Robotic Resection of Mediastinal Masses/Tumors
The mediastinum is the central compartment of the thoracic cavity, the area inside the ribcage. It is surrounded by connective tissue and contains all thoracic organs—the heart and its great blood vessels, the esophagus and trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus, and lymph nodes. The mediastinum lies between the lungs and the pleural cavities which surround them.
Anterior Mediastinal Masses
In the era of VATS and Robotic surgery the approach to the diagnosis and treatment of anterior mediastinal masses (those found in the middle section of the chest cavity) have undergone a significant change.
Traditionally to diagnose mediastinal masses, physicians would perform a transthoracic needle biospsy (TTNA) and an anterior mediastinotomy. Both techniques have a number of shortcomings.
Shortcoming of a thoracic needle biopsy include:
- Inability to provide adequate tissue sample for a meaningful diagnosis and appropriate subtyping of lymphoma
- Inability to differentiate lymphoma from thymoma
- Inability to differentiate a benign from an invasive thymoma
On the other hand, aside from the inherent risks of surgery, the anterior mediastonotomy approach suffers from:
- Inability to adequately visualize the surgical field due to a small "key hole" incision
- Risk of surgical complications resulting from inadequate exposure and visualization
- Delay in the application of radiotherapy following diagnos as it is necessary for the wound to heal prior to radiation
- Occasional incisional wound breakdown following radiation
- Need for a second definitive surgical procedure for certain types of anterior mediastinal masses
Video Assisted Thoracic Surgery and Robotic Thoracic Surgery
With the advent of Video Assisted Thoracic Surgery (VATS) and Robotic Thoracic Surgery, the formula for the diagnosis and treatment of mediastinal masses has changed.
The advantages of both approaches are:
- Minimally invasive videoendoscopic techniques provide adequate tissue samples for biopsy.
- Surgical removal can be accomplished in the same setting. The incisions are placed in the lateral chest wall away from the field of radiation.
- In patients with lymphoma there is no need to delay radiation therapy while waiting for the wound to heal.
It's not uncommon for a diagnosis of lymphoma to be suspected following a fine needle or core biopsy, but further tissue is required to confirm the diagnosis. Lymphoma is rarely localized solely to the mediastinum (middle section of the chest cavity). Occasionally a diagnosis of lymphoma will necessitate an open biopsy (transthoracic open biopsy of a mediastinal mass).
Given the fact that lymphoma is treated by nonsurgical means, and a simple biopsy is often all that is indicated, it is likely that most biopsies of large masses can be appropriately and successfully be accomplished laparoscopically.
The daVinci Robot may be a preferred surgical tool in the following instances:
- In the case in which a small mass extends into the left chest in which preservation of the phrenic nerve is a priority. The 3D magnified view together with the more precise dissection, may be advantageous in this area.
- For disease in the hilar areas of the mediastinum, which is more suited to the fine dissection and visualization achieved with the robot.
- In the case of a suspected recurrence in a previously treated chest, the robot would be preferred for dissection and biopsy.
In many instances, an ectopic parathyroid gland is situated in an area where it is difficult to remove. Previously surgical techniques to remove the gland included a median sternotomy, thoracotomy or video assisted thoracic surgery (VATS) approach.
Now thoracic surgeons at GW Hospital use the daVinci robot as it ideally suited to the fine dissection required to access the surgical site and remove the gland.
Depending on their exact location, these lesions may require dissection in difficult areas surrounded by such structures as the superior vena cava (SVC), innominate vein, phrenic nerve, aorta and pulmonary artery. Further complicating the situation, the lesion will likely be embedded in the adipose tissue of the mediastinum or the thymus, complicating visualization. Removal of the lesion is accomplished with intraoperative monitoring of parathyroid levels to ensure complete excision of the adenoma.
Thymectomy for Myasthenia Gravis
Myasthenia Gravis is an autoimmune disorder in which there is a defect in the transmission of nerve impulses to the muscles causing a weakness in the voluntary muscles.
The thymus gland is believed to play an integral in the pathogenesis of myasthenia gravis. Removal of the thymus (surgical thymectomy) is currently recommended for almost all patients with Myasthenia Gravis. It has been demonstrated that those patients who have the thymus gland removed, earlier in the course of their disease, tend to experience a relief from their symptoms, although sometimes 6-12 months after the actual surgery.
The younger patient and those with onlyocular myasthenia are often treated without surgery-at least initially. Similarly, the older patient with mild disease might also be treated without surgery. Any surgical procedure for MG should be designed to remove all thymic tissue. Current popular surgical approaches include a transsternal approach, a transcervical combined with a transsternal approach, a transcervical approach alone and lastly a Video Assisted Thoracic Surgery (VATS) approach.
