Journal of Neuro-Ophthalmology, June 1991, Volume 11, Issue 2

Echographic evaluation of optic disc drusen.

With the improved resolution of the newer B-scan instrumentation, echography can be used to confirm rapidly and accurately the diagnosis of optic disc drusen. Over a 4-year period, we retrospectively identified 48 patients with the echographic diagnosis of optic disc drusen. Ages ranged from 6 to 78 years. Drusen were echographically bilateral in 69% of these patients. In 30 eyes, drusen were not visible clinically but were detected echographically. Standardized A-scan echography also helped to confirm the diagnosis of pseudotumor cerebri (2 patients) and optic neuritis (2 patients), emphasizing the need for performing a thorough evaluation before attributing clinical findings of an ophthalmoscopically abnormal optic nerve head to optic disc drusen. Six of 48 patients had vascular occlusions at the level of the optic nerve head. In 5 of these 6 patients, unilateral deep optic disc drusen were detected on the side of the occlusion. This finding lends support to the theory of potential mechanical compression of vascular structures by optic disc drusen.

Journal of Clinical Neuro- ophthal1lloloxy 11( 2): 85- 91. 1991. ( 1) 1991 Raven Press, Ltd., New York Echographic Evaluation of Optic Disc Drusen H. Culver Boldt, M. D., Sandra F. Byrne, and Cathy DiBernardo, R. N. With the improved resolution of the newer B- scan in­strumentation, echography can be used to confirm rap­idly and accurately the diagnosis of optic disc drusen. Over a 4- year period, we retrospectively identified 48 patients with the echographic diagnosis of optic disc drusen. Ages ranged from 6 to 78 years. Drusen were echographically bilateral in 69% of these patients. In 30 eyes, drusen were not visible clinically but were de­tected echographically. Standardized A- scan echogra­phy also helped to confirm the diagnosis of pseudotu­mar cerebri ( 2 patients) and optic neuritis ( 2 patients), emphasizing the need for performing a thorough eval­uation before attributing clinical findings of an ophthal­moscopically abnormal optic nerve head to optic disc drusen. Six of 48 patients had vascular occlusions at the level of the optic nerve head. In 5 of these 6 patients, unilateral deep optic disc drusen were detected on the side of the occlusion. This finding lends support to the theory of potential mechanical compression of vascular structures by optic disc drusen. Key Words: Drusen- Echography- Ultrasonography­Optic nerve. From the Echography Department, Bascom Palmer Eye Insti­tute, Miami, Florida. Dr. Boldt is currently affiliated with The Eye Institute, Medical College of Wisconsin, Milwaukee, Wis­consin, U. S. A. This paper was presented at the American Academy of Oph­thalmology Annual Meeting, October/ November 1989, in New Orleans, Louisiana, U. S. A. Address correspondence and reprint requests to Ms. S. F. Byrne at Bascom Palmer Eye Institute, P. O. Box 016880, Miami, FL 33101, U. S. A. 85 Previous reports have shown echography to be useful in detecting optic disc drusen and to be valuable in evaluating patients with pseudo­papilledema ( 1,2). With the improved resolution of the newer B- scan instrumentation, fine calcifica­tions of the optic nerve head can be detected more readily. We describe our method for displaying op­tic disc drusen with contact B- scan and review our findings in a series of patients examined with this technique. MATERIALS AND METHODS We performed a 4- year retrospective review of the echography records at the Bascom Palmer Eye Institute from March 1985 to March 1989. Patients were identified who had been referred for possible optic disc drusen or in whom optic disc drusen had been an incidental finding. We obtained the clini­cal records of these patients to assess indications for requesting echography, past ocular history, whether the optic disc drusen were visualized clin­ically, and the final diagnosis. Only patients who had bilateral echographic evaluations and docu­mentation of optic disc findings were included. Most of these data were available in the records at our institute, but the clinical history was com­pleted by telephone call to the referring physician, when necessary. Echography examinations were performed by one or more experienced echographers, and Polar­oid photoechograms were obtained to document the findings. Contact B- scan instrumentation was the primary modality used to evaluate the optic discs of patients in this study. In most instances, methylcellulose was applied to the eye, and the probe was placed directly on the globe surface to promote optimal resolution and clarity of findings. One or more of three probe orientations were. 86 H. C. BOLDT ET AL. FIG. 1. Probe positions and corresponding B- scan echograms of normal optic disc. Top: vertical axial approach. The probe is centered on the cornea ( marker up). Using a medium- high gain setting, the sound beam is directed through the lens ( L) toward the center of the optic nerve ( arrow). Center: vertical