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Wednesday, November 23, 2011

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 

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