Carotid Artery Stenosis

Carotid Artery Stenosis :

Symptomatic only when 75% of the vessel diameter is occluded

·         TIA: Severe stenosis may result in TIA through either Global ischemia or an embolic process

·         CVA: 

o   20% mortality, 50% 5 year survival, 25% of survivors will have a second event

o   If >75% stenosis then 5.5% will have CVA (vs. 1.7% normal’s)

Differential TIA

·         Atherosclerosis

o   Inflammatory

§  Takayasu’s arthritis

§  Systemic Lupus Erythmatosis

§  Polyarteritis Nodosa

o   Non-inflammatory

§  Fibromuscular Dysplasia

§  Haemangioma

Common sites for cerebral stenosis

·         Proximal ICA > Proximal vertebral Artery > Distal ICA > proximal common carotid (CC)

Risk factors:

·         HT, Smoking Increase with > pack years, TIA

Symptoms:

·         Numbness of face, upper and lower extremities

·         ‘Ink-blot’ disturbance of visual field

Signs:

·         CT –absence of signs of haemorrhage and infarction

·         Left carotid bruit

Special examinations:

·         Carotid duplex Ultrasound – CDUS

o   B-Mode Imaging

o   Doppler US – increase flow velocity

o   94% Sensitive, 89% specific for carotid artery stenosis

o   Highly Operator dependent, less precise in detecting stenosis <50%, miss hairline residual lumens, only the cervical portion of the carotid artery can be examined

o   Uses B-mode US imaging and Doppler US to detect focal increase in blood flow

o   Normal Doppler Waveforms

§  ECA:  flow raises sharply during systole and falls rapidly in diastole, approaching zero or transiently reversing direction

§  ICA:  Large quantity of forward flow continues through diastole. The systolic peak is generally wide

§  CCA: A mix between ECA and ICA, but Common Carotid Artery generally follows ICA pattern

o   Stenotic Right ICA

§  Increased peak systolic velocity

§  Increased peak diastolic velocity

§  Spectral broadening

·         Magnetic Resonance Angiography – MRA

o   MRA good 3D of carotid bifurcation with good sensitivity for detecting high grade carotid stenosis

o   Non-invasive, less operator variability then CDUS, able to visualise the proximal CC, the distal Extracranial ICA and the intracranial vessels, Avoidance of iodinated contrast, Avoidance of Ionizing radiation

o   Difficult to define vascular anatomy in the presence of complex, turbulent or minimal flow, overestimate degree of carotid stenosis, 17% of MRA are incomplete because of patient movement

o   Carotid MRA findings: Stenotic region, post-Stenotic dilatation of the ICA

·         Digital Subtraction Angiography – DSA

o   Gold standard for carotid artery imaging. It requires catheterisation and two unimpeded views

o   Permits evaluation of the entire carotid artery system, tandem atherosclerotic disease, plaque morphology, collateral circulation which may affect management

o   Invasive with associated risks of morbidity and mortality, risk of all neurological complications is 4%, risk of serious neurologic complications is 1%, High cost, Exposure to ionizing radiation, iodinated contrast is used

o   Carotid DSA findings: Focal nodules of vessel thickening, ICA stenosis, Post-stenotic dilatation.

Fibromuscular Dysplasia – FMD

·         Non-atherosclerotic , non-inflammatory vascular disease affecting small and medium-sized arteries

·         FMD is the underlying cause of 2-5% of HT population

·         Unknown cause

·         Four histological subtypes

o   Medial Fibromuscular Dysplasia

§  70-90% of all FMD

§  Classic “string of beads” image seen with angiography

§  Thickened fibromuscular ridges alternating with thinning and widening of the vessel wall

§  Perimedial subtype primarily affects young women

o   Intimal Hyperplasia

§  1-5%

§  Circumferential of eccentric accumulation of fibrous tissue in the intima

§  Non-inflammatory, no lipid accumulation (as opposed to atherosclerosis)

o   Medial Hyperplasia

§  <5% all FMD

§  Focal concentric stenosis caused by excessive medial smooth muscle proliferation

§  Involves middle or distal part of the artery

o   Periadventitial fibroplasias

§  Rare

§  Fibroplasia wilth collagen encompasses the adventitia and extends into the surrounding tissue.

·         Abnormal perfusion from ICA

o   Washout of contrast in the anterior cerebral branches, Simultaneous perfusion of distal ECA branches with ICA branches . Indicative of decrease in ICA perfusion.

Interventional Management

o   Percutaneous transluminal catheter stent-angioplasty

§  A minimally invasive treatment option for carotid artery stenosis that has not yet been approved by the FDA and is experimental

§  Considerations for procedure versus carotid endarterectomy

·         Prior neck irradiation procedure, previous surgery, intimal hyperplasia, tandem lesion, severe comorbid disease.

·         Because FMD is a  non-atherosclerotic process of stenosis, PTCA is indicated

·         PTCA vs Carotid Endarterectomy

o   NASCET and ECST demonstrate a notable benefit for Carotid endarterectomy vs medical management in patients with symptomatic carotid artery stenosis > 70% luminal diameter.

o   Several studies claim PCTA has similar efficacy to carotid endarterectomy

§  Increase minor stroke (6.6% vs 0.6%) but a decrease rate of major stroke compared to surgical cohort

§  CREST trial – findings?

·         Flow restoration following PTCA

o   Flow through the previously Stenotic area is normal

o   “wash-out” defect no longer present in ACA

o   Maxillary artery branches now demonstrate delay filling

TIA = transient ischemic attack

CVA =cerebral vascular attack