Ronald Filippi

Computer-aided navigation in neurosurgery

The article comprises three main parts: a historical review on navigation, the mathematical basics for calculation and the clinical applications of navigation devices. Main historical steps are described from the first idea till the realisation of the frame-based and frameless navigation devices including robots. In particular the idea of robots can be traced back to the Iliad of Homer, the first testimony of European literature over 2500 years ago. In the second part the mathematical calculation of the mapping between the navigation and the image space is demonstrated, including different registration modalities and error estimations. The error of the navigation has to be divided into the technical error of the device calculating its own position in space, the registration error due to inaccuracies in the calculation of the transformation matrix between the navigation and the image space, and the application error caused additionally by anatomical shift of the brain structures during operation. In the third part the main clinical fields of application in modern neurosurgery are demonstrated, such as localisation of small intracranial lesions, skull-base surgery, intracerebral biopsies, intracranial endoscopy, functional neurosurgery and spinal navigation. At the end of the article some possible objections to navigation-aided surgery are discussed.

Surgical technique of the supraorbital key-hole craniotomy

BACKGROUND The enormous development of microsurgical techniques and instrumentation together with preoperative planning using the excellent preoperative diagnostic facilities available, enables neurosurgeons to treat more complicated diseases through smaller and more specific approaches. METHODS The technical details of the supraorbital key-hole craniotomy are described in this article as it has been evolving in our experience for more than 10 years. After an eyebrow skin incision with careful soft tissue dissection and single frontobasal burr-hole trephination, a supraorbital craniotomy is carried out with a diameter of about 1.5 x 2.5 cm. As a real frontolateral approach, the supraorbital craniotomy avoids removal of the orbital rim, the lesser sphenoid wing or the zygomatic arch. RESULTS AND CONCLUSIONS The supraorbital craniotomy allows wide intracranial exposure of the deep-seated supra- and parasellar region, according to the concept of key-hole approaches. The limited craniotomy requires minimal brain retraction thus significantly decreasing approach-related morbidity. In addition, the short skin incision within the eyebrow, the careful soft tissue dissection, and the single burr hole trephination result in a pleasing cosmetic outcome.

Bovine pericardium for duraplasty: clinical results in 32 patients

Abstract Bovine pericardium has been widely used for grafts in cardiac surgery and seems to have suitable properties for use as a dural graft. We report on the use of solvent-preserved, gamma-sterilized Tutoplast bovine pericardium for dural grafts in 32 patients undergoing cranial and spinal operations with the objective of clinically assessing this material and technique by a retrospective analysis. All available records were reviewed and information regarding the indication for grafting, complications, and outcome were collected and analyzed for all patients. Indications for grafting included tethered cord myelolysis, closure of lumbosacral myeloceles, Chiari decompression, posterior fossa craniotomy, supratentorial craniotomy, and trauma. Outcomes were excellent in 31 patients; the one poor outcome was unrelated to surgical closure. The dural graft was not intended for outcome in any patient. Bovine pericardium was found to be a flexible and easily suturable, safe and cost-effective material for duraplasty. These results confirm the excellent suitability of Tutoplast bovine pericardium for dural substitution.

Endoscope-assisted removal of colloid cysts of the third ventricle

Colloid cysts are benign space-occuping lesions, which arise from the velum interpositum or the choroid plexus of the third ventricle and are able to produce symptomatic obstruction of the foramina of Monro with resultant hydrocephalus. In our department, we have operated on colloid cysts routinely in an endoscope-assisted microsurgical manner via a key–hole approach. During a period of 10 years, 28 microsurgical resections of colloid cysts of the third ventricle were performed. Seven patients demonstrated colloid cysts inside the third ventricle with obstruction of the right foramen Monro, two patients demonstrated cysts with obstruction of the left foramen Monro. Twelve patients suffered from cysts inside the third ventricle with obstruction of both foramina Monro and five patients demonstrated cysts lying into the third ventricle without obstruction of the foramina. In 21 patients no preoperative therapy was performed outside. Three patients had received shunt systems before in other hospitals, two patients received aspiration of the cysts under stereotactic conditions and two patients received external ventricular drains. Total removal of the cyst was achieved in all patients (100%). No patient received a second operation, because none had a recurrent cyst. All cysts were removed with the cyst wall. Overall clinical improvement was achieved in a long-standing period between 6 and 83 months in 27 (96%) patients. In one patient (4%) the psychomotor disturbance was unchanged and no patient deteriorated. From the microsurgical point of view, the combination of keyhole surgery under endoscopic visual control using preexisting anatomical windows offers an effective minimally invasive approach.

