Microsurgical anatomy and approaches around the lateral recess with special reference to entry into the pons.

OBJECTIVE The lateral recess is a unique structure communicating between the ventricle and cistern, which is exposed when treating lesions involving the fourth ventricle and the brainstem with surgical approaches such as the transcerebellomedullary fissure approach. In this study, the authors examined the microsurgical anatomy around the lateral recess, including the fiber tracts, and analyzed their findings with respect to surgical exposure of the lateral recess and entry into the lower pons. METHODS Ten cadaveric heads were examined with microsurgical techniques, and 2 heads were examined with fiber dissection to clarify the anatomy between the lateral recess and adjacent structures. The lateral and medial routes directed to the lateral recess in the transcerebellomedullary fissure approach were demonstrated. A morphometric study was conducted in the 10 cadaveric heads (20 sides). RESULTS The lateral recess was classified into medullary and cisternal segments. The medial and lateral routes in the transcerebellomedullary fissure approach provided access to approximately 140º-150º of the posteroinferior circumference of the lateral recess. The floccular peduncle ran rostral to the lateral recess, and this region was considered to be a potential safe entry zone to the lower pons. By appropriately selecting either route, medial-to-lateral or lateral-to-medial entry axis is possible, and combining both routes provided wide exposure of the lower pons around the lateral recess. CONCLUSIONS The medial and lateral routes of the transcerebellomedullary fissure approach provided wide exposure of the lateral recess, and incision around the floccular peduncle is a potential new safe entry zone to the lower pons.

Prevention of postoperative visual field defect after the occipital transtentorial approach: anatomical study.

OBJECTIVE A postoperative visual field defect resulting from damage to the occipital lobe during surgery is a unique complication of the occipital transtentorial approach. Though the association between patient position and this complication is well investigated, preventing the complication remains a challenge. To define the area of the occipital lobe in which retraction is least harmful, the surface anatomy of the brain, course of the optic radiations, and microsurgical anatomy of the occipital transtentorial approach were examined. METHODS Twelve formalin-fixed cadaveric adult heads were examined with the aid of a surgical microscope and 0° and 45° endoscopes. The optic radiations were examined by fiber dissection and MR tractography techniques. RESULTS The arterial and venous relationships of the lateral, medial, and inferior surfaces of the occipital lobe were defined anatomically. The full course of the optic radiations was displayed via both fiber dissection and MR tractography. Although the stems of the optic radiations as exposed by both techniques are similar, the terminations of the fibers are slightly different. The occipital transtentorial approach provides access for the removal of lesions involving the splenium, pineal gland, collicular plate, cerebellomesencephalic fissure, and anterosuperior part of the cerebellum. An angled endoscope can aid in exposing the superior medullary velum and superior cerebellar peduncles. CONCLUSIONS Anatomical findings suggest that retracting the inferior surface of the occipital lobe may avoid direct damage and perfusion deficiency around the calcarine cortex and optic radiations near their termination. An accurate understanding of the course of the optic radiations and vascular relationships around the occipital lobe and careful retraction of the inferior surface of the occipital lobe may reduce the incidence of postoperative visual field defect.

Anterior interhemispheric transsplenial approach to pineal region tumors: anatomical study and illustrative case.

Pineal region tumors are challenging to access because they are centrally located within the calvaria and surrounded by critical neurovascular structures. The goal of this work is to describe a new surgical trajectory, the anterior interhemispheric transsplenial approach, to the pineal region and falcotentorial junction area. To demonstrate this approach, the authors examined 7 adult formalin-fixed silicone-injected cadaveric heads and 2 fresh human brain specimens. One representative case of falcotentorial meningioma treated through an anterior interhemispheric transsplenial approach is also described. Among the interhemispheric approaches to the pineal region, the anterior interhemispheric transsplenial approach has several advantages. 1) There are few or no bridging veins at the level of the pericoronal suture. 2) The parietal and occipital lobes are not retracted, which reduces the chances of approach-related morbidity, especially in the dominant hemisphere. 3) The risk of damage to the deep venous structures is low because the tumor surface reached first is relatively vein free. 4) The internal cerebral veins can be manipulated and dissected away laterally through the anterior interhemispheric route but not via the posterior interhemispheric route. 5) Early control of medial posterior choroidal arteries is obtained. The anterior interhemispheric transsplenial approach provides a safe and effective surgical corridor for patients with supratentorial pineal region tumors that 1) extend superiorly, involve the splenium of the corpus callosum, and push the deep venous system in a posterosuperior or an anteroinferior direction; 2) are tentorial and displace the deep venous system inferiorly; or 3) originate from the splenium of the corpus callosum.

