.

This is a photo of a normal left ventricular outflow tract (LVOT) showing fibrous continuity between the anterior leaflet of the mitral valve (MV) and the noncoronary cusp of the aortic valve (AV). An anatomical distinction can be made between tetralogy of Fallot (ToF) and double outlet right ventricle (DORV) by examination of the left ventricular outflow tract (LVOT). In ToF there will be normal fibrous continuity between the aortic and mitral valves as shown in this photo. In DORV such continuity will be lacking due to interposed muscle; i.e. in DORV there are bilateral conuses whereas in ToF there is a conus only on the right.

Contributed by Dr. Calvin Oyer