Solitary Intracranial Plasmacytoma Located in the Clivus: A Diagnostic and Theraputic Challenge

Abstract

Solitary intracranial plasmacytoma (SIP) is a rare entity.  To date, only 20 cases of SIP have been reported in English literature.  Occasionally, SIP is comprised of atypical plasma cells which may not be plasma cell-appearing at all.  As a result, pathologic diagnosis is extremely challenging, especially on frozen sections.  A recent case demonstrating this profile is reported here.  The patient was a 40-year-old white male who originally presented with diplopia.  MRI revealed an enhancing non-infiltrating mass (5 x 4 x 3 cm) within the clivus.  A transnasal endoscopic biopsy was done.  Frozen sections showed sheets of pleomorphic cells with abundant eosinophilic cytoplasm and round/oval nuclei with stippled chromatin. On touch prep, naked nuclei with homogenous/salt and pepper chromatin, mild crush artifacts and rare plasmacytoid cells were noted.  A frozen section diagnosis of "unclassified neoplasm, defer to permanent sections" was made.  Immunohistochemical analysis on permanent sections showed that tumor cells were positive for CD138, CD56, kappa light chain, BCL-1 and negative for chromogranin A and lambda light chain.  The Ki67 proliferation index was 5-10%.  The immunostaining pattern was consistent with plasmacytoma.  A subsequent complete work up for systemic disease revealed normal bone marrow biopsy, normal flow cytometry, and negative skeletal survey.  The patient did have a serum M-spike of 0.75 g/dL but his quantitative immunoglobulins, kappa or lamda free light chains and beta-2 microglobulin were within normal limits.  The patient was treated by radiation therapy accompanied by high-dose dexamethasone.  However, four months post-radiation, repeat MRI showed a similar mass in the same area.  His serum M-spike had dropped to 0.3 g/dL during his radiation therapy, but persisted at this level subsequently.  The diagnosis of persistent residual plasmacytoma was reached.  The patient underwent gamma knife radiosurgery and tolerated the procedure well.  This case demonstrated that SIP should be considered as one of the differential diagnoses for intracranial tumor of unknown origin.