Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006
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After retinal detachment surgery, numerous situations may arise in which management may be facilitated by ultrasonography.
Occasionally, after an encircling procedure, especially if extensive cryotherapy has been used, choroidal effusion or hemorrhage may occur and cause angle compromise with elevation of intraocular pressure. Usually, the choroidal effusion with hemorrhage is visible with the indirect ophthalmoscope. However, a cloudy cornea, a miotic pupil, or a cataract may prevent visualization. B-scan ultrasonography in this condition shows the pathognomonic appearance of a choroidal effusion, that is, a smooth, convex, circumferential elevation straddling the ora serrata. Choroidal effusion may be differentiable from choroidal hemorrhage with A-scan quantification techniques. Demonstration of a localized choroidal effusion may indicate the site for posterior sclerotomy, if this should be clinically warranted.
Figure 3.80. Left: B-scan showing the indentation of the globe wall by a sponge element. The retina remains in place. Right: A sponge element with residual retinal detachment.
The extent of settling of the retina after detachment surgery may be difficult or impossible to evaluate optically because of opaque media. In this situation, B-scan ultrasonography can provide accurate information as to the position of the retina (Figure 3.80). Posterior migration of an encircling element can be shown acoustically.
B-scan ultrasonography can also demonstrate the presence of an encircling element or large, local implant in patients where the history is unclear and the media are cloudy, as shown in Figure 3.81.
Figure 3.81. 10-MHz B-scan of eye after sponge implant for treatment of detached retina. Note the deformation of posterior globe supertemporally as a result of implant and the presence of moderate vitreous debris. Right: A residual area of detachment.
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Figure 3.82. Residual perfluorocarbon bubbles in fluid vitreous after surgery. The retina is attached. (See also
DVD.)
POSTOPERATIVE EVALUATION OF THE VITREOUS SUBSTITUTE
The use of gas and tamponade liquids in retinal detachment and vitreous surgery produces characteristic echogenic and conductive artifacts. Gas bubbles are reflective and thus distort or prevent posterior pole evaluation. Perfluorocarbon liquid is usually removed at the end of surgery, but small bubble remnants may be seen (Figure 3.82). They are highly reflective, often looking like small foreign bodies, either in the ciliary body region or at the posterior pole (Figure 3.83).
Silicone filled eyes produce a characteristic lengthening of the eye because of the slower velocity of sound transmission than saline or vitreous. Our measurements of velocities are 972.0 meters per second for 1,000 CS silicone at 37°C and 978.5 meters per second for 5,000 CS silicone at 37°C (standard deviation = 4.5). Silicone is less dense than water and floats to the top of the vitreous compartment, giving a “split” type of B-scan when viewed at the vertical or 6 to 12 meridian (Figure 3.84). Silicone can produce acoustic artifact changes that are difficult to interpret but, usually, positioning will help make the area of interest accessible acoustically.
Retinitis Proliferans
The ultrasonographic appearance of retinitis proliferans has been discussed in earlier section on vitreous abnormalities.
Macular Edema
In severe macular edema, or in the “sunny-side-up” stage of Best disease, a cystic structure may be ultrasonically demonstrable. The B-scan shows a convex anterior projection of the vitreoretinal interface echo line in the macular region, followed by a localized sonolucent (anechoic) area (Figure 3.85). Although not as useful as optical coherence tomography (OCT) in demonstrating vitreoretinal traction and edema, in most cases the traction may be visualized with B-scan ultrasound. Certainly with opaque media, the retinal changes can be well visualized with 20-MHz transducers (see Figure 3.153).
Figure 3.83. Small perfluorocarbon fragments are seen in these 50-MHz images. These small bubbles produce
ringing artifacts and are generally only seen at very high frequencies.
Age-related Macular Degeneration (AMD)
B-scan ultrasonography, in cases of elevated disciform macular degeneration, shows an elevated lesion at the posterior pole (Figure 3.86). The typical AMD lesion is usually too small to differentiate. The acoustic appearance of the interior of the lesion may vary. In predominantly hemorrhagic lesions, a cystic appearance with a bright line of front surface echoes separated from the posterior wall of the globe by a sonolucent (anechoic) zone is noted. An acoustically hypoechoic opaque appearance is noted in fibrotic, scarred lesions. This range of appearances is also characteristic of a small choroidal melanoma. The phenomenon of choroidal excavation, the appearance of replacement of the choroid with tumor (see discussion on choroidal tumors), often seen with choroidal malignant melanomas, is not seen, in our experience, with disciform macular degeneration. Because disciform lesions are restrained by Bruch's membrane and do not involve the choroid, one would not, on theoretic grounds, expect choroidal excavation to occur in this condition.
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Figure 3.84. Upper left: Contact 10-MHz B-scan in horizontal plane of globe filled with silicone oil. Artifactual increase in axial length results from the slower speed of sound in oil. Upper right: Vertical scan of the same eye 10 months later shows artifactual distortion of the superior portion of the globe as a result of the presence of the oil. Bottom: 10-MHz B-scan in horizontal plane of inferior (aqueous fluid filled) globe is not distorted. Note suggestion of peripheral choroidal/retinal detachment. There is also vitreous debris of moderate amplitude.
Figure 3.85. 20-MHz image using the Quantel Cinescan demonstrating a vitreous traction membrane in a patient with cystoid macular edema.
Figure 3.86. 10-MHz B-scan through the macula of a patient with disciform AMD (arrow) and vitreous
membranes.
