The majority of gyri and sulci of the frontoparietal and temporal opercula had a constant relationship to the insular gyri and sulci and provided landmarks for approaching different parts of the insula. The most lateral lenticulostriate artery, an important landmark in insular surgery, arose 14.6 mm from the apex of the insula and penetrated the anterior perforated substance 15.3 mm medial to the limen insulae. The superior trunk of the middle cerebral artery (MCA) and its branches supplied the anterior, middle, and posterior short gyri; the anterior limiting sulcus; the short sulci; and the insular apex. The inferior trunk supplied the posterior long gyrus, inferior limiting sulcus, and limen area in most hemispheres. Both of these trunks frequently contributed to the supply of the central insular sulcus and the anterior long gyrus. The areas of insular supply of the superior and inferior trunks did not overlap. The most constant insular area of supply by the cortical MCA branches was from the prefrontal and precentral arteries that supplied the anterior and middle short gyri, respectively. The largest insular perforating arteries usually arose from the central and angular arteries and most commonly entered the posterior half of the central insular sulcus and posterior long gyrus. Insular veins drained predominantly to the deep middle cerebral vein, although frequent connections to the superficial venous system were found. Of all the insular veins, the precentral insular vein was the one that most commonly connected to the superficial sylvian vein.

The carotid and vertebrobasilar arterial systems give rise to multiple branches that supply the dura in a complex and overlapping pattern. A knowledge of the microsurgical anatomy of these dural arteries and their assessment on pretreatment evaluations plays a major role in safe and accurate treatment of multiple lesions.

Early branches directed to the temporal and frontal lobes were found in 90 and 32% of the hemispheres, respectively. The early branches that arose more proximally from the M1 segment were larger than those arising distally. Lenticulostriate arteries arose from 81% of the early frontal branches (EFBs) and from 48% of the early temporal branches (ETBs). An average of two cortical arteries arose from the EFBs and 1.3 from the ETBs, the most common of which supplied the temporopolar and orbitofrontal areas. Although the microsurgical anatomy of the early branches demonstrates abundant diversity, they can be classified into clearly defined patterns based on anatomical features. These patterns can prove helpful in evaluating angiographic data and in planning an operative procedure.

HE two most common surgical approaches to the fourth ventricle are the transvermian and telovelar approaches. The first involves incising the inferior vermis of the cerebellum and retracting the two halves of the vermis in opposite lateral directions. 1,3,6,11,12 In the second approach, the tela choroidea and inferior medullary velum, which form the lower half of the roof of the fourth ventricle, are opened and the lower vermis is retracted as a unit to provide exposure into the fourth ventricle. 17,20,22 The technical differences between the two approaches and the anatomical structures that limit the surgical view in each approach result in differences with regard to the exposure of the fourth ventricle floor, the lateral recess, and the foramen of Luschka. The purpose of this study was to describe and compare the microanatomical features of the transvermian and telovelar approaches and to relate these features to the exposure gained through each approach. Materials and MethodsTen formalin-fixed specimens, in which the arteries had been perfused with red silicone and the veins with blue silicone, were examined in this study. The specimens were dissected in a stepwise man-ner, with the aid of an operating microscope set to ϫ3 to ϫ40, to simulate exposures that can be obtained using the transvermian and telovelar approaches. Special attention was directed to the anatomical structures that limit visualization in each approach.Three of 10 cadaveric heads were studied using MR imaging, and the data were registered on a Stealth workstation by using standard protocols. Magnetic resonance images were obtained using a 3-tesla MR imaging system (Magnetom Allegra; Siemens Medical Solutions, Malvern, PA) and transferred to a Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO). Ten fiducial markers used for image registration were attached to the skin overlying the superior sagittal sinus and the parietooccipital area. The head was placed similar to the orientation provided by the semisitting position and a suboccipital craniotomy was performed through a midline vertical skin incision. A 3D model was built and a dynamic reference array was attached to the cadaver. The specimen was registered to the 3D model and image, resulting in an estimated accuracy of better than 2 mm. An active probe was used to indicate the surgical exposure on the 3D model and on three orthogonal MR images. These images were recorded through screen captures. The superior, inferior, lateral, superolateral, and foramen of Luschka exposures through each approach to the fourth ventricle were determined using image guidance under direct microscopic visualization.We compared the operative angle of approach through the transvermian and telovelar routes. The angle was measured from the floor of the fourth ventricle in the sagittal plane. The apex of the angle was placed at three sites along the ventricle floor: the aqueduct, the midpoint (50% point) of the distance measured from the obex to the inferior border of th...

Pituicytomas are a distinct form of pituitary gland neoplasia that may recur if subtotally resected. These neurohypophysial tumors may contain a small subpopulation of previously unrecognized bcl-2-immunoreactive cells, whose role in the histogenesis of pituicytoma deserves further study.

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Although a clear guideline for cerebral revascularization procedures has not yet been established, it is important to understand various microsurgical techniques and their related anatomical structures. This will help surgeons consider surgical indications for treatment of patients with vertebrobasilar ischemia caused by aneurysms, tumors, or atherosclerotic diseases in the posterior circulation.

The far lateral and extreme lateral variants of the atlanto-occipital transarticular approach provide an alternative to the transoral approach to the anterior extradural structures at the CVJ. Compared with the transoral approach, both approaches provide a shorter operative route, avoid the contaminated nasopharynx, reduce the incidence of cerebrospinal fluid leak, and are not limited laterally by the atlanto-occipital joint.