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

Pathology associated with intraocular tumors is also ultrasonically demonstrable. Asteroid hyalosis may mask a tumor in ophthalmoscopic exam. Vitreous hemorrhages occur relatively infrequently with melanomas of the choroid but can be demonstrated ultrasonically (Figure 3.130). Retinal detachments secondary to intraocular melanomas or metastatic carcinoma are clinically important (Figure 3.131). Melanomas will often have a fluid layer between the retina and the anterior tumor surface. They appear on B-scan ultrasonograms as bullous retinal elevations with a sharp, high-amplitude leading edge. Serous retinal detachments can also be associated with choroidal hemangioma.

Conditions Simulating Choroidal Tumors

Retinal Lesions

In retinal detachment, or retinoschisis, the ultrasonic pattern may show an elevated vitreoretinal interface echo, but because the subretinal space is anechoic, the elevation is readily distinguishable from a tumor. Disciform macular degeneration also shows an elevated vitreoretinal interface. These hemorrhagic lesions show low-amplitude internal echoes on A-scan but will appear hollow at 15 and 20 MHz (or with reduced gain at 10 MHz).

Figure 3.130. An ocular melanoma with surrounding hemorrhage that obscured the clinical view. This patient had been treated with radiation, and the tumor regression could thus be followed with ultrasound only.

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Figure 3.131. This ocular melanoma was obscured and in question, as a result of an overlying retinal

detachment. The tumor is easily seen with conventional ultrasonography.

In chorioretinitis, an area of elevated retina may be seen, but the subretinal space is acoustically clear. Retinal pigment epithelium (RPE) lesions (such as CHRPE) that appear flat and highly pigmented ophthalmoscopically do not have sufficient elevation to allow ultrasonic detection, but the high reflectivity of melanin may make them highly visible, both optically and acoustically.

Choroidal Lesions

Most benign choroidal nevi fail to show significant elevation and thus cannot be demonstrated on routine B-scan ultrasonograms, though as noted previously, high frequency imaging of the choroid can be performed. Choroidal detachments present a typical convex circumferential elevation straddling the ora serrata with a sonolucent area between the retina and sclera on B-scan. Organized choroidal hemorrhage may be difficult to distinguish acoustically from a tumor, but the internal echoes are of lower amplitude. Lymphoid hyperplasia or lymphoma of the choroid (Figure 3.73) may be ultrasonically indistinguishable from an “en plaque” melanoma but may be suspected because of greater sound absorption by inflammatory tissue. Lymphoma is difficult to diagnose because of its rarity and it resembles inflammatory or metastatic disease. Vitreous debris on scanning may offer a clue to this diagnosis, particularly if the history indicates suspicion of such an entity.

Vitreous Lesions

Vitreous hemorrhages that have undergone organization may appear as echoic masses. The internal echo amplitudes are usually lower than those seen in melanoma. A posterior vitreoretinal interface appearing smoothly curved and in normal position may help in differentiating these hemorrhages. Repeated ultrasonic evaluations may be necessary to distinguish a tumor that lies within a dense, vitreous hemorrhage, a situation that arises more often with retinoblastoma than with choroidal tumors. The difficult diagnostic problem of organized hemorrhage in conjunction with retinal detachment occurs rarely.

Reliability and Limitations of Ultrasonic Differentiation

The reliability of ultrasonic diagnosis of ocular tumors in our laboratory has been reported as better than 96% for differentiation of neoplastic choroidal tumors from benign subretinal hemorrhages, vitreous hemorrhages, and retinal detachments (151). Ossoinig (11) has reported a similar figure, using his techniques. To date we have examined nearly 10,000 patients with ocular tumors, both neoplastic and benign. It has not always been possible to identify the tissue present on one examination. Serial examinations are often requested to permit growth documentation as well as to repeat the evaluation. The methods described here, even when absolute differentiation cannot be made, can direct the course of treatment, with small solid tumors being followed and patients with larger tumors referred for

metastatic workup.

