David Peace

Microsurgical anatomy of the posterior inferior cerebellar artery.

Fifty cerebellar hemispheres from 25 adult cadavers were examined. The posterior inferior cerebellar artery (PICA), by definition, arose from the vertebral artery. The vertebral artery was present in 49 and the PICA was present in 42 of the 50 hemispheres. Forty-one of the 42 PICAs arose as a single trunk and 1 arose as a duplicate trunk. The PICA was divided into five segments: the anterior medullary segment lay on the front of the medulla; the lateral medullary segment coursed beside the medulla and extended to the origin of the glossopharyngeal, vagal, and accessory nerves; the tonsillomedullary segment coursed around the caudal half of the cerebellar tonsil; the telovelotonsillar segment coursed in the cleft between the tela choroidea and the inferior medullary velum rostrally and the superior pole of the cerebellar tonsil caudally; and the cortical segment was distributed to the cerebellar surface. Thirty-seven of the 42 PICAs bifurcated into a medial and a lateral trunk. The medial trunk supplied the vermis and the adjacent part of the hemisphere, and the lateral trunk supplied the cortical surface of the tonsil and the hemisphere. The PICA gave off perforating, choroidal, and cortical arteries. The cortical arteries were divided into vermian, tonsillar, and hemispheric groups. Sixteen of the 42 PICAs passed between the rootlets of the accessory nerve, 10 passed between the rootlets of the vagus nerve, 13 passed between the vagus and the accessory nerves, 2 coursed rostral to the glossopharyngeal nerve, and 1 passed between the glossopharyngeal and the vagus nerves.

Microsurgical anatomy of the region of the foramen magnum

The anatomy needed to plan microoperative approaches to the region of the foramen magnum was examined in 25 cadaveric heads. The structures examined included the lower cranial and upper spinal nerves, the caudal brain stem and rostral spinal cord, the vertebral artery and its branches, the veins and dural sinuses at the craniovertebral junction, and the ligaments and muscles uniting the atlas, axis, and occipital bone. The transoral, transpalatal, labiomandibular, glossolabiomandibular, transsphenoidal, transcranial-transbasal, transcervical, and suboccipital operative approaches to the region are also reviewed.

Microsurgical anatomy of the deep venous system of the brain.

The microsurgical anatomy of the deep venous system of the brain was examined in 20 cerebral hemispheres. The deep venous system is composed of the internal cerebral, basal, and great veins and their tributaries. This system drains the deep white and gray matter surrounding the lateral and 3rd ventricles and the basal cisterns. The deep veins are divided into a ventricular group composed of the veins converging on the walls of the lateral ventricles and a cisternal group that includes the veins draining the walls of the basal cisterns. The internal cerebral vein is included in the ventricular group because it is predominantly related to the ventricles, and the basal and great veins are reviewed with the cisternal group because they course through the basal cisterns. The choroidal veins are included with the ventricle veins because they arise on the choroid plexus in the ventricles. The thalamic veins appear in both the ventricular and the cisternal groups because some course on the ventricular surfaces and others course in the basal cisterns. The operative approaches to the major trunks in this system are reviewed.

Microsurgical anatomy of the posterior fossa cisterns.

The microsurgical anatomy of the posterior fossa cisterns was examined in 15 cadavers using 3X to 40X magnification. Liliequists membrane was found to split into two arachnoidal sheets as it spreads upward from the dorsum sellae: an upper sheet, called the diencephalic membrane, which attaches to the diencephalon at the posterior edge of the mamillary bodies, and a lower sheet, called the mesencephalic membrane, which attaches along the junction of the midbrain and pons. Several other arachnoidal membranes that separate the cisterns were identified. These include the anterior pontine membrane, which separates the prepontine and cerebellopontine cisterns; the lateral pontomesencephalic membrane, which separates the ambient and cerebellopontine cisterns; the medial pontomedullary membrane, which separates the premedullary and prepontine cisterns; and the lateral pontomedullary membrane, which separates the cerebellopontine and cerebellomedullary cisterns. The three cisterns in which the arachnoid trabeculae and membranes are the most dense and present the greatest obstacle at operation are the interpeduncular and quadrigeminal cisterns and the cisterna magna. Numerous arachnoid membranes were found to intersect the oculomotor nerves. The neural and vascular structures in each cistern are reviewed.

