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Show Journal of Clinical Neuro- ophthalmology 10( 2): 88- 91, 1990. Intracanalicular Lipoma Nelson R. Sabates, M. D., Bradley K. Farris, M. D., and Phillip H. Stratemeier, M. D. © 1990 Raven Press, Ltd., New York We present a patient with unilateral progressive painless loss of vision leading to optic atrophy and blindness. High- resolution computed tomography and magnetic resonance imaging demonstrated adipose tissue extending from the anterior portion of an enlarged optic canal posteriorly to involve the ipsilateral optic chiasm. To our knowledge, this is the first reported case of an intracanalicular lipoma. Key Words: Visualloss- Intracanalicular lipoma- Optic canal- Optic nerve. From the Department of Ophthalmology, Dean A. McGee Eye Institute, University of Oklahoma Health Sciences Center ( N. R. S., B. K. F.), and the Department of Radiology, 51. Anthony Hospital ( P. H. S.), Oklahoma City, Oklahoma, U. S. A. Address correspondence to Dr. Nelson R. Sabates at the Department of Ophthalmology, Dean A. McGee Eye Institute, 608 Stanton L. Young Boulevard, Oklahoma City, OK, 73104, U. S. A. Address reprint requests to Dr. Bradley K. Farris at the Department of Ophthalmology, Dean A. McGee Eye Institute, r In;","'," :~"". ,', ' I, ,' lIrl-, Sciences Center, 608 Stanton L. ,', tv, () I<, 731114, USA. 88 Lipomas, one of the most common mesenchymal neoplasms, can arise in any location in which fat is normally present. Although the orbit is invested in fat, there have been few reported cases of orbital lipoma, We recently examined a patient with profound optic atrophy and blindness of one eye who was found to have adipose tissue present in an enlarged optic canal extending posteriorly to include the ipsilateral optic chiasm. This adipose tissue was consistent neuroradiologically with an intracanalicular lipoma. CASE REPORT A 63- year- old white man presented to the Dean A. McGee Eye Institute in July 1988 with a chief complaint of decreased vision in the right eye. The patient recalled that in 1970 he initially noted the onset of painless, progressive loss of vision in the right eye. By 1978, he had lost all vision in this eye. After a minor motor vehicle accident in 1983, computed tomography ( CT) of the head was obtained. The patient was told he had a " fatty" tumor around the right optic nerve. Surgery was offered but the patient refused. Past medical history and review of systems were otherwise unremarkable. Neuro- ophthalmological examination on July 8, 1988, revealed a best corrected visual acuity of no light perception right eye, and 20/ 15 left eye. Pupils were 6 mm bilaterally, with the right pupil unreactive to direct light. The left pupil was normally reactive to light. Visual fields were normal in the left eye. External examination, motility, muscle balance, and slit lamp examination were otherwise normal. Applanation tonometry readings were 15 mm Hg in each eye. Funduscopic examination of the right eye demonstrated profound optic atrophy. The left fundus was normal. Neurological examination was otherwise unremarkable. INTRACANALICULAR LIPOMA 89 FIG. 1. Computed tomographic scan of the orbit showing encapsulated low density area within the right optic canal ( arrow). High- resolution CT with contrast enhancement of the head and orbit demonstrated an encapsulated low density area within the right optic canal. This density was consistent with fat by CT measurements ( Fig. 1). " Flaring" ( widening) of the medial side of the optic canal was consistent with abnormal optic canal enlargement. Incidentally noted was a calcified internal carotid artery lying near the right optic nerve ( Fig. 2). The diameter of the optic canal was considerably larger on the right, with the anterior portion of the canal measuring 0.75 em, the middle 0.77 em, and the posterior 0.82 em. The normal left optic canal measured 0.62, 0.32, and 0.49 em in the anterior, middle, and posterior sections, respectively. Intracanalicular fat extended posteriorly, encircling the FIG. 2. Computed tomographic scan of the orbit showing " flaring" ( widening) of both the medial and lateral side of the optic canal; low density area consistent with fat in the posterior optic canal; and an enlarged, calcified internal carotid artery lying near the right optic nerve ( arrow). FIG. 3. Computed tomographic scan of the orbit showing the low density area encircling the right optic nerve as it enters the optic chiasm. Absorption coefficient measurements identified this as a fat equivalent mass. FIG. 4. Computed tomographic scan ( coronal view) demonstrating low density area consistent with fat surrounding the optic nerve on the right. The optic nerve is noted to be small in the apex consistent with optic atrophy ( arrow). I elin Neuro- ophlhalmol, Vol. 10, No. 2, 1990 90 N. R. SABATES ET AI. FIG. 5. Computed tomographic scan ( coronal view) showing the adipose tissue surrounding the optic nerve on the right as it proceeds toward the chiasm. right optic nerve as it entered the