In addition to the problems in identifying discrete lesions as discussed earlier, other difficulties in ultrasonic diagnosis of choroidal tumors exist that are related to size or position.

First, very small lesions cannot be demonstrated ultrasonically. In general, lesions causing more than 1 mm of elevation of the retina can be detected and demonstrated. When the tumor can be visualized and the ultrasonogram is performed under optimal conditions, tumors with only 0.5 mm of elevation can be depicted. Smaller lesions can certainly be missed with ultrasonography. This is a problem of equivocal significance because there is a body of opinion that eyes with small lesions should not be treated immediately, but rather be followed for demonstrated growth before being treated. Clinically, it is customary to follow a small lesion to document a growth change.

Second, large lesions filling the vitreous may be confusing in that they may resemble vitreous hemorrhages. With massive necrotic melanomas, this is a particular problem, and it also occurs with medulloepitheliomas, where cystic changes may be seen.

Finally, difficulties persist with optimal B-scan visualization of the ora serrata and pars plana regions with contact 10-MHz scans. Even with the immersion technique, structures that lie perpendicular to the examining beam are well portrayed, but structures lying parallel to the beam, such as the ocular walls at the ora, are not well outlined. Also, structures preceding a tumor will

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tend to mask some of its acoustic profile. Very high frequency scans have made this area much easier to identify and should be the procedure of choice with areas described later.

Newer tissue enhancement techniques have been found useful in enhancing the use of A- and B-scan techniques (137).

Ciliary Body Abnormalities

Ciliary body tumors occur less frequently than tumors of the choroid, representing approximately 10% of all ocular melanomas (110). Tumors of the ciliary body are often difficult to diagnose clinically because they arise in an area of the eye not easily examined and are not usually amenable to fluorescein angiography. They precipitate cataracts or secondary retinal detachments that may cause difficulty in clinical diagnosis. In addition, ophthalmoscopically visible masses may be difficult to distinguish from cystic lesions of the ciliary body, with elevation of the nonpigmented epithelium of the ciliary body in this area. Thus, ultrasonography is valuable in the diagnosis of such tumors, and the use of UBM or very high frequency ultrasound (VHFU) has greatly improved the initial diagnosis of ciliary body tumors (54,152,153).

Attention to certain technical features of the ultrasound examination will improve imaging of ciliary body tumors. First, rotating the eye as much as possible is important, bringing the mass perpendicular (in either an anterior or posterior position) to the transducer for best resolution. Second, small tumors in this region may be missed, particularly at the 6:00 and 12:00 meridians with horizontal scans, so B-scans should be made in all meridians. Third, a range of transducer frequencies should be used to optimize differentiation. Fourth, serial examinations at a later date are necessary in equivocal cases.

Ciliary Body Tumors

The ultrasonographic characteristics of ciliary body tumors will be discussed as choroidal tumors, in terms of both morphologic and acoustic characteristics. Solid lesions are nearly always melanomas but may be other solid tumors, such as medulloepithelioma, in rare instances.

The location and size of ciliary body tumors can be well demonstrated by high frequency ultrasound (Figure 3.132). Secondary changes, such as retinal detachment, hemorrhage in the vitreous, and cataractous lens changes, can also be shown.

As in tumors of the choroid, anechoic zones at the posterior part of a ciliary body tumor can be appreciated. The presence of cystic changes in the tumor is typical of medulloepithelioma, but this pattern can also be seen in melanoma, although very rarely.

Lesions Simulating Ciliary Body Tumors

B-scan ultrasonography provides the differential diagnosis between ciliary body cysts and ciliary body tumors. The interior of the cysts is sonolucent, and the A-scan trace remains at baseline throughout the cyst. High frequency B-scan ultrasonogram of ciliary body cysts are shown in Figure 3.133, demonstrating the anechoic cystic structure of the lesion. In some instances, however, debris within a cyst may produce internal echoes.

