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Management of anterior and middle mediastinal masses in children often depends on obtaining tissue for diagnosis. Conversely, most posterior mediastinal masses require resection. Historically, several modalities have been available, including percutaneous fine-needle aspiration, mediastinoscopy, mediastinotomy, thoracotomy, and sternotomy. In recent years, the indications for thoracoscopy have expanded in adult and pediatric patients. Initial reports focused on biopsying pulmonary masses and debriding empyemas. With improved video technology and finer instrumentation, thoracoscopy can now be used for many thoracic conditions, including suspicious mediastinal masses.
Indications for Workup and Operation
Mediastinal masses are often identified incidentally. However, 40% of primary masses are malignant. They may be detected on routine chest radiographs, computed tomography scans, or magnetic resonance imaging ( Fig. 36-1 ). Three-dimensional reformats may better assess the origin and extent of disease, and thus enhance operative planning. The anatomic location of the mediastinal mass is often suggestive of the specific pathology. Posterior mediastinal calcifications may be seen in neuroblastoma, whereas calcium deposits in the anterior mediastinum are often seen with germ cell tumors.
Preoperatively, consideration should be given to the child’s ability to tolerate single-lung ventilation. There is no single test to predict this, but clinical experience has shown that collapse of the ipsilateral lung is tolerated in most children. At the same time, a large anterior mediastinal mass must raise concern about overwhelming tracheal compression when general endotracheal anesthesia is administered, especially in the supine position. Therefore, preoperative anesthesia evaluation is very important.
Anesthetic Concerns and Patient Positioning
General anesthesia is induced in the supine position. The anesthetic technique varies according to patient size, pulmonary status, and required exposure. Single-lung ventilation is preferred. This can be accomplished with a double-lumen endotracheal tube in older children. The smallest double-lumen endotracheal tube (ETT) that is available currently is 27 Fr, which corresponds to a 6.0-internal-diameter single-lumen tube. In most instances, the patient needs to be older than 7 or 8 years to accept a double-lumen ETT. Selective intubation of the contralateral mainstem bronchus with a cuffed endotracheal tube is often successful. Moreover, insufflation with 6 to 10 mm Hg of CO 2 can help deflate the lung. A Fogarty or Swan-Ganz catheter can be used as a bronchial blocker, and bronchoscopy can facilitate optimal placement (see Chapter 30 for additional information).
The importance of proper positioning cannot be overemphasized. The child is situated so as to allow the lung to fall away dependently after collapse, thus allowing maximal mediastinal visualization. Thus, apical lesions may be more easily visualized in a reverse Trendelenburg position. The opposite would be true for diaphragmatic lesions. The operating table may be gently flexed at the iliac crests to enlarge the intercostal spaces ( Fig. 36-2 ). Anterior mediastinal masses are best approached with the patient in a modified supine position and posterior mediastinal masses are best seen with the patient in a modified prone position (see Fig. 30-4 ). A bean bag may be required to support larger patients. Cushioning should be placed along joints and pressure points. The patient is prepped and draped as for a standard lateral thoracotomy. The surgeon and assistant stand at the patient’s back with the monitor opposite them ( Fig. 36-3A ).
Preoperative antibiotics covering skin flora are recommended. Using an open technique, a 5-mm valved cannula is introduced in the fourth or fifth intercostal space in the midaxillary line. Insufflation can be added with initial pressure of 4 to 6 mm Hg without deleterious effects. Additional 5-mm valved ports or stab incisions are placed between the anterior and posterior axillary lines. Optimal port placement is achieved when cannulas surround the pathology in a triangular configuration ( Fig. 36-3B ).
Straight and angulated telescopes of 0, 30, and 70 degrees should be readily available. If pleural adhesions are encountered, blunt dissection with the suction-irrigation device or blunt forceps can assist in the pleural dissection. The majority of the dissection can be accomplished bluntly with the occasional use of electrocautery or the ultrasonic shears. For the typical middle mediastinal mass, there is often uncertainty as to the location of the great vessels, and preoperative imaging is essential to understanding the relationship of the mass to the surrounding vessels. Usually, the mass is located lateral to the great vessels (or at least a portion of it is located lateral to these vessels) and can be biopsied without concern for massive bleeding. If there remains uncertainty, the planned biopsy site can be aspirated using a small needle to ensure it is not a vascular structure.
For biopsy of a mediastinal mass, it is often helpful to place a suture through the site from which the biopsy is to be taken. This maneuver allows manipulation of the biopsy site without tissue trauma to the resulting specimen. Therefore, we often place a 2-0 silk suture in a figure-eight fashion through the biopsy site ( Fig. 36-4A ). Next, the area to be biopsied is outlined with either a hook cautery or a Maryland dissecting instrument connected to cautery ( Fig. 36-4B ). Once this area is outlined, scissors connected to cautery can be used to take the actual biopsy ( Fig. 36-5A ). The suture that was placed through the mass can be very helpful to manipulate the mass for appropriate exposure. Once the biopsy specimen has been removed, hemostasis can usually be controlled with the cautery. An endoscopic bag is quite helpful when exteriorizing the specimen to prevent tumor spillage and contamination of the pleural cavity ( Fig. 36-5B ). It is important to remember that numerous histologic studies may be needed to determine the patient’s diagnosis, so it is important to have an adequate volume of tissue for these studies.