Bedside Ultrasound in Neurosurgery Part 2/3

18-19 JUNE 2013Part 2/3

Ultrasound Training Course

Orbital Window

• Transorbital Doppler sonography is used for investigating the OphA and the carotid siphon.

• The patient is in the supine position, and the vessels are identified by the depth of insonation and direction of blood flow.

• Flow towards the probe is assumed to come from the OphA or C4 segment of the internal carotid artery (ICA; lower carotid siphon), whereas the upper carotid siphon (C2 segment of the ICA) leads to Doppler signals being directed away from the probe.

• Transorbital ultrasound is assumed to be safe when the lowest emission energies are used, and the insonation time is as short as possible.

• For safety reasons, the use of echo contrast agents is prohibited.

Orbital Window

Temporal Bony Window

• The posterior coronal plane depicts the PCA, distal basilar artery (BA), M2 and M3 MCA, and horizontal segment of the petrosal part of the ICA.

• Transtemporal insonation is performed using axial and coronal planes.

• The axial mesencephalic plane depicts the midbrain, which is hypoechogenic and shaped like a butterfly, the sphenoidal (M1) and insular (M2) parts of the MCA, A1 ACA, the terminal segment (C1) of the ICA, and postcommunicating (P2) PCA

• The anterior coronal plane shows M1 MCA, A1 ACA, C1 ICA, parts of the carotid siphon, and C5 ICA.

Temporal Bony Window• With advancing age, and especially in postmenopausal women, the

temporal bone window becomes smaller or may even disappear, and the frequency of ultrasonic detection of intracranial vessels decreases.

• Consequently, vascular structures located in the periphery of the insonation field, such as the petrosal part, C5 and the siphon of the ICA, A2 ACA, M3 and M2 MCA, P3 PCA, the straight-, and transverse sinus will be missed in older patients.

• The temporal window is better in men than women, and in white compared to black and Asiatic patients

• Temporal squama thickness of 2.7mm was associated with a good window, and values of 5.0mm permitted just a partial transcranial study

• 1-MHz probes increase the diagnostic yield of transcranial ultrasound in patients presenting with absent or insufficient temporal bone windows at transtemporal insonation with 2-MHz probes.

Temporal Bony Window

Foramen Magnum Window

• Transforaminal (transnuchal) insonation is performed with an axial scanning plane, and allows the distinction of the atlas loop (V3) and the intracranial segment (V4) of both vertebral arteries (VA), and the BA

Other Windows

Intracranial Occlusion

• TCD diagnosis of intracranial cerebral artery occlusion is established by the absence of Doppler signals in a cerebral artery of a patient with an appropriate acoustic window proven by the detection of at least one ipsilateral cerebral artery.

• TCCDS diagnosis of intracranial occlusion is based on the absence of color and spectral Doppler signals in the occluded vessel, whereas the adequate insonation window can also be demonstrated by depicting adjacent intracranial veins or structures

Intracranial cerebral artery stenosis

• It is not possible to differentiate cerebral artery narrowing due to a vasospasm and stenosis as well as embolic from atherosclerotic stenoses.

• Vasospasm and stenoses due to cerebral embolism typically recanalize within days, weeks, or months.

• In contrast, atherosclerotic stenoses are assumed to show no recanalization.

Thrombolysis in brain ischemia (TIBI) waveform flow grading scale

Thrombolysis in brain ischemia (TIBI)

Examples of TIBI flow grades at different depths in acute middle cerebralartery occlusion.

Diagnostic criteria for acute intracranial occlusion

Intracranial cerebral artery stenosis

Transtemporal color duplex sonography with an axial plane shows a 50% stenosis of the sphenoidal segment of the middle cerebral artery with increased intrastenotic flow velocities (a), and decreased flow velocities and pulsatility distal to the stenosis (b).

Carotid Artery StenosisLongitudinal US image of right common carotid artery ( C ) and internal carotid artery ( I ) showed a large heterogeneous plaque at the originof the internal carotid artery with calcified and fibrolipoid components( arrows ).

Longitudinal color Doppler US images showed a heterogeneous plaque with apparent severe luminal narrowing ( arrows ) at internal carotid artery origin. Note color aliasing at the pointof maximal stenosis ( arrow)

Carotid Artery StenosisPower Doppler US images showed a heterogeneous plaque with apparent severe luminal narrowing ( arrows ) at internal carotid artery origin.

Duplex Doppler image showed a peak systolic velocity of 418 cm/s at the point of maximal stenosis. This velocity represents severe stenosis (more than 70 %).

