First Case Report of Primary Central Nervous System Amyloidoma Involving Cranial Nerves V and VII

Background: Primary CNS amyloidoma is a rare lesion formed by abnormal deposition of amyloid within the brain parenchyma in the absence of systemic amyloidosis. There are fewer than 20 reported cases of Meckel's cave amyloidoma primarily involving of the trigeminal nerve. Here, we report the first case of primary CNS amyloidoma involving both CN V and VII with an unusual histological pattern.

Case Presentation: A 55-year-old previously healthy woman presented with persistent right facial droop and paresthesia unresponsive to antiviral and steroid therapy. On examination, there was V1 to V2 dysesthesia, right facial partial paralysis, and synkinesis to the right side of the face without proptosis or lagophthalmos. Magnetic resonance imaging (MRI) of the skull base showed an enhancing 1.5 cm × 0.7 cm × 0.4 cm T2-isointense mass extending along the lateral and inferior walls of the right Meckel's involving the trigeminal nerve toward the foramen ovale. The mastoid segment of the right facial nerve also showed enhancement. The patient underwent biopsy and tumor debulking via a minimally invasive lateral transorbital approach to Meckel's cave.

Results: Histologic sections showed pale eosinophilic amorphous material within the neural tissue which was birefringent to polarized light in Congo red stain consistent with amyloidoma. Immunohistochemistry was positive for amyloid A and in situ hybridization for light chains showed a polytypic pattern. Subtyping by mass spectrometry confirmed a lambda light chain amyloidoma. Laboratory studies including complete blood count, comprehensive metabolic panel, and urinalysis were unremarkable. Immunoglobulin panel and β-2 microglobulin were within normal limits. Free kappa:lambda ratio was normal with negative SPIE and UPIE. Bone marrow biopsy did not show clonal plasma cells and Congo red stain was negative. There was no evidence of cardiac amyloidosis. These findings were consistent with localized CNS amyloidoma. The patient recovered well from surgery with stable neurologic findings.

Conclusion: This is the first case of primary Meckel's cave amyloidoma affecting multiple cranial nerves, with radiographic evidence of CN-V and -VII infiltration that correlates with clinical presentation. A minimally invasive transorbital approach to Meckel's cave was successfully employed to access the tumor in the middle cranial fossa. Amyloidoma should be considered in the differential diagnoses of lesions involving Meckel's cave and multiple cranial nerves.

Publication History

Article published online:
12 February 2021