Imaging of extracranial carotid aneurysms

Extracranial carotid artery aneurysms (ECAAs) are very rare, but exact data on
the incidence are lacking. Current literature is limited to case reports and
small case series with incomplete data and lacking long-term follow-up.
Presentation is usually around the age of 60, dependent on the etiology, which
is divers and ranges from atherosclerosis, infection, fibromuscular dysplasia,
to traumatic or spontaneous dissection.
Most ECAAs are found by coincidence in asymptomatic patients during imaging of
the brain or cervical vertebrae.
When symptomatic, cerebral thrombo-embolism and local compression seem most
frequent, while the risk of ECAA rupture, although a feared complication seems
ignorable small. Local compression may lead to peripheral neurological
dysfunction of the cranial nerves or dysphagia.
At all stages, the purpose of (additional) imaging is to 1) confirm diagnosis;
2) classify the ECAA; 3) to assess the anatomy in order to plan surgical or
endovascular treatment; and 4) follow up of aneurysm growth over time. Most
aneurysms are diagnosed by using echo/duplex ultrasound imaging (DUS), but
computed tomography angiography (CTA) seem more accurate and is usually done
additionally to confirm the diagnosis. Angiography with CTA visualizes the
lumen of the carotid artery, however aneurysm changes and rupture occur in the
vessel wall.
A growing body of evidence has supported the role of aneurysm wall inflammation
in the formation, progression and rupture of intracranial aneurysms. In a
histologic analysis of ECAA two distinct types of aneurysms have been found,
degenerative and dissecting aneurysms. In some of the degenerative aneurysms
different types of inflammatory cells have been found.
Vessel wall imaging was recently made possible, for instance with 3Tesla
contrast-enhanced MRI (3T MRI). It is postulated that administration of
gadolinium during MRI results in enhancements of sites with inflammation, which
could eventually be a marker for aneurysm growth.
Another technique that can contribute to the diagnostic and therapeutic work-up
is CTA with 3-dimensional (3D) reconstructions. Different methods of
measurement of an aneurysm size have been applied, however measurement of the
diameter appears to be unreliable in aneurysms located elsewhere in the body,
with low inter- and intra-observer reliability. A recent study in abdominal
aortic aneurysms showed measurement of aneurysm sac volume, which are more
precise than diameter measurement, can be of additional value. This study
showed that sac volume changes are not detected in diameter measurements and
also aneurysm diameters can change without changing the total volume of the
aneurysm indicating morphological changes of an aneurysm.
Because the rarity of ECAA little is known about the natural course of both
asymptomatic and symptomatic ECAA. We developed this protocol to gain more
insight in aneurysm wall changes and growth to possibly be able to predict the
clinical course of an ECCA. This way the treatment can be started before any
devastating symptoms occur.

The primary objective of this study is to observe if there are differences in
diameter measurements of 3T MRI and CTA at baseline and 1 year after baseline
measured by two independent observers (radiologist) blinded for previous
imaging.
The secondary objectives are to a) assess the feasibility of volume measurement
in ECAA using CTA with 3D reconstruction, b) to assess the reliability of
diameter and volume measurement in determining growth in an ECAA, c) assess
prevalence of gadolium enhancement in the ECAA wall, d) investigate if growth
rate is higher in aneurysms with wall enhancement on 3T MRI compared to
aneurysms without enhancement and e) whether white matter abnormalities are
seen due to micro-embolism even though patients are asymptomatic.

This is a pilot study

Participation in this study takes some time but carry little risks. Patienst
will get an IV-catheter for Gadolinium administration during the MRI scan.
Very few people (less then 2.5%) that undergo a contrast enhanced MRI
experience side effect of the contrast agent. These side effects are ussualy
mild. Severe side effects are extremly rare.