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Resection of Mediastinal Teratoma

  • Alberto de Hoyos
    Affiliations
    From the Division of Cardiothoracic Surgery, Northwestern University Medical School, Chicago, IL
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  • R. Sudhir Sundaresan
    Correspondence
    Address reprint requests to R. Sudhir Sundaresan, MD, Division of Cardiothoracic Surgery, Northwestern University Medical School, 201 East Huron Street, Suite 10-105, Chicago, IL 60611
    Affiliations
    From the Division of Cardiothoracic Surgery, Northwestern University Medical School, Chicago, IL
    Search for articles by this author
      Benign mediastinal germ cell tumors, or teratomas, are the most common type of mediastinal germ cell neoplasms.
      • Nichols CR
      Mediastinal germ cell tumors.
      Primary mediastinal teratomas account for approximately 8% to 20% of anterior mediastinal neoplasms and up to 80% of mediastinal germ cell tumors. Although mediastinal germ cell tumors account for only 3% to 5% of all germ cell tumors, they are the most common extragonadal site for a primary germ cell tumor.
      • Wood DE
      Mediastinal germ cell tumors.
      Mediastinal germ cell tumors are caused by malignant change in a primordial germ cell. Like their gonadal counterparts, mediastinal teratomas are composed of tissues representing one or more of the embryonic germ cell layers foreign to the organ or anatomic site in which they occur. The tumor may attempt organ formation and can contain teeth, skin, and hair (ectodermal derivatives); cartilage and bone (mesodermal derivatives); or bronchial, intestinal, and pancreatic tissue (endodermal derivatives).
      Mature teratomas represent approximately 60% to 70% of mediastinal germ cell tumors and are well differentiated and benign.
      • Strollo DC
      • Rosado de Christenson ML
      • Jett JR
      Primary mediastinal tumors. Part 1. Tumors of the anterior mediastinum.
      Those composed exclusively of mature ectoderm are often termed “dermoids.” The presence of any fetal or immature neuroectodermal or mesenchymal elements characterizes a teratoma as immature, which has a good prognosis but a greater likelihood of recurrence or metastasis. Rarely, a mature teratoma can contain a focus of carcinoma, sarcoma, or malignant germ cell tumor; one that does is termed a “malignant teratoma” or “teratocarcinoma.”
      Most mature mediastinal teratomas occur in children and young adults, with the average age at presentation approximately 20 years.
      • Lewis BD
      • Hurt RD
      • Payne WS
      Benign teratoma of the mediastinum.
      Unlike malignant germ cell tumors, which occur nearly exclusively in men, teratomas occur with equal frequency in men and women. Although the asymptomatic lesion is more likely benign, the lack of symptoms does not ensure a benign process. Similarly, a symptomatic lesion is more likely malignant, but benign lesions also may be symptomatic. In infants and children, the relatively smaller mediastinal dimensions and the predominance of malignant lesions make most mediastinal masses symptomatic. Mature teratomas can be asymptomatic in up to 50% of patients, particularly in children and young adults.
      • Nichols CR
      Mediastinal germ cell tumors: Clinical features and biologic correlates.
      Older individuals more typically present with signs and symptoms related to intrathoracic compression from the local growth of the mass, with chest pain, cough, and dyspnea as the most common complaints. Constitutional symptoms such as fever, weight loss, and endocrine dysfunction have also been described. Digestive enzymes secreted by intestinal mucosa or pancreatic tissue in the tumor can precipitate rupture into the bronchi, pleura, pericardium, or lung. Expectoration of hair (trychoptysis) or sebum is a rare but pathognomonic event, indicating that the tumor has ruptured into a bronchus.

      Radiographic and Laboratory Features

      Most teratomas arise in the anterior-superior mediastinum. Radiologically, teratomas are rounded to lobulated, well-defined anterior mediastinal masses located in front of the roots of the aorta and main pulmonary artery. The bulk of the mass may protrude to one side of the midline and can reach a large size. On computed tomography (CT) scan, teratomas usually appear as multilocular cystic tumors with walls of variable thickness (Fig I). A combination of fluid, soft tissue, calcium, or fat attenuation in an anterior mediastinal mass is a highly specific finding that allows for a reliable diagnosis of mature teratoma.
      • Brown LR
      • Muhm JR
      • Aughenbaugh GL
      Computed tomography of mature benign teratomas of the mediastinum.
      Fat-fluid levels produced by the high lipid content in the cystic spaces are also specific for teratoma. The presence of calcification in 20% to 40% of these tumors suggests the diagnosis of benign teratoma. Organized bone or teeth may occasionally be identified. Rarely, the tumor ruptures into the pericardium or the pleura, in which case a fat-fluid level may also be present. Magnetic resonance imaging (MRI) has not been shown to provide any significant advantage over CT scans.
      Figure thumbnail gr1
      ICT scan depicting a large lobulated mass with areas of different attenuation. Note the fat plane between the mass and the aorta and the chest wall. This tumor proved to be a mature teratoma.
      Benign teratomas by definition lack alpha-feto-protein (AFP) and beta-human choriogonadotrophins (b-HCG). Elevated serum AFP or b-HCG level indicates a malignant component to the teratoma, such as embryonal carcinoma, endodermal sinus tumor, or choriocarcinoma.

