Castleman disease (angiofollicular lymph node hyperplasia) is a rare lymphoproliferative disorder. Hyaline-vascular type (90%) presents as a solitary, hypervascular mass, while plasma cell type (10%) is multicentric with systemic symptoms. Retroperitoneal Castleman is usually hyaline-vascular type characterized by intense homogeneous enhancement with enhancement intensity equal to or greater than the spleen. HHV-8 associated multicentric form occurs in HIV-positive patients and carries risk of associated Kaposi sarcoma. The disease typically presents between ages 30-50, often asymptomatically or as an incidental finding. IL-6 overproduction plays a central role in the pathophysiology of the disease.
Age Range
20-55
Peak Age
35
Gender
Equal
Prevalence
Rare
In hyaline-vascular Castleman disease, germinal centers of the lymph node become hyper-vascularized — blood vessels penetrate germinal centers in an onion-skin pattern forming hyalinized stroma. This vascular penetration represents proliferation of capillary vessels not normally present in germinal centers, resulting in germinal centers containing both vascular and hyaline components. This dense vascularization is the basis of intense arterial enhancement on CT — contrast rapidly accumulates through the rich capillary network reaching density values equal to or exceeding splenic enhancement. IL-6 overproduction plays an important role in pathogenesis; IL-6 stimulates B-cell differentiation and plasma cell formation, increases vascular endothelial growth factor (VEGF) production, and this VEGF increase is the main driver of intense neovascularization. In plasma cell type, dense plasma cell infiltration occurs in the interfollicular area with IL-6-mediated systemic inflammatory response — fever, anemia, hypergammaglobulinemia, elevated CRP, and cachexia. In HHV-8 associated multicentric type, viral IL-6 (vIL-6) production is the main pathophysiologic driver, mimicking the functions of human IL-6. Calcification develops as dystrophic calcification in hyalinized germinal centers, with the stellate pattern reflecting the radial distribution of germinal centers.
Intense homogeneous enhancement approaching or equal to spleen density in arterial phase is the most characteristic and diagnostic finding of hyaline-vascular Castleman disease. This finding is not seen at this intensity in any other benign retroperitoneal lesion and is nearly pathognomonic. Enhancement intensity results from the tumor's vascular density being 5-10 times that of normal lymph node.
In arterial phase, Castleman shows very intense homogeneous enhancement — approaching spleen or aortic density, typically measured in the 120-180 HU range. This intense enhancement is the most characteristic finding of hypervascular hyaline-vascular type and is nearly pathognomonic in the differential diagnosis of retroperitoneal masses. The feeding artery may be prominent, appearing as large-caliber, tortuous vessels. Slight heterogeneity may be seen in large tumors (>5 cm) but necrosis is not expected; presence of necrosis should raise suspicion for malignant lymphoproliferative disease. Early draining veins suggest the presence of AV shunting.
Report Sentence
A well-defined mass with intense homogeneous arterial enhancement approaching splenic density is seen in the retroperitoneal space; Castleman disease (hyaline-vascular type) should be considered.
On non-contrast CT, calcification is seen in 20-30% of Castleman disease. Calcification pattern may be stellate or punctate with central or peripheral location. In some cases, dense calcification may cover most of the tumor, and arciform (arc-shaped) pattern has also been reported. Presence of calcification is valuable in differential diagnosis from lymphoma because calcification in untreated lymphoma is extremely rare. Mass contours are smooth and well-defined; capsule presence is important for surgical planning.
Report Sentence
Stellate/punctate calcification is seen within the mass consistent with Castleman disease; this pattern of calcification is not expected in untreated lymphoma.
On T2, Castleman shows intermediate-to-high signal reflecting the water content of lymphoid cells in germinal centers. Flow voids (dilated vessels) may be seen within the tumor reflecting hypervascularity — these appear as signal voids on T2-weighted images and provide strong evidence of a vascular tumor. Hyaline areas may show low T2 signal because collagen-like matrix causes short T2 relaxation. Necrosis or cystic change is not expected; necrosis should raise suspicion for malignant transformation or lymphoma.
Report Sentence
The mass shows intermediate-to-high T2 signal with intratumoral flow voids; consistent with hypervascular lymphoproliferative disease.
On contrast-enhanced MRI, intense homogeneous enhancement is seen with degree concordant with CT findings supporting hypervascular tumor. Feeding arteries and draining veins may be prominent and can be evaluated in detail on MR angiography. Gadolinium accumulation is rapid and intense; dynamic contrast-enhanced sequences may show rapid wash-in during arterial phase and persistent enhancement (slow washout) pattern in delayed phase. This kinetic pattern is consistent with hypervascular benign tumor.
Report Sentence
The mass shows intense homogeneous enhancement with prominent feeding arteries and persistent enhancement pattern on contrast-enhanced MRI; consistent with hypervascular tumor.
On DWI, Castleman disease shows moderate diffusion restriction. ADC values are higher than lymphoma but lower than normal lymph node (typically 1.0-1.5 x 10⁻³ mm²/s). This moderate restriction helps differentiate from lymphoma because lymphoma shows markedly low ADC (0.4-0.8 x 10⁻³ mm²/s). In hyaline-vascular type, ADC values are generally higher than plasma cell type because hyalinized germinal centers are cell-poor.