Operative Management of Distal Anterior Cerebral Artery Aneurysms Through a Mini Anterior Interhemispheric Approach.

BACKGROUND: Distal anterior cerebral artery (DACA) aneurysms, also known as pericallosal artery aneurysms, are present in 1.5%-9% of all intracranial aneurysms. Here we characterize the important microsurgical anatomy of DACAs; describe the surgical approach to treating these aneurysms with a minimally invasive surgical technique, the mini anterior interhemispheric approach (MAIA); and examine the nuances of aneurysm clipping in this region. METHODS: This was a retrospective and descriptive analysis of a series of aneurysm surgeries performed at the National Institute of Neurology and Neurosurgery in Mexico City. Cadaveric dissections were used to demonstrate relevant cerebrovascular anatomy. We analyzed patient demographic data and aneurysm characteristics. Patients' neurologic grade was evaluated using the Hunt and Kosnik (H-K) scale, and surgical outcomes were evaluated using the Glasgow Outcome Scale (GOS). Other variables were analyzed using the χ2 test. RESULTS: We analyzed a total of 32 DACA aneurysms (10 nonruptured and 22 ruptured), representing 5.8% of all aneurysms. The study cohort was 64.3% females and 35.7% males. H-K grade II was the most frequent classification (32.4%); 42.8% of patients presented with a Fisher grade IV aneurysm. Aneurysm location was classified as supra-genu, genu, or infra-genu. Eight patients had multiple aneurysms, among which 50% were located at the bifurcation of the middle cerebral artery. CONCLUSIONS: Surgical clipping through a MAIA approach is an excellent treatment option for pericallosal artery aneurysms.

Key Aspects in Foramen Magnum Meningiomas: From Old Neuroanatomical Conceptions to Current Far Lateral Neurosurgical Intervention.

Foramen magnum meningiomas represent a challenge for neurosurgeons. These tumors require careful surgical manipulation as they are often located in proximity to critical neurovascular structures and the cranial nerves. The far lateral approach is considered the safest neurosurgical approach for excising foramen magnum lesions. It facilitates the access to the anterior foramen magnum and reduces the retraction of vital structures. We describe key historical, epidemiological, genetic, epigenetic, clinical, and neurosurgical aspects of foramen magnum meningiomas. We emphasize the far lateral approach for lesions arising in the foramen magnum, as well as the most appropriate patient positioning for such approach. Caring for these aspects will be rewarded with the best perioperative neurosurgical outcomes.

The accuracy of an electromagnetic navigation system in lateral skull base approaches.

OBJECTIVES/HYPOTHESIS: Image-guided optical tracking systems are being used with increased frequency in lateral skull base surgery. Recently, electromagnetic tracking systems have become available for use in this region. However, the clinical accuracy of the electromagnetic tracking system has not been examined in lateral skull base surgery. This study evaluates the accuracy of electromagnetic navigation in lateral skull base surgery. STUDY DESIGN: Cadaveric and radiographic study. METHODS: Twenty cadaveric temporal bones were dissected in a surgical setting under a commercially available, electromagnetic surgical navigation system. The target registration error (TRE) was measured at 28 surgical landmarks during and after performing the standard translabyrinthine and middle cranial fossa surgical approaches to the internal acoustic canal. In addition, three demonstrative procedures that necessitate navigation with high accuracy were performed; that is, canalostomy of the superior semicircular canal from the middle cranial fossa,1 cochleostomy from the middle cranial fossa,2 and infralabyrinthine approach to the petrous apex.3 RESULTS: Eleven of 17 (65%) of the targets in the translabyrinthine approach and five of 11 (45%) of the targets in the middle fossa approach could be identified in the navigation system with TRE of less than 0.5 mm. Three accuracy-dependent procedures were completed without anatomical injury of important anatomical structures. CONCLUSION: The electromagnetic navigation system had sufficient accuracy to be used in the surgical setting. It was possible to perform complex procedures in the lateral skull base under the guidance of the electromagnetically tracked navigation system. LEVELS OF EVIDENCE: N/A. Laryngoscope, 2016 127:450-459, 2017.

