Introduction
In the last decade, neurosonology (ultrasound examination in neurology) has been undergoing
a significant expansion of its modalities, including brain and atherosclerotic plaque
perfusion imaging, elastography, fusion imaging, super-fast Doppler, blood flow volumetry,
digital image analysis in, e. g., transcranial sonography and carotid plaque imaging,
and translation of the cerebral hemodynamics and vasoregulation into clinical decision
making [1]
[2]
[3]
[4]. This development has led to increased diagnostic confidence and, thus, a better
quality of care. However, it places high demands regarding ultrasound devices, sonographer
competence, and, above all, the required critical examination duration [5]
[6].
In parallel, various acute diseases increasingly require rapid and high-quality diagnostics
to be able to initiate treatment, starting in the prehospital setting, the emergency
department, intensive care medicine, and during surgical or interventional procedures.
There is particular demand for ultrasound examinations, exceeding the combined number
of computed tomography, X-ray, and magnetic resonance imaging procedures. In addition,
due to the high diagnostic accuracy, widespread availability, low price, non-invasiveness,
and mobility of ultrasound devices, the use of sonographic examination is often the
first choice for these patients. Thus, a new ultrasound examination concept as a method
that provides quick answers to specific clinical questions emerged, instead of a complete
standard examination. This concept was called point-of-care ultrasound (POCUS).
With the recent progress in efficient therapies, the need for a rapid answer to a
clinical question applies to various acute neurological conditions. In addition, the
COVID-19 pandemic has increased the need for neurosonological point-of-care diagnostics
in order to meet hygienic concepts, that are ideally bedside, and to minimize the
risk of virus transmission by minimizing the sonographer’s total exposure – [Fig. 1]. Thus, the Neuro-POCUS working group, a joint project of the European Academy of
Neurology Scientific Panel of Neurosonology, the European Society of Neurosonology
and Cerebral Hemodynamics, and the European Reference Centers in Neurosonology (EAN
SPN/ESNCH/ERNsono Neuro-POCUS working group) was given the task of creating a concept
for point-of-care ultrasound in neurology called “Neuro-POCUS”. Nevertheless, the
POCUS concept should not replace a comprehensive ultrasound examination, but rather
allow physicians immediate access to clinical ultrasound for rapid and direct solutions
[7].
Fig. 1 Neuro-POCUS examination in a patient with suspected COVID-19 infection.
The aim of the paper is to give the basics, concept, and outline of potential indication
fields for Neuro-POCUS.
What is Neuro-POCUS?
The definition of POCUS is slightly diverse in published documents. Nevertheless,
most definitions share some fundamental features, in particular the performance of
ultrasound by the clinician in charge of the patient’s therapy on-site, regardless
of where he or she may be located [7]
[8]. Unlike ultrasound examination of most parts and organs of the human body, neurosonological
examination of the head, neck, and neuromuscular system is not part of POCUS for intensivists,
anesthesiologists, and general practitioners. Thus, the Neuro-POCUS working group
defines Neuro-POCUS as a specific part of POCUS. After searching existing POCUS definitions
in the databases MEDLINE (via PubMed), Web of Science, Google Scholar, we define Neuro-POCUS
as a goal-directed/focused portable ultrasound examination of the head, neck, and/or
musculoskeletal system, performed at the patient’s bedside or where the patient is
being observed/treated, in order to obtain a prompt answer to a specific clinical
question related to neurological symptoms in real time for guiding diagnostics (e. g.,
symptom-based examination) and treatment, including therapeutic supporting procedures
(e. g., image guidance). Ultrasound equipment can be delivered wherever the patient
is located and, thanks to the advances in computational power, high-quality portable
ultrasound machines are now widely available.
Why is Neuro-POCUS performed?
The treatment options in various acute neurological diseases have significantly advanced
in the past two decades. The resulting work densification calls for goal-directed
diagnostics, as fast and efficient diagnostics are prerequisites for specific treatment
pathways, including their modification, both of which can significantly improve treatment
success and, therefore, the prognosis of patients [9]. For safety reasons during transport, for faster answers to clinical questions,
or for other reasons of convenience, it is frequently more appropriate to bring ultrasound
to the patient instead of the patient to the ultrasound department. Thus, Neuro-POCUS
has high potential for playing a key role in clinical neurology questions, not only
in the emergency room but also in the intensive care unit (ICU), stroke unit, surgery
ward, and outpatient clinic or in a remote village.
The potential use and benefits of the Neuro-POCUS examination are very broad. The
most important areas of use and indications identified by the Neuro-POCUS working
group, with examples of clinical questions, machine settings, and examination algorithms,
are described below.
