Amyloid in the orbital apex and cavernous sinus.

A rare case of a 78-year-old male with posterior orbital amyloidosis and cavernous sinus involvement is reported. He presented with 1 year of worsening binocular diplopia with left eye motility restriction in all directions except abduction. Magnetic resonance imaging of the brain demonstrated a well-defined mass in the posterior medial orbit extending into the left optic canal and cavernous sinus, with low T1 and high T2 signaling and minimal contrast enhancement. Given his worsening diplopia, the patient underwent surgery to decompress the left orbital apex and confirm the diagnosis. Histopathology exhibited red-green dichroism under polarization microscopy with Congo red dye, suggesting amyloidosis. Orbital amyloidosis should be considered in patients presenting with apex lesions with posterior extension. An approach to biopsy and decompression of the apex may be facilitated with a combined trans-orbital and endonasal endoscopic approach, but complete surgical excision may not be feasible. Adjunctive radiation can help stabilize disease and prevent progression in cases of orbital amyloidosis with cavernous sinus involvement.