Browsing by Author "Fieggen, Anthony Graham"

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    The Cape Town Stereotactic pointer clinical development and Applications
    (2009) Fieggen, Anthony Graham; Peter, Emeritus Jonathan C
    This dissertation describes the development and clinical use of a novel stereotactic neurosurgical system, the Cape Town Stereotactic Pointer (CTSP). This system has four main components; a halo containing three fiducials also serves as the platform for a tripod pointing device which is set with the aid of a 3D phantom or a printed setting diagram, and software which enables transformation of imaging space into patient space. Laboratory tests indicated an application accuracy of 1.9 +/- 0.6mm using the 3D phantom to set the tripod. From the first clinical application, the system underwent a series of iterations which could broadly be divided into four successive phases of refinement. This took place over a six year period, encompassing one hundred patients who underwent 115 stereotactic procedures. Indications for surgery included biopsy (62.6%), aspiration (15.7%) and cannulation (21.7%) and the surgical objective was realized in 101/109 cases (92.7%). Given the fact that six of the eight failures represented errors of surgical judgment that could not be ascribed to the device, and each of two system errors resulted in a significant modification to the system, the CTSP demonstrated a satisfactory level of accuracy in the clinical setting. This was accomplished at an acceptable complication rate, with one death five days after surgery attributable to a stereotactic procedure (mortality 0.9%) and major morbidity in two cases (1.7%); thirteen patients experienced minor complications, all of which proved to be transient (11.3%). A simple protocol for use of the CTSP evolved over the course of this study, making it easier for neurosurgeons from varying backgrounds to introduce stereotaxis into their practice with the help of this system. In addition to satisfactory levels of clinical reliability and safety, the system was versatile and also well tolerated by patients. It is hoped that the CTSP provides a costeffective alternative for neurosurgeons working in under-resourced settings. Sixty units of the production version of the CTSP have been sold and the system is now in use in ten countries.
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    Ultrasound as a non-invasive diagnostic tool in paediatric neurosurgery : relationship between the optic nerve sheath diameter (ONSD) and intracranial pressure (ICP)
    (2015) Padayachy, Llewellyn; Fieggen, Anthony Graham; Selbekk, Tormod
    Background: Assessment of intracranial pressure (ICP) is an essential aspect in the management of most neurosurgical conditions in children. While invasive ICP monitoring is considered the criterion standard, the need for a reliable, non-invasive, easy-to-use and accurate method to detect and monitor raised ICP has inspired the development of many useful techniques. The present study examined the relationship between transorbital ultrasound measurement of the optic nerve sheath diameter (ONSD) and invasively measured ICP in children, as well as the influence of relevant physiological and demographic variables on this relationship. Methodology: ONSD measurement was performed using a high frequency, small footprint linear array probe, and prior to invasive ICP measurement. All patients were under general anaesthesia and being mechanically ventilated. Physiological variables including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), pulse rate, temperature, respiratory rate and end tidal carbon dioxide (ETCO2) level were recorded at the time of ONSD measurement. The ONSD measurements were analysed for repeatability, intra- and inter-observer variability as well for correlation between images acquired in different planes and those obtained from either eye. The diagnostic accuracy of ONSD measurement for detecting ICP at different thresholds of 20, 15, 10 and 5 mmHg was analysed. This analysis included evaluation of age-related thresholds for defining different ONSD cut-off values in children. Dynamic image acquisition was performed and analysed to evaluate the relevant pulsatile motion of the ONS as a marker of the sheath stiffness. Results: One hundred and seventy four children undergoing diagnostic or therapeutic surgical procedures were included in this study. ONSD measurement demonstrated good correlation with ICP across the entire patient cohort (r = 0.66, p < 0.001), but was better in children > 1 year or with a closed anterior fontanelle (AF) (r = 0.7, p < 0.001). Age above and below 1 year was found to be an appropriate age threshold for defining two different sets of ONSD cut-off values. The study however, supported using patency of the AF as a stronger clinical marker for describing different ONSD cut-off values in children. The second part of this work described a dynamic technique for analysing the pulsatile motion of the ONS. Analysis of the deformability index (DI) as an indirect marker of ONS stiffness, revealed a statistically significant relationship with ICP (sensitivity of 90%, specificity of 87% for detecting ICP ≥ 20 mmHg). Conclusion: Measurement of the ONSD is a sensitive surrogate marker of raised ICP, but demonstrated poorer specificity. This relationship was more reliable in older children, particularly when the AF was closed. Analysis of the dynamic characteristics of the ONS appeared to provide useful additional information as an independent marker, and may contribute to our overall understanding of ONSD measurement in raised ICP.