Continuing Education Activity

Mediastinoscopy is a thoracic surgical procedure performed with a mediastinoscope to examine the mediastinum— the space in the thoracic cavity between the lungs for various indications, including diagnostic tissue sampling, mediastinal lymph node biopsy, and TNM (tissue, nodes, and metastasis) staging. Mediastinoscopy has a high sensitivity (80%) and specificity (100%) in the staging of lung cancer. This activity reviews the role of mediastinoscopy, its indications, contraindications, complications and highlights the role of the interprofessional team in the management of patients with lung cancer.

Objectives:

• Identify the location of lymph nodes in the mediastinum.
• Describe the indications for mediastinoscopy.
• Review the clinical relevance of mediastinoscopy.
• Explain the role of the health care team in the coordination of care of patients undergoing mediastinoscopy.

Introduction

Mediastinoscopy is a thoracic surgical procedure performed with a mediastinoscope to examine the mediastinum— the space in the thoracic cavity between the lungs for various indications, including diagnostic tissue sampling, mediastinal lymph node biopsy, and TNM (tissue, nodes, and metastasis) staging. Mediastinoscopy has a high sensitivity (>80%) and specificity (100%) in the staging of lung cancer. [1] 

Mediastinoscopy can be classified into 2 different procedures.

• Cervical mediastinoscopy provides access to the pre-tracheal, paratracheal, and anterior sub-carinal lymph nodes.
• Transthoracic mediastinoscopy, also known as Chamberlain’s procedure or anterior mediastinotomy, is a more involved procedure that allows for dissection of the aortopulmonary lymph nodes.

Surgery in the mediastinum was first described in 1899 when a superior mediastinal abscess was successfully drained. The procedure was advanced in Europe in the early 20th century but rarely performed outside of Europe until the late 1950s when Eric Carlens of Sweden introduced the mediastinoscope as a surgical instrument. This new rigid instrument allowed a surgeon to enter the mediastinum through a suprasternal incision and biopsy paratracheal and hilar lymph nodes.[2]

Anatomy and Physiology

To understand mediastinoscopy, one must know the anatomy of the mediastinum. The mediastinum is the region in the central chest between the two pleural cavities extending from the thoracic inlet to the diaphragm. It contains several important organs, vessels, and nerves including the heart, the great vessels, the trachea, esophagus, phrenic and vagus nerves, thymus, and lymph nodes. The mediastinum has 5 borders — superior, inferior, posterior, anterior and lateral. The lateral borders comprise the left and right pleura,  the posterior border is the vertebral column, and the anterior border is the sternum. The superior and inferior borders are the thoracic inlet and diaphragm, respectively.

The mediastinum is divided into the superior and inferior mediastinum. This division occurs at the level of the sternal angle which is located at the level of disc space T4 to 5. The inferior mediastinum is anatomically subdivided into the anterior, middle, and posterior mediastinum. The middle mediastinum contains the pericardium and all that it encloses.[3]

Indications

The major clinical indications for a mediastinoscopy are: 

• Evaluation of lymph node involvement in patients with carcinoma of the lung
• Tissue biopsy of suspected tumors 
• Removal of mediastinal masses and enlarged lymph nodes

The most common indication for mediastinoscopy is as a staging procedure in the diagnosis of non-small cell lung carcinoma. The pathological results obtained from the procedure are very important in tailoring care for the patient amongst the surgeon, oncologist, and radiation oncologist. Other indications for mediastinoscopy include the diagnosis and removal of mediastinal masses and enlarged lymph nodes. Lymphoma, both Hodgkins and non-Hodgkins, can be diagnosed via mediastinoscopy along with sarcoidosis which has similar appearances on imaging. A mediastinal mass, such as a thymoma may be excised via mediastinoscopy depending on its size. A sampling of lymph nodes may diagnose infectious processes such as tuberculosis and fungal infections.[4] Benign mediastinal cysts can be excised via mediastinoscopy. Finally, mediastinoscopy is used in the diagnosis and treatment of mesothelioma.[5][4][6]

Conditions that may present with mediastinal masses include: 

• Tumors
  • Thyroid and parathyroid tumors
  • Lymphoma
  • Esophageal cancer
  • Neurogenic tumors
• Benign conditions
  • Developmental cysts
• Granulomatous lymphadenopathy
  • Tuberculosis
  • Sarcoidosis
• Vascular
  • Aneurysms
  • Aberrant vessels, e.g., persistent left superior vena cava (SVC), anomalous left pulmonary artery 

Contraindications

Contraindications to mediastinoscopy can be classified as either absolute or relative.[7][8]

Absolute contraindications include: 

• Anterior mediastinal mass
• Inoperable tumor
• Previous recurrent laryngeal nerve injury
• Extremely debilitated patients
• Ascending aortic aneurysm
• Previous mediastinoscopy

Previous mediastinoscopy is a strong contraindication to a repeat procedure because of the elimination and distortion of the plane of dissection from scar tissue. 

