Discussion

DiGeorge syndrome or, more properly, 22q11.2 deletion syndrome (22q11.2DS) is the most common chromosomal microdeletion syndrome with a prevalence of 1 case per 3.000–6.000 live births.^{Reference McDonald-McGinn, Sullivan and Marino1} Because of its heterogenous clinical presentation, 22q11.2 deletion syndrome is not so simple to diagnose. However, since CHDs appear in about 75–80% of patients with 22q11.2 deletion, they can be considered pillars of clinical diagnosis of the syndrome.^{Reference McDonald-McGinn, Sullivan and Marino1–Reference McElhinney, McDonald-McGinn, Zackai and Goldmuntz4} In particular, conotruncal defects, including tetralogy of Fallot, truncus arteriosus, interrupted aortic arch (mainly type B), pulmonary atresia, and ventricular septal defect, are the most common heart anomalies observed in these patients.^{Reference McDonald-McGinn, Sullivan and Marino1–Reference Goldmuntz, Clark and Mitchell5} This characteristic involvement of the outflow tract is due to the deletion of specific genes (TBX1, CRKL, ERK2) localised on chromosome 22q11.2 that are involved in the anterior heart field cells differentiation and in the neural crest cells migration.^{Reference McDonald-McGinn, Sullivan and Marino1–Reference Momma3,Reference Théveniau-Ruissy, Dandonneau and Mesba6}

Major CHDs are symptomatic since the neonatal period, which allow early diagnosis of DiGeorge syndrome. However, 22q11.2 DS may also be related to minor heart anomalies without evident manifestation and therefore may remain undetected until adulthood.^{Reference Unolt, Versacci and Anaclerio2}

A peculiar type of cardiovascular congenital defect associated with 22q11 deletion is crossed pulmonary arteries. Crisscross or crossed pulmonary arteries is a rare anomaly of pulmonary artery branches where the ostium of the left pulmonary artery is above and to the right of the right pulmonary artery origin; the branches then cross each other directing to each respective lung.^{Reference Jue, Lockman and Edwards7–Reference Chen and Feng12} This malposition of pulmonary arteries may occur isolated or associated with other CHDs, especially conotruncal and aortic arch abnormalities.^{Reference Recto, Parness, Gelb, Lopez and Lai10,Reference Babaoğlu, Altun, Binnetoğlu, Dönmez, Kayabey and Anık13,Reference Cuturilo, Drakulic and Krstic14} Crossed pulmonary arteries are commonly related also to extracardiac congenital malformations and chromosomal abnormalities, and in particular to DiGeorge syndrome with a reported frequency ranging from 50%^{Reference Recto, Parness, Gelb, Lopez and Lai10,Reference Cuturilo, Drakulic and Krstic14} to 10%^{Reference Babaoğlu, Altun, Binnetoğlu, Dönmez, Kayabey and Anık13} of cases. Nevertheless, limited reports concerning crossed pulmonary arteries are available in the literature and some authors^{Reference Babaoğlu, Altun, Binnetoğlu, Dönmez, Kayabey and Anık13} suggest a probable higher prevalence in the general population, and in particular in patients with a genetic syndrome (e.g. DiGeorge-, Noonan-, Costello-, trisomy 18, or VACTERL anomalies).

The crossed pulmonary arteries, despite the abnormal position of pulmonary branches, if not associated to congenital heart disease, does not cause neither hemodynamic compromission nor airway obstruction, and therefore is always asymptomatic.

Accurate evaluation of pulmonary artery branches is crucial during echocardiography, as the finding of crossed pulmonary arteries can be a clue to associated cardiac and extracardiac anomalies and to genetic syndromes such as DiGeorge. Therefore, a careful echocardiographic examination of the pulmonary arteries position is suggested in all patients, especially when facial dysmorphisms are present, as well as genetic analysis for 22q11.2 microdeletion is required in all patients in whom malposition has been detected.^{Reference Cuturilo, Drakulic and Krstic14}