ANATOMY OF MEDIASTINUM It is the anatomic space that lies in the midthorax Separates the two pleural cavities. It is limited by the diaphragm below and the suprasternal thoracic outlet above. It contains several vital structures in a small space, Abnormalities can produce important symptoms. For clinical purposes, Divided into Anterior, Middle, Posterior compartments
ANATOMY OF MEDIASTINUM The Anterior compartment contains The Thymus, Substernal extensions of the thyroid Parathyroid glands, blood vessels Pericardium Lymph nodes
ANATOMY OF MEDIASTINUM The middle compartment contains the Heart, Great vessels, Trachea, Main bronchi, Lymph nodes, Phrenic and Vagus nerves.
ANATOMY OF MEDIASTINUM The posterior compartment The vertebrae Descending aorta, Oesophagus, Thoracic duct, Azygous and Hemizygous veins Lower portion of the vagus, Sympathetic chains, and Posterior mediastinal nodes.
Disorders of superior mediastinum Enlarged lymph nodes due to Tuberculosis Leukemia Sarcoidosis Lymphoma Tumors of the thymus Teratomas Abscesses Intrathoracic thyroid Aneurysm Cystic hygroma Carcinoma Vascular tumours Oesophageal lesions
DISORDERS OF ANT.MEDIASTINUM These include Lymphoma Lymph node enlargement due to Tuberculosis Hodgkin’s disease Sarcoidosis Thymus tumours Diaphragmatic hernia Thyroid aneurysm Parathyroid aneurysm
LYMPHOMAS These arise in the anterior Mediastinum Hodgkin's lymphoma is the most frequent Carries the best prognosis. Other malignancies with worst prognosis are Non-Hodgkin's lymphoma Plasmacytomas Angiomatous lymphoid hamartomas
Thymus masses The thymus gland is relatively large at birth. After puberty, it regresses to a small size. A Thymic mass can be a Tumour Cysts Thymic lymphoma Cysts may be single or multiple. Usually asymptomatic They manifest on chest X-ray as an enlarged thymus.
Thymus masses Thymoma is a common mediastinal tumour. It is usually malignant Usually associated with myasthenia gravis. Some are asymptomatic. Enlarging tumours present with features of mediastinal compression syndrome Chest x-ray -Rounded shadow in the Ant. Mediastinum. Lateral view gives better delineation of the tumour. Surgical resection is the best method of treatment.
THYROID MASSES Retrosternal extension of an enlarged thyroid Majority are multinodular benign goitres Cystic areas with hemorrhage and calcification. X-ray-show a sharply defined and often lobulated outline. Rarely symptomatic Compress the trachea at the thoracic inlet and result in respiratory distress Occasionally cause superior vena cava syndrome. Thyroid cancer involves the mediastinum by Direct extension Metastases to nodes.
TERATOMAS Identical to certain testicular and ovarian neoplasms, Arise from primitive germ cells Arise by migrating to the mediastinum during oncogenesis. Dermoid cysts contain disorganized mixture of all 3 layers. i.e. skin, hair, cartilage, bone, epithelium, and neural tissue. They often contain cystic areas. Should be excised To prevent further expansion To exclude malignant change
TERATOMAS . Malignant germ cell tumours are classically divided into 1) Seminomas. 2) Teratomas. Non-seminomatous germ cell tumours (malignant teratoma) can range from well-differentiated to trophoblastic. Serum levels of α-FP and β-HCG are ↑sed Seminomas tend to be non-secretory. These tumours are very malignant and invade adjacent mediastinal structures. Not cured by surgery These are responsive to chemotherapy using cisplatin-based regimes.
PERCARDIAL CYSTS Occur in the anterior compartment and cardiophrenic angle They contain clear liquid and a flattened endothelial or mesothelial lining with a bland fibrous wall. Develop embryologically in relationship to the pericardium, Rarely communicate with the pericardial sacs X-ray-Smooth, clear, demarcated densities D/D’S-Pericardial fat pad Hernia through the foramen of Morgagni. Aspiration reveals clear fluid. Surgical excision is not recommended.
