Mediastinoscopy is a surgical technique that permits minimally invasive access to the mediastinum.¹ In most cases, mediastinoscopy is used to biopsy and facilitate the histologic diagnosis of enlarged mediastinal lymph nodes (e.g., carcinoma, sarcoidosis, and tuberculosis) and masses (e.g., lymphoma, germ cell tumor, and thymoma). Mediastinoscopy currently plays a particularly important role in defining the clinical stage of bronchogenic carcinoma. Staging is the first step toward determining the optimal course of management. Staging directs treatment and implementation of protocols and permits comparison of treatment between patients.

Cervical mediastinoscopy, first described by Harken and colleagues,² involves a neck incision that facilitates access to the superior mediastinum. Carlens³ and Pearson⁴ popularized a technique using a specially designed mediastinoscope through a suprasternal incision. Cervical mediastinoscopy, however, has limited access to the aorticopulmonary window. One approach to the aorticopulmonary window is "extended" cervical mediastinoscopy, a rarely used approach in which the mediastinoscope is inserted anterior to the aortic arch between the innominate artery and the left carotid artery.⁵ A more common approach to the aorticopulmonary window is through an anterior mediastinotomy—so-called anterior mediastinoscopy.⁶ Extended and anterior mediastinoscopy are techniques used to sample mediastinal lymph nodes in the aorticopulmonary window. In addition, anterior mediastinoscopy can be used in a variety of parasternal locations to facilitate the biopsy of anterior mediastinal masses to the right or left of midline. Subxiphoid mediastinoscopy is a technique in which the mediastinoscope is used to biopsy anterior masses in the lower mediastinum.

SURGICAL PRINCIPLES

Frequent indications for mediastinoscopy include (1) staging patients with bronchogenic carcinoma⁷ and (2) obtaining tissue diagnoses in patients with unexplained adenopathy.⁸ Patients diagnosed with bronchogenic carcinoma are staged using a combination of modalities. CT scan of the chest determines the size and location of the primary tumor in conjunction with any associated lung parenchymal abnormalities (e.g., atelectasis, collapse, pneumonia, emphysema, or fibrosis). In addition, the location and size of enlarged mediastinal nodes direct further investigation to stage patients. Mediastinal nodes larger than 1 cm in their short axis are considered suspicious for tumor.

The differential diagnosis of patients with persistent and unexplained adenopathy includes sarcoidosis and lymphoma, but because these diseases may be difficult to distinguish clinically, histologic confirmation of the diagnosis usually is recommended. Sarcoidosis is characterized by noncaseating granulomas that can readily be distinguished from both Hodgkin and non-Hodgkin lymphomas.

Although cervical mediastinoscopy can be performed with low morbidity and mortality, the potential for catastrophic complications exists. Because of this risk, surgeons must be properly trained in mediastinoscopy. The procedure usually is performed as a day-surgery procedure, although it should be performed in a hospital setting because of the potential complications.

The procedure of mediastinoscopy involves a comprehensive examination of the mediastinum informed by CT scan findings. Sampling of the lymph nodes is directed by manual palpation and visual inspection (Fig. 132-1). Cervical mediastinoscopy can sample ipsilateral and contralateral nodes (stations 1, 2, 4, and 7) in patients with bronchogenic cancer. The presence of positive contralateral nodes, multistation N₂ disease, extracapsular spread, and extension into mediastinal structures (T₄) portend a generally poor outcome and usually preclude the patient from surgical therapy. Cervical mediastinoscopy in comparison with CT scans has 90% sensitivity and 100% specificity for determining pathologic mediastinal lymph nodes. In lymphomas or inflammatory diseases, lymph node mapping has limited value. The focus of the operation is on obtaining an accurate tissue diagnosis.

Anterior mediastinoscopy—performed through an anterior mediastinotomy—is often indicated in patients with a bronchogenic carcinoma of the left upper lobe. The aortopulmonary window contains lymph node stations 5 and 6, which are the first drainage sites of the left upper lobe of the lung. The secondary lymphatic drainage sites of the left upper lobe include lymph node stations 2L and 4L, which can be examined by cervical mediastinoscopy.