Microsurgical and endoscopic approaches to the pulvinar.

OBJECTIVE Approaches to the pulvinar remain challenging because of the depth of the target, surrounding critical neural structures, and complicated arterial and venous relationships. The purpose of this study was to compare the surgical approaches to different parts of the pulvinar and to examine the efficacy of the endoscope as an adjunct to the operating microscope in this area. METHODS The pulvinar was examined in 6 formalin-fixed human cadaveric heads through 5 approaches: 4 above and 1 below the tentorium. Each approach was performed using both the surgical microscope and 0° or 45° rigid endoscopes. RESULTS The pulvinar has a lateral ventricular and a medial cisternal surface that are separated by the fornix and the choroidal fissure, which wrap around the posterior surface of the pulvinar. The medial cisternal part of the pulvinar can be further divided into upper and lower parts. The superior parietal lobule approach is suitable for lesions in the upper ventricular and cisternal parts. Interhemispheric precuneus and posterior transcallosal approaches are suitable for lesions in the part of the pulvinar forming the anterior wall of the atrium and adjacent cisternal part. The posterior interhemispheric transtentorial approach is suitable for lesions in the lower cisternal part and the supracerebellar infratentorial approach is suitable for lesions in the inferior and medial cisternal parts. The microscope provided satisfactory views of the ventricular and cisternal surfaces of the pulvinar and adjacent neural and vascular structures. The endoscope provided multi-angled and wider views of the pulvinar and adjacent structures. CONCLUSIONS A combination of endoscopic and microsurgical techniques allows optimal exposure of the pulvinar.

Frontal Lobe Decortication (Frontal Lobectomy with Ventricular Preservation) in Epilepsy-Part 1: Anatomic Landmarks and Surgical Technique.

BACKGROUND: An extensive frontal resection is a frequently performed neurosurgical procedure, especially for treating brain tumor and refractory epilepsy. However, there is a paucity of reports available regarding its surgical anatomy and technique. OBJECTIVES: We sought to present the anatomic landmarks and surgical technique of the frontal lobe decortication (FLD) in epilepsy. The goals were to maximize the gray matter removal, spare primary and supplementary motor areas, and preserve the frontal horn. MATERIAL AND METHODS: The anatomic study was based on dissections performed in 15 formalin-fixed adult cadaveric heads. The clinical experience with 15 patients is summarized. RESULT: FLD consists of 5 steps: 1) coagulation and section of arterial branches of lateral surface; 2) paramedian subpial resection 3 cm ahead of the precentral sulcus to reach the genu of corpus callosum; 3) resection of gray matter of lateral surface, preserving the frontal horn; 4) removal of gray matter of basal surface preserving olfactory tract; 5) removal of gray matter of the medial surface under the rostrum of corpus callosum. The frontal horn was preserved in all 15 patients; 12 patients (80%) had no complications; 2 patients presented temporary hemiparesis; and 1 Rasmussen syndrome patient developed postoperative fever. The best seizure control was in cases with focal magnetic resonance imaging abnormalities limited to the frontal lobe. CONCLUSION: FLD is an anatomy-based surgical technique for extensive frontal lobe resection. It presents reliable anatomic landmarks, selective gray matter removal, preservation of frontal horn, and low complication rate in our series. It can be an alternative option to the classical frontal lobectomy.

Midline and off-midline infratentorial supracerebellar approaches to the pineal gland.

