ANATOMY
Depending on the classification used, the posterior compartment of the mediastinum includes the following structures found from the posterior pericardium to and including the thoracic spine and para-spinal gutters ( Fig. 44-1 ).
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Vertebral bodies
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Sympathetic chains
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Descending aorta
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Esophagus
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Azygous and hemiazygous veins
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Thoracic duct
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Posterior mediastinal lymph nodes
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Lower portion of the vagus nerve
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Fat
INTRODUCTION TO THE POSTERIOR MEDIASTINUM
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This section describes masses in the posterior mediastinum, with special emphasis on the more commonly encountered lesions ( Table 44-1 ).
TABLE 44-1 ▪
POSTERIOR MEDIASTINAL MASSES
Neurogenic Tumors
Nerve sheath tumors
Schwannoma (neurilemmoma)
Neurofibroma
Malignant nerve sheath tumors
Autonomic ganglion cell tumors
Ganglioneuroma
Ganglioneuroblastoma
Neuroblastoma
Paraganglionic tumors
Paragangliomas
Pheochromocytoma
Chemodectoma
Infectious Paraspinal Masses
Infectious paraspinal abscess
Tuberculosis (Pott’s disease)
Pyogenic bacterial infections
Fungal infections
Hematologic Disorders
Extramedullary hematopoiesis
Mediastinal Cysts
Lateral thoracic meningocele
Esophageal Masses
Benign esophageal tumors
Malignant esophageal tumors
Esophageal duplication cyst
Esophageal disorders
Hernia (e.g., Bochdalek diaphragmatic hernia)
Achalasia
Rare Presentations of Posterior Mediastinal Masses
Sarcomas (osteosarcoma, chondrosarcoma)
Other mesenchymal tumors (lipomas, fibromas, xanthogranulomas, leiomyomas, mesenchymomas, mesotheliomas, benign fibrous tumors)
Carcinoma: metastatic; rare primary
Lymphoma and other lymph node disorders
Germ cell tumors
Hemangioma
Lymphangioma
Thoracic duct cyst
Vascular (aortic aneurysm; dilated azygous or hemiazygous vein; varices)
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The differential diagnosis of posterior mediastinal masses spans multiple disciplines.
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Hematology/oncology
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Infectious diseases
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Neurology
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Neurosurgery
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Pulmonology
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Rheumatology
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Thoracic surgery
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Other specialties
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The aim of this chapter is to enable the clinician to provide a rational differential diagnosis for posterior mediastinal masses and to initiate an appropriate workup.
PRINCIPLES OF WORKUP
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Demographics
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This chapter identifies differences between pediatric and adult populations.
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Symptoms and signs
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Incidental findings (asymptomatic)
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Constitutional or systemic features (such as fever and weight loss)
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Cough
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Site-specific symptoms such as chest or back pain
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Neurologic symptoms and signs
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Other disease-specific features
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Imaging
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Plain radiographs
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May show features of a mass compatible with a posterior mediastinal location
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May include alterations of visibility of mediastinal structures or displacement of mediastinal lines/interfaces (e.g., paraspinal lines)
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Computed tomography (CT) scan is key to demonstrate the presence of a mass, along with its characteristics and location.
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Magnetic resonance imaging (MRI) scan is better than CT scan for assessment of the extension of neurogenic tumors into neural foramina or cord compression.
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Other imaging studies, including positron emission tomography (PET) or other radionuclide studies, are rarely indicated.
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Biochemical markers
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Tumor markers
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Urinary catecholamines for paraganglionic masses
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Tissue diagnosis
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The utility of fine-needle biopsy is unclear and likely not helpful for most posterior mediastinal masses. May be used to aspirate presumed benign cystic lesions (e.g., pericardial cyst). However, these are rarely posterior mediastinal in location.
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Complete surgical excision of a localized mass usually confirms the presence of a benign lesion.
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Limited surgical biopsy via thoracoscopy or open approaches may be warranted for workup of complex cases, especially when the primary treatment is not surgical. Examples include lymphoma or germ cell tumors that are not easily biopsied in a less invasive fashion. Such lesions are rare in the posterior mediastinum.
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SPECIFIC MASSES OF THE POSTERIOR MEDIASTINUM
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Neurogenic tumors
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Derived from neural crest tissue
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Asymptomatic tumors are often detected as an incidental finding on an unrelated imaging test.
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Three quarters of neurogenic tumors are benign.
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Neurogenic tumors make up 20% adult mediastinal tumors.
