Mediastinal Masses Differential
On this page
Direct answer
Which compartment the mass sits in shortens a mediastinal differential from dozens of entities to two or three. Anterior (before the pericardium): the "4 Ts" — Thymoma, Teratoma and other germ cell tumours, Terrible lymphoma, and Thyroid (retrosternal goitre) — plus parathyroid adenoma. Middle: bronchogenic and pericardial cysts, lymphadenopathy (lymphoma, metastases, tuberculosis in India) and mediastinal extensions of lung tumours. Posterior: neurogenic tumours — schwannoma and neurofibroma from nerve sheath, ganglioneuroma and neuroblastoma from sympathetic ganglia in children — plus enteric duplication cysts. Age and symptoms refine it (neuroblastoma in a child, teratoma in a young adult, lymphoma with systemic features, thymoma with myasthenia), tumour markers may spare a biopsy (elevated AFP or beta-hCG in mediastinal germ cell tumour means chemotherapy, not excision), and the surgeon's rule is that lymphoma and germ cell tumours are biopsied — usually via VATS or image-guided core — while thymoma, cysts and neurogenic tumours are resected.
What you must remember
- Compartment anatomy: classical radiological divisions on lateral chest X-ray/CT — anterior (between sternum and pericardium/brachiocephalic vessels), middle (pericardial and its reflections), posterior (behind pericardium, paravertebral gutters); the newer ITMIG scheme redefines boundaries but compartment-first thinking still drives the exam answer.
- Anterior compartment detail: thymoma is the commonest anterior mediastinal tumour in adults; teratodermoids contain fat, calcification and teeth/hair on CT; Hodgkin and non-Hodgkin lymphoma (and in India tuberculous nodes); substernal goitre (continuous with the cervical gland, enhances like thyroid, may show retrosternal extension on plain films with tracheal displacement).
- Middle compartment: pericardial cysts (right cardiophrenic angle "spring water" cyst), bronchogenic cysts (subcarinal or paratracheal, fluid density, may compress airway), foregut duplication cysts.
- Posterior compartment: neurilemmoma (schwannoma) and neurofibroma (nerve sheath, adults, dumb-bell shape if they extend through the intervertebral foramen — always get MRI to exclude intradural extension); ganglioneuroma (older child, asymptomatic); neuroblastoma (under 5 years, metastatic, urinary catecholamines); paraganglioma.
- Workup: contrast CT (fat, fluid, calcification, enhancement answer most questions), MRI for neurogenic extension and vascular invasion, thyroid function and uptake if goitre suspected, serum AFP and beta-hCG for suspected nonseminomatous germ cell tumour, and myasthenia serology with a thymic mass.
- Golden management rule: biopsy (VATS, Chamberlain procedure/anterior mediastinotomy, image-guided) for lymphoma and germ cell tumours — resection does not help and may complicate later chemotherapy; resection for thymoma, cysts, encysted empyema mimics, goitre and neurogenic tumours; observational follow-up for small asymptomatic cysts.
How to reason through a case
A 34-year-old man has a routine pre-employment chest radiograph that shows a widened mediastinum; CT demonstrates a well-defined anterior mediastinal mass with fat density and a calcified nodule. Reason by compartment and content: anterior mass with fat and calcification in a young adult is a mature teratoma (dermoid cyst) — a resectional diagnosis, so he is scheduled for excision (via median sternotomy or VATS depending on size) without biopsy, since biopsy of a teratoma only risks spillage. Now change one variable: the mass is homogeneous and soft tissue density with mediastinal nodes and the patient has night sweats — that is lymphoma territory; the next step is core biopsy or VATS biopsy for histology and immunophenotyping, not excision, because treatment is chemotherapy. Change it again: a 26-year-old man has a bulky anterior mass with gynaecomastia and serum AFP in the thousands — nonseminomatous germ cell tumour; the marker itself is diagnostic, biopsy is avoidable (bleeding and tumour seeding risks), and treatment is platinum-based chemotherapy with residual mass resection afterwards. And a 50-year-old with ptosis and diplopia plus an anterior lobular mass is a thymoma until excised with the whole thymus after myasthenia workup. One posterior example completes the map: a 29-year-old woman with a paravertebral mass and intercostal neuralgia — MRI before any surgery to map a dumb-bell schwannoma, because missing intradural extension turns a routine thoracotomy into an unplanned neurosurgical emergency.
Where students slip
The classic slip is calling every posterior mediastinal mass "neurofibroma" — the exam expects the split into nerve sheath tumours (adults: schwannoma more than neurofibroma) versus sympathetic chain tumours (children: neuroblastoma under 5, ganglioneuroma older) with the age clue. The second is excising what should be biopsied: lymphoma and nonseminomatous germ cell tumour are chemotherapy diseases, and the anterior mediastinotomy (Chamberlain) or VATS biopsy exists precisely for them. Third, forgetting MRI for the posterior mass with a neurological sign — the intraspinal component must be excluded before the thoracic operation.
Frequently asked questions
What are the "4 Ts" of the anterior mediastinum?
Thymoma, Teratoma (germ cell tumours), Terrible lymphoma and Thyroid (retrosternal goitre) — with parathyroid adenoma a fifth classic anterior entity.
Which tumours characteristically occupy the posterior mediastinum?
Neurogenic tumours — schwannoma and neurofibroma from nerve sheaths, ganglioneuroma and neuroblastoma from sympathetic ganglia — plus enteric duplication cysts.
Which mediastinal masses are biopsied rather than excised?
Lymphoma and nonseminomatous germ cell tumours — they are treated with chemotherapy; elevated AFP or beta-hCG may itself establish the diagnosis and spare a biopsy.
Which clinical syndrome accompanies thymoma most classically?
Myasthenia gravis — roughly a third to half of thymoma patients have it, and any thymic mass warrants myasthenia assessment before surgery.