American Journal of Neuroradiology 24:1769-1771, October 2003
© 2003 American Society of Neuroradiology
Case Report
HEAD AND NECK
CT Characteristics of Intraocular Perfluoro-N-Octane
John B. Christoforidisa,
Paul A. Carusob,
Hugh D. Curtinb,
Tito Fiorea and
Donald J. D’Amicoa
a Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts
b Department of Radiology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts
Address correspondence and reprint requests to Dr. Donald J. D’Amico, Retina Service FL 12, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114
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Abstract
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Summary: Perfluoro-
N-octane (PFO) is a heavy liquid that is
used as an aid for complicated retinal surgical procedures.
Although PFO is usually removed intraoperatively, the radiographic
appearance of retained PFO may mimic an intraocular foreign
body or vitreous hemorrhage. As the use of PFO in retinal procedures
has become more widespread, recognition of its imaging appearance
has become important in the differential diagnosis of intraocular
foreign body and ocular trauma.
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Introduction
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Perfluoro-
N-octane (PFO) is a perfluorocarbon liquid (PFCL)
that has been used as an aid for the surgical repair of complicated
proliferative vitreoretinopathy and giant retinal tears since
1987 (
1). Its high density and low viscosity allow PFO to provide
a significant tamponade force that stabilizes the retina and
gives the surgeon the ability to manipulate the retina with
greater ease. These properties have brought PFO into widespread
use by retina surgeons for these types of procedures. PFO is
removed intraoperatively because of the risk of ocular toxicity
if it is left in the vitreous cavity (
2). A small amount of
PFO may be inadvertently left in the vitreous cavity postoperatively,
however, and retained PFCL in the vitreous cavity after surgery
has been reported in 1–38% of cases (
3,
4). Because of
its high density, PFO may appear radiopaque and thus may mimic
an intraocular foreign body or hemorrhagic collection. As the
use of PFO in retinal surgery becomes more widespread, its recognition
on orbital images has become important.
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Case Report
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A 50-year-old woman was referred to our clinic for evaluation
of an intraocular foreign body. The patient had been in a motor
vehicle accident several days earlier and had complained of
headaches.
A nonenhanced multidetector CT scan was performed in the axial plane with coronal and sagittal reformats in bone and soft tissue algorithms. The CT scan showed an dense fluid collection (H 454–585) representing PFO layering dependently within the posterior globe (Fig 1A). There were two principal components, one layering within the posterior vitreous chamber and forming a fluid-fluid level with the native vitreous humor and the second extending along the subretinal space to the level of the ora serrata. There was an abnormal linear attenuation floating between these two components, representing the detached retina (Fig 1B). Several punctate densities corresponding to additional foci of PFO were noted within the vitreous cavity (Fig 1C). There was no evidence of fracture or dislocation and no evidence of other intra- or periorbital foreign body.
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FIG 1. A, Axial CT scan without contrast demonstrates attenuated fluid collection within the posterior vitreous cavity (asterisk) and smaller deposits in the ora serrata region (arrowheads) forming a fluid-fluid level with the native vitreous humor. PFO can also be seen within the anterior chamber (white arrow).
B, Axial CT with bone algorithm and bone windows demonstrates a retinal detachment (black arrows) and the two components of the collection, the one anterior to the detached retina and the second within the subretinal space extending to the ora serrata. PFO is also seen within the anterior chamber (white arrows).
C, Coronal CT reformat with bone windows demonstrates the corrugated surface of the PFO collection corresponding to the PFO bubbles seen intraoperatively.
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The patient’s ocular history was remarkable for recurrent retinal detachment with proliferative vitreoretinopathy in her right eye. She had undergone four previous surgical repair attempts. PFO had been used during the last surgery, 5 weeks earlier; however, hemorrhage occurred intraoperatively, and the PFO could not be removed before closure.
On her initial visit to our clinic, the patient’s visual acuity in the right eye was hand motion at 6 inches. The anterior segment examination revealed multiple PFO bubbles (Fig 2A), and the fundus examination showed PFO overlaying a detached retina. There were no corneal or scleral lacerations, and the rest of her physical examination was unremarkable. Subsequently, the patient was taken to surgery, where the PFO was seen in the preretinal and subretinal spaces without significant hemorrhage (Figs 2B). The PFO was removed and the retina reattached surgically.
