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Show Journal of Neuro- Ophthalmology 20( 1): 25- 27, 2000. © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia Anomalous Optic Disc Elevation Associated With Ultrasonographic Evidence of Increased Subarachnoid Fluid Srinivas R. Sadda, MD, Cathy DiBernardo, RN, RDMS, ROUB, and Neil R. Miller, MD The presence of increased subarachnoid fluid around the optic nerve as measured by ultrasound has been shown to be associated with elevated intracranial pressure, as well as a number of other conditions. This finding has proved useful for distinguishing optic disc elevation secondary to papilledema from disc elevation attributable to other causes. This report describes a patient with anomalous optic disc elevation and increased subarachnoid fluid around the optic nerve. Key Words: Anomalous optic discs- Disc elevation- Intracranial pressure- Papilledema- Ultrasound. Ultrasonography is a potentially useful method for imaging the optic nerve. Acoustic impedance differences between the orbital fat and the optic nerve cause refraction of sound waves, allowing the optic nerve to be imaged in cross section. Using this technique, subarachnoid fluid can be visualized within the nerve sheath as a concentric echolucent crescent surrounding the optic nerve on B- scan ( 1). In patients with elevated intracranial pressure ( ICP), the optic nerve sheaths may dilate, and the increase in subarachnoid fluid around the optic nerve can be detected by ultrasound as an enlargement of the nerve diameter ( 2- 4). Serial measurements of normal optic nerves in patients undergoing ocular ultrasound at our institution have established that the normal range of optic nerve diameters is 2.3 to 3.3 mm ( 5); this is in agreement with other investigators ( 6- 8). Higher normal values, however, have also been reported in the literature ( 1,4,9). These higher values may reflect differences in the measurement technique. Because enlargement of the optic nerve can be caused by processes other than subarachnoid fluid ( e. g., optic nerve tumors), the presence of subarachnoid fluid is usually confirmed by performing a " 30° test." After measurement of optic nerve diameter in anterior and posterior locations in the orbit, the optic nerve diameter is Manuscript received October 7, 1999; accepted November 3, 1999. From the Wilmer Ophthalmological Institute, The Johns Hopkins Medical Institutions, Baltimore, Maryland. Address correspondence to Neil R. Miller, MD, Department of Ophthalmology, Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Maumanee B- 109, 600 North Wolfe Street, Baltimore, MD 21287. remeasured with the eye looking approximately 30° temporal to the center. Eccentric gaze is believed to cause a redistribution of fluid in the nerve sheath. A 10% decrease in optic nerve diameter by the 30° test is considered to be positive evidence for increased subarachnoid fluid and elevated ICP ( 5). A change in optic nerve diameter of less than 10% suggests an alternative cause of enlarged optic nerve diameter. Previous investigators ( 2,3) have suggested that the finding of a positive 30° test is a strong indicator for the presence of elevated ICP in patients with optic disc elevation ( suspected papilledema). Other conditions ( e. g., central retinal vein occlusion, uveal effusion syndrome) ( 10) also may produce a positive 30° test, but anomalous optic disc elevation has not been described as a potential cause. In this report, we describe a patient with anomalous optic discs, who had several positive 30° tests despite normal ICP measurements on three separate occasions. CASE REPORT A 38- year- old man with an unremarkable medical history was noted at age 19 years to have " abnormal-appearing optic discs" during a routine optometric evaluation. The patient was evaluated by an ophthalmologist at age 28 years and found to have a visual acuity of 20/ 15 OU, but visual fields disclosed an enlarged blind spot OS. The right disc was mildly elevated ( Fig. 1A), whereas the left disc was moderately elevated with the retinal vessels " draped" over the surface ( Fig. IB). Because of concerns of elevated ICP, the patient underwent a magnetic resonance imaging study that gave normal results. A lumbar puncture indicated a normal opening pressure of 150 mm Hg. The cerebrospinal fluid had normal concentrations of protein and glucose and contained no cells. The patient was followed- up at regular intervals over the next 6 years, during which he had no visual or systemic complaints and no change in visual parameters. He was evaluated by a neuroophthalmologist at age 33 years and thought to have symmetric optic disc swelling OU. Repeat magnetic resonance imaging of the brain was again normal. Ultrasonography disclosed bilateral en- 25 26 S. R. SADDA ET AL. FIG. 1. Appearance of optic discs over time. A and B: right and left discs at age 28 years; C and D: right and left discs at age 36 years. Note lack of change in appearance of optic discs during the 8- year period. • V-IK. IK < K IK largement of the optic nerves with a bilaterally positive 30° test, suggesting the presence of subarachnoid fluid around the optic nerves. Neither ultrasound nor computed tomography showed evidence of drusen. Accordingly, a second lumbar puncture was performed, which was again normal, including an opening pressure of 165 mm Hg. Subsequent examinations disclosed normal visual acuity and a similar optic nerve appearance. The patient was first evaluated in the Neuro- Ophthalmology Unit of the Wilmer Eye Institute of the Johns Hopkins Hospital at age 36 years. At that time, he had a best- corrected visual acuity of 20/ 15 OU. Near vision without correction was Jl in each eye. The patient was able to identify