Write a short note on mediastinal masses.

Anatomy of the Mediastinum

The mediastinum lies between the two pleural cavities, bounded by the thoracic inlet above, the diaphragm below, the sternum in front and the vertebral column behind. It is divided for clinical purposes into three compartments, and the compartment is the single most useful predictor of the likely diagnosis.

Causes BY Compartment

Anterior mediastinum — remember the "4 T's":

Also: parathyroid adenoma, lymph nodes, lipoma, ascending aortic aneurysm

Middle mediastinum:

Lymphadenopathy — the commonest: tuberculosis and sarcoidosis (both frequent in India), lymphoma, metastatic carcinoma (especially bronchogenic); bronchogenic and pericardial cysts; aortic arch aneurysm; hiatus hernia; oesophageal lesions.

Posterior mediastinum:

• Neurogenic tumours — the commonest (schwannoma, neurofibroma, ganglioneuroma, neuroblastoma in children)
• oesophageal lesions (achalasia, duplication cyst, carcinoma)
• descending aortic aneurysm
• paravertebral abscess — Pott's disease (tuberculous spondylitis), an important cause in India
• extramedullary haemopoiesis (in thalassaemia).

Clinical Features

• Many are asymptomatic and found incidentally on a chest X-ray — a substantial proportion, particularly benign lesions.
• Compressive symptoms:
• Trachea and bronchi — cough, dyspnoea, stridor, recurrent infection, wheeze
• Oesophagus — dysphagia
• Superior vena cava — SVC obstruction (see below)
• Recurrent laryngeal nerve — hoarseness
• Phrenic nerve — diaphragmatic paralysis with elevated hemidiaphragm and dyspnoea
• Sympathetic chain — Horner's syndrome (ptosis, miosis, anhidrosis, enophthalmos)
• Spinal cord — paraparesis from a dumbbell neurogenic tumour extending through the intervertebral foramen
• Constitutional and systemic: fever, night sweats and weight loss (lymphoma, tuberculosis); B symptoms.
• Syndromic clues that point to the diagnosis: myasthenia gravis (thymoma), gynaecomastia (germ cell tumour), hypertension and flushing (phaeochromocytoma/paraganglioma), and pure red cell aplasia (thymoma).

Superior Vena Cava Obstruction

Compression or invasion of the SVC, most often by bronchogenic carcinoma (especially small cell) or lymphoma.

Features:

• facial and upper limb swelling and plethora, distended non-pulsatile neck veins with dilated collateral veins over the chest wall, headache worse on bending forward, cough, dyspnoea and, in severe cases, stridor and cerebral oedema with confusion.
• Pemberton's sign — facial plethora, cyanosis and respiratory distress on raising the arms above the head — is a useful bedside test.

Management:

• urgent oncological assessment
• obtain a tissue diagnosis before treatment wherever safely possible, since treatment differs radically between small cell carcinoma, lymphoma and germ cell tumour
• corticosteroids, radiotherapy or chemotherapy as appropriate
• endovascular stenting for rapid symptomatic relief in severe or refractory obstruction.

Investigations

• Chest X-ray (PA and lateral) — the lateral film localises the mass to a compartment; look for silhouette signs, tracheal deviation and rib erosion.
• CECT thorax — the primary investigation, defining the compartment, size, extent, tissue characteristics (fat, calcification, cystic components) and vascular involvement. MRI is superior for neurogenic tumours and spinal extension.
• Tumour markers: AFP and beta-hCG (germ cell tumours — markedly raised in non-seminomatous tumours), LDH.
• Blood tests: CBC, ESR, calcium, thyroid function; acetylcholine receptor antibodies if thymoma is suspected; Mantoux/IGRA and sputum studies for tuberculosis; serum ACE for sarcoidosis.
• Tissue diagnosis: CT-guided core biopsy (preferred over FNAC, which is inadequate for lymphoma), EBUS-TBNA or mediastinoscopy for middle mediastinal nodes, and surgical biopsy (VATS or anterior mediastinotomy) where needed.
• PET-CT for staging lymphoma and assessing metabolic activity.
• Pulmonary function tests with flow-volume loops to assess airway compression before anaesthesia.

Management

Determined entirely by the diagnosis:

• Thymoma — surgical resection (thymectomy); radiotherapy and chemotherapy for invasive disease; treat associated myasthenia gravis.
• Lymphoma — chemotherapy with or without radiotherapy; do not resect — the treatment is medical.
• Germ cell tumour — chemotherapy (highly curable), with surgery for residual masses.
• Retrosternal goitre — surgery if compressive or suspicious.
• Neurogenic tumours — surgical excision, with neurosurgical involvement for dumbbell lesions.
• Tuberculosis — antitubercular therapy; sarcoidosis — observation or corticosteroids.
• Cysts — excision if symptomatic.