Olivary body exposure through far lateral and lower retrosigmoid approaches. Comparative analysis of the exposed surface and angle of attack.

OBJECTIVES: Throughout neurosurgical history, the treatment of intrinsic lesions located in the brainstem has been subject of much controversy. The brainstem is the anatomical structure of the central nervous system (CNS) that presents the highest concentration of nuclei and fibers, and its simple manipulation can lead to significant morbidity and mortality. Once one of the safe entry points at the medulla oblongata has been established, we wanted to evaluate the safest approach to the olivary body (the most used safe entry zone on the anterolateral surface of the medulla oblongata). The proposed objective was to evaluate the working channel from the surface of each of the far lateral and retrosigmoid approaches to the olivary body: distances, angles of attack and channel content. MATERIAL AND METHODS: To complete this work, a total of 10 heads injected with red/blue silicone were used. A total of 40 approaches were made in the 10 heads used (20 retrosigmoid and 20 far lateral). After completing the anatomical study and obtaining the data referring to all the approaches performed, it was decided to expand the sample of this research study by using 30 high-definition magnetic resonance imaging of anonymous patients without cranial or cerebral pathology. The reference points used were the same ones defined in the anatomical study. After defining the working channels in each of the approaches, the working distances, angle of attack, exposed surface, and the number of neurovascular structures present in the central trajectory were analyzed. RESULTS: The distances to the cranial and medial region of the olivary body were 52.71 mm (SD 3.59) from the retrosigmoid approach and 27.94 mm (SD 3.99) from the far lateral; to the most basal region of the olivary body, the distances were 49.93 (SD 3.72) from the retrosigmoid approach and 18.1 mm (SD 2.5) from the far lateral. The angle of attack to the caudal region was 19.44° (SD 1.3) for the retrosigmoid approach and 50.97° (SD 8.01) for the far lateral approach; the angle of attack to the cranial region was 20.3° (SD 1.22) for the retrosigmoid and 39.9° (SD 5.12) for the far lateral. Regarding neurovascular structures, the probability of finding an arterial structure is higher for the lateral far, whereas a neural structure will be more likely from a retrosigmoid approach. CONCLUSIONS: As conclusions of this work, we can say that far lateral approach presents more favorable conditions for the microsurgical treatment of intrinsic bulbar and bulbomedullary lesions approached through the caudal half of the olivary body. In those cases of bulbar and pontine-bulbar lesions approached through the cranial half of the olivary body, the retrosigmoid approach can be considered for selected cases.

The temporary resection of the cranial vault by Wilhelm Wagner (1848-1900) instead of trepanation: the cornerstone of the modern craniotomy.

In this paper, the authors trace the history of cranial temporary resection, described by Wilhelm Wagner (1848-1900) in 1889, which changed the paradigm of the cranial opening from trephining to the craniotomy. The objective of the temporary resection was to obtain wide openings in the skull, keeping the cranial flap attached to the soft tissues to maintain bone vitality. The cranial temporary resection was reproduced by the authors in an anatomical study faithfully following the original technique, demonstrating the feasibility of the surgical procedure as described by Wagner. Surgical steps include a large omega-shaped skin incision and a beveled cut of the bone with the chisel and mallet until reaching the dura mater, lifting the bone flap en bloc along with all superficial soft tissues. A literature review shows that the temporary cranial resection became a great success at that time because it allowed physicians to improve a number of constraints of the cranial opening using the crown trephine: bone vitality; a wide cranial window; easy, safe, and quick surgery; and economy of surgical instruments. The crude, primitive proposal of the temporary resection was ameliorated to quickly build the successful model of the modern craniotomy.

Retrosigmoid Approach: A Simple and Safe Way to Resect Intrinsic Pontomedullary Lesions.

