胸畸胎瘤常见问题【英文讲义】

Frequently Asked Questions on the Thoracic Teratoma

                               
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What is thoracic teratoma?
A teratoma is a covered tumor with tissues or organs parts looking like normal descendents of all three germ layers. The tissues of a teratoma, although normal in themselves, may be quite different from surrounding tissues and may be highly discordant.
The mediastinum is an undelineated group of structures in the thorax, surrounded by loose connective tissue. It is the central compartment of thethoracic cavityIt contains the heart, the great vessels of the heart, the esophagus, the trachea, the phrenic nerve, the cardiac nerve, the thoracic duct, the thymus, and the lymph nodes of the central chest.
The mediastinum is frequently the site of involvement of various tumors. Mediastinitis is inflammation of the tissues in the mediastinum, usually bacterial and due to rupture of organs in the mediastinum. As the infection can progress very quickly, this is a serious condition.
The mediastinum is an area of the body in which a vast range of tissue flippancy presents. Tumors that occur in this area therefore can depict several clinical entities and pathologic processes. An understanding of the embryology of this area, as well as the anatomic relationships of the normal structures within the mediastinum, is essential in the proper determination of the exact nature of a mass or tumor located in this area.
What is the Epidemiology of Thoracic Teratoma?
It reveals that many mediastinal neoplasms and masses vary in incidence and presentation depending on patient age. Also, several thoracic tumors particularly occur in specific parts within the mediastinum.
•        When regarding mediastinal tumors or cysts in adults, germ cell tumors rank fourth in frequency, following neurogenic tumors, thymic tumors, and lymphomas. About 10% of mediastinal tumors in adults are germ cell tumors, and about 85% of these are benign.
•        In adults, germ cell tumors occur most commonly between the second and fourth decades of life and are found in equal numbers in both sexes.
•        In children and infants, neurogenic tumors also are the most commonly occurring tumors or cysts, followed by foregut cysts. Germ cell tumors rank third, followed by lymphomas, lymphangiomas and angiomas, tumors of the thymus, and pericardial cysts. Germ cell tumors make up about 25% of the mediastinal tumors found in children.
•        Seminoma represents more than 25% of primary mediastinal germ cell tumors and about 3% of all mediastinal tumors.
•        While mediastinal seminoma almost exclusively is found in males, several histologically verified cases have been described in females.
What is its Pathophysiology?
Local pathophysiology:
Because of the malleable nature and small size of the pediatric airway and other normal mediastinal structures, benign tumors and cysts can produce local symptoms. These effects are more evident in children than in adults.
Compression or obstruction of portions of the airway, the esophagus, or the right heart and great veins by an enlarging tumor or cyst easily can occur and can result in a number of symptoms. Infection can occur primarily within some of these mediastinal lesions, particularly those of a cystic nature, or can result secondarily in nearby structures (eg, lungs) as a result of local compression or obstruction.
Malignant mediastinal tumors can cause all of the same local effects as those associated with benign lesions, but they also can produce abnormalities by invasion of local structures. Local structures most commonly subject to invasion by malignant tumors include the tracheobronchial tree and lungs, esophagus, superior vena cava, pleura, and chest wall, as well as any adjacent intrathoracic nerves. Pathophysiologic changes that can be produced by invasion of specific structures are obstructive pneumonia and hemoptysis, dysphagia, superior vena cava syndrome, and pleural effusion, as well as various neurologic abnormalities such as vocal cord paralysis, Horner syndrome, paraplegia, diaphragmatic paralysis, and pain in the distribution of specific sensory nerves.
Systemic pathophysiology:
Certain mediastinal tumors can produce systemic abnormalities. Many of these manifestations are related to bioactive substances produced by specific neoplasms. Approximately 95% of patients with germ cell tumors of the mediastinum have an elevated tumor marker. Alpha-fetoprotein (AFP) is elevated more often than beta human chorionic gonadotropin (bhCG).
