TSRA Content:
Author: Rus Kanyongo, MD
This is a revision and update from the previous edition of TSRA Primer in Cardiothoracic Surgery written by Benjamin Wei, MD
Indications
The most common indication for mediastinoscopy is as a staging procedure in the diagnosis of non-small cell lung carcinoma, as it has a high sensitivity (80%) and specificity (100%) for lung cancer staging. The major clinical indications for a mediastinoscopy include evaluation of lymph node involvement in patients with carcinoma of the lung, tissue biopsy of suspected tumors, and removal of mediastinal masses and enlarged lymph nodes. However, there are few contraindications to mediastinoscopy. Prior tracheostomy obliterates the pretracheal space and should be an absolute contraindication. Prior mediastinoscopy may cause scarring that increases the risk of the procedure (although it may still be performed). Prior median sternotomy does not usually affect the ability to perform mediastinoscopy, as the pretracheal space has not been violated in most cardiac surgical procedures. The presence of a calcified aortic arch or cerebral vessels may predispose the patient to embolization of debris if the vessels are manipulated during the procedure. Therefore, consider avoiding mediastinoscopy in a patient with severe atherosclerosis of the aortic arch and a history of stroke.
Preoperative evaluation
On physical exam, the presence of scars suggesting prior surgery in the region, an inability to extend the neck, and an innominate artery that is palpable above the sternal notch should be noted. When planning for mediastinoscopy, reviewing the CT scan of the chest with abdominal windows is critical. Lymph nodes that are greater than 1 cm in the short axis on a CT scan and/or FDG avid on a PET scan are considered significant and can be biopsied to rule out malignancy. Anticoagulation and platelet inhibitors other than aspirin should be discontinued beforehand in the usual fashion.
Anesthetic considerations
General anesthesia is required. The endotracheal tube should be positioned laterally away from the operating hand of the surgeon and the mediastinoscope to minimize interference with the surgeon, as well as to permit easy access to the airway by the anesthesiologist. A right radial arterial line is placed to detect compression of the innominate artery by the mediastinoscope; having the vital signs monitor visible to the surgeon is useful because of this possibility.
Positioning/draping
The patient's head should be near the top edge of the bed for optimal surgical ergonomics. The patient should be positioned with an interscapular roll or roll below the shoulders so that the neck is maximally extended. The patient is put in a reverse Trendelenburg position. The right arm should be tucked to facilitate access by the assistant, who generally stands on the patient's right-hand side. The bed may be turned 90 degrees in order to provide more space for the surgeon.
A transverse cervical incision should be marked one fingerbreadth above the sternal notch, preferably in a skin fold for cosmesis. The neck and chest should be prepped and draped so that emergency median sternotomy can be performed if required or placement of a chest tube in case of pneumothorax. A sternal saw should be immediately accessible. A non-alcohol containing prep should be used to minimize the risk of fire.
Step I: Exposing the trachea
The skin and platysma are divided transversely. The strap muscles are identified, care should be made to identify the median raphae and to stay within the midline. The strap muscles are split vertically, and the dissection is carried down to the pre tracheal fascia which should be incised elevated anterior and allow for the blunt dissection along the trachea. During the dissection self-retaining retractors can be placed to help expose the trachea. The assistant's role in keeping the incision centered over the trachea is crucial. Be vigilant for the presence of the thyroid, which is quite vascular and if seen, should prompt the surgeon to move distally on the trachea.
The innominate artery will be anticipated to cross in front of the trachea at or below the level of the sternal notch; blind cauterization distally thus risks injury to the innominate artery. Avoid cauterizing the tracheal surface if possible; scissors can be used to open the pretracheal fascia.
A finger is inserted and firm, constant pressure is used to bluntly dissect the pretracheal space into the mediastinum, taking care to stay immediately in front of the trachea. The tip of the finger should reach the posterior surface of the aortic arch; the innominate artery will also be felt pulsating above the finger. Insert the mediastinoscope, recognizing that the tip of the scope is angled and can potentially injure structures. Keep the scope pointed downwards so that your view directly faces the anterior surface of the trachea.
Step II: Identifying landmarks & Biopsying the lymph node stations
The first step is identification of the carina. The right and left mainstem bronchi should be visualized clearly. Tactile feedback with the suction/cautery device may help in locating the bronchi. Remember that the pulmonary artery will be crossing above your scope. The goal should be to obtain biopsies from at least 3 lymph node stations. 4R is generally biopsied first, unless there is a specific node or nodes to be targeted. Prior to biopsying any suspected lymph node, it is important to dissect it away from the surrounding tissue enough to confirm that it is indeed a lymph node (as opposed to a named vascular structure). See figure 1 for a schematic of the major structures to avoid during mediastinoscopy. To obtain 4R, use the suction/cautery to pull the tissue that is located above and lateral to the right mainstem bronchus down and to the left. This will usually bring 4R into view. The azygos and possibly vena cava may come into view as bluish structures; these structures will NOT extrude out of the surrounding fat as a lymph node will. An anthracotic lung visualized beneath clear pleura may also be misidentified as a lymph node.