Microsurgery of the third ventricle: Part I. Microsurgical anatomy.

The 3rd ventricle is one of the most surgically inaccessible areas in the brain. It is impossible to reach its cavity without incising some neural structures. Twenty-five cadaveric brains were examined in detail to evaluate the surgically important relationships of the walls of the 3rd ventricle. The routes through which the 3rd ventricle can be reached are (a) from above, through the foramen of Monro and the roof after entering the lateral ventricle through the corpus callosum or the cerebral cortex; (b) from anterior, through the lamina terminalis; (c) from below, through the floor if it has been stretched by tumor; and (d) from posterior, through the pineal region or from the posterior part of the lateral ventricle through the crus of the fornix. The posterior part of the circle of Willis and the basilar artery are intimately related to the floor, the anterior part of the circle of Willis and the anterior cerebral and anterior communicating arteries are related to the anterior wall, and the posterior cerebral artery supplies the posterior wall. The deep cerebral venous system is intimately related to the 3rd ventricle; the internal cerebral vein is related to the roof, and the basal vein is related to the floor. The junction of these veins with the great veins forms a formidable obstacle to the operative approach to the pineal gland and the posterior part of the 3rd ventricle.

The pretemporal approach to the interpeduncular and petroclival regions

SummaryA pretemporal approach to the interpeduncular and petroclival regions is described.Through a frontotemporal craniotomy based very low in the middle fossa the temporal lobe is completely exposed. The Sylvian, carotid, chiasmatic, and lamina terminalis cisterns are widely opened. The arachnoid fibers between the uncus and the frontal lobe, as well as those binding the temporal lobe to the tentorial edge and to the oculomotor nerve are also separated. The bridging veins from the temporal pole to the spheno-parietal sinus are usually coagulated and sacrificed allowing for posterior displacement of the temporal lobe.The approach combines the advantages of both the classical pterional and subtemporal approaches providing unhindered exposure of the anterior portion of the tentorial incisura in dealing with vascular and tumoural lesions arising at the sellar, parasellar, and interpeduncular regions, and at the superior aspect of the petroclival region.

Anatomical and technical aspects of the contralateral approach for multiple aneurysms

SummaryMicrosurgery of multiple aneurysms is still a controversial subject. In order to avoid the risk of rebleeding and the consequent increase in morbidity in such cases all aneurysms or at least as many aneurysms as possible should be treated in the first operative procedure. To reach that goal aneurysms located on the contralateral side should also be considered for clipping during the first operation. Between 1984 and 1994 a series of 51 patients harboring multiple aneurysms of which 55 aneurysms were located on the contralateral side of the craniotomy were operated at our institution. No mortality or morbidity could be directly ascribed to the aneurysm that was clipped contralaterally. Based on that series we have described the anatomical features, technical aspects and surgical difficulties of approaching bilateral aneurysms through the same craniotomy.

Surgical Neuroanatomy and Programming in Deep Brain Stimulation for Obsessive Compulsive Disorder

Deep brain stimulation (DBS) has been established as a safe, effective therapy for movement disorders (Parkinsons disease, essential tremor, etc.), and its application is expanding to the treatment of other intractable neuropsychiatric disorders including depression and obsessive‐compulsive disorder (OCD). Several published studies have supported the efficacy of DBS for severely debilitating OCD. However, questions remain regarding the optimal anatomic target and the lack of a bedside programming paradigm for OCD DBS. Management of OCD DBS can be highly variable and is typically guided by each centers individual expertise. In this paper, we review the various approaches to targeting and programming for OCD DBS. We also review the clinical experience for each proposed target and discuss the relevant neuroanatomy.