Report Sentence
Moderate diffusion restriction is seen in the mass with ADC values (1.0-1.5 x 10⁻³ mm²/s) higher than lymphoma but lower than normal lymph node.
In portal venous and delayed phases, Castleman disease shows persistent enhancement; the intense enhancement seen in arterial phase continues in portal venous phase and may even increase in delayed phase. This persistent enhancement pattern reflects the richness of the tumor's vascular structure and interstitial gadolinium accumulation. The enhancement pattern differs from the early peripheral enhancement and centripetal filling pattern of liver hemangioma.
Report Sentence
The mass shows persistent enhancement in portal venous and delayed phases; consistent with hypervascular tumor.
On Doppler US, Castleman disease shows marked hypervascularity. Extensive vascular signal is seen within the mass and the feeding artery can be identified by Doppler. Color Doppler shows diffuse and regular intratumoral vascularity, differing from the minimal vascularity in lymphoma. Spectral Doppler may show low resistance arterial flow pattern (RI < 0.5).
Report Sentence
Marked hypervascularity with low resistance arterial flow is seen within the mass on Doppler US.
Criteria
Solitary mass, rich vascularity, hyalinized germinal centers — 90% of all cases
Distinct Features
Intense homogeneous arterial enhancement (spleen-like), calcification common (20-30%), asymptomatic, curative with surgery (>95% cure rate); intermediate T2 signal and flow voids on MRI; intermediate ADC on DWI; histologically 'onion skin' vascular penetration pattern and hyalinized germinal centers
Criteria
Multicentric, interfollicular plasma cell infiltration — 10% of all cases; systemic symptoms (fever, anemia, hypergammaglobulinemia)
Distinct Features
Multiple lymph node involvement, less intense and more heterogeneous enhancement, systemic inflammatory symptoms IL-6 mediated, requires systemic treatment (anti-IL-6: siltuximab/tocilizumab) instead of surgery, calcification rare
Criteria
In HIV-positive patients, HHV-8 positive, multicentric distribution — viral IL-6 (vIL-6) drives pathogenesis
Distinct Features
Widespread lymphadenopathy, splenomegaly, KSHV-associated Kaposi sarcoma risk (15-20% association), rituximab treatment added, POEMS syndrome in differential, more aggressive course and worse prognosis
Criteria
HHV-8 negative, multicentric, unknown etiology
Distinct Features
TAFRO syndrome variant (thrombocytopenia, anasarca, reticulocytosis, fibrosis, organomegaly) is the most severe form; anti-IL-6 (siltuximab) is first-line treatment
Distinguishing Feature
SFT shows low T2 signal due to collagen dominance, which is the most characteristic MRI finding of SFT; Castleman is differentiated by intermediate-high T2 signal and nodal location. Both tumors may be hypervascular but calcification is rare in SFT while seen in 20-30% of Castleman.
Distinguishing Feature
Lymphoma shows low-to-moderate homogeneous enhancement (does NOT show enhancement as intense as spleen in arterial phase); Castleman shows very intense arterial enhancement. Lymphoma shows very low ADC (0.4-0.8) on DWI while Castleman shows intermediate ADC (1.0-1.5). Pre-treatment calcification is extremely rare in lymphoma.
Distinguishing Feature
HPC is considered same spectrum as SFT and may be hypervascular but has extra-nodal origin (from pericytes); Castleman shows nodal origin (lymph node hyperplasia). Calcification is common in Castleman but rare in HPC. Histopathologically, Castleman shows germinal center hyperplasia while HPC shows staghorn vessel pattern.
Distinguishing Feature
Paraganglioma may be intensely enhancing hypervascular mass but typically in paraganglionic location (aortic bifurcation, organ of Zuckerkandl); Castleman has nodal location. Paraganglioma may secrete catecholamines (hypertension, palpitations); Castleman asymptomatic. MIBG scintigraphy positive in paraganglioma, negative in Castleman.
Urgency
routineManagement
surgicalBiopsy
NeededFollow-up
12-monthSurgical resection is curative in hyaline-vascular solitary Castleman with over 95% cure rate. Preoperative embolization may be considered due to hypervascularity; embolization can reduce surgical blood loss by 50-70% and is particularly recommended for masses >5 cm or cases with large feeding arteries. Multicentric type (plasma cell and HHV-8 associated) requires systemic treatment: anti-IL-6 (siltuximab — FDA approved, tocilizumab), immunomodulators, and chemotherapy when needed. Rituximab (anti-CD20) is added in HHV-8 associated multicentric type and Kaposi sarcoma screening should be performed. Doege-Potter syndrome (paraneoplastic hypoglycemia — IGF-II overproduction) may rarely accompany. Long-term follow-up after surgery is recommended because late recurrences have been reported. TAFRO syndrome variant of iMCD is the most severe form requiring urgent treatment.
Unicentric Castleman disease is curative with surgical resection and prognosis is excellent. Multicentric type has worse prognosis and requires systemic therapy (rituximab, siltuximab). HHV-8 associated multicentric type occurs in HIV-positive patients.