Discussion

Total anomalous pulmonary venous connection is a rare congenital anomaly, corresponding to approximately 1% of all CHDs. Failure of the common pulmonary vein to connect with the pulmonary venous plexus leads to the persistence of one or more earlier venous connections to the right SVC, to the left vertical vein/innominate vein, or to the umbilicovitelline vein/portal vein. ^{Reference Karamlou, Gurofsky and Al Sukhni1,Reference Xiang, Wu, Pan, Wang and Xi2}

The surgical approach varies for different types of mixed total anomalous pulmonary venous connection. Accurate diagnosis, especially regarding all four pulmonary veins drainage, has been emphasised as a critical factor for achievement. ^{Reference Furlanetto, Furlanetto and Henriques3} Chowdhury et al., who reported the largest mixed total anomalous pulmonary venous connection series in the literature, categorised three subtypes to facilitate classification and improve surgical outcomes. ^{Reference Chowdhury, Airan and Malhotra4} Similarly, St Louis et al modified classification. ^{Reference St Louis, Turk, Jacobs and O.'Brien5} Type IV A (Category I): Bilateral and symmetrical connections. This group of patients had separate anomalous connection of veins from each lung: “2 + 2” pulmonary venous drainage pattern. Type IV B (Category II): Bilateral and asymmetrical connections. This group of patients had isolated drainage of a solitary pulmonary vein and drainage of the other three pulmonary veins to a common site: “3 + 1” pulmonary venous drainage pattern. Type IV C (Category III): Bizarre anatomic variants. This group of patients had bizarre anatomic variants.

Our cases' morphological features were confident with the bizarre anatomic variant, as shown in Fig 3, and can be symbolised as 2 + 1 + 1. As far as our knowledge, this is a unique and previously undefined form of total anomalous pulmonary venous connection.

Echocardiography can provide anatomical details regarding the position of anomalous pulmonary venous connections and the presence of a venous obstruction in the majority of patients. In most cases, echocardiography is sufficient and preferable, but sometimes it can only identify two or three veins, leading to misdiagnosis. Some reports ^{Reference Wang, Qi and Hu6} have shown that the mixed type is the most challenging type, with 44.4% of patients diagnosed only after the surgical examination. ^{Reference Furlanetto, Furlanetto and Henriques3} In order to identify all four veins, CT angiography, which can provide not only an accurate description of the pulmonary venous drainage pattern but also delineate the pulmonary vein anatomy in patients with suspected asymmetrical pulmonary venous obstruction, should be applied despite the radiation exposure. ^{Reference Turkvatan, Tola, Ayyildiz, Ozturk, Ergul and Guzeltas7} The merit of CT angiography is three-dimensional reconstruction, which can provide a precise non-invasive visual description of the pulmonary vein connections. ^{Reference Turkvatan, Tola, Ayyildiz, Ozturk, Ergul and Guzeltas7}

In our case, anatomy was suspected by echocardiography and detailed with CT angiography.

As a result, surgical success in mixed total anomalous pulmonary venous connection, especially in patients with more complex pulmonary venous connections, could be achieved with complementary imaging methods such as echocardiography and three-dimensional CT.