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Superior Mediastinal Compression (SMC) Syndrome

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Shared care information

If a patient presents with symptoms of superior mediastinal syndrome (see below), discuss with the paediatric oncologist on call.

When managing the patient prior to transfer, consider the following:

  • Do not lie the patient flat. Allow child to remain supported on a parent's lap, preferably in an upright or semi-upright position, or on bed at a 45° angle.
  • Sedation is not recommended even if the child is agitated. Spontaneous ventilation is a key management goal.
  • Contact anaesthetics, surgery, respiratory, cardiology and intensive care at your hospital to inform them about potentially progressive airway and/or cardiac problems.
  • Do not delay transfer to a tertiary centre even if the child appears stable, as SVC and airway obstruction can be rapidly progressive and fatal. Discuss the patient's condition and management prior to transfer. 


Over 80% of mediastinal masses in children are malignant. Infants and children are more vulnerable to extrinsic airway compression than adults.

The causes of anterior and superior mediastinal masses in children differ in distribution to adults(2). Haematological malignancies cause the greatest concern as they are the most common and are often rapidly enlarging(3):

  • Acute lymphoblastic leukaemia (ALL)
  • Non-Hodgkin lymphoma (T cell lymphoblastic lymphoma, Burkitt's lymphoma)
  • Hodgkin Disease
  • Malignant Germ Cell Tumours

Thyroid tumours, bronchogenic cysts, cystic hygroma, granuloma and thymoma can also cause anterior mediastinal masses.

Neuroblastoma usually manifests as a posterior mediastinal mass, and should be evaluated with MRI.

Approximately 10% of tumours that occur in the anterior-superior mediastinum compress the superior vena cava (SVC) and/or the proximal tracheal airway or main bronchus.

SVCS, or Superior Vena Cava Syndrome can result from either partial or complete obstruction to blood flow via the SVC to the right atrium by extrinsic compression or invasion, fibrosis or thrombosis of the vessel(4). Reduction in venous return from the upper body and head underlies its clinical presentation.

Clinical presentation

Superior mediastinal syndrome involves obstruction of airways (trachea, main bronchi in particular) and/or cardiac or great thoracic vessel compression, usually from a mediastinal mass and represents a medical emergency.

The onset of SVC obstruction is usually insidious but can lead to sudden loss of cardiac output and rapid increases in intracranial pressure, with resulting cerebral oedema.

Look for other signs of raised intracranial pressure, including hypertension and bradycardia. Papilledema may be present but may be difficult to assess in a drowsy, confused or agitated patient. Patients may complain of headaches or visual disturbances.

Airway obstruction

Main bronchus and tracheal compression produces:

  • dyspnoea
  • orthopnoea (breathlessness lying flat)
  • cough
  • wheeze
  • hoarseness
  • stridor
  • chest pain
  • agitation
  • cyanosis - a very late sign of upper airway obstruction so do not be misled by normal SaO2
  • pleural effusion (appears to be associated with main-stem bronchus compression)

SVC obstruction

  • duskiness/plethora of the face
  • upper body swelling and venous congestion in the SVC distribution and collaterals over the chest wall
  • facial and upper body swelling with periorbital oedema (early sign)
  • other symptoms such as dizziness, epistaxis, haemoptysis, nasal congestion
  • drowsiness, confusion, headache, distorted vision and/or syncope are late signs associated with cerebral oedema.

Horner's syndrome (rare)

  • ipsilateral ptosis, miosis, and anhydrosis.

Management of SMC Syndrome

The airway is compressed at a level well below the cricothyroid membrane so that tracheostomy will not reverse the obstruction. Avoid sedation of any kind even if the patient is restless - it can tip the patient into complete upper airways obstruction; when this occurs, very little can be done to recover the airway.

Four different features associated with mediastinal masses have been shown to significantly increase the risk of peri-anesthetic complications:

  • orthopnoea
  • upper body oedema
  • main-stem bronchus compression
  • great vessel compression.

The latter two features can only be adequately assessed on CT scanning (and/or echocardiography). The presence of a pleural effusion and tracheal compression also showed a trend towards a significant increase in risk(5).


