Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006

Figure 3.69. B-scan of a proliferative membrane attached to retracted vitreous; both wide (left) and narrow (right) bands are shown, with the narrow band giving greater sensitivity to the area of vitreous traction. (See also DVD.)

Retinal Schisis

Schisis of the retina is a splitting of the neural layers of the retina producing an elevated, convex (usually peripheral) echo pattern similar to a total retinal detachment. The thickness of the “split” retina cannot usually be differentiated from full thickness retina (Figure 3.70).

Boldt (95) has pointed out that pressure of the B-scan probe directly over the schisis area will show that a schisis cavity does not collapse, unlike retinal detachments, which do collapse, as a result of a higher intraschisis pressure than vitreous pressure.

Traumatic Vitreous Hemorrhage

Vitreous hemorrhage, as a result of trauma, is discussed again in a later section, Ocular Trauma.

MISCELLANEOUS VITREOUS ABNORMALITIES

Primary Vitreous Detachment (PVD) and Asteroid Hyalosis

Normal aging of the vitreous is marked by retractions of the solid vitreous (primary vitreous detachment, or PVD) and a clear fluid replacement posteriorly in the “tertiary vitreous” (96). With B-scan, low-amplitude echoes in clear vitreous can be seen, and on kinetic scans, areas of residual attachment to the retina may be seen. This feature can be useful for looking for potential retinal tears when a history of flashing lights and floaters with opaque media is given.

Deposition of calcium soap crystals (asteroid hyalosis) produces high-amplitude echoes scattered throughout the solid or fluid vitreous and is usually accompanied by vitreous retraction so that a clear tertiary vitreous zone is seen on B-scan.

These calcium soap particles show widely scattered low-amplitude spikes on the A-scan. On kinetic A-scans, they can be seen to “dance” or move quickly. On the B-scan, asteroid hyalosis appears as a plethora of echoes

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in the vitreous cavity (Figure 3.71). As Jaffe (97) has noted, asteroid hyalosis tends to occur preferentially in the primary vitreous and thus is often best seen posterior to the lens. The peripheral vitreous may be acoustically clear as noted previously.

Figure 3.70. Two views at 10 MHz of a schisis cavity. The cavity has higher intraschisis pressure than the vitreous, thus should always remain smoothly convex. It is important to be perpendicular to the surface to maximize the B-scan. The wall thickness may be indistinguishable from retina, and balloting with the transducer may be valuable.

In the aging vitreous, cholesterol crystals (cholesterolosis) and dissolution of the vitreous can be seen on B-scan with real-time or kinetic scanning. These deposits seem to float and settle like the “snowflakes” in a decorative globe, unlike the suspended, highly reflective echoes of asteroid hyalosis.

Amyloidosis of the Vitreous

Extensive experience with ultrasonography in patients with amyloidosis of the vitreous, a rare abnormality, has not been obtained. We have examined one patient with pathologically confirmed amyloidosis of the vitreous in the fellow eye. There were irregular strandlike echoes in the vitreous, which were of low amplitude on the A-scan. This pattern is similar to that seen in vitreous hemorrhage, endophthalmitis, and hyphema.

Figure 3.71. Typical asteroid hyalosis pattern of high amplitude reflector and a clear zone separating the

retracted vitreous from the retinal surface.

Endophthalmitis

The B-scan pattern seen in patients with endophthalmitis is characteristic, though not diagnostic. The vitreous pattern will have the synchesis clefts emphasized by bacterial or detritus collections along their margins, producing a diffuse polyploid matrix (Figure 3.72; see also

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kinetic scan on DVD). The pattern may resemble convex curves that may straddle the ora serrata and simulate a choroidal detachment. This particular acoustic pattern has not been noted in any other ocular abnormality and seems related to bacterial spread different from that seen by pressure or diffusion of blood. In many, if not most cases, however, endophthalmitis is similar to a vitreous hemorrhage and, at least in early stages, is best diagnosed with caution, a good history, and a clinical indication. The extremely rare condition of CNS lymphoma should also be borne in mind, because it can also present as vitreous debris (Figure 3.73).

Figure 3.72. Two scans of a patient with endophthalmitis shown with both a wide band (top) and a narrow band (bottom) transducer. The narrow band transducer provides better sensitivity of the vitreous changes. Note that

the vitreous appears to separate from the retina with a point of contact remaining at the optic nerve. This is best seen on kinetic scan. (See also DVD.)

Figure 3.73. B-scan of a CNS lymphoma, which is relatively absorbent like a granuloma. There is also vitreous

debris present.

ULTRASONOGRAPHY AND VITREOUS SURGERY

RETINAL ABNORMALITIES

Retinal Detachment

Modern surgical techniques for retinal detachment have been considerably influenced by the widespread use of indirect ophthalmoscopy and ultrasonography, which permits a thorough evaluation of the peripheral fundus. Since optical evaluation techniques, such as indirect ophthalmoscopy, are useful in examination of the vitreous and retina only if the ocular media are clear. They are useful in examination of the subretinal space, only if the overlying retina is transparent and the subretinal fluid is clear. Ultrasonic evaluation techniques are not subject to these limitations. B-scan ultrasonic evaluation of the vitreous, retina, and subretinal space (especially in eyes with clouding or opacification of the ocular media) adds a significant dimension to the diagnosis of retinal detachment and to the management of patients with vitreoretinal abnormalities.