transverse approach. The probe is positioned temporally ( marker up). Using a medium gain setting, the sound beam is directed toward the optic nerve as it inserts into the globe ( arrow). Open arrow: cross- section of optic nerve just behind globe. Bottom: longitudinal approach. Using a low- medium gain setting, the probe is positioned temporally ( marker to cornea). The sound beam is directed parallel to the optic nerve ( arrow). used: axial, transverse or longitudinal ( Fig. 1). Al­though axial echograms are easiest for the ophthal­mologist to orient, the ultrasound beam becomes attenuated as it passes through the lens twice. In contrast, when the transverse and longitudinal probe orientations image the optic nerve head, the ~, 11J., rt :''''' 1 IT. h': l', l:'<';"'" Hw lens, resulting in better JClm Neuro- ophtiullmol. Vol. 11, No. 2. 1991 resolution. Consequently, these latter two posi­tions are often more useful in detecting subtle op­tic disc drusen. Initially, system sensitivity ( i. e., gain) was adjusted to a high level. Once the disc was displayed, gain was decreased for better res­olution. If a druse was present, its highly reflective echo persisted at low gain because of its calcified, ECHOGRAPHIC EVALUATION OF OPTIC DISC DRUSEN 87 FIG. 2. Longitudinal B- scan echograms of optic disc druse at high gain ( top) and low gain ( bottom). Note persistence of the bright foreign- bodylike signal at re­duced gain setting. foreign body- like reflectivity ( Fig. 2). Comparison was made with the fellow eye at the same or a similar sensitivity setting. In most patients, the di­ameter of the retrobulbar portion of the optic nerves was evaluated with standardized A- scan. If the nerves were thought to be enlarged, two or more precise measurements were obtained. A 30° test ( 3,4) was then performed to determine whether the enlargement was caused by increased subarachnoidal fluid or solid thickening of the op­tic nerve or its perineural sheaths. Photoechograms of the optic discs of each pa­tient were evaluated retrospectively in an indepen­dent fashion by two experienced echographers to determine drusen size and location. Optic disc drusen were categorized as large or small, based upon the experience of the two echographers. No predetermined size standard was utilized, because the absolute size of optic disc drusen varies with the gain setting. Location was divided into three categories: ( 1) at the disc surface; ( 2) near the disc surface but covered by a thin layer of tissue; and ( 3) deep within the substance of the optic nerve head near the plane of the posterior sclera. RESULTS Of the 90 patients referred for possible optic disc drusen, drusen were identified in 39 patients. In 9 additional patients, optic disc drusen were de­tected as an incidental finding during an echo­graphic examination for an unrelated cause. Thus, a total of 48 patients were found to have optic disc drusen by echography. The mean age was 40.1 years ( range: 6 to 78 years). There were 22 men and 26 women. Clini­cally, optic disc drusen were bilateral in 8 patients, unilateral in 10, and were not visualized in 30. Echographically, optic disc drusen were bilateral in 33 patients ( 69%), and unilateral in 15 ( 31 %). In 7 eyes with moderate to severe media opacity, optic disc drusen were detected echographically but not clinically. In 41 of 48 patients, optic disc drusen were lo­cated in the anterior portion of the optic nerve head. In 7 patients, the drusen were located much deeper, in the plane of the posterior sclera. Six of these drusen were solitary and unilateral. The sev­enth patient had bilateral optic disc drusen, with a superficial druse in one eye and a deep druse in the other eye. None of the deep drusen in these 7 patients was detected clinically. Optic disc drusen were considered to be large in 43 of 81 eyes and small in 38 of 81 eyes. In un­ilateral optic disc drusen, lesions tended to be small ( 11/ 15). Of the 33 bilateral cases, optic disc drusen were large in 14 patients, small in 8 pa­tients, and mixed in 11. Photoechograms docu­mented more than one druse in the same eye in 3 patients. The most frequent indication for the echography examination was to evaluate an abnormal optic nerve head ( 21/ 48). Other common indications in­cluded: acute decrease in visual acuity ( 10/ 48), opaque media ( 5/ 48), and visual field loss ( 3/ 48). In six eyes of six patients, acute symptoms resulting from vascular occlusions in the region of the optic nerve led to echographic evaluation. In five of these eyes, unilateral small deep optic disc drusen were detected. Two of these eyes had central ret­inal artery occlusions ( CRAO), and three had an­terior ischemic optic neuropathy ( AlaN). The sixth patient, who was diagnosed with anterior ischemic optic neuropathy in one eye, had bilateral superficial optic disc drusen by echography. Echo­graphic evaluations were performed on these pa- JClin Neuro- ophthalmol, Vol. 11, No. 2, 1991 88 H. C. BOLDT ET AL. tients from 3 days to 8 months after their