IDEAL PATIENT CHARACTERISTICS

Thin patients with no previous surgery in the neck are ideal candidates for mediastinoscopy. Previous cervical mediastinoscopy or mediastinal radiation therapy does not preclude mediastinoscopy, but the procedure has to be performed with caution. The risk of inadvertent injury to an adjacent structure is increased, as is the probability of poor sampling of the various lymph node stations. Large thyroid gland, cervical spine fusion, and cervical spine arthritis make introducing the scope and positioning the patient challenging but are not absolute contraindications for surgery.^9,10

PREOPERATIVE ASSESSMENT

Cervical mediastinoscopy and anterior mediastinotomy are performed under general anesthesia. Candidates for these procedures need to be suitable for general anesthesia. Preoperative assessment includes evaluation of cardiac status, pulmonary status, and clinical staging. Clinical stage is determined by history and physical examination, CT scan of the chest including the upper abdomen for evaluation of adrenal glands, and PET scan to determine metastasis (locoregional and systemic).

A history of facial swelling and plethora (e.g., superior vena cava syndrome), persistent neck or arm pain (e.g., Pancoast tumors with brachial plexus involvement), hoarseness (e.g., recurrent laryngeal nerve involvement), back pain, and headaches (e.g., systemic metastasis) suggests advanced disease that requires evaluation before subjecting patients to cervical mediastinoscopy or anterior mediastinotomy.

Paraneoplastic syndromes (e.g., syndrome of inappropriate antidiuretic hormone secretion, Eaton-Lambert syndrome, dermatomyositis, or hypercalcemia) are associated with both small cell and non-small cell lung cancers and do not necessarily suggest that the patient has metastatic disease. Large scalene or supraclavicular lymph nodes can undergo biopsy at the time of mediastinoscopy. A positive scalene or supraclavicular node renders the patient N₃ and not a candidate for surgical resection.

TECHNIQUE

Cervical Mediastinoscopy

Cervical mediastinoscopy is performed under general anesthesia. The patient is positioned with a roll under the shoulders and between the scapulae, which throws back the shoulders and extends the neck to improve tracheal exposure (Fig. 132-2). The head of the OR table is elevated to 20–30 degrees to decrease venous congestion. The neck and entire chest are draped in the event that a median sternotomy is required to manage a major complication.

A 2- to 3-cm incision is made transversely one fingerbreadth (1–2 cm) above the suprasternal notch through skin, subcutaneous tissue, and platysma (Fig. 132-3). The investing layer of deep cervical fascia is identified, and the midline is divided vertically to separate sternohyoid and sternothyroid muscles, which are retracted laterally. The strap muscles also can be divided, but lateral retraction of these muscles usually provides adequate exposure. Deep to the strap muscles and anterior to the trachea, the pretracheal fascia is identified and divided to enter the pretracheal space.

On the right side of the trachea, the superior vena cava, azygos vein, and tracheobronchial junction form the lateral boundaries of the dissection. On the left, the extent of dissection is limited by the pulmonary artery and aortic arch, with the distal extent of dissection to the left tracheobronchial angle.

An index finger is used to break through pretracheal fascia laterally to gain access to pretracheal and paratracheal lymph nodes (stations 2 and 4) (Fig. 132-4). Inability to break through the pretracheal fascia prevents biopsy of lymph nodes that lie anterior and lateral to the pretracheal fascia. The mediastinoscope is inserted along the superior surface of the trachea (Fig. 132-5). The subcarinal lymph node (station 7) biopsy is performed by using the tip of the cannula to break through the pretracheal fascia distal to the carina. Gentle blunt dissection of nodes is essential to safely separate the lymph nodes from their surrounding structures.

Normal lymph nodes usually feel rubbery and may have an anthracotic appearance with gray or bluish black pigmentation. Close proximity of nodes to vascular structures and inflammatory or malignant adhesions places these structures at risk for inadvertent injury and bleeding. Palpation of pulses or visible pulsations are not a good indicator of vascularity because the mediastinum is a small, confined space, and cardiac pulsations are transmitted easily to adjoining structures. Careful, gentle, and thorough dissection of the lymph node usually will confirm its identity. However, if there is any doubt as to whether the structure is a lymph node or a blood vessel, aspiration of tissues prior to biopsy is recommended. A spinal needle (21–22 gauge) on a small syringe can be used for the aspiration. Filling the syringe with a small amount of saline is helpful for detecting small amounts of blood. This technique is especially useful for patients with large, bulky disease, in whom veins such as the superior vena cava, azygos, and innominate are stretched over nodes and are nearly collapsed.