Objectives The main objective of this article is to describe a simple and safe protocol for the microsurgical management of ventrally located intrinsic pontomedullary lesions based on the retrosigmoid approach, cortectomy performed utilizing safe entry zones of the pons and medulla, and a delicate microsurgical resection. The intraoperative protocol includes redundant procedures that provide security in decision-making during surgery. Design A prospective series of 11 cases is presented. All patients were studied following the same clinical and imaging workup. A regular retrosigmoid craniotomy surgical approach was utilized. The peritrigeminal area in the pons and the olivary area in the medulla were considered as the safe entry zones. Neuronavigation of the white fiber tracts and electrophysiological monitoring were used as intraoperative aids to locate the lesions, the safe entry zones, and the placement of the cortectomy. Results Six lesions were pontine, two medullary, and the remaining six pontomedullary. Eight lesions were cavernomas, while the remaining three tumors. Overall, we obtained a postoperative functional improvement in the affected cranial nerves in 90.1% of the patients and a total or partial recovery of long ascending or descending pathway symptoms in 72.3% of the patients. All the patients were satisfied with the procedure and the results. Conclusions Radical resection of ventral intrinsic pontomedullary lesions displays a high degree of intraoperative reliability, and a good clinical result is possible using simple surgical procedures. The anatomical references are the first element in the decision-making process during surgery.

Magnetic Resonance Imaging Surveillance for Vestibular Schwannoma After Microsurgical Resection Using a Retrosigmoid Transmeatal Approach.

BACKGROUND: Vestibular schwannoma (VS) is a benign, usually slow-growing tumor. The drawback of radical microsurgical VS resection is the increased likelihood of neurologic injury, forcing surgeons to leave a tumor remnant in some cases. We evaluated the prognostic value of magnetic resonance imaging (MRI) enhancement patterns to determine the risk of tumor regrowth. METHODS: This clinical study included 30 patients (20 women and 10 men) with VS who underwent surgery via a retrosigmoid transmeatal approach. The extent of resection was assessed by MRI 6 months after surgery. Two subtypes of intracanalicular linear enhancement were defined: linear enhancement of the walls of the internal auditory canal (IAC) or in the cerebellopontine angle (CPA) and linear enhancement covering the end of the IAC. All patients included in the study underwent follow-up MRI every year for at least 6 years. RESULTS: Intracanalicular nodular enhancement suggestive of a tumor remnant was seen in the IAC in 11 patients (36.7%). Volume of nodular enhancements was <0.5 cm3 when measurable. The enhancement remained stable throughout follow-up except in 2 cases that showed a slight decrease in size and in 1 case with an initial tumor remnant of 0.5 cm3 showing a slight increase over the years. Eighteen patients (60%) had linear enhancement in the IAC or in the CPA. No patients with linear enhancement showed nodular enhancement. CONCLUSIONS: Although specific monitoring protocols can be designed based on MRI findings 6 months after microsurgical VS resection, follow-up should be maintained indefinitely given the slight possibility of very late regrowth.

Side-to-End Hypoglossal-Facial Neurorrhaphy for Treatment of Complete and Irreversible Facial Paralysis after Vestibular Schwannoma Removal by Means of a Retrosigmoid Approach: A Clinical and Anatomic Study.

BACKGROUND: Facial paralysis secondary to a complete and irreversible anatomic or functional lesion of the facial nerve (FN) causes severe functional and psychological disorders for the patient. A large number of surgical techniques have therefore been developed for FN repair. Our objective was to propose a surgical FN reanimation protocol for patients with irreversible anatomic or functional postsurgical injury of the FN in the cerebellopontine angle after vestibular schwannoma resection. METHODS: The clinical study included a total of 16 patients undergoing side-to-end hypoglossal-facial neurorrhaphy (SEHFN) since 2010, in which the FN injury was always secondary to vestibular schwannoma surgery in the cerebellopontine angle using a retrosigmoid approach. All patients had complete clinical facial paralysis at the time of the SEHFN. The anatomic study was conducted using 3 heads and necks (6 SEHFN). RESULTS: Twelve months after surgery, FN function assessment with the House and Brackmann scale showed 2 patients with grade II, 13 patients with grade III, and only 1 patient with grade IV, and after 2 years, 4 patients had grade II, 11 patients had grade III, and 1 patient had grade IV. The average length of the anastomotic translocation portion of the FN in the anatomic study was 34.76 mm. CONCLUSIONS: Side-to-end epineural suture of the FN, mobilizing its mastoid segment on the hypoglossal nerve with partial section of the dorsal aspect of the hypoglossal nerve, is a safe anatomic surgical technique for FN reanimation with outstanding clinical results.

