Discussion

Pulmonary embolism is a very rare disease in children (0.14–0.9 in 100.000) and most cases are diagnosed in previously sick children and in-hospital circumstances. The majority of paediatric PE patients have at least one underlying risk factor like central venous catheter insertion, immobility, infection, malignancy and renal disease and so like. ^{Reference Zaidi, Hutchins and Rajpurkar1} Excellent cardiopulmonary reserve of children, inability to vocalise symptoms and presence of more serious primary disorders or underlying comorbid conditions could mask the symptoms and reduces the level of suspicion by doctors in children with PE. Children and adults were also different in terms of massive PE. First, the mortality rate is higher in children, with almost 50% dying suddenly. Second, instead of deep venous thrombosis in the lower extremities, the aetiology of massive PE in children is tumour emboli in the majority. ^{Reference Baird, Killinger and Kalkbrenner2}

Our patient had multiple hereditary risk factors for PE. The impact of the hereditary causes of thrombosis on the risk of PE in children is not being as straightforward as in adult patients. Revel-Vilk et al. ^{Reference Revel-Vilk, Chan and Bauman3} found that inherited prothrombotic coagulation proteins do not contribute significantly to the pathogenesis of VTE in children. Moreover, the deficiency of MTHFR results in hyperhomocysteinemia/homocystinuria and although an association was shown between MTHFR C677T/A1298 C combined mutations and PE in the Turkish population, the evidence on the impact of MTHFR polymorphisms on the risk of PE still remains weak. ^{Reference Basol, Karakus and Savas4} On the other hand, in a meta-analysis by Young et al., ^{Reference Young, Albisetti and Bonduel5} it was stated that the presence of the thrombophilia traits of antithrombin, protein C, and protein S produced the odds ratios (OR) of 8.73, 7.75 and 5.77, respectively, for paediatric VTE and revealed a significant association with the first onset of VTE, as well as recurrence. In an analysis by Kemer et al. ^{Reference Kenet, Limperger, Shneyder and Nowak-Göttl6} it was concluded that significant associations between paediatric venous thrombosis and presence of protein C, protein S and antithrombin deficiency, factor V (F5: rs6025), factor II (F2: rs1799963) have been revealed in many studies and it was also stated that the risk is even more pronounced when combined inherited thrombophilias are involved.

In paediatric massive PE, there are several options for treatment like anticoagulation, systemic thrombolysis, embolectomy, catheter-directed therapies (thrombolytics with/without ultrasound-accelerated thrombolysis), extracorporeal life support (ECLS) or combination of these methods. In a paper by Eini et al., ^{Reference Eini, Houri and Cohen7} 41 children with massive PE were analysed and pulmonary embolectomy was performed in the 68% of the patients and 80% of them survived. In 23% of the patients, thrombolysis was used as initial treatment with an 80% failure rate. Moreover, 14% of the patients were treated with only anticoagulation and only 33% of them survived. They concluded as pulmonary embolectomy could be superior to all other treatment modalities in children with massive PE. While ECLS, as an adjunctive measure, has been used for hemodynamic stabilisation before embolectomy/thrombolysis, its impact of survival was reported to be non-significant in massive PE in adults. ^{Reference Weinberg, Tapson and Ramzy8} In children while pharmacological thrombolysis is advised as an initial step in the management of massive PE with systemic hypotension and cardiac strain, mechanical thrombolysis and surgical embolectomy may be utilised for patients with a high risk of bleeding or with contraindications to anticoagulation, if pharmacologic treatment has failed or if the patient presents with hemodynamic collapse. ^{Reference Baird, Killinger and Kalkbrenner2} Recently catheter-directed therapies have been emerging as an alternative therapy in children with sub-massive and massive PE and the outcome was reported to be promising. ^{Reference Akam-Venkata, Forbes and Schreiber9}

In conclusion, it seems to be essential to pay a higher level of suspicion for massive PE in children with syncope and unexplained cardiopulmonary instability. Emergent pulmonary embolectomy is a lifesaving procedure in children with massive PE and could be regarded as a first-line therapy in cases with massive PE with severe hemodynamic instability and cardiac arrest.