visual events. Using standardized A- scan, enlarged optic nerves due to increased subarachnoid fluid were detected in four patients. Clinically, this fluid was felt to be due to pseudotumor cerebri ( two pa­tients) and optic neuritis ( two patients). ILLUSTRATIVE CASES Patient 1 A 76- year- old white woman with a history of hypertension developed sudden loss of 3/ 4 of her visual field as, sparing only the inferotemporal quadrant. Fundus photographs taken by her refer­ring ophthalmologist eleven days later show whit­ening of the superotemporal, superonasal, and in­feronasal quadrants. Evaluation at Bascom Palmer 3 months later concurred that the visual loss was the result of a central retinal artery occlusion. The optic nerve ( Fig. 3) was pale and the arteries were narrow, but no drusen were ophthalmoscopically visible. Echography, obtained to evaluate subtle chorioretinal folds in the juxtapapillary region, ( Fig. 4) revealed a small unilateral calcification lo­cated deep within the substance of the optic nerve head, near the level of the lamina scleralis. No cause was found for the chorioretinal folds. Al­though medical evaluation for cardiac and carotid disease was negative, the possibility of a calcified embolus still exists. Patient 2 A 26- year- old white woman with a history of bilateral lid swelling and an infiltrating lacrimal gland process initially received the diagnosis by FIG. 3. Optic disc photograph of Patient 1. Note marked disc pallor and narrowed arteries. 1(/ 11/ Neuro- ophthalmol, Vol. 11, No. 2, 1991 FIG. 4. B- scan echograms of Patient 1 at low- medium gain settings. Echograms show small, de~ p calcific~ ­lion within optic nerve head at level of lamina sclerahs ( arrows). Vertical transverse ( top) and longitudinal ( bottom) views. biopsy of sarcoidosis; she was seen for a second opinion regarding an abnormal- appearing optic disc. Examination revealed an abnormal disc 00, with modest elevation and indistinct borders ( Fig. 5). There was concern that the optic nerve might be affected by granulomatous inflammation. Echography revealed bilateral optic disc drusen, right larger than left ( Fig. 6), and normal retrobul­bar optic nerves. After review of the original bi­opsy, the diagnosis was changed to lymphocytic dacryoadenitis with optic disc drusen. DISCUSSION Optic disc drusen are observed clinically in 0.3% of the population ( 5). Autopsy studies, however, have indicated that the true incidence is 1- 2% ( 6,7). These figures suggest that many optic disc drusen are not detectable or are not appreciable on routine clinical examination. Fluorescein angiogra­phy ( 8) increases the detection of bUried optic disc drusen because they may exhibit autofluorescence. However, fluorescein angiography is not useful in patients with opaque media, or in detecting deeply buried drusen. Computerized tomography ( CT) ECHOGRAPHIC EVALUATION OF OPTIC DISC DRUSEN FIG. 5. Optic disc photograph of Patient 2. Note the indistinct margins. fullness. and anomalous vasculature of the optic disc. 89 can also detect calcifications in the optic nerve head ( 9), but this technique is relatively costly and requires exposure to ionizing radiation. Also, sen­sitivity in detection of optic disc drusen decreases as CT sections which are greater than 2 mm are obtained or if the patient moves slightly between sections. With the higher resolution of the newer B- scan instruments, the detection of optic disc drusen is simple, rapid, and reliable. Another ma­jor advantage of echography is that standardized A- scan also can be applied to evaluate the retro­bulbar optic nerve to rule out other concomitant optic nerve disorders ( 3). In the 4 patients with optic disc drusen and echographic evidence of increased subarachnoid fluid, the final clinical diagnoses were pseudo­tumor cerebri ( 2) and optic neuritis ( 2). Results in these patients indicate that standardized echo­graphy is useful not only to detect optic disc drusen, but also to detect the presence of concom­itant optic nerve disorders. They also emphasize that the mere presence of optic disc drusen in a patient with visual symptoms or an abnormal disc does not mean that other disease cannot be present. Indeed, loss of central visual acuity due to optic disc drusen had been thought to occur very rarely ( 10). Therefore, one should be cautious about at­tributing a loss of central vision to optic disc drusen. Although on clinical examination it is com­mon to see more than one druse in an affected optic disc, only one druse is usually detected echo­graphically. There are several possible explana­tions for this discrepancy. Tso ( 11) described optic disc drusen as having a multilobulated histopath­ologic appearance. Therefore, a single large druse could be situated mainly within the substance of the optic nerve, with only its multiple protuber­ances close enough to the surface to be visible clin­ically. A second explanation is that current ultra­sound instruments are not capable of resolving multiple small calcifications in close proximity