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Mediastinoscopy and mediastinotomy

Jennifer L. Wilson and Eric Vallières

HISTORY

Recognition of advanced lung cancer by using a novel cervicomediastinal exploration technique was first described in 1954 by Dwight Harken. The publications of Eric Carlens in Sweden and F. Griffith Pearson in Canada, in 1959 and 1964, respectively, helped popularize the procedure. Today, mediastinoscopy remains an excellent minimally invasive technique to evaluate the mediastinal lymph nodes (see Figure 8.1) as well as anterosuperior mediastinal masses to histologically distinguish benign, malignant, and infectious processes.

Although the design of the modern mediastinoscope remains very similar to the original, the advancement to video mediastinoscopy, which was first described in 1989 by Lerut, has significantly improved visualization, teaching, safety, dissection, and reproducibility. In addition to permitting access to paratracheal and pericarinal superior mediastinal lymph nodes (stations 2R, 2L, 4R, 4L, and 7), due to superior visualization, video mediastinoscopy also allows access to the central N1 stations. Although there are no randomized controlled trials comparing video with the nonvideo original approach, several retrospective reviews suggest that video mediastinoscopy results in better nodal access and sampling.

The para-aortic (station 5) and aortopulmonary (station 6) lymph nodes are not accessible by conventional cervical mediastinoscopy (CM); to that effect, in 1966, McNeill and Chamberlain developed a technique known as “anterior mediastinotomy,” the so-called Chamberlain procedure, to access these nodes. In the 1980s, the extended cervical mediastinoscopy (ECM) approach was described, where one accesses the station 5 and 6 lymph nodes through the CM incision by advancing the mediastinoscope over the aortic arch, medial to the left common carotid artery.

Ongoing methods of lymph node sampling continued to evolve and, in 1999, the first dedicated endobronchial ultrasound (EBUS) bronchoscopy system became commercially available. This allows ultrasound-guided needle biopsy aspirates of lymph node stations 2, 4, 7, 10, 11, and 12. Furthermore, transesophageal endoscopic ultrasound (EUS) was developed, which allows needle biopsy aspirates of lymph node stations 4L, 5, 7, 8, and 9.

Hürtgen described another novel technique in 2003: video-assisted mediastinal lymphadenectomy (VAMLA). This technique allows even better nodal sampling of stations 2R, 2L, 4R, 4L, and 7. The following year, Kuzdzal et al. described transcervical extended mediastinal lymphadenectomy (TEMLA), which allows near complete mediastinal lymphadenectomy, removing most lymph nodes in stations 1, 2R, 2L, 3a, 4R, proximal 4L, 5, 6, 7, and 8.

In summary, many complementary techniques exist for complete histologic evaluation of the mediastinum. To date, cervical video mediastinoscopy remains the gold standard for the mediastinal nodal staging of lung cancer. All lung cancer surgeons should be proficient at this technique and at anterior mediastinotomy, which allow access to the paraaortic and aortopulmonary lymph nodes. Here, these two most commonly employed techniques will be described, along with two emerging techniques, VAMLA and TEMLA. Other techniques of mediastinal lymph node sampling, such as ECM, EBUS, EUS-guided biopsy, as well as video-assisted thoracoscopic surgery (VATS) and percutaneous biopsy, while beyond the scope of this chapter, can also be useful mediastinal staging methods.

PRINCIPLES AND JUSTIFICATION

Accurate clinical staging of patients with lung cancer is imperative to offer patients appropriate therapy and imaging alone is insufficient. Results of the American College of Surgeons Oncology Group Z0050 trial in 2003 demonstrated that computed tomography (CT) plus fluorodeoxyglucose positron emission tomography (FDG PET) correctly identified N2/N3 disease in 53% of patients, which was significantly superior to CT alone (32%). In the study, FDG PET had a sensitivity of 61%, specificity of 84%, positive predictive value of 56%, and negative predictive value of 87%. In addition, the sensitivity of positron emission tomography (PET) for Ml disease was 83% and the specificity was 90%. Integrated CT/PET scans have improved imaging accuracy; however, in patients who are otherwise potential candidates for resection, enlarged lymph nodes on CT that are FDG PET avid do require at least cytological confirmation of involvement for accurate staging.

CM is an excellent procedure to access and biopsy several mediastinal lymph node stations. CM is better known as a modality used for lung cancer staging, but it is also very helpful to evaluate the etiology of mediastinal lymphadenopathy for conditions such as sarcoidosis and lymphoma in which cytology or smaller needle biopsies may not provide sufficient diagnostic tissue.

The proficiency and use of mediastinoscopy to clinically stage patients with lung cancer varies among surgeons. In a U.S. survey of 729 hospitals, preoperative mediastinoscopy was only performed in 27.1% of patients and node biopsy was successful in only 46.6% of these procedures. The fact that nodal tissue was sampled in less than half of mediastinoscopies is disappointing and may be related to the fact that non-thoracic-trained general surgeons performed many of these procedures. To support this theory, Wei et al. demonstrated that nodal tissue was sampled 100% of the time when mediastinoscopy was performed by a thoracic surgeon in a single center retrospective review of 1907 cases.