  1. Do not force the patient to lie flat. In the situation of airway compromise, airway patency is often best maintained in a semi-elevated, forward sitting, prone or lateral position, depending on the exact location of the mass in relation to airway and great vessels within the thorax. The patient will often adopt the position where the airway is most patent. In older children it may be helpful to experiment with positioning the patient in various positions while awake to assess for respiratory distress, maximal comfort and optimal oxygen saturations.
  2. Contact anaesthetics and intensive care to inform them about a potential airway problem. Discuss potential SVC obstruction with cardiology.
  3. Examine carefully for enlarged extrathoracic lymph nodes which could be candidates for diagnostic biopsy. Supraclavicular and axillary lymph nodes, which can be readily missed, are frequently associated with malignant disease.
  4. CXR alone is inadequate for assessment of a mediastinal mass. CT scanning of the chest is the ideal imaging modality to assess the location and extent of obstruction of airways or great vessels, pericardial and pleural effusion, and presence of SVC obstruction and collateral blood supply and to differentiate between intravascular thrombosis and extrinsic compression as a cause of SVC syndrome. Discuss this with your radiologist as it may be impossible to lie the child flat without the risk of precipitating acute cyanosis and decreased cardiac output. CT scan can often be performed in the prone, lateral or semi upright (Fowler's position).
  5. Consultation between the paediatric oncologist, paediatric radiologist, paediatric cardiologist and paediatric anaesthetist is required.
  6. Sedation is not recommended even if the child is agitated. Induction of anaesthesia has been associated with severe complications, even in asymptomatic children.
  7. Echocardiography - to look for direct tumour invasion of the pericardium, pericardial effusion which may need to be tapped if acute clinical deterioration occurs. The SVC and pulmonary vessels will have been assessed by the CT Scan. The right atrium can be compressed by tumour and echo will determine this. Involve a paediatric cardiologist.
  8. Ongoing assessment is vital. A patient can initially appear stable but deteriorate within hours due to rapidly progressive mediastinal mass or thromboembolism. Have a low threshold for PICU admission.

Initial management

  1. Prevention of Tumour Lysis syndrome: Start hyperhydration and recombinant urate oxidase (or allopurinol if this is not available) with 6 hourly monitoring of electrolyte and urate levels (refer to tumour lysis syndrome).
  2. Avoid accessing veins draining into the SVC. Do not insert central venous catheter until SMC syndrome resolved. Do not insert IV cannula into a vein draining into SVC, i.e., put into foot vein or greater saphenous.
  3. Try to establish the diagnosis without resorting to sedation or a general anaesthetic:
    1. Full Blood Count - immunophenotyping on peripheral blood.
    2. Fine needle aspirate or core biopsy of palpable, pathological lymph node under local anaesthetic. In addition to cytology/histology, specimens must be sent for immunophenotyping.
    3. Aspirate of pleural effusion. Procedures such as diagnostic pleural aspiration should not be performed on the ward without the presence of an anesthetist or intensivist and resuscitation equipment ready. Guidelines need to be followed, including avoidance of drainage of large volumes of pleural fluid, due to the risks of re-expansion pulmonary oedema and precipitating airway collapse, risks which are higher in children.
    4. Lumbar Puncture by an experienced clinician for CSF cytospin.
    5. Bone marrow aspiration should be performed as soon as possible. Older children may tolerate a bone marrow aspirate with local anaesthetic only.
    6. If there is no detectable extrathoracic disease, discuss alternative means of diagnosis with a surgeon e.g., mediastinal thorascopy and biopsy.
    7. A general anaesthetic is often high risk and should be avoided if possible.
    8. Systemic steroids may be necessary to shrink the mass and reduce medistinal compression prior to biopsy. Systemic steroids can rapidly reduce the size of a mass but significantly alters tissue quality, due to its oncolytic effects(6). This can delay accurate diagnosis on biopsy and staging. This decision should involve a paediatric oncologist, with multi-disciplinary consultation.

Deciding appropriate treatment

The on-call paediatric or adult oncologist at the regional oncology centre should be contacted immediately by the examining physician if a mediastinal mass is suspected.

Any decision regarding initiation of steroids should be made in conjunction with the oncologist.

All possible efforts should be made to obtain tissue samples, including a small diagnostic aspirate if a pleural effusion, prior to starting steroids or other oncolytic treatment.

Involved field radiation is generally no longer performed prior to tissue diagnosis as it may preclude proper interpretation of biopsy in at least 50% of cases(7).


  1. Cervantes A, Chirivella I. Oncological emergencies Annals of Oncology 2004; 15 (Supplement 4):iv299-iv306.
  2. Slinger P, Karsli C. Management of the patient with a large anterior mediastinal mass: recurring myths. Current Opinion in Anaesthesiology 2007; 20:1-3.
  3. Hack H.A, Wright N.B, Wynn R.F. The anaesthetic management of children with anterior mediastinal masses. Anaesthesia 2008; 63:837-846
  4. Cervantes A, Chirivella I. Oncological emergencies Annals of Oncology 2004; 15 (Supplement 4):iv299-iv306.
  5. Anghelescu, DL et al. Clinical and diagnostic imaging findings predict anesthetic complications in children presenting with malignant mediastinal masses. Pediatric Anesthesia 2007; 17:1090-1098.
  6. Saraswatula A, McShane D, Tideswell D. et al. Mediastinal masses masquerading as common respiratory conditions of childhood: a case series. European Journal of Pediatrics 2009;168:1395-1399.

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Document Control

  • Date last published: 08 June 2016
  • Document type: Clinical Guideline
  • Services responsible: National Child Cancer Network
  • Owner: Ruellyn Cockcroft
  • Review frequency: 2 years