within the optic nerve head. Previous reports have documented an associa­tion between optic disc drusen with central retinal artery occlusions ( 12,13), retinal vein occlusions ( 14), and anterior ischemic optic neuropathy ( 15­20). In our series, 6 eyes were evaluated for acute decrease in visual acuity due to CRAO or AION. Unilateral deep drusen were detected echograph­ically but not clinically in the involved optic nerve head in 5 of 6 patients, whereas only one patient had a superficial druse. All drusen in previously published reports of vascular occlusions associated with optic disc drusen were visible on clinical ex­amination. In our series, we found that deep drusen were associated with vascular accidents of the disc more frequently than superficial drusen. Drusen located in the region of the lamina cribrosa may cause more compressive effects on vascular structures than those present in the more superfi­cial regions of the optic nerve head. If drusen do cause vascular compression and thrombosis in the optic nerve head, then some cases of CRAO and AION may be caused by deep drusen that are not clinically visible. The echographic differential diagnosis of optic I Gin Neuro- ophthalmol, Vol. 11. No. 2, 1991 90 H. C. BOLDT ET AL. FIG. 6. B- scan echograms of Patient 2 at reduced gain setting. Echograms show large, highly reflective druse located in the anterior aspect of the optic nerve head ( arrows). Vertical transverse ( top) and longitudinal ( bottom) views. disc drusen is relatively limited. A foreign body lodged at the optic nerve head could mimic optic disc drusen. The history and clinical examination should be helpful in such a case. Occasionally, a small, bright superficial echo can be seen on the surface of an elevated optic nerve head. However, in contrast to the echoes from optic disc drusen, these echoes do not persist when the gain is re­duced, and they are rarely displayed in more than one probe orientation. However, calcification of a granuloma, a vascular lesion of the optic nerve head, or a small astrocytoma ( as in tuberous scle­rosis) could mimic optic disc drusen. Calcified nodules in the middle of the optic nerve have previously been described in 3 patients ( 21). The clinical and echographic appearance in these patients led the authors to suggest that these lesions may represent phleboliths of the central retinal vein. Such lesions differ echographically from optic disc drusen because of their location in the orbital portion of the optic nerve. However, if such calcifications occurred more anteriorly at the level of the optic nerve head, they could mimic optic disc drusen. If this is true, some of the " deep drusen" in our series may not represent actual , Clin Neuro- ophthalmol, Vol. 11, No. 2, 1991 drusen. Instead, they may represent calcified thrombi or emboli within the optic disc vessels. Calcified thrombi in the central retinal vein in the region of the lamina cribrosa have been docu­mented histopathologically ( 22). The echographic appearance of such calcifications would probably appear similar to the deep drusen in this study. Indeed, since the completion of this study, we have examined 3 patients with the clinical diagno­sis of unilateral CRVO who have unilateral " deep drusen" in the eye with CRVO. Vascular calcifica­tion, however, seems a much less likely explana­tion for the deep drusen present in our 3 cases of AlaN. It seems improbable that thrombosis and calcification of the fine feeding posterior ciliary ar­tery vessels could produce calcifications large enough to be detectable echographically. In addi­tion, the 3 patients with deep drusen and AlaN were all evaluated with echography within 2 weeks of their visual events, and it is unlikely that significant calcification of a thrombus would occur so quickly. However, we could not differentiate a deep drusen from a calcified embolus. In summary, most of the drusen in our study were found to be bilateral ( 69%) and were located within the anterior portion of the optic nerve head ( 85%). Of the 6 eyes with unilateral deep drusen ( 13%), 5 had undergone a vascular occlusion in the region of the optic nerve head. Standardized echography has proven to be an effective, reliable method of evaluating eyes with suspected optic disc drusen. High resolution B- scan echography is useful for detecting drusen in both clear and opaque media. Standardized A- scan is additionally helpful to assess the retrobulbar optic nerve to rule out other concomitant conditions. REFERENCES 1. Green RL, Byrne SF. Diagnostic ophthalmic ultrasound. In: Ryan SJ, Ogden TE, eds. Retina. Vol. 1. St. Louis: c. v. Mosby, 1989: 191- 273. 2. Friedman AH, Beckerman B, Gold DH, et al. Drusen of the optic disc. Surv OphthalmoI1977; 21: 375-- 90. 3. Ossoinig KC, Cennamo G, Byrne SF. Echographic differen­tial diagnosis of optic nerve lesions. Doc Ophthalmol Proc Series 1981; 29: 327- 32. 4. Gans M, Byrne SF, Glaser JS. Standardized A- scan echog­raphy in optic nerve disease. 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