Mediastinal Masses Differential
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Direct answer
A mediastinal mass is a space-occupying lesion within the mediastinum, and its position sorts the differential into anterior, middle and posterior compartments. The anterior compartment holds the four Ts: thymoma, teratoma and other germ cell tumours, thyroid enlargement and lymphoma, which together explain most adult anterior masses. Contrast CT of the chest, or MRI when needed, localises and characterises the lesion before any tissue is taken.
What you must remember
- Anterior compartment: the four Ts are thymoma, teratoma and germ cell tumours, thyroid and terrible lymphoma, with thymoma the commonest primary anterior mediastinal tumour in adults.
- Middle compartment: lymph node enlargement from lymphoma, sarcoidosis or tuberculosis, bronchogenic cysts, pericardial cysts and oesophageal lesions.
- Posterior compartment: neurogenic tumours such as neurofibroma, schwannoma and ganglioneuroma, plus hiatus and oesophageal lesions and extramedullary haematopoiesis.
- Thymoma and myasthenia: a substantial share of thymomas coexist with myasthenia gravis, so every thymic mass deserves a look for fatigable weakness.
- Germ cell markers: alpha-fetoprotein points to yolk sac elements and beta-hCG to choriocarcinoma or seminoma, and both guide treatment.
- Testicular check: an anterior mediastinal germ cell tumour in a male needs a testicular examination and scrotal ultrasound to exclude a primary testicular tumour.
- Dumbbell neurogenic mass: an intraspinal extension through the neural foramen can compress the cord, so MRI of the spine is needed.
- Airway caution: a large anterior mass can compress the airway or great vessels, so anaesthesia and sedation are planned with care.
Compartment-wise causes on chest imaging
A mass on the chest radiograph is first assigned to a compartment, because each compartment has a short and predictable list of causes. The table lists the most examined lesions in each compartment, the imaging clue that points to each, and the usual way the patient presents.
| Compartment | Common lesions | Imaging clue | Typical presentation |
|---|---|---|---|
| Anterior | Thymoma, teratoma, lymphoma, goitre | Mass in front of the great vessels | Chest pain, cough, superior vena cava features |
| Middle | Lymph nodes, bronchogenic cyst, pericardial cyst | Hilar or subcarinal location | Often asymptomatic, cough or dysphagia if large |
| Posterior | Neurofibroma, schwannoma, oesophageal lesion | Paravertebral, sometimes with rib erosion | Back pain, radicular symptoms, incidental finding |
Most exam stems expect the candidate to name the compartment before the diagnosis, because the compartment alone narrows the list of likely lesions sharply. Symptoms such as dysphagia, hoarseness or back pain add a second clue that is often the decisive one in a viva.
Where the exam tries to catch you
The stem often describes age, sex and symptoms, and the trap is the commonest lesion rather than the one the clues support.
- Trap: calling every anterior mass a thymoma Correct: in young patients lymphoma and germ cell tumours are common, so markers and tissue come before a firm label.
- Trap: assuming a middle compartment cyst is malignant Correct: bronchogenic and pericardial cysts are benign congenital lesions, usually found incidentally.
- Trap: reading a posterior mass as a lymph node Correct: posterior compartment masses are mainly neurogenic, and spinal extension needs MRI.
- Trap: giving general anaesthesia without planning for a large anterior mass Correct: compression can collapse the airway on induction, so the airway is secured with care.
Frequently asked questions
Which compartment does a thymoma occupy?
Thymoma occupies the anterior mediastinum, lying in front of the great vessels. It is the commonest primary anterior mediastinal tumour in adults and is linked with myasthenia gravis and pure red cell aplasia.
Which markers suggest a germ cell tumour of the mediastinum?
Serum alpha-fetoprotein and beta-human chorionic gonadotropin are the key markers for mediastinal germ cell tumours. Raised alpha-fetoprotein suggests yolk sac elements, and raised beta-hCG suggests choriocarcinoma or seminoma.
Why is a testicular examination needed for an anterior mediastinal mass in a man?
A testicular primary can present as an anterior mediastinal germ cell tumour, so the testes must be examined and scanned. Excluding a testicular source changes the staging and the treatment plan.
What is the typical imaging feature of a neurogenic posterior mediastinal tumour?
A neurogenic posterior mediastinal tumour lies paravertebrally and may extend through an intervertebral foramen as a dumbbell shape. MRI of the spine is needed to check for cord compression when this pattern is seen.
Which mediastinal masses cause the most airway compromise in adults?
Large anterior masses, especially thymoma, teratoma and lymphoma, are the commonest causes of airway or venous compression. Lymphoma in particular can cause rapid compression, so anaesthetic and sedation plans must be made before any procedure.