The detection of intracranial aneurysms by non-invasive imaging methods and the epidemiology of aneurysmal subarachnoid haemorrhage within the Scottish population
The aims of the research project, which led to the writing of this thesis were to:
Examine whether non -invasive imaging methods could replace intra- arterial angiography (IADSA) in
the detection of intracranial aneurysms by: a) systematically reviewing the literature; b) prospectively
determining the accuracy of the non -invasive imaging methods currently available in Scotland, including
the effect of observer experience on diagnostic performance and the patient acceptability of the
alternative imaging modalities. To establish the incidence of aneurysmal subarachnoid haemorrhage
(SAH) in families by a national retrospective study of occurrences of SAH in a one year period in
Scotland, in parallel with a follow -up study of the families of patients who were admitted to the Institute
of Neurosciences with aneurysmal SAH a decade earlier. The thesis is divided into three parts:PART ONE: a) summarises the current understanding of the epidemiology and pathophysiology of
intracranial aneurysms; b) an overview of cerebrovascular anatomy with reference to aneurysm
formation; c) the modalities available for imaging intracranial aneurysms and the current knowledge
about their diagnostic performance are considered; d) an overview of the methods available for the
treatment of intracranial aneurysms; e) the concept of screening for unruptured intracranial aneurysms is
discussed and placed in context by comparison to other screening programmes.PART TWO: a) describes a systematic review of the non -invasive imaging of intracranial aneurysms. CT
and MR angiography had similar accuracy compared to IADSA of ~90 %. Data on Transcranial Doppler
Sonography (TCDS) were scanty but indicated poorer performance. Detection of very small aneurysms
(<3mm diameter) was significantly poorer for the non -invasive tests; b) describes a prospective study of
200 patients examining CTA, MRA and TCDS vs IADSA in the detection of intracranial aneurysms.
CTA and MRA had an accuracy (per subject) of 0.85. TCDS had similar accuracy per subject but poorer
accuracy per aneurysm than CTA or MRA. Detection of aneurysms ≤5mm was significantly poorer than
for those >5mm. Interobserver agreement was good for all modalities; c) combining TCDS with CTA or
MRA improved the detection of aneurysms on a per subject basis. Non-invasive imaging tests, especially
when used in combination, are reliable at detecting aneurysms >5mm; d) examines the effect of observer
experience. Neuroradiologists were more consistent and had better agreement with IADSA than non -
neuroradiologists. Small aneurysms and cavernous /terminal internal carotid aneurysms were poorly
detected by all observers; e) assessment of patient preferences indicated that TCDS was preferred to the
other non -invasive tests and CTA to MRA, with the differences being statistically significant.PART THREE describes: a) the rationale behind the epidemiological studies; b) the methodology used; c)
describes the results: Comparative risk for 1st vs 2nd degree relatives suffering a SAH was 2.29 for the
Scotland wide study (SWS) and 2.43 for the West of Scotland study (WOS). Absolute lifetime SAH risk
was 4.7% for 1st degree and 1.9% for 2nd degree relatives in the SWS compared to 4.2% and 2.3%
respectively in the WOS. Prospective 10 -year SAH risk was 1.2% for a 1st degree and 0.5% for a 2nd
degree relative compared to background population risk of ~0.1%. The hierarchy of risk was greatest for
a member of a family with ≥ 2 other 1st degree relatives affected by SAH, with a more than 20-fold
increased risk over the background population risk; d) discusses the implications of the findings and
examines the strengths and weaknesses of the study. Routine screening of families of patients who have
had a SAH is not supported by these data; e) reviews the implications for i) clinical practice and ii)
future research arising from the imaging and epidemiological studies
