Peritoneal lymphomatosis is diffuse peritoneal spread of lymphoma, a rare clinical entity that may mimic peritoneal carcinomatosis. Most commonly associated with non-Hodgkin lymphoma (especially diffuse large B-cell lymphoma — DLBCL and Burkitt lymphoma); Hodgkin lymphoma rarely shows peritoneal involvement. Peritoneal involvement is reported in 5-10% of all lymphoma cases. Clinical presentation is characterized by ascites, abdominal pain, weight loss, and B symptoms (fever, night sweats, weight loss). CT shows diffuse peritoneal and omental thickening, ascites, and massive mesenteric and retroperitoneal lymphadenopathy. Differential from peritoneal carcinomatosis is critical as treatment and prognosis are entirely different — lymphoma is highly chemosensitive with cure rates reaching 50-70%. PET-CT is the gold standard for staging and treatment response. Diagnosis is made by peritoneal biopsy (laparoscopic or image-guided) or ascites cytology + flow cytometry. R-CHOP is the standard first-line regimen for DLBCL.
Age Range
30-75
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Peritoneal lymphomatosis results from lymphoma cell spread to the peritoneal cavity. Spread mechanisms: (1) Hematogenous — lymphoma cells reach peritoneal capillaries via bloodstream and implant on peritoneal surfaces; this is the most common mechanism. (2) Transdiaphragmatic — passage from lymphomatous pleural effusion through diaphragmatic lymphatics. (3) Direct invasion — direct extension from retroperitoneal or mesenteric lymphadenopathy. (4) Serosal penetration — full-thickness wall invasion of GI lymphoma (especially MALT or Burkitt) reaching serosal surface with tumor cell spillage into peritoneal cavity. Lymphoma cells proliferate on peritoneal surfaces creating diffuse thickening; unlike carcinomatosis, desmoplastic reaction is not prominent — therefore peritoneal thickening is more homogeneous with smoother contours. Ascites results from increased peritoneal capillary permeability and lymphatic drainage obstruction by tumor cells. The high metabolic activity of lymphoma cells causes prominent FDG uptake on PET-CT — due to GLUT-1 overexpression and high glycolytic rate. CT enhancement reflects dense cellular composition with relatively sparse stromal component — homogeneous low-to-moderate density enhancement is characteristic.
Sandwich sign is mesenteric lymphadenopathy encasing superior mesenteric artery and vein branches bilaterally, creating a 'sandwich' appearance where vascular structures are compressed between two lymphadenopathy masses. This is a pathognomonic CT finding of mesenteric lymphoma (especially non-Hodgkin lymphoma). Vascular lumen is preserved — lymphoma does not infiltrate vessel walls, only surrounds them. The contrast difference between enhanced vessels and surrounding hypodense lymphadenopathy in portal venous phase best demonstrates this sign.
Portal venous phase CT shows diffuse peritoneal thickening — unlike carcinomatosis, thickening is more homogeneous with smoother contours and less nodular component. Peritoneal thickening is uniform and thin-to-moderate (3-10 mm). Omental involvement may show diffuse infiltrative pattern rather than nodular cake — 'omental haze' with homogeneous density increase. The most important distinguishing finding is accompanying massive mesenteric and retroperitoneal lymphadenopathy — sandwich sign (mesenteric vessels encased by lymphadenopathy bilaterally) is pathognomonic. Lymphadenopathy typically shows homogeneous low-to-moderate enhancement without necrotic foci (in low-grade lymphomas). High-grade lymphomas (DLBCL, Burkitt) may develop central necrosis with rapid growth.
Report Sentence
Diffuse homogeneous peritoneal thickening with ascites and massive mesenteric/retroperitoneal lymphadenopathy (sandwich sign) consistent with peritoneal lymphomatosis.
FDG PET-CT shows very high metabolic activity at peritoneal involvement sites. SUVmax values are usually >10, significantly higher than epithelial carcinomas (typically SUVmax 3-8). Diffuse peritoneal FDG uptake, omental involvement, and intense FDG accumulation in lymphadenopathies constitute the metabolic signature of lymphoma. PET-CT is critical for staging — Lugano classification uses Ann Arbor staging with peritoneal involvement as extranodal disease (Stage IV). Deauville scoring for treatment response: post-treatment FDG uptake compared to mediastinal blood pool (Deauville 1-3) or liver (Deauville 4-5). Interim PET (after 2 cycles) provides early response assessment guiding treatment strategy.