Thymoma is a type of cancer that begins in the thymus. The thymus is a small organ located under the breastbone that makes white blood cells and is considered part of the lymphatic system. Thymomas can be either benign or malignant. Often, the distinction between a benign and a malignant thymoma is made during the actual surgery by assessing the degree to which the thymoma has invaded surrounding structures.
Many patients with a thymoma are asymptomatic. Approximately 10 to 15% of patients with Myasthenia Gravis will have a thymoma. About 30% of those patients diagnosed with a thymoma will have MG.
The goal of surgery is complete removal of the mass. Surgical approaches to removing a thymoma include a median sternotomy, clamshell incision and more recently Video Assisted Thoracic Surgery (VATS). The minimally invasive VATS procedure is reserved for early stage tumors. As experience with the daVinci robot is gained, a minimally invasive robotic approach to thymoma is considered appropriate for early stage lesions.
Should preoperative studies indicate that the lesion is invasive or malignant, surgeons will not attempt removal using minimally invasive techniques.
Germ Cell Tumors
These tumors may be divided into benign and malignant categories.
- Benign germ cell tumors: Includes teratomas and dermoid cysts. Diagnosed preoperatively, these cysts can be removed using the daVinci Robot. Removal would be similar to process described in thymectomy (above).
- Malignant germ cell tumors: Includes seminomas and nonseminomatous tumors. In the majority of cases, these types of tumors are treated non-surgically. Seminomas are usually treated with radiation. Nonseminomatous tumors are treated with chemotherapy (includes immature teratomas, choriocarcinomas, embryonal cell carcinomas, yolk sac tumors and mixed germ cell tumors).
In the unusual case that a malignant tumor is managed surgically, minimally invasive surgical approaches are not considered suitable and an open procedure would need to be performed.
Lymphadenectomy consists of the surgical removal of one or more groups of lymph nodes and is almost always performed as part of the surgical management of cancer.
In certain clinical circumstances, a mediastinal lymphadenectomy or biopsy would be recommended. This includes lymph nodes that are diseases or enlarged for unknown reasons such as possible sarcoid, lymphoma or metastatic disease from lung cancer or other malignancies.
Robotic surgery is ideally suited to dissection and biopsy of both mediastinal and hilar lymph nodes. The latter may be particularly difficult to biopsy through a Video Assisted Thoracic Surgery technique.
Posterior Mediastinal Masses
In both adults and children, the majority of posterior mediastinal masses start with the nerves or the nervous system (neurogenic origin). Most of these masses in adults (95%) are benign and are usually asymptomatic. On the other hand, the majority of neurogenic tumors in children are malignant. Neurogenic tumors may arise from intercostals nerves (neurofibroma, neurilemoma and neurosarcoma), sympathetic ganglia (ganglioma, ganglioneuroblastoma and neuroblastoma) or paraganglia cells (paraganglioma).
A CT scan is usually sufficient for diagnosing neurogenic tumors, although any possibility of intraspinal extension should be evaluated with a MRI.
Preoperative biopsy in an adult is usually not indicated unless the tumor displays unusual characteristics and a malignant tumor is likely.
Although a combined Video Assisted Thoracic Surgery and neurosurgical approach has been described for dumbbell tumors, we have excluded these tumors currently from a robotic approach.
These cysts are the most common cysts of the mediastinum. Bronchogenic cysts form during fetal development and consist of small pockets lined with respiratory epithelium, which is characterized by the presence of small hair like structures called cilia. Cysts can be found around the trachea, lungs, and upper area of the sternum. They may also be located within the pulmonary parenchyma. While most patients are likely to be asymptomatic, there is a possibility of infection within the cysts or compression of the esophagus, trachea or bronchi. For most people, a bronchogenic cyst poses no threat. However in some adults bronchogenic cysts sometimes rupture, leading to infection, and they have also been linked with some cases of obstructive pneumonia.
Surgical removal is indicated in all cases to confirm the diagnosis, to alleviate any symptoms and to prevent complications. However, if a patient is not a good candidate for surgery, the doctor may recommend a wait and see approach to see if the cyst can be managed without surgery.
Malignant transformation has rarely been described. These cysts may adhere to surrounding tissue and complete removal of the tumor is not always possible.
The second most common type of mediatinal cysts, pericardial cysts are cysts formed in the fluid filled sac that surrounds the heart—the pericardium. These cysts have been described as‚ "spring water cysts‚" due to their clear fluid content.
Patients are usually asymptomatic. If a cyst is diagnosed incidentally, observation or simple aspiration is the initial treatment of choice. Should these cysts recur following aspiration or should the diagnosis be questionable, then surgical removal is recommended.