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David Perlmutter and Albert L. Rhoton Jr.

✓ The microsurgical anatomy of the distal anterior cerebral artery (ACA) has been defined in 50 cerebral hemispheres. The distal ACA, the portion beginning at the anterior communicating artery (ACoA), was divided into four segments (A2 through A5) according to Fischer. The distal ACA gave origin to central and cerebral branches. The central branches passed to the optic chiasm, suprachiasmatic area, and anterior forebrain below the corpus callosum. The cerebral branches were divided into cortical, subcortical, and callosal branches. The most frequent site of origin of the cortical branches was as follows: orbitofrontal and frontopolar arteries, A2; the anterior and middle internal frontal and callosomarginal arteries, A3; the paracentral artery, A4; and the superior and inferior parietal arteries, A5. The posterior internal frontal artery arose with approximately equal frequency from A3 and A4 and the callosomarginal artery. All the cortical branches arose more frequently from the pericallosal than the callosomarginal artery. Of the major cortical branches, the internal frontal and paracentral arteries arose most frequently from the callosomarginal artery. The distal ACA of one hemisphere sent branches to the contralateral hemisphere in 64% of brains. The anterior portions of the hemisphere between the 5-cm and 15-cm points on the circumferential line showed the most promise of revealing a recipient artery of sufficient size for an extracranial-intracranial artery anastomosis. The distal ACA was the principal artery supplying the corpus callosum. The recurrent artery, which arose from the A2 segment in 78% of hemispheres, sent branches into the subcortical area around the anterior limb of the internal capsule.

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Arnold A. Zeal and Albert L. Rhoton Jr.

✓ In order to define the microsurgical anatomy, 50 posterior cerebral arteries (PCA's) were examined using × 3 to × 40 magnification. The PC A was divided into four segments: Pt was the segment proximal to the posterior communicating artery (PCoA); P2 extended from the PCoA to the posterior margin of the midbrain and was subdivided into an equal anterior (P2A) and posterior (P2P) half; P3 began at the posterior midbrain, ran within the quadrigeminal cistern, and ended at the anterior limit of the calcarine fissure. The PCA had three types of branches: 1) cortical branches to the cerebrum; 2) central branches to the brain stem; and 3) ventricular branches to the choroid plexus. The largest branches reaching the lateral surface of the cerebrum were located immediately anterior to the preoccipital notch, and in most cases were branches of the posterior temporal artery. This area offers a greater than 75% chance of finding a vessel large enough to perform a microvascular anastomosis. The central branches were of two types: 1) direct perforating, and 2) circumferential. The direct perforating branches arising on P1 were the posterior thalamoperforating arteries. The “thalamogeniculate artery,” the vessel said to be occluded in the “thalamic syndrome,” was also of the direct perforating type, but it was a series of small arteries arising from P2A and P2P rather than being a single vessel. The circumferential arteries usually arose from P1 and encircled the midbrain providing branches as far posteriorly as the colliculi. The branches to the choroid plexus were the medial and lateral posterior choroidal arteries; the former usually arose from P2A and entered the roof of the third ventricle, and the latter arose as a series of arteries from P2P and passed over the pulvinar to enter the lateral ventricle.

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Wayne S. Paullus, T. Glenn Pait and Albert L. Rhoton Jr.

✓ Occlusion of the cervical portion of the internal carotid artery (ICA) has been treated by vein graft bypass from the common carotid to the supraclinoid segment. However, this procedure has the disadvantages of requiring temporary occlusion of collateral flow, the short length of ICA available for anastomosis, and the retraction required for exposure of the supraclinoid area. In an attempt to find a more suitable bypass site for grafting, the petrous portion of 50 carotid arteries was studied in cadavers. It was found that there was a 1-cm length of the horizontal segment of the petrous carotid that could be exposed in the floor of the middle fossa lateral to the trigeminal nerve. This segment was covered by dura only or a thin layer of cartilage in approximately half of the specimens. In the remainder, there was often a thin shell of bone covering the artery, which could be drilled away. The petrous portion of the carotid artery had branches in only 38% of specimens, a Vidian branch in 30%, and a periosteal branch in 8%. The carotico-tympanic artery, previously reported to be the most common branch, was not found in a single case. These branches allow the retrograde flow needed to maintain the patency of this segment following proximal occlusions. The relationship of the carotid artery to structures that might be injured in exposing the petrous portion of the artery was reviewed; these structures include the cochlea, middle ear, Eustachian tube, tensor tympani muscle, geniculate ganglion, and facial, greater petrosal, and trigeminal nerves.

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Naokatsu Saeki and Albert L. Rhoton Jr.

✓ The microvascular anatomy of the posterior part of the circle of Willis, important in surgery of pituitary tumors and basilar aneurysms, was defined in 50 cadaver brains. Significant findings were as follows: 1) Anomalies of the posterior half of the circle of Willis were found in 46% of cases. 2) Hypoplastic P-1 (posterior cerebral segment) and posterior communicating segments gave origin to the same number and size of perforating arteries, having the same termination as normal-sized segments. Thus hypoplastic segments should be handled with care and divided to aid in exposure of the basilar bifurcation only after careful consideration. 3) An average of four perforating branches arose from P-1; most from the superior and posterior surfaces. No branches arose from the anterior surface of the basilar bifurcation. The most proximal P-1 branch originated 2 to 3 mm distal to the basilar bifurcation. It was most commonly a thalamoperforating artery. The largest P-1 branch was usually a thalamoperforating or a posterior choroidal artery. 4) An average of seven branches emerged from the superior and lateral surfaces of the posterior communicating artery. The anterior half was a richer source of perforators than the posterior half. The largest communicating branch in 80% of specimens supplied the premamillary area. 5) The anterior choroidal artery originated from the carotid artery on both sides in all cases. A double anterior choroidal artery was present in 4% of cases.

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Albert L. Rhoton Jr.

✓ Microsurgical exploration of 15 adults with Arnold-Chiari malformation with and without hydromyelia using 3 to 20 × magnification has led to the following conclusions. Hydromyelia, associated with Arnold-Chiari malformation, is a progressive mechanical disorder that causes spinal cord deficits by pressure distention of the cord. Arnold-Chiari malformation causes slowly or suddenly progressive bulbar dysfunction by impaction of the malformation in the foramen magnum. Decompression of both can be achieved by a suboccipital craniectomy, upper cervical laminectomy, establishing an outlet from the fourth ventricle, and opening the distended cord in the thinnest exposed area, which is usually along the dorsal root entry zone. If Pantopaque myelography in patients in the supine position shows the Arnold-Chiari malformation, hydromyelia can be established as a cause of central cord deficit even if myelography shows the cord size to be normal. Syringomyelia, traditionally considered a degenerative disease, is a less common cause of a slowly progressive central cord deficit than either hydromyelia or intramedullary tumor.

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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.

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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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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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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%.