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In a period of 10 years fifteen patients bearing sixteen aneurysms arising at the posterior cerebral artery were operated at our institution. Based on the approaches selected for each location a division of the posterior cerebral artery into three surgical segments is proposed. The first segment (S1), or anterior extends from the basilar artery bifurcation to the point where the artery reaches the level of the most lateral edge of the cerebral peduncle, the second segment (S2), or middle extends from the posterior limit of S1 to a point located just before the most medial extent of the artery in the quadrigeminal cistern (collicular point), and the third segment (S3), or posterior corresponds to the collicular point and to the portions of the posterior cerebral artery distal to it. Utilizing the concept of surgical segments all aneurysms in our series were satisfactorily exposed. Those arising at the S1 segment (8 cases) were operated either through a pterional or a pretemporal approaches; those from the S2 segment (6 cases) were operated either via the subtemporal or the subtemporal transventricular routes; and that arising from the S3 segment (1 case) was managed through the occipital interhemispheric approach. Among the aneurysms eleven were small, one was large, and four were large or giant. Ten of these aneurysms were surgically clipped, two coagulated, three treated by trapping and in one case the aneurysm was resected and the posterior cerebral artery was reconstructed by a termino-terminal anastomosis. The surgical results were considered good in all cases but one, where the patient died due to clinical complications three months after surgery. It is our belief that the use of this classification can provide the means to best select the most appropriate surgical approach to treat aneurysms arising at the posterior cerebral artery.

Objective: We present our microsurgical lateral orbital approach for intraorbital lesions, with special emphasis on the microanatomy of the orbit., Methods: Among 26 patients, such lesions included tumors of the lacrimal glands, cavernous angioma, meningioma, neuroma, and other tumors. These intraorbital lesions were removed through a 35- to 40-mm lateral skin incision, and this was followed by lateral orbitotomy featuring a microsurgical dissecting technique. If it was necessary to gain access to the deep lateral portion of the muscle cone, the lateral orbitotomy was extended to the anterior temporal dura. There are two microsurgical routes into the muscle cone, one above and the other below the lateral rectus muscle. The structures encountered along these two routes were demonstrated in an anatomic study of the orbit in cadavers., Results: Lesions located in the lateral compartment of the orbit could be exposed through lateral orbitotomy and were completely removed in most cases. Complications in our series of 26 patients included one case of postoperative visual impairment, one case of tonic pupil, and three cases of transient impairment of eye movement., Conclusion: We think that, with an intimate understanding of the anatomy of the orbit, intraorbital lesions located in the lateral compartment of the orbit, and even those in the lateral apex, can be safely removed through lateral orbitotomy.

Microsurgery of multiple aneurysms is still a controversial subject. In order to avoid the risk of rebleeding and the consequent increase in morbidity in such cases all aneurysms or at least as many aneurysms as possible should be treated in the first operative procedure. To reach that goal aneurysms located on the contralateral side should also be considered for clipping during the first operation. Between 1984 and 1994 a series of 51 patients harboring multiple aneurysms of which 55 aneurysms were located on the contralateral side of the craniotomy were operated at our institution. No mortality or morbidity could be directly ascribed to the aneurysm that was clipped contralaterally. Based on that series we have described the anatomical features, technical aspects and surgical difficulties of approaching bilateral aneurysms through the same craniotomy.

The significant factors in the development of the neurosurgery program at the University of Florida have been the funding for 10 endowed chairs and a Brain Institute, the achievement of departmental status in the College of Medicine, the collaborative research with a strong Department of Neuroscience, and the strong commitment by the faculty to subspecialty neurosurgery and to service in the national neurosurgical organizations.

