Answers

Short answers

1 The radiograph shows complete opacification of the right hemithorax and a mass effect. The differential diagnosis includes a right sided pleural effusion, right sided pneumonia, and a large mediastinal mass. This patient had a large mediastinal mass and was later diagnosed with T cell lymphoma. The lesions felt by the patient’s mother are likely to be subcutaneous malignant deposits.

2 Peripheral blood film and pleural effusion needle aspiration should be undertaken. The peripheral blood film can then be examined microscopically for cell morphology and the cells in the pleural fluid analysed after centrifugation (cytospin).

3 Early referral and transfer to a paediatric oncology centre with experience and expertise in managing patients with anterior mediastinal mass is recommended. Hyperhydration and intravenous rasburicase and steroids should be administered and chemotherapy initiated.

Long answers
1 Radiographic signs and differential diagnosis
The initial radiograph showed complete opacification of the right hemithorax and a mass effect. Emergency bronchoscopy revealed complete collapse of the right main bronchus. The left bronchus was partially collapsed and was intubated. The patient’s subsequent chest radiograph is shown in fig 2.

View larger version (65K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2 Chest radiograph after intubation. An endotracheal tube is evident in the trachea and left main bronchus with the left lung inflated. A right internal jugular venous central line can also been seen

View larger version (162K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3 Computed tomogram of the chest at the level of the great vessels. These lie anterior to the trachea, which is intubated (arrowhead), and the oesophagus, marked by a nasogastric tube (long arrow). The right brachiocephalic vein contains a central line and is displaced laterally (curved arrow). A large mass displacing and encasing these structures can be seen extending from the sternum anteriorly to the great vessels posteriorly and is centred in the anterior mediastinum

2 Further investigations
Although biopsy under general anaesthetic has the highest yield in establishing a diagnosis, there is plenty of evidence stating that the administration of a general anaesthetic to a child with an anterior mediastinal mass can lead to respiratory or circulatory collapse, even in children without symptoms.^{2 3 4 5} If at all possible, diagnosis should be made using the least invasive investigations and avoiding a general anaesthetic. Diagnostic investigations that do not require a general anaesthetic include: 1) peripheral blood film for T cell acute lymphoblastic leukaemia; and 2) pleural tap under local anaesthetic (if pleural effusion present and the child can tolerate the procedure) for T cell lymphoblastic lymphoma.

If a diagnosis cannot be made with these investigations, the oncology team together with the anaesthesia team will need to carefully assess the risk versus benefit in performing biopsy under a general anaesthetic. In addition, the parents of the patient should be fully informed of the risks.

In this patient, the peripheral blood film showed the presence of lymphoblasts. The pleural fluid suspension was also packed with lymphoid blast cells. Immunophenotyping of these cells confirmed the diagnosis of T cell lymphoblastic malignancy. T cell lymphoblastic lymphoma is a relatively rare condition—the incidence in the United Kingdom is approximately 1-2 new cases per million population.⁶ It is important, therefore, that children with a large anterior mediastinal mass are referred early to a paediatric oncology centre with experience and expertise in the management of lymphoid malignancies.

3 Emergency treatment
Children presenting with large superior anterior mediastinal masses represent a medical emergency. Such children are at extremely high risk of tracheal compression leading to respiratory or circulatory compromise.^{2 4 5} To minimise the risk of cardiopulmonary arrest, initiating basic airway management—such as sitting the patient upright and avoiding causing unnecessary distress to the patient—is critically important. If such patients do lose their airway, turning them to the prone position might be life saving as the weight of the mass is lifted off the airway, making intubation and ventilation possible.

The treatment developed by the Berlin-Frankfurt-Münster group has the best results for children with T cell lymphoblastic lymphoma. This regimen involves a steroid pre-phase followed by combination chemotherapy for two years. The five year event free survival rate is in the region of 90%.⁷ The United Kingdom has now adopted a chemotherapy treatment protocol based on the Berlin-Frankfurt-Münster strategy.

Patients with T cell lymphoblastic lymphoma are at high risk for tumour lysis syndrome, which is the most common acute complication after initiation of steroid treatment. Management focuses on prevention with intravenous rasburicase and hyperhydration.⁸ Rasburicase is a recombinant urate oxidase and might cause allergic reactions and haemolytic anaemia in patients with glucose-6-phosphate dehydrogenase deficiency. Rasburicase is, however, a more effective treatment option than allopurinol—another drug used to treat hyperuricemia. In a multicentre randomised trial comparing rasburicase with oral allopurinol in children at high risk of tumour lysis syndrome, the plasma uric acid levels decreased by 86% within four hours of the first dose in the rasburicase group versus 12% in allopurinol group (P<0.0001).⁹ There was also significant reduction in creatinine levels in the rasburicase group.

Patient outcome
The patient described is presently completing his treatment as an outpatient.

Conclusion
Children with T cell lymphoblastic malignancies have an excellent long term prognosis; therefore, it is critically important to manage these children appropriately from the time of initial presentation in order to reduce the risk of avoidable morbidity and mortality.

Cite this as: BMJ 2009;339:b2787