Who should perform Neuro-POCUS?
Neurosonology examination is critically dependent on each patient’s clinical settings,
including working and differential diagnoses. Thus, Neuro-POCUS should ideally be
performed by a physician who has experience in clinical neurology, as well as in at
least the specific area of neurosonology that is in question. Otherwise, close cooperation
between all involved specialists is mandatory. Nevertheless, it needs to be emphasized
that questions with different degrees of complexity require different levels of neurosonology
experience. The requirements for each Neuro-POCUS question include substantial theoretical
knowledge of the subject, clinical and anatomical knowledge, technical knowledge including
sensitivity and specificity of the technique applied, and sonographic skills, including
having examined a sufficient number of patients with relevant/similar diagnoses using
recommended sonographic modalities.
Where to perform Neuro-POCUS?
In principle, the Neuro-POCUS examination can be performed in any setting where the
patient is located and the clinical workflow is immediately driven by ultrasound findings,
depending only on the ultrasound equipment’s size and mobility and the patients themselves.
It might be applied at the very first contact with a doctor/paramedic at the patient’s
home, in an ambulance, or even in a helicopter [8]
[10]
[11], bedside in a hospital, in the emergency room [12]
[13]
[14], ICU [13]
[14]
[15]
[16], stroke unit, neurology, surgery or other hospital wards, outpatient clinic, or
in a remote village by means of telemedicine [17]
[18].
Neuro-POCUS could be used in the four basic scenarios:
1) Triage in the emergency room
Emergency wards are often the primary place in which neurologists have contact with
patients presenting acute neurological symptoms, and neurosonology examinations can
detect pathological findings in various diseases and pathological conditions ([Table 1], indications 1, 2, 3, 7, and 8). Stroke diagnosis is the prevailing application
as, given the elderly population, vascular pathologies are among the most common pathological
findings. Although it should not delay CT or MR imaging and revascularization treatment,
Neuro-POCUS may rapidly provide information about a large vessel occlusion or significant
stenosis or suggest a carotid dissection often even in agitated patients, thereby
guiding the examiner to specific treatments, e. g., CT imaging under sedation [19]. In acute amaurosis, US can help with the differential diagnosis and allow faster
treatment [20].
Table 1
List of potential indications for the Neuro-POCUS examination.
|
No.
|
Clinical situation/ symptoms/diagnosis
|
Pathological findings that may be detected by Neuro-POCUS examination
|
|
1.
|
Acute stroke (incl. transient ischemic attack), stroke prevention and stroke mimics
(e. g., dizziness, paresthesia, disturbance of consciousness)
|
Acute large artery occlusion, including central retinal artery occlusion [5]
[6]
[10]
[19]
[20]
[26]
[28]
[44]
[46]
[49]
[54]
[58]
[59]
[60]
|
|
Recanalization of occluded artery [5]
[13]
[22]
[26]
[27]
[28]
[49]
|
|
Arterial reocclusion [5]
[13]
[26]
[61]
|
|
Arterial dissection [5]
[27]
[62]
|
|
Vasospasm/aneurysm [5]
[7]
[14]
[23]
[31]
[63]
|
|
Intracerebral hemorrhage [64]
[65]
[66]
|
|
Arterial stenosis [5]
[33]
[44]
[49]
|
|
Microembolization to cerebral arteries [26]
[37]
[38]
[39]
[40]
[42]
[52]
[53]
[67]
[68]
|
|
Malignant brain edema [14]
[23]
[60]
|
|
Hyperperfusion syndrome [2]
[5]
[49]
[60]
[69]
[70]
|
|
Intracranial flow acceleration in sickle cell disease [71]
|
|
2.
|
Impaired consciousness (qualitative and quantitative) or unconsciousness
|
Basilar artery occlusion [5]
[19]
[44]
[72]
[73]
[74]
|
|
Local increase in blood flow velocities in the intracranial arteries and/or increased
pulsatility and/or resistance indices as a sign of neuroinfection/vasculitis (meningitis,
encephalitis) [75]
[76]
|
|
Intracranial hypertension [9]
[14]
[24]
[59]
[77]
[78]
|
|
Local increase in blood flow velocities in the intracranial arteries as a sign of
posterior reversible encephalopathy syndrome/acute hypertensive encephalopathy [13]
|
|
3.
