View TSDA Curriculum Online for this topic
A. Compartments
· Mediastinal borders: thoracic inlet (superior), diaphragm (inferior), sternum (anterior), spine (posterior), pleura (lateral)
· Anterosuperior compartment is anterior to pericardium
· Contents include thymus and great vessels
· Middle, or visceral, compartment is between anterior and posterior pericardial reflections
· Contents include heart, phrenic nerves, tracheal bifurcation, major bronchi, lymph nodes
· Posterior, or paravertebral, compartment is posterior to posterior pericardial reflection
· Contents include esophagus, vagus nerves, sympathetic chains, thoracic duct, descending aorta, and azygos/hemiazygos
A. Mediastinal Emphysema
· Introduction of air from esophagus, tracheobronchial tree, neck, or abdomen
· Causes include penetrating or blunt trauma, or spontaneous mediastinal emphysema
· Presents as substernal chest pain, crepitation, and pericardial crunching sound
· May result in tamponade
· Treat underlying cause; may require chest tube placement for pneumothorax
B. Mediastinitis
· Occurs in about 1% of patients after median sternotomy
· Risk factors include prolonged surgery or CPB, re-exploration, wound dehiscence, shock, and use of bilateral internal
mammary artery grafts in patients who are older or have diabetes
· Presents as fever, elevated WBC, and tachycardia
· Best treatment results with wound debridement and tissue flaps
C. Mediastinal Hemorrhage
· Caused by trauma, aortic dissection, aneurysm rupture, or surgical procedures
· May result in mediastinal tamponade, which is more insidious than pericardial tamponade
· Meticulous hemostasis and adequate chest tube drainage will prevent this syndrome
· Spontaneous mediastinal hemorrhage can result from mediastinal masses, altered coagulation status, and severe hypertension
D. Superior Vena Cava Obstruction
· Acute and chronic syndromes occur
· See CTSN lecture on SVC Syndrome
· Lesions are predictable to some degree predictable
· Most common tumors are neurogenic (20%), thymomas (20%), primary cysts (20%), lymphomas (13%), and germ-cell tumors (10%)
· Most are located in anterosuperior compartment (54%), followed by posterior (26%) and middle (20%) tumors
| Tumors and Cysts by Location | ||
| Anterior | Middle | Posterior |
| Thymoma Germ cell tumor Lymphoma Hemangioma Parathyroid adenoma Thymic cyst Lipoma Aberrant thyroid Lymphangioma |
Enterogenous cyst Mesothelial cyst Lymphoma Thoracic duct cyst Granuloma Hamartoma |
Neurogenic origin Neurenteric cyst Lymphoma |
· A significant portion (25-40%) of mediastinal tumors are malignant
· Anterosuperior tumors are more likely to be malignant, as are tumors of patients between the ages of 10 and 40
· Neurogenic tumors and non-Hodgkin's lymphomas are the most common tumors in children
· About two-thirds of patients will have symptoms at the time of diagnosis
· The absence of symptoms is a reasonably good indicator that a diagnosed tumor is benign
· Most common symptoms include chest pain, cough, and fever
· Signs of mechanical compression or invasion of mediastinal structures are more common with malignant tumors
· Paraneoplastic syndromes are not uncommon and include Cushing's syndrome, thyrotoxicosis, hypertension, hypercalcemia, hypoglycemia, diarrhea, and gynecomastia
· CXR will localize the tumor and give information on calcification and relative density of the tumor
· CT scanning identifies chest wall invasion, multiple masses, and extension into spinal column
· MRI is more accurate for vascular involvement and intracardiac pathology
· Echocardiography is useful for patients with middle compartment tumors to localize between intracardiac and pericardial tumors
· Guided needle biopsy can make a diagnosis of malignancy in 80-90% of patients
· Mediastinoscopy/mediastinotomy may be necessary to make a diagnosis and establish resectability
A. Features
· Represents 20% of all mediastinal masses in adults
· Peak incidence is in 3rd to 5th decades of life; rare in children
· About half are of mixed cell type, followed by epithelial (28%) and lymphocytic (20%) types
· Between 15 and 65% of thymomas are benign
· Frequently associated with paraneoplastic syndrome, most commonly myasthenia gravis
· Myasthenia gravis is diagnosed in 30-50% of patients with a thymoma, and 15% of myasthenia patients will have a thymoma
· Autoimmune reaction directed against the postsynaptic nicotinic receptors results in skeletal muscle fatigability and weakness, especially in axial muscles
B. Operative Technique
· Remove all anterior mediastinal tissue and any invasive disease, including involved lung, pleura, pericardium, and SVC/innominate vein
· Thymic blood supply arises from the internal mammary arteries
· Patients with stage IIa or higher disease should receive postoperative radiation
· Chemotherapy is indicated for stage III or IV disease
· Debulking may be appropriate for stage IV disease, although there is no evidence for increased survival
· At 5 years after resection, 25-30% of patients will have complete resolution of myasthenia symptoms and 30-50% will be improved
· Prognosis is dependent on stage of tumor, not on presence of myasthenia gravis
· Most occur in males and about two-thirds are symptomatic
· Originate from Kulchitsky cells in the thymus, but are not associated with myasthenia gravis or the carcinoid syndrome
· May cause other paraneoplastic syndromes, however, most commonly Cushing's syndrome (33%)
· Presence of such syndromes is a very poor prognostic factor
· Up to 75% will develop local recurrence or metastases
· Low overall cure rate and mean survival is 3 years
· Between 40 and 70% of lymphoma patients will have mediastinal involvement during their disease course
