Vascular Studies of the Orbital Cavity

Vascular Studies of the Orbital Cavity ALAN L. SUSAL, MD

Abstract: The orbital cavity is a dynamic region filled with pulsatile vascular structures. Newly developed ultrasonic-imaging equipment enables the physician to study the in-vivo motion of orbital tissues and their blood vessels to obtain pertinent diagnostic information relating to orbital diseases. Evidence of enhanced vascular activity is observed in endocrine ophthalmopathy and other orbital inflammatory conditions . Blood vessels within tumors help to localize the abnormalities and give clues relating to an accurate tissue diagnosis. These examinations are performed repeatedly and noninvasively in a clinical environment. [Key words: orbital blood vessels, orbital ultrasound, tissue motion, thyroid ophthalmopathy, vascular activity.] Ophthalmology 88:548-552, 1981

The orbital cavity contains a number of prominent blood vessels that can be studied in vivo, using advanced ultrasonic apparatus. The ophthalmic artery and its major branches in addition to other vascular structures (such as the posterior ciliary arteries and active vessels from the interior of tumors), can be imaged for diagnostic evaluation using this technique. These ultrasonic studies enable the physician to recognize specific areas of orbital inflammation where the tissue demonstrates abnormal vascular pulsations. These examinations aid in the diagnosis of thyroid ophthalmopathy and its differentiation from other orbital diseases. To observe relatively small vascular structures in vivo, the examining equipment must generate rapid images without motion artifact induced by mechanically moving transducers. This necessitated the devel-

From the Department of Ophthalmology. Stanford Medical Center, Stanford. Presented at the Eighty-Fifth Annual Meeting of the American Academy of Ophthalmology, Chicago, November 2-7, 1980. The development of Ophthalmic Array System was supported by the Department of Health, Education and Welfare under grant no. P01 GM 17940 in cooperation with the Integrated Circuits Laboratory, Stanford University. Supported in part by an unrestricted grant from Research to Prevent Blindness. Reprint requests to Alan L. Susal , MD, Division of Ophthalmology, A-227, Stanford University Medical Center, Stanford, CA 94305.

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opment of ultrasonic apparatus that could produce images faster than 20 frames per second.' The ultrasonic beam is swept across the eye region by electronically switching several ultrasonic transducers fabricated along a line to obtain a 35- x 4.0-mm linear array containing 35 individual ultrasonic transducers. This array is placed directly on the closed eyelids for contact scanning of the eye, or it can be used in conjunction with a water-immersion bath (Fig 1). By electronically switching from one element to another, a moving ultrasonic scan is generated at rapid rates to image a 32- x 60-mm plane in the eye region. 2 The visual presentation of that plane on the equipment produces a B-scan image (a planar "slice" through the eye and orbit as illustrated in Fig 2). To increase the clinical utility of the instrument, an A-mode presentation supplies the echo-amplitude information along the center of the B-scan plane. 3 Both A- and B-mode displays are generated and imaged at 60 frames per second so that ultrasonic images can be observed on a television monitor as they occur. The examination can be directly video taped because the display is presented in standard television format. Clinical video tapes of these ultrasonic studies facilitate the recognition of subtle diagnostic details that may initially escape detection but become more apparent after repeated observations or after orbitotomy and biopsy. Computerized tomography (CT) can also reveal an area of orbital abnormality that can be studied in greater detail by means of video tape. Realtime sonographic examination and CT scan are mutu0161 -6420/8110600/0548/$00.75

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American Academy of Ophthalmology

SUSAL • VASCULAR STUDIES OF THE ORBITAL CAVITY

Fig 1. Emersion scanning of the eye region. The transducer is dipped into a water bath suspended above the patient's eye. A- and B-mode images are viewed on the television monitor ill the ultrasonic apparatus.

ally complimentary techniques for the more comprehensive evaluation of the orbital cavity.

METHODS The orbit is examined in real time by either contact scanning or water-immersion baths. In contact scan-

ning, the hand-held probe with a linear-array transducer is pressed gently against the closed eyelid. 4 An ultrasonic contact gel or 1.5% methylcellulose between the transducer and eyelid ensures good ultrasonic coupling. Adequate orbital examinations are possible by this technique; however, some ultrasonic information is lost as the result of lid absorption of sonic energy, primarily by the tarsal plates (Fig 3). Direct contact to topically-anesthetized eyes or water-immersion methods 5 have greater sensitivity and enable a more detailed observation of the orbital apex. Rapid screening tests, ultrasonic studies on apprehensive children and elderly patients, and examination of eyes with open wounds are performed routinely by contact scanning through the closed eyelids. The eyes and hand-held probe should be held as stationary as possible during observations for orbital vasculature; the slightest motion will tend to obscure the imaging of the vessels. Larger arterial vessels are observed directly as the walls of the artery expand with each cardiac pUlsation; these pulsations are synchronous with the carotid or radial pUlse. The location of smaller vessels (such as the posterior ciliary arteries) is determined by the expansile perturbation of the orbital fat tissue around these arteries. The ultrasonic equipment operates at 7.2 MHz