OBJECTIVE A common approach to lesions of the pineal region is along the midline below the torcula. However, reports of how shifting the approach off midline affects the surgical exposure and relationships between the tributaries of the vein of Galen are limited. The purpose of this study is to examine the microsurgical and endoscopic anatomy of the pineal region as seen through the supracerebellar infratentorial approaches, including midline, paramedian, lateral, and far-lateral routes. METHODS The quadrigeminal cisterns of 8 formalin-fixed adult cadaveric heads were dissected and examined with the aid of a surgical microscope and straight endoscope. Twenty CT angiograms were examined to measure the depth of the pineal gland, slope of the tentorial surface of the cerebellum, and angle of approach to the pineal gland in each approach. RESULTS The midline supracerebellar route is the shortest and provides direct exposure of the pineal gland, although the culmen and inferior and superior vermian tributaries of the vein of Galen frequently block this exposure. The off-midline routes provide a surgical exposure that, although slightly deeper, may reduce the need for venous sacrifice at both the level of the veins from the superior cerebellar surface entering the tentorial sinuses and at the level of the tributaries of the vein of Galen in the quadrigeminal cistern, and require less cerebellar retraction. Shifting from midline to off-midline exposure also provides a better view of the cerebellomesencephalic fissure, collicular plate, and trochlear nerve than the midline approaches. Endoscopic assistance may aid exposure of the pineal gland while preserving the bridging veins. CONCLUSIONS Understanding the characteristics of different infratentorial routes to the pineal gland will aid in gaining a better view of the pineal gland and cerebellomesencephalic fissure and may reduce the need for venous sacrifice at the level of the tentorial sinuses draining the upper cerebellar surface and the tributaries of the vein of Galen.

The endoscopic anatomy of the middle ear approach to the fundus of the internal acoustic canal.

OBJECTIVE The application of the endoscope in the lateral skull base increases the importance of the middle ear cavity as the corridor to the skull base. The aim of this study was to define the middle ear as a route to the fundus (lateral end) of the internal acoustic canal and to propose feasible landmarks to the fundus. METHODS This was a cadaveric study; 34 adult cadaveric temporal bones and 2 dry bones were dissected with the aid of the endoscope and microscope to show the anatomy of the transcanal approach to the middle ear and fundus of the internal acoustic canal. RESULTS In the middle ear cavity, the cochleariform process is one of the key landmarks for accessing the fundus of the internal acoustic canal. The triangle formed by the anterior and posterior edges of the overhang of the round window and the cochleariform process provides a landmark to start drilling the bone to access the fundus of the internal acoustic canal. CONCLUSIONS The external acoustic canal and middle ear cavity combined, using endoscopic guidance, can provide a route to the fundus of the internal acoustic canal. A triangular landmark crossing the promontory has been described for reaching the meatal fundus. This transcanal approach requires an understanding of the relationship between the middle ear cavity and the fundus of the internal acoustic canal and provides a potential new area of cooperation between otology and neurosurgery for accessing pathology in this and the bordering skull base.

Quantitative anatomical analysis and clinical experience with mini-pterional and mini-orbitozygomatic approaches for intracranial aneurysm surgery.

