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Mediastinal Diseases

1. MEDIASTINAL TUMOURS

Thymoma

  • A primary anterior mediastinal tumour, well circumscribed mass
  • Most common 30-50 year olds; rare in children
  • Histology – mixture of epithelial cells and mature lymphocytes

Clinical features

  • Can be asymptomatic
  • Large tumours cause symptoms of mass effect – chest pain, dyspnea, haemoptysis, cough, superior vena cava syndrome

Associated conditions

  • Myasthenia gravis – patients have circulating antibodies to acetylcholine receptor
  • Red cell aplasia
  • SLE

Treatment

  • Surgical resection – complete excision of tumour with total thymectomy

Thymic carcinoma

  • Can be low-grade or high-grade
  • Have a propensity for early invasion and metastasis – often leads to malignant pleural and pericardial effusion
  • Poor prognosis
  • Complete resection can increased survival but thymic carcinomas have a tendency to recur
    • Post-operative radiation and chemotherapy can be given

Neurogenic tumours

Nerve sheath tumour

  • Neurilemoma/schwannomas
    • Arise from Schwann cells – generally benign
    • Two types – Antoni A and Antoni B
    • Can lead to cord compression and paralysis if the tumour extends into intervertebral foramen
    • Treatment – resection
  • Neurofibroma
    • Most are benign, but some can degenerate into malignant neurofibrosarcoma
    • Associated with neurofibromatosis type 1 – autosomal dominant condition characterised by brown spots on the eyes, neurofibromas, scoliosis, learning disabilities, café au lait spots and epilepsy
    • Treatment – resection

Ganglion cell tumours

  • Ganglioneuroma
    • Well differentiated, benign tumour
    • Patients are normally asymptomatic – diagnosis is usually made incidentally
    • Treatment – complete resection
  • Ganglioneuroblastoma
    • Histology – mixture of benign ganglion cells and malignant neuroblasts
    • Two patterns
      • Nodular – high incidence of metastasis
      • Diffuse – rarely metastasises
    • Most common in infants and children <3 years old
    • Treatment – resection (good prognosis)
  • Neuroblastoma
    • Very malignant
    • Most common in children under 2 years old
    • Treatment – resection and chemotherapy

Lymphoma

  • Most common malignancy of the mediastinum – anterior compartment is usually involved
  • Two main types – Hodgkin and non-Hodgkin lymphoma
  • Can occur in the lymph nodes, spleen, thymus or bone marrow
  • Clinical features – fever, weight loss, night sweats, pain, dyspnea
  • Early stage Hodgkin lymphoma has a good response to chemotherapy and/or radiation

Mediastinal germ cell tumours

  • Germ cell tumours are more commonly gonadal in origin – less than 5% occur as a primary mediastinal tumour

Teratoma – most common type

  • Most common in children/young adults. Usually asymptomatic
  • Contain two or three embryonic layers
    • Ectoderm – teeth, skin, hair
    • Mesoderm – cartilage, bone
    • Endoderm – bronchial, intestinal or pancreatic tissue
  • Treatment – surgical resection has excellent prognosis
    • Teratocarcinoma (malignant version) is usually unresectable and has a poor prognosis

Seminoma

  • Most common in young Caucasian men
  • Slow growing, bulky tumour, can produce effects of local compression – superior vena cava syndrome, dyspnea, chest discomfort
  • Treatment
    • Chemotherapy (cisplatin, bleomycin, etoposide) – good response rate
    • Surgical resection

Non-seminomatous germ cell tumour

  • Types
    • Embryonal cell carcinoma
    • Endodermal sinus tumour – ↑AFP
    • Choriocarcinoma – ↑hCG
  • Most common in the anterior mediastinum
  • Frequently metastasise to regional lymph nodes, pleura and lungs
  • Treatment
    • Chemotherapy is preferred – cisplatin, bleomycin, etoposide
    • Followed by surgical resection