Report Sentence
Intense FDG uptake (SUVmax: [value]) in peritoneal surfaces, omentum, and lymphadenopathies on FDG PET-CT consistent with lymphomatous peritoneal involvement.
Portal venous phase CT shows mesenteric lymphadenopathy encasing superior mesenteric artery (SMA) and vein (SMV) branches bilaterally creating 'sandwich' appearance. Conglomerate lymphadenopathy envelops mesenteric vessels but vascular lumen is usually preserved (lymphoma does not cause vascular invasion). Lymphadenopathies show homogeneous low-to-moderate enhancement and are usually >2 cm. Retroperitoneal lymphadenopathy often accompanies — conglomerate nodal masses around aorta and IVC. Splenic involvement (splenomegaly or focal lesions), hepatic involvement, and bone marrow infiltration may be present indicating advanced-stage disease.
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Mesenteric lymphadenopathy encasing SMA and SMV branches forming sandwich sign consistent with lymphoma; vascular lumen preserved.
DWI shows marked diffusion restriction in peritoneal lymphomatous involvement — hyperintensity at high b-values (b=800-1000) and low ADC values (<0.8 × 10⁻³ mm²/s) on ADC map. Very high cellular density and large nuclei of lymphoma cells restrict water diffusion. Mesenteric and retroperitoneal lymphadenopathies also show marked diffusion restriction. DWI helps distinguish lymphomatous (restricted diffusion) from reactive/inflammatory (free diffusion) peritoneal thickening. Post-treatment ADC increase indicates treatment response — as cellular density decreases, water diffusion increases and ADC rises.
Report Sentence
Marked diffusion restriction (low ADC) in peritoneal thickening and lymphadenopathies on DWI consistent with lymphoproliferative disease.
B-mode ultrasonography shows ascites with smooth peritoneal thickening and enlarged lymph nodes in mesenteric/retroperitoneal region. Ascites usually appears as homogeneous anechoic fluid; septated or echogenic ascites suggests high protein content (exudative). Peritoneal thickening is smooth and thin — different from nodular thickening in carcinomatosis. Mesenteric lymphadenopathies appear as hypoechoic, round nodes with hilum loss. Spleen size should be assessed — splenomegaly (>13 cm) suggests lymphoma involvement.
Report Sentence
Ascites, smooth peritoneal thickening, and mesenteric lymphadenopathy on ultrasonography; further imaging (CT/PET-CT) recommended for differential of lymphoproliferative disease.
Arterial phase shows homogeneous low-to-moderate enhancement of mesenteric and retroperitoneal lymphadenopathies. Conglomerate lymphadenopathy masses (>4-5 cm) with smooth or lobulated contours. Arterial enhancement is faint and homogeneous — lower than hypervascular carcinoma metastases (renal, thyroid). Central necrosis is generally absent in low-grade lymphomas (follicular, MALT); however necrotic areas may be seen in high-grade (DLBCL, Burkitt) and post-treatment lymphomas. Calcification is very rare in untreated lymphoma — calcified lymphadenopathy suggests post-treatment or alternative diagnoses (tuberculosis, silicosis).
Report Sentence
Conglomerate homogeneously enhancing lymphadenopathies in mesenteric and retroperitoneal region consistent with lymphoproliferative disease.
Criteria
Most common cause of peritoneal lymphomatosis. Aggressive course, rapid growth. Ki-67 index 60-90%. CT may show large conglomerate lymphadenopathies with necrosis. Very high FDG uptake on PET-CT (SUVmax >15). R-CHOP is standard treatment with 60-70% complete response rate.
Distinct Features
Rapid progression and large tumor burden. May have necrotic areas. CD20+ B-cell marker (rituximab target). Hans algorithm classifies into GCB or non-GCB subtypes with different prognosis. Double-hit/triple-hit lymphomas (MYC + BCL2/BCL6 translocations) are very aggressive requiring intensive chemotherapy (R-EPOCH, DA-R-EPOCH).
Criteria
Most aggressive lymphoma subtype, tumor doubling time 24-48 hours. Ki-67 index 95-100%. Ileocecal region is most common primary GI location. Peritoneal involvement is rapid and extensive. CT shows very rapidly growing masses, prominent ascites. Highest FDG uptake on PET-CT (SUVmax >20). High risk of tumor lysis syndrome — pre-treatment prophylaxis mandatory.