Coordinate-Based Lead Location Does Not Predict Parkinson's Disease Deep Brain Stimulation Outcome

Background Effective target regions for deep brain stimulation (DBS) in Parkinsons disease (PD) have been well characterized. We sought to study whether the measured Cartesian coordinates of an implanted DBS lead are predictive of motor outcome(s). We tested the hypothesis that the position and trajectory of the DBS lead relative to the mid-commissural point (MCP) are significant predictors of clinical outcomes. We expected that due to neuroanatomical variation among individuals, a simple measure of the position of the DBS lead relative to MCP (commonly used in clinical practice) may not be a reliable predictor of clinical outcomes when utilized alone. Methods 55 PD subjects implanted with subthalamic nucleus (STN) DBS and 41 subjects implanted with globus pallidus internus (GPi) DBS were included. Lead locations in AC-PC space (x, y, z coordinates of the active contact and sagittal and coronal entry angles) measured on high-resolution CT-MRI fused images, and motor outcomes (Unified Parkinsons Disease Rating Scale) were analyzed to confirm or refute a correlation between coordinate-based lead locations and DBS motor outcomes. Results Coordinate-based lead locations were not a significant predictor of change in UPDRS III motor scores when comparing pre- versus post-operative values. The only potentially significant individual predictor of change in UPDRS motor scores was the antero-posterior coordinate of the GPi lead (more anterior lead locations resulted in a worse outcome), but this was only a statistical trend (p<.082). Conclusion The results of the study showed that a simple measure of the position of the DBS lead relative to the MCP is not significantly correlated with PD motor outcomes, presumably because this method fails to account for individual neuroanatomical variability. However, there is broad agreement that motor outcomes depend strongly on lead location. The results suggest the need for more detailed identification of stimulation location relative to anatomical targets.

Postoperative lead migration in deep brain stimulation surgery: Incidence, risk factors, and clinical impact

Introduction Deep brain stimulation (DBS) is an effective treatment for multiple movement disorders and shows substantial promise for the treatment of some neuropsychiatric and other disorders of brain neurocircuitry. Optimal neuroanatomical lead position is a critical determinant of clinical outcomes in DBS surgery. Lead migration, defined as an unintended post-operative displacement of the DBS lead, has been previously reported. Despite several reports, however, there have been no systematic investigations of this issue. This study aimed to: 1) quantify the incidence of lead migration in a large series of DBS patients, 2) identify potential risk factors contributing to DBS lead migration, and 3) investigate the practical importance of this complication by correlating its occurrence with clinical outcomes. Methods A database of all DBS procedures performed at UF was queried for patients who had undergone multiple post-operative DBS lead localization imaging studies separated by at least two months. Bilateral DBS implantation has commonly been performed as a staged procedure at UF, with an interval of six or more months between sides. To localize the position of each DBS lead, a head CT is acquired ~4 weeks after lead implantation and fused to the pre-operative targeting MRI. The fused targeting images (MR + stereotactic CT) acquired in preparation for the delayed second side lead implantation provide an opportunity to repeat the localization of the first implanted lead. This paradigm offers an ideal patient population for the study of delayed DBS lead migration because it provides a large cohort of patients with localization of the same implanted DBS lead at two time points. The position of the tip of each implanted DBS lead was measured on both the initial post-operative lead localization CT and the delayed CT. Lead tip displacement, intracranial lead length, and ventricular indices were collected and analyzed. Clinical outcomes were characterized with validated rating scales for all cases, and a comparison was made between outcomes of cases with lead migration versus those where migration of the lead did not occur. Results Data from 138 leads in 132 patients with initial and delayed lead localization CT scans were analyzed. The mean distance between initial and delayed DBS lead tip position was 2.2 mm and the mean change in intracranial lead length was 0.45 mm. Significant delayed migration (>3 mm) was observed in 17 leads in 16 patients (12.3% of leads, 12.1% of patients). Factors associated with lead migration were: technical error, repetitive dystonic head movement, and twiddler’s syndrome. Outcomes were worse in dystonia patients with lead migration (p = 0.035). In the PD group, worse clinical outcomes trended in cases with lead migration. Conclusions Over 10% of DBS leads in this large single center cohort were displaced by greater than 3 mm on delayed measurement, adversely affecting outcomes. Multiple risk factors emerged, including technical error during implantation of the DBS pulse generator and failure of lead fixation at the burr hole site. We hypothesize that a change in surgical technique and a more effective lead fixation device might mitigate this problem.