What is its Relevant Anatomy?
The portion of the thorax defined as the mediastinum extends from the posterior aspect of the sternum to the anterior surface of the vertebral bodies and includes the paravertebral sulci when defining the location of specific mediastinal masses. It is limited bilaterally by the mediastinal parietal pleura and extends from the diaphragm inferiorly to the level of the thoracic inlet superiorly.
Traditionally, the mediastinum is artificially subdivided into 3 compartments for better descriptive localization of specific lesions. Most commonly, the compartments or spaces are defined as the anterior, middle, and posterior when the location or origin of specific masses or neoplasms is discussed.
The anterior compartment extends from the posterior surface of the sternum to the anterior surface of the pericardium and great vessels. It normally contains the thymus gland, adipose tissue, and lymph nodes. The vast majority of teratomas and other germ cell tumors arise in this area of the mediastinum.
What are the Contraindications?
Although open biopsy may be required to make a diagnosis, surgical resection is not indicated as primary treatment for mediastinal tumors of germ cell origin, including seminoma or nonseminomatous germ cell malignancies of the mediastinum.
What is its medical therapy?
While most tumors and cysts of the mediastinum are treated surgically, medical therapy is the primary form of treatment in several diseases.
Germ cell Seminomas:
Radiation therapy is the primary treatment for seminoma. A dose range of 3000-4500 cGy is recommended. Chemotherapy often is used in patients older than 35 years or those with features of advanced disease. Cisplatin-based chemotherapy regimens are found very effective in seminoma. Some evidence suggests that chemotherapy should become the primary form of treatment for seminoma and that radiotherapy should be used for the treatment of locoregional areas of involvement. Surgery has almost no indication in seminoma except for purposes of diagnosis. Patients should receive radiotherapy even if complete resection appears to have been achieved.
What is its Surgical Therapy?
Surgical resection is the treatment of choice for most neoplasms that occur in the mediastinum, except for malignant germ cell neoplasms.
The most common mediastinal tumors for which nonsurgical forms of therapy are considered the primary treatment are seminomas, malignant nonseminomatous germ cell tumors, lymphoma, and advanced-stage neuroblastoma in children.
In cases of benign neoplasms, complete excision of the lesion itself generally is sufficient. Benign teratomas are tumors for which surgical excision is adequate therapy. All benign neoplasms that are encapsulated should be resected without violation of the capsule. VATS techniques have been introduced in teratoma resection with promising results.
Surgical resection is advised in nonseminomatous malignant germ cell tumors of the mediastinum when radiographic studies show residual mediastinal disease present after appropriate chemotherapeutic treatment has been administered. Residual masses are observed in 10-20% of cases after treatment. Resection of residual masses in these cases is performed to determine the presence or absence of residual malignancy. If the former is the case, additional chemotherapeutic treatment may or may not be considered.
In cases of seminoma, some controversy exists regarding resection of residual posttreatment masses. Some authors state that no surgical intervention is needed and that radiographic follow-up is the appropriate course of action. Others state that residual masses greater than a specified size should be resected.
What is Preoperative management of thoracic Teratoma?
Standard preoperative management applicable to all chest surgical cases applies to the preoperative management of individuals undergoing resection of mediastinal tumors. Airway management is of paramount importance when dealing with tumors that can produce a mass effect on these structures. Consider detailed preoperative assessment of the airway, as well as adequate visualization and readily available supplementary equipment (eg, flexible bronchoscope), for safe management of the airway distorted or narrowed by a mediastinal mass. Placement of a double-lumen endotracheal tube to provide single-lung ventilation usually is preferred for any procedure in which a thoracotomy approach is used.
Some mediastinal tumors may require extensive resection of adjacent tissues, and blood loss may be substantial in these cases. Provide for adequate intravenous access, appropriate monitoring capability and necessary blood products (all of paramount importance) before the operation is begun.
