The Fontan and Glenn Procedures

The Glenn operation is diversion of superior vena caval blood to the right pulmonary artery. The classic, or unidirectional Glenn procedure involved proximal ligation of the right pulmonary artery separate it from the main and left pulmonary arteries and to divert all superior vena caval blood into the right pulmonary artery. The bidirectional Glenn procedure skips the ligation, allowing vena caval blood to be distributed to both lungs. For the Glenn procedure to work, we need to have normal pulmonary arterial pressures, patent pulmonary arteries, and enough function in the left ventricle to handle pumping blood through the body and the lungs.

The Glenn procedure is now considered the first stage of a complete systemic venous to pulmonary arterial anastomosis, also known as a Fontan procedure. The Fontan procedure is basically a Glenn procedure combined with a right atrium–to–left pulmonary artery connection. Different connections may be used to the left pulmonary artery. The Hancock conduit is a porcine aortic valve sutured into the center of a woven fabric conduit.

Acquired arteriovenous malformations can occur following Glenn or modified Fontan procedures. This is of unknown etiology. One idea is that they develop as a result of loss of "hepatic factor," with blood reaching the right lung through the superior vena cava absent of this mysterious humour, leading to pulmonary arteriovenous malformations on the right. It is also known that the Glenn shunt favors flow to the lower lobes, leading some to suggest this maldistribution of pulmonary blood flow to the lower lobes as a causative factor.

The patient shown here had tricuspid atresia, for which he had a unidirectional Glenn procedure when he was 2 and a modified Fontan when he was 13, followed by a stent of the Hancock conduit in his 20s. The unidirectional Glenn can be seen in the top pair of images, showing a direct connection between the superior vena cava and the right pulmonary artery. The bottom image pair shows the second stage of the procedure, with diversion of inferior vena caval blood into the left pulmonary artery via a Hancock conduit. Multiple clipped pulmonary arteriovenous malformations are seen.

References

Pike NA, Vricella LA, Feinstein JA, Black MD, Reitz BA. Regression of severe pulmonary arteriovenous malformations after Fontan revision and "hepatic factor" rerouting. Ann Thorac Surg. 2004 Aug;78(2):697-9.