2. MEDIASTINAL CYSTS

  • Most commonly occur in the middle mediastinum; CT scan is usually diagnostic

Pericardial cyst

  • Usually asymptomatic – found incidentally
  • Located in the right costophrenic angle
  • Cysts are lined with a layer of mesothelial cells and contain clear fluid

Treatment

  • Asymptomatic cysts – observation
  • Symptomatic cysts – surgical resection or aspiration

Bronchogenic cyst

  • Developmental anomaly that occurs due to abnormal budding of the tracheobronchial tree
  • Cysts are line with respiratory epithelium and contain a protein rich mucoid material with smooth muscle and cartilage

Clinical features

  • Most cases are asymptomatic when found incidentally, but can eventually cause symptoms
  • Chest pain, cough, dyspnea, fever
  • Complications – airway obstruction, infection, rupture, fistula

Treatment

  • Asymptomatic cysts – observation
  • Symptomatic/large/infected cyst – complete removal of cyst

Oesophageal duplication cyst

  • They are a congenital malformation and occur due to aberrant division of the dorsal foregut
  • Cysts are lined by gastric epithelium which has a tendency to cause serious complications – haemorrhage, infection, perforation
  • They should always be removed even if they are asymptomatic
  • Treatment – surgical resection

Ectopic endocrine glands

  • Around 5% of all mediastinal masses are of thyroid origin
    • Most are non-toxic and can be completely resected
  • Parathyroid cysts can also be found in the mediastinum – associated with hyperparathyroidism
    • Can cause pressure symptoms – airway obstruction, recurrent laryngeal nerve palsy
    • Treatment – surgical excision

3. MEDIASTINAL EMPHYSEMA

  • Presence of gas in the mediastinum

Etiology

  • Chest trauma – blunt or penetrating
  • Iatrogenic – secondary to neck or thoracic surgery
  • Oesophageal perforation
  • Tracheobronchial perforation
  • Asthma
  • Infection – tuberculosis, mediastinitis
  • Barotraumas – diving, ventilator
  • Connective tissue disorder – polymyositis/dermatomyositis

Clinical features

  • Severe central chest pain, shortness of breath
  • Subcutaneous emphysema – affecting face, neck, chest

Investigations

  • Chest XR
  • CT

Treatment

  • Most cases require conservative treatment – high flow oxygen
  • Drainage – to prevent cardiac tamponade
  • Surgery – to repair

4. SUPERIOR VENA CAVA SYNDROME

  • Superior vena cava (SVC) is a thin walled/low pressure vessel – makes it vulnerable to extrinsic compression and obstruction

Etiology

  • Malignant tumours that compress the SVC – most common cause
    • Lung carcinoma
    • Lymphoma
  • Vascular diseases – aortic aneurysm, vasculitis
  • Mediastinal fibrosis
  • Infections – TB, syphilis

Pathophysiology

  • The SVC is the major drainage vessels for venous blood from the head, neck, upper extremities and upper thorax
  • SVC obstruction leads to formation of collateral veins to restore venous return to the heart
  • The collaterals formed depend on the site of obstruction
    • Pre-azygous obstruction – right superior intercostal veins drain into the azygous vein
    • Azygous obstruction – connection between the SVC and IVC is formed via minor communicating channels
      • SVC → internal mammary veins → superior and inferior epigastric veins → iliac veins → IVC
    • Post azygous – blood from the SVC is distributed to the azygous and hemiazygous veins and then into the IVC

Clinical features

  • Difficult breathing, headache, facial swelling
  • Distended veins in neck and upper thorax
  • Upper limb edema
  • Pemberton sign – facial congestion and cyanosis when patient elevates both arms until forearms touch the sides of the face

Investigations

  • Chest X-ray
  • CT – imaging modality of choice
    • Shows location and severity of SVC obstruction, mediastinal mass, collateral vessels, associated lung mass

Treatment

  • Respiratory support
  • Steroids – to decrease inflammatory response to tumour invasion (especially in lymphoma)
  • Diuretics (furosemide) – relieves symptoms by decreasing venous return to the heart
  • Endovascular stenting
  • Treat the primary tumour/disease causing the obstruction
  • Anticoagulants
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