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Evaluation of the A-scan trace through the lesion is also important for differentiation. In disciform macular degeneration, irregular echoes, often of low amplitude, follow the high-amplitude echo from the retinal surface, and in melanomas gradual echo decay follows the high-amplitude echo from the retinal surface, although a small melanoma may be too small to show this well on A-scan (see Small Melanomas in later section).
Choroid in Age-related Macular Degeneration
A new technique for evaluating the macular area, especially the choroid behind the macula, involves the use of parameter image tissue characterization. Defining the choroid can be useful in documenting progressive aging changes as well as effects of therapy.
Parameter imaging and tissue characterization were discussed in Chapter 2. Choroidal measurement is discussed in later section on small melanoma evaluation.
Normal choroid and globe wall thickness can best be seen at 20 MHz and higher frequencies (Figure 3.87) (107).
Figure 3.87. Left: In vivo 22 MHz B-scan through the posterior pole of the eye, with measurements of retinal, choroidal, and scleral thickness. Right: Comparative histologic section. Note relative thinness of choroid in the
absence of perfusion. (see color image)
Coleman, Rondeau, et al. (105) have developed a special analytic mathematical modeling technique for imaging the “normal” choroid using wavelet analysis. The definition of the choroidal thickness and appreciation of vascular channels is outlined by the scattering elements that surround them. Digital RF scans of the macular region are acquired, and power spectrum and wavelet analysis were used to identify changes in the backscatter architecture, providing uniquely enhanced images, as shown in Figure 3.88. This technique is being explored for evaluation of disease progression as well as effects of therapy.
UVEAL TRACT ULTRASOUND AND TUMORS
Retinoblastoma
Retinoblastoma is the most common primary intraocular malignancy in children. A highly malignant retinal tumor found in infants and young children, it usually presents with focal areas of calcification within the tumor. B-scan ultrasonography is frequently used for the initial and follow-up evaluation of retinoblastoma. Ultrasound can clearly reveal calcium, which is characterized by highly reflective foci within the tumor or vitreous. When small, the tumors are smooth, dome
shaped, and have low to medium reflectivity. As the tumors grow, they become more irregular in configuration and more highly reflective as the amount of calcium accumulates (Figure 3.89). There may also be associated retinal detachment. Ultrasound has become a useful and cost-effective way to follow these tumors as treatment is delivered. Baseline tumor size measurements and tumor locations are obtained, and these parameters are monitored closely during and after treatment. Ultrasound may have its major application in following therapy of such tumors.
Figure 3.88. Wavelet analysis of a parameter image of scatterers that outline the interstitial elements of the choroid (ch), thus also outlining the vascular elements. Top: This scan (a) is of a normal subject. Bottom: This scan (b), also of macular degeneration, is of drusen (sd) in a patient with wet AMD but taken in an area adjacent to the macula.
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Figure 3.89. 10-MHz ultrasonogram of an eye containing a retinoblastoma. It is estimated that over 95% of retinoblastomas have calcium deposition, which is highly reflective. In this case, the short arrow indicates a concentrated area of calcium in a surrounding area of tumor. The long arrow indicates a smaller calcium element. Note the shadowing behind the concentrated calcium.
Choroidal Effusions
Synopsis
Choroidal effusion and hemorrhage usually extend anterior to the ora serrata and thus are distinguishable from a localized retinal detachment, which is limited by the ora. The posterior extent of a choroidal detachment is usually limited by the ampullae of the vortex veins.
Hypotony and ciliary body separation are best visualized using VHF or UBM ultrasound.
Choroidal effusions (detachments) occur occasionally following intraocular surgery and often after trauma. In some patients, these cannot be diagnosed clinically because of a cloudy cornea, hazy aqueous or vitreous, or miotic pupil. A choroidal effusion appears ultrasonographically as a convex surface of echoes extending into the vitreous compartment from the globe wall in any quadrant. In a fully developed choroidal effusion, the echo lines may extend into the central vitreous from each side of the eye (baseball-stitch sign) and may even appear to touch (“kissing choroidals”) (Figure 3.90). The choroidal effusion is nearly always seen to straddle the ora serrata anteriorly, and at its juncture with the posterior wall echo forms an acute angle. It is limited posteriorly by a vortex vein. The space internal to the line of echoes is acoustically clear (anechoic). This characteristic differentiates a choroidal detachment from a choroidal hemorrhage, which shows low-amplitude echoes in the choroidal space, similar in amplitude to echoes obtained in vitreous hemorrhage. Infrequently, however, large choroidal effusions will show scattered low-amplitude echoes in the subchoroidal space, indicative of organized cells or exudate (Figure 3.91). Other ocular abnormalities, such as retinal detachment, may coexist with choroidal effusion (Figure 3.78).
Figure 3.90. Typical “kissing choroidal” elevations. They are smoothly convex as a result of the pressure producing them. They are limited posteriorly by the vortex vein ampulla and extend anterior past the ora serrata.
A flat or shallow anterior chamber is most commonly encountered as a postoperative condition. It may also appear in other situations, such as penetrating injury,
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pupillary block, dislocated lens, swollen lens, choroidal hemorrhage, or intraocular tumors. Most flat chambers are associated with a serous choroidal detachment (effusion). Examination of the posterior segment may therefore provide information useful for the diagnosis and management of each individual case.
Figure 3.91. Choroidal hemorrhages demonstrating the lower amplitude echoes from blood in the choroid. The
clear zone, noted in one bullae, indicates hemolysis, and this feature can be used to indicate areas and timing
for drainage.