BRONCHOGENIC CYSTS Arise in association with the major airways Dvp. around the paratracheal area or carina Middle and posterior compartments Lined by respiratory epithelium. Contain inspissated mucus. Cough or wheezing due to local pressure on airways Occasionally they communicate with the trachea There is an increased tendency to recurrent infections. Symptomatic pt.s need surgical removals of the cysts
MEDIASTINAL LYMPHADENOPATHY Middle mediastinum is the commonest site of intrathoracic lymphadenopathy. Gross lymphadenopathy is a feature of 1)Tuberculosis 2)Histoplasmosis. 3) Metastatic carcinoma 4) Lymphomas, 5)Sarcoidosis.
Giant follicular lymph node hyperplasia (Castleman's disease) Its Aetiology is unknown. The lesion consists of a vascular tumour with satellite lymphadenopathy. Two histological subgroups are described, (1) a more common hyaline vascular picture with lymphoid follicles and penetrating capillaries (2) a plasma cell type characterized by sheets of plasma cells between germinal centres. It causes pressure effects Systemic symptoms with fever, anaemia, and weight loss. Small group of patients with multicentric disease have progressive hyperplasia, recurrent infections, and subsequently develop a frank lymphoma.
Enteric cysts Are located in the posterior mediastinum Lined by gastric or intestinal epithelium. All cysts may become1) Infected 2) Bleed 3)Rupture Rupture into the Mediastinum. Pleural cavity.
Tumours of post.mediastinum Found in the paravertebral gutters, Neural in origin. Benign tumours tend to be asymptomatic, Malignant tumours cause pressure effects. Occasionally, spinal cord compression results from direct extension into the intravertebral foramen. Tumours arising from peripheral nerve cell sheaths include Neurilemmoma (Schwannoma) Neurofibroma Malignant counterparts. Tumours of the autonomic chain include Ganglioneuroma Neuroblastoma.
NEUROGENIC TUMOURS There are 4 histological types. 1.neurilemmoma Benign and is classically a dumbbell-shaped mass. compress the spinal cord and produce pressure symptoms. 2.ganglioneuroma Benign, elongated and large. Usually occurs in children but may be found at any age. Causes flushing,hypertension,headache,sweating,diarrhoea. 3.neurofibroma Associated with generalized neurofibromatosis (von Recklinghausen's disease). 4.NEUROBLASTOMA Malignant and found frequently in children.
AORTIC ANEURYSMS causes : Hypertension Atherosclerosis Blunt chest trauma Mycotic dissection Cystic medial necrosis in Marfans syndrome Ehlers- Danlos syndrome Aortitis in tertiary syphilis Coarctation of aorta
VASCULAR TUMORS Vascular tumors may originate in the mediastinum. Vascular hamartomas Lymphangiomas and Hemangiomas are benign tumors. Hemangiopericytomas are malignant. Mesenchymal benign -lipoma Malignant-Liposarcoma Mesothelioma Rhabdomyosarcoma Mesenchymoma These rarely cause mediastinal masses.
PNEUMOMEDIASTINUM There are 3 possible causes - 1) penetrating chest wall injuries; 2) tear or defect in trachea, bronchus or oesophagus; 3) tear or defect in alveolar wall Air from alveoli enters the interstitial space, Travels along the perivascular sheath into the mediastinum Enters the subcutaneous tissues of the neck and chest wall Results in surgical emphysema. Pt. gets sudden pain in the substernal areas and dyspnoea. X-ray –Air accumulation parallel to the heart and aorta. In surgical emphysema-subcutaneous crepitations are felt . Treatment of the underlying disorder is necessary. Rarely needs surgical incision.
MEDIASTINITIS It usually results from Oesophageal rupture Bronchial rupture Tuberculous lymphadenitis. Infection from subphrenic abscess Osteomyelitis of spine. Treatment- 1.Appropriate Antibiotics. 2.Surgery.
