AMYLOIDOMA (PRIMARY SOLITARY AMYLOIDOSIS)

Clinical and Radiological Features

Amyloidomas occur more frequently in men between the fifth and seventh decades of life. They are rare mass lesions that occur in many diverse sites including the brain, base of skull, cranial nerves, or spinal epidural space, causing back pain and possibly a compressive myelopathy or radiculopathy. Elsewhere in the brain, they present as single or multiple mass lesions with little or no mass effect on surrounding structures.

There is typically no association with a plasma cell dyscrasia or malignancy since they may possibly originate in the microglial processing of plasma proteins (Cohen et al., 1992); however, because of the occasional involvement of the spinal column by multiple myeloma, diagnostic measures should be taken to exclude systemic or plasma cell dyscrasia. MRI indicates a hypointense lesion on T1- and T2-weighted imaging with contrast enhancement (Figure 3.115a) (Gandhi et al., 2003).

Pathology

Amyloidomas have been described with varying amounts of chronic inflammation as well as in circumstances in which virtually no inflammation is noted. Microscopy typically reveals amorphous or globular acellular masses, birefringent with polarized light (Figure 3.115b). The presence of otherwise typical plasma cells within a mixed chronic inflammatory infiltrate should not be considered suspicious for a plasma cell malignancy. However, if this consideration persists, immunostaining and in situ hybridization may be used to reveal the presence of clonality in the plasma cell infiltrate.