Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006
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changes (i.e., formation of strands or membranes producing permanent opacification of the media and retinal detachment). Biologic changes occur relatively early, and to intervene surgically is often desirable. The decision for surgical intervention requires a careful appraisal of the extent of the pathologic changes in the vitreous, including ultrasonic evaluation of the retina, choroid, and hemorrhage character.
Figure 3.56. A 50-MHz scan of the anterior segment demonstrating the lens haptics position following
uneventful cataract removal and lens implantation in the capsular “bag.”
Cibis (87) was a pioneer in demonstrating the changes that take place within the vitreous body secondary to blood and its breakdown products. Cibis and Yamashita (88) documented retinal degeneration secondary to hemosiderogenic changes. Regnault (89) supplemented these studies with a description of the temporal relationships in the formation of vitreous membranes, as did Machemer and Williams (90). Fibroblasts, which spread along the path of hemorrhage into the solid vitreous, organize the vitreous along the hemorrhagically disrupted plane into membranes (90, 91, 92). These membranes, as they contract, tend to produce stress on the retina that may lead to retinal detachment. Even if detachment does not ensue, the eye may remain visually useless because of optically dense membranes.
Knowledge of the pathology cascade is important to the ultrasonographer because vitreous changes as a result of diabetes or trauma are not static, and repeat evaluations are often indicated to determine present or impending retinal or choroidal detachment (93). In the normal eye, the vitreous appears as an acoustically clear (anechoic) cavity. On the A-scan, no echoes are seen above baseline between the posterior lens capsule and the retina. On B-scan, the vitreous appears as a uniformly sonolucent area. The retina in the normal eye appears on B-scan ultrasonograms as a smooth, concave, acoustically opaque (20) surface formed by echoes arising from the vitreoretinal interface (Figure 3.59). These echoes are contiguous with, and inseparable from, the choroid-sclera complex. At 10 MHz, hemorrhagic vitreous, which is opaque to optical examination methods, remains acoustically clear on B-scan at low gain. Denser hemorrhages appear as irregular, opaque areas (Figure 3.60; see also kinetic scan on DVD). The location, extent, and density of vitreous hemorrhage can be shown by ultrasonography.
Figure 3.57. A slightly horizontally displaced intraocular acrylic haptic lens as a result of folding of one of the haptics. Despite the minimal displacement, patient symptoms were severe enough to warrant lens replacement.
Figure 3.58. Top: A 50-MHz ultrasonogram of a lens haptic adherent to the iris with resultant traction of the iris. Bottom: A similar situation as above with more severe retraction of the iris plane as a result of adhesions.
EXTENT AND DENSITY OF VITREOUS HEMORRHAGE
Light, diffuse, unclotted blood produces little echo response, so that the vitreous may appear sonolucent (Figure 3.61; see also DVD). Clumps of cells will produce echoes
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higher than the normal baseline echo of the vitreous. Low-amplitude echoes are usually best seen on the A-scan display or with a narrow band transducer with B-scan (see later text), because the amplitude of the echoes from small clumps of cells is low (94) (Figure 3.61; see also DVD). The density of hemorrhage is estimated from the character of echoes and the area of vitreous involvement, as determined from the B-scan. Thus, comparison of A- and B-scans is critical. Movement of the eye causes these low-amplitude echoes to move freely within the globe and helps to distinguish them from more fixed vitreous membranes. A more damped, lesser movement is apparent when the clumps are restrained by the “solid” primary vitreous.
Figure 3.59. Left: The posterior segment of an eye at 10 MHz and Right: at 20 MHz showing a smooth contour on sector scan. The retina, choroidal, and scleral reflections form a smooth transition with separation of sclera and Tenon's, often emphasized by higher amplitude echoes.
Figure 3.60. A moderately dense retrohyaloid hemorrhage with accentuation of the posterior hyaloid. (See also
DVD.)
The extent of clotted blood is more easily appreciated on the B-scan (Figure 3.62), and serial sectioning can be used to delineate the hemorrhage. A coagulum within the hemorrhage is indicated by moderately high-amplitude, closely spaced echoes, giving the appearance of a solid mass. Changes in appearance can be useful, if surgery is contemplated, particularly if rebleeding can be detected.
