MRI and intraocular tamponade media

[Perfluorocarbon liquids and vitreoretinal surgery in 2011]

Perfluorocarbon liquids (PFCLs) are one of the most innovative recent tools for vitreoretinal surgery. PFCLs are characterized by their number of carbon atoms, which has an impact on the density, viscosity, surface tension, vapor pressure, the boiling point, and the refraction index. PFCLs are routinely used because of their high gravity (double that of water) and their low viscosity. Furthermore, they are immiscible in water, optically clear with refraction indices similar to that of water, allowing visualization of an interface between the PFCL and saline. The use of intravitreally injected liquid PFCLs as adjunctive agents to vitreoretinal surgery plays an important role in facilitating retinal reattachment, especially in cases of giant retinal tear, trauma, and/or proliferative vitreoretinopathy. PFCLs are also used as intraoperative instruments to re-establish intraocular volume, assist in separating membranes adherent to the retina (in proliferative diabetic retinopathy, for example), and manage the dislocated crystalline lens and intraocular lens.

Radiologic findings in infected and noninfected scleral buckles

PURPOSE

To present the radiologic findings in scleral buckle infections and in the early postoperative period after scleral buckling.

METHODS

Retrospective multicenter orbital computed tomography (CT) study of 14 patients and brain magnetic resonance (MR) in one patient with scleral buckle infections, some with the referring diagnosis of endophthalmitis, proliferative vitreoretinopathy, orbital cellulitis, or unilateral headache. The control population consisted of early postoperative prospective CT study of 38 consecutive patients with scleral buckle without clinical infection.

RESULTS

Diffuse scleral thickening and preseptal soft tissue swelling were noted in acute scleral buckle infections. Scleral thickening decreased radiologically following prompt antibiotic therapy in five patients with acute infections. Silicone sponge had low attenuation without infection and high attenuation with infection. In chronically infected scleral buckle, the sclera was thickened around the buckle, with scleral melt under the buckle. MR showed increased signal intensity in the preseptal region in one patient with chronic fungal infection. In the controls, two had thickening of the sclera without soft tissue swelling.

CONCLUSIONS

CT or MR can assist in the early diagnosis and management of scleral buckle infections.

3D MRI-based tumor delineation of ocular melanoma and its comparison with conventional techniques

The aim of this study is to (1) compare the delineation of the tumor volume for ocular melanoma on high-resolution three-dimensional (3D) T2-weighted fast spin echo magnetic resonance imaging (MRI) images with conventional techniques of A- and B-scan ultrasound, transcleral illumination, and placement of tantalum markers around tumor base and (2) to evaluate whether the surgically placed marker ring tumor delineation can be replaced by 3D MRI based tumor delineation. High-resolution 3D T2-weighted fast spin echo (3D FSE) MRI scans were obtained for 60 consecutive ocular melanoma patients using a 1.5 T MRI (GE Medical Systems, Milwaukee, WI), in a standard head coil. These patients were subsequently treated with proton beam therapy at the UC Davis Cyclotron, Davis, CA. The tumor was delineated by placement of tantalum rings (radio-opaque markers) around the tumor periphery as defined by pupillary transillumination during surgery. A point light source, placed against the sclera, was also used to confirm ring agreement with indirect ophthalmoscopy. When necessary, intraoperative ultrasound was also performed. The patients were planned using EYEPLAN software and the tumor volumes were obtained. For analysis, the tumors were divided into four categories based on tumor height and basal diameter. In order to assess the impact of high-resolution 3D T2 FSE MRI, the tumor volumes were outlined on the MRI scans by two independent observers and the tumor volumes calculated for each patient. Six (10%) of 60 patients had tumors, which were not visible on 3D MRI images. These six patients had tumors with tumor heights < or = 3 mm. A small intraobserver variation with a mean of (-0.22 +/- 4)% was seen in tumor volumes delineated by 3D T2 FSE MR images. The ratio of tumor volumes measured on MRI to EYEPLAN for the largest to the smallest tumor volumes varied between 0.993 and 1.02 for 54 patients. The tumor volumes measured directly on 3D T2 FSE MRI ranged from 4.03 to 0.075 cm3. with a mean of 0.87 +/- 0.84 cm3. The tumor shapes obtained from 3D T2 FSE MR images were comparable to the tumor shapes obtained using EYEPLAN software. The demonstration of intraocular tumor volumes with the high-resolution 3D fast spin echo T2 weighted MRI is excellent and provides additional information on tumor shape. We found a high degree of accuracy for tumor volumes with direct MRI volumetric measurements in uveal melanoma patients. In some patients with extra large tumors, the tumor base and shape was modified, because of the additional information obtained from 3D T2 FSE MR images.

Retinal detachment: imaging of surgical treatments and complications

Rhegmatogenous retinal detachment occurs in 5%-7% of the population with a peak prevalence between 40 and 80 years of age. The objects of treatment are to create a chorioretinal scar at the site of the retinal tear and to mechanically appose the detached sensory retina to the underlying retinal pigment epithelium. This apposition is achieved by means of scleral buckling or intraocular tamponade. In scleral buckling, the eye wall is indented under the retinal tear with a silicone buckling element. In intraocular tamponade, the eye is filled with a bubble of air, gas, or silicone oil. In patients treated with these techniques, neuroimaging commonly demonstrates incidental orbital findings. Familiarity with these techniques is essential if the radiologist is to differentiate normal postoperative findings from ocular disease. Furthermore, the ability to recognize the appearance of uncomplicated ocular surgery is a prerequisite for aiding the surgeon in diagnosis of postoperative complications.

MR imaging of intraventricular silicone: case report

A 42-year-old man with human immunodeficiency viral infection developed cytomegaloviral retinitis that was complicated by retinal detachment and was treated with an intravitreous injection of silicone. Fifteen months later, magnetic resonance imaging revealed intraocular and intraventricular silicone. Signal intensity characteristics and chemical shifts of silicone in the two locations were identical.

Advances in neuroimaging of the visual pathways

PURPOSE

To provide a practical review for the ophthalmologist of advances in neuroimaging of the visual pathways.

METHODS

We reviewed recent advances in computed tomography, magnetic resonance imaging, and angiography that are applicable to visual pathways imaging.

RESULTS

For detailed ocular imaging, computed tomography complements ocular sonography for imaging of calcification, trauma, and masses. Magnetic resonance imaging may be helpful for localization and characterization of ocular masses in the setting of hemorrhage. For orbital imaging, computed tomography is most appropriate in the evaluation of suspected thyroid ophthalmopathy, infection, and trauma; otherwise, either computed tomography or magnetic resonance imaging is useful for detection and characterization of abnormality. For disorders affecting the sellar, retrochiasmal, and brainstem pathways, magnetic resonance imaging is the study of choice, except for acute hemorrhage, for which noncontrast computed tomography is preferable. Although magnetic resonance angiography has a role in the elective evaluation of cerebrovascular disease, conventional angiography is the definitive study for suspected aneurysm and for surgical planning.

CONCLUSIONS

A practical approach for selection of the most appropriate imaging modalities by the ophthalmologist is suggested on the basis of the anatomic location and type of disease suspected.