White Matter Relationships Examined by Transillumination Technique Using a Lateral Transcortical Parietal Approach to the Atrium: Three-Dimensional Images and Surgical Considerations.

BACKGROUND: Numerous lesions are found in the ventricular atrium (VA). Access is gained through many white matter tracts with great relevance and specific neurologic functions. It is important to understand the configuration of the most relevant structures surrounding this zone and, thus, select the safest entry zone on the lateral cerebral surface. OBJECTIVE: We studied the white matter layers traversed in the lateral transcortical parietal approach through the intraparietal sulcus (IPS), adding a transillumination technique. With this knowledge, we selected the safest highway to improve this particular approach. METHODS: An in-depth study of the white matter tracts was performed on 24 cerebral hemispheres (12 human whole brains). The Klingler technique and microsurgical dissection techniques were used under ×6 to ×40 magnification. The transillumination technique (torch illuminating the ventricular cavity) was used to expose the layers surrounding the VA and, thus, guide the dissection. RESULTS: Taking the IPS on the cerebral surface as a reference, we identified the following white matter layers ordered from the surface to the ependyma: U fibers, superior longitudinal fascicle, arcuate fascicle, vertical occipital fascicle, sagittal stratum with the optic radiations, and tapetum fibers. The transillumination technique allowed for the easier identification of the white matter deep periventricular layers. CONCLUSIONS: Knowledge of the main fascicles in the path and neighborhood of the VA allowed us to understand how certain neurologic functions can be affected by lesions at this level and to select the most appropriate way to avoid damaging relevant fascicles.

Combined Extradural and Intradural Pterional Transzygomatic Approach to Large Sphenoid Wing Meningiomas. Operative Technique and Surgical Results.

Objectives Describe a unique and safe surgical procedure for the microsurgical management of large sphenoid wing meningiomas (SWMs) aimed to a radical resection of these tumors. Design A prospective series of 26 cases with SWMs larger than 3 cm in one of its main diameter is presented. All patients were studied following the same clinical and imaging procedures. The surgical approach was through a pterional transzygomatic craniotomy. The surgical procedure has the following steps: 1. Extradural tumor devascularization and resection of the hyperostotic and/or infiltrated bone and then intradurally; 2. Intradural tumor debunking; 3. Microdissection of vascular branches and perforators from the capsule; 4. Identification of the optic and oculomotor nerves and internal carotid artery; 5. Tumor capsule dissection and resection; 6. Dural resection or cauterization; 7. Dural and bone reconstruction and closing. Results All lesions were completely removed. Most complications were transient. The most relevant complication was a large middle cerebral artery infarct with permanent hemiplegia despite a decompressive craniotomy. Conclusion Large SWMs can be considered as a single pathology regarding the surgical approach and intraoperative microsurgical procedure strategies. The pterional transzygomatic approach allows an extradural devascularization of the tumor and an extensive bone resection that facilitates the intradural stage of tumor resection. The proposed approach allows a wide and radical resection of the duramater and bone that increases the Simpson grade. However, surgery does not control other biological or molecular prognostic factors involved in tumor recurrence.

[Transzygomatic pterional approach. Part 2: Surgical experience in the management of skull base pathology]. / Abordaje pterional transcigomático. Parte 2: Experiencia quirúrgica en la patología de base de cráneo.

