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Case 13 Internal Carotid Artery Stenosis in Fibromuscular Dysplasia and Wegener Granulomatosis
206
Conclusion
Right ICA occlusion secondary to FMD. Suspected collateralization via the contralateral A1-ACA (cross-flow) and
ipsilateral OA.
Degree of Neurosonologic Difficulty: Medium
Final Diagnosis
Large territorial MCA infarction caused by artery-to-artery
embolism originating from the right ICA that was severely
affected by FMD. Thrombocytosis due to WG may have
been a predisposing co-factor. Secondarily, clinically
asymptomatic right extracranial ICA occlusion.
Fig. B13.3 Extracranial duplex, longitudinal plane. Color-mode
imaging demonstrates elongation, caliber variations and stenosis
(arrow) of the right distal ICA. Maximum peak systolic flow velocity
was 250 cm/s (not shown). Note the blue-colored internal jugular
vein.
Fig. B13.5 DSA, left VA injection, lateral view. Mild caliber variations
of the distal left-sided VA. Note the looping elongation of the distal
VA segment (arrow).
Fig. B13.4 DSA, right ICA injection, posteroanterior view: Multiple
irregular constrictions in a “string of beads” appearance in the right
distal ICA asa characteristic, pathognomonic angiographic finding of
FMD.NotetheseverestenosiswithinthemiddlesegmentoftheICA
(arrowhead). Note also the extension into the proximal part of the
petrous C6 segment of the ICA (arrow).
Fig. B13.6 Unenhanced CT, axial plane. Large residual infarction of
the right MCA territor y 6 months after presentation. (Reproduced
from Brann et al. 2006, Fig. B, with kind permission of Springer
Science and Business Media.)
Fig. B13.7 MRI, T2-weighted image, coronal plane. Residual right
MCA infarction and wallerian degeneration of the pyramidal tract
down to the pyramidal decussation (arrows) 6 months after presentation.
Discussion
Fig. B13.8 Extracranial duplex, longitudinal plane. Occlusion of the
right ICA. A high-resistance flow signal with bidirectional flow components (“to-and-fro-signal”) can be detected in the carotid sinus.
Note the normal color imaging of the CCA and ECA.
207
Degree of Neurosonologic Difficulty: Medium
Discussion
Clinical Aspects
Here we report of a rare coincidence of an inflammatory
(WG) and a noninflammatory (FMD) vessel disease. Both
conditions have the potential to cause ischemic stroke.
FMD is a nonatherosclerotic, noninflammatory segmen-
talvasculardiseaseofunknownorigin(SlovutandOlin
2004). Depending on the affected vessel segments, degree
of resulting stenosis and the type of FMD, the clinical
picture may range from asymptomatic to severe multivessel disease imitating a necrotizing vasculitis (Olin
1991). The histopathologic classification of three distinct
types of FMD is based on the arterial layer affected. We
differentiate an intimal fibroplasia, a medial fibroplasia,
and a subadventitial (perimedial) fibroplasia of the arterial
wall (Harrison and McCormack 1971). The medial type of
FMD is by far the most common and is classically diagnosed on angiography after noting its “string of beads”
appearance. This phenomenon is explained by the presence of luminal stenoses alternating with aneurysmal outpouchings.It may be found overa length of 3–5 cm, mainly
within the middle and distal parts of the affected vessels.
Involvement of proximal segments is hardly ever seen.
Within the general vascular system, the renal arteries are
most frequently affected with an incidence of 85 %, often
resulting in renovascular hypertension. The cervicocranial
arteries are the second most common location, being affected in 25–30 % of cases. Of these, up to 95 % involve the
ICA, 60–85 % bilaterally (Healton 1986). About a third of
patients with ICA pathology also demonstrate renal in-
Fig. B13.9 Extracranial duplex, longitudinal plane. Right ECA with a
low resistance flow signal indicating that the ECA is now a brainsupplying artery (“internalized” flow signal).
volvement. Affliction of the VA is observed in up to 10 %
of cases. Other vessels, for example, the intestinal arteries,
may also be involved (Slovut and Olin 2004).
Peak age of FMD manifestation is around the fiftieth
year, with a clear female predominance (Stewart et al.
