Keywords

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Mediastinal masses are varied and present at all ages, from newborn to adolescence. There is a wide spectrum of pathology that may include congenital, inflammatory, infectious, and neoplastic processes. Because of the limited space and confined geometry of the region, masses can interfere with both the respiratory and cardiovascular systems, sometimes with grave results. Urgent consultations from oncologists and pediatric intensivists are common, and most of these patients will require some form of surgical intervention, such as biopsy, resection, or venous access. Applicable techniques range from minimally invasive procedures to large thoracotomy or sternotomy. Expertise with these procedures as well as a detailed knowledge of the anatomy and wide range of pathology of the region are essential. An in-depth understanding of the decision-making regarding pre-anesthetic work-up and management can help prevent potentially disastrous complications.

The mediastinum is defined most simply as the space that lies between the two pleural cavities. It is bounded by the sternum and by the vertebral bodies, and extends from the thoracic inlet to the diaphragm. Most importantly for pediatric surgeons, the region is divided into anterior, visceral (or middle), and posterior (or paravertebral) (Fig. 41.1). The anterior compartment is bounded anteriorly by the sternum and posteriorly by the pericardium and anterior aspect of the great vessels. Normally it contains the thymus, lymph nodes, and fat but can also house thyroid or parathyroid tissue. The middle mediastinum contains the heart, great vessels, esophagus, large airways, and major nerves (vagus and phrenic), and is populated with lymph nodes as well. The thoracic duct is often difficult to clearly identify and thus susceptible to injury during mediastinal surgery. It ascends through the mediastinum just anterior to the vertebral column and posterior to the esophagus and pericardium. Inferiorly, it is found more towards the right. It then curves toward the left side at the level of the fifth thoracic vertebra and ascends through the upper aspect of the mediastinum behind the aortic arch and left subclavian artery intimately associated with the left posterior esophagus. The posterior mediastinum is essentially the paravertebral space, defined by the costovertebral sulcus, and contains the sympathetic chain. Various lesions arise from these tissues and thus differential diagnoses can be narrowed significantly by anatomic location. It is important to recognize, however, that when a lesion gets large enough, it can extend from one region into another. This is especially true of lymphomas. It can sometimes be difficult to tell if such a mass originates in the anterior or middle compartment.

Fig. 41.1
figure 1_41

The mediastinum can be divided into three compartments: anterior, visceral (or middle), and posterior (paravertebral) (From Sheilds T. Mediastinal surgery. Philadelphia: Lea & Febiger; 1991. Reprinted with permission from Lippincott Williams & Wilkins)

Full size image

Anterior mediastinal masses are most often neoplastic. The most common lesion found in the anterior mediastinum in the pediatric population is lymphoma. However, germ cell tumors, thymomas, and thyroid tumors can occur as well. The middle mediastinum is more likely to be involved with a more congenital anomaly, such as a foregut duplication or bronchogenic cyst. The posterior mediastinum is a characteristic location for neurogenic tumors. Lymphatic and vascular malformations can be present in any of these spaces and are sometimes contiguous with a cervical component.

Diagnosis

Symptoms of a mediastinal mass are usually a direct result of compression of surrounding structures, mainly the airway and large blood vessels. This can manifest as noisy breathing, dyspnea, shortness of breath on exertion, or orthopnea. Orthopnea is considered the most worrisome symptom, especially when caused by an anterior mediastinal mass. Children can present with true respiratory distress, in which case the diagnosis and treatment become emergent. In younger patients, these symptoms can sometimes be more subtle. Constitutional symptoms can also occur, especially with the lymphomas. One should always inquire specifically about fever, chills, weight loss and night sweats. Incidentally found mediastinal masses are most commonly found in the posterior compartment because of their distance from the airways. As well, it is important to note that both non-Hodgkin’s lymphoma (NHL) and Hodgkin’s disease (HD) can present with cervical adenopathy only and a related mediastinal mass found only on work-up.

Physical examination should be thorough. Examination of the head and neck should focus on cervical masses as well the presence of venous distension. A careful respiratory and chest exam is important. One should palpate the abdomen for organomegaly and masses.

Because of the diversity of the lesions seen in the mediastinum, one needs to take into account the patient’s age, history, symptoms, and signs. The work-up not only involves making the diagnosis but also assessing the child for an anticipated general anesthetic. The chest X-ray (two views) is usually the first imaging study to investigate a mediastinal mass and often provides a great deal of important information in this regard. The anatomic location of the mass can usually be identified, which helps narrow the differential. The association of the mass with adjacent structures is important to note, especially if there is displacement or luminal compromise of the trachea or mainstem bronchi. Related phenomena such as pleural effusion, lung consolidation, or air trapping should be noted and carefully documented.