      Therapy and Clinical Outcome

      Although mature teratoma is a benign tumor, excessive enlargement may lead to compression and displacement of neighboring thoracic organs. Complete excision, usually performed through a median sternotomy, results in cure.
      • Ginsberg RJ
      Mediastinal germ cell tumors: The role of surgery.
      However, resection may be difficult because of the tumor's large size and adherence to adjacent and vital intrathoracic structures. Occasionally a mature teratoma induces life-threatening complications by virtue of a mass effect on these vital structures. Radiation and chemotherapy have no role in the treatment of benign teratomas.
      In immature teratomas, patient age, not histology, appears to be the most significant prognostic factor. This contrasts with ovarian and, to a lesser degree, saccrococcygeal teratomas, in which immature histology denotes malignancy. In the mediastinum, immature teratomas arising in patients younger than age 15 years behave as mass lesions or mature teratomas. Total resection allows long-term survival. In individuals over age 15 years, immature teratomas act as highly malignant neoplasms that can metastasize widely. When an immature teratoma is combined with a malignant germ cell tumor, growth is usually very aggressive, and surgery plays a secondary role in treatment.

      Anesthetic Management

      Although most patients undergo surgical procedures safely, a subset of patients—particularly children with large anterosuperior or middle mediastinal masses—have an increased risk of severe cardiorespiratory complications during general anesthesia. Exacerbation of superior vena caval obstruction or extrinsic airway compression can occur during general anesthesia because of the loss of negative intrathoracic pressure during respiration, bronchial smooth muscle relaxation that increases bronchial compressibility, and reduced tidal volumes in ventilation. A reduction in tracheal cross-sectional area of more than 35% by CT scan indicates an increased risk with general anesthesia; similarly, reduced pulmonary flow mechanics are a sensitive indicator of functional airway compression and susceptibility to intraoperative airway compromise.
      In patients with large mediastinal masses who have an increased anesthetic risk, recommendations for anesthetic management include (1) fiberoptic evaluation of the tracheobronchial tree for evidence of severe extrinsic compression; (2) induction of anesthesia in a semierect position, with the option of changing to the lateral or prone position; (3) use of long endotracheal tubes to advance beyond the site of obstruction; (4) standby rigid bronchoscopy to reestablish an adequate airway; (5) avoidance of muscle relaxants and use of spontaneous ventilation whenever possible; (6) lower extremity intravenous cannulation to provide access to the systemic venous circulation if a sudden superior vena caval obstruction should occur; and (7) standby cardiopulmonary bypass with bilateral groin preparation.