· Only 5-10% of lymphoma patients will have isolated mediastinal disease, and are usually symptomatic
· Characteristic Hodgkin's lymphoma symptoms are chest pain after alcohol consumption and cyclic Pel-Ebstein fevers
· Nodular sclerosing and lymphocyte predominance forms of Hodgkin's lymphoma are the most common to cause mediastinal involvement
· Up to 40% of patients with lymphoblastic non-Hodgkin's lymphoma will have mediastinal disease
· Surgery is indicated if fine-needle aspiration is inconclusive or to evaluate residual mass after chemotherapy
· Surgical options include cervical mediastinoscopy, parasternal mediastinotomy, and thoracoscopy
· Comprise 15-25% of anterior mediastinal masses
· Most common in children and young adults
· Includes teratomas, teratocarcinomas, seminomas, embryonal cell carcinomas, choriocarcinomas, and endodermal cell or yolk-sac tumors
· Identical to germ cell tumors originating in the gonads, but are not metastatic lesions from primary gonadal tumors
· About 60% are benign and 40% are malignant
A. Predominantly Benign Tumors
· Teratomas are complex, multiple tissue element tumors
· Symptoms are related to mechanical effects
· Simplest form is the dermoid cyst, which consists of mostly dermal and epidermal tissue
· More complex teratomas may have well-differentiated bone, cartilage, nerve, or glandular tissue
· Malignant tumors are differentiated upon histologic identification of embryonic tissue
B. Malignant Tumors
· Male predominance and most patients are symptomatic
· 40% are seminomas and 60% are nonseminomas (embryonal cell, choriocarcinoma, yolk-sac, and teratocarcinoma)
| Seminomas | Non-seminomas | |
| AFP/B-HCG | rare | 90% |
| Associated syndromes | none | Klinefelter's, trisomy 8, 5q deletion |
| Radiosensitivity | High | Insensitive |
| Metastatic behavior | Remain intrathoracic | Frequently disseminated |
| Treatment | Radiation | Cis-platinum chemotherapy |
| Remission | Over 80% | CR in 55-60%, PR in 30-35% |
| 5-year survival | 50-80% | 50-60% |
| Remission | CR=complete | PR=partial |
· Initial surgical intervention typically only for diagnosis due to high radiosensitivity of seminomas and frequent metastatic disease in non-seminomas
· Surgical resection after induction of chemotherapy may have a role in non-seminomatous tumors
A. Intrathoracic Thryoid
· 80% are substernal extensions of a cervical goiter
· True intrathoracic thyroid (derives blood supply from thoracic vessels) comprises only 1% of all mediastinal tumors
· More common in women and in the 6th to 7th decades, most are adenomas
· Usually presents with tracheal or esophageal compression; thyrotoxicosis is uncommon
· I-131 scanning should be done to identify presence of functioning cervical thyroid tissue before resecting these tumors
· Resect substernal extensions through a cervical incision and true intrathoracic lesions through the chest
B. Parathyroid
· Most are adenomas and are found by the superior pole of the thymus due to common embryogenesis from the third branchial cleft
· Symptoms are usually due to hyperparathyroid syndrome
· Parathyroid cysts are not usually hormonally active
A. Bronchogenic Cysts
· Most common primary cysts in the mediastinum (5%)
· Arise from ventral foregut and are usually located in the subcarinal or right paratracheal region/a>
· Two-thirds are asymptomatic; symptoms include tracheobronchial or esophageal compression and infection from tracheobronchial communication
· Complete excision is recommended, even if asymptomatic, to prevent late complications
B. Esophageal/Enteric Cysts
· Comprise 3-5% of mediastinal tumors
· More common in children and tend to occur in the lower third of the esophagus
· Dysphagia is the most common symptom
· CT scanning is essential in patients with vertebral anomalies to evaluate for possible spinal cord involvement (neuroenteric cyst)
· Avoid endoscopic biopsy, as this may cause cyst perforation and infection
· Complete excision is indicated; a thoracoscopic approach can be used for uninfected cysts
C. Pleuropericardial Cysts
· Uncommon, classically occur at the pericardiophrenic angles, 70-80% on the right side
· Usually asymptomatic and may communicate with the pericardium
· Guided needle aspiration is the initial therapy of choice
· Surgical excision is indicated if the cyst recurs or if the diagnosis is in doubt
A. Etiology and Diagnosis · Most posterior mediastinal masses are of neurogenic origin
· 95% of these tumors in adults are benign and are usually asymptomatic
· In children, most neurogenic tumors are malignant
· Classified according to cell origin; most arise from intercostal nerve or sympathetic chain
| Intercostal nerve | Sympathetic ganglia | Paraganglia cells |
| Neurofibroma Neurilemoma Neurofibrosarcoma | Ganglioma Ganglioneuroblastoma Neuroblastoma | Paraganglioma (pheochromocytoma) |
· Neurilemomas are the most common and originate from Schwann's cells
· These are encapsulated tumors which stain with S-100 protein immunostain
· Two primary types: Antoni A (organized pallisading pattern) and Antoni B (loose reticular pattern)
· Neurofibromas originate from peripheral nerve
· Form a pseudocapsule and have more variability with the S-100 stain
· Both types of tumors are associated with von Recklinghausen's disease, although more commonly neurofibromas
· Chest CT is sufficient for diagnosis of most of these tumors, and MRI should be used when an intraspinal component is present
B. Operative Indications
· Benign tumors (neurofibroma, neurilemoma, ganglioneuroma) can be effectively treated with local excision
· Combined thoracic and neurosurgical approach is indicated for tumors with intraspinal extension
· Recurrence is rare for benign tumors
· Local recurrence is common for malignant tumors and overall prognosis is poor