J. Neurosurg. / Volume 31 / September, 1969

The Arterial Supply of the Human Optic Chiasm

RICHARD BERGLAND, M.D.,* AND BRONSON S. RAY, M.D. Department of Surgery (Neurosurgery), New York Hospital-Cornell Medical Center, New York, New York

HE visual field changes that accom- pany pituitary tumors are among the T most certain localizing signs in neurol- ogy. Most textbooks of anatomy demon- strate the decussation of the medial retinal fibers in the central chiasm by descriptions of the bitemporal field defects that occur in chiasmal compression. However the distortion of the visual path- ways by pituitary tumors is seldom limited to the central chiasm; more often pressure is distributed along the inferior surfaces of the optic nerves, optic chiasm, and optic tracts (Fig. 1). The altitudinal visual field de- fects that might be anticipated from such compression are rarely found. Moreover, an- terior third ventricle tumors, which equally distort the optic pathways from above, cause patterns of visual loss that are less predict- able and less regular. 7 The central portion of the chiasm in which the decussating fibers are found appears to be especially vulnera- FIG. 1. A pathological specimen of a pituitary tumor. The tumor is several centimeters wide and ble to distortion and compression from distorts the inferior aspects of the optic nerves, below. chiasm, and optic tracts. The central chiasm is This report includes observations at au- not selectively distorted, yet "examination re- topsy of the arterial blood supply of the ex- vealed a bitemporal hemianopsia with a central tra-cerebral parts of the visual pathways. scotoma of the right eye." (Published through the courtesy of Armed Forces Institute of Pathology; The peculiar derivation of the blood supply Acc. Number 219933-14.) of the central chiasm suggests that vascular compression rather than neural compression The initial anatomical observations were contributes to the bitemporal hemianopsia so made during the course of the dissection of commonly seen in pituitary tumors. 225 autopsy specimens. These were obtained Method by removing the brain but leaving the ante- nor hypothalamus, infundibulum, optic The removal of the brain at autopsy by chiasm, and optic nerves in situ. The block traditional methods involves cutting across of bone containing the pituitary and sur- the visual pathways and inevitably destroy- rounding structures was then removed with a ing their vascular relationships. To circum- motor saw for further dissection. These dis- vent this problem, several techniques of ob- sections were performed to delineate the pat- taining and studying autopsy material were terns and frequency of the anatomical varia- employed. tions that surround the pituitary, 1 but there was ample opportunity to observe the vascu- Received for publication November 25, 1968. lar anatomy pertinent to the local visual * Markle Scholar in Academic Medicine. structures. 327 328 Richard Bergland and Bronson S. Ray In 50 additional autopsies the chiasm and jected specimens, those vessels above the optic nerves were left attached to the brain optic pathways were partially or totally dis- which was removed in the traditional man- rupted by the oblique section through the ner by sectioning the optic nerves at the chiasm. In the fixed specimens, the vessels optic foramina and dividing the pituitary in- below the visual pathways were disrupted fundibulum at the level of the diaphragm. despite the care during removal. The totality Care was taken to preserve the chiasmal of the blood supply to these structures could arachnoid and small vessels surrounding the be appreciated only by combining the obser- visual pathways. Following fixation in for- vations from the various specimens. malin the chiasmal arachnoid was removed Fresh Autopsy Specimens. These speci- and the small arteries surrounding the visual mens included the posterior portion of the pathways demonstrated by dissections. circle of Willis; the small vessels extending In 200 additional autopsy specimens, the from the circle of Willis to the visual path- brain was removed leaving the anterior hy- ways were usually preserved allowing dissec- pothalamus, infundibulum, optic chiasm, and tion and descriptions of the inferior group of optic nerves in situ. The bony blocks were arteries. Most if not all of these arteries removed with a motor saw and fixed in for- coursed toward the median eminence and in- malin. Then the pituitary gland and attached fundibulum and are properly designated su- infundibulum, hypothalamus, and chiasm perior hypophyseal arteries. Between four were dissected free from the surrounding and eight small vessels may be found on ei- structures and embedded en bloc in paraffin. ther side; rarely were these symmetrical in Either sagittal or coronal sections of this their number, size, or course. Numerous material were cut to include these several anastomoses were found in this arterial com- structures and appropriately stained. Only plex, and many small branches were seen to the microscopic observations pertinent to the penetrate the inferior surfaces of the optic vascular supply of the visual structures are nerves, chiasm, and optic tracts. included in this report. Fixed Specimens. The fixed brains in- In five additional blocks of bone, the ca- cluded the optic nerves and pituitary infun- rotid arteries were injected after removal dibulum in continuity with the rest of the with red silastic (Microfil) to demonstrate brain. Despite careful removal, the inferior more clearly the arteries surrounding the group of vessels was often disrupted, but chiasm. those vessels above the visual pathways were invariably preserved and could be studied in Results detail. Moreover, these fixed specimens in- The optic nerves, chiasm, and optic tracts cluded the third ventricle and lamina termi- pass through the circle of Willis, coursing nalis, structures which bear important rela- below the anterior cerebral arteries and ante- tionships to the superior group of vessels. rior communicating artery and above the Superior Arteries. The superior group of posterior cerebral arteries, basilar artery, arteries consisted of several small vessels and posterior communicating arteries (Fig. that were derived from the two anterior ce- 2). This allows a natural separation of the rebral arteries as they pass above the optic chiasmal blood supply into a superior and an pathways. Between one and four small ves- inferior group of arteries. The superior group sels arose from either anterior cerebral, more of vessels is derived from the two anterior often than not the number was symmetrical. cerebral arteries and, occasionally, from the These vessels extended to the upper surfaces anterior communicating artery above the op- of the optic nerves and optic tracts but only tic pathways. The inferior group is derived to the lateral portions of the chiasm (Figs. from the basilar, the posterior communicat- 3-5). Occasionally a single small artery ing, the posterior cerebral, and the internal arose from the anterior communicating, but carotid arteries. in most instances this artery was not present Invariably during removal of the speci- and it was always of much smaller diameter mens the vascular relationships were par- than the vessels in the lateral groups. tially disrupted. In the fresh specimens, the The lamina terminalis, covering the su- specimens for microscopic study, and the in- pra-chiasmal extension of the third ventricle,