21st February 2025

Mediastinal masses

Differentials for mediastinal masses

The mediastinum is the space between the lungs within the thorax and is separated into three compartments: anterior, middle and posterior. This separation is helpful in identifying the potential causes of a mediastinal mass.

Table 6 Differentials for mediastinal mass by compartment

Anterior mediastinal masses

Around 50% of mediastinal masses are in the anterior mediastinum and the most common causes can be remembered by the 4 Ts: Thymus, Thyroid, Teratoma (and other germ cell tumours) and ‘Terrible’ lymphoma. 

Thymic mass:

• Around a third of anterior mediastinal masses are thymic neoplasms (thymoma or more rarely, carcinoma)
• Thymomas are associated with paraneoplastic syndromes, particularly myasthenia gravis

Germ cell tumour:

• The mediastinum is the most common place outside the testes and ovaries to find germ cell tumours
• Benign germ cell tumours include teratomas and dermoid cysts
• Malignant tumours can be split into seminomatous (more common) and non-seminomatous germ cell tumours (GCT)

Lymphoma:

• Lymphomas are normally found in the anterior mediastinum and tend to grow quickly compared to other causes of anterior mediastinal masses

Presentation of mediastinal masses

Mediastinal masses are often asymptomatic and are frequently identified incidentally on thoracic imaging. 

Symptoms and signs will reflect the nature and location of the mass and the structures it involves or compresses. Involvement of the recurrent laryngeal nerve can lead to hoarseness, and damage to the sympathetic chain may result in Horner’s syndrome. Bulky mediastinal masses may cause dysphagia via oesophageal compression.

Emergency presentations are possible and include airway compression and superior vena cava obstruction.

Investigation of mediastinal masses

Investigations depend on the likely differentials, for example:

• Suspected lymphoma: full blood count, blood film and flow cytometry
• Suspected thoracic thyroid tissue: thyroid function tests
• Suspected germ cell tumour: tumour markers including LDH, alpha fetoprotein, beta-HCG. beta-HCG and LDH may be raised in either seminomatous or non-seminomatous tumours, whereas AFP will only be raised in non-seminomatous tumours
• Suspected thymic mass: anti-acetylcholine receptor (AChR) antibodies to evaluate for myasthenia gravis

CT can give information as to the location and composition of a mediastinal mass and may also be helpful in planning for a biopsy.

Ultrasound of the testes should be considered in men presenting with a mediastinal mass to look for evidence of a germ cell tumour.

References

• Muniappan A. Assessment of mediastinal mass [Internet]. BMJ Best Practice. 2020 [cited 2022 Jan 31]. Available from: https://bestpractice.bmj.com/topics/en-gb/998
• 1.Berry M, Bograd A. Approach to the adult patient with a mediastinal mass [Internet]. Muller N, Midthun D, Vallières E, Collins K, Sadhna Vora, editors. www.uptodate.com. 2020 [cited 2022 Jan 31]. Available from: https://www.uptodate.com/contents/approach-to-the-adult-patient-with-a-mediastinal-mass