2  Imaging the Postoperative Orbit	65

2.16\ Orbital Tissue Expanders

2.16.1\ Discussion

Orbital tissue expanders are implanted devices used for enlarging the orbital cavity in patients with congenital anophthalmia and microphthalmia and can obviate surgery. The main types of orbital expanders include hydrophilic osmotic hydrogel devices or inflatable saline globes. The placement

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and volume of the expanders can be evaluated via CT or MRI. Hydrogel expanders appear as either spherical or hemispherical structures with nearly fluid attenuation on CT and low T1 and high T2 MRI signal intensity and do not enhance (Fig. 2.59). Saline expanders appear as spherical fluid-density structures on CT adjacent to the metal-density T-plate. The saline expanders have similar imaging characteristics as the aqueous on CT and MRI and are attached to metallic T-plate.

Fig. 2.59  Hemispheric hydrogel expander. Axial T2-weighted (a) and T1-weighted (b) MR images show bilateral orbital implants with similar signal characteristics as fluid. Photograph of the hydrogel hemispheric implants when dry and hydrated (c) (Courtesy of Osmed)