Anterior mediastinal masses in children

Key points.

• •Thorough preoperative assessment and a multidisciplinary plan are essential to guide best management for patients with an anterior mediastinal mass.
• •A CXR and high-resolution CT before anaesthesia facilitate risk prediction.
• •A subjective history of the patient's preferred position to minimise symptoms may guide positioning for surgery.
• •A spontaneously breathing technique is recommended.
• •Repositioning or a rigid bronchoscope can be used to relieve airway obstruction during surgery.

Learning objectives.

By reading this article you should be able to:

• •Distinguish which signs and symptoms in a patient with an anterior mediastinal mass may predict an increased risk of complications under anaesthesia.
• •Compare the various anaesthetic techniques and their potential issues in a patient with an anterior mediastinal mass.
• •Discuss rescue techniques that could be used in a situation of airway or cardiovascular collapse in a patient with an anterior mediastinal mass.

Surgery for patients with an anterior mediastinal mass is known to be challenging and high risk, particularly in paediatric patients. Anterior mediastinal mass surgery is performed less commonly now than in the past because alternative options for management are available. However, reduced exposure of anaesthetists to this particular type of surgery can result in decreased familiarity with the problems that may occur. Management for such patients should involve multidisciplinary discussions to determine the best course of action for each individual patient. Anaesthetic expertise is required for a spectrum of procedures that may be required in these patients.

An anterior mediastinal mass provides challenges for the anaesthetist because of its impact on the surrounding mediastinal structures, coupled with the effects of anaesthesia on them.1, 2 There is potential for severe and potentially fatal respiratory and cardiovascular compromise. The airway can be potentially obstructed at any point, or multiple points along its length. Alternatively, the mass may obstruct venous return and cause obstruction to cardiac output. Further, in an awake patient, the respiratory and airway muscle tone may be integral in maintaining a patent airway. The loss of this tone under anaesthesia can potentially lead to complete and possibly fatal airway obstruction.³ Children are at particular risk during this surgery and are overrepresented in case reports describing poor outcomes. This may be secondary to the more compressible nature of the paediatric airway and surrounding structures. In addition, a small decrease in a tracheal lumen that is already reduced by extrinsic compression will lead to a relatively large increase in airway resistance. The severity of airway obstruction in children may also be underestimated before surgery as a result of difficulties in obtaining a clear history or symptomatology.4, 5, 6

This type of surgery has become less common, after the availability of alternate diagnostic and management strategies. This has been partly attributed to the recognised high risk of surgery. One alternative to mediastinal surgery is to sample or biopsy a distant site such as a pleural effusion, peripheral lymph node, or a bone marrow aspirate under local anaesthetic.1, 7 Similarly, imaging alone can be used to guide treatment, with modern imaging being faster and providing more detailed information, meaning diagnostic biopsies may be avoided.⁴ Another alternative used commonly is pretreatment with steroids or chest irradiation before obtaining a biopsy. This effectively shrinks the tumour and reduces both symptoms and the degree of mass effect before biopsy or definitive surgery, therefore reducing the risks of anaesthesia.¹ Surgery should ideally be scheduled within 24 h of finishing steroid treatment. There is concern that radiotherapy or preoperative steroids may affect a clear histological diagnosis; this should be discussed in a multidisciplinary forum.¹ These alternative treatment regimens also carry risks in these patients and need to be carefully planned. For instance, complications associated with sedation for bone marrow biopsy or CT imaging have been reported.4, 7

Despite the changes in approach to management of anterior mediastinal masses, there are still patients that require diagnostic or therapeutic surgical intervention, which may pose a significant challenge to the anaesthetist. This article reviews the strategies for the management of anaesthesia for a patient with an anterior mediastinal mass.

