Introduction

The anesthetic management of children and adults who present for tissue diagnosis or surgical resection of anterior mediastinal masses poses one of the greatest challenges we see in anesthesiology. This is because these patients can suffer life-threatening extrinsic compression of the airway, obstruction of cardiac output, or obstruction of venous return during the induction of anesthesia and at any point during the anesthetic. A seemingly asymptomatic patient may develop one of the aforementioned catastrophic events while under anesthesia. Despite better understanding of the pathophysiology and management of patients with anterior mediastinal masses, perioperative complications ranging from mild airway obstruction to complete cardiopulmonary collapse are estimated to occur in approximately 9% to 20% of anesthetic procedures. What is the safest way to go about anesthetizing these patients? How do we determine who is at greatest risk preoperatively? Are there ways to reduce a patient’s risk while optimizing the ability to obtain a tissue diagnosis? These are some of the challenges posed by patients who present with anterior mediastinal masses.

Definition

The mediastinum is defined as that portion of the thorax between the medial aspects of the pleura, above the diaphragm and below the thoracic inlet. It is bound anteriorly by the sternum and posteriorly by the thoracic vertebrae. A line between the fourth thoracic vertebra and the sternal angle subdivides the mediastinal space into inferior and superior compartments. The inferior space is further subdivided by the pericardium into anterior, middle, and posterior regions. The anterior mediastinum lies between the sternum anteriorly and the pericardial sac. The middle mediastinum includes the pericardial sac and its contents, and the posterior mediastinum includes the space between the pericardial sac and the thoracic vertebrae. There are no fascial planes that separate these regions, so masses that originate in one compartment may cross over to another. Mediastinal masses can affect many intrathoracic structures. Most significant are those that compress the heart or major vessels within their respective compartments. Most commonly, they involve the anterior mediastinum and, to a lesser extent, the middle and posterior mediastinum. The location of a mediastinal mass, whether benign or malignant, is characteristic. It provides the clinician with clues to the origin of the mass and determines what physiologic effects it will have on surrounding mediastinal and other thoracic structures. The differential diagnosis for anterior mediastinal masses include the terrible T ’s: T errible lymphoma, T hymoma, T eratoma, and T hyroid tumor. The most commonly reported of these in children are malignant lymphomas, accounting for as many as 45% of anterior mediastinal masses. In adults, thymomas and lymphomas have been reported to account for more than 50% of anterior mediastinal masses. Other potential pathology of anterior mediastinal masses include metastases, intrathoracic goiter, neuroblastoma, thymic cysts, bronchogenic cysts, and pericardial cysts.

Recognition

Adult patients with anterior mediastinal masses present with a variety of signs and symptoms. Most, however, are either asymptomatic or have minimal to moderate symptoms, including cough, dyspnea on exertion, chest pain, fatigue, and vocal cord paralysis. Severe symptoms in a minority of adults include orthopnea, stridor, cyanosis, jugular vein distention, or superior vena cava syndrome. Children may present for medical evaluation of seemingly benign respiratory ailments such as persistent colds, wheezing, cough, or stridor, but a chest radiograph clues the medical provider to a more sinister etiology. Regardless of the presentation, a tissue biopsy is crucial in establishing an accurate diagnosis to guide definitive treatment. This is especially true in children where there is significant variation in chemotherapeutic regimens depending on the tissue diagnosis.

Risk Assessment

A thorough preoperative evaluation of the patient with an anterior mediastinal mass is essential for safe provision of anesthesia. Typical laboratory evaluations performed include a complete blood count, blood smear, electrolytes, uric acid, lactate dehydrogenase, and flow cytometry, to name a few. Patients may also undergo a variety of diagnostic procedures, including lumbar puncture, bone marrow aspirate, CT, transthoracic echocardiography, and pulmonary function testing. These patients come to the attention of the anesthesiologist for care during surgical procedures that include cervical lymph node biopsy, Chamberlain procedure (mediastinal node biopsy), bone marrow biopsy, central line placement for chemotherapy, and (less commonly) tumor resection. Anesthetic considerations for patients presenting with an anterior mediastinal mass will vary depending on the individual anatomy, symptoms, age of the patient, and proposed surgical procedure. Although there are general principles for safe provision of anesthesia, there is a definite need to individualize management for each presenting patient. All patients should have a targeted history and physical examination, a chest x-ray, and CT scan as part of their preoperative evaluation. The presence of orthopnea, cough when positioned supine, stridor, wheezing, facial engorgement, or upper body edema should alert the anesthesiologist to the possibility of increased perioperative risk. It should be noted that the absence of clinical signs does not preclude the potential for life-threatening complications. Of particular importance, the anesthesiologist should determine whether there is a positional component to the symptoms and establish those positions in which the patient is least symptomatic.

A CT scan will show the extent of the mass, presence and degree of airway compression, and invasion and/or compression of other surrounding structures. Magnetic resonance imaging is not routinely obtained and in small children would require the need for sedation or general anesthesia to procure. In patients with concern for cardiovascular involvement of an anterior mediastinal mass, an echocardiogram can be used to evaluate for cardiac function; tumor infiltration of the pericardial and myocardial tissue; compression of the superior vena cava, pulmonary arteries, right atrium, and right ventricle; and presence of pericardial effusion, and to assess for tamponade physiology. Pulmonary function tests (PFTs) in the upright and supine positions have been advocated by some authors in the workup of anterior mediastinal masses in children and adults. Flexible bronchoscopy with airway topicalization is another useful tool to assess for dynamic airway obstruction.

Peak expiratory flow rates have been used to assess for dynamic airway collapse. The shape of the flow-volume loop may give clues to the site of airway obstruction (intrathoracic versus extrathoracic) and indicate whether the obstruction is fixed or variable. It has been reported in literature that a supine peak expiratory flow rate less than 50% of predicted or PFTs with a mixed restrictive and obstructive pattern correlated with an increased rate of preoperative respiratory complications. More recent literature questions the need for PFTs and suggests that PFTs are rarely useful in the preoperative evaluation of patients with anterior mediastinal masses. One such study found that flow-volume loops had a poor correlation to the presence of symptoms or to the degree of airway compression found on a CT scan.

Aggregating the clinical signs and symptoms with the results of diagnostic studies can help identify those patients who are at high risk for preoperative complications. Predictors of cardiopulmonary compromise under general anesthesia include the following:

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  The presence of severe preoperative symptoms, especially orthopnea

  
  
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  Patients with superior vena caval obstruction

  
  
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  Evidence of pulmonary artery outflow obstruction

  
  
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  Ventricular dysfunction

  
  
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  Presence of pericardial effusion/tamponade physiology

  
  
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  Tracheal compression with greater than 50% reduction in cross-sectional area on CT and/or carinal or bronchial compression

  
  
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  Supine peak expiratory flow rate less than 50% of predicted

  
  
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  Combined obstructive and restrictive pattern on pulmonary function testing

Careful consideration should be given to patients with any of these findings as to their suitability to safely undergo general anesthesia. The possibility of obtaining a tissue biopsy under local anesthesia with or without sedation should be strongly entertained. For those patients deemed to be at very high risk, consideration should be given to preoperative corticosteroid therapy and/or radiation therapy. Treatment can cause widespread tumor lysis and alleviate airway obstruction and cardiovascular symptoms, thus reducing the patient’s anesthetic risk. The concern with this approach is that steroids and radiation may obscure the ability to later obtain a tissue diagnosis. However, a study reported up to 95% successful tissue diagnosis rate in patients who were treated with a brief period of corticosteroids up to an absolute maximum of 5 days.