LOCATION AND SOURCE OF VITREOUS HEMORRHAGE
The localization of hemorrhage to areas of solid or fluid vitreous is based on the position and movement of the
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hemorrhage. Hemorrhage localized in the anterior vitreous compartment is usually an indication of incorporated solid vitreous. Often blood along the posterior limiting membrane or “hyaloid face” of the solid vitreous will form a “veil” or membrane that separates and outlines the fluid and solid compartments (Figure 3.63). This veil may be studied with kinetic B-scanning. Kinetic scans are obtained by asking the patient to move his or her eye while fast sector scanning is performed. The “after” movements of hemorrhage and membranes are observed after the eye has come to rest in its new position. Motion of hemorrhage in the solid vitreous is damped more quickly than that of hemorrhage in the fluid vitreous. The final or resting position of an area of hemorrhage varies with gravity in fluid vitreous but remains constant in solid vitreous.
Figure 3.61. A light hemorrhage along the posterior hyaloid of the vitreous with variable amplitude and usually a marked variability on kinetic scanning. (See also DVD.)
Figure 3.62. B-scan at 10 MHz showing an area of dense coagulum, with a border of solid primary and more
diffusely represented tertiary vitreous.
Figure 3.63. B-scan of blood in the tertiary vitreous outlining the hyaloid face of the primary vitreous.
Figure 3.64. Recent hemorrhage in a patient with a solid vitreous demonstrating the location of a probable
bleeding site.
The importance of localizing the hemorrhage in the solid or fluid vitreous is important in that patients with spontaneous hemorrhage of light density limited to the posterior vitreous have a good chance of clearing within a short time. Patients with dense hemorrhage into the solid vitreous, whether anterior or posterior, regardless of etiology, clear more slowly, if at all. Such organized hemorrhages in one study had only about a 33% chance of clearing (94).
The position of hemorrhage relative to the limbusiris plane, lens, and optic nerve can be determined with B-scan ultrasound. In younger patients with a solid vitreous, the source of bleeding can be frequently recognized as the point where echoes extend to the globe wall on the B-scan display (Figure 3.64) (42). A kinetic scan of the moving eye can aid in tracing the point of origin of a vitreous hemorrhage. The vitreous attachments to the optic nerve and/or to the macula can often be seen (Figure 3.65). When only attachment to the nerve is noted, vitreous veils along the posterior limiting membrane of the vitreous may simulate and resemble retinal detachment.
VITREOUS VEILS (MEMBRANES)
Blood cell collection along the vitreous surfaces or the hyaloid can resemble a veil or even a membrane. Vitreous veils are usually distinguishable from hemorrhagic clots by their pattern (Figure 3.66) and echo height (which is moderately high but usually lower than that of the retina). Occasionally, vitreous veils and membranes may be difficult to distinguish from a localized retinal
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detachment, particularly when retinitis proliferans is present (Figure 3.67). Tracing the veils to their attachment on the globe wall may be helpful; if the attachment is anterior to the ora serrata, a vitreous membrane is indicated (or possibly a choroidal detachment), whereas if attachment to the ora serrata and the optic nerve head is demonstrable, a retinal detachment is usually present. The B-scan is essential for tracing membranes, because it provides the topographic pattern of amplitude contours that is not readily apparent from the A-scan alone. Kinetic B-scanning may graphically define a membrane by showing its failure to attach at the optic nerve. On A-scan, echoes from a retinal detachment have a higher amplitude than most vitreal membranes. The retina echo is equivalent in height to the sclera, whereas membranes are usually about 50% or less of the scleral echo height. Membranes, however, can be of variable amplitude, and they will appear as incomplete “lines” on the B-scan, with occasional high amplitude segments (Figure 3.68; see also DVD).
Figure 3.65. A recent dense vitreous hemorrhage with a retracted primary vitreous—a fluid zone and
hemorrhage anterior to the retina. A retinal adhesion of vitreous to the macula is shown here. (See also DVD.)
Figure 3.66. Vitreous hemorrhage with complex pattern as a result of retracted vitreous and blood along the
syneretic vitreous cavity walls.
Figure 3.67. B-scan at 10 MHz demonstrating vitreous attachment to a proliferative membrane (arrow) in a
patient with diabetes. The echoes produce a characteristic “x” shape at the nexus of vitreous and proliferative
membrane. It is best seen with a kinetic scan. (See also DVD.)