Preoperative considerations

Signs, symptoms, and prediction of difficulty

A detailed and thorough history should be taken from the child where possible and from the child's primary carers. Careful clinical examination should be performed without causing too much distress or exacerbation of symptoms. In patients with a mediastinal mass, there is no one individual symptom or test that will accurately forewarn of complications during anaesthesia.¹ However, a number of signs and symptoms may predict an increased risk if undergoing GA. Respiratory complications may be predicted by the presence of a cough when supine, orthopnoea, stridor, or wheeze.2, 4, 8 Syncopal symptoms and upper body oedema are signs of superior vena caval (SVC) obstruction and indicate increased risk of cardiovascular complications.4, 7 In terms of imaging, a reduction of >70% in tracheal cross-sectional area, carinal or bronchial compression, or both is associated with an increased risk of complications.1, 7 Great vessel compression and pericardial effusion also predict a greater complication rate.2, 4, 7 However, problems may still occur in patients without these symptoms or signs (Table 1).

Table 1.

Risk factors for perioperative complications.

Signs and symptoms	Imaging findings
Orthopnoea	Reduction (<70%) in tracheal cross-sectional area
Cough when supine	Carinal or bronchial compression
Stridor	Great vessel compression
Wheeze	Pericardial effusion
Syncopal symptoms
Upper body oedema

Imaging/investigations

Adequate investigation preceding any procedure is essential to adequately prepare and guide management. If an anterior mediastinal mass is suspected either from history or a widened mediastinum on CXR, then a CT scan is recommended. It reveals the size of the mass, its anatomic location, and impact on other structures such as airway compression at a tracheal or bronchial level. It can demonstrate other factors such as a pleural effusion that may impact the patient's respiratory reserve.1, 8

Cardiovascular abnormalities are often detected on CT or MRI in patients with an anterior mediastinal mass, though the clinical findings rarely match. The exception is when the mass causes SVC obstruction, which is often accompanied by symptoms and signs. Reported cardiovascular complications are less common, but this may be confounded by other factors such as attributing a decline to respiratory causes alone.³

Lying flat for imaging may exacerbate symptoms or even cause life-threatening events. However, modern imaging is rapid and patients can be placed in a position of comfort during the scan, including a lateral or prone position if it alleviates symptoms; this may facilitate successful completion of the scan. Despite the advantages of current imaging, the degree of compression demonstrated may be an underestimate of the degree of compression once under anaesthesia.¹ In addition, obtaining a CT scan is not without its own limitations, with some young children requiring sedation or a GA in order to perform the imaging.

Transthoracic echocardiography may reveal pericardial effusions or mass compression on the heart or great vessels, and the effect on ventricular function. It may be considered in those with cardiovascular symptoms and also when the patient is unable to give an adequate history.1, 4

Some authors advocate the use of flow-volume loops, as expiratory flow limitations may demonstrate a risk of airway collapse with anaesthesia, particularly if they change with positioning.⁹ However, the usefulness of this test is debatable, as there may be a high false negative and the test is unlikely to reveal any additional clinically useful information not obtained from CT imaging.⁴

Pathology

The most common causes of an anterior mediastinal mass in children are haematological malignancies, most commonly Hodgkin's or non-Hodgkin's lymphoma. Other potential causes include acute lymphoblastic leukaemia, vascular malformations, neurogenic tumours, teratomas, and other germ cell tumours and cysts.2, 8, 9 In patients with newly diagnosed lymphoma, the possibility and risks of a mediastinal mass should always be considered.

Procedure

Patients with an anterior mediastinal mass may present for a variety of procedures, including sedation for imaging, radiotherapy or a diagnostic biopsy. The degree of sedation or anaesthesia required for these procedures is largely determined by the individual child. Similar considerations and plans for adverse consequences need to be made for those undergoing procedures under sedation as for a GA. Specific preparations should also be made for a procedure in an environment remote to the operating theatre. For those requiring a GA, the procedure may be diagnostic or therapeutic and include mediastinoscopy, video-assisted thoracoscopy, thoracotomy, sternotomy, or biopsy of sites remote to the mediastinal mass. Rarely, a patient with an anterior mediastinal mass may present for anaesthesia for an unrelated surgical emergency.⁴

There is a clear role for multidisciplinary discussion regarding the need and type of surgery required and the risks involved. Involvement of different surgical specialties, including general paediatric surgery, ENT, and cardiothoracic surgery, should be sought as appropriate. Each patient will have individual surgical considerations regarding positioning, duration, potential blood loss and airway requirements.

