Retroperitoneal lymphoma is a lymphoproliferative neoplasm showing primary or secondary (nodal/extranodal) retroperitoneal involvement. Non-Hodgkin lymphoma (especially DLBCL and follicular lymphoma) is the most common type. The most characteristic imaging finding is encasement of vessels without occlusion (sandwich sign) — reflecting the soft, deformable nature of lymphoma cells and the most valuable finding for differentiation from sarcomas. It shows homogeneous, mild-to-moderate enhancement and necrosis is rare pre-treatment. Marked diffusion restriction on DWI (very low ADC) reflects high cellular density. Responds dramatically to treatment (chemotherapy) with rapid size reduction.
Age Range
20-75
Peak Age
55
Gender
Male predominant
Prevalence
Common
Retroperitoneal lymphoma is a clonal lymphocyte proliferation from lymph node or extranodal lymphoid tissue. Tumor cells are soft, deformable, and grow around vessels without invading the vessel wall — this is the pathoanatomic basis of the sandwich sign. Lymphocyte-derived cells lack the capacity to invade the elastic lamina and adventitia of vessel walls; instead they grow by expanding around vessels, leaving the vessel lumen patent. Lymphoma cells show lymphoid proliferation rather than fibrous stroma, producing homogeneous soft tissue density and homogeneous T2 signal. Mild-to-moderate enhancement results from low-vascularity solid proliferation — neovascularization is minimal with small-caliber capillaries. Necrosis is rare pre-treatment because lymphoma cells show homogeneous proliferation with low metabolic requirements. Very low ADC values on DWI result from dense packing of small lymphocytes (7-15 μm), minimizing extracellular space.
Retroperitoneal lymphoma encasing the aorta and IVC (or other great vessels) without occlusion on contrast-enhanced CT — vessel lumen remains patent. This finding is pathognomonic for lymphoma and the key criterion for differentiating from sarcomas showing vessel invasion. The presence of sandwich sign reflects the soft, non-invasive nature of lymphoma cells and determines the primary diagnosis to consider in retroperitoneal mass differential.
On contrast-enhanced CT, retroperitoneal lymphoma encases the aorta and IVC without occlusion — 'sandwich sign' or 'aortic mantle'. Vessel lumen remains patent and opacified with contrast. Tumor tissue appears as homogeneous soft tissue density mass between and around vessels. This finding is pathognomonic for lymphoma and the most valuable finding for differentiation from sarcomas (vessel invasion and occlusion).
Report Sentence
Conglomerate lymphadenopathy encasing the aorta and IVC without occlusion is seen in the retroperitoneal space with sandwich sign; lymphoma should be primarily considered.
On DWI, lymphoma shows marked diffusion restriction. ADC values are very low (0.4-0.8 × 10⁻³ mm²/s) — among the lowest ADC values of retroperitoneal masses. This reflects high cellular density and small round cell morphology. ADC rises with treatment response (cell death → increased diffusion) — this characteristic shows response earlier than RECIST size criteria in treatment response assessment.
Report Sentence
Marked diffusion restriction with very low ADC values is seen in the mass consistent with high-cellularity lymphoproliferative disease.
On T2, lymphoma shows homogeneous intermediate signal — higher than muscle but markedly lower than fluid. This homogeneous signal reflects lymphoma's uniform cellular composition. Necrosis, hemorrhage, or cystic areas are not expected pre-treatment. This signal characteristic is valuable for differentiation from retroperitoneal sarcomas (usually high T2) and ganglioneuroma (very high T2).
Report Sentence
The mass shows homogeneous intermediate signal on T2 without necrosis or hemorrhage.
On non-contrast CT, lymphoma appears as conglomerate lymphadenopathy at homogeneous soft tissue density (30-50 HU). Calcification is very rare pre-treatment — post-treatment calcification may develop (especially in Hodgkin lymphoma). Necrosis not expected pre-treatment. Multiple retroperitoneal lymph node groups may coalesce (matted/conglomerate) forming a large mass and may involve the renal hilum, ureteral level, and pelvic region.
