Asem Salma

Deep Brain Stimulation for Neurological Disorders

Deep brain stimulation (DBS) involves the delivery of precise electrical signals to specific deep anatomical structures of the central nervous system, with the objective of altering or modulating neural functioning and achieving a reversible, adjustable and therapeutic or clinically beneficial effect. The exact mechanism of action of DBS is still the subject of ongoing investigations. However, based on extensive clinical investigations, it has become an established modality for the surgical treatment of advanced and medication intractable movement disorders such as Parkinsons disease, essential tremor and dystonia. DBS is also being investigated for conditions such as intractable epilepsy, neurobehavioral and psychiatric disorders such as treatment resistant depression, obsessive compulsive disorders, addiction, obesity, Alzheimers disease and traumatic brain injury. The advantage of DBS over older deep brain lesioning procedures is its reversibility and adjustability. The design of the DBS systems allows for dynamic adjustment of the effects of electrical stimulation by altering the contacts at which electrical pulses are delivered to the brain and changing the stimulation parameters of those pulses. The clinical results from studies on DBS show that it has great potential making it one of most promising fields which could be used to address challenging neurological problems.

Lateral supraorbital approach vs pterional approach: an anatomic qualitative and quantitative evaluation.

BACKGROUND: Several minimally invasive modifications of the standard pterional approach have been proposed recently. The lateral supraorbital approach is one of these modifications. OBJECTIVE: To provide a qualitative and quantitative anatomic comparison of the surgical exposure and the operability afforded by the standard pterional approach and the lateral supraorbital approach. METHODS: Eight pterional approaches and 8 lateral supraorbital approaches were used in 8 fresh human cadaver heads. One qualitative and 2 quantitative tools were used to assess the surgical exposure. RESULTS: Qualitatively, the lateral supraorbital approach has the advantages of reduced trauma to the temporalis muscle and exposure that is comparable to that provided by the standard pterional approach to the sellar and suprasellar regions. This approach offers limited exposure of the interpeduncular fossa compared with the pterional one. Quantitatively, the pterional approach provides a greater surgical volume than the lateral supraorbital approach (32.90 mL vs 23.60 mL with P < .05). Also, the pterional approach provides a greater associated surgical operability than the lateral supraorbital approach (exposure score of 66 and 53, respectively). However, the lateral supraorbital approach offers an equivalent access to the anterior communicating artery complex, optic nerve, optic chiasm, and sellar area (the exposure scores were 19 for both approaches). CONCLUSION: From an anatomic point of view, both approaches provide similar exposure to the sellar, suprasellar, and anterior communicating artery areas. The pterional approach provides better exposure of the retrosellar area. The ability to operate in the retrosellar area, as judged by our model, was higher with the pterional than with the lateral supraorbital approach.

Real Time Parallel Intraoperative Integration of Endoscopic, Microscopic, and Navigation Images: A Proof of Concept Based on Laboratory Dissections

Endoscope, microscope, and neuronavigation systems are integrated in neurosurgical procedures mainly by using a serial combination algorithm, where, the user must switch his/her field of view from one platform display to another. The integration of theses devices could be optimized by incorporating different displays into one viewing platform thus achieving a parallel combination. In this study, we investigated the feasibility and the applicability of parallel integration of microscopic, endoscopic, and neuronavigation images by real time displaying the endoscope and neuronavigation image datasets in the main operative microscope oculars. The proposed set-up was effective in displaying the three images dataset in an operationally actionable mode. Ergonomically, the ability of using the different image dataset without the need of taking the eyes off the microscope oculars did not disrupt the flow or the tempo of the operative procedure. However, new endoscopes specific to this application are recommended.

