Approach

Many mediastinal tumours are asymptomatic (incidental finding) or associated with only vague complaints. The likelihood of malignancy depends on mass location, patient age, and the presence of symptoms.[8][32][33] Malignant masses are found in the anterior, middle, and posterior mediastinum in approximately 60%, 30%, and 15% of cases, respectively.[7] Symptoms are present in 80% to 90% of patients with malignant mediastinal tumours at presentation, compared with 46% of patients with benign masses.[7] Approximately 25% of patients with thymoma have myasthenia gravis, and 15% of patients with myasthenia gravis have thymoma.[34] Neurogenic tumours are commonly observed in children. Acute lymphocytic leukaemia may occur in children (commonly <5 years) or adults. Lymphoma, chronic lymphocytic leukaemia, thymomas, and thyroid tumours tend to occur in adults.[35][36]

History

Although many mediastinal tumours may be asymptomatic, certain symptoms may raise concern for a mediastinal tumour and relate to its location. These include the following:

  • Airway compression: dyspnoea, stridor, haemoptysis, cough

  • Oesophageal compression: dysphagia, odynophagia, weight loss

  • Recurrent laryngeal nerve compression: hoarse voice

  • Superior vena cava obstruction: facial swelling, headache

  • Sympathetic ganglion involvement: Horner's syndrome, in which the patient may note pupillary constriction (miosis), drooping eyelids (ptosis), and absence of sweating (anhidrosis)

  • Chest wall invasion: myasthenic pain, palpable mass

  • Myasthenic symptoms: easy fatigability, drooping eyelid, double vision, dysarthria

  • Constitutional symptoms of malignancy: weight loss, night sweats, fever.

Physical examination

The mediastinum is inaccessible to direct physical examination except during surgery. Specific physical findings are related to compression or invasion of adjacent structures, or paraneoplastic syndromes:

  • Airway compression: stridor, prolonged inspiration/expiration, haemoptysis

  • Recurrent laryngeal nerve compression: hoarseness

  • Superior vena cava obstruction: facial swelling, collateral veins, plethora

  • Sympathetic ganglion involvement: Horner's syndrome, with miosis, ptosis, and anhidrosis

  • Myasthenic symptoms: ptosis, diplopia, dysarthria

  • Evidence of haematological malignancy: fever, pallor, petechiae, hepatosplenomegaly, abdominal mass.

Laboratory tests

Laboratory testing is indicated depending on the suspected aetiology:

  • Thymoma: FBC and acetylcholine receptor antibody

  • Mediastinal goitre: thyroid function tests 

  • Parathyroid adenoma: serum calcium, phosphate, and parathyroid hormone 

  • Germ cell tumour: alpha-fetoprotein and beta-human chorionic gonadotrophin

  • Phaeochromocytoma: 24-hour urinary metanephrines and catecholamines, and plasma free metanephrines

  • Neurogenic tumour: 24-hour urinary homovanillic acid and vanillylmandelic acid

  • Haematological malignancy: lactate dehydrogenase, FBC and blood smear, flow cytometry, HIV serology, and hepatitis B and C serology.

Imaging studies 

Chest x-ray

Chest x-ray with posteroanterior and lateral views is indicated in all cases. It provides information on the size, anatomical location, density, and composition of the mass.

Computed tomography (CT) scan

CT with intravenous contrast enhancement provides information concerning the vascularisation of the mass and its relationship to adjacent structures. It can also determine the content (calcium, fat, or necrotic tissue) and characteristics (cystic or solid) of the mass. CT scan is an essential test and is indicated in virtually all cases to further evaluate a mediastinal mass.com.bmj.content.model.assessment.Caption@d7a0394[Figure caption and citation for the preceding image starts]: Necrotic mediastinal lymphadenopathyFrom the collections of Dr Mario Gasparri and Dr Nicholas Choong [Citation ends].com.bmj.content.model.assessment.Caption@3b3a9f19[Figure caption and citation for the preceding image starts]: CT image of pericardial cystFrom the collections of Dr Mario Gasparri and Dr Nicholas Choong [Citation ends].com.bmj.content.model.assessment.Caption@19e4c40d[Figure caption and citation for the preceding image starts]: CT image of large thymic carcinoma (white arrow) with sternal invasion (yellow arrow)From the collections of Dr Mario Gasparri and Dr Nicholas Choong [Citation ends].

Magnetic resonance imaging (MRI)

Provides useful information in evaluating spinal, vascular, or cardiac invasion. It is also useful for assessing the relationship of the mass to vascular structures. In the evaluation of the posterior compartment of the mediastinum, MRI is more sensitive than CT for determining involvement of the neural foramen or spinal canal invasion. MRI is useful for evaluating thyroid masses when iodinated contrast is contra-indicated.

MRI is increasingly used for differentiating between benign thymic hyperplasia and thymic neoplasms.[37]

Trans-oesophageal echocardiogram

The preferred initial test for diagnosis of aortic aneurysms and aortic dissection, especially during emergencies.

Barium swallow

Assesses the relationship of an oesophageal cyst to the oesophagus proper, and determines whether there is a communication with the oesophageal lumen, which is the case in approximately 20% of patients.