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Neurogenic tumors make up 25% to 35% of pediatric mediastinal tumors.
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Neurogenic tumors make up 75% of primary posterior mediastinal tumors.
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Nearly all mediastinal neurogenic tumors are located in the posterior mediastinum (90%–95%).
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Nerve sheath tumors are more common in adults and are usually benign.
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Ganglion tumors are more common in children and often are malignant.
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In adults, the ratio of schwannomas to neurofibromas is 3:1 to 4:1.
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Nerve Sheath–Related Tumors
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Schwannomas (neurilemmomas)
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Pathology
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Arise from the nerve sheath of spinal nerve roots of the intercostals or sympathetic nerves
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Found in any thoracic location
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They are rarely malignant.
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May erode bone locally and compress nerves
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Generally appear as a lobulated mass encapsulated and containing varying numbers of Schwann cells and myxoid tissue.
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May exhibit cystic degeneration or hemorrhage
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Fibroblasts and mast cells are often contained in the tumor mass.
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Demographics
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Affect men and women equally
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Age: 30 to 50 years
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Clinical features
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Majority of schwannomas are asymptomatic
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Compression symptoms can occur including
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Pain (more typical in malignant tumors)
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Paresthesias
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Neurologic deficits (e.g., with intraspinal extension)
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Imaging
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Spherical, with smooth or lobulated borders
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Variable size, but potentially large when asymptomatic
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May extend horizontally along nerve axis
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May span one to two rib spaces
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May erode adjacent ribs or vertebra
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Variable appearance on CT scans
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May show reduced attenuation more consistent with fat or fluid
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Occasionally show punctuate calcifications (10%)
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May have contrast enhancement
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MRI scan with gadolinium (T1 and T2) may be useful to evaluate neural foramina extension.
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When extending into the spinal canal Schwannomas form a dumbbell or hourglass shape in less than 10% of cases ( Figs. 44-2 and 44-3 ).
Figure 44-2
Posteroanterior ( A ) and lateral chest radiograph ( B ) showing posterior mediastinal mass (nerve sheath tumor; schwannoma).
Figure 44-3
A, Computed tomography scan of chest depicting nerve sheath tumor with extension into the spinal foramen (dumbbell tumor). B, Transaxial magnetic resonance imaging (MRI) scan depicting the same. C, MRI coronal view with clear depiction of dumbbell shape and intraspinal extension.
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Management
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Such tumors often require combined thoracic surgical and neurosurgical intervention because removal of only the thoracic component of the tumor can compress the spine and cause paralysis (see later).
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Neurofibromas
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Pathology
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Nonencapsulated
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Well-marginated and lobulated like schwannomas
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Homogenous collection of myelinated and/or unmyelinated nerve elements, nerve sheath cells, fibroblasts, and matrix
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May exhibit cystic degeneration
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One variant, plexiform neurofibroma, may involve entire nerve trunks or plexi.
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Risk of malignant transformation
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Five percent of lesions undergo malignant transformation in adults.
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Much higher malignant transformation rates in children
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Demographics
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Equal male-to-female ratio
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Usually present in 3rd to 4th decades
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Thirty to forty-five percent of cases occurring in the setting of neurofibromatosis.
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Clinical features
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Commonly asymptomatic
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May exhibit features of neurofibromatosis (see below)
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Multiple neurofibromas or a single plexiform lesion are criteria for neurofibromatosis, a common disease.
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Pain at presentation increases the likelihood of malignant transformation.
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Compressive symptoms can be observed, as in cases of schwannomas.
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Recurrence and malignancy rates are higher in the setting of neurofibromatosis (10% lifetime hazard).
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Imaging
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Similar to schwannoma
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In comparison with schwannoma, neurofibromas are less commonly calcified and more homogeneous in contrast enhancement
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Malignant degeneration may be associated with pulmonary nodules or with pleural effusion.
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Neurofibromatosis
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Neurofibromatosis 1 (NF1) accounts for 85% of cases.
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Autosomal dominant genetic disorder
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1:3000 individuals
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Fifty percent are familial; 50% are acquired mutations.
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Clinical criteria include
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Café-au-lait macules
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Neurofibromas
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Axillary/inguinal freckling
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Optic gliomas
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Lisch nodules (iris hamartomas)
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Sphenoid dysplasia or thinning of long bone cortex
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Pseudarthroses
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First-degree relative with NF1
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Share abnormalities of chromosome 17q11
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Meningiomas, neurilemmomas, and neurosarcomas (in children) have been associated with neurofibromatosis.