OBJECTIVES: To present our experience with the transzygomatic pterional approach in the treatment of neurosurgical pathology of the base of the skull located in the middle cranial fossa and surrounding areas. METHOD: A retrospective study of pathological findings, surgical outcomes and complications in a series of 31 cases operated on between 2009 and 2011 using a transzygomatic pterional approach. RESULTS: The lesions involved the sphenoid wing (25.9%), several regions due to invasive growth pattern (19.5%), the temporal lobe (16.1%) and cavernous sinus (12.9%). The others were located in the floor of the middle fossa, Meckel's cave, incisural space, cisterns and infratemporal region. The pathological nature of the lesions was: benign meningioma (42%), temporal lobe tumour (19.5%), vascular disease (12.9%), inflammatory lesions (6.4%), atypical meningioma (6.4%), epidermoid cyst (6.4%), neurinoma (3.2%) and poorly differentiated infratemporal carcinoma (3.2%). The approach was usually combined extra-intradural (58.1%) and, less frequently, just extradural (16.1%) or intradural (25.8%). Approach-related complications were minor: haematomas in the wound not requiring treatment (67.8%), superior transient facial paresis (9.7%), transient temporomandibular joint dysfunction (12.9%) and atrophy of the temporal muscle (16.2%). There were no hardware-related complications or cosmetic issues related to the osteotomy and posterior osteosynthesis of the zygomatic arch. CONCLUSIONS: The pterional approach combined with osteotomy of the zygomatic arch allows mobilising the temporalis muscle away from the temporal fossa, consequently exposing its entire surface to complete the temporal craniotomy up to the middle fossa; it helps to access and treat pathology in this region or it can be used as a corridor to approach surrounding areas.

[Transzygomatic pterional approach. Part 1: anatomical study]. / Abordaje pterional transcigomático. Parte 1: estudio anatómico.

OBJECTIVE: Cadaveric study of the anatomical structures of the temporal region, as well as the technical aspects of the transzygomatic pterional approach. MATERIAL AND METHODS: Six human formalin-fixed heads, whose arterial circulatory system was injected with red-dyed silicone, were studied (12 temporal regions). Dissections were performed using standard microsurgical techniques and instruments. RESULTS: We confirm the existence of a double superficial and deep layer within the superficial temporal fascia, which makes possible to perform the zygomatic arch osteotomy without damaging the temporal muscle and the branches of the superficial temporal artery and the facial nerve. The shape and location of the osteotomies to preserve the témporo-mandibular joint and ligaments and to provide correct reconstruction of the bone flap are described. We compare the exposure of intracranial structures obtained by this approach with those obtained by the conventional pterional approach and the orbitozygomatic approach. CONCLUSIONS: The transzygomatic pterional approach provides wide exposure of the temporal lobe for trans-sylvian, pre-temporal and/or subtemporal approaches in selected cases of neurosurgical pathology. A detailed anatomical knowledge of the temporal region is necessary to achieve the best surgical, functional and cosmetic results.

Abordaje pterional transcigomático. Parte 2: Experiencia quirúrgica en la patología de base de cráneo / No disponible

Objetivos Exponer la experiencia con el abordaje pterional transcigomático en el tratamiento de la patología neuroquirúrgica de la base de cráneo situada en la fosa craneal media y zonas vecinas. Material y método Estudio retrospectivo de la patología, resultados quirúrgicos y complicaciones obtenidos en 31 casos intervenidos entre 2009 y 2011 usando un abordaje pterional transcigomático. Resultados Se han intervenido lesiones del ala del esfenoides (25,9%), afectando varias regiones por su crecimiento invasivo (19,5%), del lóbulo temporal (16,1%) y del seno cavernoso (12,9%), involucrando el resto al suelo de la fosa media, cavum de Meckel, región incisural, cisternas y región infratemporal. La naturaleza de las lesiones intervenidas fue la siguiente: meningioma benigno (42%), tumor parenquimatoso (19,5%), patología vascular (12,9%), lesiones inflamatorias (6,4%), meningioma atípico (6,4%), tumor epidermoide (6,4%), neurinoma (3,2%) y carcinoma pobremente diferenciado infratemporal (3,2%). La mayor parte de las veces el abordaje fue combinado extra-intradural (58,1%), y con menor frecuencia extradural (16,1%) o intradural (25,8%) puro. Las complicaciones relacionadas con el abordaje fueron menores: hematomas en la herida que no requirieron tratamiento (67,8%), paresia facial superior transitoria (9,7%), de disfunción transitoria de articulación temporomandibular (12,9%) y atrofia del músculo temporal (16,2%). No hubo ningún caso de aflojamiento de material ni problemas estéticos relacionados con la osteotomía y osteosíntesis del arco cigomático. Conclusiones La modificación del abordaje pterional asociando una osteotomía del arco cigomático, que permite rebatir el músculo temporal de toda la fosa temporal y exponer así toda su superficie para completar la craneotomía temporal hasta la base de la fosa media, nos facilita el acceso para tratar patología de la misma o utilizarla como corredor para el acceso a zonas vecinas (AU)