The microsurgical anatomy of the superior orbital fissure was examined in cadaver specimens. The cavernous sinus fills the posterior margin and the orbital contents fill the anterior margin of the fissure. All of the nerves coursing in the walls of the cavernous sinus pass through the superior orbital fissure to reach the orbit. The fissure has a narrow lateral part and a larger medial part. The annular tendon from which the rectus muscles arise is situated in front of the upper half of the medial part of the fissure and is attached to the lateral margin near the junction of the lateral and medial parts. The fissure is divided into three sectors: lateral, central, and inferior. The lateral sector, which corresponds to the narrow lateral part, transmits the trochlear, frontal, and lacrimal nerves and the superior ophthalmic vein, all of which course outside the annular tendon. The central sector, which is situated behind and is aligned with the lateral part of the annular tendon, transmits the superior and inferior divisions of the oculomotor nerve, the abducens and nasociliary nerves, and the sensory and sympathetic roots of the ciliary ganglion, all of which pass through the annular tendon. The inferior sector, which is located below the annular tendon and origin of the inferior rectus muscle, is filled with a posterior extension of the orbital fat and transmits the inferior ophthalmic vein. The relationship and course of the nerves in each sector and the incisions that may be used to open and expose the contents of the fissure are reviewed.

An anatomical study of three microsurgical intraorbital routes to the optic nerve and orbital apex, which can be reached through a fronto-orbital craniotomy, was conducted on cadaver specimens. The structures that could be exposed via the medial, central, or lateral approaches directed through the orbital roof were defined. The medial approach, directed through the space between the superior oblique and the levator muscles, provides good access to all parts of the intraorbital optic nerve. The central approach, between the levator and the superior rectus muscles, provides the shortest route to the optic nerve. Two variants of the central approach were examined. In the first, the levator muscle and frontal nerve are retracted medially and the superior rectus muscle laterally. This variant provides access to only the midportion of the intraorbital segment of the optic nerve. In the second variant, the frontal nerve is retracted laterally together with the superior rectus muscle. This variant provides access to the posterior two-thirds of the intraorbital portion of the optic nerve. The lateral approach is directed between the levator and lateral rectus muscles. This approach also has two variants, depending on whether the superior ophthalmic vein is retracted medially or laterally. The variant in which the superior ophthalmic vein is retracted medially with the levator and superior rectus muscles provides access to the lateral side of the optic nerve except in the region adjacent to the superior orbital fissure. The variant in which the superior ophthalmic vein is retracted laterally together with the lateral rectus muscle provides excellent access to the optic nerve in the region of the superior orbital fissure. It is an ideal approach for lesions that involve both the cavernous sinus and orbit.

The most commonly occurring meningiomas in the posterior cranial fossa are located along the posterior surface of the temporal bone in the region of the cerebellopontine angle. Topics discussed in this article include clinical features, radiologic findings, surgical techniques, postoperative care, alternative treatments, and meningiomas of the foramen magnum. The author underscores the need for early diagnosis of these lesions so that surgical intervention can result in optimal chances for recovery.

The microsurgical anatomy that provides the basis for dealing with lesions arising in the petroclival region was reviewed in 15 adult cadaver heads and 25 dry skulls. The eight surgical approaches studied were the retrosigmoid, extreme lateral transcondylar, translabyrinthine, transcochlear, combined supra and infratentorial presigmoid, subtemporal anterior transpetrosal, subtemporal preauricular infratemporal, and the postauricular transtemporal approach. Considerations important in the selection of these approaches are discussed. Special attention was directed to the course of the facial nerve and internal carotid artery in the temporal bone and the major venous pathways draining the region.

The complex functional and anatomic relationships between the structures in and around the temporal lobe are central to the problem of intractable partial complex seizures. Resecting those areas that are responsible for seizures and protecting those that are essential for the normal functioning of the patient are the fundamental tasks of the epilepsy surgeon. A thorough understanding of the structural and functional anatomy of this region is essential to achieve these goals.

