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Technique of Thoracoscopic Resection of Posterior Mediastinal Tumors

  • Michael F. Reed
    Correspondence
    Address reprint requests to Michael F. Reed, MD, Penn State Milton S. Hershey Medical Center, Penn State College of Medicine, Heart and Vascular Institute, 500 University Drive, H165, Hershey, PA 17033
    Affiliations
    Penn State Milton S. Hershey Medical Center, Penn State College of Medicine, Heart and Vascular Institute, Hershey, Pennsylvania
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      Tumors of the posterior mediastinum, located in the paravertebral sulcus, account for about 25% of all mediastinal tumors. They are typically related to the sympathetic chain or the rami of intercostal nerves. Mediastinal neurogenic tumors are among the more frequent mediastinal masses seen in adults. Although they are often malignant in children, over 90% are benign in the adult population. Surgical resection is usually indicated.
      Posterior mediastinal tumors are frequently nerve-related neoplasms. Neurogenic tumors originate from embryonal neural crest cells, which constitute the ganglia, paraganglionic, and parasympathetic systems. Nerve sheath tumors are the most common posterior, paravertebral tumors, accounting for 40 to 60% of all neurogenic tumors. Approximately 10% have spinal canal involvement (“dumbbell” or “hourglass” tumors), thus impacting the approach to resection. Nerve sheath tumors commonly originate from Schwann cells of intercostal nerves. Although almost always benign, malignant degeneration may rarely occur. Neurofibromas also arise from peripheral nerves, with 30 to 40% of neurofibromas occurring in the setting of neurofibromatosis. Multiple tumors may occur in these individuals. The patients with von Recklinghausen's disease frequently present at a younger age and have a higher risk of malignancy.
      Ganglioneuromas and ganglioneuroblastomas arise from sympathetic ganglion nerve cells. Although ganglioneuromas are benign, they tend to adhere to adjacent structures, making resection more challenging than with schwannomas. This is the most frequent benign neurogenic tumor in children. In contradistinction to ganglioneuromas, neuroblastomas frequently metastasize.
      Most posterior mediastinal neurogenic tumors are benign, slow growing, and asymptomatic. They may be present for a long period of time before diagnosis. However, with growth, they can produce symptoms by local compression of adjacent tissue, bone erosion, and spinal canal involvement. Large intrathoracic tumors may produce dyspnea, pain, and cough. Neurologic deficits may also occur. Spinal cord compression from dumbbell tumors may cause abnormal gait, urinary and fecal incontinence, and loss of sensation below the lesion. Radicular pain at the level of the tumor may present with a dermatomal distribution. Occasionally a high thoracic tumor may result in Horner's syndrome.
      Currently, most posterior mediastinal tumors are identified incidentally, often on plain chest radiography obtained for other, unrelated indications. Chest computed tomography is indicated to effectively demonstrate size, location, and relationship to adjacent structures. Tumors of nerve sheath origin are typically smooth, spherical, solitary, and discrete. They usually abut vertebral bodies. In the setting of neurofibromatosis, they may be multifocal and appear lobulated. In contrast, tumors of autonomic ganglion (nerve cell) origin may be less circumscribed and often are oblong. Bony changes related to pressure or erosion may be present. Occasionally magnetic resonance imaging (MRI) may be useful for evaluating proximity to the neural foramen (Fig. 1) and for determining spinal cord involvement with dumbbell tumors. Percutaneous biopsy is not required for most posterior mediastinal neurogenic tumors because radiographic diagnosis is sufficient to mandate resection. Observation of posterior mediastinal tumors is rarely appropriate, unless the patient is at prohibitively high risk for thoracoscopic surgery due to significant medical comorbidities. Surgical resection simultaneously provides both diagnosis and therapy. Moreover, permitting growth may result in expansion of the tumor into the neural foramen, requiring a more complex multistage operation involving both posterior and anterior approaches.
      Dumbbell tumors possess both an intrathoracic and an intraspinal component. Surgery requires exposure of the pleural space and the spinal canal. A number of open approaches are feasible, including a lateral extracavitary approach as well as a combined anterior and posterior approach using thoracotomy for pleural exposure. However, video-assisted thoracoscopic surgery (VATS) offers equivalent pleural exposure, avoiding the side effects of thoracotomy. For these patients, a collaborative strategy involving neurosurgical or orthopedic spine surgeons with thoracic surgeons will optimize safe preoperative planning.
      Due to their frequently benign nature and relatively small size, posterior mediastinal neurogenic tumors are particularly amenable to resection using a minimally invasive, thoracoscopic technique. Indeed, as VATS was gaining wider acceptance in the early 1990s, one of its earlier applications was removal of posterior mediastinal tumors.
      • Landreneau R.J.
      • Dowling R.D.
      • Ferson P.F.
      Thoracoscopic resection of a posterior mediastinal neurogenic tumor.
      Thoracoscopic resection remains ideal for all but the very large tumors. Compared with thoracotomy, VATS allows an equivalent intrathoracic operation with the same resection margin. As with other VATS procedures, this minimally invasive approach results in diminished postoperative pain, fewer complications, shorter length of stay, and more rapid return to normal functional status.

