Superior Mediastinum Syndrome

Children presenting with an anterior mediastinal mass pose a significant haemato-oncological emergency. This subset of patients is at risk of encountering severe and potentially life-threatening complications either upon presentation or during sedation/general anaesthesia. These complications typically arise due to extrinsic compression of the airway, obstruction of venous return, or impediment to cardiac output.

Fortunately, with the advent of modern chemotherapy regimens, the prognosis for the majority of children with an anterior mediastinal mass is highly favourable in the long term. Prompt initiation of appropriate initial management is paramount, as it can effectively mitigate the risk of unnecessary morbidity and mortality associated with this condition. Early intervention not only ensures optimal outcomes but also minimizes the potential for adverse events, thereby optimizing the overall clinical trajectory for these patients.

Superior vena cava syndrome is a group of symptoms caused by obstruction of blood flow through the superior vena cava (SVCS). A patient with SVCS requires immediate diagnostic evaluation and therapy.

Superior mediastinum syndrome is a combination of symptoms caused by SVC compression with blood flow obstruction plus compression of the trachea. Both syndromes usually occur together.

The superior vena cava (SVC) is the major drainage vessel for venous blood from the head, neck, upper extremities, and upper thorax. It is located in the middle mediastinum and is surrounded by relatively rigid structures (sternum, trachea, right bronchus, aorta, pulmonary artery, and the perihilar and paratracheal lymph nodes). SVC is a thin-walled and low intraluminal pressure vascular structure.  

There are three mechanisms of pathogenesis SVCS:  

• thrombosis of SVC
• obstruction of SVC by intrinsic pressure and direct tumor invasion to the venous wall (frequently associated with secondary intravascular thrombosis)
• compression of SVC – extrinsic pressure of a tumor mass against the relatively thin-walled SVC.

Aetiology

Intrinsic causes: vascular thrombosis following the introduction of a catheter, intravascular tumor thrombosis (Wilms, lymphoma).

Extrinsic causes: malignant anterior mediastinal tumors

• Hodgkin lymphoma.
• Non-Hodgkin lymphoma.
• Teratoma and other germ cell tumor.
• Thyroid cancer.
• Thymoma.

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