|
Headache
|
Local increase in blood flow velocities in the intracranial arteries and/or decreased
pulsatility and/or resistance indices as a sign of migraine [79]
[80]
[81]
|
|
Local increase in blood flow velocities in the intracranial arteries as a sign of
reversible cerebral vasoconstriction syndrome, vasospasm [31]
[32]
|
|
Arterial dissection [5]
[27]
[62]
|
|
Local increase in blood flow velocities in the intracranial arteries and/or increased
pulsatility and/or resistance indices as a sign of neuroinfection/vasculitis (meningitis,
encephalitis) [9]
[14]
[24]
[59]
[77]
[78]
Giant cell arteritis with halo sign [82]
|
|
4.
|
Abnormal shunts
|
Detection of the right-left-shunt, intracardiac/extracardiac paradoxical embolism
[26]
[83]
[84]
[85]
|
|
Quantification of right-left shunt [84]
|
|
Detection of the residual right-left shunt after patent foramen ovale or pulmonary
arteriovenous malformation closure [86]
[87]
|
|
Detection of the dural fistula [88]
[89]
|
|
5.
|
Surgery and intraarterial interventions
|
Monitoring of changes in cerebral blood flow (hypoperfusion/hyperperfusion) [16]
[24]
[31]
[32]
|
|
Microemboli detection [26]
[37]
[38]
[39]
[40]
|
|
Detection of residual flow in arteriovenous malformation or aneurysm after embolization/clipping/coiling,
etc. [90]
[91]
|
|
Monitoring of third ventricle diameter in hydrocephalus [15]
[16]
[92]
|
|
6.
|
Lumbar, venous, and arterial puncture, intramuscular/intraglandular Botulinum toxin
injection
|
Find the optimal way for puncture [41]
[93]
[94]
|
|
Venous thrombosis detection [95]
[96]
|
|
7.
|
Intracranial hypertension and brain death
|
Midline shift detection and monitoring [14]
[15]
[16]
[24]
[97]
|
|
Optic nerve papilloedema [77]
[98]
|
|
Optic nerve sheath diameter measurement [9]
[15]
[16]
[59]
[77]
[78]
[98]
|
|
Measurement of change in the width of ventricles [14]
[15]
[16]
[92]
|
|
Monitoring of intracranial pressure using pulsatility and resistance indices (in the
middle cerebral artery) [14]
[15]
[16]
[24]
[98]
|
|
Brain death diagnostics [9]
[14]
[35]
[36]
[99]
|
|
Hydrocephalus, measurement of ventricles [15]
[16]
[92]
|
|
8.
|
Cranial trauma and peripheral nerve injury
|
Intracranial/intracerebral hemorrhage [92]
|
|
Midline shift [14]
[15]
[16]
|
|
Detection of increased intracranial pressure [9]
[14]
[15]
[16]
[24]
[59]
|
|
Vasospasm [7]
[63]
[100]
[101]
|
|
Peripheral nerve lesions (nerve disruption, edema, oppression) [25]
[102]
[103]
|
A recent meta-analysis of 45 studies, which analyzed 18 304 acute stroke patients
and employed vascular neurosonography beyond CTA, MRI, and/or digital subtraction
angiography, found an ipsilateral non-stenotic carotid plaque in 51 % of patients
(95 % CI: 45–59) [21]. Moreover, the Neurosonology in Acute Ischemic Stroke study group published occlusion
rates of 33 % to 66 % in cervical and/or intracranial brain-supplying arteries detected
by ultra-early duplex sonography [22].
Elevated intracranial pressure (ICP) is a serious and relatively common pathological
condition that may lead to neurological and ophthalmological symptoms, which can be
life-threatening or highly debilitating, and is easily treatable using various neurosonographic
methods [23]
[24].
Patients with suspected cranial trauma or peripheral nerve trauma represent a significant
percentage of patients in the emergency room [25]. Sonography might help detect both peripheral nerve lesions and complement CT scans
in traumatic brain injury (e. g., intracranial/parenchymal hemorrhage, midline shift,
increased ICP, or vasospasm) [13]
[25].
2) Examination in the ICU/stroke unit
Noninvasive neuromonitoring with bedside neurosonography plays an important role in
the ICU and, especially, in stroke units ([Table 1], indications 1,2,3,6,7, and 8). It can be used in acute ischemic stroke patients
to monitor arterial recanalization during systemic thrombolysis, after endovascular
treatment, as well as the spontaneous course of the disease [26]
[27]. Using neurosonology examination in the acute phase of ischemic stroke in patients
treated with thrombolysis has been associated with a better outcome, perhaps reflecting
a potential impact on patient management [28]
[29]
[30]. In stroke patients with acute deterioration of their neurological status, bedside
neurosonological examination can rapidly detect several pathologies that may cause
this worsening (e. g., arterial re-occlusion, microembolic signals [MES] and recurrent
stroke, parenchymal/intracranial bleeding, hyperperfusion syndrome, malignant brain
edema, or vasospasms) [31]
[32]. Neuro-POCUS might also be helpful in rapid identification of the specific cause
of ischemic stroke bedside, such as arterial dissection or cerebral MES suspicious
for acute endocarditis, which may lead to optimization of treatment without time delay.