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Treatment considerations of nerve sheath tumors
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Prognosis
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For benign neurogenic tumors, prognosis with surgery is excellent.
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By contrast, the outcome remains poor with malignant tumors, despite aggressive treatment measures.
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Surgical removal is routinely recommended.
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Tumors will slowly increase in size, with resultant compressive or neurologic signs and symptoms.
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Surgical removal can rule out malignancy.
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Video-assisted thoracic surgery (VATS) has replaced the posterolateral thoracotomy approach as the preferred operative approach.
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Relative contraindications to VATS
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Tumors greater than 6 cm in size
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Paragangliomas, owing to their vascularity
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Dumbbell tumors may be amenable to a combined approach.
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Posterior laminectomy, initially
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Thoracoscopic resection, subsequently
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Invasion of foramina or vertebral body
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En bloc resection may be feasible in some cases
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Plexiform neurofibromas
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Frequently infiltrate or invade a trunk or nerve plexus.
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Complete excision is not usually possible.
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Malignant nerve sheath tumors
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Complete surgical removal is the procedure of choice.
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For unresectable or incomplete resections, chemotherapy and radiotherapy are considerations, although response rates are not high.
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Prognosis is poor.
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Surgical complications
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Partial sympathectomy
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Horner’s syndrome
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Paraplegia
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Recurrent laryngeal nerve injury
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Malignant tumors of nerve sheath origin .
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Pathology
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Spindle cell sarcomas
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Malignant neurofibroma
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Neurogenic fibrosarcoma
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Rare, malignant schwannoma
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May arise from neurofibromas
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50% associated with NF1
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Sporadic or associated with risk factors such as radiation
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Originate in isolated or plexigenic neurofibroma
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Usually cellular, high-grade sarcomas
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Demographics
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Male and female equal prevalence
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3rd to 5th decades
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Clinical features
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Signs of neurofibromatosis may be present.
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More likely to have symptoms and signs of nerve or vertebral compression
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Metastases most frequently to the lung
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Imaging
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Often large in size (e.g.,>5 cm) but well circumscribed
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CT appearance
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Heterogeneous appearance
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Necrosis and/or hemorrhage are characteristic of malignant lesions.
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Compression/invasion of adjacent structures may be noted.
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Treatment
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Complete surgical excision with wide tumor free margins is the treatment of choice.
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When complete excision is not possible
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Simple excision
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High-dose radiation
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The role of chemotherapy has not been well defined.
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Adjuvant chemotherapy may not add benefit.
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Survival is poor.
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Less than 35% 5-year survival
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SYMPATHETIC GANGLION TUMORS
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General considerations
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Rare tumors
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Subtypes
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Neuroblastoma (more than 95% of cases)
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Ganglioneuroblastoma
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Paraganglioma (often considered with above)
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Range in behavior
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Benign (ganglioneuroma)
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Aggressive (metastatic neuroblastoma)
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Sympathetic ganglion cell tumors may represent a continuum.
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Origins
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Neuronal primordial neural crest cells
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Adrenals (50% neuroblastoma)
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In general, rare tumors
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Neuroblastoma
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Pathology
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Nonencapsulated elongated mass with varying degree of necrosis, cystic degeneration, and hemorrhage
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Sheets of small round cells
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Locally invasive or metastatic, or both
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Demographics
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Children younger than 5 years; most younger than 3 years
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No gender bias
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Clinical features
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General malaise and weight loss
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Symptoms attributable to metastatic disease in two thirds
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Pain
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Neurologic deficits, weakness, paralysis, ataxia
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Horner’s syndrome
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Ptosis, pupillary miosis, and facial anhidrosis
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Arises from injury to stellate ganglion and T1
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This affects the oculosympathetic pathway
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May result from tumor compression or infiltration
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Respiratory compromise
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Paraneoplastic syndrome
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Catecholamines (hypertension, flushing)
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Vasoactive intestinal peptide (abdominal pain and watery diarrhea)
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Psoclonus-polymyoclonus ataxia (cerebellar and truncal ataxia, and bouncing eye movements)
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Imaging
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Typically elongated heterogeneous paraspinal mass (necrosis and hemorrhage)
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Often extends across midline
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Local compression/invasion
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Calcification usually evident: more than 85% on CT; 10% plain films; fine
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MRI scan again modality of choice for intraspinal extension
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Treatment is determined by disease stage.
