mediastinal lymphoma

Radiopaedia • CC-by-nc-sa 3.0 • de

Mediastinal lymphoma is common, either as part of disseminated disease or less commonly as the site of primary involvement.

Epidemiology

Lymphomas are responsible for approximately 15% of all primary mediastinal masses, and 45% of anterior mediastinal masses in children . 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%) .

Clinical presentation

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, <10% non-Hodgkin lymphoma) . As such, patients are often asymptomatic from the mediastinal component but present with systemic manifestations of lymphoma, most commonly constitutional symptoms .

Symptoms directly attributable to the mediastinal component include :

retrosternal chest pain
SVC compression with SVC syndrome
dyspnea
cough

Pathology

Mediastinal lymphomas usually arise from either the thymus or lymph nodes, thus accounting for their predilection for the anterior and middle mediastinum . 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 Organization 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 :

nodular sclerosing Hodgkin lymphoma

primary mediastinal large B-cell lymphoma

lymphoblastic lymphoma

Radiographic features

The majority of patients have anterior mediastinal and paratracheal involvement. Isolated hilar nodal involvement is uncommon .

Plain radiograph

A soft tissue mass may be clearly visible, or more frequently the mediastinum is widened, and the retrosternal airspace is obscured.

CT

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 :

parenchymal invasion: uncommon
pleural effusion(s)
- 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 .

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) . As such CT is not ideal for assessing for treatment response when a decrease in size is not present.

MRI

Appearance of lymphomas on MRI varies with treatment and type of lymphoma .

T1: replace
T2
- 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
- absence of decrease following treatment suggests the continued presence of viable neoplastic tissue

Gallium and FDG-PET

Both gallium-67 scintigraphy and FDG-PET are better able to assess for tumor viability following treatment than CT, as residual mass does not necessarily represent residual viable neoplastic tissue .

Unfortunately, up to 20% of cases are gallium negative at diagnosis .