Aggregoma

Deposition of monoclonal light chains in B-cell dyscrasias can be systemic or localized, and fibrillar and non-fibrillar, and can be categorized under the broad definition of monoclonal immunoglobulin deposition diseases: "monoclonal expansion of a B-cell and plasma-cell population producing an excess immunoglobulin polypeptide with structural characteristics predisposing to tissue deposition in either the fibrillar or nonfibrillar state."

Systemic forms of amyloid (fibrillar) deposition include light chain (AL) and heavy chain (AH) amyloidosis, while systemic forms of non-amyloid (non-fibrillar) deposition include light chain deposition disease (LCDD), heavy chain deposition disease (HCDD) and light–heavy chain deposition disease (LHCDD).

The localized form of amyloid deposition is known as an amyloidoma. By analogy, aggregomas are localized tumoral masses of monoclonal light chain deposition, consisting of nonfibillar and Congo-red-negative proteins.

Imaging findings have not been described, but are presumably similar to those of amyloidomas.

References

• Rostagno A, Frizzera G, Ylagan L, Kumar A, Ghiso J, Gallo G. Tumoral non-amyloidotic monoclonal immunoglobulin light chain deposits ('aggregoma'): presenting feature of B-cell dyscrasia in three cases with immunohistochemical and biochemical analyses. Br J Haematol. 2002 Oct;119(1):62-9.
• Buxbaum J, Gallo G. Nonamyloidotic monoclonal immunoglobulin deposition disease. Light-chain, heavy-chain, and light- and heavy-chain deposition diseases. Hematol Oncol Clin North Am. 1999 Dec;13(6):1235-48.