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Fig 2. Pictorial representation of the transducer and ultrasonic displays. The linear-array transducer (on the left) images a planer' 'slice" of the eye seen on the A- and B-mode displays.

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OPHTHALMOLOGY. JUNE 1981 • VOLUME 88 • NUMBER 6

Fig 3. Contact scanning of orbital hemangioma. This localized vascular tumor (arrows) pulsated synchronously with the cardiac cycle. The orbital apex is not imaged due to partial absorption of the sonic signal by the lids.

which produces a resolution of better than 0.5 mm in the axial (anterior to posterior) direction, and this resolution is adequate for the observation of the ophthalmic artery and its immediate major branches. Because smaller vessels are localized by the concentric pulsation of surrounding tissue, it is possible to detect such relatively small arteries as the tarsal arcades or nutrient vessels within the interior of neoplasm. The lateral resolution of this apparatus is limited to 1 to 2 mm which is not as fine as the axial resolution. This disparity makes it easier to image more clearly the vessels whose course is perpendicular to the direction of the ultrasonic beam (such as the ophthalmic artery as it crosses over the optic nerve).

RESULTS In the normal orbital cavity, vascular activity is observed primarily from the ophthalmic artery and its immediate branches, and this artery is imaged in all patients. The easiest way to study the artery is when it's adjacent to the optic nerve as it crosses over to the nasal orbit (Fig 4). The lacrimal and supraorbital arteries are infrequently imaged and are more difficult to observe because of their axial orientation (a field of diminished ultrasonic resolution). The presence of the posterior ciliary arteries is indicated by the concentric localized region of pulsations in the retrobulbar fat. Detection of the ophthalmic and posterior ciliary arteries is a significant landmark in the localization of abnormal processes through orbital sonography. Orbital veins have not been observed in normal patients but can be imaged when abnormally dilated. A Valsalva maneuver during real-time examination will enlarge abnormal venous channels to facilitate the de550

Fig 4. Ophthalmic artery deep in the orbit. The ophthalmic artery (OA) is imaged adjacent to the optic nerve (ON). Branches of the ophthalmic artery are more readily recognized by pulsations they cause in surrounding orbital fat.

tection of venous abnormalities. Dilated venous channels are spontaneously observed without the Valsalva maneuver when associated with arteriovenous fistulas. 6 The pulsations of arterial structures are restricted to well-defined localized regions in the normal orbital cavity and are fully damped out within a few millimeters of the artery. As a result, the largest majority of orbital fat tissue does not demonstrate any pulsatile movement. Orbital diseases cause alterations in the observed vascular pattern, which makes it easier to detect and outline the pathologic process. This altered pattern may be the result of the presence of abnormal vascular channels (as in orbital neoplasms) or a localized region of greater vascular activity (as in inflammatory diseases). The increased vascular activity observed in orbital inflammation cannot be attributed solely to more active or engorged blood vessels. Some inflammatory edema probably accumulates in these areas. This fluid is relatively incompressible and transmits pulsations from the vascular structures to the surrounding tissues, and this movement of tissues in and adjacent to the inflammation can be quickly recognized with realtime ultrasound. THYROID DISEASE

In thyroid ophthalmopathy, the orbital fat and extraocular muscles are engorged with round-cell infiltration and interstitial edema. 7 The extracellular edema fluid separates the orbital fat and muscle fibers, which reduces the spacing and amplitude of the ultrasonic signals. Sonographically, the fat tissue appears less dense and more mottled in the affected areas (Fig 5). The transmission of sonic waves through the edema fluid makes it easier to observe the boundaries to the affected region and the orbital bony wall and pathway of the extraocular muscles. 9 A prominent

SUSAL • VASCULAR STUDIES OF THE ORBITAL CAVITY

Fig 5. Edema of orbital fat in endocrine ophthalmopathy (arrows). Decreased echo density and increased localized vascular activity was noted in this region of inflammatory infiltration.