Because acoustic neuromas most frequently arise in the posteriorly placed vestibular nerves, they usually displace the facial and cochlear nerves anteriorly (Figs. 11, 12, and 13). The facial nerve is stretched around the anterior half of the tumor capsule. Variability in the direction of growth of the tumor arising from the vestibular nerves may result in the facial nerve being displaced, not only directly anteriorly, but also anterior-superiorly or anterior-inferiorly. The nerve is infrequently found on the posterior surface of the tumor. Because the facial nerve always enters the facial canal at the anterior-superior quadrant of the lateral margin of the meatus, it is usually easiest to locate it here, rather than at a more medial location where the degree of displacement of the nerve is more variable. The cochlear nerve also lies anterior to the vestibular nerve and is most frequently stretched around the anterior half of the tumor. The strokes of the fine dissecting instruments used in removing the tumor should be directed along the vestibulocochlear nerve from medial to lateral rather than from lateral to medial because traction medially may tear the tiny filaments of the cochlear nerve at the site where these filaments penetrate the lateral end of the meatus to enter the cochlea. The landmarks that are helpful in identifying the facial and vestibulocochlear nerves at the brain stem on the medial side of the tumor have been reviewed. These nerves, although distorted by tumor, can usually be identified on the brain stem side of the tumor at the lateral end of the pontomedullary sulcus, just rostral to the glossopharyngeal nerve and just anterior-superior to the foramen of Luschka, flocculus, and choroid plexus protruding from the foramen of Luschka. After the facial and vestibulocochlear nerves are identified on the medial and lateral sides of the tumor, the final remnants of the tumor are separated from the intervening segment of the nerves. In the three approaches to the meatus and cerebellopontine angle--retrosigmoid, translabyrinthine, and middle fossa--a communication may be established between the subarachnoid space and the mastoid air cells that requires careful closure to prevent a cerebrospinal fluid leak.

The microsurgical anatomy of the cerebellopontine cistern around the porus acusticus was studied under the surgical microscope, using the heads of 20 cadavers. The relationships among the porus acusticus, facial and acoustic nerves, and neighboring arteries were noted carefully. The arteries were the meatal loop of the cerebellar artery, the internal auditory artery (I.A.A.), the subarcuate artery (S.A.), and the perforating artery (P. A.). The cerebellar arteries made the meatal loop and the arterial-nerve complex while they passed in front of the porus acusticus. Most of the cerebellar arteries were the main or rostral trunk of the AICA. The I.A.A. supplying the facial and acoustic nerves usually originated from the meatal segment of the cerebellar artery and ran into the anterior part of the porus acusticus to enter the internal auditory canal. The S. A. penetrating the subarcuate fossa made a common trunk with I. A. A. or branched from the cerebellosubarcuate artery. One recurrent P. A., a special type of the P. A., was usually present on each side. Since the artery ran between the nerve bundles of the facial and acoustic nerves, it could not be seen through the lateral suboccipital approach.

A 69-year-old white woman presented with a left hemiparesis which progressed to quadriparesis and encephalopathy. Computerized tomography and magnetic resonance imaging revealed a Chiari I malformation and a hydromyelic cavity extending from C-2 to T-6. Rostrally, the cavity extended through the ventral medulla, pons, and right cerebral peduncle into the right cerebral hemisphere, where the cavity enlarged and was associated with mass effect. The patient has made a dramatic neurological recovery following suboccipital craniectomy with insertion of a dural graft to decompress the Chiari malformation and upper cervical laminectomy and dorsal root entry zone myelotomy to decompress the hydromyelia.

