Oncoanatomy: Mediastinum

AC presents the resident portion of the Oncoanatomy module on the Mediastinum

Anterior, middle and posterior mediastinal compartments have no intrinsic discriminating planes, however the division is useful for differential diagnosis. Primarily the middle compartment contains the heart, great vessels and airways, the anterior and posterior compartments are simply in front of or behind these structures.

Anterior Compartment
Contents include Internal mammary vessels, thymus, fat pad.
DDx for masses: 4Ts - Thymic lesions, Thyroid, Teratoma, (Terrible) Lymphoma PMBCL or Lymphoblastic lymphoma

Primary mediastinal b-cell lymphoma - variant of DLBCL. R-CHOP often used. Consolidative RT is often used. Outcomes may be more favorable than other variants of DLBCL. Peak age in the 30s and 40s.

Lymphoblastic Lymphoma: Pre B or C cells, blurred line between this and lyphoblastic lymphoma. Male predominance, peak incidence in 2nd and 3rd decades. Thymic origin CD7+, CD5+, CD2+. Mediastinal involvement in 60-70%. Treated along leukemic protocols (VPDC). Role of RT is unclear. In T-cell cases, CNS prophylaxis is indicated (intrathecal MTX +/- cranial RT).

Middle Mediastinum: Great vessels, Heart, Trachea and Airways.
Primarily metastasis or lyphoma.

Posterior Mediastinum: Esophagus, Lymph nodes, Fat, Sympathetic chains, the Azygous vein, Thoracic duct.
DDx: Neurogenic tumors, esophageal tumors, aortic lesions.

Hodgkin Lymphoma. Historically treated with RT alone with a 5yr survival of approximately 30%.

Mantle field: superior edge is at the mastoid tips, inferior at T9-10 spaces, lateral borders include the axillary nodal regions. Custom blocking is used for bilateral lungs, and humeral heads, shaped to include the bilateral hila. Lanrynx block is placed around 20Gy.

JAMA 2003;290:2831 (Hull) - 415pts with HL treated with RT or CTRT, with 80% recieving mantle fields. 10% developed CAD by 20 years. 6% had valvular dysfunction at 22yrs.

RT + doxorubicin. Myrehaug, Leukemia Lymphoma 49:1486. Doxorubicin seems to have a supra additive effect on cardiac toxicity with an HR for cardiac morbidity of 2.77 vs HR 1.82 with RT alone.