correctly 10 of 10 Hardy- Rand- Rittler color plates OU. The patient reported some areas of distortion in the superior and inferior portion of the Amsler grid OD, and in the inferotemporal quadrant OS. Kinetic perimetry was normal to all isopters OU. Static perimetry using a Humphrey perimeter with the 10- 2 strategy was normal OU. The 24- 2 strategy showed an enlarged blind spot OD and enlarged blind spot with a mild inferior nasal step OS ( mean deviation, - 2.48 dB). Repeat 24- 2 testing disclosed only an enlarged blind spot OS. There was no relative afferent pupillary defect. Ophthalmoscopy showed somewhat small, elevated optic discs OU with absolutely normal peripapillary nerve fiber layers ( Figs. IC and ID). The retinal vessels were not obscured but were draped over the surface of the discs OU. There were no spontaneous venous pulsations Ultrasonographic evaluation indicated enlarged optic nerves and a positive 30° test OU consistent with increased subarachnoid fluid ( Figs. 2 and 3). Results of a third lumbar puncture 1 month later were again normal, including an opening pressure of 160 mm Hg. Despite the normal ICP, the patient elected to begin acetazol-amide 500 mg by mouth twice per day. Two months after beginning therapy, follow- up results of ophthalmoscopic and ultrasonographic examinations were unchanged. Ac-etazolamide was discontinued, and subsequent clinical examinations have remained unchanged. CONCLUSION This case indicates that anomalous optic disc elevation can be associated with ultrasonographic evidence of in- FIG. 2. B- scan ultrasound of optic nerves at age 36 years. Top left and right: Transverse ( cross- sectional) sections showing the optic nerves and echolucent crescents ( arrows) of fluid within the arachnoid sheaths. Bottom left and right: Axial scans showing mild optic disc elevation and flattening of the posterior globe wall. Left, top and bottom: right eye. Right, top and bottom: left eye. J Neuro- Ophlhalmol, Vol. 20, No. 1, 2000 ULTRASOUND OF ANOMALOUS OPTIC DISCS 27 » FIG. 3. Top left and right: Standardized A-scans from the left optic nerve in primary gaze both anteriorly ( left) and posteriorly ( right), showing marked enlargement ( between arrows) of the retrobulbar optic nerve. Bottom left and right: Standardized A-scans of the left optic nerve both anteriorly ( left) and posteriorly ( right) with the patient fixating approximately 30° temporally. A 10% decrease in the measurement ( between arrows) from primary to 30° gaze indicates fluid within the sheaths. creased subarachnoid fluid around the nerve and a positive 30° degree test, despite normal ICP results (< 250 mm Hg). It is possible that the ICP in our patient was actually intermittently elevated despite apparently normal lumbar punctures; however, normal ICP on three consecutive lumbar punctures makes this unlikely. Furthermore, the appearance of the fundi in this patient was typical for anomalous elevation: the optic discs were not hyperemic, the peripapillary vasculature was not obscured, the peripapillary retinal nerve fiber layer was not distorted, and no hemorrhages or exudates were ever seen. In addition, serial fundus photographs indicated that the appearance of the optic discs did not change significantly over an 8- year period. The dilation of the optic nerve sheaths in this patient may reflect an increase in nerve sheath compliance. Previous studies have shown that there may be significant variation in the compliance of optic nerve sheaths among patients ( 9). Thus, the optic nerve sheaths in some patients may dilate at normal levels of ICP. Alternatively, the nerve sheaths in this patient simply may have been patulous, rather than dilated. Whatever the mechanism underlying the ultrasonographic findings in this patient, it is important to recognize that ultrasonographic evidence of increased subarachnoid fluid in a patient with presumed papilledema does not assure that the patient has increased ICP and thus should not be used in place of a lumbar puncture. REFERENCES 1. Ossoinig KC. Standardized echography of the optic nerve. Doc Ophthalmol Proc Ser 1993; 55: 3- 99. 2. Cennamo G, Gnagemi M, Stella L. The comparison between en-docranial pressure and optic nerve diameter: an ultrasonographic study. Doc Ophthalmol Proc Ser 1987; 48: 603- 6. 3. Gangemi M, Cennamo G, Maiuri F, et al. Echographic measurement of the optic nerve in patients with intracranial hypertension. Neurochirurgia 1987; 30: 53- 5. 4. Helmke K, Hansen HC. Fundamentals of transorbital sonographic evaluation of optic nerve sheath expansion under intracranial hypertension. I. Experimental study. Pediatr Radiol 1996; 26: 701- 5. 5. DiBernardo C. Chapter 8: Optic nerve. In: DiBernardo C, Schachat AP, Fekrat S, eds. Ophthalmic ultrasound: a diagnostic atlas, New York: Thiemes Medical Publishers, 1998: 109- 18. 6. Beatty S, Good PA, McLaughlin J, et al. Correlation between the orbital and intraocular portions of the optic nerve in glaucomatous and ocular hypertensive eyes. Eye 1998; 12: 707- 13. 7. Gerling J, Janknecht P, Hansen LL, et al. Diameter of optic nerve in idiopathic optic neuritis and in anterior ischemic optic neuropathy. Int Ophthalmol 1997; 21: 131- 5. 8. Helmke K, Hansen HC. Fundamentals of transorbital sonographic evaluation of optic nerve sheath expansion under intracranial hypertension. II. Patient study. Pediatr Radiol 1996; 26: 706- 10. 9. Hansen HC, Helmke K. Validation fo the optic nerve sheath response to changing cerebrospinal fluid pressure: ultrasound findings during intrathecal infusion tests. J Neurosurg 1997; 87: 34- 40. 10. Hupp SL, Glaser JS, Frazier- Byrne S. Optic nerve sheath decompression: review of 17 cases. Arch Ophthalmol 1987; 105: 386- 9. J Neuro- Ophthalmol, Vol. 20, No. I, 2000 |