Recent literature has suggested that late recurrence of pituitary adenoma after radiotherapy is common. We hypothesized that late failures might be a result of inadequate dose (less than 4500 cGy). To investigate, we analyzed 105 patients treated at our institution between 1965 and 1986 (analysis, 2/89). The minimum observation time was greater than or equal to 5 years in 58% and greater than or equal to 10 years in 30% of the patients. All patients received megavoltage radiotherapy (range, 4200-5500 cGy; mean, 4821 cGy) at a mean dose per fraction of 172 cGy; 100 patients received greater than or equal to 4500 cGy tumor dose. Twenty-nine patients received radiotherapy alone, and 76 had postoperative radiotherapy after frontal craniotomy (20 patients) or transsphenoidal hypophysectomy (56 patients). At presentation, 71% of patients had extrasellar disease, 57% had visual field deficits, and 50% had endocrinopathy. Of patients treated postoperatively, 74% had gross residual disease. Four local failures occurred at 13, 16, 57, and 64 months after postoperative radiotherapy, all within the irradiated volume (tumor doses of 4700, 4715, 5000, and 5100 cGy). All four patients had presented with moderate to extensive extrasellar disease with visual field defects. Two of the four remain free of second recurrence at 7 and 13 years after salvage transsphenoidal hypophysectomy. The local control rate with radiotherapy (product-limit method) at 10 years was 100% in the radiotherapy-alone group and 92% in the postoperative radiotherapy group (95% for all patients). To prevent bias, seven patients who received bromocriptine, none of whom demonstrated a recurrence, were censored from the local control analysis at the initiation of the drug. No patient in this study suffered recurrence greater than 64 months after radiotherapy, with 31 patients (none with bromocriptine) observed 10 to 21 years. We conclude that treatment of pituitary adenoma with greater than or equal to 4500 cGy in 25 fractions can result in a high (greater than or equal to 90%) probability of stable long-term control.

Optic neuropathy induced by radiation is an infrequent cause of delayed visual loss that may at times be difficult to differentiate from compression of the visual pathways by recurrent neoplasm. The authors describe six patients with this disorder who experienced loss of vision 6 to 36 months after neurological surgery and radiation therapy. Of the six patients in the series, two had a pituitary adenoma and one each had a metastatic melanoma, multiple myeloma, craniopharyngioma, and lymphoepithelioma. Visual acuity in the affected eyes ranged from 20/25 to no light perception. Magnetic resonance (MR) imaging showed sellar and parasellar recurrence of both pituitary adenomas, but the intrinsic lesions of the optic nerves and optic chiasm induced by radiation were enhanced after gadolinium-diethylenetriaminepenta-acetic acid (DTPA) administration and were clearly distinguishable from the suprasellar compression of tumor. Repeated MR imaging showed spontaneous resolution of gadolinium-DTPA enhancement of the optic nerve in a patient who was initially suspected of harboring recurrence of a metastatic malignant melanoma as the cause of visual loss. The authors found the presumptive diagnosis of radiation-induced optic neuropathy facilitated by MR imaging with gadolinium-DTPA. This neuro-imaging procedure may help avert exploratory surgery in some patients with recurrent neoplasm in whom the etiology of visual loss is uncertain.

The decade of the 1990's has provided neurosurgery with multiple challenges and opportunities. Numerous developments hold a promise for making the 1990's the most rewarding decade of the 20th century for neurosurgery. The "Decade of the Brain" resolution, adopted by the United States House and Senate and signed into law by President Bush in 1989, has provided the specialty with staggering opportunities. Neurosurgery and the basic and clinical neurosciences would be strengthened by the development of a major new philanthropic organization called the "American Brain Association" that would carry the activities of the Decade of the Brain into the 21st century. Major efforts are being made to improve organized neurosurgery's responsiveness to member needs. These include the strategic planning project undertaken by the Board of Directors of the American Association of Neurological Surgeons (AANS) and efforts to strengthen the Joint Council of State Neurosurgical Societies. The AANS has been extremely active in representing the specialty in legislative matters in Washington and in multiple other forums. This Association has joined The American Board of Neurological Surgery and the Residency Review Committee in responding to orthopedic surgery's proposal for spine fellowships. It is proposed that the logo of the state, regional, and national neurosurgical societies be changed to depict our involvement in spinal surgery (as well as brain surgery) because spinal surgery represents more than half of the total effort of this specialty. The standards of worth and value that provide the driving force behind our work emphasize the need to grow in compassion as manifested by our kindness, sincerity, and concern as we grow in professional competence as reflected by our training, knowledge, and skill.

