Necmettin Tanriover

MICROSURGICAL APPROACHES TO THE PERIMESENCEPHALIC CISTERNS AND RELATED SEGMENTS OF THE POSTERIOR CEREBRAL ARTERY: COMPARISON USING A NOVEL APPLICATION OF IMAGE GUIDANCE

OBJECTIVE:To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. METHODS:Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. RESULTS:The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbé limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. CONCLUSION:Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.

Comparison of the far lateral and extreme lateral variants of the atlanto-occipital transarticular approach to anterior extradural lesions of the craniovertebral junction.

OBJECTIVEManaging lesions situated in the anterior aspect of the craniovertebral junction (CVJ) remains a challenging neurosurgical problem. The purposes of this study were to examine the microsurgical anatomy of the anterior extradural aspect of the CVJ and the differences in the exposure obtained by the far lateral and extreme lateral atlanto-occipital transarticular approaches. The far lateral approach, as originally described, is a lateral suboccipital approach directed behind the sternocleidomastoid muscle and the vertebral artery and just medial to the occipital and atlantal condyles and the atlanto-occipital joint. The extreme lateral approach, as originally described, is a direct lateral approach deep to the anterior part of the sternocleidomastoid muscle and behind the internal jugular vein along the front of the vertebral artery. Both approaches permit drilling of the condyles at the atlanto-occipital joint but provide a different exposure because of the differences in the direction of the approach. METHODSFifteen adult cadaveric specimens were studied using a magnification of ×3 to ×40 after perfusion of the arteries and veins with colored silicone. The microsurgical anatomy of the extradural aspects of the CVJ and the two atlanto-occipital transarticular approaches were examined in stepwise dissections. RESULTSThe far lateral atlanto-occipital transarticular approach provides excellent exposure of the extradural lesions located in the ipsilateral anterior and anterolateral aspects of the extradural region of the CVJ. The extreme lateral atlanto-occipital transarticular approach provides excellent exposure, not only on the side of the exposure, but also extending across the midline to the medial aspect of the contralateral atlanto-occipital joint and the lower clivus. CONCLUSIONThe 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.

Microsurgical anatomy of the dural arteries.

OBJECTIVE: The objective was to examine the microsurgical anatomy basic to the microsurgical and endovascular management of lesions involving the dural arteries. METHODS: Adult cadaveric heads and skulls were examined using the magnification provided by the surgical microscope to define the origin, course, and distribution of the individual dural arteries. RESULTS: The pattern of arterial supply of the dura covering the cranial base is more complex than over the cerebral convexity. The internal carotid system supplies the midline dura of the anterior and middle fossae and the anterior limit of the posterior fossa; the external carotid system supplies the lateral segment of the three cranial fossae; and the vertebrobasilar system supplies the midline structures of the posterior fossa and the area of the foramen magnum. Dural territories often have overlapping supply from several sources. Areas supplied from several overlapping sources are the parasellar dura, tentorium, and falx. The tentorium and falx also receive a contribution from the cerebral arteries, making these structures an anastomotic pathway between the dural and parenchymal arteries. A reciprocal relationship, in which the territories of one artery expand if the adjacent arteries are small, is common. CONCLUSION: 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.

Three-dimensional microsurgical anatomy and the safe entry zones of the brainstem.

BACKGROUND: There have been no studies of the structure and safe surgical entry zones of the brainstem based on fiber dissection studies combined with 3-dimensional (3-D) photography. OBJECTIVE: To examine the 3-D internal architecture and relationships of the proposed safe entry zones into the midbrain, pons, and medulla. METHODS: Fifteen formalin and alcohol-fixed human brainstems were dissected by using fiber dissection techniques, ×6 to ×40 magnification, and 3-D photography to define the anatomy and the safe entry zones. The entry zones evaluated were the perioculomotor, lateral mesencephalic sulcus, and supra- and infracollicular areas in the midbrain; the peritrigeminal zone, supra- and infrafacial approaches, acoustic area, and median sulcus above the facial colliculus in the pons; and the anterolateral, postolivary, and dorsal medullary sulci in the medulla. RESULTS: The safest approach for lesions located below the surface is usually the shortest and most direct route. Previous studies have often focused on surface structures. In this study, the deeper structures that may be at risk in each of the proposed safe entry zones plus the borders of each entry zone were defined. This study includes an examination of the relationships of the cerebellar peduncles, long tracts, intra-axial segments of the cranial nerves, and important nuclei of the brainstem to the proposed safe entry zones. CONCLUSION: Fiber dissection technique in combination with the 3-D photography is a useful addition to the goal of making entry into the brainstem more accurate and safe. ABBREVIATION: DTI, diffusion tensor imaging

Endoscopic endonasal approach to the orbital apex and medial orbital wall: anatomic study and clinical applications.