Involvement of associated intrathoracic structures by tumor may mandate their resection. Pulmonary resection, excision of nervous structures (eg, phrenic, vagus, sympathetic chain), or even resection of major vascular structures (eg, superior vena cava) may be required. The surgeon must be prepared for this, and the patient must be informed preoperatively that such resection may be required because this may have additional impact on recovery and perioperative risk.
Although uncommon in cases of germ cell tumors for which surgical resection is the indicated treatment, several mediastinal tumors can produce important effects that should be taken into account preoperatively.
What is Intraoperative management of thoracic Teratoma?
As with all thoracic surgery, positioning the patient properly for the indicated procedure is of paramount importance. Tumors or cysts located in the anterior mediastinum generally are approached through a median sternotomy. This approach would be used for tumors of the thymus. Those located in the posterior or middle mediastinum and paravertebral sulci, such as most neurogenic tumors and foregut cysts, are approached through a posterolateral thoracotomy incision.
Standard single-lumen endotracheal intubation is appropriate for resections performed via the median sternotomy approach. Use of a double-lumen endotracheal tube for single-lung ventilation is preferable for those procedures performed through a thoracotomy incision and for all procedures performed using VATS. VATS techniques have been introduced in teratoma resection with promising results in several centers. Additional exposure includes a hemiclamshell thoracotomy with or without neck extension, which may be preferred for tumors in the anterior mediastinum with extensive involvement of the hemithorax. A neck extension or supraclavicular extension can be incorporated with involvement that extends into the neck or subclavian vessels, respectively. A clamshell incision can also be used for tumors that extend into both hemithoraces. A tumor may extend to adjacent structures, and resection of the thymus, pericardium, lung, phrenic nerve, innominate vein, and superior vena cava can be appropriate.
What is Postoperative management of thoracic Teratoma?
Care of patients after resection or biopsy of a mediastinal tumor is similar to that for any noncardiac surgery of the chest. Extubation can be performed at the completion of the case or shortly thereafter in the postanesthesia recovery area. Some patients require ventilatory support for a longer time, and their cases should be managed accordingly. Pulmonary toilet is an essential part of postoperative management after any kind of chest surgery to prevent atelectasis and to mobilize and clear any bronchial secretions. Various methods to assist with pulmonary toilet are available.
Pain control also is a critical factor in postoperative management after thoracic surgery. Adequate cough effort and ventilatory excursion cannot be maintained without satisfactory pain control. Administration of analgesic agents by thoracic epidural catheter is an excellent and highly effective method of pain management. Lumbar epidural catheters also can be used and, with proper choice of analgesic agents, can provide good pain relief. Patient-controlled analgesia (PCA) is another widely used method and is preferred to traditional intramuscular or intravenous administration of narcotics and other agents. It is not as efficient for pain control as epidural analgesia.
What are the complications in thoracic teratoma?
Complications that occur after resection of mediastinal tumors are similar to those that can occur after any thoracic surgical procedure. As with any thoracic surgical procedure, postoperative pulmonary complications are most common. Atelectasis is a common postoperative complication and can develop into pneumonia if not treated aggressively. As noted previously, aggressive pulmonary toilet and pain management are the key factors in the prevention of these complications. Wound infections after sternotomy or thoracotomy are rare. The chest wall possesses excellent blood supply and, with few exceptions, healing occurs readily. Also, existing intrathoracic infection generally is not a factor during resection of any of the noted mediastinal tumors, and these operations are considered clean procedures. The exception to this might be in cases of resection of some foregut cysts that may have secondary infection present.
Conclusion:
In conclusion, thoracic teratomas are uncommon in the pediatric age group. The tumor is generally located at the conus site in adult patients, while it is frequently larger sized in children and located at thoracic and cervical sites. Should the tumor not be removed radically, the survival without recurrence may be extended. And Tumors or cysts located in the anterior mediastinum generally are approached through a median sternotomy while Pain control also is a critical factor in postoperative management after thoracic surgery.