ANATOMY OF MEDIASTINUM AND ITS DISORDERS

Dr.G.GIREESH,P.G Resident

Dept.Of Gen.Medicine.

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 MEDIASTINUMThe 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.

•

MIDDLE MEDIASTINUM

• Aortic aneurysm• Pericardial cyst • Bronchogenic cyst • Lipoma• Lymphoma• Neoplasm• Morgagni’s hernia

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.

Posterior mediastinum

• Esophageal lesions• Neurogenic tumours• Cysts• Diaphragmatic hernia• Aortic Aneurysm• Meningocoele• Parasitic cysts

BOCHDALEK HERNIA

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.GANGLIONEUROMABenign, 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 ANEURYSMScauses :1. Hypertension2. Atherosclerosis3. Blunt chest trauma4. Mycotic dissection5. Cystic medial necrosis in Marfans syndrome6. Ehlers- Danlos syndrome7. Aortitis in tertiary syphilis8. 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 RhabdomyosarcomaMesenchymoma

• 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 ruptureTuberculous 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.• Fibrosing mediastinitis• 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 involved Symptoms 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

Diagnostic approach• 1.chest x-ray• 2. Computed tomography (CT) –• 3. Magnetic resonance imaging-For spinal tumours.• 4.Fine-needle aspiration biopsy – valuable .• 5. Anterior mediastinotomy.• 6. Bronchoscopy –limited value

THANK YOU

• Thymoma• • 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%