      Operative Technique

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      Figure 1MRI demonstrates that this left posterior mediastinal neurogenic tumor abuts the vertebral body, but does not invade the intervertebral foramen. (A) Axial view; (B) coronal view; (C) sagittal view. Pathologic analysis demonstrated a schwannoma.
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      Figure 2After the induction of general anesthesia, a double lumen endotracheal tube is inserted and its position is verified bronchoscopically. Alternatively, a bronchial blocker may be utilized to achieve single-lung ventilation. The patient is then placed in the lateral decubitus position. Proper positioning of the patient is critical to preventing certain complications.
      • Reed M.F.
      Thoracic incisions.
      The operating table flexion point is located between the iliac crest and the costal margin. The arms are extended, but shoulder hyperextension greater than 90° must be avoided to prevent brachial plexus neuropathy. The upper arm is supported with pillows or a padded armrest, ensuring that both ulnar nerves are protected from pressure damage. The operating table is flexed to widen the intercostal spaces on the operative side, a simple maneuver that may diminish postoperative pain. Either soft rolls or a beanbag is used to secure the patient on the table. The patient is draped as for standard posterolateral thoracotomy.
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      Figure 3The lung and the diaphragm can inhibit adequate visualization of the paravertebral sulcus. To improve exposure, the patient can be rotated anteriorly, thereby allowing gravity to move the lung away from the posterior mediastinum. For inferior tumors, the reverse Trendelenburg position may permit the diaphragm to drop away from the tumor, thus further increasing exposure. The surgeon stands at the patient's front. The assistant may also stand at the patient's front because instrumentation is directed posteriorly.
      Figure thumbnail gr4
      Figure 4VATS allows operative exposure using small incisions. Even when a limited utility incision is required, no rib spreading occurs. As with thoracotomy, morbidity is related to intercostal nerve trauma. During VATS, intercostal nerve injury can be minimized by using the smallest port that is feasible, depending on the necessary instrumentation. An angled, usually 30°, thoracoscope can be used to diminish pressure on the nerve. Port insertion should be directed toward the intrathoracic region where the majority of the surgery will occur to avoid using the inferior edge of a rib as a fulcrum for the camera when attempting visualization at awkward angles. Typically 3 port sites are chosen. Long-acting local anesthetic, such as bupivacaine, can be injected into the first planned port site, anesthetizing the intercostal nerve. Before subsequent port insertion, each site can be injected with local anesthetic using thoracoscopic visualization to verify medication delivery in the extrapleural plane. The first port is typically placed at the anterior axillary line. For higher tumors, this port is located at the fourth or fifth intercostal space. For lower tumors, the first port can be placed in the sixth or seventh intercostal space. Two additional ports are inserted, placed at a sufficient distance from each other, triangulating the ports, to facilitate best instrument conversion on the target without interfering with each other (“swordfighting”). The ports can be used interchangeably as needed. If the lung or diaphragm interferes with exposure, a fourth port can be placed for a retractor. Additionally, low pressure insufflation can be used to more rapidly achieve pulmonary atelectasis and to push the diaphragm inferiorly. When insufflating, attention should be directed toward hemodynamics, although instability is rare with low insufflation pressure.
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      Figure 5The tumor is identified and potential involvement of adjacent structures is assessed. Proximity to the neural foramen is verified. Most benign tumors are not invasive and can be mobilized thoracoscopically in a straightforward manner. Dissection may be performed with electrocautery, except when close to critical neural structures such as the phrenic nerve, recurrent laryngeal nerve, and stellate ganglion. Alternatively, ultrasonic shears can be utilized. The pleura is incised circumferentially around the tumor, allowing a reasonable edge to achieve an adequate margin. Furthermore, the rim of normal pleura can be used for grasping to facilitate retraction. Additional retraction can be achieved by gently manipulating the tumor with a blunt-tipped instrument. Dissection is continued to expose the base of the lesion and then to develop a well-defined plane between the lesion and the prevertebral fascia.
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      Figure 6The pleura overlying the tumor may have increased vascularity. Intercostal vessels may also require division. Additionally, radicular vessels are present in a random distribution, with some entering intervertebral foramina. When possible, they should be preserved, although resection of dumbbell tumors frequently requires their sacrifice. Hemostasis is maintained with electrocautery for smaller blood vessels. Larger vessels should be controlled with endoscopic clips.
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      Figure 7After the tumor has been completely excised, it is placed in an endoscopic bag to minimize the risk of seeding the tract with tumor cells. Also, if the tumor is fractured during removal, the pleural space will not be contaminated with tumor cells. The bag is brought through one of the port sites. Typically, it should be removed through the most inferior and anterior port because the intercostal spaces are wider at this location. Frequently the port incision needs to be slightly enlarged, carefully limiting trauma to the intercostal nerve, to withdraw the specimen through the chest wall. Even with larger tumors, rib spreading should be avoided because that negates much of the benefit of VATS.
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      Figure 8Multimodal analgesic strategies should be employed for minimally invasive thoracoscopic surgery, as for thoracotomy. With shorter lengths of stay and less acute pain, thoracic epidural anesthesia is less frequently required for VATS procedures. However, it should be considered in patients at increased risk of severe postoperative pain, pulmonary dysfunction, or postthoracotomy pain syndrome. For most patients undergoing VATS, other regional analgesic strategies can be applied. The intercostal nerve at port sites can be locally anesthetized and multilevel injection may achieve intercostal nerve blockade. Long-acting local anesthetic such as 0.25% bupivacaine can be injected using thoracoscopic visualization. The needle is placed percutaneously and is carefully advanced into the intercostal space, avoiding injury to the vessels. With the needle tip in the extrapleural plane, approximately 2 mL can be injected, thereby raising a pleural bubble. By placing intercostal blocks from at least 1 level above the highest port site, to at least 1 level below the most inferior port site, effective analgesia can be achieved during the early postoperative period. Additional analgesia can be achieved using continuous catheter infusion of local anesthetic into the paravertebral extrapleural space, providing multilevel intercostal nerve blockade. Patients can be safely discharged with the continuous infusion apparatus in place.
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      Figure 9The spinal cord and the proximal portion of the emerging nerve roots are located in the spinal canal. The nerve roots traverse the intervertebral foramina, formed cephalad and caudad by the pedicles, posteriorly by the superior and inferior articular facets, and anteriorly by the vertebral bodies and intervertebral discs. (A) The term dumbbell refers to the shape of the tumor with intrathoracic and intraspinal components connected by a narrow waist at the intervertebral foramen. (B) Attempted transthoracic resection without exposure of the spinal canal can result in traction on the tumor and subsequent hemorrhage in the spinal canal, resulting in devastating neurologic injury. Cerebrospinal fluid leaks can also be a complication. Additionally, incomplete excision of tumor in the canal is associated with recurrence, often manifesting with neurologic deficits. A thoracoscopic approach is feasible for dumbbell tumors. A 2-stage operation in a single setting is most appropriate.
      • Vallieres E.
      • Findlay J.M.
      • Fraser R.E.
      Combined microsurgical and thoracoscopic removal of neurogenic dumbbell tumors.
      The intraspinal portion of the tumor is excised first by the neurosurgeon or orthopedic spine surgeon. (C) With the patient prone, a vertical midline incision is created over the spinous processes, centered at the level of the involved intervertebral foramen. Laminectomy with extensive foraminal enlargement is then performed. The nerve root is divided at its medial attachment to the tumor. After resection, the dura is closed; the foramen is sealed to prevent spinal fluid leak, and the posterior incision is closed. The patient is then repositioned to lateral decubitus and the thoracic surgeon achieves thoracoscopic completion of the resection.

