Amyloidoma Involving the Orbit, Meckel's Cave and Infratemporal Fossa: 3T MRI Findings

Abstract

Amyloidoma is a rare lesion characterized by tissue deposition of an abnormal fibrillary protein (amyloid). It is the focal and localized counterpart of systemic amyloidosis, where the deposition of amyloid diffusely involves several organs. The few literature reports of intracranial amyloidomas include lesions involving the pituitary gland, orbit, cerebral hemispheres, temporal bone, cerebellopontine angle and jugular foramen. We describe the case of a 27-year-old woman presenting with painless slowly progressive proptosis of the right eye. The patient underwent a contrast-enhanced CT study of the head, followed by 3T MRI which disclosed a homogeneous mass in the right Meckel's cave and cavernous sinus, extending through an enlarged foramen ovale to the infratemporal fossa. The right optic nerve and ocular muscles were enlarged and infiltrated along with the retrobulbar fat by contrast-enhancing tissue. Thin contrast-enhanced MRI scans through the area of interest showed the mass to extend posterior to the gasserian ganglion, involving the cerebellopontine angle cistern, where the intracisternal parts of the III, V, and VI nerves bilaterally appeared enlarged and showed perineural enhancement. The lesion closely mimicked a malignant tumor with perineural tumor infiltration, so we performed fine needle biopsy of the portion of the lesion near the right foramen ovale under fluoroscopic guidance. Histopathology revealed that the lesion was an amyloidoma. Further clinical and blood examinations, serum chemistry, followed by biopsy of the periumbilical fat showed no signs of systemic amyloidosis or an underlying inflammatory or neoplastic disorder. No further treatment was instituted, follow-up MRI six months later showed no enlargement of the mass.