OBJECTIVE The aim of this investigation was to modify the mini-pterional and mini-orbitozygomatic (mini-OZ) approaches in order to reduce the amount of tissue traumatization caused and to compare the use of the 2 approaches in the removal of circle of Willis aneurysms based on the authors' clinical experience and quantitative analysis. METHODS Three formalin-fixed adult cadaveric heads injected with colored silicone were examined. Surgical freedom and angle of attack of the mini-pterional and mini-OZ approaches were measured at 9 anatomical points, and the measurements were compared. The authors also retrospectively reviewed the cases of 396 patients with ruptured and unruptured single aneurysms in the circle of Willis treated by microsurgical techniques at their institution between January 2006 and November 2014. RESULTS A significant difference in surgical freedom was found in favor of the mini-pterional approach for access to the ipsilateral internal carotid artery (ICA) and middle cerebral artery (MCA) bifurcations, the most distal point of the ipsilateral posterior cerebral artery (PCA), and the basilar artery (BA) tip. No statistically significant differences were found between the mini-pterional and mini-OZ approaches for access to the posterior clinoid process, the most distal point of the superior cerebellar artery (SCA), the anterior communicating artery (ACoA), the contralateral ICA bifurcation, and the most distal point of the contralateral MCA. A trend toward increasing surgical freedom was found for the mini-OZ approach to the ACoA and the contralateral ICA bifurcation. The lengths exposed through the mini-OZ approach were longer than those exposed by the mini-pterional approach for the ipsilateral PCA segment (11.5 ± 1.9 mm) between the BA and the most distal point of the P2 segment of the PCA, for the ipsilateral SCA (10.5 ± 1.1 mm) between the BA and the most distal point of the SCA, and for the contralateral anterior cerebral artery (ACA) (21 ± 6.1 mm) between the ICA bifurcation and the most distal point of the A2 segment of the ACA. The exposed length of the contralateral MCA (24.2 ± 8.6 mm) between the contralateral ICA bifurcation and the most distal point of the MCA segment was longer through the mini-pterional approach. The vertical angle of attack (anteroposterior direction) was significantly greater with the mini-pterional approach than with the mini-OZ approach, except in the ACoA and contralateral ICA bifurcation. The horizontal angle of attack (mediolateral direction) was similar with both approaches, except in the ACoA, contralateral ICA bifurcation, and contralateral MCA bifurcation, where the angle was significantly increased in the mini-OZ approach. CONCLUSIONS The mini-pterional and mini-OZ approaches, as currently performed in select patients, provide less tissue traumatization (i.e., less temporal muscle manipulation, less brain parenchyma retraction) from the skin to the aneurysm than standard approaches. Anatomical quantitative analysis showed that the mini-OZ approach provides better exposure to the contralateral side for controlling the contralateral parent arteries and multiple aneurysms. The mini-pterional approach has greater surgical freedom (maneuverability) for ipsilateral circle of Willis aneurysms.

The white matter tracts of the cerebrum in ventricular surgery and hydrocephalus.

OBJECTIVE The relationship of the white matter tracts to the lateral ventricles is important when planning surgical approaches to the ventricles and in understanding the symptoms of hydrocephalus. The authors' aim was to explore the relationship of the white matter tracts of the cerebrum to the lateral ventricles using fiber dissection technique and MR tractography and to discuss these findings in relation to approaches to ventricular lesions. METHODS Forty adult human formalin-fixed cadaveric hemispheres (20 brains) and 3 whole heads were examined using fiber dissection technique. The dissections were performed from lateral to medial, medial to lateral, superior to inferior, and inferior to superior. MR tractography showing the lateral ventricles aided in the understanding of the 3D relationships of the white matter tracts with the lateral ventricles. RESULTS The relationship between the lateral ventricles and the superior longitudinal I, II, and III, arcuate, vertical occipital, middle longitudinal, inferior longitudinal, inferior frontooccipital, uncinate, sledge runner, and lingular amygdaloidal fasciculi; and the anterior commissure fibers, optic radiations, internal capsule, corona radiata, thalamic radiations, cingulum, corpus callosum, fornix, caudate nucleus, thalamus, stria terminalis, and stria medullaris thalami were defined anatomically and radiologically. These fibers and structures have a consistent relationship to the lateral ventricles. CONCLUSIONS Knowledge of the relationship of the white matter tracts of the cerebrum to the lateral ventricles should aid in planning more accurate surgery for lesions within the lateral ventricles.

Fiber Tracts of the Medial and Inferior Surfaces of the Cerebrum.

OBJECTIVE: Fiber dissection studies of the cerebrum have focused on the lateral surface. No comparable detailed studies have been done on the medial and inferior surfaces. The object of this study was to examine the fiber tracts, cortical, and subcortical structures of the medial and inferior aspects of the brain important in planning operative approaches along the interhemispheric fissure, parafalcine area, and basal surfaces of the cerebrum. METHODS: Twenty formalin-fixed human hemispheres (10 brains) were examined by fiber dissection technique under ×6-×40 magnifications. RESULTS: The superior longitudinal fasciculus I, cingulum, inferior longitudinal fasciculus, uncinate fasciculus, optic radiations, tapetum, and callosal fibers were dissected step by step from medial to lateral, exposing the nucleus accumbens, subthalamic nucleus, red nucleus, and central midline structures (fornix, stria medullaris, and stria terminalis). Finally, the central core structures were dissected from medial to lateral. CONCLUSIONS: Understanding the fiber network underlying the medial and inferior aspects of the brain is important in surgical planning for approaches along the interhemispheric fissure, parafalcine area, and basal surfaces of the cerebrum.