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FIG 2. A, External view of the eye showing multiple PFO bubbles over the inferior third of the anterior chamber.
B, Intraoperative view in the vitreous cavity showing the retracted opacified retina (upper left) and the extrusion canula removing multiple PFO bubbles from the subretinal space.
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Phantom Study
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An enucleated porcine eye was injected with 0.5 mL of PFO (Perfluoron;
Alcon Laboratories, Ft. Worth, TX). This was placed in an 8-ounce
(237-mL) polystyrene container filled with water, which has
similar radiodensity as vitreous humor, with the cornea turned
superiorly. Nonenhanced CT and MR imaging were performed on
the enucleated specimen in the axial plane. CT showed the PFO
as an attenuated, round, smoothly marginated globular fluid
collection (H 643–673) in the dependent portion of the
posterior vitreous cavity (
Fig 3A). T1- and T2-weighted MR imaging
showed the PFO as an oval hypointense collection layering dependently
without significant chemical shift artifact (
Fig 3B).
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FIG 3. A, Axial nonenhanced CT image of an enucleated porcine globe demonstrates the attenuated smoothly marginated globule of PFO deposited into the vitreous cavity.
B, T2-weighted MR image of an enucleated porcine globe demonstrates a hypointense oval collection lying dependently in the vitreous cavity.
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Discussion
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PFO (C
8F
18) is a colorless, odorless synthetic fully fluorinated
carbon compound. It possesses a high density (1.76 specific
gravity) and low viscosity (0.8 centistokes) (
5). These properties
make PFO a highly desirable substance for retinal surgery because
it provides a significant tamponade force that helps to stabilize
the retina intraoperatively. This allows other maneuvers to
be done on the retina, such as extrusion of subretinal fluid,
manipulation of retinal edges, or the application of laser treatment.
As a result, the use of PFO for complex retinal surgical procedures
has become more widespread. PFO is removed from the vitreous
cavity after its intraoperative use because of the potential
for ocular toxicity, including retinal inflammation and atrophy
of the dependent retina from mechanical compression (
2).
CT shows PFO as an attenuated fluid that may layer within the compartment where it is placed, usually anterior to the retina within the vitreous chamber. It may extrude into the subretinal space through an opening in the retina, as was seen in this case. PFO may mimic a dense hemorrhage or a metallic or dense foreign body. The Houndsfield attenuation in this case may be helpful in distinguishing the PFO collection from vitreous or subretinal hemorrhage, because PFO demonstrates a higher attenuation value than that of blood products as in our case, H 454–585 in the human subject and H 643–673 in the enucleated porcine specimen.
The volume of residual PFO seen postoperatively is usually less than that seen in our case. It is often one or more droplets, which may resemble small intraocular foreign bodies on CT scans. In the experimental porcine eye, PFO formed a rounded globule with smooth margins within the posterior vitreous and, in such cases, may mimic a focal foreign body such as a BB. Correlation with a clinical history of previous retinal surgery is important in forming the differential diagnosis. Imaging findings that may aid in the diagnosis of intraocular PFO include the high Houndsfield attenuation on CT or hypointensity on MR imaging, the corrugated surface appearance of the collection corresponding to the PFO bubbles, and lack of streak artifact on CT, which may occur with metallic foreign bodies but is not seen with PFO.
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Conclusion
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PFO is a heavy liquid that is used as an aid for complicated
retinal surgical procedures. A small amount of PFO is often
left behind in the vitreous cavity postoperatively. Because
of its high Hounsfield attenuation and radiopaque properties,
PFO should be part of the differential diagnosis of intraocular
opacities when seen on CT scan.
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Footnotes
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Supported in part by the Vitreoretinal Research Fund (to D.J.D’A.)
and the Iacocca Research Foundation.
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References
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Received November 11, 2002;
accepted after revision April 6, 2003.
TOP
Abstract
Introduction