By: Robert L. Bard, MD and Dr. Pierre Kory, MD
We have learned over the last century that blockages of coronary arteries to the heart and carotid arteries to the brain are precipitated by inflammation of the inner walls of the vessel, called the “intima”
While thickening of the interior wall of vessels gradually occurs over time and is aggravated by diet, stress and hypertension (high blood pressure), the acutely disabling event is when there is an abrupt tear of the overlying plaque which ruptures debris which then forms a blood clot which blocks blood flow or the clot travels deeper into the brain and blocks blood flow. Similarly, abnormal heart rhythms such as “atrial fibrillation”, causes the pooling of blood in the heart which predisposes to clot formation and the clots can then travel into the brain causing a stroke. In Covid-19, the virus causing severe inflammation in the blood which then promotes clot formation which can travel through the vascular system and affect almost every organ system in the human body, with the brain and lungs being the most affected.. An article in September NEUROLOGY reported by Medscape documented the incidence of large artery stroke as the presenting symptom of COVId-19 was highest in men under the age of 50 years.
However, the chronic and diffuse nature of arteritis often weakened the vessel wall producing aneurysmal dilation and rupture. Today we find sophisticated non-invasive or minimally invasive modalities to be the first line of interrogation of vasculitis.
- CAROTID SONOGRAM
|- 3D/4D VESSEL DENSITY HISTOGRAM
- ENDOARTERIAL 3D DOPPLER
- RETINAL OCT
- SOFT TISSUE OCT
- REFLECTANCE CONFOCAL MICROSCOPY
- SMALL COIL MRI
- 7 TESLA MRI
CAROTID SONOGRAM: While cerebrovascular disease is often diagnosed ex post facto after a catastrophic episode with MRI and CT, the non invasive Doppler analysis of the vascularity is generally checked with ultrasound for plaque and obstruction. A useful measure of the risk of coronary and cerebrovascular disorder is the carotid intimal thickness (CIMT). Standard depth of the inner wall thickness is a measure best obtained by high resolution sonograms since a reading over 0.9mm indicates increased risk. The newer sonogram units have depth resolution of 0.02mm making this a preferred non invasive option.
CAROTID DOPPLER: Flow abnormalities of turbulence and absence are commonly evaluated with this modality. Plaque forms more readily in aberrant flow patterns and high velocity regions accompanying narrowing.
EYE SONOGRAPHY: Sonofluoroscopy of the orbital soft tissues and eyes is performed in multiple scan planes with varying transducer configurations and frequencies. Power and color Doppler use angle 0 and PRF at 0.9 at optic nerve head. 3D imaging of optic nerve and carotid, central retinal arteries and superficial posterior ciliary arteries performed in erect position before and after verbal communication. Retinal arterial flow is measured. Optic nerve head bulging is checked as increased intracranial pressure may be demonstrable.
TRANSORBITAL DOPPLER: R/L ciliary arteries have normal Doppler flows of 10cm/s which is symmetric.
CONTRAST ENHANCED ULTRASOUND: Widely used European nonionic contrast injection allows imaging capillary size vessels and perfusion characteristics
TRANSCRANIAL DOPPLER: This measures the flow in the anterior, middle and posterior cerebral arteries as well as Circle of Willis.
3D/4D VESSEL DENSITY HISTOGRAM: Multiple image restoration and reconstruction shows retinal vessel density of 25% at the optic nerve head and adjacent region with quantitative accuracy.
ENDOARTERIAL 3D DOPPLER: Microcatheters inserted into the arterial or venous system provide measurement of wall thickness and presence of inflammatory vessels inside the intima.
RETINAL OCT: Subtraction techniques done with OCT optical coherence tomography may show changes in the caliber of the retinal vessels with verbal ideation.
SOFT TISSUE OCT: The depth of penetration may be extended to 2-3mm allowing for analysis of vascular changes in erythematous or erythropoor dermal areas. Thrombosis may be observed.
REFLECTANCE CONFOCAL MICROSCOPY: This microscopic analysis of the cells also quantifies microvascular pathology and is a potential modality for studying vasculitis.
SMALL COIL MRI: High resolution systems used for animal study and superficial organs can image the intra-arterial anatomy including dynamic contrast imaging on standard 1.5T and 3T units.
7 TESLA MRI: High field systems analyse signal abnormalites rapidly with high resolutions.
HYBRID IMAGING: Hybrid imaging refers to combining diagnostic modalities to assess disease and monitor therapy.
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