1986). Some patients may remain asymptomatic, but a
number of unspecific symptoms such as dizziness, headaches, and tinnitus may occur.High-grade arterial stenoses
or thromboembolic events may result in transient ischemic attacks (TIAs) and ischemic stroke. An association of
intracranial aneurysms (Mettinger and Ericson 1982) and
ICA dissections (Desfontaines and Despland 1995) has
been reported in up to 20 % of cases. Little is known about
the natural course and the incidence of asymptomatic FMD
patients. In cases of accidental diagnosis, no specific treatment is recommended. Treatment approaches are therefore reserved for symptomatic patients. After the occur-
Case 13 Internal Carotid Artery Stenosis in Fibromuscular Dysplasia and Wegener Granulomatosis
208
rence of a first ischemic stroke, patients are often commenced on an antiplatelet therapy. In recurrent ischemia
or cases with a hemodynamically relevant stenosis, endovascular or surgical approaches might be required depending on the appearance of the lesion. In recent years,
endovascular balloon dilatation or stent placement have
been the favored approaches. There have been no controlled trials, however, the reported cases suggest good
results (Curry and Messina 2003).
In our case, mainly the ICAs were affected. The right
renal artery as well as the left VA were also involved but
remained clinically silent. Vascular intervention was not
advisable because of the immunologic comorbidity. During the 5-year follow-up the patient developed an occlu-
Degree of Neurosonologic Difficulty: Medium
sion of the right extracranial ICA which was clinically
completely asymptomatic. It is only retrospectively that
we can question whether an initial endovascular intervention might have prevented a secondary occlusion. However, the clinically stable course with medical therapy and
the high periprocedural risk of interventional treatment
justifies the chosen approach in our case.
WG is an inflammatory multisystemic disease charac-
terized by necrotizing granulomas within the upper and
lower respiratory tract. Other locations of manifestation
are a segmental glomerulonephritis as well as a necrotizing systemic vasculitis affecting small and middle-sized
arteries (Drachman 1963). The disease may occur at any
age but the peak incidence is in the fourth and fifth decades of life. There is no known gender difference. Laboratory analysis frequently demonstrates a raised ESR,
raised C-reactive protein (CRP), leucocytosis, thrombocytosis, and a mild normochromic anemia. A positive cANCA
titer with proteinase 3 specificity is found in 95 % of patients with a systemic WG (de Groot and Gross 1998). WG
diagnosis is based on the four American College of Rheumatology (ACR) criteria of which at least two have to be
present: (1) oral or nasal inflammation, (2) abnormal chest
radiograph,(3)microhematuria,and(4)apositivebiopsy
showing granulomatous inflammation within the wall or
in the perivascular space of an artery or arteriole. Neurologic manifestations of WG are reported in 22–54 % of
cases (Drachman 1963, Nishino et al.1993). The peripheral
nervous system is most frequently affected. Neuropathies
occur in approximately 16 % of cases and are associated
with renal involvement. There is cerebral or meningeal
involvement in less than 10 % of patients. In these cases,
intracranial or subarachnoid hemorrhages in addition to
arterial or venous occlusions might occur. Generally these
cerebrovascular events are caused by the inflammatory
vasculitis. However, secondary arterial occlusions due to
direct invasion of the granulomatous infection originating
from nasal or paranasal locations have also been reported
(Drachman 1963, Nishino et al. 1993). Generally, ischemic
strokes are a rare complication of WG and are often the
result of microangiopathic lesions based on a coexisting
hypertension (Nishino et al. 1993).
Treatment of WG usually comprises a combined approach with glucocorticoids and cyclophosphamide. In
severe disease, sulfonamides and drugs such as mycophenolate mofetil and leflunomide are being used. Other
treatment protocols involve a cyclophosphamide bolus
therapy, administration of intravenous immunoglobulins,
methotrexate, ciclosporin, and sulfasalazine.
In our case we assumed that FMD was the factor responsiblefortheischemicstroke.Asthepatientpresented3
days after the onset of symptoms, thrombolysis was not
possible.Fromtheinfarctpattern,itwasthoughtthatthe
most likely cause was an artery-to-artery embolic event,
from the predominantly affected ICA. Although a secondary thrombocytosis is not a recognized independent risk
factor for stroke, we consider the concomitant thrombocytosis caused by the WG to be a potential factor facilitating the formation of a thrombus (Hart and Kanter 1990).
Angiologic and Anatomic Aspects
Diagnosis of FMD can be achieved by several methods.
Duplex ultrasound has a rather low sensitivity as the vascular changes are often found in the middle and distal ICA
segments, which are frequently not accessible by this
technique (Wells and Smith 1982). However, if the typical “string of beads” pattern can be visualized, the
diagnosis can also be made by ultrasound (see also chapter
5, Fig. A5.13). In comparison to DSA, small vascular
changes will often escape the sonographic assessment
(Arning and Grzyska 2004). If the disease causes arterial
stenoses, additional direct and indirect hemodynamic criteria can be determined by duplex ultrasound. In our case,
we were able to visualize an elongated vessel course as
wellascaliberchangeswithinthemiddleICAsegment.