Objective: The objective of this study was to recognize the endoscopic anatomy of the orbital apex and medial orbital wall to understand the pure endoscopic endonasal approaches to this region and their clinical applications. These basic information will facilitate our surgical procedures and decrease the rate of surgical complications. Material and Methods: Five fresh adult cadavers were studied bilaterally (N = 10). We used Karl Storz 0- and 30-degree 4-mm, 18-cm, and 30-cm rod-lens rigid endoscopes in our dissections. After cadaver specimen preparation, we approached each orbital apex and medial orbital wall through each nostril. After resection of medial orbital wall, an endoscopic intraorbital approach was performed. Results: The orbita could be exposed by using 0- and 30-degree endoscopes. We preferred to start the approach from the sphenoid sinus instead of transethmoidal approaches that are less familiar to the neurosurgeons. The posterior and anterior ethmoidal arteries are in close relation to the supralateral wall of ethmoid sinus, thus care must be taken not to injure these arteries during dissection. In this way, we can safely expose the whole medial wall of the orbita. Optic canal decompression can be safely done by bone resection starting from the optic nerve toward the optic canal. We continued bone resection from the posterior to the anterior of the medial orbital wall, thus we can perform medial orbitotomy. The intraorbital approach can be done medially by introducing the endoscope between the medial and inferior rectus muscles. Conclusions: Our anatomic study offered the facility to learn the endoscopic anatomy of the orbital apex and the medial wall of the orbita and understand the appropriate approaches (such as medial orbitotomy and optic canal decompression) to some pathologic lesions of this region. With skilled and experienced hands, it can superimpose many traditional orbital approaches with minimal invasiveness and less postoperative complications.

Microsurgical anatomy and surgical exposure of the petrous segment of the internal carotid artery: Commentary

OBJECTIVE The petrous segment of the internal carotid artery has been exposed in the transpetrosal, subtemporal, infratemporal, transnasal, transmaxillary, transfacial, and a variety of transcranial approaches. The objective of the current study was to examine anatomic features of the petrous carotid and its branches as related to the variety of approaches currently being used for its exposure. METHODS Twenty middle fossae from adult cadaveric specimens were examined using magnification of ×3 to ×40 after injection of the arteries and veins with colored silicone. RESULTS The petrous carotid extends from the entrance into the carotid canal of the petrous part of the temporal bone to its termination at the level of the petrolingual ligament laterally and the lateral wall of the sphenoid sinus medially. The petrous carotid from caudal to rostral was divided into 5 segments: posterior vertical, posterior genu, horizontal, anterior genu, and anterior vertical. Fourteen (70%) of the 20 petrous carotids had branches. The branch that arose from the petrous carotid was either a vidian or periosteal artery or a common trunk that gave rise to both a vidian and 1 or more periosteal arteries. The most frequent branch was a periosteal artery. CONCLUSION An understanding of the complex relationships of the petrous carotid provides the basis for surgically accessing any 1 or more of its 5 segments.

Visual field defects in selective amygdalohippocampectomy for hippocampal sclerosis: the fate of Meyer's loop during the transsylvian approach to the temporal horn.

OBJECTIVEMeyers loop, the most vulnerable part of the optic radiations during approaches to the temporomedial region, extends to the tip of the temporal horn and is often encountered in epilepsy surgery. The risk of damaging Meyers loop during transsylvian selective amygdalohippocampectomy peaks while accessing the temporal horn through its roof by opening the inferior limiting sulcus of the insula. In this prospective study, we sought to evaluate and identify the incidence of visual field deficits in a homogeneous group of patients who had temporal lobe epilepsy with hippocampal sclerosis and who underwent transsylvian selective amygdalohippocampectomy. METHODSWe studied 30 patients who were referred for epilepsy surgery for intractable complex partial and/or secondary generalized seizures and evaluated according to a noninvasive protocol. All patients underwent selective amygdalohippocampectomy for temporal lobe epilepsy with hippocampal sclerosis using the standard transsylvian approach. Visual field deficits were examined preoperatively in 30 patients, by either a confrontation method (n = 18) or standard Goldmann perimetry (n = 12) and postoperatively in all patients using standard Humphrey digital perimetry. RESULTSVisual field examination was normal in all patients before surgery. Humphrey perimetric measurement revealed visual field deficits in 11 patients (36.6%) after surgery. CONCLUSIONWe have shown that there is a considerable risk of having visual field deficits after standard transsylvian selective amygdalohippocampectomy owing to the interruption of the anterior bundle of the optic radiation fibers, which most likely occurs while opening the temporal horn through the inferior limiting sulcus of the insula.

Microsurgical and angiographic anatomy of middle cerebral artery aneurysms: prevalence and significance of early branch aneurysms.

OBJECTIVE To determine the prevalence of early branch aneurysms, characterize these lesions angiographically and anatomically, and determine their clinical significance. METHODS The authors conducted a retrospective review of 125 consecutive patients with a diagnosis of middle cerebral artery (MCA) aneurysm. Eighty-four patients harboring 100 MCA aneurysms were studied; 41 patients were excluded for lack of adequate imaging or for fusiform morphology of the aneurysm. Demographic characteristics including age, side, sex, subarachnoid hemorrhage, intracerebral hematoma, multiple aneurysms, and type of treatment were obtained. RESULTS The average patient age was 57.3 years (range, 29–79 yr); 69 were women and 15 were men. Fifty-eight were right MCA aneurysms and 42 were left aneurysms. Fourteen patients had multiple MCA aneurysms. Thirty-nine of 100 aneurysms were associated with subarachnoid hemorrhage. Twelve of 100 aneurysms were associated with an intracerebral hematoma. The average aneurysm sizes were 9.1 mm overall (range, 2.0–27.0 mm), 12.3 mm for ruptured aneurysms, and 7.5 mm for unruptured. There were 36 M1 bifurcation aneurysms, 39 early frontal branch aneurysms, 18 early temporal branch aneurysms, four lenticulostriate artery aneurysms, and three trifurcation aneurysms. CONCLUSION In our retrospective review, the majority of MCA aneurysms arose along the M1 segment proximal to the M1 bifurcation. Early frontal branch aneurysms were more common than typical M1 segment bifurcation aneurysms. M1 segment aneurysms arising from early frontal and early temporal branches have distinct anatomic features that impact surgical management and outcome. Understanding the relationship between the recurrent lenticulostriate arteries arising from the proximal segments of these early branches and the aneurysm neck should allow surgeons to avoid many postoperative ischemic complications when dealing with these challenging lesions.

Middle fossa approach: microsurgical anatomy and surgical technique from the neurosurgical perspective

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.

One-piece versus two-piece orbitozygomatic craniotomy: quantitative and qualitative considerations.

OBJECTIVE: The orbitozygomatic (OZ) craniotomy minimizes brain retraction and improves cranial base exposure by providing a multidirectional view, increased operative angles and working space. The two main variations of the approach include the one-piece and the two-piece types. The microsurgical anatomy of the one- and two-piece OZ craniotomies are presented with the goal of comparing the extent of orbital roof removal between these two craniotomies and the effect of orbital roof removal on operative exposure. METHODS: Ten two-piece and 11 one-piece OZ craniotomies were performed in a stepwise manner simulating the approaches on formalin fixed specimens. The orbital surface area removed above the frontozygomatic suture extending medially over the orbital roof was measured from each bone flap. The two-sided unpaired t test using STATA 7.0 software was used to compare the amount of orbital roof removed using the two approaches. RESULTS: The two-piece OZ craniotomy allowed for the removal of a larger portion of the roof and lateral wall of the orbit than the one-piece. The total orbitotomy, including the orbital roof plus the part of the lateral wall above the frontozygomatic suture, had an average surface area of 996 ± 229 mm2 for the two piece and 372 ± 103 mm2 for the one-piece. The orbital roof made up 27 ± 18% of the orbital osteotomy for the one-piece craniotomies and 67 ± 10% of the osteotomy for the two-piece craniotomies (P < 0.001). CONCLUSION: The two-piece OZ craniotomy allows for more extensive orbital roof removal and better visualization of the basal frontal lobe. Therefore, the two-piece may result in a lower incidence of enophtalmus and poor cosmetic outcomes, particularly if the remaining orbital roof must be removed piecemeal during the one-piece OZ craniotomy in order to obtain satisfactory exposure.