The surgical approaches to the cavernous sinus were examined in 50 adult cadaveric cavernous sinuses using magnification of X3 to X40. The following approaches were examined: 1) the superior intradural approach directed through a frontotemporal craniotomy and the roof of the cavernous sinus; 2) the superior intradural approach combined with an extradural approach for removing the anterior clinoid process and unroofing the optic canal and orbit; 3) the superomedial approach directed through a supraorbital craniotomy and subfrontal exposure to the wall of the sinus adjacent to the pituitary gland; 4) the lateral intradural approach directed below the temporal lobe to the lateral wall of the sinus; 5) the lateral extradural approach for exposure of the internal carotid artery in the floor of the middle cranial fossa proximal to the sinus; 6) the combined lateral and inferolateral approach, in which the infratemporal fossa was opened and the full course of the petrous carotid artery and the lateral wall of the sinus were exposed and; 7) the inferomedial approach, in which the medial wall of the sinus was exposed by the transnasal-transsphenoidal route. It was clear that a single approach was not capable of providing access to all parts of the sinus. The intracavernous structures best exposed by each route are reviewed. The osseous relationships in the region were examined in dry skulls. Anatomic variants important in exposing the cavernous sinus are reviewed.

The microsurgical anatomy of the supraclinoid portion of the internal carotid artery (ICA) was studied in 50 adult cadaver cerebral hemispheres using X 3 to X 40 magnification. The ICA was divided into four parts: the C1 or cervical portion; the C2 or petrous portion; the C3 or cavernous portion; and the C4 or supraclinoid portion. The C4 portion was divided into three segments based on the origin of its major branches: the ophthalmic segment extended from the origin of the ophthalmic artery to the origin of the posterior communicating artery (PCoA); the communicating segment extended from the origin of the PCoA to the origin of the anterior choroidal artery (AChA); and the choroidal segment extended from the origin of the AChA to the bifurcation of the carotid artery. Each segment gave off a series of perforating branches with a relatively constant site of termination. The perforating branches arising from the ophthalmic segment passed to the optic nerve and chiasm, infundibulum, and the floor of the third ventricle. The perforating branches arising from the communicating segment passed to the optic tract and the floor of the third ventricle. The perforating branches arises from the choroidal segment passed upward and entered the brain through the anterior perforated substance. The anatomy of the ophthalmic, posterior communicating, anterior choroidal, and superior hypophyseal branches of the C4 portion was also examined.

The microsurgical anatomy of the tentorial incisura was evaluated in 25 adult cadavers using X 3 to X 40 magnification. The area surrounding the incisura is divided into the anterior, middle, and posterior incisural spaces. The anterior incisural space is located anterior to the brain stem and extends upward around the optic chiasm to the subcallosal area; the middle incisural space is located lateral to the brain stem and is intimately related to the hippocampal formation in the medial part of the temporal lobe; and the posterior incisural space is located posterior to the midbrain and corresponds to the region of the pineal gland and vein of Galen. The neural, cisternal, ventricular, and vascular relationships of each space were examined. The arterial relationships in the anterior incisural space and the venous relationships in the posterior incisural space are extremely complex, since the anterior incisural space contains all the components of the circle of Willis and the bifurcation of the internal carotid and basilar arteries, and the posterior incisural space contains the convergence of the internal cerebral and basal veins and many of their tributaries on the vein of Galen. The discussion reviews tentorial herniation and operative approaches to the incisura.

The topographic and internal anatomy of the sphenoid bone is reviewed with an emphasis on the relationships important to the transcranial and subcranial surgical approaches to the sphenoid sinus, sella turcica and cavernous sinus. A stepwise method of study and dissection is outlined. The equipment and materials needed for sphenoid bone dissection in the laboratory are reviewed.