In general, early detection of the stroke cause is essential for early secondary prevention
treatment [33].
Neurosonology, especially TCD examination, plays an important role in patients with
acute subarachnoid hemorrhage by early detection of complications, such as vasospasm,
hyperperfusion, hydrocephalus, and rising ICP [34]. Monitoring intracranial hypertension and the effect of treatment is among the most
important roles of bedside neurosonology examination. Neurosonology (with the possibility
of serial examination) is also useful for early cerebral circulatory arrest diagnostics,
especially in organ donation after brain death [35]
[36].
3) Control and support during interventions
Besides monitoring arterial recanalization in acute stroke patients using different
methods (e. g., intravenous thrombolysis, endovascular mechanical thrombectomy, stenting,
carotid revascularization), as mentioned above, specific sonographic applications
may also be helpful to monitor various interventions ([Table 1], indications 5 and 6). TCD monitoring can be used for the early detection of MES
or cerebral hypoperfusion during cardiac surgery, coronary artery stenting, carotid
artery endarterectomy or stenting, orthopedic surgery, or other interventions with
a high risk of stroke [37]
[38]
[39]
[40]. Duplex sonography can support finding the optimal route during lumbar, arterial,
or venous puncture [41]. In general, in all such situations the Neuro-POCUS concept is typically employed
instead of standard comprehensive neurosonology examination in the ultrasound department.
4) Differential diagnosis and decisions regarding further management in ambulatory
neurology
Although there is currently no common reason in ambulatory neurology for patients
to be indicated for Neuro-POCUS instead of standard neurosonological examination,
the COVID-19 pandemic has shown that not only the clinical condition of patients but
also the risk of spreading the infection may limit patient transport. Moreover, rapid
neurosonology examination may play an important role in ambulatory neurology for differential
diagnosis and decisions regarding further management of selected patients with various
neurological symptoms ([Table 1], indications 1, 3, and 4). Examples might be rapid tracking for significant cerebral
arterial circulation lesions in patients with transient symptoms (e. g., TIA due to
large vessel disease, Bow Hunter’s syndrome, subclavian steal syndrome), helping to
distinguish arterial dissection, or detection of transient vasospasms in patients
with headache.
When to perform Neuro-POCUS?
Neuro-POCUS examination is indicated mainly when the physician or consultant responsible
for a patient´s care decides that transporting the patient to the ultrasound department
is not feasible (e. g., during interventional procedure) or is risky due to time delay
of treatment or intervention, unstable patient condition, or spreading of infection,
or when a rapid answer is needed or beneficial for a patient.
The portability of ultrasound devices makes it possible to select the optimal timing,
according to the best incorporation of the information in the clinical workflow of
the patient with neurological symptoms or the acutely unwell patient, during intensive
care rounds, or during and after several interventions. The optimal time for performing
the Neuro-POCUS examination is immediately after a clinical question is raised that
can be answered by neurosonology examination, without undue delay.
What is required to perform Neuro-POCUS?
Neuro-POCUS requires a portable (mobile) duplex (Doppler plus echography imaging)
ultrasound device that can potentially access the patient at the bedside, in both
the prehospital and hospital settings. This equipment allows studying of the cervical
and/or intracranial vessels, as well as examining of other body parts. Thanks to the
advances in clinical ultrasound, we have access to high-quality, portable duplex sonographic
devices, offering high resolution and clearly defined images. The machine and battery
stand-by/fast power-up mode has developed to allow true routine and widespread use
at the patient’s bedside. The TCD machines, which have no echography imaging, are
useful mainly for cerebral hemodynamics monitoring because the small Doppler probes
can be mounted bilaterally in a cranial helmet, allowing continuous blood flow velocity
and MES monitoring without operator assistance [42].
The requirements for probes and imaging quality do not differ from classical neurosonological
examination. For extracranial (cervical) vessel examination, a medium-frequency (5–12
MHz; optimally 3–15 MHz) linear array probe is required. A high-frequency 12–18 MHz
linear array probe is required for superficial temporal artery and musculoskeletal
examinations, as well as for small children. A low-frequency (2.5 MHz; optimally broad-band
1–5 MHz) phased array is required to examine intracranial arteries and/or intracranial
parenchymal structures using TCD, TCCS, or transcranial B-mode sonography (TCS). For
continuous monitoring of MES as well as to obtain information about cerebral hemodynamics
during therapeutic interventions, we need a TCD device with 2-MHz monitoring probes
with customized software.