The false-negative rate of mediastinoscopy in identifying the presence of N2 nodal involvement is reported to be around 8%. However, one must recognize that about half of the missed involved nodes are located outside of the mediastinoscopy range.

As a consequence, thorough mediastinal lymph node sampling is imperative during lung resection and remains the standard of care.

Anterior mediastinotomy can be used to biopsy and diagnose anterior mediastinal masses on the right or left hemithorax. In situations where the involvement of station 5/6 mediastinal lymph nodes is suspected radiographically (see Figure 8.2), a left anterior mediastinotomy may allow direct biopsy to rule in or out such involvement. Alternatively, one may prefer a VATS approach for such biopsies, though this approach requires double lumen intubation and patient repositioning. In this scenario, a CM should be completed first, as a significant proportion of patients with involved stations 5 and 6 will also have involvement of the central superior mediastinal nodes and, if these are positive on frozen section analysis, one does not need to perform the mediastinotomy.

PREOPERATIVE ASSESSMENT AND PREPARATION

Mediastinotomy and CM can be safely performed in an ambulatory surgical setting. There are very few absolute contraindications to CM or mediastinotomy. The only absolute contraindication to CM is the presence of an aortic arch aneurysm and the only absolute contraindication to mediastinotomy is the presence of an internal mammary artery cardiac bypass graft. If the aortopulmonary window (AP window) needs to be sampled and the patient has an internal mammary graft or coronary artery bypass graft, a VATS approach is recommended.

In addition, patients with severe kyphosis or fused cervical vertebrae may not be able to extend their neck adequately for CM. Relative contraindications to CM include severe atherosclerotic disease of the aortic arch and right innominate and/ or vertebral arteries, as this can put the patient at risk for an embolic stroke. Superior vena cava obstruction historically was considered a contraindication to CM, but this has been shown to be safe in experienced hands. Similarly, experience allows the possibility of safely performing repeat CM and mediastinotomy, which may be technically challenging due to scarring and fibrosis. Patients with large thyroid masses or prior irradiation that require CM may also be more challenging and, in these cases, CM and mediastinotomy should be performed by experienced surgeons.

MEDIASTINOSCOPY

Anesthesia and patient positioning

The patient is placed in the supine position. General endotracheal anesthesia is induced and the endotracheal tube is taped to the side of the patient’s mouth to prevent dislodgement during the procedure. The use of a laryngeal mask airway has also been shown to be safe. Maximal cervical extension is very important. This may be accomplished by placing a roll beneath the shoulders while maintaining support of the head (see Figure 8.3). At times, one may have to drop the head of the operating table to maximize such extension. Both arms are tucked at the patient’s side. The neck, chest, and upper abdomen are prepped and draped into the surgical field in case one needs to proceed to an emergent sternotomy in the very rare case of massive hemorrhage.

Equipment

• Standard surgical equipment: scalpel, forceps, Metzenbaum scissors
  
• Video (Lerut) mediastinoscope (see Figure 8.4)
  
• Insulated combined suction and cautery device connected to a foot pedal
  
• Mediastinoscopy biopsy forceps, straight and up biting
  
• Sternal saw (in the room)

Operation

A 2 cm transverse skin incision is made approximately 1.5 fingerbreadths above the sternal notch in the midline (see Figure 8.5a). Electrocautery is used to transect soft tissues and the platysma muscle transversally. Once the strap muscles are reached, the dissection is then carried out vertically in between the muscles overlying the trachea. Vertical dissection avoids injury to the anterior jugular veins laterally. Intermittent gentle blunt up-and-down finger dissection over the trachea is helpful to reorient oneself periodically during the procedure, as well as to palpate and identify the thyroid isthmus.

Once the pretracheal fascia is identified inferior to the thyroid isthmus, it is grasped and incised sharply with scissors (see Figure 8.5b and c). A right-angle retractor is then placed in the pretracheal space, gently lifting upward. Simultaneously, gentle pressure on the anterior wall of the trachea pushes the airway posteriorly, which allows dissection of the pretracheal plane under direct vision. One should aim to carry this visualized dissection below the level of the innominate artery, which crosses anteriorly to the trachea at various distances from the thoracic inlet. In some patients, this visualized dissection will reach the level of the carina. Once this dissection is completed beyond the field of view, blunt dissection using an index finger is then performed (see Figure 8.6). The finger pad should be positioned anteriorly and blunt digital dissection into the mediastinum is performed by advancing the finger into the mediastinum with care to maintain position directly over the trachea. The right innominate artery will be palpated at this time (see Figure 8.7a). The video mediastinoscope is then inserted into the tract, visualizing the trachea at all times to maintain orientation.

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