Most patients will then proceed to computed tomography with intravenous contrast. This study typically provides accurate images to help assess the nature of the mass, its anatomy, whether or not it is calcified, and its relationship to the critical structures of the mediastinum. Airway and vascular impingement can be quite clearly seen. Magnetic resonance imaging is most often used for posterior mediastinal masses. This is because most of these are of neural origin and this study nicely defines extension into the spinal canal. Also, posterior lesions rarely cause respiratory issues and these patients can tolerate MRI scans quite easily. An echocardiogram is obtained if there is any suspicion of heart or great vessel impingement and is often obtained at the insistence of the anesthetist prior to a planned surgical procedure. Other imaging studies are rarely necessary initially.

Laboratory studies should be tailored to the possible diagnoses. All patients should have a complete blood count with peripheral smear and a chemistry panel. Tumor-specific markers should be sent depending on clinical suspicion. For example, anterior mediastinal tumors suspected of being of germ cell origin warrant sending human chorionic gonadotropin (HCG) and alpha fetoprotein (AFP). In a young child with a posterior mediastinal mass where there is suspicion of neuroblastoma, urine studies for homovallinic acid (HVA) and metanephrines should be sent. Most other lesions require no specific laboratory testing.

The key to the diagnosis and subsequent treatment usually lies in obtaining a tissue diagnosis. This involves biopsy in some cases and surgical resection in others. A close relationship with both a pediatric oncologist and experienced pathologist is important. Educated decision making will allow for the safest and most efficacious plan of action. If time permits, new cases should be discussed at a multi-disciplinary tumor board.

When caring for a patient with a mediastinal mass, any procedure requiring general anesthesia can be extremely hazardous. The potential for airway compromise must always be in the mind of the surgeon. A discussion of airway assessment in patients with large lesions must always occur. The safest approach is usually the least invasive procedure available. Blasts seen on peripheral smears can sometimes help in the diagnosis of acute leukemia with mediastinal involvement. Pleural effusions or bone marrow sampling can yield diagnostic cells. Quite often with HD and less so with NHL, cervical or other easily accessible lymph node masses might be amenable to biopsy and thus avoid the need for a more invasive and potentially very dangerous procedure. Patients with an anterior mediastinal mass are at the greatest risk for respiratory or cardiac arrest during general anesthesia or even deep sedation and consideration should therefore be given to the possibility of performing a diagnostic procedure under local anesthesia with minimal, if any, sedation. For example, percutaneous core biopsies performed by an interventional radiologist commonly yields excellent diagnostic results and can often be done with only a local anesthetic. Nonetheless, if less invasive steps are not possible or fail to yield a diagnosis, biopsy of the mediastinal mass itself is indicated.

Preoperative Preparation

This is a commonly discussed topic among pediatric surgeons and anesthesiologists. It is well-recognized that life-threatening airway obstruction can develop in these patients when undergoing anesthesia. Impingement on the heart and great vessels can also produce deleterious effects that are acutely exacerbated by general anesthesia. Tumor bulk and size as well as tracheal and vascular compression have all been implicated as factors associated with adverse anesthetic outcomes. In addition, NHL imparts a greater risk than other tumors. The reason for respiratory collapse on induction of general anesthesia in these patients is multi-factorial. Anesthesia reduces functional residual capacity and decreases lung compliance. Relaxation of the chest wall musculature and diaphragm and the institution of positive pressure ventilation results in a loss of the normal negative intrathoracic pressure transmitted to the airways. Narrowed regions can progress and become critical. Positive pressure disrupts the normal resistance-lowering effect of laminar airflow and worsens the ability to move air. Unfortunately, the critical compression commonly occurs at or near the carina, distal to the end of the endotracheal tube where even a surgical airway may not be of any help. There have been numerous reports in the literature of death under these circumstances.

Assessment of anesthetic risk commences at the bedside with an appropriate history and physical examination, but predictions based solely on clinical findings have been known to be inaccurate. Two widely available tests have been shown to fairly useful in determining risk: assessment of cross-sectional area of the trachea by CT scan and pulmonary function tests. The trachea is measured at its narrowest point and in the appropriate radiographic window. This value is then compared to expected values for age and patients with areas less than 50% of expected are considered to be at risk for significant airway compromise. Intrathoracic tracheal compression affects flow-volume loops mainly at the maximum expiratory flow rate. The peak expiratory flow rate (PEFR) can be assessed with a handheld device at the bedside and correlates with central airway size. PEFR less than 50% of predicted is concerning. These two criteria have been used together to define anesthetic risk. If both studies are less than 50% of predicted, general anesthesia should be considered too risky. If either is less than 50% of predicted, general anesthesia is risky and local anesthesia or other means of obtaining diagnosis should be considered if at all possible. If the values are both greater than 50%, general anesthesia is considered a safe option.