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Stage 1: Complete macroscopic removal of tumor is indicated for limited disease
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Stage 2: (local invasion) surgery plus postoperative chemotherapy and radiation
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Stage 3: (extension across the midline plus regional lymph node involvement) surgery plus postoperative chemotherapy and radiation
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Stage 4 (metastatic disease): chemotherapy and radiation. Surgery is controversial and may have limited value if a good response to chemotherapy.
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In high-risk cases, surgery, chemotherapy, and blood stem cell transplantation have been performed.
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Prognosis
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Poor prognostic features include
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Late stage
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Older patient
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Poorly differentiated
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Large tumor size
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Extrathoracic origin
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Stages
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Stages 1, 2, and 4S (stage 1 or 2 with metastasis to liver, skin or bone marrow): 75% to 90% 3-year event-free survival (EFS)
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Stage 3: younger than 1 year of age; similar to stage 1 and 2; older than 1 year of age: 50% 3-year EFS
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Stage 4: younger than 1 year of age: 60% to 75% 3-year EFS; older than 1 year of age: 15% 3-year EFS
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Ganglioneuromas
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Pathology
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Encapsulated
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Clusters of ganglion cells and matrix
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Demographics
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Afflicted children older than 3 years of age; adolescents and adults in the second to third decade
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No gender bias
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Clinical features
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Asymptomatic in 50%
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Symptoms associated with local compression or intra spinal extension possible
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Imaging
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Typically elongated, well-marginated tumors that extend vertically along the anterolateral aspect of the spin. May extend across three to five vertebrae.
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Coarse calcification may be evident
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Benign pressure erosion of vertebrae may be evident
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MRI scan modality of choice for intraspinal extension
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Treatment
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Complete surgical resection
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Tumors with intraspinal extension require combined thoracic and neurosurgical procedures.
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Prognosis excellent with surgical resection alone
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Ganglioneuroblastomas
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Pathology
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Exhibit histologic features of ganglioneuroma and neuroblastoma
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Falls between ganglioneuromas and neuroblastoma in terms of differentiation and invasiveness.
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Varying admixture of ganglion and neuroblast cells
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Demographics
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Presents mainly in children younger than 10 years of age
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No gender bias
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Least common neurogenic tumor
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Clinical features
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Can be asymptomatic
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Symptoms due to compression, intraspinal extension, or local invasion
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Can exhibit metastatic disease
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Imaging
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Typically elongated and extend vertically
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Coarse calcification may be evident
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Again, MRI scan is the modality of choice for intraspinal extension.
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Treatment
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Therapy is often based on histologic pattern.
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Some subtypes have promising prognosis with surgical resection.
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Others require chemotherapy based on histology, age, and stage of disease.
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Paraganglionic tumors
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Pathology
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Vascular tumors arising from aorticosympathetic paraganglia and vagus nerve.
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Histology shows amine precursor uptake and decarboxylation (APUD) cells and vascular spaces
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Rare tumors, often termed extra-adrenal pheochromocytomas.
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Usually occur in paravertebral sulcus but may be found in the brachial arch of the middle mediastinum.
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Ten percent of patients have multiple paragangliomas.
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Demographics
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Uncommon in children; usually appear 2nd to 3rd decade.
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Male-to-female ratio is 2:1.
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Infrequent chemodectomas are reported in patients older than 40.
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Clinical
- ▪
Can present with symptoms and signs of catecholamine excess (e.g., flushing, headaches, hypertension refractory to medical management, anxiety, etc.). Incidence of 48% in a case series of 31 patients
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Locally invasive with neurologic signs in 5 of 31 patients
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Metastatic disease in 2 of 31 patients
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As many as 50% hereditary lesions associated with
- ○
Familial paraganglioma
- ○
NF1 or von Hippel–Lindau disease.
- ○
Carney’s triad (paraganglioma, pulmonary chondroma, and gastric leiomyoscarcoma).
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Multiple endocrine neoplasia (MEN) type 2 syndrome
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Imaging/investigations
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CT and MR: avid homogeneous contrast enhancement
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PET: may show uptake
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I 123 metaiodobenzylguanidine (MIBG) radionuclide scan: MIBG radionuclide study is positive in 70% of patients.
- ▪
Biochemical: document catecholamine and fractionated metanephrine hypersecretion before imaging
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- ○
Treatment
- ▪
Complete surgical excision, usually by thoracotomy
- ○
These are bloody tumors, and there may be less manipulation with an open procedure.
- ○
The aim is to release less catecholamines and maintain better hemodynamic control
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- ▪
Need preoperative catecholamine blockage
- ○
Alpha blockade with phenoxybenzamine is the first-line treatment, although few controlled trials have been reported.