Comparative anatomical analysis of the transcallosal-transchoroidal and transcallosal-transforniceal-transchoroidal approaches to the third ventricle.

OBJECTIVE Access to the third ventricle is a veritable challenge to neurosurgeons. In this context, anatomical and morphometric studies are useful for establishing the limitations and advantages of a particular surgical approach. The transchoroidal approach is versatile and provides adequate exposure of the middle and posterior regions of the third ventricle. However, the fornix column limits the exposure of the anterior region of the third ventricle. There is evidence that the unilateral section of the fornix column has little effect on cognitive function. This study compared the anatomical exposure afforded by the transforniceal-transchoroidal approach with that of the transchoroidal approach. In addition, a morphometric evaluation of structures that are relevant to and common in the 2 approaches was performed. METHODS The anatomical exposure provided by the transcallosal-transchoroidal and transcallosal-transforniceal-transchoroidal approaches was compared in 8 fresh cadavers, using a neuronavigation system. The working area, microsurgical exposure area, and angular exposure on the longitudinal and transversal planes of 2 anatomical targets (tuber cinereum and cerebral aqueduct) were compared. Additionally, the thickness of the right frontal lobe parenchyma, thickness of the corpus callosum trunk, and longitudinal diameter of the interventricular foramen were measured. The values obtained were submitted to statistical analysis using the Wilcoxon test. RESULTS In the quantitative evaluation, compared with the transchoroidal approach, the transforniceal-transchoroidal approach provided a greater mean working area (transforniceal-transchoroidal 150 ± 11 mm2; transchoroidal 121 ± 8 mm2; p < 0.05), larger mean microsurgical exposure area (transforniceal-transchoroidal 101 ± 9 mm2; transchoroidal 80 ± 5 mm2; p < 0.05), larger mean angular exposure area on the longitudinal plane for the tuber cinereum (transforniceal-transchoroidal 71° ± 7°; transchoroidal 64° ± 6°; p < 0.05), and larger mean angular exposure area on the longitudinal plane for the cerebral aqueduct (transforniceal-transchoroidal 62° ± 6°; transchoroidal 55° ± 5°; p < 0.05). No differences were observed in angular exposure along the transverse axis for either anatomical target (tuber cinereum and cerebral aqueduct; p > 0.05). The mean thickness of the right frontal lobe parenchyma was 35 ± 3 mm, the mean thickness of the corpus callosum trunk was 10 ± 1 mm, and the mean longitudinal diameter of the interventricular foramen was 4.6 ± 0.4 mm. In the qualitative assessment, it was noted that the transforniceal-transchoroidal approach led to greater exposure of the third ventricle anterior region structures. There was no difference between approaches in the exposure of the structures of the middle and posterior region. CONCLUSIONS The transforniceal-transchoroidal approach provides greater surgical exposure of the third ventricle anterior region than that offered by the transchoroidal approach. In the population studied, morphometric analysis established mean values for anatomical structures common to both approaches.

The double massa intermedia.

BACKGROUND: To describe the rare finding of a double massa intermedia (MI). Typically, the MI (interthalamic adhesion) is a single bridge of gray matter connecting the medial surfaces of the thalami. METHODS: Twelve formalin- and alcohol-fixed human third ventricles were examined from superior to inferior by fiber dissection technique under ×6 to ×40 magnifications and with the endoscope. RESULTS: In all hemispheres, the anterior and posterior commissure were defined. The MI, which bridges the medial surfaces of the thalami, was defined in all hemispheres. In one hemisphere, there was a second bridge between the thalami, located posteroinferior to the common MI. Endoscopic view confirmed that there was a second MI in this specimen. The MI usually traverses the third ventricle posterior to the foramen of Monro and connects the paired thalami. The MI is an important landmark during endoscopic and microscopic surgeries of the third ventricle. Although a double MI is very rare, surgeons should be aware of the possibility in their surgical planning. CONCLUSION: The surgeon should be aware of the possibility of a double MI to avoid confusion during third ventricle surgery.