CHRONIC FIBRINOUS MEDIASTINITIS Its a chronic slowly progressive fibrosis. Similar to idiopathic retroperitoneal fibrosis. Various theories have been put forward but not proven. Involves S.V.C, Azygos and Innominate veins. Apart from engorged neck veins, swelling of face and neck, one may get headache, breathlessness, giddiness and epistaxis. X-ray chest-Widening of the upper mediastinum. Secondary causes of mediastinal fibrosis like tuberculosis and histoplasmosis must be ruled out. Corticosteroids can be tried. Surgical removal of fibrotic bands relieves the symptoms.
Superior Vena Cava Syndrome Obstruction of blood flow through the superior vena cava causes dilation of the collateral veins of the upper thorax and neck and edema and congestion of the face patients may have headache, dyspnea, dysphagia, and wheezes. Malignancy is the most frequent cause of this syndrome, bronchogenic carcinoma lymphoma a distant second. Fibrosingmediastinitis Methysergide ingestion. Aortic aneurysm Retrosternal thyroid Invasive procedures are contraindicated. When the obstruction is thought to be caused by tumor, effort must be made to obtain tissue elsewhere. Irradiation, chemotherapy, or stent placement should be initiated before attempts are made to obtain mediastinal tissue.
Organ involvedSymptoms and signs 1. Trachea, main bronchi -Stridor, dyspnoea, cough, features of lung collapse 2. Oesophagus- Dysphagia (extrinsic compression on barium swallow) 3. Superior vena cava -Engorged non-pulsatile neck veins, oedema and cyanosis of face, neck and arms 4. Left recurrent laryngeal nerve- Hoarseness of voice, bovine cough 5. Phrenic nerve- Hemi-diaphragm paralysis 6. Sympathetic trunk- Horner’s syndrome
General Considerations Most common anterior mediastinal mass Accounts for 50% of anterior mediastinal masses and 25% of all mediastinal tumors Most are solid lymphoepithelial tumors of the thymus, some are cystic About 1/3 are malignant under 20 and over 40 years of age About half are malignant in those 20-40 Rare in children — most common around 5th or 6th decade Mean age of 52 They can be classified into four types which occur in about equal frequency Lymphocytic Epithelial Mixed Spindle cell (Hassall’s corpuscles in this type) There are World Health Organization classifications and surgical staging classifications as well Clinical Findings Most benign thymomas are asymptomatic Most with malignant thymomas are symptomatic Symptoms include Cough Chest pain Dyspnea Dysphagia Superior vena caval syndrome Red cell aplasia, hypogammaglobulinemia or collagen vascular disease such as dermatomyositisand lupus Imaging Findings Conventional radiographs of the chest may show Oval round or lobulated soft tissue mass, sharply demarcated, usually smaller than teratomas Superior aspect of anterior mediastinum Project predominantly to one side or the other May displace heart and great vessels posteriorly On CT
Normal thymic tissue may be seen as a triangular density in the anterior mediastinum up to 30 years of age at which time fatty involution occurs Thymus should be < 1.8 cm up to 20 years and < 1 cm after 20 years A small percentage (5%) may contain curvilinear or amorphous calcification Absence of fat planes and invasion of adjacent structures favors malignancy A homogeneously enhancing capsule favors benignancy MRI May be more sensitive to small thymic masses than CT Hypointense to mediastinal fat on T1 On T2, signal is isointense or hyperintense ro surrounding fat Differential Diagnosis Non-Hodgkin’s lymphoma can occur in thymus Thymolipomas are rare, fatty tumors of the thymus that have been associated with Aplastic anemia Hypogammaglobulinemia Grave’s disease Hodgkin’s disease Chronic lymphocytic leukemia Anterior Mediastinal Masses – 3 T’s and an L Thymoma Teratoma Thyroid enlargement Lymphoma Treatment Most thymomas are treated surgically Degree of invasiveness rather than histopathology is best determinant of malignancy versus benignancy Complications About 15% of patients with myasthenia gravis have thymomas and about 33-50% of patients with thymomas have myasthenia Thymomas are associated with leukemia Prognosis Surgical evaluation of encapsulation or invasion is better indicator of prognosis than actual histology In patients with myasthenia, about 50% improve following removal of the thymoma For those with invasive thymoma, 15 year survival is 12.5% For those with non-invasive thymoma, 15 year survival is 47%