Markedly T2-Hypointense Clival Plasmacytoma With Light Chain Deposition Disease: A Case Report.

Plasmacytomas are rare monoclonal neoplastic plasma cell proliferations in soft tissue or bone, with clival plasmacytomas being extremely rare and occasionally presenting with light chain deposition disease (LCDD). While imaging findings for clival plasmacytomas have shown variable T2 signal characteristics, complete T2 signal loss has not been previously reported. We present a case of a 61-year-old female found to have a 1.9 cm expansile lytic lesion in the clivus on CT. MRI revealed intermediate T1 signal and near-complete T2 signal loss. Histopathology demonstrated kappa-restricted plasma cells with extracellular light chain deposition, while bone marrow biopsy showed 5-10% plasma cells without evidence of multiple myeloma. The patient was diagnosed with a solitary plasmacytoma of the clivus with associated LCDD and underwent endoscopic resection and radiotherapy, showing a favorable initial response at a seven-month follow-up. This case highlights the importance of considering plasmacytoma with associated LCDD for marked T2 hypointense, enhancing skull base lesions. The combination of plasmacytoma and LCDD may explain the unusual imaging characteristics, underscoring the need for comprehensive diagnostic approaches in patients presenting with unusually hypointense clival lesions.