The use of A-scan ultrasound in the diagnosis of retinal detachment was first described by Oksala and Lehtinen (98) in 1957. B-scan ultrasonography of retinal detachments was subsequently reported by Baum (99), Baum and Greenwood (100), Purnell (28), Coleman and Jack (101), and numerous others.

Rhegmatogenous Retinal Detachment

The retina normally appears on B-scan ultrasonograms as a smooth, concave, acoustically opaque surface formed by echoes from the vitreoretinal interface. These echoes are contiguous and, with the attached retina, inseparable from echoes from the choroid and the sclera. A detached retina also appears on B-scan ultrasonograms as a thin, continuous, acoustically opaque line of echoes separate from, and anterior to, echoes from the wall of the globe (Figure 3.74). A relatively flat detachment has a narrow, acoustically empty (sonolucent) space between detached retina and the globe wall. A highly elevated, totally detached retina appears as convex bullae extending far into the vitreous from attachment points at the ora serrata and at the optic nerve. The space posterior to the elevated retina is sonolucent (anechoic).

The extent of a detachment (whether partial or total) is ascertained by performing ultrasonic B-scans in serial, horizontal, or radial planes of the eye. Starting above the superior limbus, scans are made at roughly 2-mm intervals along the vertical dimension of the globe. The serial sections thus obtained differentiate a true retinal detachment from simulating structures, such as a

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choroidal detachment, which extends anterior to the ora serrata, and from a vitreous veil (hemorrhage along the posterior hyaloid face), which cannot usually be traced back to the optic disc. The amplitude characteristics of returned echoes, best observed on the A-scan, further differentiate retinal detachments from vitreous

membranes, because retinal echoes have uniformly higher amplitude than do vitreous membrane echoes. Retinal echoes are approximately as high in amplitude as the normal posterior globe wall echoes, whereas membrane echoes are typically only about 50% of this height, as noted previously. If the anterior segment is particularly dense acoustically, as in a calcified cataract, the amplitude of the retinal echo can obviously be greatly reduced.

Figure 3.74. A relatively flat detachment exhibiting uniformly high amplitude. This will usually move freely on

kinetic scan.

B-scan ultrasound indicates the thickness of the detached retina and the extent of retinal organization and shrinkage. A freshly detached retina appears as a thin white line, equal in length to the scleral arc from ora to ora. On kinetic scans it is flexible and dances with eye movement (Figure 3.75; see also DVD). In long-standing detachments, the retina is thickened and its overall length often shrinks to form a cord from the optic disc to the ora serrata, thus often forming a funnel-shaped or “morning-glory” configuration. A contracted retinal detachment of this type is shown in Figure 3.76. Cystlike structures of the retina in long-standing detachments are indicated ultrasonically by a thickened and convoluted echo pattern (Figure 3.77).

Rhegmatogenous retinal detachments are usually the result of traction of vitreous membranes or bands on the retina. Vitreous membranes and bands, as noted previously, are demonstrable ultrasonically, as are sites of vitreous membrane attachment and their associated traction of the retina, indicating the “stress sites” at which retinal holes may be expected to have occurred.

Figure 3.75. A freshly detached retina is highly reflective along its entire surface, as is seen on both A- and

B-scans. (See also DVD.)

Figure 3.76. A long-standing retinal detachment with blood in the preretinal and postretinal spaces, producing a

“morning glory” shape. The retina is rigid on kinetic scanning, and contraction membrane can be seen connecting the retinal leaves.

Retinal detachment may be seen in conjunction with choroidal detachment. Choroidal detachments are limited posteriorly by the ampullae of the vortex veins and, as noted in a later section on choroidal effusion, will extend anterior to the ora serrata. Both retinal detachment and choroidal separation will have high amplitude walls and are best distinguished by the B-scan pattern (Figure 3.78). See Choroidal Effusion in later section.

Nonrhegmatogenous Retinal Detachment

Retinal Detachment Secondary to Choroidal Melanoma.

The use of binocular indirect ophthalmoscopy and scleral transillumination significantly aids in the clinical diagnosis of retinal detachment secondary to choroidal malignant melanoma. Mistaken diagnoses do occur, however, and a significant incidence of operation of retinal detachment in eyes containing choroidal melanoma occurs (2% in one series) (102). As Norton (103) has emphasized: “The most serious misdiagnosis of retinal separation is the failure to recognize an underlying malignant melanoma of the choroid as the cause of the retinal elevation. Once the patient is subjected to retinal surgery and the integrity of the sclera disrupted, the patient's life may be in jeopardy. On the other hand, removal of an eye with an idiopathic retinal detachment because of misinterpretation of the fundus changes is a similar tragedy.”

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Figure 3.77. 10-MHz scans of an eye with a long-standing detachment. Left: Immersion B-scan shows total

retinal detachment with membranes and with cystlike structures produced by coaptations of the walls and resulting adhesions. Right: Coronal plane shows retina in cross section with dense vitreous debris.

The use of B-scan ultrasonography can reliably demonstrate the presence or absence of a tumor underlying a retinal detachment. Upon serial sectioning, the profile of a choroidal mass can be detected and characterized. Tumors appear as acoustically solid (echoic) masses at low examining frequencies and can be differentiated from hemorrhages or exudative elevations, which are acoustically clear. Because certain detachments overlie tumors, patients with suspected secondary detachments benefit from B-scan ultrasonography to detect the obscured etiology of the detachment. All cases of retinal detachment do not necessarily require ultrasonic evaluation. This diagnostic test is most valuable in selected cases of clinically atypical retinal detachment. The following features are clinical suggestive, but not always diagnostic, of a nonrhegmatogenous retinal detachment: