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  • By Author: Rhoton, Albert L. x
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Necmettin Tanriover, Hiroshi Abe, Albert L. Rhoton Jr., Masatou Kawashima, Galip Z. Sanus and Ziya Akar

Object

The purpose of this study was to define the patterns of drainage of the superior petrosal venous complex (SPVC) along the petrous ridge in relation to the Meckel cave and internal acoustic meatus (IAM) and to delineate its effect on the surgical exposures obtained in subtemporal transtentorial and retrosigmoid suprameatal approaches.

Methods

The patterns of drainage of the SPVC along the petrous ridge were characterized according to their relation to the Meckel cave and the IAM based on an examination of 30 hemispheres. Subtemporal transtentorial and retro-sigmoid suprameatal approaches were performed in three additional cadavers to demonstrate the effect of the drainage pattern on the surgical exposures.

Conclusions

The SPVC emptied into the superior petrosal sinus (SPS) within a distance of 1 cm from the midpoint of the Meckel cave. The patterns of drainage of the SPVC were classified into three groups. Type I emptied into the SPS above and lateral to the boundaries of the IAM. The most common type, Type II, emptied between the lateral limit of the trigeminal nerve at the Meckel cave and the medial limit of the facial nerve at the IAM, within an area of approximately 13 mm. Type III emptied into the SPS above or medial to the Meckel cave. The ideal SPVC for a subtemporal transtentorial approach (with or without anterior extradural petrosectomy) seems to be a Type I. In SPVC Type III and those Type II cases in which the SPVC is located near the Meckel cave, the amount of working space is significantly limited in a subtemporal transtentorial approach. In contrast, the ideal type of SPVC for a retrosigmoid suprameatal approach would be a Type III, and the SPVC must be divided in the majority of Type I and II cases for a satisfactory surgical exposure along the Meckel cave and middle fossa dura. The proposed modified classification system and its effect on the surgical exposure may aid in planning the approach directed along the petrous apex and may reduce the probability of venous complications.

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Masatou Kawashima, Albert L. Rhoton Jr., Necmettin Tanriover, Arthur J. Ulm, Alexandre Yasuda and Kiyotaka Fujii

Object. Revascularization is an important component of treatment for complex aneurysms that require parent vessel occlusion, skull base tumors that involve major vessels, and certain ischemic diseases. In this study, the authors examined the microsurgical anatomy of cerebral revascularization in the anterior circulation by demonstrating various procedures for bypass surgery.

Methods. Twenty-five adult cadaveric specimens were studied, using 3 to 40 magnification, after the arteries and veins had been perfused with colored silicone. The microsurgical anatomy of cerebral revascularization in the anterior circulation was examined with the focus on the donor, recipient, and graft vessels. The techniques discussed in this paper include the superficial temporal artery (STA)—middle cerebral artery (MCA), middle meningeal artery (MMA)—MCA, and side-to-side anastomoses; short arterial and venous interposition grafting; and external carotid artery/internal carotid artery (ICA)—M2 and ICA—ICA bypasses. Bypass procedures for cerebral revascularization are divided into two categories depending on their flow volume: low-flow and high-flow bypasses. A low-flow bypass, such as the STA—MCA anastomosis, is used to cover a relatively small area, whereas a high-flow bypass, such as the ICA—ICA anastomosis, is used for larger areas. Cerebral revascularization techniques are also divided into two types depending on the graft materials: pedicled arterial grafts, such as STA and occipital artery grafts, and free venous or arterial grafts, which are usually saphenous vein and radial artery grafts. Pedicled arterial grafts are mainly used for low-flow bypasses, whereas venous or arterial grafts are used for high-flow bypasses.

Conclusions. It is important to understand the methods of bypass procedures and to consider indications in which cerebral revascularization is needed.

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Masatou Kawashima, Albert L. Rhoton Jr., Necmettin Tanriover, Arthur J. Ulm, Alexandre Yasuda and Kiyotaka Fujii

Object. Revascularization is an important component of treatment for complex aneurysms, skull base tumors, and vertebrobasilar ischemia in the posterior circulation. In this study, the authors examined the microsurgical anatomy related to cerebral revascularization in the posterior circulation and demonstrate various procedures for bypass surgery.

Methods. The microsurgical anatomy of cerebral and cerebellar vessels as they relate to revascularization procedure and techniques, including extracranial-to-intracranial bypass grafting, arterial interposition grafting, and side-to-side anastomosis, were examined by performing stepwise dissections in 22 adult cadaveric specimens. The arteries and veins in the specimens were perfused with colored silicone.

Dominant cerebral and cerebellar revascularization procedures in the posterior circulations include superficial temporal artery (STA)—posterior cerebral artery (PCA), STA—superior cerebellar artery (SCA), occipital artery (OA)—anterior inferior cerebellar artery, OA—posterior inferior cerebellar artery (PICA), and PICA—PICA anastomoses. These procedures are effective in relatively small but critical areas including the brainstem and cerebellum. For revascularization of larger areas a saphenous vein graft is used to create a bypass between the PCA and the external carotid artery. Surgical procedures are generally difficult to perform in deep and narrow operative spaces near critical vital structures.

Conclusions. 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.

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Necmettin Tanriover, Albert L. Rhoton Jr., Masatou Kawashima, Arthur J. Ulm and Alexandre Yasuda

Object. The purpose of this study was to define the topographic anatomy, arterial supply, and venous drainage of the insula and sylvian fissure.

Methods. The neural, arterial, and venous anatomy of the insula and sylvian fissure were examined in 43 cerebral hemispheres.

Conclusions. 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.

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Necmettin Tanriover, Masatou Kawashima, Albert L. Rhoton Jr, Arthur J. Ulm and Robert A. Mericle

Object. The cortical arteries arising from the main trunk of the middle cerebral artery, proximal to its bifurcation or trifurcation, are called “early branches.” The purpose of this study was to characterize these early branches.

Methods. The early branches were characterized according to their sites and patterns of origin, diameters, and relative proximity to the internal carotid artery bifurcation, as well as the course and area of supply of their cortical branches based on an examination of 50 hemispheres. Special attention was directed to the perforating arteries that arose from the early branches and entered the anterior perforated substance. The anatomical findings were compared with data obtained from 109 angiograms.

Conclusions. 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.

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Masatou Kawashima, Necmettin Tanriover, Albert L. Rhoton Jr. and Toshio Matsushima

Object. The microsurgical anatomy of the C3–6 transverse processes and their relationship to the intertransverse space and vertebral artery (VA) were examined with special attention to the aspect exposed in the anterior surgical approach.

Methods. Ten adult cadaveric spines were examined (magnification levels × 3–40) after perfusion of the arteries and veins with colored silicone. The morphological detail of the transverse process and intertransverse space, the distances between selected surgical landmarks and the VA were measured, and the means and standard deviations were calculated. The osseous changes in the anterior root of the transverse process were classified according to their extent.

The transverse processes became smaller, and the anterior intertransverse spaces and the width of the VA exposed in the space increased in size proceeding from caudal to rostral levels, thus exposing the VA to increased risk of injury during procedures at cephalad levels. The distance between the medial border of the longus colli muscle and the VA decreased when proceeding caudally from C2–3 to C4–5 interspaces but began to increase at the level of C5–6. The VA coursed closer to the lateral border of the vertebral body than to the medial border of the anterior tubercle of the transverse process. Osseous changes consisting of thinning or defects in the anterior root of the transverse process were observed from C-3 to C-5. The thinning was most prominent in the lower half of the anterior root just above where the VA ascends behind the lower edge of the anterior root. The osseous change may reflect the erosive effect of the VA on the anterior root of the transverse process.

Conclusions. This study provides new information regarding the transverse process and especially the anterior root. An awareness of the thinness and defects in the anterior root of the transverse process and the relationships to the surrounding area will aid in reducing VA injury during anterior approaches to the cervical spine.