finding in real-time sonographic examination is an increase in vascular pulsatile movement in and adjacent to the infiltrated orbital tissues; the affected region tends to pulsate en mass, but specifically-dilated blood vessels have not been recognized. In endocrine ophthalmopathy, the extraocular muscles are often congested with interstitial edema and round-cell infiltration. The affected muscles are enlarged and more apparent during ultrasonic examination (Fig 6). The reason for this, in part, is a greater sonic contrast between the infiltrated muscle and adjacent denS'e fat tissue and also because the infiltrated muscle has irregularly-spaced internal echoes resulting when the muscle fibers are separated by the interstitial edema. A consistent finding with real-time ultrasound is that the increased pulsatile motion of the enlarged muscle is not associated with any recognized dilatation of the anterior ciliary arteries. These muscles are easier to recognize than adjacent static orbital tissue because of their pronounced vascular pulsations. The dilated muscle segments are also easier to detect as the patient is directed to move his eyes during the examination.

Fig 6. Enlarged lateral rectus muscle in endocrine ophthalmopathy (arrows). This deep muscle segment pulsated prominently on the dynamic display.

with the cardiac cycle. Its course can also be traced posteriorly where it is found to be contiguous with the ophthalmic artery at the lateral aspect of the optic nerve. Static B-mode images will sometimes demonstrate the artery as a linear echo crossing over the optic nerve. This was incorrectly attributed to possible oblique sectioning ofthe inflamed nerve by Coleman. l l POSTERIOR SCLERITIS

Localized inflammatory processes, such as posterior scleritis, are also characterized by increased vessel activity in the affected region. With posterior scleritis, the scleral echoes are thicker, less dense, and sonically more distinguishable from orbital fat tissue. Fluid may be identified in Tenon's space as an echofree zone closely outlining the contour of the globe (Fig 7).12 Pronounced vascular activity in this region is observed during real-time examination of the inflamed scleral tissue. ORBITAL NEOPLASMS

OPTIC NEURITIS

Optic neuritis of an inflammatory (rather than ischemic) nature is also associated with increased localized vascular activity. In the area of inflammation, the perineural sheaths are enlarged and separated from the optic nerve lO (presumably by edema). Real-time sonography reveals the enlarged nerve sheath with prominent vascular pUlsations in the area. In retrobulbar neuritis, the crossing of the ophthalmic artery over the nerve may be accentuated as the result of localized edema. The artery is imaged as a high-amplitude linear or tubular structure overlying the optic nerve. This structure is recognized as the' continuing ophthalmic artery (just after branching of the lacrimal artery) since it pulsates synchronously

It is possible to observe vascular activity within different orbital neoplasms. Here, the blood vessels can be studied directly, particularly in the case of cavernous hemangiomata where active large channels are recognized from the interior of the tumor. Pulsations tend to occur synchronously throughout the cardiac cycle and in direct correspondence with the carotid or radial pulse. This is in contrast to a few fast-growing metastatic carcinomas where the interior of the tumor appears to writhe in dysynchronous movement. These twisting pulsations may be the result of new elastic vessels within the tumors and the simultaneous observation of both arterial and venous channels. Identification of vascular activity within neoplastic masses aids in obtaining a more accurate differential diagno551

OPHTHALMOLOGY. JUNE 1981 • VOLUME 88 • NUMBER 6

pulsate by expanding to approximately 50% of its size. Static pictures comparing the expansile and contractile state ofthe artery do not convincely demonstrate these small pulsations although they are readily observed on the real-time display. Dynamic ophthalmic ultrasound has been used for over two and one-half years in the Division of Ophthalmology, Stanford University. Real-time examinations on more than 400 patients have verified the clinical material presented. This paper is intended to encourage other investigators to recognize orbital vascular phenomenon and utilize their observations for improved diagnosis of orbital disease.

REFERENCES

Fig 7. Posterior scleritis. The scleral echoes (s) are thickened and separated from the adjacent orbital fat by fluid in Tenon space (T).

sis; however, a definitive tissue diagnosis still is not possible with current ultrasonic techniques.

CONCLUSION With real-time sonography, it is possible to image normal and abnormal vessels within the orbit and to detect localized inflammatory changes such as occUr in endocrine ophthalmopathy. Dynamic ultrasonic studies enable the physician to identify more definitively the presence and extent of pathologic changes within the orbit and to infer a tissue diagnosis with greater accuracy. In this paper, dynamic studies are discussed which are best corroborated by actual real-time observation of the data or video-tape recordings. The static pictures in this report are meant to call attention to those orbital regions where these dynamic observations can be made. The ophthalmic artery (the most active normal pulsatile structures in the orbit) is observed to

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