Whenever the quality of the temporal bone window is low, insufficient, or absent,
or a large intracranial artery occlusion is suspected, an ultrasound echocontrast
agent (UEA) may improve the sensitivity and specificity of the examination [43].
How to perform Neuro-POCUS?
The physician/neurosonographer should perform a clinically oriented fast-track examination
at the patient’s bedside in a convenient supine position, mostly but not exclusively
from behind the patient’s head or at the patient’s side. In case patient positioning
is not possible due to the patient’s medical condition or if there is no time to position
the patient, Neuro-POCUS can be performed in any patient position that allows the
necessary ultrasound application. Depending on time, the clinical question, and requirements,
duplex sonography of cervical vessels, orbit, intracranial vessels, parenchyma, or
even other targets is performed.
For example, a Neuro-POCUS cerebrovascular examination in acute stroke should be done
as a “fast track” study [5]:
-
the examination is focused on the symptomatic vascular territory where the examination
should start,
-
case-specific clinical competence is necessary for planning the steps of the examination,
-
the examination might be performed even after the start of therapy to ensure the earliest
possible initiation of treatment,
-
despite the time pressure, emergency diagnostics should be performed both extra- and
intracranially when it is suitable for the diagnosis; but only limited vessels usually
need to be examined to answer the acute clinical question, in contrast with standard
comprehensive neurosonology [44].
-
color duplex sonography allows an anatomical overview and significantly simplifies
and speeds up the identification of vessel occlusion. In addition, clear documentation
of the findings is possible at the push of a button,
-
it is possible to adapt the workflow of the examination whenever patients are agitated,
confused, anxious, or aphasic.
Also, for TCD, the time of Neuro-POCUS TCD monitoring is set individually by the clinician
and sonographer to answer the target clinical question compared to standard TCD monitoring
[45].
In general, the choice of the scope of the neurosonological examination depends on
the clinical question and the condition of the patient.
During the COVID-19 pandemic, special attention must be paid to hygiene concepts.
The ultrasound providers (physicians, sonographers) involved in the care of stroke
patients with/without COVID-19 must assure safety, avoid spreading infection, and
ensure the delivery of hyper-acute treatment [46].
Creating Neuro-POCUS clinical questions
The implementation of Neuro-POCUS with contracting target questions should consider
the setting (e. g., hospital/pre-hospital; intensive/semintensive/regular care), the
clinical scenario (e. g., acute/chronic; stroke/headache), alternative investigations
available (e. g., CT/CTA, MRI/MRA), its impact on diagnosis, and its therapeutic implications
([Table 2]) [47]. For example, the role of Neuro-POCUS in assessing a large vessel occlusion in a
stroke patient in the prehospital setting where no other imaging modalities are available
is much different than its role when evaluating the same patient in a tertiary care
center.
Table 2
Recommended methodology for creation of Neuro-POCUS clinical questions with examples.
|
(P)opulation
|
|
(I)ntervention
|
|
(C)omparator
|
|
(O)utcome
|
|
Symptoms/disease
|
Location
|
Neuro-POCUS protocol
|
Timing
|
Other diagnostic method(s)
|
Considerations
|
Role
|
|
Stroke
|
Ambulance/ED/SD unit/ICU/ward
|
TCD/TCCS +/–
Carotid/vertebral US
|
Urgent
|
CT/CTA
MRI/MRA
|
Radiation exposure, absolute/relative contraindications, cost, availability
|
Establish diagnosis & guide treatment
|
|
Headache
|
Ambulance/ED/ward
|
TCD/TCCS
Carotid/vertebral/superficial temporal artery US
|
Urgent
|
CT/CTA
MRI/MRA
|
Radiation exposure, absolute/relative contraindications, cost, availability
|
Rule out vascular abnormalities (e. g., dissection, RCVS) & cerebral edema,
diagnosis of giant cell arteritis
|
|
Impaired consciousness
|
Ambulance/ED/SD unit/ICU/ward
|
TCD/TCCS
|
Urgent
|
CT/CTA
MRI/ MRA
|
Radiation exposure, absolute/relative contraindications, cost, availability
|
Rule out vascular abnormities (e. g., occlusion, vasospasm) & cerebral edema
|
|
TCD/ carotid vertebral US or TCCS/ carotid vertebral US