Abordaje pterional transcigomático. Parte 1: estudio anatómico / Transzygomatic pterional approach. Part 1: anatomical study

Objetivo: Estudio cadavérico de las estructuras anatómicas de la región temporal, así como de los aspectos técnicos del abordaje pterional transcigomático. Material y métodos: Fueron utilizados 6 especímenes cadavéricos (12 regiones temporales) previamente formolizados, cuyo sistema circulatorio arterial fue inyectado con silicona teñida de rojo. Las disecciones se realizaron utilizando el instrumental y la técnica microquirúrgica estándar. Resultados: Se confirma la existencia de una doble capa superficial y profunda en la fascia temporal superficial, lo que permite la osteotomía cigomática respetando la integridad del músculo temporal y de las ramas de la arteria temporal superficial y del nervio facial. Se detallan las líneas de la osteotomía para preservar la articulación témporo-mandibular y una correcta reposición del colgajo óseo. La exposición de estructuras intracraneales obtenida mediante dicho abordaje se compara favorablemente con aquellas obtenidas mediante el abordaje pterional convencional y el abordaje órbito-cigomático. Conclusiones: El abordaje pterional transcigomático ofrece una amplia exposición del lóbulo temporal para la realización de abordajes transsilvianos, pretemporales y/o subtemporales en casos seleccionados de patología neuroquirúrgica. Es necesario un detallado conocimiento anatómico de la región temporal para obtener los mejores resultados quirúrgicos, estéticos y funcionales (AU)

Objective: Cadaveric study of the anatomical structures of the temporal region, as well as the technical aspects of the transzygomatic pterional approach. Material and methods: Six human formalin-fixed heads, whose arterial circulatory system was injected with red-dyed silicone, were studied (12 temporal regions). Dissections were performed using standard microsurgical techniques and instruments. Results: We confirm the existence of a double superficial and deep layer within the superficial temporal fascia, which makes possible to perform the zygomatic arch osteotomy without damaging the temporal muscle and the branches of the superficial temporal artery and the facial nerve. The shape and location of the osteotomies to preserve the témporo-mandibular joint and ligaments and to provide correct reconstruction of the bone flap are described. We compare the exposure of intracranial structures obtained by this approach with those obtained by the conventional pterional approach and the orbitozygomatic approach. Conclusions: The transzygomatic pterional approach provides wide exposure of the temporal lobe for trans-sylvian, pre-temporal and/or subtemporal approaches in selected cases of neurosurgical pathology. A detailed anatomical knowledge of the temporal region is necessary to achieve the best surgical, functional and cosmetic results (AU)

Microsurgical Relations between Internal Carotid Artery-Posterior Communicating Artery (ICA-PComA) Segment Aneurysms and Skull Base: An Anatomoclinical Study.

