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

Figure 3.92. Upper left: Immersion B-scan shows thickened choroid posteriorly and possible cyclodialysis cleft (arrow) temporally. Upper right: 50-MHz ultrasonogram shows internal echoes in lens consistent with cataract. Bottom left: Ciliary body is detached nasally (arrow).Bottom right: Complete cyclodialysis temporally with complete separation of the iris root (arrow).

In evaluating an eye with a flat or shallow anterior chamber, it is useful to search for relevant abnormalities in the anterior segment, to search carefully for evidence of external fistulization, to measure the intraocular pressure, and to determine the presence or absence of a choroidal detachment in the posterior segment. Factors, such as corneal edema, hyphema, cataract, miosis, and vitreous hemorrhage, may intercede to prevent adequate visualization of the posterior segment. Such problems are likely to be encountered in the more complex cases where information regarding the posterior segment is most needed.

Figure 3.93. An example of a patient's anterior segment with pupillary block glaucoma is shown, with evidence

of occluded angles and a flat iris.

An eye with a flat chamber following a filtering procedure for angle-closure glaucoma always raises the possibility of malignant glaucoma. In this condition, aqueous humor is trapped within the vitreous compartment, despite a patent iridectomy, and the lens is anteriorly displaced (Figure 3.92). Malignant glaucoma is distinguished from postoperative pupillary block glaucoma (Figure 3.93) and is characterized by lack of a patent iris coloboma and aqueous humor trapped in the posterior chamber causing iris bombé (Figure 3.94), without anterior displacement of the lens. In malignant glaucoma, the intraocular pressure is usually high, but it may fall within the normal range during the early phase. The tension in the flat chamber syndrome is generally soft but may transiently rise to a normal level in some cases, despite the continued presence of a choroidal detachment. Hence, a differential diagnosis between malignant glaucoma and the flat chamber syndrome cannot always be made by tonometry alone. In equivocal cases, the presence of a choroidal detachment would be diagnostic of the flat chamber syndrome, whereas the absence of such a finding would strongly suggest incipient malignant glaucoma. Thus, when visualization of the posterior segment is not possible, and the intraocular pressure is not elevated, ultrasonography may be helpful.

Choroidal Thickening and Choroidal Folds

Choroidal folds can be seen generally as thickened choroid at 10 MHz and may simulate a displaced implant or band or even a foreign body on B-scan. Higher frequencies can help document the choroidal thickening, but 10 MHz is required to define the retrobulbar space to determine whether a retrobulbar mass is present.

Hypotony and Ciliary Body Detachment

Very high frequency ultrasound or UBM is essential for evaluating any form of ciliary body elevation or separation from the sclera. A 10-MHz B-scan can detect ciliary body separation in some cases, if a standoff is used, but the definition is clearly suboptimal compared to the higher frequency examinations.

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Figure 3.94. Iris bombe is demonstrated with adhesions of the sphincter to the lens capsule and typical bulging

of the iris, and a narrowed iridocorneal angle.

The characteristic picture on B-scan of a ciliary body detachment is shown in Figure 3.95. An anechoic region is characteristic of the separation of detachment and its extent can be measured in terms of meridians involved with serial scans. We have found that hypotony typically has two or more quadrants of ciliary body detachment involved (108). In prolonged hypotony, the surgical management (either suturing or gas tamponade) can thus be directed by the determination of the location and extent of the separation.

Detachment of the ciliary body can be seen in both hypotony and trauma of the eye. A case of detachment is shown in Figure 3.96, where the iris root was totally

separated.

OCULAR TUMORS

Synopsis

CHOROIDAL TUMORS

Melanoma, hemangioma, and metastatic carcinoma are the most common choroidal tumors.

Distinguishing Characteristics

Melanoma: solid; shapes vary, but convex to collar-button; most common; reflectivity decreases rapidly on A-scan. Hemangioma: solid; convex to flat shape; A-scan reflectivity remains high amplitude as a result of vascular clefts.

Metastatic: solid; placoid to convex shape; A-scan reflectivity moderate and uniform, that is, less than hemangioma but posterior segment higher than melanoma, which is more homogeneous.

Tissue characterization techniques can subclassify melanomas in terms of lethal extravascular matrix (EVM) patterns. Observation for growth of small melanomas and the follow-up of treated tumors are important to both diagnosis and treatment. Accurate measurement of thickness, perhaps including 3-D ultrasound for volume, is clinically important.

