Cerebral Amyloidoma (CA) is very rare; approximately 40 cases have been reported in the literature. Mostly found near ventricles within the white matter, these intracerebral masses appear as single or multiple macroscopic nodules formed by amyloid deposits of monoclonal immunoglobulin light chains. The etiology remains poorly understood.
The clinical course of CA is generally, but not universally, favorable (1-3). Some authors advocate complete resection, when possible, to avoid continued expansion and associated neurological complications. Clinical features, most completely described in a review of 27 total patients by Fischer, et al (1), include a slight male to female predominance (1.17:1) and a mean age at diagnosis of 48.9 years (range 15 to 71 years). Presenting symptoms vary and include seizure, hemiparesis, gait disturbance, impaired vision, and cognitive disturbance. While no cases to date have described concomitant systemic amyloidosis, most authors still recommend a complete evaluation to investigate this possibility.
Radiographic findings for CA are variable and not specific (1). In our case, the leading radiographic diagnosis was primary CNS neoplasm, with a broad differential diagnosis that included glioblastoma, lymphoma, metastatic disease, cerebritis, and subacute infarction. In reported cases, CA is usually hyperdense on CT; reported MRI findings are more variable and describe hypo-, iso-, or hyperintense lesions on T1- and T2-weighted images, commonly with surrounding edema on T2-weighted scans. On post-contrast CT and MRI, CA shows enhancement. All reported cases have been supratentorial, though rare examples also show infratentorial involvement.
The histomorphologic features of our case are similar to those of reported cases, and suggest a differential diagnosis that may include: Calcifying Pseudoneoplasm of the Neuraxis (CAPNON), Cerebral Amyloid Angiopathy (CAA), Cerebral Amyloidoma, or other infectious/inflammatory entities. Non-specific features such as lymphoplasmacytic cells and macrophages are often present. Focal foreign body giant cell reaction to the amyloid, noted only focally in our case, might also suggest a diagnosis of amyloid beta related angiitis (ABRA). The most reliable histochemical features for diagnosis include apple green birefringence with Congo Red staining under polarized light, bright yellow-green fluorescence with thioflavin S staining, and immunoreactivity for immunoglobulin light chain.
Most cases of CA that have been characterized by immunohistochemistry (14/16 cases, 88%) have been found to be of the AL lambda light chain subtype (1). A minority of cases (2/16 cases, 12%) has been described as a composition of mixed lambda and kappa light chains, without any significant predominance. In a separate report by Rodriguez and colleagues, five cases were analyzed by liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) (4); all five were found to harbor lambda, with no kappa, light chains. Other constituents variably detected in the amyloid deposits included serum amyloid P, ApoE, Apo-AI, Apo-AII, Apo-AIV, IgG, IgA, and immunoglobulin J polypeptide.
Contributed by Patrick J. Cimino, MD, PhD, Richard J. Perrin, MD, PhD