Carotid Artery StenosisTwo centimeter distal to the stenosis, duplexDoppler showed a peak systolic velocity of 82 cm/s, within normal limits, but with turbulent flow features.

Digital angiography con firmed a severe stenosis in the proximal internal carotid artery ( arrow ). An endovascular stent was placed.

Carotid Artery Stenosis

Measurement of fibrous cap thickness in a carotid atheromatous plaque by a new semi-automatic system. Fibrous cap is defined as the hyperechoic structure existing between two anechoic surroundings (blood and lipid core).


Schematic examples of intra-arterial angiographic measurements for the degreeof stenosis for different configurations of ICA lesions. N ‘NASCET method’; E ‘ECSTmethod

NASCET method describes predominantly the hemodynamic significance of ICA stenosis (relation of the inflow to outflow diameter)1/3

ESCT method reflects more the amount of atherosclerotictissue at the stenosed segment1/2


Nonstenotic ICA plaque without hemodynamic changes, plaque length is about 15mm, plaque thickness 3.9 mm;

approximately 60–70% ICA stenosis

approximately 90% ICAstenosis

proximal ICA occlusion

The upper panel shows longitudinal colorDoppler-assisted duplex imaging where right is proximal

The bottom left panel shows the transverse view of the narrowest part of the stenosis and cross-sectional luminal area reduction measurement

The bottom right panel displays the Doppler shift recording andspectrum analysis, the maximum peak systolic shift is given in kilo Hertz (kHz).

Carotid Artery DissectionLongitudinal color Doppler ultrasound of the right internal carotid artery demonstrating a low-reflective intramural hematoma ( arrows ) compressing the true lumen of the internal carotid artery 2 cm cranially fromthe bulb. These findings are strongly suggestive of internal carotid artery dissection with intramural hematoma.

Color and spectral Doppler ultrasound of internal carotid artery immediately proximal to the lesion shows a high-resistance triphasic waveform.

Carotid Artery DissectionSpectral Doppler at the point of maximal lumen stenosis showsa very high peak systolic velocity (4 m/s).

Digital angiography confirmed an irregular stenosis ( arrowheads ) starting 2 cm distal to the carotid bulb.

Carotid Artery Dissection

Color duplex sonography (power Doppler imaging) with longitudinal (a) and axial (b) planes shows a spontaneous dissection of the cervical internal carotid artery.

•Luminal narrowing and the hypoechogenic and thickened vessel wall (white arrows) begin distal to the carotid bulb. •The unequivocal depiction of the border between the vessel wall and the lumen including the presence of an intimal reflex (arrowheads) suggests that mural thickening is mainly due to a wall hematoma and not an intraluminal thrombus.

Cross-Flow through the Circle of Willis

• Crossflow through the anterior communicating artery was diagnosed in the presence of reversed flow in the ACA located on the side of the obstructed carotid artery.

• If this ACA was missed, decrease of flow velocity in the homolateral MCA during digital compression of the contralateral common carotid artery was used for diagnosis.

• The corresponding sensitivity was 98%, specificity 100%, PPV 100%, and NPV 98%.

• Ultrasound contrast agents increase the detection rate of Willisian collaterals compared to nonenhanced TCCDS

Extracranial-Intracranial Bypass• Catheter- and MR-based angiography are typically used to evaluate

the postoperative bypass patency.• Short-term effects of ECIC bypass on cerebral hemodynamics have

been investigated with various neuroradiologic techniques, including positron-emission tomography (PET), single-photon emission CT (SPECT), and xenon-enhanced CT scanning, these modalities are complicated, expensive, time consuming, and invasive because they expose patients to radiation, making them ill suited for use in the outpatient setting or for long-term routine follow-up of ECIC bypass.

• The ipsilateral STA mean blood flow velocity is a highly sensitive parameter to predict regional cerebral blood flow (rCBF) in the ipsilateral middle cerebral artery (MCA) territory at 14 days after ECIC bypass in patients with internal carotid artery occlusion or middle cerebral artery stenosis.