Positioning

With current practices, a life-threatening adverse event is more likely to happen before surgery when a child is made to lie supine to obtain imaging, or when a child with an undiagnosed mediastinal mass is anaesthetised for other reasons.⁵ Throughout the perioperative period, a head-up position may help to maintain functional residual capacity (FRC) and reduce further cephalad movement of the diaphragm.⁹ Alternatively, a lateral position may improve airway patency and reduce cardiac or vascular compression. An early detailed discussion is essential to determine which the position in which the child feels most comfortable and which positions accentuate or alleviate symptoms. This may give an insight into the best position for induction of anaesthesia, or how to reposition the child if airway or cardiovascular compromise to occur during operation.4, 8, 9 Similarly, discussion should be had with the person performing the procedure to find an optimal compromise between a suitable patient position for the planned procedure while maintaining patient stability. An example is remaining in the left lateral position for bilateral bone marrow aspirates in the clinical case described below.

Other oncological considerations

When planning and preparing for the case, other onco-anaesthetic factors should be considered. The patient may need early preoperative assessment in order to assess the biochemistry, haematology, and coagulation profiles and allow for the potential correction of abnormalities or pre-emptive ordering of blood products.¹⁰

Nitrous oxide impairs methionine synthetase activity, which disturbs folate metabolism and therefore vitamin B12 metabolism. Prolonged exposure to nitrous oxide is associated with bone marrow suppression. This can still theoretically occur with short periods of administration, so should only be used after careful consideration.³

Tumour lysis syndrome may occur with initial treatment of the mass. It is characterised by significant destruction of tumour cells causing the rapid release of cellular contents that may cause renal failure and other organ damage. Adequate prehydration can reduce the risk of tumour lysis syndrome and both fasting and perioperative fluid maintenance should be monitored carefully. Similarly, dexamethasone may trigger tumour lysis syndrome, so discussion with an oncologist is suggested if its used as an antiemetic or for possible airway oedema is intended.²

Patients are likely going to need long term i.v. access, and opportunistic placement of long term access while under anaesthesia may be worthwhile. Lines can be accessed for repeated blood testing and chemotherapy. If central access is already in situ then a sterile technique to access it should be used.¹⁰

Intraoperative management

Clinical case.

A 6-yr-old boy with a likely diagnosis of lymphoma was admitted for diagnostic bilateral bone marrow biopsies. There was a history of breathlessness when lying flat and on the right side, and he would only voluntarily lie on his left side. Examination revealed distended neck veins and some facial oedema. On investigation, there was significant mediastinal widening on CXR. CT was performed awake which showed a large mediastinal mass with superior vena cava compression and significant lower airway compression.

After discussion with the treating team, the anaesthetic plan was for a gaseous induction with spontaneous breathing and maintenance via a facemask. Inhalation induction was performed on his left side and proceeded uneventfully. The right-sided bone marrow aspirate was performed without incident, however, after rotating the patient onto his right side for the left-sided bone marrow aspirate, the patient became hypotensive and ventilation was severely compromised. He was immediately repositioned back on the left side with resolution of symptoms. It was decided the left-sided biopsy was not possible and the patient was woken up and recovered on his left side with no further events occurring. He was confirmed to have lymphoma and proceeded to chemotherapy with eventual remission.

Techniques

Local anaesthesia

Although obtaining a tissue sample under local anaesthesia in adults is a viable option, needle biopsy or bone marrow aspirate under local anaesthesia alone is difficult to achieve in children. Lack of understanding and fear are likely to affect success rate, exacerbate symptoms, or result in trauma. Older children may be more compliant with this technique. Similarly, an awake anterior mediastinoscopy or awake fibreoptic intubation under topicalisation is not achievable in most children.⁴ More invasive procedures are not suitable to local anaesthesia.