Biopsy Techniques

The least invasive technique to achieve a diagnostic biopsy or resection should always be entertained. In general, a suspected lymphoma should be biopsied while likely germ cell tumors, neural tumors, thymic masses, and congenital anomalies should be treated by resection. There are various ways to gain access to the mediastinum, almost all of which require general anesthesia.

Mediastinoscopy is uncommonly used in children but has been shown to be useful and safe as technique to sample pre- and paratracheal lymph nodes in the retrovascular plane. The mediastinoscope is inserted through a transverse incision in the suprasternal notch and tunneled just anterior to the trachea. Thoracoscopy allows excellent access to all three compartments of the mediastinum with superb visualization of difficult areas. Fig. 41.2 shows the CT scan of a 9-year-old boy with persistent constitutional symptoms and a small mass just superior to the right pulmonary hilum. It was biopsied successfully thoracoscopically and found to be HD.

Fig. 41.2
figure 2_41

Nine-year-old boy with persistent constitutional symptoms. A small mass can be seen on the right side of the mediastinum adjacent to the superior vena cava and superior right hilar structures. This was biopsied thoracoscopically. Pathology revealed nodular sclerosing Hodgkin disease

Full size image

The Chamberlain procedure is a small anterior mediastinotomy used to biopsy lesions in the anterior mediastinum. A transverse incision is made over the second intercostal space, the underlying pectoralis major muscle is split, and the second costal cartilage is resected, providing access to the anterior mediastinum. This can be done under local anesthesia if necessary. For patients with airway issues, the head of the bed should be elevated.

For larger tumors, such as germ cell tumors and neuroblastoma, thoracotomy or sternotomy is indicated. Advances in single lung ventilation in smaller patients have helped achieve success in thoracic procedures. Double-lumen endotracheal tubes for older children, selective bronchial intubation, and bronchial blockers are techniques commonly used by pediatric anesthesiologists. Also, during thoracoscopy, the application of pneumothorax with carbon dioxide can help keep the lung deflated. A detailed discussion with the anesthesia team pre-operatively about each particular patient is very important.

Treatment

Anterior compartment lesions make up almost half of mediastinal masses and are malignant 80% of the time. These most commonly include lymphomas, germ cell tumors, and thymic masses. Both non-Hodgkin’s lymphoma (NHL) and Hodgkin’s disease (HD) will be quite frequently seen in this location by the pediatric surgeon. More than half of all children with lymphoblastic lymphoma present with an anterior mediastinal mass, while over a third of all NHLs have their primary sites in the mediastinum. NHL tends to occur in a younger age group (mean age 9 years) and can often be dramatic with a rapid onset of symptoms and a large mass (Fig. 41.3). Doubling rates can be as short as 12 h. There is often a pleural effusion. Symptoms due to local compressive effects are more than twice as common as in HD patients (Fig. 41.4). The two most common types of NHL affecting the pediatric mediastinum are lymphoblastic and large cell lymphoma. Sampling a pleural effusion is a quick and minimally morbid procedure that can often achieve diagnosis. HD is slower growing and occurs more frequently in adolescents.

Fig. 41.3
figure 3_41

Nine-year-old girl with dramatic symptoms that came on rapidly. She was unable to lie flat and had her CT done in the prone position. It revealed complete obstruction of the superior vena cava, compression of the heart, large airways, and right pulmonary artery, as well as a large right pleural effusion. The diagnosis of T-cell lymphoblastic lymphoma was made by sampling the pleural effusion

Full size image
Fig. 41.4
figure 4_41

CT scan of a typical HD patient with a moderate-sized mediastinal mass and no compressive symptoms. On physical examination, she had enlarged cervical lymph nodes and the diagnosis of nodular sclerosing HD was obtained quite easily by cervical lymph node biopsy

Full size image

For the lymphomas, the issue of permanent central venous access will need to be discussed with the oncology team. When a mass is large and there is airway or vascular compression, peripherally inserted central venous catheters are an excellent way to be able to administer therapy with less risk. After the lesion has decreased in size, a mediport or other permanent access can be placed in a much safer fashion.

The anterior mediastinum is a common location for germ cell tumors. Teratomas and endodermal sinus (yolk sac) tumors predominate. These lesions can be very impressive in size and have a characteristic appearance on CT scan. They are heterogeneous, containing fat, calcifications, cysts, and soft tissue (Fig. 41.5). Pre-operative work-up must include the tumor markers AFP and β-HCG. Surgical removal is indicated. Although surgeons have approached small germ cell tumors thoracoscopically with success, most will require a thoracotomy or, for a very large tumor, a median sternotomy. Avoidance of tumor rupture is important. In general, teratomas can be treated with surgical resection alone while malignant germ cell tumors require platinum-based adjuvant chemotherapy.