MRA has not gained a predominant position in diagnosticalgorithmsofFMD.Thisisbecausethemostfrequently
used TOF MRA often demonstrates spontaneous artifacts
that may simulate alternating stenoses in the absence of
any pathology. Contrast-enhanced MRA might be less susceptible to this problem (Furie and Tien 1994, Willoteaux
et al. 2006). CTA analysis is a promising tool as modern
systems nearly reach the spatial resolution of DSA. For
renal artery FMD, a sensitivity comparable with DSA has
been reported (Sabharwal et al. 2007). However, for brainsupplying arteries, to date there have been only singular
reports (de Monye et al. 2007).
Finally, important hemodynamic aspects of our presented case should be discussed. On the day of admission,
our patient demonstrated different flow velocities in both
M1-MCA segments (right: 57/25cm/s, left: 111/57 cm/s).
As the proximal MCA segments usually follow an similar
course, flow velocity differences between both sides
should be small. The clearly reduced velocity in our patient’s right MCA was therefore suggestive of a distal M1
occlusion or an occlusion of a dominant M2-MCA branch.
Depending on the location of an MCA occlusion, different
effects can be observed in the proximal vessel segments
Discussion
209
(for further details, see Chapter 5, “Intracranial Pathology,”
p. 94). For instance in proximal M1-MCA occlusion, flow
will be absent. A more distal M1-MCA occlusion beyond
the lenticulostriate branches will result in a reduced flow
velocity and increased pulsatility within the proximal M1MCA segment (for further details see Case 10, p.176). In M2
branch occlusion, proximal M1-MCA flow may vary depending on the relevance and number of M2-MCA
branches. In case of a major M2 branch occlusion, proximal
M1-MCA flow will be similar to a distal M1-MCA occlusion.
In case of a small M2 branch involvement, flow in the
proximal M1-MCA can be normal (see also Chapter 5, Table
A5.4, p. 97). Based on initial TCD experiences in acute
stroke, Zanette and coworkers developed an index permitting conclusions regarding MCA patency and level of MCA
occlusion (Zanette et al. 1989). This “asymmetry index”
(AI) is calculated as follows:
AI (%) = (V
(AI = asymmetry index, V
MCA, V
– Va)/(Vn+Va) × 200
n
=meanflowvelocityofthenormal
= mean flow velocity of the affected MCA).
a
n
Using TCD it works when velocities are assessed at similar
insonation depths. A complete occlusion results in the
maximal achievable index of 200 %. Side-to-side differencesofmorethan21%areconsideredpathologic.High
values argue in favor of a distal M1 occlusion and low
values are suggestive of a M2-MCA occlusion. Developed
for transcranial Doppler (TCD), the index can be transferred to transcranial color-coded sonography (TCCS) in
acute stroke but verification has not been performed (Kenton et al. 1997). In clinical practice the use of systolic flow
velocities for AI calculation would be worthwhile, as their
assessment is more practical and reliable. A more simplified approach is to use a 30 % bilateral difference as a
pathologic cut-off. Again, this is only true if comparable
vessel segments are being used for evaluation. Practically,
the latter index has been used to establish the Thrombolysis In Brain Ischemia (TIBI) criteria at TIBI grade 2 and 3
with a blunted or dampened flow signal and mildly raised
pulsatility. The advantage of a simple right and left comparison is its fast assessment even under acute stroke
conditions. Saqqur and coworkers found sensitivity, specificity, and positive and negative predictive values for
identifying proximal occlusion in the anterior circulation
of 94%, 100 %,100 %, and 86 %, respectively, if the V
a/Vn
ratio
was<0.6(Saqquretal.2005).Inourcase,consideringthe
systolic flow velocities, the AI was 64 and the difference
between the two sides was 51%, and the right to left ratio
was 0.51. Therefore, a distal M1-MCA occlusion or an occlusionofmorethanoneM2-MCAbrancheshadtobe
assumed. The follow-up CT demonstrated a large MCA
infarction excluding the basal ganglia, supporting a distal
M1-MCA occlusion as the cause of stroke. DSA 5 days later
did not show a persisting vessel occlusion indicating spontaneous recanalization.
Degree of Neurosonologic Difficulty: Medium
210
Case 14
Isolated Carotid Siphon Stenosis
Clinical Presentation
A 17-year-old Caucasian woman presented with recurrent
transient episodes of right-sided sensorimotor deficits and
speech disturbance, each lasting up to 60 minutes. The
symptoms first occurred 3 years prior to presentation
with a transient numbness of the fingers of her right
hand. One week before admission to a district general
hospital, she developed brachiofacial hemiparesis and
Broca aphasia. These symptoms gradually resolved after
15 minutes. She had no vascular risk factors and no history
ofmigraineorstrokeinherfamily.Shehadneverused
illicit drugs. Clinical examination yielded no focal neurologic deficit. She was started on a combination of aspirin
and clopidogrel and was then referred to our department
for further evaluation following magnetic resonance angiography (MRA) and digital subtraction angiography
(DSA), which showed contradictory findings.
