Focal Amyloidosis of the Orbit Presenting as a Mass: MRI and CT Features

Abstract

Focal orbital amyloidosis is a rare entity and little is known about its magnetic resonance imaging (MRI) features. In this case report, imaging features of a case of focal orbital amyloidosis presenting as a mass have been documented together with its histopathological findings. On MRI, a well-defined mass was seen as isointense with rectus muscle on T1-weighted images and heterogeneously hypointense on T2-weighted images. Punctuate calcifications were observed on the computerized tomography (CT) examination.

Keywords: Amyloidosis; Magnetic Resonance Imaging; Orbit; Tomography, Spiral Computed.

Figure 1. A 60-year-old woman with swelling of the left eye.

A, Axial CT scan shows a few small punctate calcific foci (arrow) in a relatively homogeneous soft tissue mass with a well-demarcated margin at the intraconal region of the left orbit. There is minimal expansion in the medial wall of the orbit, and no bone erosion is seen; B, Coronal T1-weighted MR image shows a soft tissue mass (arrows) that is isointense to the rectus muscle. The mass causes lateral displacement of the bulbus oculi and lateral rectus muscle. The medial rectus muscle is not seen at the level of the mass; C, Postcontrast coronal T1-weighted MR image shows heterogeneous enhancement in the soft tissue mass (arrows); D, Axial T2-weighted MR image shows a soft tissue mass (arrow) that is heterogeneously hypointense to the rectus muscle. The mass has caused anterior and lateral displacement of the bulbus oculi; E, An intraoperative photograph shows the soft tissue lesion at the intraconal region of the left orbit; F, Histological section of the lesion shows the homogeneous and amorphous amyloid matrix (Hematoxylin and Eosin × 10); G, Histological section of the lesion shows positive interaction between crystal violet (magnification × 20) and the amyloid accumulation.