Vascular Medicine. Thomas Zeller

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malformation

      

Possibly in cases of elongation and kinking at the site of the stenosis

      

Measurement of the relevant parameters during cardiac irregularities—e.g., after extrasystoles with a compensatory pause, or in absolute arrhythmia after a longer RR interval, or with an increased ejection volume in cases of aortic insufficiency or marked bradycardia

      There is a risk of underestimating stenoses in the internal carotid artery:

      

In cases of tandem stenoses of the internal carotid artery or highgrade flow obstructions in the area of the carotid “T” or main trunk of the middle cerebral artery

      

With hyperventilation (intracerebral vasoconstriction)

      

In cases of marked cerebral microangiopathy or raised intracranial pressure with disturbed distal outflow

      

When measurements are carried out during hemodynamically compromising tachycardic heart action

      

In cases of upstream high-grade flow obstructions

      Occlusion can be differentiated from “pseudo-occlusion” or filiform stenosis by:

      

Low flow–optimized setting of the device (PRF low, line thickness increased, etc.)

      

Increasing the color enhancement appropriately (caution: artifacts)

      

Using alternative color scales (mixed mode), color procedures (power mode), and imaging modes (B flow, color B flow)

      

Optimizing the transducer head position and beam position

      

Using ultrasound contrast enhancement

      

Including the intracranial findings

      Check-up examinations postoperatively or after stent angioplasty in the internal carotid artery:

      

In both procedures: residual stenosis, recurrent stenosis, intimal hyperplasia in the internal carotid artery, intraluminal thrombi, flow conditions at the external carotid artery orifice?

      

After surgery: intimal flap, proximal/distal step formation, aneurysmal dilation in the patch area (TEA)

      

After internal carotid artery stenting: is the stent well opposed or is there flow behind it; is the stenotic area completely covered?

      In-stent restenosis:

      

Slightly altered velocity criteria have been described (by Armstrong et al. 2007, among others), partly due to reduced wall compliance in the stent area and loss of the luminal dilation (“bulb”) often (but not always) located in the internal carotid artery orifice area.

      External carotid artery

      There is no established classification of stenosis grades for external carotid artery stenoses based on maximum velocities. In addition to general stenotic characteristics (see under internal carotid artery stenoses), the peak velocity ratio can be used.

      The differential diagnosis should include distal arteriovenous malformations in the afferent areas for branches of the external carotid artery, as well as dural fistulas; flow acceleration/aliasing is then seen over long stretches and not only focally in the “stenotic area.”

      

      Table 1.1–4 Stenosis grades after stent angioplasty in the internal carotid artery.

	> 70%	> 50%
PSV (cm/s)	> 350	> 225
ICA–CCA ratio	> 4.75	> 2.5

      CCA, common carotid artery; ICA, internal carotid artery; PSV, peak systolic velocity.

      Fig. 1.1–9 An aneurysm in the internal carotid artery. A typical “coffeebean” fragmented color pattern in an internal carotid artery aneurysm, with relative stenosis in the outflow area.

      Fig. 1.1–10 Stenosis of the external carotid artery. A typical undulation phenomenon is seen in the external carotid artery, with evidence of moderate stenosis.

      In cases of occlusion of the external carotid artery, side branches are often collateralized via the corresponding external carotid artery branches on the contralateral side or branches of the thyrocervical trunk or costocervical trunk.

      Subclavian artery

      See section A 4.1.

      Vertebral artery

      For findings involving the subclavian steal effect/syndrome, see section A 4.1.

      There is no established classification of stenosis grades based on maximum velocities for vertebral artery stenoses. The criteria mentioned in connection with the internal carotid artery can be used, but it should be noted that minor flow disturbances in the obtusely angled orifice area of the vertebral arteries must be regarded as physiological. The velocities given should be lower, as the physiological maximum systolic flow velocity is approximately 60–100 cm/s. Values above 100 cm/s must be regarded as suspicious. The critical velocity after which the presence of a > 50% stenosis must be assumed is 120 cm/s (Baumgartner et al. 1999). The peak velocity ratio may also be used.

      Differential diagnoses in cases of flow acceleration

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