|
Semi-urgent
|
CT/CTA
Perfusion scintigraphy/SPECT
|
Exposure to contrast agents, need of transportation of mechanically respirated patients,
cost, availability
|
Proof of cerebral circulatory arrest
|
|
Other neurological symptoms
|
ICU
|
Transorbital sonography
|
Semi-urgent
|
Fundoscopy
|
Technical challenges, use of mydriatics
|
Monitoring/follow-up of intracranial pressure
|
|
Subacute Sensory/motor symptoms in extremities
|
ED/SD unit/ICU/ward
|
Peripheral nerve US
|
Semi-urgent
|
EMG
|
Availability
|
Diagnosis of neuropathies/plexopathies & prognostication
|
|
Muscle US
|
Semi-urgent or Elective
|
CT, EMG
|
Availability
|
Intramuscular botulinum toxin injection in painful nerve compression syndromes (e. g.,
thoracic outlet syndrome, piriformis syndrome)
|
|
Dysphagia with hypersalivation
|
ED/SD unit/ICU/ward
|
US of parotid and submandi-bular gland
|
Semi-urgent or Elective
|
Injection without US guidance
|
Availability
|
Intramuscular botulinum toxin injection in relative hypersalivation due to dysphagia
with imminent aspiration
|
CT – computed tomography; CTA – computed tomography angiography; DSA – digital subtraction
angiography; ED – emergency department; EMG – electromyography ICU – intensive care
unit; MRI – magnetic resonance imaging; MRA – magnetic resonance angiography; POCUS
– point-of-care ultrasound; RCVS – reversible cerebral vasoconstriction syndrome;
SD – step-down unit; SPECT – single photon emission computed tomography; TCCS – transcranial
color-coded duplex sonography; TCD – transcranial Doppler; US – ultrasound.
The sonographer applying Neuro-POCUS in the clinical setting should be well acquainted
with the ultrasound protocol and technical requirements, to be able to answer a specific
clinical question while also deeply understanding the inherent advantages and limitations
of ultrasound compared to other imaging techniques, for a given clinical setting.
Finally, before initiating any Neuro-POCUS protocol, the examiner should set a clear
target for the specific information to be obtained from the examination, the translation
of the provided information to patient care, and whether the information provided
by Neuro-POCUS is expected to have an impact, and at which level, on the patient’s
outcome. Examples of potential Neuro-POCUS questions can be found in [Table 3], [4], [5] and in 2 cases in the supplemental material and [Fig. 2], [3].
Table 3
Examples of Neuro-POCUS key findings: Patients with acute stroke symptoms.
|
Diagnosis
|
TCCS finding
|
Confirmation
|
Tips & limitations
|
|
MCA main stem occlusion
|
Absence of ipsilateral MCA color-coded in red [skill level low]
|
Visualization of the ipsilateral and contralateral ACA (blue and red)
|
Perform flow measurements in order not to miss MCA low flow
|
|
Carotid-T occlusion
|
Absence of ipsilateral MCA color-coded (red) and ACA (blue) [skill level low]
|
Visualization of the contralateral ACA (red) and ipsilateral PCA
|
|
|
Basilar artery occlusion
|
Absence of both PCAs in the P1-segments (= top of the basilar) [skill level low]
|
Visualization of the anterior circulation (MCA, ACA)
|
Visualization of both P2-segments in a non-comatose patient may be due to fetal type
origin of the PCA
|
|
ICA occlusion or high-grade stenosis
|
Reversal of flow in the ipsilateral ACA [skill level moderate]
|
“Musical murmurs” in the anterior communicating artery
|
|
|
Space-occupying lesions (ICH, subdural hematoma or brain tumor, etc.)
|
Midline displacement of the third ventricle [skill level high]
|
Increase of pulsatility index in the MCAs
|
The finding may be non-specific and should correlate with the patient’s neurological
status
|
|
ICH
|
Hyperechoic mass lesion [skill level high]
|
Location in the basal ganglia and thalamus has the highest sensitivity
|
ICH detection is difficult, as hyperacute ICH, cortical, cerebellar, frontal, and
occipital ICH can be missed
|
Minimal requirement is an ultrasound machine: 1.5–3 MHz phased array transducer
Location: prehospital, emergency ward, stroke unit, outpatient clinic
Diagnostic boost: application of an echo-enhancing agent increases diagnostic confidence,
increases diagnosis in a poor temporal bone window, and saves time
ACA – anterior cerebral artery; ICA – extracranial internal carotid artery; ICH –
intracerebral hemorrhage; MCA – middle cerebral artery; PCA – posterior cerebral artery.