Figure 3.132. Ciliary body tumors, as well as iris tumors, are best evaluated using 50-MHz scans. This figure demonstrates the hyperreflective, internally solid mass of the ciliary body, consistent with a ciliary body melanoma.

Choroidal detachments or effusions can simulate a ring melanoma of the ciliary body, but ultrasonography should differentiate them based on their hypoechoic or hyperechoic internal structures, respectively.

Figure 3.133. This figure demonstrates a ciliary body/iris cysts, which appear similar clinically to the ciliary body tumor seen in Figure 3.132. A clear cystic outline indicates a benign ciliary body cyst. Top: Ciliary body/iris cyst with internal debris. Bottom: “classic” ciliary body cyst with no internal echoes.

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Metastatic tumors are most unusual in a position anterior to the ora serrata, and the diagnosis of a metastatic tumor can, if so evaluated, usually be made clinically on the basis of multiple ocular tumors and/or a known primary tumor.

Abnormalities of the Optic Nerve Head

Papilledema, papillitis, pseudopapilledema, drusen, and melanocytoma may be visualized ultrasonically as a protrusion of the intrascleral portion of the optic nerve into the vitreous, with increased reflectivity from this region. Papilledema and papillitis usually cannot be distinguished by the ultrasonic appearance of the scleral portion of the nerve alone, although subretinal fluid may, occasionally, be seen with papilledema (Figure 3.134). The appearance of the orbital portion of the nerve may indicate the correct diagnosis ophthalmoscopically, in cases of both visible and nonvisible elevations of the optic nerve head. In cases of pseudopapilledema as a result of drusen (Figure 3.135), the orbital echoes are normal, corresponding to the histologic findings that drusen in the nerve are not found posterior to the lamina cribrosa. Drusen may be so large that shadowing or internal echoes can cause apparent enlargement or internal reflections in the anterior nerve segment.

In cases of optic neuritis, echoes from the nerve wall may produce a contiguous line, appearing to separate the nerve and the sheath. When optic neuritis is seen in association with enlarged, inflamed rectus muscles, this “doubling of the wall sign” may indicate the diagnosis of Graves disease. When optic neuritis is associated with pseudotumor of the orbit, the inflammatory character of these mass lesions can be suspected by the nerve changes as well as edema of normal structures, such as Tenon's capsule.

Figure 3.134. 10-MHz ultrasonogram showing prominence of the optic nerve head. This usually indicates papilledema, but differentiation from pseudopapilledema may be difficult. The presence of a fluid area may help indicate true papilledema.

Figure 3.135. Drusen of the optic nerve head are very highly reflective and can help in the differentiation of papilledema and pseudopapilledema. Conventional (left) and midband fit (right) are shown here in “stretched”

format.

We believe that shrinkage or atrophy of the optic nerve cannot be reliably appreciated with a B-scan 10-MHz ultrasound. Standardized echographers state that they can measure the optic nerve diameter very accurately with A-scan techniques (154). However, given the orientation of the nerve to the interrogating beam, we question the accuracy of this technique. When the optic nerve is invaded by tissue which is acoustically dissimilar to that of the normal optic nerve tissue (normally anechoic as a result of alignment of nerve fibers), acoustic interfaces occur, and abnormal echoes are returned from within the nerve. As an example, when a juxtapapillary melanocytoma extends into the nerve, many abnormal intraneural echoes can be identified. Melanocytomas are composed of polyhedral cells with large amounts of pigment.

Optic nerve cupping is not usually demonstrable ultrasonically in its early stages because the beamwidth used in ocular evaluation is too wide to permit resolution of a small depression with standard 10-MHz ultrasound. The standard beamwidth causes the nasal and temporal cup edges to merge, and the beamwidth artifact causes merging of echoes from the floor of the optic cup, with echoes from adjoining tissue. Studies using precisely focused, very narrow beamwidth transducers, can demonstrate cupping of the optic nerve head; higher frequency (20 MHz) focused transducers do allow such imaging (Figure 3.136).

