NEUROSONOLOGY
Intima-media thickness (IMT)
Created 01.08.2019 , last update 05.11.2021
- carotid intima-media thickness (IMT) measurement can quantify atherosclerosis burden in asymptomatic patients, which may need a more aggressive approach to managing the vascular risk factors
- the standard measurement is performed in B-mode on the far wall of CCA, 10 mm proximal from the bifurcation
- use high-resolution images
- optimize the angle of insonation (90° to the vessel wall)
- distance of 2 echogenic lines is measured
- the 1st line is the lumen-intima interface
- the 2nd line is the media-adventitia interface
- get at least five measurements on each side and get an average value (“average IMT”); specialized software can be helpful
[Baldassare, 2000] - avoid atherosclerotic plaques when measuring IMT (lesions > 1.5 mm are already evaluated as plaque)
- echogenicity, especially of the media, can increase in the presence of fatty infiltration and thickening
- IMT > 95th. percentile for age and sex is taken as abnormal (usually IMT >1 mm is abnormal)
| Female (P95) |
Male (P95) |
||||
|
45 y
|
55 y |
65 y |
45 y | 55 y |
65 y |
|
0.73
|
0.91 | 1.04 |
0.89
|
1 | 1.3 |
95.th percentile [Howard, 1993]
| Age |
P25 | P50 |
P75 |
|---|---|---|---|
| Men <30 | 0.39 | 0.43 | 0.48 |
| Men 31-40 | 0.42 | 0.46 | 0.50 |
| Men 41-50 | 0.46 | 0.50 | 0.57 |
| Men >50 | 0.46 | 0.52 | 0.62 |
| Women <30 | 0.39 | 0.40 | 0.43 |
| Women 31-40 | 0.42 | 0.45 | 0.49 |
| Women 41-50 | 0.44 | 0.48 | 0.53 |
| Women >50 | 0.50 | 0.54 | 0.59 |
Prognostic value of IMT measurement
- not only atherosclerotic plaques, but IMT as well can quantify atherosclerosis burden in asymptomatic patients
- IMT should be assessed in each extracranial ultrasound exam
- an increase in the intima-media thickness is the first stage of atherosclerosis, and if untreated, it is followed by plaque formation
- clinical and epidemiologic studies showed an association of IMT with coronary artery disease (CAD), stroke, and peripheral vascular disease (PAD) (ROTTERDAM, ACAPS trials ) [Lorenz, 2007]
- thickening of IMT correlates with the occurrence of traditional vascular risk factors (BMI, hypertension, hypercholesterolemia, diabetes, smoking)
- some authors recommend including IMT and the AS plaques presence among the classic vascular risk factors [Chambless, 2010]
- some publications question the importance of IMT in the CV events predictions [Costanzo, 2010] [Ruijter, 2012]
- detection of subclinical atherosclerosis is important in patients with borderline risk and multiple risk factors, as it moves the patient to the high-risk category (≥ 5% by SCORE) with all therapeutic consequences
- pharmacological studies have shown a reduction in the rate of progression of IMT on hypolipidemic therapy and antihypertensives (ACAPS, METEOR)
- rosuvastatin did not induce disease regression
- on the other hand, a meta-analysis of 41 randomized trials showed regression of cardiovascular events on hypolipidemic drugs but did not show a relationship between a decrease in CV events and regression of the IMT [Costanzo, 2010]
- an increase in IMT can also be found in non-atherosclerotic diseases (e.g., Takayasu arteritis)