Table 4
Example of Neuro-POCUS-specific clinical questions: Is the intracranial pressure increased?
|
Parenchymal diagnostics
|
Hemodynamic findings
|
Orbital sonography
|
|
Modalities/techniques/modes
|
B-mode
Monitoring of midline shift and third ventricle
(malignant cerebral infarction, intracerebral hemorrhage, hydrocephalus)
|
TCD- and TCCS-derived parameters, especially increased pulsatility index [104]
|
B-mode
|
|
Minimal level of experience required
|
Intermediate skill
(US > 100 measurements and > 20 compared with the CT scan)
|
Intermediate skill
(> 25 examination)
|
Intermediate skill
(> 15 examination)
|
|
Location/scenario
|
Neurointensive care/stroke unit
Emergency department
|
Prehospital
Emergency department
Neurointensive care/stroke unit
|
Prehospital
Emergency department
Neurointensive care/stroke unit
|
|
Minimal requirements for ultrasound probe
|
2–4 MHz probe
|
2–4 MHz probe
|
At least 7.5 MHz linear probe, at best
> 12 MHz
MI 0.2 reduction
|
|
Restricted examination protocol
|
|
Measurement of PI (or RI) in one intracranial artery (optimally middle cerebral artery)
bilaterally
|
Depth of 3 mm behind the retina
|
|
Cut-off values
|
Third ventricle diameter (7 and 10 mm for subjects < 60 and ≥ 60 years of age, respectively)
[55]
|
Normal values = 0.7 +-1
PI values above 2 with normal mean arterial blood pressure in a normocapnic patient
can indicate elevated ICP
|
Normal values
5.4 ± 0.6 mm [105]
Abnormal values between 6–7 mm
|
|
Pitfalls
|
Lack of adequate acoustic temporal bone window
|
Hemicraniectomy
|
Optic nerve atrophy
Glaucoma
Ocular trauma
|
CT – computed tomography; ICP – intracranial pressure; PI – pulsatility index; RI
– resistance index; TCCS – transcranial color-coded duplex sonography; TCD – transcranial
Doppler; US – ultrasound.
Table 5
Example of Neuro-POCUS-specific clinical questions: Is a shunt indicated during a
carotid endarterectomy?
|
Hemodynamic findings
|
|
TCD (TCCS) monitoring
|
|
Minimal level of experience required:
|
Low skill (5 repeated examinations or TCD monitoring)
|
|
Location/scenario:
|
Hospital – operating room
|
|
Time (when is Neuro-POCUS indicated):
|
During carotid endarterectomy (clipping carotid artery)
|
|
Minimal requirements for ultrasound machine:
|
TCD/TCCS machine
|
|
Minimal requirements for ultrasound probe:
|
2-MHz TCD probe
|
|
Restricted examination protocol
|
Continuous or repeated measurement of PSV and MFV in MCA
|
|
Cut-off values during clamping predicting postinterventional new brain ischemic lesion:
|
MFV in MCA < 25 cm/s has SE = 100 % and SP = 69 %.
MFV in MCA < 6 cm/s has SE = 22 % and SP = 100 %.
Decrease of MFV in MCA compared with baseline ˃48 % has SE = 100 % and SP = 86 %.
Decrease of MFV in MCA compared with baseline ˃70 % has SE = 78 % and SP = 100 %.
[106]
|
|
Pitfalls:
|
Missed signal due to movement of the probe
Inaccurate measurement of PSV and/or MFV due to inadequate acoustic temporal bone
window
Drop of blood flow velocity due to decrease/low blood pressure
|
ICA – internal carotid artery; MCA – middle cerebral artery; MFV – mean flow velocity;
PSV – peak systolic velocity; SE – sensitivity; SP – specificity; TCCS – transcranial
color-coded duplex sonography; TCD – transcranial Doppler.
Fig. 2 Neuro-POCUS examination of orbita in patient with idiopathic intracranial hypertension
A with a detection of papilloedema 1.3 mm B and a distal enlargement of the optic nerve sheath diameter of 6 mm C.
Fig. 3 A case of complementary neuroimaging in a patient with acute stroke. Brain CT: a
left insular infarction A. CT angiography: a middle cerebral artery occlusion B. Transcranial color-coded duplex sonography: absence of flow in the middle cerebral
artery and good flow in a deep middle cerebral vein C and decreased resistance index in the ipsilateral anterior cerebral artery is suggestive
of collateral flow D. Digital subtraction angiography: excessive anterior cerebral artery collaterals
E. Digital subtraction angiography: restored middle cerebral artery blood flow F. Transcranial color-coded duplex sonography: blood flow without hyperperfusion in
the middle cerebral artery G. Diffusion-weighted magnetic resonance imaging: subinsular lesions H.