optic chiasm ( Fig. 3). Coronal views on CT confirmed the presence of intracanalicular fat surrounding the optic nerve within the optic canal ( Fig. 4) and extending posteriorly toward the chiasm ( Fig. 5). Sagittal and coronal T- l weighted magnetic resonance imaging ( MRI) was performed and confirmed an enlarged right optic canal with adipose tissue present within the canal, extending posteriorly to involve the ipsilateral optic chiasm ( Figs. 6 and 7). DISCUSSION The orbit and retrobulbar space normally contain adipose tissue. The retrobulbar fat provides a bed of support for the globe and its movement. As the fascial layers of Tenon's capsule slacken, orbital fat can sometimes herniate anteriorly and produce the appearance of a " dermolipoma" ( 1,2). Posteriorly herniated fat is an entity which has not been described To our knowledge, the presence of FIG. 6. T- 1 weighted magnetic resonance image. sagittal section, showing fat in an enlarged optic canal proceeding posteriorly to the optic chiasm. primary intracanalicular adipose tissue in an enlarged optic canal such as our case has not been heretofore reported. The optic canal is formed by the union of the two coats of the lesser wings of the sphenoid. The optic nerve enters the optic canal anteriorly through the optic foramen. The optic canal normally shows a gradual widening from its orbital and to its intracranial end. Its length usually averages around 9 mm in length, 4.8 mm in width at the orbital end, and 7.2 mm in width at the cranial end ( 3). Lipomas, which can arise in any location in which fat is normally present, have been reported in the orbit in a few detailed cases ( 4). Related in neuroradiological appearance, spindle cell lipoma of the orbit, a cellular variant of lipoma, has been reported ( 5,6). Primary liposarcoma of the orbit with an appearance of a " pseudocapsule" ( 7) as well as dermoid cysts of the orbit, a developmental choristoma, have also been reported ( 8). These cysts can be distinguished by the presence of other elements in the mass in addition to fat. INTRACANALICULAR LIPOMA 91 FIG. 7. T- 1 weighted magnetic resonance imaging, coronal section, demonstrating high intensity signal tissue surrounding the right optic nerve. Intracranial lipomas are much more common than orbital lipomas. These relatively rare congenitallesions have been extensively described in both the neurosurgical and neuroradiologicalliterature. The lesion is an incidental finding usually without clinical significance. With CT the diagnosis of intracraniallipomas is straightforward since fat has low photon attenuation. On T- l weighted MRI, lipomas demonstrate a high signal intensity similar to intraorbital fat ( 9). Intracranial lipomas are com-monly midline and have been reported in the corpus callosum ( 10,11), conus medullaris ( 10), cerebellopontine angle ( 12,13), superior medullary velum ( 9), quadrigeminal plate ( 14), and septum pellucidum ( 15). In summary, our case is not only unique due to the radiographic appearance of an intracanalicular lipoma, but also because of a markedly dilated optic canal. The presence of the adipose tissue in the optic canal presumably caused the enlargement of the canal and also the gradual compression of the optic nerve leading to profound atrophy and loss of vision. REFERENCES 1. Jordan DR, Tse DT. Herniated orbital fat. Can JOphthalmol 1987; 22: 173- 7. 2. Galamena ML, Burner WE. Acquired fat hernia of the eye and orbit. Ann Ophthalmol 1984; 16: 675- 6. 3. Miller NR. Walsh and Hoyt's clinical neuro- ophthalmology; vol. 1. 4th ed. Baltimore: Williams and Wilkins, 1987: 41-- 68. 4. Koganei Y, Ishikawa S, Abe K, Mukeno K, Shioya N. Orbital lipoma. Ann Plas Surg 1988; 20: 173- 82. 5. Bartley GB, Yeatts RP, Garrity JA, Farrow GM, Campbell RJ. Spindle cell lipoma of the orbit. Am J Ophthalmol 1985; 100: 605- 9. 6. Johnson BL, Linn JG Jr. Spindle cell lipoma of the orbit. Arch OphthalmoI1979; 97: 133- 4. 7. Jakobiec FA, Rini F, Char 0, et al. Primary liposarcoma of the orbit. Ophthalmology 1989; 96: 180-- 191. 8. Grone AS Jr. Giant dermoid cysts of the orbit. Ophthalmology 1979; 86: 1513- 20. 9. Freidman RB, Segal R, Latchaw RE. Computerized tomographic and magnetic resonance imaging of intracranial lipoma. JNeurosurg 1986; 65: 407- 10. 10. MacPherson RI, Halgate RD, Gudenan SK. Midline central nervous lipomas in children. J Lassovation Can Radiol 1987; 38: 264- 70. 11. Tahmouresie A, Keall G, Shucart W. Lipoma of the corpus callosum. Surg NeuroI1979; 11: 31- 4. 12. Pensak ML, Glasscock ME, Gulya AJ, et aI. Cerebellopontine angle lipomas. Arch Otolaryngol Head Neck Surg 1986; 112: 99- 101. 13. Steimle R, Pageant G, Jacquinet G, et al. Lipoma in the cerebellopontine angle. Surg NeuroI1985; 24: 73-- 6. 14. Halmagyi GM, Evans WA. Lipoma of the quadrigeminal plate causing progressive obstructive hydrocephalus. J Neurosurg 1978; 49: 453-- 6. 15. Wilberger JE, Abla A, Rothfus W. Lipoma of the septum pellucidum: case report. JComput Tomogr 1987; 11: 79- 82. J Clin Neuro- ophtlullmol, Vol. 10, No. 2, 1990 |