Infraorbital nerve: a surgically relevant landmark for the pterygopalatine fossa, cavernous sinus, and anterolateral skull base in endoscopic transmaxillary approaches.

OBJECTIVE Endoscopic transmaxillary approaches (ETMAs) address pathology of the anterolateral skull base, including the cavernous sinus, pterygopalatine fossa, and infratemporal fossa. This anatomically complex region contains branches of the trigeminal nerve and external carotid artery and is in proximity to the internal carotid artery. The authors postulated, on the basis of intraoperative observations, that the infraorbital nerve (ION) is a useful surgical landmark for navigating this region; therefore, they studied the anatomy of the ION and its relationships to critical neurovascular structures and the maxillary nerve (V2) encountered in ETMAs. METHODS Endoscopic anatomical dissections were performed bilaterally in 5 silicone-injected, formalin-fixed cadaveric heads (10 sides). Endonasal transmaxillary and direct transmaxillary (Caldwell-Luc) approaches were performed, and anatomical correlations were analyzed and documented. Stereotactic imaging of each specimen was performed to correlate landmarks and enable precise measurement of each segment. RESULTS The ION was readily identified in the roof of the maxillary sinus at the beginning of the surgical procedure in all specimens. Anatomical dissections of the ION and the maxillary branch of the trigeminal nerve (V2) to the cavernous sinus suggested that the ION/V2 complex has 4 distinct segments that may have implications in endoscopic approaches: 1) Segment I, the cutaneous segment of the ION and its terminal branches (5-11 branches) to the face, distal to the infraorbital foramen; 2) Segment II, the orbitomaxillary segment of the ION within the infraorbital canal from the infraorbital foramen along the infraorbital groove (length 12 ± 3.2 mm); 3) Segment III, the pterygopalatine segment within the pterygopalatine fossa, which starts at the infraorbital groove to the foramen rotundum (13 ± 2.5 mm); and 4) Segment IV, the cavernous segment from the foramen rotundum to the trigeminal ganglion (15 ± 4.1 mm), which passes in the lateral wall of the cavernous sinus. The relationship of the ION/V2 complex to the contents of the cavernous sinus, carotid artery, and pterygopalatine fossa is described in the text. CONCLUSIONS The ION/V2 complex is an easily identifiable and potentially useful surgical landmark to the foramen rotundum, cavernous sinus, carotid artery, pterygopalatine fossa, and anterolateral skull base during ETMAs.

The cochlea in skull base surgery: an anatomy study.

OBJECTIVE The object of this study was to examine the relationships of the cochlea as a guide for avoiding both cochlear damage with loss of hearing in middle fossa approaches and injury to adjacent structures in approaches directed through the cochlea. METHODS Twenty adult cadaveric middle fossae were examined using magnifications of ×3 to ×40. RESULTS The cochlea sits below the floor of the middle fossa in the area between and below the labyrinthine segment of the facial nerve and greater petrosal nerve (GPN) and adjacent to the lateral genu of the petrous carotid. Approximately one-third of the cochlea extends below the medial edge of the labyrinthine segment of the facial nerve, geniculate ganglion, and proximal part of the GPN. The medial part of the basal and middle turns are the parts at greatest risk in drilling the floor of the middle fossa to expose the nerves in middle fossa approaches to the internal acoustic meatus and in anterior petrosectomy approaches. Resection of the cochlea is used selectively in extending approaches through the mastoid toward the lateral edge of the clivus and front of the brainstem. CONCLUSIONS An understanding of the location and relationships of the cochlea will reduce the likelihood of cochlear damage with hearing loss in approaches directed through the middle fossa and reduce the incidence of injury to adjacent structures in approaches directed through the cochlea.

Microsurgical Approaches to the Ambient Cistern Region: An Anatomic and Qualitative Study.