Endoscopic ultrasound

May be used to differentiate between an intramural or extramural mass and delineate the relation of the cyst to surrounding structures.

Testicular ultrasound

Has a high sensitivity and is able to detect intratesticular lesions as small as 2 mm.

Radionuclide studies

Nuclear scans and biochemical studies are useful in diagnosing and evaluating the following conditions.

Suspected substernal thyroid

Radioactive iodine thyroid scan to define the nature and extent of thyroid gland; toxic multinodular goitre shows multiple hot and cold areas consistent with areas of autonomy and suppression; malignant thyroid nodules are generally cold.

Suspected catecholamine-secreting tumour

Metaiodobenzylguanidine (MIBG) scan to define the nature and extent of the tumour.

Malignancy 

Fluorine 18 fluorodeoxyglucose (18F-FDG) PET scan to define the extent and stage of a malignancy. 18F-FDG uptake occurs in most malignancies including lymphomas, metastatic carcinomas, thymic carcinomas, and lung cancers.

18F-FDG PET-CT was found to be beneficial in detecting lymph node metastases and extrathoracic metastases in patients with non-small cell lung cancer (NSCLC). It confers significantly higher sensitivity and specificity than contrast-enhanced CT and higher sensitivity than 18F-FDG PET in staging NSCLC.[38][39]

Neuroendocrine tumour

Gallium 68 or GaTate PET-CT scans are especially suited for diagnosis of neuroendocrine tumours, such as thymic carcinoid. They increase the sensitivity with which metastatic disease can be identified.[40]

Biopsy techniques

While clinical assessment in combination with radiographic imaging can often narrow the diagnostic possibilities, definitive pathological diagnosis is often required prior to initiating therapy. There are many modalities to obtain a pathological diagnosis, and each modality has its advantages and limitations.

Image-guided percutaneous needle biopsy

This type of biopsy is performed with either CT or ultrasound, using local anaesthesia and light sedation. Samples are taken using either a fine needle or a core needle. It is mainly indicated for anterior mediastinal masses.

The advantages of using an image-guided percutaneous needle biopsy are that it is minimally invasive, associated with low risk, and can be done as an outpatient procedure.[41] The disadvantage is that tissue may be insufficient to render a definitive diagnosis, especially with lymphoma and thymoma.

Endoscopic biopsy with or without ultrasonography

Endoscopic biopsy with ultrasonography can be performed bronchoscopically (EBUS) or through the oesophagus (EUS) using a fine needle.[42] The accessible areas are those immediately adjacent to the tracheobronchial tree and oesophagus, which limits what can be biopsied. The American Thoracic Society has standardised the nomenclature of lymph nodes in the chest. There are 14 numbered nodal stations; lymph nodes considered to be in the mediastinum are stations 1 to 9. EBUS can access mediastinal nodal stations 2, 4, and 7, while EUS can access nodal stations 5, 7, 8, and 9.

The advantages of EBUS are that it is minimally invasive, associated with low risk, and can be done as an outpatient procedure.[43] Use of EBUS may also reduce the need for surgical staging.[44] The disadvantages are that only limited areas are amenable to biopsy, and it requires special equipment and technical expertise (both endoscopes and cytopathologist), which are not available at all institutions.

Mediastinoscopy

This is a surgical procedure requiring general anaesthesia. Incision is made just above the manubrium, and a mediastinoscope is passed along the pretracheal plane into the mediastinum. The high (station 2) and low (station 4) paratracheal lymph nodes, as well as the subcarinal lymph nodes (station 7) can be sampled. It is generally used for diagnosis and staging of lung cancer and lymphoma.

Mediastinoscopy has a high diagnostic yield.[19] It is associated with low risk and usually done as an outpatient procedure. The risk of major complications, such as great vessel injury, is extremely low.

Mediastinotomy/Chamberlain procedure

Typically used for masses of the anterior mediastinum or within the aortopulmonary window. A small transverse parasternal incision allows excellent exposure and has a high diagnostic yield. It is an invasive procedure requiring general anaesthesia and may require tube thoracostomy if the pleural space is violated.

Thoracoscopy

Video-assisted thoracoscopic surgery (VATS), a minimally invasive surgical technique, is a valuable tool in the diagnosis and management of mediastinal masses. Almost all traditionally open procedures can be performed via VATS, including thymectomy, duplication cyst excision, pericardial cyst excision, and posterior mediastinal mass resection. It allows excellent exposure of all compartments of the mediastinum for diagnostic biopsy or therapeutic excision. VATS also permits the accurate determination of local invasion or intrapleural metastatic spread. VATS requires general anaesthesia and hospitalisation.

Sternotomy or thoracotomy

Sternotomy gives excellent exposure to the anterior mediastinum, and thoracotomy gives excellent exposure to the middle and posterior mediastinum. Sternotomy or thoracotomy is useful when excision of large lesions (>5 to 7 cm) are required.

Bone marrow biopsy

Indicated if clinical features are suggestive of an underlying haematological malignancy such as lymphoma or acute or chronic lymphocytic leukaemia.

Peripheral lymph node biopsy

Haematological and metastatic malignancies may have abnormal lymph nodes peripherally. Excision of a complete lymph node provides valuable information on the malignant cell type based on histological appearance or immunohistochemical staining.

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