0424 - Mediastinal Tumours

Question 1

What is the mediastinum?

Answer 1

A central portion of the thorax that contains all thoracic structures except lungs and pleura. Divided into superior and inferior (anterior, middle, and posterior) compartments. Lymph nodes, small vessels, nerves, loose CT and adipose tissue in all compartments.

Question 2

What are the contents of the superior portion of the mediastinum?

Answer 2

Thymus, thyroid, parathyroid Great vessels Oesophagus, trachea, thoracic duct.

Question 3

What are the contents of the inferior posterior mediastinum?

Answer 3

Descending aorta, Inferior thoracic vertebrae Oesophagus Thoracic nerves

Question 4

What are the contents of the inferior middle mediastinum?

Answer 4

Pericardium Heart Great vessels Phrenic nerves Main bronchi

Question 5

What are the contents of the inferior anterior mediastinum?

Answer 5

In infancy contains the thymus. In adults smallest subdivision.

Question 6

What is a good approach to analysing tumours?

Answer 6

Is it neoplastic or non-neoplastic? If neoplastic, is it benign/malignant? Primary/secondary? Cell type - epithelial, mesenchymal, mixed, lymphoid, melanocytic, Germ cell, unclassified. If non-neoplastic - infection/inflammation/deposit/hamartoma/congenital?

Question 7

What is required in the macro description of a tumour

Answer 7

Site, size, shape, margins, capsule, colour, consistency 3 S’s, M, 3 C’s

Question 8

What are three common tumours of the mediastinum?

Answer 8

Thymoma - Superior and inferior anterior Lymphoma - Superior and inferior middle/anterior Germ Cell tumours - inferior anterior

Question 9

Describe the normal thymus under light microscopy

Answer 9

Divided into lobules by a fibrous septa/capsule around each one. Lobules contain cortex and medulla Cortex - basophilic lymphocytes (thymocyteS) Medulla - Epithelial cells and Hassall Corpuscles (round, keratinised whorls of epithelial cells). Increased fat with age.

Question 10

Describe a thymoma

Answer 10

Taken to mean a neoplasm of thymic epithelial cells Adult >40yrs, M=F Found by myasthenia gravis (50% cases), local pressure symptoms, or incidental discovery Found on imaging, but biopsy required for diagnosis. Can invade local tissue, but not metastasise.

Question 11

Describe the macro and micro appearance of a thymic epithelial neoplasm.

Answer 11

Macro - Encapsulated, lobulated pale cut surface with cystic change, calcification, and ossification. Micro - 3 components, fibrous tissue dividing into lobules, epithelial cells - too many, may be cytologically benign to malignant, lymphocytes are non-neoplastic,jsut immature T-cells.

Question 12

What is the difference between thymoma and thymic carcinoma?

Answer 12

Both thymic epithelial neoplasms Thymoma is well differentiated, with no cellular atypia Thymic carcinoma is poorly differentiated with cellular features of malignancy. Thymic carcinoma can metastasize, but thymoma wont.

Question 13

What is myasthenia gravis

Answer 13

Autoimmune disease attacking ACh receptors, leading to muscle weakness, fatigue, and death by respiratory failure. F>M 15% associated with thymoma, 65% with thymic hyperplasia.

Question 14

What is non-Hodgkin lymphoma?

Answer 14

Neoplasm of a group of nodes, from indolent to aggressive.

85% from B cells, remainder T cells - all monoclonal.

Need systemic treatment due to lymphatic circulation

Lymph node tissue gets replaced by lymphoma nodules

Question 15

What is Hodgkin lymphoma

Answer 15

Neoplasm of a single node or group of nodes according to staging.

Potentially curable - spreads in an orderly fashion.

Contains Reed-Sternberg “Owls Eye” cells.

Question 16

Provide a definition of lymphoma and difference between Hodgkin and non-Hodgkin

Answer 16

Malignant tumour of lymphocytes occurring as a discrete tissue mass. Non-Hodgkin - B or T cells, 85% B. Systemic spread, so systemic treatment. Range of behaviour, but progressive disease Hodgkin - contains Reed-Sternberg cells. Orderly spread, so local treatment. Range of behaviour, but potentially curable.

Question 17

How can you diagnose a lymphoma?

Answer 17

Requires Biopsy, then 3 paths to confirm.

1. Morphology on H&E - node replaced by malignant follicles, loss of architecture and infiltration into fat.
2. IHC - B Cells have CD20, T-cell CD3, Reed Sternberg (Hodgkins) - CD15 and CD30,
3. Cytogenetics - Particularly t(14; 18), leading to over-expression of anti-apoptotic Bcl-2

Question 18

Describe lymphoma in the mediastinum

Answer 18

Can be Hodgkin and non-Hodgkin - generally Hodgkin Can be primary mediastinal, or part of systemic disease Most commonly Hodgkin>Diffuse large cell lymphoma (B cell) >Lymphoblastic leukaemia (B or T cell).

Question 19

Describe a germ cell tumour in the mediastinum

Answer 19

M>F. Broad age range but usually 10-30 yrs. Found in anterior superior mediastinum. Symptoms occure due to compression or invasion of structures. Can be teratomatous or non-teratomatous Non-teratomatous most aggressive.

Question 20

What are the types of teratomatous and non-teratomatous mediastinal GCTs?

Answer 20

Teratomatous - mature (benign), immature (aggressive in adults) Non-teratomatous - Seminoma, yolk sac tumour, choriocarcinoma, embryonal carcinoma.