Sedation and regional anaesthesia

In a paediatric patient unable to tolerate a biopsy under local anaesthesia, sedation may facilitate the procedure. The use of dexmedetomidine and ketamine for sedation and analgesia has been described, as these agents are less likely to cause respiratory depression, and the sympathomimetic properties of ketamine can help to maintain haemodynamics.¹¹ The addition of midazolam (0.1 mg kg⁻¹) may be beneficial in reducing psychotropic effects and an antisialagogue (such as glycopyrrolate 10 μg kg⁻¹) may be warranted with the use of ketamine. Dosing regimens for dexmedetomidine for invasive procedures have been described using a loading dose of 1 μg kg⁻¹ over 10 min followed by a titrated infusion of 0.25–2 μg kg⁻¹ h⁻¹. A suggested dosing regimen for ketamine is an initial dose of 1–2 mg kg⁻¹ over 2 min and subsequent doses of 0.5 mg kg⁻¹ as required.11, 12, 13

In older children, regional techniques with sedation to obtain lymph node biopsies have been described, but the use of this technique is clearly determined by the type of tissue sampling required and the compliance of the child.¹⁴ Consideration should be made for potential coagulopathy associated with malignancies.¹⁰ Airway compromise may be severe even under sedation.

General anaesthesia

For some patients or some procedures, a GA cannot be avoided (Fig. 1). Ideally, i.v. access should be secured before induction. A spontaneously breathing technique is most commonly advocated where the aim is to maintain airway tone and therefore limit potential compression.3, 4, 9 Spontaneous ventilation maintains the transpleural pressure gradient that prevents airway collapse. The pressure gradient is maintained in part by respiratory muscle activity. Avoiding neuromuscular blocking agents mitigates a loss of chest wall tone and a potential worsening of compression effects.⁹ In paediatric patients, this is typically achieved by an inhalation induction of anaesthesia, usually with sevoflurane. The use of an i.v. induction while maintaining spontaneous ventilation, usually propofol-based with or without adjuncts, is also an option in those with skill and experience with its use in paediatrics. Extreme care must be taken to avoid inducing apnoea, as there is a real potential that one will be unable to pass a tracheal tube, resolve the obstruction, or re-establish a patent airway.

Fig 1.

Intraoperative management. OLV, One-lung ventilation.

An unexpected anterior mediastinal mass when a child is induced for a coincidental procedure is an uncommon, though potentially disastrous scenario. Although a thorough preoperative assessment may detect symptomatology, this is not always the case. Potential consequences may be inadvertently avoided if an incidental inhalation induction was performed, although this cannot be assured. Assistance should be called for immediately, including alerting a surgeon to attend and preparing equipment for the management of a difficult airway. Attempts should be made to revert to spontaneous ventilation by antagonising the effects of neuromuscular blocking agents or lightening of anaesthesia. With unexpected respiratory obstruction or cardiovascular collapse, a high index of suspicion for a mediastinal mass is required to allow consideration of the following management options.

Initial management if respiratory collapse

If ventilation becomes impaired, immediate action should be taken to improve or reverse airway compression and prevent hypoxic arrest. Increasing F_IO₂ is a clear first step to mitigate hypoxia. The application of CPAP will splint open airways and reduce extrinsic compression. It will also restore FRC that is typically reduced under anaesthesia from a decrease in muscle tone.⁹ Maintaining FRC can improve ventilation/perfusion mismatching and reduce hypoxaemia. This should be applied while the patient is still spontaneously breathing. Repositioning the patient may be key in resolving the airway obstruction. A lateral position is often effective at reducing the patient's symptoms, especially if identified before surgery. In extreme cases, positioning prone may be required to allow gravity to aid in relieving the airway obstruction.²

If these actions do not resolve the obstruction, attempts to ventilate with positive pressure and PEEP may be considered. A tracheal tube should be placed and an attempt to advance it beyond the obstruction should be made. This may require ventilating a single lung if the obstruction is at the carina or beyond. The airway may be obstructed at more than one point.