      Surgical Technique

      Figure thumbnail fx2
      1Median sternotomy. The patient is positioned supine on the operating table for median sternotomy, the preferred approach. The arms may be abducted and placed on arm boards, but are best secured at the patient's side.
      A skin incision is made from the jugular notch to just below the xiphoid process. The incision is carried down through the subcutaneous tissues to the superficial pectoral fascia overlying the sternal origins of the pectoralis major muscles and the linea alba. In the caudal portion of the wound, the linea alba is divided, exposing the preperitoneal fat. Cephalad, the sternal origins of the two sternomastoid muscles, can be seen. The suprasternal space is a slit-like space between the two layers of the deep cervical fascia in the midline. Lying within the suprasternal space is the jugular arch, a vein of varying size that joins the two anterior jugular veins across the midline. To avoid troublesome bleeding, care should be taken to control the jugular arch at this stage of the median sternotomy incision.
      By using electrocautery, the pectoral fascia and anterior periostium of the sternum are divided in the midline. A nearly constant vein crossing the upper part of the xiphoid cartilage should be controlled to prevent bleeding. The sternum is divided in the midline with a reciprocating electric saw, such as the Sarns sternal saw. This saw has a footpad, which is placed behind the manubrium at the suprasternal notch. With upward traction exerted to hold the footpad snugly against the posterior aspect of the sternum, the sternum is sectioned along the line made with electrocautery in the anterior periosteum. Positive pressure ventilation is discontinued during division of the sternum to reduce the risk of entering the pleural cavities. The sternal division is performed equally well from the sternal notch to the xiphoid and in the opposite direction, depending on the surgeon's preference. Bleeding from the sternal periosteum is best controlled with electrocautery. In the past, bone wax was routinely used to control marrow bleeding, but its use has been abandoned because of the possibility of impaired wound healing and pulmonary complications related to the embolization of wax to the lungs. If the tumor is quite large or there is extension into the hilum of the lung, then a clamshell incision may be considered. For tumors that extend preferentially to one hemithorax, a posterolateral or axillary thoracotomy may be the preferred approach.
      Figure thumbnail fx3
      2A sternal retractor with broad blades is positioned carefully and opened slowly. The crossarm of the retractor may be positioned in either the upper or lower end of the incision, depending on the surgeon's preference. By opening the retractor only a few turns at a time, the surgeon is usually able to avoid sternal fractures. The sternum should be opened only as wide as is necessary to obtain adequate exposure.
      Figure thumbnail fx4
      3Mediastinal dissection. After a sternal spreader is placed, the thymic fat pad is identified and dissected up to the level of the brachiocephalic vein. An avascular plane is readily identified but is crossed by a few thymic veins, which are electrocoagulated or divided between fine silk ties or small hemoclips.
      Figure thumbnail fx5
      4With the sternal retractor in place, the mediastinal mass is assessed. The boundaries and extent of the mass are noted, with specific attention paid to any evidence of invasion into mediastinal structures, including the pericardium, aorta, pulmonary artery, superior vena cava, brachiocephalic vein, pleura, and phrenic nerves. In benign teratomas, dissection is relatively easy once the appropriate cleavage plane is identified, and an extracapsular dissection is usually achieved. Some teratomas may have erosion or inflammatory adhesions to nearby pericardium, lung, great vessels, chest wall, or diaphragm. The plane of dissection can be easily established circumferentially around the tumor using a right-angled “walking” technique.
      Figure thumbnail fx6
      5Any area of resistance should be assessed for possible resection of adjacent structures. Adherence or erosion into the lung may necessitate adjacent wedge resection. In lesions located in the anterosuperior mediastinum, early isolation of the brachiocephalic vein is recommended to avoid injury to this vessel.
      Figure thumbnail fx7
      6Dissection in this area is performed with electocautery, with care taken to control lymphatic vessels with fine silk ligatures or hemoclips. The blood supply to the tumor is identified and controlled with 2-0 silk ligatures or medium-size hemoclips. When the tumor extends laterally, we prefer to open the pleura to expose and protect the phrenic nerve.
      Figure thumbnail fx8
      7With the tumor under gentle traction, a U-shaped incision is made in the mediastinal pleura 1 cm superior to the phrenic nerve. Using the right-angled clamp and a combination of sharp and blunt dissection technique, the surgeon pulls the mediastinal fat up from the area above the phrenic nerve toward the tumor. The lateral vessels coming from the internal mammary vessels are then carefully divided and ligated with 3-0 silk. The tumor is then mobilized cephalad toward the junction of the innominate vein and the superior vena cava until the midline is exposed, to identify and control any vascular tributaries. The same steps are then carried out on the opposite side. Again, a blunt dissection technique in the critical area where the phrenic nerve runs close to the tumor helps prevent injury to the nerve. The cautery is not used, to avoid inadvertent nerve injury. Rarely, a phrenic nerve involved by an invasive malignant teratoma may need to be sacrificed to achieve a complete resection.
      Figure thumbnail fx9
      8In patients with densely adherent teratomas or invasive teratomas, pericardial resection or partial resection and reconstruction of vascular structures may be necessary. Sharp dissection of the tumor plane away from the vital organ is performed with no need for extensive radial margins. For large pericardial defects, we prefer to reconstruct the pericardium with a prosthetic patch, such as bovine pericardium, to avoid dense adhesions to the heart in the event of the need for repeat sternotomy in the future, such as for coronary revascularization.
      Figure thumbnail fx10
      9Once the operative procedure has been completed and hemostasis meticulously obtained, one or more 28–32 F chest tubes are placed and led out through stab wounds at the lower end of the incision. The sternum is approximated with five to eight heavy stainless steel wires passed through the sternum or, if the surgeon prefers or when the sternum is too friable, around the sternum. Care must be taken to avoid injury to the internal mammary vessels. Traction is placed on these wires as they are carefully tightened, to achieve uniform approximation of the sternum. The twisted wires must be carefully turned down into the sternum so that they do not protrude externally and are not palpable. The linea alba is approximated with nonabsorbable sutures, as is the fascia. Subcutaneous tissues may be closed with continuous absorbable sutures. For skin closure, subcuticular closure with a continuous absorbable suture provides excellent cosmetic results.

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