Transcranial Doppler Sonography In Underwent Decompressive

Craniectomy For Traumatic Brain Injury

• Cerebral blood flow (CBF) velocity by means of transcranial Doppler sonography (TCD) can be performed in patients post decompressive craniectomy for traumatic brain injury

Transcranial Doppler Sonography In Underwent Decompressive

Craniectomy For Traumatic Brain Injury

Transcranial Doppler spectral waveforms obtained from the right middle cerebral artery of patientA, before decompressive craniectomy, the cerebral circulation was characterized by reduced blood flowvelocity and high pulsatility index (PI) (18 cm/s and 7.09, respectively). Note that during the diastolic phase, the blood flow velocity decreases continuously reaching zero value, and straight away, there is a reversion of flow direction (see arrow). This finding can indicate the presence of critical intracranial hypertension with a severe impairment of cerebral blood flow. B, immediately after surgery, the blood flow was restored to a unidirectional pattern, with more acceptable flow dynamics in terms of flow velocity and PI (65 cm/s and 0.92, respectively).

Acute Stroke: Perfusion Imaging

• Ultrasound perfusion imaging of the human brain is a new semi-invasive bedside technique based on the detection of ultrasound contrast agent (UCA) in the brain tissue to evaluate brain perfusion.

• Current UCAs consist of microbubbles composed of a gas that is associated with various types of shells for stabilization.

• Because of their small size, they can pass through the microcirculation several times, thus representing optimum blood pool tracers.

• Multiple pulse technologies receive contrast-agent-specific signals in the fundamental frequency band (so-called nonlinear fundamental signals) with a higher sensitivity than conventional single-pulse approaches.

• As a measure of energy impinging on the tissue, the mechanical index (MI) is defined as the peak pressure of a longitudinal ultrasound wave propagating in a uniform medium divided by the square root of the center frequency of the transmitted ultrasound pulse

Acute Stroke: Perfusion Imaginga Follow-up CT, 48 h after symptom onset, of a 67-year-old woman suffering from middle cerebral artery occlusion. Ultrasound perfusion imaging (Harmonic imaging1.8/3.6 MHz, MI 1.6, 2.4 ml SonoVueTM bolus injection, investigation depth 10 cm, frame rate 0.67 Hz) was performed 2.5 h after symptom onset. b Contrast image with area of reduced contrast enhancement in the middle cerebral artery territory.

Parametric images:c Pixelwise peak intensity image showing the area of reduced signal enhancement (dark) in the middle cerebral artery territory,

d time to peak image showing the dark blue area ofdelayed perfusion, invalid data being displayed in gray,

e area under the curve image, and

f slope image.

Sonothrombolysis:Experimental Evidence

• The combination of ultrasound with thrombolytic agents may enhance the potential benefit by means of enzyme-mediated thrombolysis.

• When ultrasound is applied externally through skin or chest, attenuation will be very low.

• Attenuation, however, is significantly higher if penetration through the skull is required.

• Attenuation is frequency dependent, with ultrasound intensity being 10% of the output intensity for diagnostic frequencies (1 MHz).

• This ratio nearly reverses in the kiloHertz range (500 kHz).


• Ultrasound insonation is efficient for accelerating enzymatic thrombolysis within a wide range of intensities, from 0.5W/cm2 (MI 0.3) to several watts per square centimeter, particularly in the non focused ultrasound field.

• Insonation with ultrasound increased tPA-mediated thrombolysis up to 20% in a static model, while it enhanced the recanalization rate from 30 to 90% in a flow model.

• Most studies demonstrated the potential usefulness of ultrasound for the treatment of arterial or venous thrombosis.

• Ultrasound may also have pro-thrombic effects.


Flow rate over time in a tube model. Measurement of recanalization after complete occlusion from a fibrin clot in different treatment groups:spontaneously (A), when treating with rt-PA only (B), when treating with rt-PA and ultrasound (1 MHz pulsed wave) (D)*, and (C) when treating with rt-PA and ultrasound (1 MHz pulsed wave) transcranially (cadaver skull bone). The addition of ultrasound to tPA treatment showed a further decrease of recanalization time.

Application of Ultrasound through the Skull

• Within 0.25- and 6.0-MHz ultrasound frequencies, the increase of insertion loss through the skull is not only roughly proportionally related to an increased intensity, but also directly linked to the thickness of the diploë and the skull bone

• Ultrasound at low to mid-kiloHertz frequencies and suggest that only those frequencies may reach the brain and intracranial vessels with thermally acceptable levels.

The diagram demonstrates the attenuation of ultrasound through the skulldependent on the used frequency, showing the strong reversed correlation between decrease of intensity and increase of frequency.

Endovascular Application of Ultrasound

• Miniaturized transducers have also been attached to catheters for direct endovascular use, offering the potential of localized ultrasound thrombolysis, while avoiding attenuation of intensity through the skull and reducing insonation of the surrounding tissue.

