Fig. 12.7 Synovial sarcoma, left orbit. (a) Coronal postcontrast CT demonstrates a lesion within the superior left orbit with impression upon and inferior displacement of the globe (arrow). (b) Sagittal postcontrast CT shows the superior left orbital mass (arrow) indenting the globe

12.4.5 Orbital Pseudotumor

Orbital pseudotumor is an idiopathic inflammatory process usually presenting as unilateral painful ophthalmoplegia, proptosis, and lid erythema. This process may affect any intraorbital soft tissue. Pseudotumor is the most common cause of an intraorbital mass in adults, but it may occur at any age, usually in young women. Orbital pseudotumor presents as a moderately enhancing, poorly defined mass with inflammation of the orbital fat and extraocular muscles. On CT, there is increased density of the retro-orbital fat and variable enhancement (Fig. 12.8). Pseudotumors are isointense on T1 images and hypointense to isointense on T2 images with variable enhancement. The primary alternative lesion to consider in the differential diagnosis in children is primary orbital rhabdomyosarcoma. When extraocular muscle involvement occurs, pseudotumor involves the tendon insertion, in contradistinction to Graves disease, which spares the tendon.

12.4.6 Orbital Metastases

In adults, metastases to the orbit arise most commonly from primary tumors in the breast or lung. In children, orbital metastases may occur from neuroblastoma, Ewing sarcoma, and Wilms tumor. On CT, metastases from solid tumors are usually of intermediate density to muscle and demonstrate enhancement. On MRI, these