Parasternal Mediastinotomy

Anatomy and Physiology

The mediastinum is the central component of the chest between the two pleural spaces. The mediastinum can be divided into the superior, anterior, middle, and posterior mediastinum. The middle mediastinum contains the heart and root of the great vessels. The superior mediastinum is above the heart and contains the aortic arch and root of the carotid and subclavian arteries, as well as the nodes about the vessels.

The anterior mediastinum will be behind the sternum and in front of the pericardium. The posterior mediastinum is behind the pericardium and heart. For the purposes of the mediastinotomy, there will be access to the superior and anterior mediastinum, but the main portion of access is the superior mediastinum, as this is the location of the AP window nodes the peribronchial nodes, and the structures of interest for this procedure.[2][3] 

The structures in jeopardy include the aorta, the pulmonary artery and vein, and the pericardium. Neural structures include the phrenic nerve medially along the pericardium as well as the left recurrent laryngeal nerve, which wraps underneath the aortic arch, heading back into the neck to supply the vocal cord. The resultant injury to the phrenic nerve includes an ipsilateral elevated hemidiaphragm, and the injury to the recurrent nerve results in hoarseness and a paralyzed vocal cord on the ipsilateral side.

Indications

Mediastinotomy is used to biopsy and facilitate the histologic diagnosis of enlarged mediastinal lymph nodes. In the setting of a known pulmonary lesion, particularly the left upper lobe, it is important to have a tissue diagnosis to confirm the pathologic stage and resectability of the primary index lesion. Generally, with lesions appearing as lung cancer, the surgeon would order a PET CT scan to look for metastatic disease. Nodes more than 1cm or "hot" nodes would need a pathologic diagnosis. The diagnosis can be made through endobronchial ultrasound-guided biopsy (EBUS), CT-guided biopsy, and sometimes with the mediastinotomy.

The AP window nodes are not accessible by EBUS, so the mediastinotomy is preferred. Other indications would be for enlarged lymph nodes in the mediastinum or a mass that would need a pathologic diagnosis that could not be accessed or accomplished with less invasive means. The differential diagnosis for some of these masses and nodes is wide-ranging, including carcinoma, tuberculosis, and sarcoidosis, as well as lymphomas, thymomas, and other germ-cell tumors etc.[4]

Contraindications

Contraindications of mediastinotomy include the following:[5]

• Superior vena cava syndrome
• Previous mediastinal irradiation
• Previous median sternotomy
• Tracheostomy
• Aneurysm of the aortic arch

Equipment

Equipment for the mediastinotomy is the same as for the mediastinoscopy. There should be self-retaining retractors, periosteal elevators, and bone cutters to assist in removing the anterior cartilaginous portions of the ribs. Kitner dissection and blunt dissection with the finger help guide into the appropriate area for diagnostic tissue. The mediastinoscopy can be introduced for a closer and deeper look into this small area, and biopsy forceps of the mediastinoscope are needed, as well as the long Kitner dissectors.

Personnel

The procedure is usually done with one surgeon and one assistant. The pathologist may be on standby for frozen section analysis to make sure enough tissue has been submitted. An anesthetist is a crucial team member as this procedure is done under general anesthesia.

Preparation

There is minimal patient preparation for this procedure. Many of these can be done safely as outpatient procedures. The patient should withhold food and fluids after midnight prior to the operation and present to the pre-operative holding area before surgery. In the operating room, the patient would undergo general anesthesia. The whole neck, chest, and upper abdomen should be prepped into the field in case catastrophic bleeding occurs and emergent median sternotomy or thoracotomy is needed for control of massive hemorrhage.

Technique or Treatment

Mediastinotomy is performed in the following manner:

• Anterior mediastinotomy for biopsy purposes is performed under general anesthesia with endotracheal intubation.
• Proper positioning with 15 degrees elevation of the head of the bed.
• 2nd intercostal incision with removal of cartilage and preservation of the perichondrium.
• Ligation of internal mammary vessels.
• Opening the extrapleural space followed by blunt dissection pushing pleura away from the mediastinum to gain access to nodal envelopes of interest.
• Obtain biopsy of nodes and record stations of the nodes biopsied for pathology.
• Frozen section for the adequacy of tissue samples.
• Open pleura if a pleural biopsy is performed.
• Small chest tube, if pleura opened, placed through a separate stab incision.
• Closure of the wound in layers.
• Valsalva maneuver while chest tube removed.
• Awakening and extubation of the patient.[6][7]

Complications

Potential complications of diagnostic anterior mediastinotomy include:

• Hemorrhage from the internal mammary or the other major vessels like the aortic arch in areas of dissection and biopsy
• Wound infection
• Pneumothorax
• Complications attendant upon injury to any of the mediastinal structures accessible through this approach, such as the phrenic, left recurrent laryngeal, and vagus nerves, the thoracic duct, and the major arteries and veins.

Clinical Significance

Anterior mediastinotomy (the Chamberlain procedure) is surgical entry to the mediastinum via an incision in the parasternal 2nd left intercostal space. The use of this technique is decreasing and is very specific now. EBUS and other techniques have replaced the mediastinotomy except for certain instances. The procedure is used for obtaining enough viable tissue for histologic confirmation of a diagnosis or obtaining enough viable tissue for cultures in cases of infection. The primary significance is obtaining tissue that supports an accurate staging of lung carcinoma, which has AP window node involvement or enlargement.

Enhancing Healthcare Team Outcomes

Anterior mediastinotomy is a surgical procedure performed in order to obtain a histological diagnosis of mediastinal tumors and enlarged AP lymph nodes in patients with metastatic disease or in patients who are unfit to undergo video-assisted thoracoscopic surgery (VATS), thoracotomy, or median sternotomy so as to radically resect the tumor or the lung cancer and concurrently perform extended lymph nodes dissection. Although it is a minimally invasive procedure, it is done under general anesthesia and has specific contraindications and complications.

In a study, anterior mediastinotomy was successful at sampling one or more lymph nodes in 67% of patients. Five patients (4.3%) who underwent mediastinotomy were spared a thoracotomy by the identification of metastases to AP lymph nodes.[8] [level 4] When lymph nodes are accessible, EUS and EBUS are preferred because they are significantly less invasive and because they allow taking samples from more lymph node stations.[9] [Level 4]