Purpose The study of the clinical, anatomic, imaging, and microsurgical characteristics of the aneurysms of the internal carotid-posterior communicating artery (ICA-PComA) segment and their relationships with the skull base structures. Methods The anatomic relationships of PComA with neurovascular elements and skull base structures were studied in cadavers. The clinical, imaging, and microsurgical findings of 84 microsurgically treated ICA-PComA aneurysms compiled in a prospective database were reviewed. Results The most important anatomic relations of the PComA and ICA-PComA aneurysms are with the oculomotor nerve around the oculomotor triangle that forms the roof of the cavernous sinus. Aneurysms of the ICA-PComA are classified according to the orientation of the aneurysmal sac in infratentorial, supratentorial, and tentorial. Infratentorial aneurysms frequently present with subarachnoid hemorrhage (SAH) and oculomotor nerve paralysis. They have relations with skull base structures that often make it necessary to totally or partially resect the anterior clinoid process (6.7%) or anterior petroclinoid dural fold (15%). Supratentorial aneurysms course with SAH and without oculomotor nerve involvement, but they often are associated with intracranial hematoma. Conclusion ICA-PComA aneurysms have complex anatomic relations. The orientation of the aneurysmal fundus induces relevant differences in the anatomic relations, clinical presentation, and microsurgical approach to ICA-PComA aneurysms.

Tumoral presentation of primary central nervous system lymphomatoid granulomatosis.

PURPOSE: Lymphomatoid granulomatosis (LYG) is an angiocentric Epstein-Barr virus (EBV) related B-cell proliferation associated with a reactive T-cell component with an uncertain malignant potential. LYG present at diagnosis as a mass lesion in the central nervous system (CNS) is rare, and only a few cases have been reported. In this article we present four cases of tumoral CNS-LYG and propose some guidelines for its management. METHODS: Clinical, pathological, imaging and laboratory information of four immunocompetent patients, all of them treated surgically, with a final diagnosis of LYG and presenting with an isolated intracranial tumoral mass is reviewed. RESULTS: Two parenchymal lesions were located in the cerebellum and temporal lobe, and the other two involved the cavernous sinus. At surgery they were avascular, hard, lard-like, necrotic and plastic well-defined lesions, with invasion of the leptomeninges and thrombosis of the small leptomeningeal arteries and veins. Intraoperative pathology excluded any tumor. Pathological studies showed a polymorphic and polyclonal infiltration around, in the wall and into the lumen of medium-sized cortical and leptomeningeal vessels causing their obstruction and tissular necrosis. EBV-infected cells were present. CONCLUSIONS: Making a preoperative diagnosis of CNS-LYG appearing initially as a tumoral mass is difficult because of the lack of pathognomonic clinical symptoms or imaging signs. Surgical management with radical resection of the mass is almost always followed by the long-term local control of the lesion, although the disease may have a disseminated, systemic or malignant evolution.

Multimodal navigation in the functional microsurgical resection of intrinsic brain tumors located in eloquent motor areas: role of tractography.

OBJECT: Nowadays the role of microsurgical management of intrinsic brain tumors is to maximize the volumetric resection of the tumoral tissue, minimizing the postoperative morbidity. The purpose of this paper was to study the benefits of an original protocol developed for the microsurgical treatment of tumors located in eloquent motor areas where the navigation and electrical stimulation of motor subcortical pathways have been implemented. METHODS: A total of 17 patients who underwent resection of cortical or subcortical tumors in motor areas have been included in the series. The preoperative planning for multimodal navigation was done by integrating anatomical studies, motor functional MR (fMR) imaging, and subcortical pathway volumes generated by diffusion tensor (DT) imaging. Intraoperative neuromonitoring included motor mapping by direct cortical stimulation (CS) and subcortical stimulation (sCS), and localization of the central sulcus by using cortical multipolar electrodes and the N20 wave inversion technique. The location of all cortically and subcortically stimulated points with positive motor response was stored in the navigator and correlated with the cortical and subcortical motor functional structures defined preoperatively. RESULTS: The mean tumoral volumetric resection was 89.1 +/- 14.2% of the preoperative volume, with a total resection (> or = 100%) in 8 patients. Preoperatively a total of 58.8% of the patients had some kind of motor neurological deficit, increasing 24 hours after surgery to 70.6% and decreasing to 47.1% at 1 month later. There was a great correlation between anatomical and functional data, both cortically and subcortically. A total of 52 cortical points submitted to CS had positive motor response, with a positive correlation of 83.7%. Also, a total of 55 subcortical points had positive motor response; in these cases the mean distance from the stimulated point to the subcortical tract was 7.3 +/- 3.1 mm. CONCLUSIONS: The integration of anatomical and functional studies allows a safe functional resection of the brain tumors located in eloquent areas. Multimodal navigation allows integration and correlation among preoperative and intraoperative anatomical and functional data. Cortical motor functional areas are anatomically and functionally located preoperatively thanks to MR and fMR imaging and subcortical motor pathways with DT imaging and tractography. Intraoperative confirmation is done with CS and N20 inversion wave for cortical structures and with sCS for subcortical pathways. With this protocol the authors achieved a good volumetric resection in cortical and subcortical tumors located in eloquent motor areas, with an increase in the incidence of neurological deficits in the immediate postoperative period that significantly decreased 1 month later. Ongoing studies must define the safe limits for functional resection, taking into account the intraoperative brain shift. Finally, it must be demonstrated whether this protocol has any long-term benefit for patients by prolonging the disease-free interval, the time to recurrence, or the survival time.