      Conclusions

      Surgical resection is the ideal treatment for posterior mediastinal neurogenic tumors. Benign neurogenic tumors rarely recur and no adjuvant therapy is required. Minimally invasive resection with thoracoscopic techniques is safe. Standard risks of thoracic surgery, including bleeding, infection, and pulmonary complications, are rare. The risks specific to resection of neurogenic tumors are related to nerve injury. Deficits such as Horner's syndrome, partial sympathectomy, recurrent laryngeal nerve injury, and phrenic nerve injury are possible when the tumors originate from these specific nerves. Many of these complications can be avoided by precise identification of the specific neurologic structures and avoidance of electrocautery when dissecting in close proximity to them.
      For benign posterior mediastinal lesions, complete resection is typically achieved with a thoracoscopic strategy. Minimally invasive resection is not usually indicated when an invasive malignant tumor is identified preoperatively. In this setting, resection of adjacent bony structures is often required, typically negating the benefits of VATS.
      Dumbbell tumors are amenable to VATS resection. When an intraspinal component is clearly compressing the cord, a combined posterior and anterior approach is indicated to achieve negative margins. Even when slight intraforaminal involvement is present, based on computed tomography and MRI, a combined thoracic surgery and spinal surgery approach is safest. Resection of the posterior mediastinal neurogenic tumor with intraforaminal involvement, while relying only on VATS exposure, or even thoracotomy alone, may require excessive retraction of the mass. Potential undetected hemorrhage in the spinal canal can result in devastating neurologic sequelae.
      Thoracoscopic resection of posterior mediastinal tumors results in shorter duration of the operation, compared with the open approach. This is primarily due to avoidance of the time required to open and close a thoracotomy. As with numerous other thoracic procedures, the adoption of VATS techniques for resection of posterior mediastinal neurogenic tumors is associated with diminished postoperative morbidity, including shorter length of stay, less pain, better shoulder function, fewer pulmonary complications, and more rapid return to normal functional status.
      • McKenna Jr, R.J.
      • Houck W.
      • Fuller C.B.
      Video-assisted thoracic surgery lobectomy: experience with 1,100 cases.
      It is the preferred approach for the resection of benign posterior mediastinal tumors, including dumbbell tumors. Thoracotomy is reserved for very large tumors, in which rib spreading would be required for removal through the chest wall, as well as for patients with significant adhesions from prior ipsilateral thoracic surgery or pleural intervention.

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