Mediastinal lymphoma is common, either as part of disseminated disease or less commonly as the site of primary involvement.
Lymphomas are responsible for approximately 15% of all primary mediastinal masses, and 45% of anterior mediastinal masses in children 1. Only 10% of lymphomas which involve the mediastinum are primary (i.e. mediastinal involvement not part of systemic disease) and the majority are Hodgkin lymphomas (~ 60%) 5.
The mediastinum is commonly involved in systemic lymphomas. Approximately 60% of all Hodgkin lymphoma and 20% of non-Hodgkin lymphoma involves the mediastinum at presentation. Less frequently, the disease is isolated to the mediastinum (3% Hodgkin lymphoma, <1 0% non-Hodgkin lymphoma) 1. As such, patients are often asymptomatic from the mediastinal component but present with systemic manifestations of lymphoma, most commonly constitutional symptoms 5.
Symptoms directly attributable to the mediastinal component include 4-5:
Mediastinal lymphomas usually arise from either the thymus or lymph nodes, thus accounting for their predilection for the anterior and middle mediastinum 1. The anterior mediastinal and para-tracheal nodes are the most frequently involved regions while isolated hilar node enlargement is uncommon without accompanying mediastinal node enlargement. Posterior mediastinal involvement is also infrequent.
Current World Health Organisation classification of neoplastic diseases of the lymphoid tissues includes lymphomas and leukaemias, and is according to the cell of origin, with the main division being:
- B-cell neoplasms
- T-cell and natural killer cell neoplasms
- Hodgkin lymphoma
Primary mediastinal lymphomas are most frequently of three histologic varieties 5:
- nodular sclerosing Hodgkin lymphoma
- primary mediastinal large B-cell lymphoma 3
- lymphoblastic lymphoma
The majority of patients have anterior mediastinal and paratracheal involvement. Isolated hilar nodal involvement is uncommon 6.
A soft tissue mass may be clearly visible, or more frequently the mediastinum is widened, and the retrosternal airspace is obscured.
CT demonstrates a soft tissue attenuating mass, with smooth or lobulated margins which conform to surrounding structures. Cystic/ low-density areas are common. Other features include 6:
- parenchymal invasion: uncommon
- seen in 50% of cases
- usually unilateral
- usually exudates
- pleural deposits may be present
- pericardial effusion
- chest wall invasion
Calcification is usually seen following therapy and can have varying morphology, including irregular, diffuse or even egg-shell 6.
Following treatment nodal masses usually reduce in size, however in some instances the size of the mass remains the same or even increases (in cases of thymic hyperplasia) 2. As such CT is not ideal for assessing for treatment response when a decrease in size is not present.
Appearance of lymphomas on MRI varies with treatment and type of lymphoma 2.
- T1: replace
- at diagnosis: variable but present
- following treatment: decreases
T1 C+ (Gd)
- at diagnosis: variable but present
- following treatment: decreases and becomes more heterogeneous due to necrosis and fibrosis 2
- absence of decrease following treatment suggests the continued presence of viable neoplastic tissue 2
Gallium and FDG-PET
Both gallium-67 scintigraphy and FDG-PET are better able to assess for tumour viability following treatment than CT, as residual mass does not necessarily represent residual viable neoplastic tissue 2.
Unfortunately, up to 20% of cases are gallium negative at diagnosis 2.
Treatment and prognosis
Specific treatment depends on the type of lymphoma and the stage, but broadly requires chemotherapy and or radiotherapy 5.
Similarly, the prognosis is very variable. Stage I and II Hodgkin lymphoma have the best prognosis with a greater than 90% cure rate 5.
- vascular compression 4
- SVC syndrome
- compression of the aorta
- compression of the pulmonary arteries
On CT the differential includes:
- 1. Shields TW. General Thoracic Surgery. Lippincott Williams & Wilkins. (2009) ISBN:0781779820. Read it at Google Books - Find it at Amazon
- 2. Rahmouni A, Divine M, Lepage E et-al. Mediastinal lymphoma: quantitative changes in gadolinium enhancement at MR imaging after treatment. Radiology. 2001;219 (3): 621-8. Radiology (full text) - Pubmed citation
- 3. Shaffer K, Smith D, Kirn D et-al. Primary mediastinal large-B-cell lymphoma: radiologic findings at presentation. AJR Am J Roentgenol. 1996;167 (2): 425-30. AJR Am J Roentgenol (abstract) - Pubmed citation
- 4. Shields JJ, Cho KJ, Geisinger KR. Pulmonary artery constriction by mediastinal lymphoma simulating pulmonary embolus. AJR Am J Roentgenol. 1980;135 (1): 147-50. AJR Am J Roentgenol (abstract) - Pubmed citation
- 5. Duwe BV, Sterman DH, Musani AI. Tumors of the mediastinum. Chest. 2005;128 (4): 2893-909. doi:10.1378/chest.128.4.2893 - Pubmed citation
- 6. Collins J, Stern EJ. Chest radiology, the essentials. Lippincott Williams & Wilkins. (2007) ISBN:0781763142. Read it at Google Books - Find it at Amazon
- overview of lymphoma
WHO classification of tumours of haematopoietic and lymphoid tissues
- Hodgkin lymphoma
- mature B-cell lymphoma
- mature T-cell and NK-cell lymphoma
- post-transplant lymphoproliferative/lymphoproliferation disorders
- location-specific lymphomas
- central nervous system
- head and neck lymphoma
- thoracic lymphoma
- gastrointestinal lymphoma
- hepatobiliary lymphoma
- genitourinary lymphoma
- musculoskeletal lymphoma
- cutaneous lymphoma
- lymphoma staging