Modified Fontan procedure - venous admixture

Case contributed by Dr Brian Gilcrease-Garcia

Presentation

Double inlet left ventricle with pulmonary atresia s/p modified Fontan procedure with fenestrated lateral tunnel

Patient Data

Age: 30 years
CT

CT pulmonary embolism protocol - upper extremity injection

Findings of modified Fontan procedure as treatment for a univentricular system:

  • double inlet left ventricle
    • markedly hypoplastic right ventricle communicates with an overdeveloped left ventricle via a large ventricular septal defect
    • right atrium (RA) directly communicates with left atrium via an atrial septal defect (ASD)
    • pulmonary atresia - essentially no communication between right ventricular outflow and pulmonary arteries
  • changes of total cavopulmonary shunt (i.e. modified Fontan)
    • inferior vena cava (IVC) and superior vena cava entirely supply the main pulmonary arteries
    • an intra-atrial baffle ("lateral tunnel") is partially visualized, as linear hyperdensity between the unopacified IVC and RA
  • rotated configuration of aortic root
    • right coronary artery originates anteriorly ~ 1 o'clock position
    • left coronary artery originates posteriorly ~ 6 o'clock position

Note - IVC and central pulmonary arteries are poorly opacified due to non-opacified caval blood entering from caudal via the total cavopulmonary shunt, limiting evaluation for pulmonary embolism and atrial baffle integrity

CT

CT pulmonary embolism protocol - dual upper/lower extremity injections

Due to the technical problems on the prior study, this CT was performed using tandem injections from a lower extremity and upper extremity IV. The upper extremity injection was delayed by 10 seconds in attempt to compensate for the longer lower extremity venous pathway.

On the earliest images, there is now dense opacification of IVC, although evaluation of the central pulmonary arteries remains limited by venous mixing. Therefore, additional images were obtained 30 seconds later, which show homogenous opacification of cavopulmonary shunt, cardiac chambers, and great vessels.

Significant new findings:

  • early retrograde pooling of contrast in hepatic veins, indicating elevated cavopulmonary venous pressure
  • early leakage of contrast from vena cava to the right atrium, indicating a patent fenestration in the intra-atrial baffle
  • collateral vessels
    • multiple small vessels originating at distal aortic arch, connecting to left main pulmonary artery (arterial-to-pulmonary collaterals)
    • preferential pulmonary arterial flow into the right lung along with numerous hyperdense intra-pulmonary hyperdense vessels, which might indicate some degree of intra-pulmonary shunting
Annotated image
  1. Double inlet left ventricle configuration, featuring large ASD (asterisk) connecting right and left atria (hypoplastic RV and large VSD not depicted)
  2. Inter-atrial baffle (yellow arrow). It is situated between the anterior midatrial wall to the posterior margin of the ASD, bisecting the atrial chamber into the lateral channel and medial neoatrium
  3. Contrast streaming from vena cava to the right neoatrium, forming a right-to-left shunt. This most likely indicates a patent fenestration through the baffle, although baffle leak could appear similar
  4. Maximum intensity projection depicts the total cavopulmonary shunt
  5. Collaterals which have formed between pulmonary arteries and aorta. (the origins of the bronchial artery appears to originate more distally at the proximal descending aorta

Case Discussion

This case highlights the difficulties in CT imaging of congenital heart disease, where unusual circulatory patterns may cause unexpected results. In the first study, evaluation of the heart and pulmonary arteries is limited due to the upper extremity injection and scan timing. This is predictable given the patient's history.

Given the limitations of the prior study, the subsequent study was performed with contrast injection from both lower and upper extremities, and the radiologist was present at the scanner during injection in order to coordinate appropriate timing. After the first images were acquired, it was quickly decided that additional delayed images would be necessary to properly evaluate the pulmonary arteries, and so the scan was quickly repeated. Although a multi-phase study was not planned a priori, both sequences provide meaningful information in this particular case.

One point of particular interest is the fenestration within the intra-artrial baffle. A fenestration is commonly performed at the time of surgery in order to provide "escape" shunting in case the pulmonary arterial system is overwhelmed, at the cost of hypoxic shunting and risk of paradoxical embolus (similar to patent foramen ovale). Although these fenestrations often spontaneously close over time, it remains patent in this case.

 

Thanks to Dr. Benjamin Strnad.

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Case information

rID: 65834
Published: 26th Jan 2019
Last edited: 27th Jan 2019
System: Cardiac
Inclusion in quiz mode: Excluded
Institution: Mallinckrodt Institute of Radiology at Washington University

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