The pre-operative CT anatomic delineation showed 100% correlation with the true anatomical configuration found at surgery. Of the eight patients who were diagnosed as mixed TAPVC, three patients had type I configuration (3+1), one patient had type II configuration (2+2) and four patients had type III configuration (Bizarre pattern) as per the Choudhury classification. While the term ‘bizarre’ denotes a complex, unclassifiable anatomy, some of the cases in this category were not as surgically challenging as anticipated and hence, although this was a more simple, user-friendly classification, type III seemed to be an over-simplification of the anatomy. Of the 3 patients with Bizarre type, only one patient had an adverse surgical outcome (due to severely congested lungs with surfactant deficiency). We found the Choudhury classification to be a more simple and user-friendly over the one proposed by Xiang et al in giving the surgeon an overview of the pulmonary venous anatomy

5 of the 8 patients had obstructive TAPVC, the sites of obstruction included individual vein, common ostium, intracardiac obstruction due to narrow patent foramen ovale, or narrowing of vertical vein. All the infracardiac vertical veins were obstructed either along the course of the vein or at the site of drainage in the left portal vein. Echocardiography was more accurate than CT angiography in assessing obstructive patterns due to functional measurement of the flow acceleration in the individual veins. In these cases of obstructed TAPVC due to narrowing at the ostium of one of the drainage sites, patients required reconstruction and rechanneling of the vein rather than rechanneling alone.

The surgical technique was individualized in every case, which was more fundamentally based on the size and length of the individual veins, presence or absence of ostial narrowing and their distance from the closest common confluence or intended draining chamber, rather than the site and type of drainage pattern. For example, two of our patients had the 3+1 pattern (Chowdhury et al) or CS + SVC (Xiang et al). However different surgical approach was used for both, as the first patient had an obstructed morphology and hence the coronary sinus was separated from the confluence and complete TAPVC repair was performed using suture less surgery. The second case with similar morphology had an unobstructed pattern and hence the simpler technique of unroofing the coronary sinus and connecting to the individual vein draining into the innominate vein to the left atrial appendage was performed.

1 patient had single ventricle morphology in which case CT again played an important role in determining which atrial chamber was closer to the common anomalous venous chamber guiding the surgical planning. This child also had severe pulmonary stenosis and needed Glenn surgery in addition to TAPVC repair.

1 patient had a stormy post-operative course due to complex surgical anatomy- both ascending and descending vertical veins were noted with multiple sites of obstruction.

Only 1 patient, who was pre-term and LBW, died due to dismal state of the lung parenchyma with extensive areas of air space collapse because of premature birth. Numerous tiny tortuous venous channels were observed in the superior mediastinum of this patient with supracardiac and infracardiac type of TAPVC which could have formed secondary to the obstruction or would be persistent embryonic veins in the pre-term baby. Presurgical CT proved to be an excellent guide to anticipate this and correctly prognosticate.

Suture less surgery was considered in all patients with small individual veins or narrow ostia as it provided luminal widening and improved flow gradient post-surgery.

Our comprehensive CT report included 1. Detailed anatomy of pulmonary venous drainage pattern-delineating each individual vein with its site of drainage accompanied by a depictive diagram, 2. Diameter of the individual veins and their ostia, 3. Diameter and length of the common channel/ vertical veins, 4. Proximity to cardiac chambers 5. Other intracardiac abnormalities including chamber sizes 6. Airway assessment 7. Lung parenchymal abnormality