Biopsy of levels 3 (pretracheal) and 2R and 2L (proximal right and proximal left paratracheal) can be performed if these lymph nodes are identified.
To obtain station 7, first break into the fascia that surrounds the node, which then permits biopsy. The remaining level 7 lymph node tends to bleed and require electrocautery for hemostasis; in some situations, taking the entire lymph node may be the easier solution to the bleeding. Remember that from your vantage point, the esophagus is located below the level 7 lymph node. To obtain 4L, push the tissue down and to the left of your visual field lateral to the origin of the left main stem bronchus. The recurrent laryngeal nerve is located here and can often be visualized. Aggressive dissection in this space can injure the nerve and should generally be avoided. Cautery in this area is also undesirable for this reason.
Clearly state the location of the lymph node being sampled to the scrub nurse, as misidentification of the node can lead to important therapeutic consequences (i.e. false upstaging of patient from N2 toN3 if the wrong side is labeled). For suspected lymphoma or other situations in which extensive testing of the specimen must be done, try to obtain at least a cubic cm worth of lymph node tissue.
Step III: Hemostasis and closure
Bleeding which is non pulsatile, gradually filling the field of the scope, or coming from an obvious small unnamed vessel should generally be controlled with packing and tamponading. Indiscriminate use of cautery on structures that cannot be identified should be avoided at all cost. Pushing the scope in deeper against the trachea in this situation, while not instinctive, may prevent the camera from getting smudged by tamponading the bleeding against the surrounding structures until you are able to suction away the blood. If the camera does get smudged during the operation, flush saline down the scope to clear it; it is difficult to clean the camera lens directly because the housing of the scope interferes with access.
Topical hemostatics such as surgicel can be useful when low-grade non-localized bleeding exists (ex. from the remaining level 7 lymph node after biopsy) or when bleeding in a sensitive location precludes cautery. Once discrete bleeding sites are controlled, the mediastinum may be packed with a sponge to ensure hemostasis. Place a retractor to lift the skin (making sure to have the innominate artery ABOVE (anterior) you) and pack the sponge DEEPLY into the mediastinum to get effective tamponade. The sponge is left in place for 2-3 minutes and then removed, if the sponge is dry or colored. thinly with blood, the wound may be closed. If the sponge is overly bloody, the wound should be repacked, and the above steps repeated as many times as necessary until adequate hemostasis is achieved.
Some surgeons prefer to partially re-approximate the strap muscles to protect the trachea. If this is done, care should be taken not to completely close the strap muscles in order to allow for a "vent" incase hemorrhage occurs. Finally, the platysma and skin are closed in the standard fashion.
Pitfalls/Emergencies
Azygos injuries usually require a right anterolateral thoracotomy to repair. A caval injury usually requires median sternotomy to repair, although it can be accessed via right thoracotomy if it was mistaken for an azygos injury. Innominate artery injury is pulsatile and should be controlled with pressure from a finger until better exposure is achieved; a partial or complete sternotomy may be necessary in this case.
A pulmonary artery injury is characterized by a "black out" of the field that makes it appear as if the light of the scope was extinguished. If this occurs (and is not truly the result of a light cord disconnection or malfunction), a sponge should be packed into the mediastinum to tamponade the bleeding until median sternotomy is performed. Cardiopulmonary bypass should be made available, as it may be required if the injury is significant. Recurrent laryngeal nerve injuries can occur when dissecting 4L. These injuries tend to be temporary and manifest as hoarseness following surgery. Swallowing issues may justify prompt evaluation and a hospital stay to monitor for aspiration. Persistent deficits may be an indication for ENT consultation and possible medialization of the vocal cord. Esophageal and aortic injuries are exceedingly rare and are the result of surgical misadventure.
Postoperative considerations
A chest radiograph should be obtained to rule out pneumomediastinum from a tracheal/bronchial injury and pneumothorax from a pleural/lung injury. Bleeding causing compression of the trachea and respiratory distress should precipitate emergent opening of the incision, at the bedside if necessary. Patients can generally be discharged after a brief stay in the recovery room. Common complaints after mediastinoscopy are sore throat, cough, mild swelling and/or induration of the incision. Wound infections are rare.