Andreas Falk

Operative approach due to results of functional magnetic resonance imaging in central brain tumors.

Since 1995 we have been investigating the localization of the cortical motor strip by functional magnetic resonance imaging (fMRI) in central brain tumor cases. Forty patients have been operated on using these data for preoperative planning. Intraoperative sensory evoked potentials (SEP) and cortical motor evoked potential (performed in 18 patients) showed a good correlation with fMRI data with the exception of two cases. Only 12.5% of cases were permanently worsened as a result of increasing postoperative pareses.

Preoperative planning and intraoperative navigation: status quo and perspectives.

An essential step in modern microneurosurgery involves preoperative planning of procedures. For difficult lesions neuronavigation is being used in conjunction with complex and detailed radiological investigations. This article shows how these examinations are used for computerized planning of surgical steps. Although planning and navigation are still two separate entities, the combination of the two may help in neurosurgery.

Reintitan als Knochenersatzmaterial

Computergestützt vorgefertigte Schädelimplantate aus Reintitan als Knochenersatzmaterial werden seit 1994 in 22 Kliniken eingesetzt. Die Erfahrungen mit 104 Implantaten umfassen klinische (Indikationsstellung; Implantatlager; Operationstechnik; Patientenführung), aber auch geometrische und materialspezifische Aspekte (CT-Datenakquisition, -transfer und -auswertung; Konstruktion; Fertigung; Reinigung; postoperative Einsatzmöglichkeit bildgebender Verfahren). Während die klinischen Aspekte im Verantwortungsbereich ärztlichen Handelns definiert werden, gilt für die geometrischen und materialspezifischen Aspekte bei individuellen Implantaten das Medizinproduktegesetz. Prospektiv werden entsprechend für jedes Implantat die Spiral-CT-Akquisitionsparameter, die Geometriedaten des rechnerinternen Schädelmodells und des Implantats, das Reinigungsverfahren und die individuelle Kennzeichnung dokumentiert. Medizinisch spezifiziertes Reintitan wird ausschließlich durch Fräsung bearbeitet, sodass weder Reinheit noch Gefüge Änderungen erfahren. Eine eigens entwickelte Frästechnik garantiert die Umsetzung aller konstruierter Elemente bis zu einer Feinheit von 50 μm. Im Hinblick auf die bei tumorbedingten Defekten notwendige bildgebende Verlaufskontrolle werden sämtliche Patienten der eigenen Klinik postoperativ mit MRT untersucht, z. T. mit einer präoperativen Darstellung als intraindividuelle Kontrolle. Eine umfassende Dokumentation und Qualitätssicherung ist für Techniken des vorgefertigten Knochenersatzes unabdingbar. Parallel zur forscherischen Entwicklung und ärztlichen Anwendung müssen diese formalen Kriterien für das jeweilige Verfahren bearbeitet und erfüllt werden. Die erfolgreiche Erarbeitung von eigens adaptierten MRT-Sequenzen geht darüber noch hinaus: Spinechosequenzen minimieren die durch die Titanimplantate erzeugten Feldinhomogenitäten und erlauben eine aussagekräftige postoperative Dokumentation und Diagnostik insbesondere nach Tumoroperationen in der Verlaufsbeobachtung. Computer-assisted prefabricated skull implants of pure titanium as a bone replacement material have been used in 22 departments since 1994. Our experience with 104 implants includes clinical aspects (indication; tissue quality; surgical technique; patient guidance), but also geometric and material-specific parameters (acquisition, transfer, and evaluation of CT data; construction; manufacturing; cleaning; postoperative use of radiologic techniques). While the clinical aspects are responsibly defined by the respective surgeon, the geometric and material-specific parameters of individual implants have to comply with the laws on medical products. Therefore, the prospective documentation for each implant includes: helical CT acquisition parameters; geometric data of the computer-based skull model and implant; the cleaning procedure; and the individual marking. Medically specified pure titanium is processed by milling only so that neither purity nor structure is impaired. A specially developed milling technique guarantees the fabrication of all constructed elements down to fine details of 50 μm. Considering the necessary radiologic follow-up of defects after tumor surgery, all patients in our hospital undergo postoperative MRI examination, partly with preoperative documentation as an intraindividual control. Such comprehensive documentation and quality assurance is essential for techniques of prefabricated bone substitution. Hand in hand with scientific research and clinical application, these formal criteria have to be elaborated and fulfilled for the respective techniques. The successful determination of specifically adapted MRI sequences goes even one step further: spin-echo sequences minimize inhomogeneities of the magnetic field induced by the titanium implants and enable accurate postoperative documentation and diagnostics especially in the follow-up after tumor surgery.Computer-assisted prefabricated skull implants of pure titanium as a bone replacement material have been used in 22 departments since 1994. Our experience with 104 implants includes clinical aspects (indication; tissue quality; surgical technique; patient guidance), but also geometric and material-specific parameters (acquisition, transfer, and evaluation of CT data; construction; manufacturing; cleaning; postoperative use of radiologic techniques). While the clinical aspects are responsibly defined by the respective surgeon, the geometric and material-specific parameters of individual implants have to comply with the laws on medical products. Therefore, the prospective documentation for each implant includes: helical CT acquisition parameters; geometric data of the computer-based skull model and implant; the cleaning procedure; and the individual marking. Medically specified pure titanium is processed by milling only so that neither purity nor structure is impaired. A specially developed milling technique guarantees the fabrication of all constructed elements down to fine details of 50 microns. Considering the necessary radiologic follow-up of defects after tumor surgery, all patients in our hospital undergo postoperative MRI examination, partly with preoperative documentation as an intraindividual control. Such comprehensive documentation and quality assurance is essential for techniques of prefabricated bone substitution. Hand in hand with scientific research and clinical application, these formal criteria have to be elaborated and fulfilled for the respective techniques. The successful determination of specifically adapted MRI sequences goes even one step further: spin-echo sequences minimize inhomogeneities of the magnetic field induced by the titanium implants and enable accurate postoperative documentation and diagnostics especially in the follow-up after tumor surgery.