Fig. 41.5
figure 5_41

CT scan shows a large heterogeneous anterior mediastinal mass (12 cm) in a 9-year-old boy containing both fat and calcifications. This was completely resected by median sternotomy and found to be a malignant germ cell tumor containing endodermal sinus tumor as well as immature teratoma

Full size image

Thymic masses in the pediatric population are quite uncommon and diagnostic confusion may occur, though most are benign. Cysts should be resected because of the risk of bleeding and infection. Although rare, thymomas do occur in the pediatric population and about half are malignant. These are treated primarily by resection. Both thoracoscopy and median sternotomy have been used safely and effectively to remove tumors of the thymus.

Posterior mediastinal masses are most commonly of neural origin with ganglioneuroma and neuroblastoma predominating. They arise from the sympathetic chain in the paravertebral sulcus. Ten to twenty-five percent of neuroblastomas are found in this location. They are often found incidentally but can produce respiratory symptoms. Neurologic symptoms can occur because of extension through the neural foraminae into the spinal canal. Neuro­blastomas are usually found in children under the age of 2 years. For these tumors, near-complete surgical resection is the primary goal and is often possible. Those patients with extension into the spinal canal may require neurosurgical decompression or chemotherapy prior to an attempt at resection. Pre-operative chemotherapy is also indicated if a primary resection is thought to be too morbid. The prognosis for these children is significantly more favorable than for abdominal neuroblastomas, with overall survival around 75%. Ganglioneuromas predominate in older children and are most often found incidentally on a chest X-ray (Fig. 41.6). Because there is no absolutely reliable way to distinguish ganglioneuromas from neuroblastomas, resection is usually indicated.

Fig. 41.6
figure 6_41

Chest MRI of a large posterior mediastinal/paravertebral mass found incidentally by CXR. It was resected by thoracotomy and found to be ganglioneuroma

Full size image

Benign foregut cysts are congenital anomalies most commonly found in the middle compartment of the mediastinum. They are thought to arise from abnormal budding of the forming esophagus or tracheobronchial tree. They are most often divided into two groups: bronchogenic cysts and enteric duplications.

Patients with bronchogenic cysts are frequently asymptomatic and the abnormalities are often found incidentally. If a cyst is very close to the airway and causing compression, respiratory symptoms may be present. They can produce respiratory distress in newborns and recurrent pulmonary infections in older children. Imaging reveals a non-enhancing, homogeneous, smooth-walled, cystic lesion. Bronchogenic cysts are most often found near the carina but can also be found in the pulmonary hilum or parenchyma. Only rarely do they communicate with the tracheobronchial tree. The cysts are lined by a respiratory epithelium and contain thick mucous. The treatment is complete excision. Frequently, they can be removed safely thoracoscopically. If the cyst is adherent to the airway, one can leave a small part of the cyst wall in place but the mucosa should be stripped.

Enteric duplications include esophageal duplications and neuroenteric cysts. Esophageal duplications (Fig. 41.7) are found intimately associated with the esophageal wall, arising within a muscular layer. They may produce esophageal obstructive symptoms as they slowly grow and can impinge on the lumen. They typically have muscular walls lined with gastric or intestinal mucosa, although respiratory epithelium may be found. Most can be resected thoracoscopically with careful dissection to excise the cyst from the esophagus without entering the lumen. Neuroenteric cysts are rare anomalies that communicate posteriorly with the meninges. Their removal is more complex and requires the assistance of a neurosurgery team.

Fig. 41.7
figure 7_41

Chest MRI was performed as part of a neurologic work-up. Esophageal duplication was found incidentally

Full size image

Postoperative Care

The most feared complication of surgery for mediastinal masses is respiratory collapse, as discussed above. The obvious potential risks with resection or biopsy of mediastinal masses involve inadvertent injury of neighboring structures. A detailed pre-operative discussion with the family is important and parents should be informed of the likelihood of a chest tube and how long it may need to be in place. These lesions can be intimately associated with the great vessels and bleeding can be very difficult to control. This is particularly true for mediastinoscopy. Injury to the lung or bronchus can result in air leak. Injury is often not readily apparent at the time of surgery and presents post-operatively as a chylothorax. With chest tube drainage and enteral nutritional support, most of these will seal. The phrenic and recurrent laryngeal nerves are also susceptible to injury with resulting diaphragmatic and laryngeal dysfunction.