Report Sentence
Conglomerate lymphadenopathy at homogeneous soft tissue density is seen in the retroperitoneal space.
On FDG PET-CT, lymphoma typically shows homogeneous high FDG uptake. DLBCL SUVmax may be >10-20 — aggressive lymphomas show the highest FDG uptake. Deauville criteria (comparison with mediastinal blood pool and liver — 5-point scale) are used for treatment response assessment. Complete metabolic response shows disappearance of FDG uptake (Deauville 1-2). Indolent lymphomas (follicular) may show low-to-moderate FDG uptake.
Report Sentence
Homogeneous high FDG uptake is seen in the retroperitoneal mass consistent with lymphoproliferative disease.
On contrast-enhanced CT portal venous phase, lymphoma shows mild-to-moderate homogeneous enhancement. Enhancement is typically 50-80 HU and markedly different from hypervascular tumors (SFT, Castleman). Heterogeneous enhancement suggests aggressive type or post-treatment changes. Contrast-enhanced phase is also critical for evaluating ureteral obstruction, hydronephrosis, and renal function.
Report Sentence
The retroperitoneal mass shows mild-to-moderate homogeneous enhancement in portal venous phase.
Criteria
Most common NHL type (30-40%), aggressive, rapid growth, CD20 positive
Distinct Features
Rapid growth, very high FDG uptake (SUVmax >10-20), 60-80% complete remission with R-CHOP chemotherapy, dramatic size reduction with chemotherapy
Criteria
Indolent NHL, slow growth, BCL2 translocation t(14;18), CD10/CD20 positive
Distinct Features
Slow growth, multiple small nodules, low-to-moderate FDG uptake, long survival but usually incurable, transformation risk (3%/year to DLBCL)
Criteria
Highly aggressive, MYC translocation t(8;14), very high proliferation (Ki-67 ~100%), young adult/child
Distinct Features
Very rapid growth (days-weeks), very high FDG (SUVmax >20), abdominal/retroperitoneal mass in young patient, high tumor lysis syndrome risk
Distinguishing Feature
Leiomyosarcoma shows vessel invasion/occlusion and heterogeneous necrosis; lymphoma encases vessels (sandwich sign) and is homogeneous — leiomyosarcoma usually originates from IVC
Distinguishing Feature
Castleman shows intense homogeneous enhancement (hypervascular, prominent in arterial phase); lymphoma mild-to-moderate enhancement — Castleman usually smaller and solitary
Distinguishing Feature
ECD shows coated aorta sign (periaortic fibrous sheath) and hairy kidney; lymphoma shows nodal sandwich sign — bilateral symmetric bone osteosclerosis accompanies ECD
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthRetroperitoneal lymphoma is treated with chemotherapy — no surgical indication because lymphoma is a chemosensitive disease and complete remission can be achieved with chemotherapy. Biopsy (preferably core or excisional) is required for diagnosis — FNA may be insufficient for subtype determination because architectural pattern of lymphoid cells requires flow cytometry and immunohistochemistry. R-CHOP (rituximab + cyclophosphamide + doxorubicin + vincristine + prednisone) is standard treatment for DLBCL with 60-80% complete remission rate. Treatment response is assessed by PET-CT (Deauville criteria — mediastinal blood pool and liver as reference). Lugano classification is used as standard for staging and response assessment. Follow-up PET-CT every 3-6 months, continued with annual follow-up after complete remission. Tumor lysis syndrome risk should be considered especially in aggressive types (Burkitt) and prophylactic measures (hydration, allopurinol/rasburicase) should be taken.
Retroperitoneal lymphoma shows excellent response to chemotherapy. PET-CT is the gold standard for staging and treatment response assessment. Biopsy (core or excisional) is required for definitive diagnosis. R-CHOP for NHL and ABVD for HL are primary treatment regimens.