Relative contraindications include:

• Thoracic inlet obstruction
• SVC syndrome
• Severe tracheal deviation
• History of radiation therapy to the chest 

Anything that distorts the anatomy, such as those contraindications listed above, increases the risk of vascular or airway injury which can be catastrophic in this location.[9]

Equipment

Equipment needed include:

• A mediastinoscope
• Fiberoptic light cable
• Biopsy forceps 

A cardiothoracic set up on standby and an anesthesia machine are needed to perform the procedure under general anesthesia.

Personnel

Mediastinoscopy is a surgical procedure that is performed in the operating room. It requires a cardiothoracic or general surgeon trained in mediastinoscopy capable of performing an emergency thoracotomy and/or sternotomy. The procedure also requires general anesthesia and thus requires an anesthesiologist and operating room support staff.

Mediastinoscopy can be performed under local or general anesthesia. General anesthesia is the technique of choice at most institutions if the patient has no preoperative signs or symptoms of airway obstruction.[7][2] 

Preparation

A preoperative evaluation of a patient undergoing a mediastinoscopy is important in decreasing morbidity and mortality. Particular attention should be paid to respiratory symptoms such as wheezing, dyspnea, and orthopnea. It is important to find out whether the respiratory symptoms are exacerbated by exercise or by assuming the supine position which may indicate airway obstruction secondary to a mediastinal mass. Preoperative workup should include chest x-ray with posteroanterior and lateral views, CT scan of the chest and neck pulmonary function tests with flow-volume loops. If tracheal deviation is suspected, specific studies such as neck films or tomograms should be obtained to evaluate the location and extension of the mass as well as the degree of airway compromise. Flow-volume loops in both the upright and supine positions are useful in determining whether the obstruction is fixed, and whether it is intrathoracic or extrathoracic. 

An intravenous line must be in place before proceeding to the operating room. The general anesthetic technique can involve inhalational or intravenous agents, or most commonly, a combination of the two. Following induction and intubation, the use of muscle relaxants provides the surgeon with an operative field safe from sudden movements, which might lead to injury of the adjacent organs by the mediastinoscope.  If the preoperative workup is indicative of airway compromise, the patient may be intubated via an awake fiberoptic technique where the patient remains spontaneously breathing. The patient is intubated with a standard single lumen endotracheal tube unless there are contraindications that require one-lung ventilation. In that case, the patient may be intubated with a large 7.5 mm or above a single lumen tube to allow the easy passage of a bronchial blocker or a double lumen endotracheal tube. Following intubation, additional vascular access is established in the form of another large bore IV and an arterial catheter. The arterial catheter allows for beat-to-beat blood pressure monitoring which may be able to detect vascular compression or massive hemorrhage during the procedure and also allows for arterial blood gases to be regularly checked during the procedure. To detect innominate artery compression by the mediastinoscope when inserted, constant palpation of the right radial or carotid pulse, placement of a right radial arterial line, or monitoring of a continuous plethysmographic tracing of a pulse oximeter is advocated.[10]

Technique or Treatment

Mediastinoscopy is performed in the operating room under general anesthesia. A patient is generally in the supine position for the procedure unless an anterior mediastinal mass causes airway compromise when lying flat. In a patient without such a mass, intravenous induction is performed, and following intubation, the patient’s head is extended and turned to the side. A 3-cm incision is performed 2 cm above the suprasternal notch between the anterior borders of the sternocleidomastoid muscle. The superficial fascia of the neck, deep cervical fascia, and pretracheal fascia must be dissected to reach the level of the trachea. Blunt dissection down to the anterior trachea allows entrance into the superior mediastinum. As the tract continues to be developed via blunt dissection, a tract into the superior mediastinum will develop between the anterior trachea and posterior to the great vessels. A mediastinoscope is then inserted and advanced along the tract allowing for the sampling of lymph nodes and masses.[2]

Complications

During the procedure when the mediastinoscope is inserted, it can cause compression of the innominate artery. This can lead to a decrease in pulse oximeter signal and blood pressure when these are placed in the right upper extremity, as a result of the decreased blood flow to the extremity when the artery is compressed. Compression of the innominate artery can lead to intracerebral hypoperfusion which can in turn lead to cerebral ischemia and stroke.