Thirteen cases of cervical carotid dissecting aneurysm have been seen at the University of Florida during the past 3 years. In our experience, two groups of patients with this disease can be distinguished clearly by either clinical or angiographic criteria. One group of cervical carotid dissecting aneurysms is characterized by spontaneous onset, unilaterality, and the absence of pseudoaneurysm formation. These lesions have a strong tendency to resolve with appropriate medical therapy. The other group is characterized by an association with obvious predisposing factors, such as fibromuscular dysplasia, angiography, or trauma. These lesions are often associated with pseudoaneurysms and rarely resolve spontaneously. These two groups of lesions probably represent a spectrum of the same basic disease process. The natural history of patients who survive a cervical carotid dissection is usually one of stability or improvement. A trial of medical therapy (to prevent embolic symptoms) and repeat arteriography are indicated before the consideration of surgical therapy.

The relationship of the anterior inferior cerebellar artery (AICA) to the facial (7th) and vestibulocochlear (8th) nerves was studied using 3x to 20x magnification in 50 cerebellopontine angles (CPAs) from 25 adult cadavers. The AICA originated from the basilar artery as a single (72% of the CPAs), duplicate (26%), or triplicate (2%) artery. Each of the 50 CPAs had one or more arterial trunks that coursed in close proximity to the 7th and 8th cranial nerves and thus were said to be nerve-related. The nerve-related arterial trunks were divided into three segments based on their relationship to the nerves and meatus: the premeatal, meatal, and postmeatal segments. The meatal segment projected to the meatus or into the canal in 64% of the CPAs. In relation to the nerves, the premeatal segment was most commonly anteroinferior, the meatal segment was inferior, and the postmeatal segment was posteroinferior. The nerve-related branches of the AICA gave rise to internal auditory arteries in 100% of the 50 CPAs, recurrent perforating arteries in 82%, and the subarcuate artery in 72%. The internal auditory and recurrent perforating arteries arose most commonly from the premeatal segment, and the subarcuate artery arose most commonly from the postmeatal segment. There were one to four internal auditory arteries per CPA, zero to three recurrent perforating arteries, and zero or one subarcuate artery. The effects of occlusion of the nerve-related arteries and their involvement in conditions treated by neurosurgeons are reviewed.

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 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.

There is a consistent set of relationships on the brainstem surface facing an acoustic neuroma that provides the basis for identifying the displaced facial nerve on the medial side of the tumor. This review of the microsurgical anatomy of the brainstem surface facing an acoustic neuroma is based on the examination of the side of the brainstem during 42 operations for the removal of acoustic neuroma, and on the study of 50 cadaveric brains in the microsurgery laboratory. In the operative series, which included many large tumors, the facial nerve was preserved at operation in over 90% of the 42 patients. There was no mortality, and no need for cerebellar resection to remove the tumor in any patient.

Primary leptomeningeal gliomas are rare. Historically, they have been found in the spinal canal more frequently; however, in the recent literature nearly all have been found within the cranium. In the only cadaveric study of leptomeningeal glial nests, the most frequent site was the medulla and pons. Until now, no leptomeningeal glioma has been found at this site. We report what we believe to be the first such case mimicking an acoustic neuroma.

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The superior cerebellar artery (SCA) was present in each of the 50 hemispheres. Forty-three SCAs arose as a single trunk, and 7 arose as duplicate trunks. One solitary trunk and the rostral trunk of one duplicate vessel arose from the posterior cerebral artery. The remainder arose from the basilar artery. The SCA was divided into four segments: the anterior pontomesencephalic segment lay below the oculomotor nerve; the lateral pontomesencephalic segment course; below the trochlear and above the trigeminal nerve; the cerebellomesencephalic segment coursed in the groove between the cerebellum and the upper brain stem; and the cortical segment was distributed to the cerebellar surface. The SCAs arising as a single trunk bifurcated into a rostral and a caudal trunk, corresponding to the runks formed by a duplicate origin. The rostral trunk supplied the medial and the caudal trunk supplied the lateral parts of the cerebellar cortex. The SCA gave off perforating, precerebellar, and cortical arteries. The perforating arteries penetrated the interpeduncular fossa, the cerebral peduncles, the junctions of the superior and middle cerebellar peduncles, and the colliculi. The precerebellar branches arose within the cerebellomesencephalic groove and supplied the adjoining parts of the cerebellum and brain stem. The cortical branches were divided into vermian, hemispheric, and marginal arteries. The 50 SACs had points of contact with 32 oculomotor, 46 trochlear, and 26 trigeminal nerves. (Neurosurgery, 6: 10--28, 1980)

