CASE DISCUSSIONMediastinal Masses
The commonest site for mediastinal masses is the anterior compartment 35-55%. About 30-40 % of mediastinal masses present in the posterior compartment while 15 % will present in the middle compartment (Fraser et al 1).
The differential diagnosis of anterior mediastinal masses in 85% of the cases will be: Thymoma, Teratoma, Ectopic thyroid and Lymphoma. Half of those patients are diagnosed incidentally from a plain chest radiograph 2. The rest will be symptomatic secondary to extrinsic compression of the airways or due to involvement of the heart and great vessels by infiltrating or compressing effect.
The respiratory symptoms will be one of the following: cough, dyspnea, chest pain, orthopnea, dysphagia or recurrent pulmonary infection. Some patients may present with pericardial effusions or constrictive pericarditis secondary to mass effect.
Compression of the main pulmonary artery or one of its branches will cause a Superior vena cava syndrome (SVCS). When sedating those patients in supine position the weight of the mass and the loss of negative intrapleural pressure with the induction of anesthesia causes compression of pulmonary artery and sudden onset of hypoxemia and hypotension, which may lead to cardiac arrest. Extreme precaution should be taken when operating on those patients 3. Schamberger ET al 4 noted that the presence or severity of symptoms did not correlate with the degree of tracheal narrowing as evidenced by CAT scanning. Kirks et al 5 found that a CT scan of the chest could detect sub-clinical tracheal compression in 50% of children.
Dynamic changes in the caliber of the trachea or bronchi are best defined using flow- volume loops or fiberoptic bronchoscopy.
2D echocardiogram can be helpful to assess myocardial function and rule out cardiac involvement like pericardial effusion, pericardial extension of tumour or great vessel compression.
A barium swallow will assess the oesophageal involvement. If the cross-sectional diameter of the trachea is decreased by 50% or more, airway obstruction will occur during general anaesthesia. In such cases a local anesthesia will be a safe approach to get a sample from a peripheral site, lymph node, bone marrow or a soft tissue lesion. It was found that tissue diagnosis was preserved in 95% of the children who had up to 24 hours of high-dose steroids to regress the size of the tumor before removing it surgically 6.
Post-operative Complications should be watched for and treated appropriately such as unilateral re-expansion pulmonary edema (RPE) or bleeding into the tumour and chest leading to hemopericardium and hemothorax. Pneumothorax and airway obstruction can happen.
Tumors of the anterior mediastinum are the commonest, reaching up to 50% of all mediastinal masses. Thymomas are most common. Thymic carcinomas and thymic carcinoids are rare 7. In surgically resected lesions 60% were neurogenic tumors, thymomas, and benign cysts. And 30% were lymphoma, teratomas, and granulomatous diseases. Two thirds of all mediastinal tumors were benign. It was found that 75% of asymptomatic patients have benign lesions, while two thirds of symptomatic patients with have malignant lesions 2. The anterior mediastinal masses can be classified into neoplastic or non-neoplastic tumors. Neoplastic tumors include: thymoma, thymic carcinoma, thymic carcinoid, thymolipoma, germ cell tumors, and parathyroid adenoma. Nonneoplastic tumors include thymic cyst, lymphangioma, and intrathoracic goiter.