Elevation of the optic nerve head may also be seen with intrinsic tumors of the optic nerve, such as melanocytoma, which, ultrasonically, may resemble drusen.

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Figure 3.136. 22-MHz ultrasonogram of the posterior pole of a normal eye demonstrating resolution of the optic nerve, the superior orbital vein, and the boundary between Tenon's and sclera, as well as the choroidal measurements. Note the increasing thickness of the sclera adjacent to the optic nerve. Top image is in axially

“stretched” format.

OCULAR TRAUMA

Synopsis

Ultrasound scans can be made with sterile normal saline bath or a sterile sleeve over the transducer, even with lacerating injuries.

Rupture of the globe can be suspected by irregular wall outline.

A CT scan or plain film x-rays are recommended prior to ultrasound to optimize ultrasound examination. Foreign bodies can be better localized with ultrasound, relative to ocular structures, but are detected easier with CT or plain film x-rays. Consideration of radiation exposure should be discussed when children are injured.

TABLE 3.5 Improvements in Management Aided by Ultrasound

The preceding sections of ocular diagnosis have been presented in a manner based on the anatomic divisons of the eye. Changes produced in these structures by trauma have been alluded to; however, the importance of ultrasound in the evaluation of a traumatized globe merits a separate discussion so that specific changes, examining techniques, and approaches to clinical management may be more adequately summarized.

Ocular trauma may be classified into three broad categories: contusion or concussion injuries, penetrating or lacerating wounds, and foreign body injuries. Eyes subjected to any of these forms of trauma often exhibit cloudy media as a result of corneal or lens damage, hyphema, or vitreous hemorrhage. In these situations, ultrasonography becomes essential for complete evaluation of the globe prior to primary repair and for evaluation prior to secondary repair, if required. Effective medical and surgical therapy of the traumatized eye is thereby enhanced with ultrasonic examination. Table 3.5 summarizes some of the conditions subject to evaluation by ultrasound and the modes of treatment that may be initiated or expedited.

Careful visual inspection and radiographic and/or CT scan examination for ocular foreign bodies should be performed first. Identification of an ocular foreign body by x-ray or CT enables the examiner to more rapidly localize the foreign body in relation to ocular structures, shortening the total time required for the examination and decreasing the chance of missing a small foreign body. MR imaging should be avoided because of the possibility of a magnetic foreign body (155,156). CT exposure should be minimized in children.

In patients with recent ocular trauma, every attempt should be made to maintain sterile technique. We do not sterilize our transducer, but it is cleaned with alcohol or immersed in an approved antibacterial wash prior to scanning. Alternatively, a sterile latex sheath can be placed over the end of the transducer. An antibiotic solution can be instilled in the sterile normal saline bath, if immersion is used. With a severely traumatized globe, clinical judgment would determine whether immersion B-scan or contact A- or B-scan is indicated. We generally

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use a latex sheath cover (Figure 3.137) with saline between the transducer and the sheath to provide a cushion so that no significant pressure is placed on the eye and a benefit of a standoff is obtained (Chapter 2) with contact B-scanning (Figure 3.138).

Figure 3.137. Use of a sterile sheath with normal saline can provide an ideal standoff for examining infants or severely traumatized eyes. This can be used with A- or contact B-scan equipment and is particularly useful with inexperienced examiners who have a tendency to push the probe harder to get a better image.

Contusion and Concussion Injuries

Hyphema

Hyphema may be noted ultrasonically. A moderately dense hyphema can be appreciated ultrasonically as echoes occurring within the anterior chamber, whereas a relatively light, nonclotted hyphema may be anechoic, as discussed previously. Extension of the hyphema into the posterior chamber may be discerned. Figure 3.139 demonstrates hemorrhage into the anterior chamber as well as deepening, probable angle recession and hemorrhage into the posterior chamber.