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Show J. Gin. Neuro-ophthalmol. 5:209-212, 1985 © 1985 Raven Press, New York Neuro-anatomical Feature Photo The "Phantom" Optic Nerve ARTHUR H. SHEDDEN, M.D. J. LAWTON SMITH, M.D. PATRICK S. O'CONNOR, M.D. RONALD M. BURDE, M.D. DAVID W. WHITE, M.D. Figure 1. What is your impression about the right optic nerve in the computed tomographic scan above? Look at the ner\"e. marked with a small white arrowhead, and make your diagnosis before turning the page. September 1985 209 Neuroradiological Feature Photo Figure 2. Preoperative axial computed tomographic scan made on November 20, 1984. Note large right optic nerve glioma. Figure 3. Preoperative axial computed tomographic scan made on November 20, 1984. Note enlarged right optic canal (small black arrowheads) and large optic nerve tumor (large white arrow). 210 Figure 4. Surgical specimen of excised orbital optic nerve glioma. Journal of Clinical Neuro-ophthalmology Shedden et al. Figure 5. Histologic section of the optic nerve glioma. Figure 6. Top: The "phantom" optic nerve in axial computed tomographic scan made on January 14. 1985 (1 month postoperatively). Bottom: The coronal reformatted image shows the normal small left optic nerve (outlined by small white arrowheads). A large black space with no apparent nerve is seen on the right (outlined with small black arrowheads). September 1985 211 Neuroradiological F~atur~ Photo A 4-year-old boy presented with proptosis of the right eye of 6 months' duration in November 1984. Visual acuity was 3/200 in that eye, a Marcus Gunn pupil was present, only a small upper temporal field remained, the optic disc appeared swollen and choked, and there was a large cafe-au-Iait spot on the right side of his neck. The left eye was normal. Computed tomographic scans showed typical findings of an optic nerve glioma, as seen in Figure 2. Figure 3 shows a bone window setting to demonstrate enlargement of the optic canal on the right (small black arrowheads), and the large optic nerve tumor is evident (large white arrow). On December 4, 1984, the intracranial portion of the nerve was removed by craniotomy, and on December 12, 1984, the orbital portion of the tumor was removed by a transconjunctival anterior approach. Figure 1 (on the preceding page) shows a postoperative computed tomographic scan made January 14, 1985, 1 month after the optic nerve had been completely removed. Confirmation that the optic nerve glioma had been removed is seen in Fig. 4, which shows the orbital nerve specimen, and in Fig. 5, which is a histologic section of the optic glioma. This patient was discussed at the Neuro-ophthalmology Course in Miami, Florida, in December 1984. One of us (P.S.O.) mentioned that after excising an optic nerve glioma a postoperative axial computed tomographic scan showed the presence of an apparently intact optic nerve. One might be immediately skeptical about whether the nerve had truly been 212 removed when confronted with such a picture. However, another participant (R.M.B.) immediately confirmed having had a similar experience. Therefore, we asked for postoperative computed tomography in this patient. Indeed, in Fig. 1 there truly appears to be an optic nerve on the right side. A helpful point, however, is seen in Fig. 6, which shows a coronal reformatted image made from the same study. One can see the normal optic nerve on the left side (small white arrowheads), whereas on the right side, where an optic nerve apparently is seen on the axial study, a large empty space is apparent where the optic nerve would be seen (small black arrowheads). There apparently is a condensation plane or an interface surface between the optic nerve and adjacent tissues in these cases that can cause an axial computed tomographic scan to show an optic nerve when no nerve is present. How long this "phantom" optic nerve shadow persists postoperatively remains to be determined. There has been some suggestion that the phenomenon lessens after several months. The problem is easy to resolve with history, however, and, for any question, coronal reformats will give the answer The medicolegal aspect of such a finding is of interest. If one were told that the optic nerve had been surgically removed in a patient, and yet a computed tomographic scan 1 month postoperatively showed the picture seen in Fig. 1, one could actually question whether or not the nerve had been removed. This case illustrates the fact that it is possible to see indeed, but perceive not. Journal of Clinical Neuro-ophthalmology |