Transpleural mediastinoscopy is useful for investigating mediastinal involvement of bronchogenic carcinoma. Right Pancoast tumors, for example, can be readily assessed using transpleural mediastinoscopy. Through a standard cervical incision, the mediastinoscope is advanced into the right pleural space. In the absence of lung injury, positive-pressure ventilation should prevent the development of pneumothorax, particularly if an end-inspiratory hold is used at the end of the procedure to exclude any residual pneumothorax. The suprasternal notch incision also can be used to access supraclavicular lymph nodes or drain mediastinal cysts.

Subxiphoid mediastinoscopy is performed through a similar-length incision located vertically below the xiphoid process. Once the midline fascia has been incised, a finger can be inserted into the retrosternal space. In patients with scaphoid abdomen, the mediastinoscope can be readily inserted for examination and biopsy.

Bleeding during mediastinoscopy is avoided by gentle dissection of lymph nodes. Judicious use of force and judgment during biopsy of tissue is essential. It is not necessary to harvest the entire lymph node to make a pathologic diagnosis; therefore, lymph node fragments are adequate if the entire lymph node cannot be removed safely. Correctly identifying the lymph node station during the procedure is essential to correctly stage patients. In addition, identification of extracapsular spread or involvement of adjoining mediastinal structures is important to correctly stage patients.

Packing of the mediastinal space controls mild bleeding. Removal of the mediastinoscope after packing is helpful in obtaining hemostasis because this allows the tissues to collapse and obliterate the mediastinal space created by the instrument. Lymph node tissue can be cauterized using the metal-tip cannula. Thermal energy should be used judiciously because it can spread and cause recurrent laryngeal nerve damage and increase the chances of injury to vascular structures. Biopsy of subcarinal lymph nodes is associated occasionally with brisk bleeding from bronchial arteries. This complication is usually managed with packing, as described previously. Occasionally, identified arteries can be clipped with an endoscopic clip applier (EndoClip 5 mm, Autosuture, U.S. Surgical, Norwalk, CT).

After completion of the procedure and securing hemostasis, the incision is closed in layers. The strap muscles are approximated in the midline using 3-0 silk or Vicryl suture. The platysma can be approximated as a separate layer with absorbable suture. The skin is approximated using absorbable subcuticular suture.

Anterior Mediastinotomy

Anterior mediastinotomy is performed under general anesthesia. The patient is placed in the supine position. The entire chest is draped in the unlikely event that conversion to median sternotomy is required to control bleeding. The incision classically is made in the second intercostal space on the left side (Fig. 132-6). The incision can be as small as 2 cm in length. The incision is made through the skin and subcutaneous fat, and the pectoral muscle fibers are split to expose underlying intercostal muscles. A small (2-cm) portion of the costal cartilage is excised in the subperichondrial plane. The perichondrium is incised to enter the subperichondrial plane and dissected carefully to avoid injury to the internal mammary vessels and the intercostal vessels and nerve (Fig. 132-7). Alternatively, the intercostal muscles are divided at the superior border of the costal cartilage, the pleura is identified, and the mediastinum is entered without excision of the cartilage. The internal mammary vessels should be safeguarded and retracted laterally or identified and ligated.

The mediastinal pleura is swept laterally, and the mediastinum is entered. The mediastinoscope can be introduced through this incision into the mediastinum to facilitate dissection and biopsy of lymph nodes or masses. Vagus and phrenic nerves course in cephalocaudad direction and must not be injured. The level 6 mediastinal lymph nodes are found at the base of the innominate artery near the course of the phrenic and vagus nerves. The level 5 lymph nodes are closer to the proximal pulmonary artery. The entire dissection typically is performed within the mediastinum. The pleura can be opened to examine the hilum of the lung and to perform wedge biopsy of lung tissue. If the pleura is opened or inadvertently injured, placement of a chest tube is not essential as long as there is no injury to the lung. The pleura may be repaired over a red rubber catheter with positive pressures of 30–40 cm H₂O applied to the lung. In the event of lung biopsy or injury to the lung, a chest tube is placed in the pleural space.

After ensuring adequate hemostasis, the incision is closed with reapproximation of the perichondrium with absorbable suture. The pectoralis muscle is reapproximated similarly, and the skin is closed using subcuticular suture. Removal of perichondrium creates a slight, permanent depression on the chest wall after healing. Overall, bleeding from injury to major vascular structures is rare.