OBJECTIVE: We used microscopy to conduct qualitative and quantitative analysis of 4 surgical approaches commonly used in the surgery of the ambient cistern: infratentorial supracerebellar (SC), occipital interhemispheric, subtemporal (ST), and transchoroidal (TC). In addition, we performed a parahippocampal gyrus resection in the ST context. METHODS: Each approach was performed in 3 cadaveric heads (6 sides). After the microscopic anatomic dissection, the parahippocampal gyrus was resected through an ST approach. The qualitative analysis was based on anatomic observation and the quantitative analysis was based on the linear exposure of vascular structures and the area of exposure of the ambient cistern region. RESULTS: The ST approach provided good exposure of the inferior portion of the cistern and of the proximal segments of the posterior cerebral artery. After the resection of the parahippocampal gyrus, the area of exposure improved in all components, especially the superior area. A TC approach provided the best exposure of the superior area compared with the other approaches. The posterolateral approaches (SC/occipital interhemispheric) to the ambient cistern region provided similar exposure of anatomic structures. There was a significant difference (P < 0.05) in linear exposure of the posterior cerebral artery when comparing the ST/TC and ST/SC approaches. CONCLUSIONS: This study has demonstrated that surgical approaches expose dissimilarly the different regions of the ambient cistern and an approach should be selected based on the specific need of anatomic exposure.

Fiber tracts of the dorsal language stream in the human brain.

OBJECT The aim of this study was to examine the arcuate (AF) and superior longitudinal fasciculi (SLF), which together form the dorsal language stream, using fiber dissection and diffusion imaging techniques in the human brain. METHODS Twenty-five formalin-fixed brains (50 hemispheres) and 3 adult cadaveric heads, prepared according to the Klingler method, were examined by the fiber dissection technique. The authors' findings were supported with MR tractography provided by the Human Connectome Project, WU-Minn Consortium. The frequencies of gyral distributions were calculated in segments of the AF and SLF in the cadaveric specimens. RESULTS The AF has ventral and dorsal segments, and the SLF has 3 segments: SLF I (dorsal pathway), II (middle pathway), and III (ventral pathway). The AF ventral segment connects the middle (88%; all percentages represent the area of the named structure that is connected to the tract) and posterior (100%) parts of the superior temporal gyri and the middle part (92%) of the middle temporal gyrus to the posterior part of the inferior frontal gyrus (96% in pars opercularis, 40% in pars triangularis) and the ventral premotor cortex (84%) by passing deep to the lower part of the supramarginal gyrus (100%). The AF dorsal segment connects the posterior part of the middle (100%) and inferior temporal gyri (76%) to the posterior part of the inferior frontal gyrus (96% in pars opercularis), ventral premotor cortex (72%), and posterior part of the middle frontal gyrus (56%) by passing deep to the lower part of the angular gyrus (100%). CONCLUSIONS This study depicts the distinct subdivision of the AF and SLF, based on cadaveric fiber dissection and diffusion imaging techniques, to clarify the complicated language processing pathways.

Surgical anatomy and utility of pedicled vascularized tissue flaps for multilayered repair of skull base defects.

OBJECT The objective of this study was to describe the surgical anatomy and technical nuances of various vascularized tissue flaps. METHODS The surgical anatomy of various tissue flaps and their vascular pedicles was studied in 5 colored silicone-injected anatomical specimens. Medical records were reviewed of 11 consecutive patients who underwent repair of extensive skull base defects with a combination of various vascularized flaps. RESULTS The supraorbital, supratrochlear, superficial temporal, greater auricular, and occipital arteries contribute to the vascular supply of the pericranium. The pericranial flap can be designed based on an axial blood supply. Laterally, various flaps are supplied by the deep or superficial temporal arteries. The nasoseptal flap is a vascular pedicled flap based on the nasoseptal artery. Patients with extensive skull base defects can undergo effective repair with dual flaps or triple flaps using these pedicled vascularized flaps. CONCLUSIONS Multiple pedicled flaps are available for reconstitution of the skull base. Knowledge of the surgical anatomy of these flaps is crucial for the skull base surgeon. These vascularized tissue flaps can be used effectively as single or combination flaps. Multilayered closure of cranial base defects with vascularized tissue can be used safely and may lead to excellent repair outcomes.