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Albert L. Rhoton Jr., Jack L. Pulec, George M. Hall and Allen S. Boyd Jr.

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Albert L. Rhoton Jr., Shigeaki Kobayashi and W. Henry Hollinshead

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Kristin Gudmundsson, Albert L. Rhoton Jr. and Joseph G. Rushton

✓ Fifty trigeminal nerves were studied at autopsy under various magnifications. Two findings that could explain the preservation of sensation after rhizotomy of the main sensory root are: 1) anastomosis between the motor and sensory root in the majority of nerves, and 2) aberrant sensory rootlets that arose from the pons separately from the main sensory root in one half of the nerves. The motor root is composed of as many as 14 separately originating rootlets that usually join about 1 cm from the pons. At the pontine level, the first division fibers are usually dorsomedial and the third division fibers caudolateral within the main sensory root. However, the third division fibers may vary from being almost directly lateral to directly caudal to the first division fibers. This may explain the variability of sensory loss with partial section in the posterior fossa.

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Subdivision of the trigeminal sensory root

Experimental study in the monkey

W. Frank Emmons and Albert L. Rhoton Jr.

✓ In 16 rhesus monkeys, rhizotomy of the whole trigeminal nerve and selective rhizotomy of each division were carried out, and neural degeneration techniques used, to determine whether a trigeminal root component exists which projects only to the main sensory or spinal nucleus of the trigeminal nerve. Such a root component was not found. Section of the rostral trigeminal fibers resulted in degeneration in both the main sensory nucleus and the spinal trigeminal nucleus. Section of the caudal fibers of the root produced degeneration similar to third division transection, indicating that the caudal fibers are from that division. The first- and third-division fibers were found to project to the ventral and dorsal portions of the main sensory nucleus and spinal nucleus. Findings showed that the most rostral portion of the root immediately adjacent to the motor root is predominately from the ophthalmic division. Some proprioception from the trigeminal area appears to be mediated through the medial cuneate nucleus because all the trigeminal divisions send some fibers to this nucleus.

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Albert L. Rhoton Jr. and Manuel R. Gomez

✓ A patient with postinflammatory hydrocephalus had a multiloculated, lateral ventricular system that was treated by a routine shunting procedure after the multiloculated system had been converted into a uniloculated system by direct intraventricular surgery.

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Albert L. Rhoton Jr. and Robert Buza

✓ The authors conducted an autopsy study of 50 jugular foramina and surrounding tissue, using the dissecting microscope. Anatomical findings from this study are presented.

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Wade H. Renn and Albert L. Rhoton Jr.

✓ Fifty adult sellae and surrounding structures were examined under magnification with special attention given to anatomical variants important to the transfrontal and transsphenoidal surgical approaches. The discovered variants considered disadvantageous to the transsphenoidal approach were as follows: 1) large anterior intercavernous sinuses extending anterior to the gland just posterior to the anterior sellar wall in 10%; 2) a thin diaphragm in 62%, or a diaphragm with a large opening in 56%; 3) carotid arteries exposed in the sphenoid sinus with no bone over them in 4%; 4) carotid arteries that approach within 4 mm of midline within the sella in 10%; 5) optic canals with bone defects exposing the optic nerves in the sphenoid sinus in 4%; 6) a thick sellar floor in 18%; 7) sphenoid sinuses with no major septum in 28% or a sinus with the major septum well off midline in 47%; and 8) a presellar type of sphenoid sinus with no obvious bulge of the sellar floor into the sphenoid sinus in 20%.

Variants considered disadvantageous to the transfrontal approach were found as follows: 1) a prefixed chiasm in 10% and a normal chiasm with 2 mm or less between the chiasm and tuberculum sellae in 14%; 2) an acute angle between the optic nerves as they entered the chiasm in 25%; 3) a prominent tuberculum sella protruding above a line connecting the optic nerves as they entered the optic canals in 44%; and 4) carotid arteries approaching within 4 mm of midline within or above the sella turcica in 12%.

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Thomas J. Reagan, Harry F. Bisel, Donald S. Childs Jr., Donald D. Layton, Albert L. Rhoton Jr. and William F. Taylor

✓ The authors report 63 patients with biopsy-proved malignant (Grades 3 and 4) astrocytomas who were randomly placed in one of three treatment schedules within 2 weeks of surgery. One group (22 patients) received radiation therapy alone; the second group (22 patients) received 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) orally at intervals of 8 weeks; and the third group (19 patients) received combined radiation and drug therapy. Patients who received radiation therapy, with or without the drug, had a significantly longer survival than did those who received the drug alone. There was no difference in survival between the two groups who received radiation. The nitrosourea derivative CCNU does not seem to be an effective agent in the therapy of primary malignant brain tumors.

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Anatomy of the cavernous sinus

A microsurgical study

Frank S. Harris and Albert L. Rhoton Jr.

✓ Fifty cavernous sinuses from cadavers were studied in detail using magnification, with special attention to the relationships important in surgical approaches on the intracavernous structures, and to understanding arterial contributions to arteriovenous fistulas involving the cavernous sinus. Significant findings were: 1) The three main branches of the intracavernous portion of the carotid artery were the meningohypophyseal artery, present in 100% of the specimens, the artery of the inferior cavernous sinus (84%), and McConnell's capsular arteries (28%). In addition, the ophthalmic and dorsal meningeal arteries arose from the carotid artery within the cavernous sinus in 8% and 6%, respectively. The three main branches of the meningohypophyseal trunk were the tentorial artery, present in 100%, the dorsal meningeal (90%), and the inferior hypophyseal (80%). 2) The carotid artery was separated from the trigeminal nerve just proximal to the sinus by only dura in 84% of the specimens, and the artery was exposed in the floor of the middle fossa lateral to the trigeminal nerve in 38%. 3) The intracavernous portion of the carotid artery indented the lateral side of the pituitary gland in 28% of dissections but could be as far as 7 mm from it. 4) A triangular area, described by Parkinson, through which the intracavernous portion of the carotid artery could be exposed surgically was found in all specimens. 5) The sixth cranial nerve may split into as many as five rootlets as it passes lateral to the intracavernous portion of the carotid artery. 6) The three major venous spaces within the sinus were posterosuperior, anteroinferior, and medial to the intracavernous portion of the carotid artery.

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David Perlmutter and Albert L. Rhoton Jr.

✓ The microvascular relationships important to surgery of aneurysms in the anterior communicating region were defined in 50 cadaver brains. The recurrent artery of Heubner was frequently exposed before the A-1 segment in defining the neck on anterior cerebral aneurysms because it commonly courses anterior to A-1. It arose from the A-2 segment of the anterior cerebral artery (ACA) in 78% and most commonly terminated in the area of the anterior perforated substance, and lateral to it in the Sylvian fissure. The anterior communicating artery (ACoA) frequently gave rise to perforating arteries which terminated in the superior surface of the optic chiasm and above the chiasm in the anterior hypothalamus. This finding contrasts with previous reports that no perforating branches arise from the communicating artery. The proximal half of the A-1 segment was a richer source of perforating arteries than the distal half. The A-1 branches most commonly terminated in the anterior perforated substance, the optic chiasm, and the region of the optic tract. The ACoA increased in size as the difference in the diameter between the right and left A-1 segments increased. Frequent variants such as double or triple ACoA's, triple A-2 segments, and duplication of the A-1 segments were encountered. The clinical consequences of occlusion of the recurrent artery and of the perforators from the ACoA and medial and lateral segment of A-1 are reviewed.