Discussion
POCUS was described as “the stethoscope of the future” ten years ago, and today it
is becoming an integral tool for clinical decisions in patient management [34]. POCUS examination is becoming an exceptionally valuable tool both in Europe and
worldwide. In the United States, POCUS is applied in outpatient and inpatient departments
as an urgent noninvasive diagnostic tool for multiorgan ultrasound diagnostics of
lung, skeletal, muscular, and abdominal pathologies, among others, and is integrated
into medical schools and residency training programs [48]. Neurological and neurovascular disease management can also clearly benefit from
Neuro-POCUS, thereby improving patient outcome.
Compared to standard neurosonology examination performed in the ultrasound department,
Neuro-POCUS provides the possibility of getting a prompt answer to a well-defined
question by noninvasive ultrasound earlier and in real-time at the patient’s bedside.
This is particularly essential in patients who need rapid diagnostics prior to urgent
treatment initiation (e. g., acute stroke) [28]
[44]
[49] and in critically ill patients where transport is associated with a higher risk
of complications (e. g., intubated patients on artificial ventilation in the ICU)
[14]
[23]. The second main difference between the Neuro-POCUS and the standard neurosonology
examination is that Neuro-POCUS uses a restricted examination protocol. This protocol
is question-related to save time without decreasing the accuracy. Nevertheless, it
should be noted that only future studies may answer the question whether Neuro-POCUS
results in better patient outcome than in a standard neurosonological department in
specific situations, especially in cases where the indication for Neuro-POCUS is not
yet routinely considered.
Thanks to the rapid bedside examination, Neuro-POCUS is especially useful in a case
of emergent and urgent neurological disorder to modify the diagnosis and guide ongoing
therapy, so that the management plan can be corrected without delay. Neuro-POCUS also
significantly differs from the “ICU-sound” protocol for so-called “head-to-toe” ultrasound
(optic nerve, thorax, heart, abdomen, and venous system), which was developed for
a rapid global assessment of critically ill patients to increase diagnostic accuracy
(screening protocol) and may lead to incidental findings unrelated to the current
disease. Moreover, as it is easily repeatable in case the patient’s condition changes,
Neuro-POCUS might maximize benefit, reduce health care costs, and help avoid unnecessary
harm, such as radiation, and repeated CT/CTA, MR, or digital subtraction angiography
examinations.
Ultrasound examination is an operator-dependent diagnostic method, and the reliability
and validity of the achieved results depend on the sonographer’s skills and experience.
Bedside neurosonology examination is today frequently applied by operators confined
to a very specialized setting and a restricted question (e. g., emergency physician,
anesthesiologist, intensivist, or technologists). The examination is performed by
operators working at the point of care who are specifically trained in a selective
ultrasound application but often do not have comprehensive experience in general neurosonology.
Thus, the Neuro-POCUS questions must consider the sonographer’s level of experience,
and a sonographer with an appropriate level of experience should be called to perform
the Neuro-POCUS examination and answer a relevant, well-defined question [49].
Introducing Neuro-POCUS into daily clinical practice has become even more important
during the COVID-19 pandemic [46]
[50]. Since ultrasound examination involves direct contact between the patient and the
sonographer, this examination should be considered a procedure with a potentially
high risk of COVID-19 transmission. Indeed, a standard neurosonology examination often
takes several tens of minutes. However, by using the restricted examination protocol
at the bedside, Neuro-POCUS saves significant time and thus reduces the risk of spreading
infection.
In the last decade, some new sonographic techniques have become a common part of neurosonology
examination. TCD machines with a robotic probe allow rapid detection of blood flow
signals from intracranial arteries, assess intracranial autoregulation, and reduce
the examination quality’s dependence on the sonographer’s experience [51]. It can even eliminate the need for a sonographer at the bedside, and the measured
values can be assessed remotely (using telemedicine or online) [18]. Automated MES detection is developed to improve the identification, differentiation
between types, and quantification of MES [52]. It could be useful to optimize early prevention treatment in patients with ischemic
stroke [53] or to optimize surgery or endovascular interventions to minimize the risk of ischemic
stroke [54].
Non-imaging transcranial perfusion sonography is another promising ultrasound method.
In the future, it could be used bedside in patients with acute stroke to monitor brain
perfusion [55]. Great hopes have been placed on the development of artificial intelligence in neurosonology.
Developments in robotization, automatic digital image analysis, new software, and
diagnostic algorithms are potential ways to improve the reliability, validity, and
accuracy of the Neuro-POCUS examination and reduce the dependence on the sonographer’s
insonation skills and experience [56]
[57].