Placement of thoracolumbar pedicle screws using O-arm-based navigation: technical note on controlling the operational accuracy of the navigation system

Suboptimal placements of pedicle screws may lead to neurological and vascular complications. Computer-assisted image guidance has been shown to improve accuracy in spinal instrumentation. Checking the accuracy of the navigation system during pedicle screw placement is fundamental. We describe a novel technique of using continuous accuracy check of the navigation system during O-arm-based neuronavigation to instrument the thoracolumbar region. Forty thoracic and 42 lumbar screws were inserted in 12 patients. The Mirza evaluation system was used to evaluate the accuracy of the inserted screws. There was no neurological injury and no need to reposition any screw. The accuracy of the screws placement was excellent. Our technique of continuous at will operational accuracy check of the neuronavigation system is associated with extreme accuracy of screw placement, no need to bring a patient back to the operating room to reposition a pedicle screw, and with excellent outcome.

Extradural Endoscope-Assisted Subtemporal Posterior Clinoidectomy: A Cadaver Investigation Study

BACKGROUND Surgical treatment of distal basilar artery aneurysms is challenging because of the narrow surgical corridor, presence of vital perforating vessels, deep location, and difficulty in obtaining proximal control. OBJECTIVE To investigate using a cadaver model the feasibility of performing a transcranial extradural posterior clinoidectomy via a subtemporal route between V2 and V3 using an endoscope-microscope combination. METHODS Fourteen dissections were performed in 14 fresh cadaver heads. A standard pterional approach with removal of the zygomatic arch was followed by a 2-stage dissection to remove the posterior clinoid process. In stage 1 (microscopic stage), the area between the second and third trigeminal divisions (V2 and V3) was exposed and the anterior half of the bone between them was drilled to the sphenoid sinus cavity inferior to the carotid sulcus. In stage 2 (endoscopic stage), the drilling was continued to the carotid sulcus. Next, the endosteal layer of the dura lining the carotid sulcus was dissected from the bone that was then removed. At the end of this stage, the dura reflection that forms the posterior part of the pituitary capsule was exposed and the base of the posterior clinoid process was removed using a high-speed drill and curet. Finally, the dura was opened to confirm the removal of the posterior clinoid process. RESULTS It was possible to remove the posterior clinoid process in every specimen without any obvious anatomic injury to the surrounding structures. CONCLUSION This study demonstrated the feasibility of the resection of the posterior clinoid process extradurally. This maneuver could be incorporated in multiple cranial base approaches to the retrosellar area and interpeduncular cistern region.

A microanatomical map of the structures hidden in the middle fossa based on the facial nerve hiatus: measurements and their variability.

The aim of this study was to investigate the relationships/variations between the facial nerve hiatus (FNH) and middle cranial fossa neuro‐vascular structures. Twenty CT‐scanned middle cranial fossae of fresh adult cadavers were used; the greater superficial petrosal nerves, and critical neuro‐vascular structures were identified. Using the FNH as a reference point, a neuronavigation system was used to measure the distance between each structure and the FNH. The coefficient of variation (CV) was used to quantify the degree of variation among each distance. The mean distances and standard deviations between the various landmarks and the FNH, and the associated CV were analyzed. Furthermore, a microanatomical map of the structures hidden in the middle fossa based on the greater superficial petrosal nerve was generated. The most reliable relationships of the FNH were with the internal auditory canal (CV = 14.59), and with the vertical portion of the intrapetrous internal carotid artery (CV = 15.54). Our data demonstrate that the FNH can be used as anatomical landmark to plot the position of several hidden neurovascular structures when performing a middle‐fossa skull base approach. However, the pattern and the variation of these structures had to be recognized. Clin. Anat. 2013.

Accuracy validation in a cadaver model of cranial neuronavigation using a surface autoregistration mask.