POSTOPERATIVE CARE

After cervical or anterior mediastinoscopy, if there is no suspected injury to pleura, a cheat x-ray is not essential, and patients can be discharged home. At most institutions, chest x-rays are still performed to rule out a pneumothorax or new pleural effusion. Diagnosis of a pneumothorax does not mandate tube thoracostomy placement. The size of the pneumothorax, percentage volume loss of lung, and symptoms of the patient dictate placement of a chest tube. After patients are ambulatory, tolerate liquids by mouth, have good pain control, and are able to pass urine, they are discharged to home with oral analgesics, which typically are required for only a few days.

PROCEDURE-SPECIFIC COMPLICATIONS

Cervical Mediastinoscopy

Cervical mediastinoscopy is a safe procedure with mortality rates of less than 0.1% and complication rates of less than 1%.^9,11 Injudicious use of the biopsy forceps or aggressive attempts to biopsy complete mediastinal lymph nodes may result in hemorrhage. Bleeding is usually minor and can be controlled with packing. Cauterization of bleeding tissue should be performed judiciously. Fortunately, major bleeding from the superior vena cava, azygos vein, brachiocephalic artery or vein, aortic arch, and pulmonary artery is rare. Major bleeding occasionally can be controlled with packing only, and this is recommended while arrangements are made to open the chest. Bleeding from major vessels will require a median sternotomy, which provides access to all mediastinal vessels. Alternatively, a thoracotomy may be performed depending on the location of the suspected injury, resectability of the tumor, and condition of the patient.

Pneumothorax can develop occasionally after mediastinoscopy. Chest x-ray is performed either routinely postoperatively or selectively according to surgeon preference. Pneumothorax is managed nonsurgically by aspiration or chest tube placement depending on the symptoms and percentage of lung volume loss. Injury to pleura sometimes can be recognized by the appearance of a new pleural effusion, caused by mediastinal blood draining into the pleura space. Injury to recurrent the laryngeal nerve is more common on the left side because the 2L and 4L lymph node stations are located near the nerve in the tracheoesophageal groove. Vocal cord dysfunction usually is transient.

Tracheobronchial injuries can result in subcutaneous emphysema or persistent air leak. The air leak usually is small and needs packing of mediastinum with surgical cellulose. Large injuries require direct or pedicled repair with flaps. Similarly, esophageal injuries are also rare and usually are not recognized immediately. Small, contained esophageal leaks can be managed conservatively by draining the mediastinum via the mediastinoscopy incision. Substantial injuries to the esophagus or a delay in diagnosis may require thoracotomy and repair or even esophageal exclusion.

Anterior Mediastinotomy

Anterior mediastinotomy is performed less frequently than cervical mediastinoscopy, and there are no large series to determine the risk of complications. There is the potential risk of bleeding from the aorta, pulmonary artery and vein, and internal mammary vessels, but this is uncommon. Injury to phrenic and vagus nerves is possible, resulting in diaphragmatic paralysis and hoarseness of voice. Removal of costal cartilage is associated with a depression under the skin and occasionally lung herniation.

Caution is to be exercised when performing an anterior mediastinotomy in patients after coronary artery bypass graft surgery. The patent internal mammary vessel used to perform the bypass must be protected. It runs along the course of the phrenic nerve and lies anterior to the hilum of the lung and mediastinal nodes. It is at risk for injury when gaining access to the mediastinum and during lymph node biopsy. Most surgeons would consider previous coronary artery bypass graft surgery with a left internal mammary artery as a contraindication to anterior mediastinotomy on the left side.

SUMMARY

Cervical mediastinoscopy is the mainstay for staging of mediastinal lymph nodes in patients with bronchogenic carcinoma. It is also used for biopsy of mediastinal masses. It is an invasive procedure with extremely low morbidity and mortality. The advent of whole-body PET scanning and CT/PET scanning has improved noninvasive staging of bronchogenic cancer but has not eliminated the need for mediastinoscopy. Mediastinoscopy continues to play an important role in staging of mediastinal disease. Anterior mediastinoscopy, in contrast, is used to sample lymph nodes in the aorticopulmonary window (stations 5 and 6) in patients with left-sided lung cancer or to biopsy anterior mediastinal masses.

EDITOR'S COMMENT

Mediastinoscopy is a remarkably simple, yet effective tool for obtaining diagnostic tissue. A skilled mediastinoscopist can obtain tissue from anywhere in the mediastinum with the exception of the posterior inferior mediastinum. This relative "blind spot" of mediastinoscopy can be effectively explored with thoracoscopy.

–SJM

REFERENCES