Mediastinal non-Hodgkin lymphoma (NHL) is a heterogeneous group of malignant lymphoproliferative neoplasms arising in the mediastinum. Primary mediastinal (thymic) large B-cell lymphoma (PMBCL) is the most common subtype, showing predominance in young women (20-40 years). It forms a large, bulky mass in the anterior and middle mediastinum and frequently causes superior vena cava (SVC) syndrome. Other mediastinal NHL subtypes include lymphoblastic lymphoma (usually T-cell, adolescents), mantle cell lymphoma, and follicular lymphoma. On CT, a typically large (>10 cm), lobulated, mildly to moderately heterogeneously enhancing mass is seen in the anterior mediastinum. The 'sandwich sign' — encasement of great vessels by tumor tissue on both sides — is a characteristic CT finding of mediastinal lymphoma. Treatment is chemotherapy-based (R-CHOP, DA-EPOCH-R); radiotherapy may be used for consolidation.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Primary mediastinal large B-cell lymphoma (PMBCL) originates from thymic (medullary) B cells. At the molecular level, JAK-STAT, NF-kB, and PD-L1/PD-L2 signaling pathways are overactivated — particularly 9p24.1 amplification leads to PD-L1/PD-L2 overexpression enabling tumor immune evasion. This intense cellular proliferation and fibrosis forms the basis of the large, bulky anterior mediastinal mass on imaging. The tumor grows rapidly, compressing mediastinal structures — SVC compression/invasion leads to SVC syndrome, pericardial invasion to pericardial effusion. Homogeneous lymphoid cell proliferation and variable fibrosis determine the homogeneous to mildly heterogeneous enhancement pattern on CT. The sandwich sign represents the tumor encasing great vessels from both sides — the perivascular growth pattern of tumor cells underlies this finding. In T-lymphoblastic lymphoma, uncontrolled proliferation of immature T-cell precursors in the thymus occurs and may be accompanied by bone marrow/peripheral blood involvement.
Encasement of great mediastinal vessels by tumor tissue from both sides — vessels appear like filling between sandwich bread. Reflects lymphoma's perivascular growth pattern and typically preserves vessel lumen.
On CT, a large (typically >10 cm), lobulated mass is seen in the anterior mediastinum. The mass frequently completely replaces the thymus. Enhancement is generally homogeneous or mildly heterogeneous — areas of necrosis, cystic degeneration, and fibrosis contribute to heterogeneity. The mass may compress surrounding mediastinal structures and extend into the chest wall. Pleural and pericardial effusions frequently accompany.
Report Sentence
Bulky mass in the anterior mediastinum replacing the thymic lodge, measuring approximately X×Y×Z cm, with lobulated margins and mildly heterogeneous enhancement; lymphoma is primarily considered.
The sandwich sign describes encasement of great vessels (SVC, aorta, pulmonary arteries) by tumor tissue from both sides in mediastinal lymphoma. The vessels appear like 'filling between sandwich bread' — the vessel lumen typically remains patent. This finding reflects lymphoma's perivascular growth pattern and differs from vascular invasion by solid tumors — vessel lumen is typically preserved.
Report Sentence
The mediastinal mass encases the SVC and pulmonary arteries from both sides (sandwich sign) with patent vessel lumina; consistent with mediastinal lymphoma.
Anterior mediastinal lymphoma may compress the SVC, causing SVC syndrome. On CT, the SVC may appear narrowed or occluded — distension of proximal SVC and brachiocephalic veins is observed. Venous collateral development (azygos, hemiazygos, internal mammary vein, chest wall veins) emerges as compensatory mechanism. Subcutaneous edema of face, neck, and upper extremities accompanies.
Report Sentence
The anterior mediastinal mass compresses the SVC with prominent venous collateral development and subcutaneous edema of face/neck; consistent with SVC syndrome.
On MRI, mediastinal NHL shows heterogeneous hyperintense signal on T2-weighted images. Viable tumor tissue demonstrates intermediate to high T2 signal, while fibrosis areas exhibit low T2 signal. On DWI, viable tumor shows marked diffusion restriction (ADC <1.0 × 10⁻³ mm²/s). T2 signal intensity is important in post-treatment residual mass assessment.
Report Sentence
The anterior mediastinal mass shows heterogeneous hyperintense signal on T2-weighted images with diffusion restriction.
On FDG PET-CT, mediastinal NHL demonstrates high metabolic activity — SUVmax typically >10-15 (DLBCL/PMBCL). FDG uptake is generally heterogeneous with necrosis and fibrosis showing low uptake. PET-CT is the gold standard for staging — superior to CT in detecting nodal and extranodal involvement. Post-treatment PET-CT evaluates response using Deauville scoring.
Report Sentence
Intense FDG uptake is observed in the anterior mediastinal mass (SUVmax: X); consistent with lymphoma, staging is recommended.
Necrosis and cystic degeneration are seen in 30-50% of large mediastinal NHL masses, appearing as low-density areas (10-20 HU) without enhancement. Necrosis is typically central with viable tumor tissue showing rim enhancement peripherally.
Report Sentence
Central necrotic/cystic degeneration areas are seen within the mass with peripheral rim enhancement.
Criteria
Most common mediastinal NHL. Originates from thymic B cells. Predominant in women aged 20-40. CD20+, CD23+, MAL+, PD-L1/PD-L2 amplification.
Distinct Features
Large homogeneous mass in anterior mediastinum, SVC syndrome frequent. High FDG-PET uptake. Treatment: DA-EPOCH-R or R-CHOP + RT. Good prognosis (>80% 5-year survival).
Criteria
From immature T-cell precursors. Predominant in adolescent and young adult males. Anterior mediastinal mass + pleural effusion. Bone marrow involvement frequent. TdT+, CD3+, CD7+.
Distinct Features
Large anterior mediastinal mass, rapid growth, elevated LDH. Homogeneous, low to moderate enhancement on CT. ALL-type aggressive chemotherapy required.
Criteria
Overlapping features between PMBCL and classic Hodgkin lymphoma. CD20+, CD30+, CD15 variable.
Distinct Features
CT findings similar to PMBCL but more aggressive. Treatment not standardized. Prognosis worse than PMBCL.
Distinguishing Feature
Hodgkin involves contiguous stations while NHL may show skip lesions. Reed-Sternberg cells are specific to Hodgkin. Hodgkin usually shows more homogeneous enhancement.
Distinguishing Feature
Thymoma is well-defined, encapsulated with more homogeneous enhancement. Calcification more common in thymoma, pleural 'drop metastasis' characteristic. Usually 40-60 years. Myasthenia gravis association supports thymoma.
Distinguishing Feature
Mature teratoma contains fat and calcification — fat-fluid level is pathognomonic. Fat is not expected in lymphoma. Seminoma: young male profile and tumor markers are distinguishing.
Distinguishing Feature
Thymic carcinoma shows direct invasion of adjacent structures (bone, lung). Pleural and pericardial metastases common. More heterogeneous enhancement.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
specialist-referralMediastinal NHL is aggressive. SVC syndrome requires emergency intervention. Core biopsy is required. PMBCL: DA-EPOCH-R or R-CHOP + consolidation RT. T-lymphoblastic: ALL-type chemotherapy. FDG PET-CT is gold standard. >80% 5-year survival for PMBCL.
Non-Hodgkin lymphoma treatment protocols vary by subtype. R-CHOP chemotherapy and radiotherapy are standard treatment for PMBCL. PET-CT is critical for staging and treatment response assessment.