Operations on the 4th ventricle offer the potential for injury of the brain stem, cerebellum, cranial nerves, and major cerebellar arteries and veins. Twenty-five cadaver brains were examined using 3x to 25x magnification to define the relationship of these vital structures to the 4th ventricle. The 4th ventricle has a roof, a floor, and two lateral recesses. Most of the cranial nerves arise near the floor, which sits on the pons and medulla. The superior half of the roof, formed by the superior medullary velum, lingula, and cerebellar peduncles, is intimately related to the cerebellomesencephalic fissure, the superior cerebellar arteries, and the vein of the cerebellomesencephalic fissure. The inferior half of the roof, formed by the inferior medullary velum, tela choroidea, nodule, and uvula, is intimately related to the cerebellomedullary fissure, the posterior inferior cerebellar arteries, and the veins of the cerebellomedullary fissure. The lateral recesses and adjoining parts of the roof and floor are intimately related to the cerebellopontine fissures, the anterior inferior cerebellar arteries, and the veins of the cerebellopontine fissure. The cerebellar peduncles converge on and form a major part of the ventricular surface. The hili of the dentate nuclei abut on the superolateral recesses of the ventricle near the superior poles of the tonsils.

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The posterior inferior cerebellar artery (PICA), by definition, arose from the vertebral artery. The vertebral artery was present in 49 and the PICA was present in 42 of the 50 hemispheres. Forty-one of the 42 PICAs arose as a single trunk and 1 arose as a duplicate trunk. The PICA was divided into five segments: the anterior medullary segment lay on the front of the medulla; the lateral medullary segment coursed beside the medulla and extended to the origin of the glossopharyngeal, vagal, and accessory nerves; the tonsillomedullary segment coursed around the caudal half of the cerebellar tonsil; the telovelotonsillar segment coursed in the cleft between the tela choroidea and the inferior medullary velum rostrally and the superior pole of the cerebellar tonsil caudally; and the cortical segment was distributed to the cerebellar surface. Thirty-seven of the 42 PICAs bifurcated into a medial and a lateral trunk. The medial trunk supplied the vermis and the adjacent part of the hemisphere, and the lateral trunk supplied the cortical surface of the tonsil and the hemisphere. The PICA gave off perforating, choroidal, and cortical arteries. The cortical arteries were divided into vermian, tonsillar, and hemispheric groups. Sixteen of the 42 PICAs passed between the rootlets of the accessory nerve, 10 passed between the rootlets of the vagus nerve, 13 passed between the vagus and the accessory nerves, 2 coursed rostral to the glossopharyngeal nerve, and 1 passed between the glossopharyngeal and the vagus nerves.

A set of suction tubes has been designed for both conventional neurosurgery done with the naked eye and microneurosurgery. All of the suction tubes have blunt, rounded tips that allow them to be used for manipulating tissue as well as for suction, and they are designed so that the surgeon's hand can rest comfortably on the wound margin while holding the tube in a pencil-type grip. The set includes the range of diameters needed for microsurgery and macrosurgery and the different lengths needed for superficial and deep intracranial and transsphenoidal operations.

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.

The operative approaches to the 3rd ventricle are divided on the basis of whether they are suitable for reaching the anterior or posterior part of the 3rd ventricle. The approaches suitable for lesions within or compressing the anterior portion of the 3rd ventricle are the trans-sphenoidal, subfrontal, frontotemporal, subtemporal, anterior transcallosal, and anterior transventricular. The approaches suitable for reaching the posterior portion of the 3rd ventricle are the posterior transcallosal, posterior transventricular, occipital transtentorial, and infratentorial supracerebellar. Considerations important in selecting one of these approaches are reviewed.