Histological Findings in Coil-packed Experimental Aneurysms 3 Months after Embolization

OBJECTIVE Knowledge regarding tissue reactions within coil-packed aneurysms is poor. The purpose of this study was to analyze histological changes in a chronic experimental bifurcation aneurysm model that might explain the protective effect of Guglielmi detachable coils. METHODS The aneurysms were produced by means of a venous graft pouch at a surgically created bifurcation of the carotid artery in the neck of rabbits. After 3 weeks, embolization with Guglielmi detachable coils was performed in the treatment group but not in the control group (seven rabbits each). At the time of embolization, six of seven treated aneurysms were completely occluded according to radiological criteria. Twelve weeks later, all aneurysms were explanted after final angiography. Histological examinations were performed with coils in situ. RESULTS Six of seven embolized aneurysms demonstrated complete occlusion in final angiography. But gross pathology revealed that all specimens had differently sized open cavities between the coils. In only two cases, these spaces were very small and the aneurysmal sacs were filled with coils and tissue by more than 90%. Light microscopy demonstrated intraluminal granulation tissue and strong chronic inflammatory wall thickening with numerous foreign body cells at the interface between coils and tissue. Coils were partially incorporated into the aneurysmal wall, sometimes close to the surface and occasionally even outside the wall within the surrounding tissue. CONCLUSION The protective effect of Guglielmi detachable coil treatment in our chronic experimental bifurcation aneurysms results from formation of intraluminal granulation tissue and wall thickening attributable to chronic inflammation.

Brain tissue pO2 related to SjvO2, ICP, and CPP in severe brain injury.

Abstract The aim of this report is to present first experience in comparing the course of brain tissue oxygen pressure values (PtiO2) to changes in jugular vein oxygen saturation (SjvO2), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) after severe brain injury. PtiO2 monitoring was done using a polarographic Clark type microcatheter (LICOX pO2 probe) (GMS, Kiel, Germany) with a diameter of 0.5 mm and a sensitive area 7.9 mm long inserted in a right frontal position. The microcatheter was connected to a LICOX pO2 device. A fiber-optic catheter was used to measure SjvO2 and placed into the right internal jugular vein. The ICP monitoring was performed with a fiber-optic intraparenchymal device (Camino Laboratories, San Diego, Calif.) inserted in a left frontal position. Consistent correlations could be noticed between reduced PtiO2 and higher ICP and lower CPP levels. However, the absolute value of a single SjvO2 data point seemed to be less relevant diagnostically than its trend over a period of time. Owing to their experience, the authors suppose that PtiO2 monitoring will be a very important and reliable tool in the treatment of brain injury in the future, especially in its correlation to ICP and CPP.

Topographic microsurgical anatomy of the paraclinoid carotid artery.

In this publication, the authors describe the microanatomic topography of the entire paraclinoid area with respect to the paraclinoid segment of the internal carotid artery and its surrounding anatomical structures. Special attention was given to the borders of the paraclinoid area, cavernous sinus, arterial vessels, and cranial nerves passing through the region. The paraclinoid region was defined as a pyramid-formed space formed by the dural covering of the anterior clinoid process. The superior border is formed by the continuity of the anterior petroclinoid fold, anteriorly on the superior surface of the anterior clinoid process and medially in the direction of the diaphragma sellae. This dural sheet encircles the internal carotid artery and forms the so-called distal dural ring of the internal carotid artery. The medial border of the paraclinoid region is formed by the body of the sphenoid bone and the adjacent periosteal sheet. The inferior border is formed by a fibrous plate between the middle and anterior clinoid processes. This so-called proximal dural ring separates the venous compartments of the cavernous area from the paraclinoid area. The lateral border is formed by the lateral surface of the anterior clinoid process with its dural covering. The arterial supply of this region is provided by branches of the intracavernous carotid segment and the ophthalmic artery. The important nerves in close vicinity to the paraclinoidal area are the optic and the oculomotor nerves. Understanding and knowledge of the topographic anatomy of the paraclinoid area is essential for microsurgical exposure of this region.

Tightness of duraplasty in rabbits: a comparative study.