Mediastinoscopy is not a benign procedure; the morbidity associated with the procedure is reported to be between 1.5% to 3%, with an overall mortality rate of 0.09%. Intraoperative complications can occur with mediastinoscopy and include bleeding, which is the most common complication of this procedure. Injury to the great vessels causes hemorrhage that can be life-threatening; an emergent thoracotomy or median sternotomy may be necessary to gain control of the hemorrhage while using the mediastinoscope to tamponade the site of bleeding. The procedure has a risk of air embolism given that the patient is in a head-up position/reverse Trendelenburg and the mediastinoscope can lead to vascular injury which could lead to air being entrained into the vascular system; this can be monitored via end-tidal CO2 and end-tidal nitrogen. Some recommend the use of precordial Doppler to monitor for any venous air embolism. Instrumentation can lead to airway rupture; however; this complication requires an immediate thoracotomy. During the procedure, the recurrent laryngeal nerve can be injured. The left is at more risk because of its more caudal path under the aorta. Bilateral recurrent laryngeal nerve injury can lead to complete respiratory failure and the need to re-intubate and then perform a surgical airway on the patient. Damage to the thoracic duct can lead to chylothorax.

There are times when mediastinoscopy is indicated in the presence of an anterior mediastinal mass. It is important that surgeon, anesthesiologist, and operating room staff appreciate potential complications of the mass. The patient may not be able to lie flat, making endotracheal intubation more difficult. Even in the presence of successful intubation with proper airway placement, the airway may be compromised by the mass distal to the airway after muscle paralysis is induced. Therefore, it is recommended that muscle relaxants be avoided in high-risk patients and that the patient be intubated while spontaneously breathing either via a fiberoptic bronchoscope or direct/indirect laryngoscopy following mask induction. An otorhinolaryngology (ENT) surgeon competent with rigid bronchoscopy should be present if necessary to bypass the obstruction. Changing patient position from to supine or either lateral or prone may be a temporizing measure that relieves the obstruction of the mass on the airway. In cases where there is a large anterior mediastinal mass that may result in cardiovascular collapse with induction of anesthesia, cardiopulmonary bypass should be available.

Patients who have suspected airway obstruction due to a mediastinal mass on physical examination should undergo pulmonary function tests (PFTs) with flow-volume loops. The tests should be performed in both the upright and supine positions. If the PFTs show obstruction while supine during inhalation, the patient’s mass is extra-thoracic, if the obstruction occurs during expiration, the patient’s mass is intrathoracic. A review of CT imaging can be extremely helpful in evaluating any compression or deviation of the great vessels.

In patients with a large mediastinal mass, SVC syndrome may be present. Obstruction of the superior vena cava will cause facial swelling, distension of neck, development of collateral venous drainage along the thoracic wall. It associated with dyspnea and dysphagia commonly. Diagnostically, it can be seen on imaging. A positive Pemberton’s sign also characterizes it. A positive Pemberton’s sign occurs when a patient lifts both of their arms over their head in the upright position causing marked facial plethora to occur, indication profound compression of the jugular veins. It is important to have intravenous access in these patients in the lower extremities because of the resistance of upper extremity drainage being recirculated.[11][2][12][13]

Clinical Significance

Along with endobronchial ultrasound with biopsy, mediastinoscopy is an important clinical procedure performed in the diagnosis of disease pathologies that occur in the mediastinum, most notably bronchogenic carcinoma. It is recommendations that patients that patients initially receive an endobronchial ultrasound biopsy before induction therapy, and then mediastinoscopy following the therapy. Many centers are using video-assisted mediastinoscopy as it improves surgical visualization and allows the surgeon to use multiple instruments at once. These are both methods for staging non-small cell lung cancer. It is expected that both treatment modalities will increase in number in the future. A single institution study showed that mediastinoscopy was marginally cheaper than the endobronchial ultrasound biopsy.[14][15]

Enhancing Healthcare Team Outcomes

Mediastinoscopy is a well-known and common procedure. It is paramount to educate the patient, physicians, all others that are involved in mediastinoscopy cases what to expect before, during, and following the procedure. In many instances, there is a close association of the procedure with a lung cancer diagnosis, and patient care must be well coordinated with other physicians and care staff to make sure the patient is optimized for the procedure. As ultrasonic methods become more advanced endobronchial ultrasound with biopsy of the mediastinum may largely overtake mediastinoscopy, but at this time both have a major role in thoracic surgery.