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.

The anatomy needed to plan microoperative approaches to the lateral ventricles was examined in 20 cadaveric cerebral hemispheres. The neural, arterial, and venous structures in the walls of the lateral ventricles and the relationship of the lateral ventricles to the third ventricle and basal cisterns were examined. The operative approaches to the lateral ventricle are reviewed.

Three facets of the anatomy of saccular aneurysms that should be considered when planning an operative approach are reviewed for each of the common aneurysm sites. Several basic anatomical principles helpful in selecting and planning the surgical approach to these aneurysms are discussed.

This report concerns a clip for aneurysm surgery which has (a) a stabilizing wire that prevents the scissoring of the blades, (b) a stronger coil spring that allows longer blades and a reduced possibility of slippage, and (c) grasping sites that allow the clip to be positioned in both an applier that holds the clip rigidly in one position, and in one that allows the clip to be rotated for optimal placement. The clip is made from stainless-steel wire 2 mm in diameter, which is larger than that used for other clips. The 2-mm diameter permits the clip to have wider clamping surfaces than other clips made from wire, it permits the grasping sites to be notched so that it may be held in a rotating clip applier, and permits the clip to be tooled for a stronger coil spring. The coil springs are of either a standard or a strong tension, and have opening pressures of approximately 175 g and 320 g, respectively.

The microsurgical anatomy of the veins of the posterior fossa was defined in 25 cadavers. These veins are divided into four groups: superficial, deep, brain-stem, and bridging veins. The superficial veins are divided on the basis of which of the three cortical surfaces they drain: the tentorial surface, which faces the tentorium and is exposed in a supracerebellar approach, is drained by the superior hemispheric and vermian veins; the suboccipital surface, which is below and between the lateral and sigmoid sinuses and is exposed in a wide suboccipital craniectomy, is drained by the inferior hemispheric and inferior vermian veins; and the petrosal surface, which faces forward toward the posterior surface of the petrous bone and is retracted to expose the cerebellopontine angle, is drained by the anterior hemispheric veins. The deep veins course in the three fissures between the cerebellum and the brain stem, and on the three cerebellar peduncles. The major deep veins in the fissures between the cerebellum and brain stem are the veins of the cerebellomesencephalic, cerebellomedullary, and cerebellopontine fissures, and those on the cerebellar peduncles are the veins of the superior, middle, and inferior cerebellar peduncles. The veins of the brain stem are named on the basis of whether they drain the midbrain, pons, or medulla. The veins of the posterior fossa terminate as bridging veins, which collect into three groups: a galenic group which drains into the vein of Galen; a petrosal group which drains into the petrosal sinuses; and a tentorial group which drains into the tentorial sinuses near the torcula.

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

The anterior perforating arteries, the group of arteries that enter the brain through the anterior perforated substance (APS), were examined using X 3 to X 40 magnification in 50 cerebral hemispheres obtained from 25 adult cadavers. These arteries arose from the internal carotid, middle and anterior cerebral, and the anterior choroidal arteries. The carotid branches to the APS arose distal to the origin of the anterior choroidal artery. The anterior choroidal artery branches arose from the main or superior branch of the artery. The middle cerebral artery branches to the APS (the lenticulostriate arteries) arose from the M1 and M2 segments and were divided into medial, intermediate, and lateral groups, each of which had a characteristic configuration. The anterior cerebral artery branches arose from the A1 segment and from the recurrent artery. The internal carotid and anterior choroidal artery branches entered the posterior half of the central portion of the APS. The lenticulostriate branches entered the middle and posterior portions of the lateral half of the APS. The A1 segment gave rise to branches which entered the medial half of the APS above the optic nerve and chiasm. The recurrent artery sent branches into the anterior two-thirds of the full mediolateral extent of the APS. The relationship of these branches to the cerebral structures above the APS and to the common aneurysm sites is reviewed.