A rigid bronchoscope may be used to pass beyond the obstruction under direct vision and allow ventilation distal to the obstruction. CPAP may also be applied here by attaching a Mapleson F breathing circuit to the bronchoscope. Care must be taken to avoid air trapping if positive pressure ventilation is applied this way, as expiration is also obstructed and resistance is greatly increased when ventilating through a narrow bronchoscope.¹⁵ If airway obstruction occurs, rapid desaturation will follow, therefore access to a rigid bronchoscope and personnel skilled in its use need to be immediately available.

Helium may have beneficial effects by reducing resistance in a narrowed airway. However, helium displaces oxygen in the inspired gases, which is not desirable in situations of hypoxia. While it may be beneficial in initial management, it is unlikely to be advantageous during a crisis.

Initial management if cardiovascular collapse

In situations of cardiovascular collapse, first-line therapy includes a rapid fluid bolus i.v., reducing the depth of anaesthesia and repositioning, including to the prone position. If there is no improvement with these initial manoeuvres, then in dire situations sternotomy and lifting of the mass from the central thoracic structures may be required.

Respiratory and cardiovascular complications are likely to be interrelated or occur simultaneously. Cardiovascular complications are less common, but it is unknown to what degree reduced venous return or obstructed cardiac output may have contributed to a reduction in pulmonary perfusion and increase ventilation/perfusion mismatch, augmenting hypoxia and patient deterioration.¹ In refractory hypoxia, cardiovascular complications should be considered and optimised. Similarly, management of one system may improve the other.

Both preemptive and rescue extracorporeal membrane oxygenation (ECMO) have been suggested as management of high risk patients or severe deterioration. Whilst theoretically appealing, in practice the utility is unlikely to be high. Preemptive ECMO has the significant challenge of placing ECMO cannulae in children without significant sedation, or managing the risks of heavy sedation in these patients. Using ECMO as a rescue runs the significant risk of prolonged hypoxia occurring while the circuit is established.2, 4

Postoperative care

A number of factors influence the most appropriate level of care after surgery, but it is beneficial to ensure that the ICU is aware the patient is undergoing the procedure, in case of perioperative complications. In adults, airway complications are more likely to occur immediately after operation than during the procedure.⁴ Where a biopsy is performed and the mass effect is still present, then an increased level of care after the procedure is warranted. It is desirable that the patient is fully awake and whose trachea has been extubated at the end of surgery. When the mass has been removed, then the compression effects are likely to have been alleviated. Postoperative complications, such as bleeding, should still be closely monitored for.

Summary

Clear communication and teamwork and an organised, pre-prepared plan are paramount to the successful management of a child with an anterior mediastinal mass. Multidisciplinary discussions should determine the most appropriate course of action for investigation and management of the lesion. If GA cannot be avoided, then a spontaneously breathing technique is recommended with the ability to ventilate the lungs via a rigid bronchoscope immediately available in the case of respiratory collapse; and repositioning and potential sternotomy discussed as potential life-saving measures for cardiovascular collapse.

Declaration of interest

The authors declare that they have no conflicts of interest.

MCQs

The associated MCQs (to support CME/CPD activity) will be accessible at www.bjaed.org/cme/home by subscribers to BJA Education.

Biographies

Monique McLeod DRANZCOG (Adv), M. Bioethics, FANZCA is a senior clinical fellow in paediatric anaesthesia at the Royal Hospital for Children, Glasgow. Her clinical interests include paediatric and neonatal anaesthesia, prehospital and developing world medicine, and advanced airway management.

Michael Dobbie FANZCA is a senior consultant at the John Hunter Hospital Newcastle, Australia. He is Director of Paediatric Anaesthesia and Deputy Director of the John Hunter Department of Anaesthetics. His major clinical interests are paediatric anaesthesia and in particular shared airway and ear, nose, and throat surgery (ENT); he also has a strong interest in teaching and is a senior instructor in the HNE simulation centre.

Matrix codes: 1C01, 2A01, 3A01