Plasma cell predominant lymphoplasmacytic-rich meningioma, grade I (WHO), with crystalline inclusions.
Although the large cells resembled rhabdoid cells, the tumor cells were cytologically different and lacked increased proliferation activity. Immunoreactivity for CD79a and light chains, together with the ultrastructural features, confirmed plasma cell origin of those large cells. The inflammatory component of this lymphoplasmacytic-rich meningioma consisted predominantly of plasma cells. Although plasma cell predominant lymphoplasmacytic-rich meningioma is not uncommon (1, 2), to our knowledge, similar crystalline inclusions in plasma cells have not been reported previously in meningioma.
There is an inconsistency about the terminology of inclusion bearing plasma cells in the literature. There are a few published cases with plasma cell predominant inflammatory lesions in the stomach and the oesophagus, having been called Russell body gastritis or Mott cell gastritis (3-7). One of these cases showed plasma cells with crystalline inclusions similar to our case (5). However, Russell bodies were originally described as having round hyalin-like inclusions by electron microscopy and these were not found in our case (8). Therefore, we felt that using terminology such as 'Mott cell predominant meningioma' may not be entirely correct.
Crystalline plasma cell inclusions are not uncommon in lymphoplasmacytoid tumors and thought to be more suggestive of a diagnosis of lymphoma over a reactive process (9, 10). In our case the features of the inclusions were most in keeping with those of described in crystal-storing histiocytosis (CSH). CSH is an uncommon phenomenon (less, than 100 cases reported so far) with presence of inclusion containing plasma cells and histiocytes, also involving the bone marrow (11, 12). It is almost always associated with expression of monoclonal immunoglobulins (multiple myeloma, monoclonal gammopathy of undetermined significance [MGUS], lymphoplasmacytic lymphoma, extramedullary plasmacytoma), only occasional cases of CSH have been reported without paraproteinemia (11). It is presumed to be an intralysosomal accumulation of secreted paraproteins or immunoglobulins, which aggregate in crystals. Immunoglobulins of kappa light chain type have been almost exclusively involved without a consistent association with a particular heavy chain (12). This suggests that CSH results from the storage of crystals produced by plasma cell tumors that either overproduce light chain or express a structurally aberrant molecule.
In our case, we noticed excess of kappa-positive cells but no obvious monoclonal plasma cell proliferation was seen. Although the large cells were positive with CD68, there was no indication of bone marrow involvement; therefore, usage of the term CSH was not justified. However, the mechanism of crystal formation might well be similar to CSH.
Contributed by Istvan Bodi, MD, Tibor Hortobágyi, MD and Stefan Buk