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Background: The purpose of this study was to call attention to the subtemporal approach directed through the petrous apex to the IAM. We studied the microsurgical anatomy of the middle floor to delineate a reliable angle between the GSPN and the IAM to precisely localize and expose the IAM from above. A new technique for the elevation of middle fossa floor in an anterior-to-posterior direction has also been examined in cadaveric dissections and performed in surgery., Methods: The microsurgical anatomy of the middle fossa floor was studied in 10 adult cadaveric heads (20 sides) after meatal drilling on the middle fossa. Five latex-injected specimens were dissected in a stepwise manner to further define the microsurgical anatomy of the middle fossa approach. The middle fossa approach is illustrated in a patient for the decompression of the facial nerve to demonstrate the surgical technique and limitations of bone removal., Results: Elevation of middle fossa dura in an anterior-to-posterior direction leads to early identification of the GSPN, where the nerve passes under V3. The most reliable and easily appreciated angle to be used in localizing the IAM is between the IAM and the long axis of the GSPN, which is approximately 61 degrees . Beginning drilling the meatus medially at the petrous ridge is safer than beginning laterally, where the facial and vestibulocochlear nerves become more superficial. The cochlea anteromedially, vestibule posterolaterally, and superior semicircular canal posteriorly significantly limit the bone removal at the lateral part of the IAM., Conclusions: The surgical technique for the middle fossa approach which includes an anterior-to-posterior elevation of middle fossa dura starting from the foramen ovale and uses the angle between the IAM and the long axis of the GSPN to localize the meatus from above may be an alternative to previously proposed surgical methods.

Background: Managing lesions situated in the atrium of the lateral ventricle remains a challenging neurosurgical problem. The purposes of this study were to examine the microsurgical anatomy of the atrium of the lateral ventricle and the optic radiation and to define the differences in the exposure obtained by various surgical approaches., Methods: Fifteen adult cadaveric specimens were studied using magnification x3 to x40 after perfusion of the arteries and veins with colored silicone. The microsurgical anatomy of the atrium of the lateral ventricle was examined. The relationship between the optic radiation and the atrium was studied using the white matter fiber dissection technique. Surgical approaches to the atrium of the lateral ventricle were examined in stepwise dissection., Results: The medial and inferior walls of the atrium were free from optic radiation fibers. Surgical approaches to the atrium of the lateral ventricle are divided into 3 routes: (1) anterior approach: transsylvian approach, (2) posterior approaches: posterior transcortical, posterior transcallosal, occipital, and supracerebellar transtentorial approaches, and (3) lateral approaches: transtemporal and subtemporal approaches., Conclusion: Knowledge of the microsurgical anatomy of the atrium of the lateral ventricle and surrounding vital structures and the choice of an appropriate surgical approach will help surgeons perform safe and minimally invasive surgery.

Background: The cerebellar hemorrhage reported in numerous cases after supratentorial craniotomy has uniformly exhibited the characteristics of hemorrhage associated with venous infarction rather than arterial bleeding. The cause has remained obscure, although previous reports suggested that the cause may be obstruction of flow in the internal jugular vein immediately below the base of the skull., Methods: The microsurgical anatomy of 36 internal jugular veins in the upper cervical region were defined in adult cadaveric specimens using 3-40x magnification with special attention to the relationship of the vein to the atlas., Results: In every specimen, the posterior wall of the internal jugular vein rested against the transverse process of the atlas as the vein descended immediately below the jugular foramen. In 14 of 36 specimens, the transverse process indented the posterior wall of the vein, causing the vein to be slightly or moderately angulated as it descended across the anterior surface of the transverse process. Three veins were severely kinked as they descended across the transverse process of the atlas., Conclusions: Obstruction of flow in the internal jugular vein at the site where the vein descends across the transverse process of the atlas is a likely cause of the venous hypertension that has resulted in the cerebellar hemorrhage reported in numerous cases after supratentorial craniotomy. An examination of the biomechanics of the region confirms that turning the head to the side opposite a supratentorial craniotomy and extending the neck, common practices with unilateral supratentorial craniotomy, further aggravates the angulation and obstruction of the internal jugular vein at the transverse process of C1 on the side ipsilateral to the craniotomy.

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 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.

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.

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.

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.

This article reviews the selection and use of instruments for the microsurgical removal of acoustic neuromas by the suboccipital-transmeatal approach. The accurate use of carefully selected instruments for perineural dissection when combined with the use of the operating microscope can lead to frequent preservation of the facial nerve and occasional retention of hearing.

The anatomy needed to plan microoperative approaches to the region of the foramen magnum was examined in 25 cadaveric heads. The structures examined included the lower cranial and upper spinal nerves, the caudal brain stem and rostral spinal cord, the vertebral artery and its branches, the veins and dural sinuses at the craniovertebral junction, and the ligaments and muscles uniting the atlas, axis, and occipital bone. The transoral, transpalatal, labiomandibular, glossolabiomandibular, transsphenoidal, transcranial-transbasal, transcervical, and suboccipital operative approaches to the region are also reviewed.

The topographic and internal anatomy of the temporal bone is reviewed with emphasis on the relationships important to the suboccipital, middle fossa and translabyrinthine surgical approaches to the internal auditory canal. The equipment and materials needed for temporal bone dissection in the laboratory are reviewed. A stepwise method of dissection for each of the three surgical approaches to the internal acoustic meatus is outlined for both the dry and wet temporal bone.

The anatomy of the anterior choroidal artery was studied in 25 adult brains (50 cerebral hemispheres). The point of origin and the distribution of this artery were determined. The surgical and clinical implications of these findings are discussed.