BACKGROUND Image guidance systems are widely used in neurosurgical practice. OBJECTIVE To compare the operational accuracy of a neuronavigation system when registration was accomplished with a commercially available surface-based autoregistration system vs other fiducial-based registrations. METHODS We evaluated the operational accuracy of different registration methods in 20 cadaveric heads. Every specimen was prepared with 10 titanium microscrews functioning as external/internal targets and as bone fiducials. Six scalp fiducials were also affixed to each specimen that was registered with bone, scalp fiducials, and the autoregistration mask. The coordinates of all the target points were measured, first manually on the screen of the navigation system and then by touching the head of the implanted screw on the specimen. The difference between the real and virtual coordinates was calculated. RESULTS Means of the differences for external anterior targets were 1.96, 3.12, and 3.20 mm and 1.95, 3.24, and 3.19 mm for external posterior targets for the bone fiducials, adhesive fiducials, and autoregistration mask, respectively. Means of the differences for internal anterior targets were 2.60, 3.65, and 2.16 mm and 2.91, 3.83, and 2.41 mm for internal posterior targets for the bone fiducials, adhesive fiducials, and autoregistration mask, respectively. CONCLUSION Bone fiducial registration is associated with a statistically greater operational accuracy than scalp adhesive fiducials and the autoregistration mask in reaching anterior and posterior external targets (P < .001). Registration accomplished with the autoregistration mask is associated with a statistically greater operational accuracy in reaching internal targets than adhesive fiducials registration (P < .001) or bone fiducials registration (P < .05 and P < .01 for anterior and posterior targets, respectively).

Setting up a microneurosurgical skull base lab: technical and operational considerations

Microneurosurgical cadaveric dissections have become popular due to their usefulness in obtaining a working knowledge of the microneurosurgical anatomy in a controlled environment. This same controlled environment is also conducive to experiment with new surgical approaches. These factors have increased the number of microneurosurgical anatomic laboratories. Despite the increase in microneurosurgical laboratories, there is very little literature regarding the logistics of starting and maintaining a new neurosurgical laboratory. The aim of this paper is to provide a general road map and basic guidelines in starting and running a microneurosurgical dissection laboratory. The information in this paper is based on a review of the literature and on the experience we gained in organizing and managing the Dardinger Microneurosurgical Skull Base Laboratory at The Ohio State University.

An endoscopic, cadaveric analysis of the roof of the fourth ventricle

We performed endoscopic dissections of the roof of the fourth ventricle in eight fresh human cadaveric heads to characterize the endoscopic anatomy of the roof of the fourth ventricle and the anatomical configuration of the structures forming its roof. We also made three-dimensional (3D) silicone casts of the fourth ventricle in seven formalin-fixed specimens to evaluate the 3D configuration of the structures that create the roof of the fourth ventricle. The roof of the fourth ventricle can be divided into three zones. The upper zone is formed by the superior cerebellar peduncle and superior medullary velum and is associated with the lingula. The middle zone is formed by the inferior cerebellar peduncles and inferior medullary velum and is associated with the nodule in the midline and with the peduncle of the flocculus. The lower zone is formed by the tela choroidea and is associated with the tonsils. The 3D shape of the roof the fourth ventricle resembles that of a rhomboid-based pyramid; the edges of the base represent the borders of the ventricle, and the apex is the cerebellar fastigium. The lateral recess is shaped like a triangular-based pyramid, with its base connected to the cavity of the fourth ventricle and its tip opening into the lateral cerebellomedullary cistern through the foramen of Luschka. Our results may help in the endoscopic exploration of and microsurgical approaches to the fourth ventricle through its roof.

Microscopic and endoscopic anterior communicating artery complex anatomy as seen through keyhole approaches

The purpose of this anatomical study is to illustrate the microscopic and endoscopic anatomy of the anterior communicating artery complex as viewed through three keyhole approaches (keyhole pterional, lateral supraorbital and supraorbital) and to compare them. Each approach was carried out once on each side in five glutaraldehyde-fixed human cadaveric heads. A microscope and microscope-endoscope combination were used to grade access and visualization of the structures qualitatively using a previously published surgical exposure grading system. All three approaches provided good access and visualization of ipsilateral structures in the anterior communicating artery complex, but the pterional keyhole and the lateral supraorbital approaches gave the best access. Exposure of contralateral structures was limited overall, but was enhanced somewhat by the use of the endoscope.