• The potential endovascular use of microcatheters for acute stroke treatment is limited to specialized centers and a broader applicability seems unrealistic.

Acute Stroke: Therapeutic Transcranial Doppler Sonography

• Proximal intracranial occlusion is a target for more advanced reperfusion strategies, among them ultrasound-enhanced thrombolysis

• High frequencies lead to greater attenuation of ultrasound, lower frequencies may be harmful due to tissue heating.

• The TRUMBI study, a phase II clinical trial testing the use of low frequency ultrasound insonation in acute stroke patients treated with i.v. t-PA, showed a significant increase in hemorrhage, both symptomatic and asymptomatic

• Phase II randomized controlled trial CLOTBUST (Combined Lysis of Thrombus in Brain Ischemia using Transcranial Ultrasound and Systemic TPA), which demonstrated that enhancement of the thrombolytic activity of tPA could be safely achieved by using higher frequency (2 MHz) and low intensity (<700 mW/cm2) single element pulsed-wave ultrasound


• A phase III trial has been planned for quite some time and protocols have been published. The problem, however, is still the lack of an investigator independent device.

• CLOTBUST-Hands Free Initial Safety Testing of a Novel Operator-Independent Ultrasound Device in Stroke-Free Volunteers study published in 2013 showed all subjects were safely insonated with no adverse effects as indicated by the neurological examinations during, immediately after the exposure, and at 24 hours, and no abnormality of the blood brain barrier was found on any of the MRIs.


TCDS of the circle of Willis, showing an occlusion of the MCA-M1 (left).Please note the missing Doppler spectra and the lateral fissure displayed as an echogenicstructure marked by the arrows in the detail of the picture showing the occlusion (middle).Reconstituted flow after recanalization with normalized Doppler spectra (right).

Cerebral Aneurysms

• The prime criterion for the diagnosis of an aneurysm is a color-coded appendix connected with a vessel; additional criteria are – (1) a red and a blue zone within the lumen of the aneurysm due

to bidirectional flow within larger aneurysms and – (2) a circular echogenic structure in B-mode imaging,

demonstrated by fast switching from color-coded mode to B-mode.

• Aneurysms with thrombosed components appear as an echogenic, often calcified shell, which surrounds the less echogenic thrombosed portions.

• The maximum diameter of the color-coded lumen of the aneurysm should be measured in two planes.

Cerebral Aneurysms

Middle cerebral artery aneurysm. Coronal plane section, insonation through thetemporal bone window: the arrow indicates a large aneurysm of the middle cerebral artery with a bicolored zone, which results from simultaneous inflow and outflow within the aneurysmal lumen. The echo-intense small structure in the midline is caused by the cerebral falx.

Cerebral Aneurysms

Basilar artery aneurysm. Transversal insonation plane, insonation through the temporal bone window: this figure demonstrates the circle of Willis with a giant aneurysm (surrounded by dotted line) at the top of the basilar artery compressing the brain stem.LMCA =Left middle cerebral artery; LACA = left anterior cerebral artery; RMCA =right middle cerebral artery; F = frontal; T = temporal.

Cerebral Aneurysms

Thrombosed aneurysm. Transversal insonation plane, insonation through thetemporal bone window: this figure shows a particularly thrombosed large aneurysm (arrows) of the distal segment of the internal carotid artery. Half of the aneurysm is occluded by thrombosed (black signal) and calcified material (bright signal), while blood flow is detectable in the other half of the lesion. The bright signal in frontomedial position to the aneurysm is the base of the skull (os sphenoidale). F = Frontal, T = temporal.

Cerebral Aneurysms

Cerebral Arteriovenous Malformations

• Using TCCS, large (4 cm) cerebral arteriovenous malformations (AVMs) can be depicted by B-mode imaging as echodense areas interspersed with zones of lower echo intensity.

• The color-coded illustration of intravascular flow phenomena allows the distinct identification of the major feeding vessels, venous drainage, and vascular convolution of the AVM.

• Information on hemodynamics, such as the blood supply of the angioma, may be obtained by analysis of the Doppler spectrum, in addition to color-coded identification of flow direction.



Arteriovenous malformation, transverse. Transversal insonation through thetemporal bone reveals a large arteriovenous malformation with convolutes of arterial and venous vessels in the temporal lobe and the basal ganglia. Aliasing phenomena reflect increased flow velocities in all vessels. The echo-intense (bright) signal at the bottom of the figure is caused by the contralateral temporal bone.

Thank You

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Bedside Ultrasound in Neurosurgery Part 2/3