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Castleman disease (

Castleman disease is an uncommon benign B-cell lymphoproliferative condition presenting as a solitary mediastinal mass in unicentric form or diffuse lymphadenopathy in multicentric form. Imaging is typically performed for routine exams in asymptomatic unicentric disease or to evaluate systemic symptoms in multicentric disease.

Key Images

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Look For First
  • Solitary hypervascular round mediastinal or hilar mass with homogeneous enhancement on contrast-enhanced CT
  • Early rapid enhancement with washout on dynamic CT—early arterial phase enhancement followed by delayed washout is characteristic
  • Prominent feeding vessels to the lymph node or mass, with exuberant vascularity on Doppler ultrasound
  • In multicentric disease: bilateral hilar and mediastinal lymphadenopathy with diffuse abdominal lymphadenopathy, hepatosplenomegaly, and ascites
Key Image Findings
  • On contrast-enhanced CT, the hyaline-vascular type shows intense homogeneous enhancement following contrast administration with early rapid arterial phase enhancement and washout in the delayed phase, creating a characteristic dynamic perfusion pattern.
  • CT typically demonstrates a solitary well-defined round mediastinal or hilar mass, though multiple hypervascular thoracic lymphadenopathy or matted lymphadenopathy in a single mediastinal compartment may be present.
  • Prominent feeding vessels entering the lymph node hilum are commonly visualized on CT, reflecting the hypervascular nature of the lymphoid hyperplasia.
  • Calcifications are relatively rare but when present show variable patterns including dense, coarse, or arborizing configuration; on MRI, arborizing calcifications appear as low signal on T2-weighted sequences.
  • On MRI, lesions are typically iso- to hyperintense on T1-weighted sequences and show significant gadolinium enhancement; diffusion-weighted imaging shows hyperintensity with low ADC values reflecting cellularity.
  • For mediastinal lesions larger than 5 cm, central hypoattenuation consistent with necrosis may be present despite peripheral enhancement.
  • On ultrasound, both hyaline-vascular and plasma-cell variants present as hypoechoic masses; Doppler reveals exuberant vascularity with predominantly peripheral flow and low-resistance arterial waveform.
  • In multicentric disease, bilateral hilar and mediastinal lymphadenopathy is seen along with pleural or pericardial effusions, centrilobular nodules, diffuse abdominal lymphadenopathy, and hepatosplenomegaly; HHV-8-associated multicentric disease may show reduced enhancement compared to unicentric types.
Differential Diagnosis
  • Lymphoma—the most common mimic; distinguished by the characteristic dynamic enhancement pattern (early rapid enhancement with washout), prominent feeding vessels, and homogeneous appearance of Castleman disease versus the typical nodal enhancement and involvement patterns of lymphoma.
  • Paraganglioma or other neurogenic tumors (schwannoma, neurofibroma)—distinguished by location in the posterior mediastinum, lower metabolic activity, and lack of the rapid washout enhancement pattern seen in Castleman disease.
  • Systemic infections (CMV-, HIV-, or EBV-associated lymphadenopathy)—distinguished by the degree of nodal enhancement, distribution pattern, and clinical context; Castleman disease shows more homogeneous hypervascular enhancement.
  • Sarcoidosis—distinguished by the pattern of mediastinal and hilar lymphadenopathy, which is typically bilateral and symmetric; Castleman disease usually presents as a solitary mass.
  • Autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosus, adult-onset Still disease)—distinguished by clinical presentation and imaging showing polyarticular involvement rather than localized lymphadenopathy.
  • Mediastinal teratoma or other germ-cell tumors—distinguished by heterogeneous composition with fat, fluid, and calcification; Castleman disease is more homogeneous and hypervascular.
Discussion

Castleman disease is a chronic low-grade inflammatory process of unknown etiology with interleukin-6 (IL-6) playing a critical pathogenic role in unicentric disease and both IL-6 and HHV-8 in multicentric disease.

The hyaline-vascular variant (HVV) shows characteristic 'onion-skinning' arrangement of lymphocytes forming concentric rings and 'lollipop appearance' with penetrating hyalinized vessels—the most common histologic type.

Unicentric Castleman disease (UCD) presents in the fourth decade without gender preference, is usually asymptomatic and incidentally discovered, and is curable with surgical resection.

Multicentric Castleman disease (MCD) presents in the fifth to sixth decade with systemic symptoms (fever, night sweats, fatigue, weight loss) and laboratory abnormalities including anemia, hypergammaglobulinemia, elevated IL-6, and requires systemic treatment with chemotherapy, steroids, or biologic agents.

All HIV-positive patients with MCD are coinfected with HHV-8, making this association an important risk factor; HHV-8-associated multicentric disease may show reduced enhancement compared to other types.

TAFRO-MCD is a distinct variant characterized by thrombocytopenia, anasarca, fever, bone marrow reticulin fibrosis, and organomegaly; POEMS-associated MCD shows osseous lesions (sclerotic, lytic, or mixed) on imaging.

Reporting Pearls

Describe Castleman disease as a solitary, well-circumscribed, hypervascular mediastinal (or specify location) mass showing homogeneous enhancement with early rapid arterial enhancement and delayed washout on dynamic CT, often with prominent feeding vessels and, if present, characteristic arborizing calcifications—note the distribution (unicentric vs. multicentric with bilateral adenopathy) and associated findings (pleural effusion, hepatosplenomegaly) that support the diagnosis.

Pitfalls
  • Mistaking Castleman disease for lymphoma: the dynamic enhancement pattern (early rapid washout) and prominent feeding vessels are key distinguishing features; always obtain dynamic or multi-phase imaging to assess washout.
  • Failing to recognize multicentric disease: bilateral hilar and mediastinal lymphadenopathy with systemic features (ascites, hepatosplenomegaly, centrilobular nodules) indicates multicentric rather than unicentric disease and changes management significantly.
  • Overlooking extranodal sites of involvement: Castleman disease can rarely present in extranodal locations including lungs, pleura, pericardium, adrenal gland, larynx, retropharyngeal space, parotid glands, pancreas, meninges, muscles, and bones.
  • Reduced enhancement in HHV-8-associated multicentric disease can be misleading: nodal masses in HIV patients with HHV-8-MCD may show minimal enhancement, potentially leading to underestimation of disease burden; correlation with clinical context and metabolic activity (PET-CT) is essential.
Source: Reference source

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