Klippel-Feil syndrome associated with posterior fossa dermoid cyst. Case report.

A patient with association of Klippel-Feil syndrome and posterior fossa dermoid cyst is presented. The patient, a 36-year-old man, presented with an acute obstructive hydrocephalus due to the cyst and exhibited the typical triad of the Klippel-Feil abnormality with short neck, low hairline implantation and limited neck motion along with a complex cervical vertebrae fusion. The anatomical and clinical features as well as the pathophysiology of this rare association are discussed after a review of the literature.

ACoA angle measured by computed tomographic angiography and its relevance in the pterional approach for ACoA aneurysms.

The purpose of this study was to analyze the spatial disposition of the anterior communicating artery (ACoA) complex and the orientation of the ACoA plane by computed tomographic angiography with three-dimensional reconstruction (3D-CTA) and to evaluate the relevance of the orientation of the ACoA plane in the planification of the surgical approach to the ACoA complex aneurysms. The dominance of the right or left A1 segment of the anterior cerebral artery, the position of the A1-A2 junction in relation to the transverse plane and the angulation of plane of the ACoA traject were studied using 3D-CTA in 30 patients with subarachnoid hemorrhage. Twelve patients harbored an aneurysm on the ACoA complex and the most relevant anatomic characteristics of these lesions were recorded. In 56.7% of cases both A1 segments were similar in size, whereas in 33.3% of cases the left A1 segment was dominant and in the remaining 10% the right A1 segment was dominant. The position of the left A1-A2 junction was anterior to the transverse plane in 30% of cases with an angulation of the ACoA plane of 42+/-6 degrees. All patients with this anatomical arrangement and left A1 dominance (seven cases) harbored an aneurysm of the ACoA complex located on the left A1-A2 junction. The right A1-A2 junction was anterior to the transverse plane in 13.3% of cases with an angulation of the ACoA plane of 37+/-9 degrees. All patients in this situation and right A1 dominance (three cases) had an aneurysm on the ACoA complex. Finally, in 50% of cases the ACoA plane was on the transverse plane. In this group of cases only two patients harbored an aneurysm located on the ACoA segment. The dominance of an A1 segment of the anterior cerebral artery may develop anatomical changes in the ACoA complex due to the hemodynamic stress. The main result is the advance of the A1-A2 junction point in the dominant side and the angulation of the ACoA plane in relation to the transverse plane as well as the development of aneurismatic lesions. The angulation of the ACoA plane, in combination with the orientation of the aneurysm, must be included among the criteria for the selection of the route of the surgical approach. This information is given by the 3D-CTA. All of these data allows a pre-operative simulation of the surgical approach to the lesion for a safer clipping of the neck of the aneurysm.

Effects of prior anaesthesia on autotomy following sciatic transection in rats.

The animal model for chronic pain following sciatic nerve section in the rat has been studied varying the sensory afferents prior to nerve section, using the anaesthetic blocking of the sciatic nerve. The experimental parameters used were the day of onset of autotomy and the time course of autotomy. The results show that the anaesthetic blocking prior to nerve section significantly reduces the degree of autotomy.