Distinct Features
More common in children and young adults. MYC translocation (t(8;14)) is diagnostic marker. 'Starry sky' histological appearance. Three variants: endemic (EBV-related, Africa), sporadic, and immunodeficiency-related. Intensive chemotherapy (R-CODOX-M/R-IVAC or R-hyper-CVAD) achieves 80-90% cure rate.
Criteria
Indolent low-grade NHL. Peritoneal involvement seen in late stage. CT shows multiple small-to-moderate lymphadenopathies, minimal ascites. Moderate FDG uptake on PET-CT (SUVmax 5-10). Watch-and-wait strategy applicable; rituximab ± bendamustine for symptomatic disease.
Distinct Features
t(14;18) BCL2 translocation is diagnostic marker. Transformation risk (to DLBCL) is 2-3%/year — sudden clinical deterioration or increasing SUV on PET suggests transformation. Lymphadenopathies on CT are smaller and more numerous compared to carcinomatosis-like nodular peritoneal implants.
Distinguishing Feature
Peritoneal carcinomatosis represents secondary spread from known epithelial primary (ovarian, GI, pancreatic). Differences from lymphomatosis: carcinomatosis has more nodular and irregular peritoneal thickening; lymphomatosis is more homogeneous and smooth. Mesenteric/retroperitoneal lymphadenopathy is less prominent in carcinomatosis; massive conglomerate lymphadenopathy (sandwich sign) is pathognomonic in lymphomatosis. CA-125 elevated in carcinomatosis vs normal in lymphomatosis. LDH elevated in lymphomatosis. SUVmax significantly higher (>10) in lymphomatosis on PET-CT.
Distinguishing Feature
Peritoneal tuberculosis shows granulomatous peritoneal thickening and ascites. TB peritoneal thickening may be smooth mimicking lymphomatosis. Differences: TB mesenteric lymphadenopathy characteristically shows central necrosis (rim enhancement) — lymphoma shows homogeneous enhancement. TB ascites has high ADA (>40 U/L); ADA is normal in lymphoma. TB implants may calcify. Endemic area history and positive PPD/QuantiFERON support TB.
Distinguishing Feature
PPC presents with peritoneal thickening, omental cake, and ascites — may resemble lymphomatosis. Differences: CA-125 markedly elevated in PPC vs normal in lymphomatosis. PPC occurs in women; lymphoma affects both sexes equally. Omental cake more prominent in PPC; omental haze more typical in lymphomatosis. PET-CT SUVmax 3-8 in PPC vs >10 in lymphomatosis. Massive mesenteric lymphadenopathy and sandwich sign not expected in PPC.
Distinguishing Feature
Peritoneal mesothelioma shows diffuse peritoneal thickening. Differences: mesothelioma has asbestos exposure history; lymphoma does not. Mesothelioma peritoneal thickening may be nodular with calcification; lymphomatosis is smooth without calcification. Massive lymphadenopathy not expected in mesothelioma; sandwich sign present in lymphomatosis. Immunohistochemistry provides definitive differentiation.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
3-monthRapid histopathological confirmation is critical in peritoneal lymphomatosis as treatment and prognosis differ entirely from peritoneal carcinomatosis. Diagnostic methods: (1) Ascites cytology + flow cytometry — least invasive, 80-90% diagnostic accuracy; monoclonal B or T cell population detected. (2) Image-guided percutaneous biopsy — core biopsy from peritoneal thickening or lymphadenopathy. (3) Laparoscopic peritoneal biopsy — highest diagnostic accuracy with histology + immunohistochemistry + genetic analysis. Treatment: R-CHOP (6-8 cycles) for DLBCL with 60-70% complete response rate. Intensive regimens for Burkitt. Watch-and-wait or rituximab ± bendamustine for follicular lymphoma. Treatment response: interim PET-CT (after 2 cycles) with Deauville scoring; end-of-treatment PET-CT for metabolic response confirmation. Follow-up CT/PET-CT at 3-month intervals for first 2 years, then 6-monthly.
Peritoneal lymphomatosis usually indicates advanced-stage lymphoma. B symptoms (fever, night sweats, weight loss) may be present. PET-CT is the most valuable modality for staging and treatment response assessment. Excisional biopsy is needed for subtyping.