Castleman Disease, Hyaline Vascular Variant with Increased Background CD30-Positive Immunoblasts

Lessons from the Friday Unknowns

The lymphoid follicles are large and contain small, lymphocyte-depleted germinal centers and broad mantle zones.

Some of these follicles contain 2 or 3 germinal centers.

A subset of the germinal centers is penetrated by radial arterioles with sclerotic walls and a few hyaline-vascular lesions are observed.

Some follicles contain dysplastic follicular dendritic cells.

The mantle zones show linear arrays of lymphocytes (so-called onion skin change).

At the periphery of the mantle zones some areas suggestive of marginal zone differentiation are present.

The interfollicular regions show a proliferation of blood vessels with sclerotic walls, foci of dystrophic calcification, scattered large immunoblasts and clusters of plasma cells.

CD30 stain highlighting numerous background immunoblasts

The interfollicular immunoblasts are positive for CD20, CD30 and MUM1/IRF4 , and negative for CD15. These cells could be misinterpreted as Hodgkin cells.

The follicles are composed of numerous B-cells, positive for CD20, Oct-2 and Bcl-2, and negative for CD3 and CD10. A small subset of the mantle zone cells is weakly positive for CD5 and many of the lymphocytes are weakly positive for MUM1/IRF4. PD-1+ cells are present within germinal centers. The antibody specific for CD21 highlights numerous follicular dendritic cells that form irregular networks. T-cells are highlighted by CD3 and CD5.

Plasma cells in the interfollicular region are positive for MUM1/IRF4 and CD138. Cyclin D1, HHV8, HSV I, HSV II and CMV are negative. In situ hybridization analysis for Epstein-Barr virus encoded RNA (EBER) performed elsewhere, no EBER+ cells are present.

In summary, these findings support the diagnosis of Castleman disease, hyaline-vascular variant. The large cells in the interfollicular regions that are positive for CD20, CD30, and MUM1/IRF4 are a part of the spectrum of this disease. There is no morphologic evidence of lymphoma.

Link to digital slides: bit.ly/3zQyMCb | Slides labeled case 4

Further read: https://pubmed.ncbi.nlm.nih.gov/32152665/

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Siba El Hussein, MD

Hematopathology | Cytopathology | Molecular pathology | Digital pathology | Data science | Machine learning