Accurate diagnosis of choroidal masses remains a challenge to ophthalmologists. Lesions demanding different therapy may have similar clinical appearances. Even with the use of indirect ophthalmoscopy and scleral depression (109); scleral transillumination (110); fluorescein angiography (111, 112); visual field studies (113, 114); and MR, CT, and OCT (115, 116, 117, 118, 119), inaccurate diagnosis of ophthalmoscopically visible masses still occurs. The recent Collaborative Ocular Melanoma Study (COMS) claims an accuracy of 99% with all modalities used for melanoma diagnosis confirmed for enucleated eyes, but, significantly, any eye with a questionable diagnosis was not included in the study. Diagnosis of tumors with concurrent trauma and hemorrhage or other opacity thus probably remains in the accuracy range of approximatley 97% (120, 121, 122, 123, 124).

Figure 3.95. Ciliary body detachment at 10 MHz (top) and at 50 MHz (bottom). The 10-MHz scan shows typical changes, such as a shorter eye and choroidal thickening in hypotony. The 50-MHz scans show the ciliary body detachment with greater accuracy.

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Figure 3.96. Separation of the ciliary body from the sclera in a typical case of hypotony. Meridional scans can outline the full extent of the separation and can be very helpful, not only in diagnosing the condition, but in selecting surgery location and monitoring resolution.

TABLE 3.4 Differential Diagnostic Criteria for Choroidal Tumors

Ultrasound is particularly useful in distinguishing solid choroidal tumors from simulating lesions filled with blood. Echo amplitude studies with A-scan can usually differentiate an acoustically “solid” ocular tumor from conditions simulating an ocular tumor, such as choroidal detachment or retinal detachment with subretinal hemorrhage or fluid. In addition, A- and B-scan acoustic criteria may help identify the various types of choroidal tumors (Table 3.4).

The A-scan ultrasonographic appearance of a choroidal melanoma was first reported by Oksala (125) in 1959. Further discussions of choroidal tumor patterns were published by Oksala (126), Ossoinig (127), and Poujol (128). The B-scan appearance of choroidal tumors has been described in papers by Baum (129), Purnell (28), Coleman et al. (130), and more recently by Greenwald (131), Ossoinig (132), Byrne (133), and DiBernardo (134).

The important role of ultrasonography in choroidal tumor diagnosis in eyes with opaque media has been well documented by the previously mentioned researchers.

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Eyes with opaque media often harbor unsuspected malignant melanomas (10% of enucleated eyes in one study from the Armed Forces Institute of Pathology contained malignant melanomas) (135) and thus may present a diagnostic problem. Ultrasound is the only test for preoperatively discerning a tumor in such eyes, other than MR or CT scans, which are not as accurate or economically reasonable.

In a famous series of 529 eyes with clear media and ophthalmoscopically visible lesions clinically thought to be malignant melanomas that were enucleated (prior to the use of ultrasound), the clinical diagnosis was incorrect in 100 (19%) (136). Combined A- and B-scan ultrasonography of eyes with suspected intraocular tumors provides morphologic and acoustic characteristics, which can help significantly in making a correct diagnosis in these cases, just as in those with opaque media.

Consistent and systematic techniques must be used to follow tumors over time. Although the information presently obtainable with ultrasound does not allow absolute “tissue diagnosis,” tumor differentiation can be performed with a high degree of reliability by combining ultrasonic information with a knowledge of tumor characteristics. Newer tissue characterization data are described later that not only diagnose melanomas but can provide high sensitivity in identifying “high-risk” melanomas (56).

In general, there are three tumor types and one simulating pathology that must be differentiated, because their treatment differs: malignant melanoma, metastatic carcinoma, hemangioma, and organized subretinal hemorrhage. Although metastatic carcinoma is the most common neoplastic choroidal tumor, malignant melanoma is most commonly presented to the ophthalmologist as an unknown, and the subsequent discussions of tumor differentiation will be in terms of variation from melanoma patterns.

We have found it useful to describe ultrasonic features of tumors in terms of their morphologic characteristics, primarily two-dimensional analysis, and in terms of their acoustic characteristics, primarily one-dimensional amplitude or A-scan analysis. Obviously, the acoustic properties will affect, indeed produce, the patterns seen in the two-dimensional portrayal, and the diagnostic A- and B-scans are performed together. The discussion of morphology and tissue characterization is undertaken here to emphasize the different features.

The progression of ultrasonic evaluation from morphologic characterization, primarily from B-scan diagnosis, to acoustic characterization, primarily from A-scan diagnosis, proceeds much as histologic evaluations proceed from gross inspection through increasingly higher powers of microscopic examination. Because the evaluation is in vivo, dynamic tissue characteristics, such as vascularity, provide unique insights not comparable to any histologic technique.