OBJECTIVE The purpose of this study was to test, in rabbits, the tightness of seven dural substitution materials commonly used in neurosurgery, i.e., Lyodura (B. Braun Melsungen AG, Melsungen, Germany), Tutoplast dura (Tutogen Medical, Inc., Parsippany, NJ), Tutoplast fascia lata (Tutogen Medical, Inc.), autologous periosteum, Neuropatch (B. Braun Melsungen AG), Dacron (E.I. du Pont de Nemours and Co., Wilmington, DE), and Ethisorb (Ethicon, Inc., Somerville, NJ). METHODS Duraplasties were performed with sutures alone or were additionally fixed with fibrin glue. Leakage pressures were assessed by infusion of artificial cerebrospinal fluid, containing sodium fluorescein, into the cisterna magna and detection of fluorescence using a charge-coupled display camera with background substraction, 3 days, 3 weeks, or 3 months after surgery. RESULTS Three days after implantation, the mean tightness values of duraplasties with Lyodura or Neuropatch were significantly higher (P = 0.007) than the values for the other substitutes. A significant improvement of tightness with increasing implantation time could be demonstrated for autologous periosteum (P = 0.0063). Improvement of tightness with the use of fibrin glue could be proven only for the heterologous grafts (P = 0.0071). The tightness values for Neuropatch fixed only with sutures were similar to those for the best heterologous substitutes implanted with additional fibrin glue. Lyodura, Tutoplast dura, and Neuropatch demonstrated favorable implantation characteristics; they were thin, flexible, and easily suturable. Neither adhesions to the brain nor space-occupying scars were noted. CONCLUSION These results confirm the excellent suitability of Lyodura and Neuropatch for dural substitution.

TUMORS OF THE LATERAL AND THIRD VENTRICLE

OBJECTIVE Intraventricular tumors usually are managed by approaches and microsurgical techniques that need retraction and dissection of important brain structures. Minimally invasive endoscopic procedures achieve a remarkable alternative to conventional microneurosurgical techniques. Endoscope-assisted microneurosurgery may be a minimally invasive technique with maximally effective treatment. Using the keyhole concept for planning the surgical strategy, the reduction of the brain retraction is achieved, which is one of the main benefits of this technique. METHODS We treated 35 patients (16 female patients and 19 male patients) with tumors in the lateral (n = 8) and the third (n = 27) ventricle. Patient age at the date of surgery ranged from 5 to 73 years. The follow-up period ranged from 6 to 83 months. The tumors were operated on using transcortical, transcallosal, or suboccipital transtentorial or infratentorial supracerebellar approaches after precise planning of the skin incision, the trephination, and the trajectory to the center of the tumor, performed earlier with a magnetic resonance imaging scan. RESULTS Total removal of the tumor was achieved in 28 patients (78.5%). In 2 patients (6.5%), recurrent tumor occurred. In 5 patients (15%), parts of the tumors remained because of infiltration of eloquent areas. Overall clinical improvement was achieved in 31 patients (87%). Three patients (10%) were unchanged and 1 patient (3%) deteriorated. CONCLUSION Endoscope-assisted keyhole neurosurgery seems to be a safe method of removing tumors in all regions inside the ventricular system with a low risk of permanent neurological deficits. The exact surgical corridor planning on the basis of the keyhole strategy offers less traumatic exposure of even deep-seated endoventricular tumors.

New method of bone reconstruction designed for skull base surgery

The direct endonasal or transoral transclival approaches to the skull base permit effective, minimally invasive surgery along the clivus. Developing long-term, effective techniques to prevent cerebrospinal fluid (CSF) leaks and their consequences (infection and delayed healing) remains a major challenge. In this study we describe a method of bone reconstruction newly developed by us, which uses a custom designed silicone plug for bone replacement after minimally invasive skull base surgery with a low incidence of postoperative CSF leaks. German Landrace pigs were used to test the efficiency of the new technique. Twelve craniotomies were performed in six pigs using a subtemporal approach and subsequently the dura was opened. After these preparations the craniotomy defects were occluded with a silicone ball, which had a near spherical shape. The ball elastically adapts to the bone defect. Each pig also received an intracranial pressure (ICP) catheter and a subdural catheter for later fluorescein injection. Then we increased ICP by infusion of artificial CSF and detected fluorescein leaks from the craniotomy using ultraviolet illumination and a photomacroscope equipped with appropriate filters and a charge-coupled device camera. In all pigs we increased ICP to 75-80 mmHg by infusing 25-30 mL saline containing 0.05% sodium fluorescein. For the first four craniotomies infusions were interrupted after CSF leaks occurred due to technical failures, which were subsequently rectified. The following eight craniotomies were watertight without CSF leakage. This novel medical device allows a leak-proof closure of bone defects after minimally invasive craniotomies; no additional surgery or other therapies were necessary. The application of the silicone plug, which is made of a cost-effective and biocompatible material, is easy and fast, making use of a specially developed toolkit.