Technique of Thoracoscopic Resection of Posterior Mediastinal Tumors

Abstract

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.