Morphologic Characteristics

Size

Malignant melanoma and metastatic carcinoma occur in a continuum of sizes ranging from minimally elevated masses to lesions almost filling the globe, all of which can be well demonstrated on the B-scan display. Hemangiomas, in our experience, have not typically shown an elevation higher than 5 to 6 mm; however, they can have a very wide cross section. Subretinal hemorrhages sent for ultrasonic evaluation have characteristically low elevations, usually less than 4 mm.

20 MHz systems offer axial resolution of as little as 75 microns. However, highly accurate tumor measurements are made difficult because the base of the tumor may not be clearly distinguishable from the scleral echoes, and subsequent measurements may not obtain the same fiducial points, particularly if different examiners and equipment are used. The standard method is to measure maximal tumor thickness (or tumor height). With our equipment, using 10 MHz, we consider measurement to be accurate to 0.1 mm for purposes of chronologic comparison.

Shape

Malignant melanomas occur primarily in two characteristic shapes, polypoid or convex, as seen on B-scan. The most common form of melanoma is an elevated convex mass (Figures 3.97 and 3.98), which occurs when growth of the lesion is restrained by Bruch's membrane. A

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polypoid, or “collar-button” shape, is assumed when the tumor breaks through Bruch's membrane into the subretinal space and protrudes into the vitreous. Ultrasonically, these tumors have a mushroom appearance when the scan plane is passing through the tumor stalk (Figures 3.99 and 3.100). However, when the scan plane does not intersect the stalk, this type of lesion could resemble an isolated intravitreal mass. In such an instance, serial ultrasound sections are essential to trace the stalk of the tumor emanating from the choroid.

Figure 3.97. 10-MHz B-scan of a melanoma, showing the characteristic convex shape with a small area of

adjacent retinal detachment.

collar-button metastatic adenocarcinoma has been described (137). In general, metastatic masses have a lower silhouette (i.e., a lower height-to-base ratio) than do malignant melanomas. Choroidal hemangiomas and organized subretinal hemorrhages are also usually flattened or slightly convex. In relatively flat lesions, all four tumor types can appear as a simple convex mound and require A-scan and often repeat examinations for diagnosis, unless they are thick enough that tissue typing can be used (generally greater than 1.5 mm).

3-D Ultrasound and Volume

Although height and base or chord measurements have a long history of acceptability for tumor measurement, volume measurements are clearly superior as a means of following tumor growth or regression posttreatment (138). Recent instruments make these measurements more feasible and practical. Because volume relates to a cube function of measurements, accuracy of volume is increased, but the error percentage also increases. We use a 10% change from baseline volume for a significant growth bench mark (Figure 3.102).

Location

Localization of the tumor may aid in differentiation because hemangiomas tend to occur in the posterior pole, particularly near the optic nerve; metastatic tumors at the posterior pole; and malignant melanomas throughout the choroid.

Localization of tumors should be done with respect to normal ocular structures (Figure 3.103), because proximity to the optic nerve may have prognostic significance,

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and measurement of distance from the lens or ciliary body may be useful when considering placement of a radioactive plaque.

Figure 3.100. Immersion A- and B-scans of collar-button melanoma. Note high amplitude echoes in the “button” (A) versus lower amplitudes in base (B).

Figure 3.101. 10-MHz A- and B-scans (left) and 20-MHz A- and B-scans (right) of a metastatic carcinoma demonstrating a relatively placoid shape and moderate reflectivity throughout entire tumor.

Evidence of Spread

It is possible to preoperatively identify subclinical extension of a melanoma beyond the globe with ultrasound. In the case shown in Figure 3.104 (see also DVD), ultrasonography was consistent with extension of the tumor into the optic nerve and was confirmed pathologically. In general, the diagnosis of subtle extrascleral extension cannot be made with high confidence and must be confirmed with additional imaging and clinical data. Massive orbital extension, however, can be easily shown, as demonstrated by Figure 3.105, with a flat intraocular choroidal melanoma.

Size Progression

Repeating ultrasonic evaluation at various time intervals has been valuable to document the progressive growth (Figure 3.106) or regression of a mass lesion. Variation in scan plane is unavoidable in scans performed at different times, but scans through the area of maximum elevation with maximization of the A-scan vitreoretinal echo height will reduce measurement error. Ultrasonography has also been useful in following the response of tumors to local radiotherapy (I-125 plaques) (Figure 3.107) as well as proton beam radiation and transpupillary thermotherapy (TTT) (139) (Figure 3.108). Hemangiomas can also be followed after photocoagulation to document regression when hemorrhage is encountered, or with other causes of opaque media.

Metastatic carcinoma usually grows more rapidly than malignant melanoma, but we seldom have the opportunity to follow ultrasonically a patient with such a lesion because of other medical priorities.

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