Transcranial colour duplex ultrasound reveals novel venous haemodynamic changes following brain arteriovenous malformation resection

<p dir="ltr">Colour duplex ultrasound (CDU) is a rapidly evolving imaging technique capable of providing accurate non-invasive, visual assessment and serial follow-up of cerebrovascular vessels whilst furnishing clinically important quantitative haemodynamic indices. The scope of its clinical application is expected to proliferate over the coming few years.</p><p dir="ltr">Presently, challenges remain in post-operative clinical management following resection of brain arteriovenous malformations (bAVMs), including devastating post-operative haemorrhage. The causative mechanism remains unclear. Current post-operative follow-up imaging techniques, include computed tomography and magnetic resonance imaging, to guide peri-operative management are relatively cumbersome, especially when patients are still in the intensive care unit (ICU). An advantage of CDU is the potential capability of delivering serial bed-side assessment in critical peri- and post-operative periods non-invasively.</p><p dir="ltr">The primary aim of this thesis was to explore clinical merits of CDU, particularly, the application of transcranial colour duplex (TCCD) in the diagnosis, evaluation, and post-operative management, of complex intracranial vascular anomalies including bAVMs. Surgical intervention is associated with the risk of devastating peri-operative complications, especially intracranial haemorrhage. One recognised method of diminishing the risk of peri- and post-operative haemorrhage is maintaining a rigorous post-operative blood pressure regime and a protracted stay in the ICU.</p><p dir="ltr">Therefore, a systematic review was conducted to ascertain areas requiring further research. From this two hypotheses were proposed 1) that haemodynamic analysis using TCCD could elucidate a temporal course of when post-operative haemorrhage was likely to occur and/or 2) that there may a venous mechanism for haemorrhage given that no TCCD studies had imaged or considered post-operative venous changes following bAVM resection. A protocol was implemented using TCCD and central aortic pressure (CAP) measurements to evaluate 15 bAVM patients pre-operatively and daily, up to 14 days post-operatively.</p><p dir="ltr">TCCD measurements of middle cerebral artery and veins included peak systolic velocity (PSV), end diastolic velocity (EDV) and pulsatility index (PI). Parameters were compared with 7 craniotomy patients (non-bAVM craniotomy/surgical group). Normal reference values included 20 healthy volunteers.</p><p dir="ltr">Significant middle cerebral vein (MCV) changes in bAVM patients occurred. Maximal PSV was higher (median 47 cm/s) compared to non-bAVM craniotomy/surgical controls (median 17 cm/s, p=0.012); maximal PI was higher (median 0.99, p=0.005) compared to the non-bAVM craniotomy/surgical controls (median 0.49).</p><p dir="ltr">In 8 of 15 patients, increased MCV velocity and pulsatility stabilised within 14 days post-operatively. Mean number of days for the 8 patients to reach stable state was 6 days (range 0–9 days).</p><p dir="ltr">This is the first imaging study demonstrating significant venous changes post bAVM resection. Increased venous flow occurs in pial veins bilaterally. Increased pressure of venous flow is evidenced by a significant increase in diameter and pulsatility. Consequently, haemorrhagic complications may be due to distal constriction of the pial veins causing venous hypertension. The cause of the dilated vascular bed is unknown.</p><p dir="ltr">This scholarly work has culminated in six peer-reviewed journal publications, including an elaboration on the use of CDU to determine the prevalence of anomalous branches of the internal carotid artery. The classical anatomic descriptions describe the internal carotid artery (ICA) as having no branches. However, CDU detected a prevalence of 4% having branches in 400 patients.</p><p dir="ltr">This thesis places a strong argument for the merit of CDU in transcranial examination with potential applications for post-operative haemorrhage risk prediction and anomalous cerebral vasculature.</p>