- ○
Nonselective beta blockade for epinephrine secreting tumors only after alpha blockade
- ○
Beta blockade without alpha blockade runs risk of accelerated hypertension due to unopposed alpha as well as beta-blocker related vasospasm
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- ▪
Locally invasive and metastatic disease
- ○
I 131 MIBG with or without combination chemotherapy
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- ○
OTHER EXTRADURAL TUMORS
- ▪
Metastatic disease
- ○
Most spinal malignancies are located extradurally.
- ○
These are usually metastatic
- ▪
In metastatic cancer, vertebral metastases are commonly found at autopsy.
- ▪
Prostate, breast and lung cancer are common cancers metastasizing to the vertebra.
- ▪
- ○
Most of these tumors arise from the vertebral body.
- ○
Symptoms usually result from epidural extension.
- ▪
Constant pain
- ▪
Night-time awakenings
- ▪
Distal sensory deficits
- ▪
Muscular weakness
- ▪
Paralysis
- ▪
- ○
Extradural tumors can cause spinal cord compression by intradural invasion.
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- ▪
Sarcomas
- ○
Most arise from mesenchymal components and erode into bone.
- ▪
Osteosarcoma
- ○
Ten to fifteen percent of sarcomas in general
- ○
Can be seen in 1% of patients with Paget’s disease.
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- ▪
Chondrosarcoma
- ○
Most common malignant tumor of the chest wall
- ○
Twenty percent of all bone tumors
- ○
Seen in third and fourth decades
- ○
May represent malignant conversion of benign tumors
- ○
More typically found in the anterior costochondral region
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- ▪
Ewing’s sarcoma (ES)
- ○
Rare in this anatomic location; typically extremities
- ○
Fewer than 5% of cases in adults older than 40
- ○
Part of Ewing’s sarcoma family of tumors (EFT); neuroectodermal origin likely, related to neuroblastoma
- ○
Arise from spine, paravertebral area, or even chest wall; extraosseous ES more typically found in these regions
- ○
Generally, treatment is chemotherapy.
- ○
- ▪
Leiomyosarcoma—rare
- ▪
Chordoma
- ○
Rare
- ○
Originate from primitive notochord
- ○
Highly resistant to radiation
- ○
Notable for recurrence at surgical sites.
- ○
- ▪
- ○
- ▪
Primary carcinoma
- ○
Accounts for a minority of mediastinal masses
- ○
Large cell, undifferentiated tumors are most common but still rare presentation
- ○
PRIMARY CYST
- ▪
Lateral thoracic meningocele
- ○
Rare
- ○
Cyst containing cerebrospinal fluid and neural tissue that herniates through spinal foramina. Wall of cyst is made of dural tissue.
- ○
Majority associated with neurofibromatosis. May also be associated with spinal trauma
- ○
Demographics: fourth to fifth decade; no gender bias
- ○
Clinical: asymptomatic or radicular intercostal pain
- ○
CT and MRI imaging modalities of choice. Well-circumscribed, 2- to 3-cm, fluid-containing mass. May note evidence of bony erosion and widening of spinal foramina
- ○
Surgical resection required in symptomatic cases
- ○
- ▪
Other mediastinal cysts
- ○
Paravertebral, thin-walled cysts are benign.
- ○
Often present as an incidental finding during workup for another disease.
- ○
Cysts may be found during workup for back pain, but the pain is almost always unrelated to the cyst and removal of the cyst will not relieve the pain.
- ○
Generally, resection is not indicated.
- ○
See Chapter 43 on Masses of the Middle Mediastinum.
- ○
EXTRAMEDULLARY HEMATOPOIESIS
- ▪
Extramedullary hematopoiesis is a compensatory adaptation to chronic severe anemias
- ▪
Most common predisposing conditions
- ○
Thalassemia
- ○
Chronic hemolytic anemias
- ○
Sickle cell anemia
- ○
Congenital spherocytic anemia
- ○
Myelofibrosis
- ○
Gauchers
- ○
- ▪
Lobulated paraspinal masses containing hematopoietic tissue
- ○
Mostly asymmetric
- ○
- ▪
Most commonly multiple and bilateral but can be unilateral. Usually below mid-thoracic region
- ▪
Imaging
- ○
CT
- ▪
Lobulated
- ▪
No calcification
- ▪
Enhances with contrast
- ▪
No evidence of bony compression sequelae ( Fig. 44-4 )
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- ○