Initial Neuroradiologic Findings
Cerebral magnetic resonance imaging (MRI) revealed no
ischemic parenchymal lesions. Time-of-flight (TOF) MRA
demonstrated a severe left carotid siphon stenosis. Also a
fetal-type left posterior cerebral artery (PCA) was noted
(Figs. B14.1, B14.2). In contrast with the MRA findings,
conventional DSA 1 day later demonstrated only a mild
stenosis in the left distal carotid siphon despite the use of
different oblique projections (Figs. B14.3–B14.7).
Suspected Diagnosis
• What was the conformation and grading of the left
carotid siphon stenosis?
• Was there evidence of any further intracranial stenotic
process, overrated by MRA or underrated by DSA?
Initial Neurosonologic Findings
Extracranial Duplex Sonography
B-mode and color-mode imaging revealed no atherosclerosis or other vascular pathology. Doppler spectrum analysis showed normal and symmetric flow signals.
Transcranial Duplex Sonography
Increased flow velocities with turbulence were found in
the left proximal M1-MCA segment (flow velocity: 141/
61 cm/s). No poststenotic flow pattern was detected in the
distal M1-MCA segment and M2-MCA branches. Using the
transtemporal axial insonation approach, the carotid siphon presented flow velocities reaching peak systolic values of 300 cm/s. Both anterior cerebral arteries (ACAs) and
posterior cerebral arteries (PCAs), and the right MCA
showed normal flow signals. A positive oscillation effect
was observed in the left P2-PCA segment upon ipsilateral
extracranial internal carotid artery (ICA) artery oscillation
(Figs. B14.8–B14.10).
Conclusion
High-grade stenosis of the left carotid siphon with turbulent flow in the proximal M1-MCA segment. Left fetal-type
PCA.
Recurrent transient ischemic attacks (TIAs) in the left middle cerebral artery (MCA) territory caused by a carotid
siphon stenosis of undetermined origin and unknown degree.
Questions to Answer by Ultrasound Techniques
• Were there pathologic vascular changes in the extracranial vessels?
Clinical Course
The patient’s recurrent TIAs were interpreted as hemodynamic or embolic events in the left MCA territory, triggered by the high-grade carotid siphon stenosis. The etiology of the stenosis remained unclear. Blood pressure
measurements were normal. Other causes, such as vasculitis or chronic inflammatory disease were considered unlikely because of the clinical presentation, normal blood
tests, and normal cerebrospinal fluid (CSF) studies. Differ-
ential diagnoses such as early moyamoya syndrome or
fibromuscular dysplasia (FMD) could not be confirmed at
the stage of disease at which she presented. We changed
the secondary stroke prevention to monotherapy with
clopidogrel and recommended follow-up ultrasound examination after 1 year. Unfortunately, the patient was lost
to follow-up.
Final Diagnosis
Final Diagnosis
Repeated TIA in the left MCA territory caused by a highgrade carotid siphon stenosis of unknown etiology, clearly
underrated by conventional DSA.
211
Degree of Neurosonologic Difficulty: Medium
Fig. B14.1 Intracranial 3D TOF MRA, coronal MIP, slightly rotated to
the left side. High-grade carotid siphon stenosis of the left ICA is
suggested (arrowhead).
Fig. B14.3 DSA, left ICA injection, posteroanterior view. No stenosis
in the left carotid siphon is visible.
Fig. B14.2 Intracranial 3D TOF MRA, coronal MIP, slightly rotated to
the right side. Comparable high-grade carotid siphon stenosis of the
left ICA (arrowhead).
Fig. B14.4 DSA, left ICA injection, lateral view. DSA only demonstrates a low-grade stenosis in the left carotid siphon distal of the
ophthalmic artery origin (arrowhead). Note the fetal-type PCA (arrow).
Case 14 Isolated Carotid Siphon Stenosis
212
Degree of Neurosonologic Difficulty: Medium
Fig. B14.5 DSA, left ICA injection, left anterior oblique view. The
carotid siphon stenosis is not visualized.
Fig. B14.7 MRA (left) and DSA (right). Comparative views by both
methods using a similar plane and magnification.
Fig. B14.6 DSA, left ICA injection, right anterior oblique view. On
this projection, again a low-grade stenosis in the left carotid siphon
distal of the ophthalmic artery origin was assumed (arrowhead).
Fig. B14.8 TCCS (transtemporal approach), left-sided insonation,
upper pontine plane. Doppler spectrum analysis showed increased
flow velocities in the left carotid siphon (flow velocity: 300/
150 cm/s).
Fig. B14.9 TCCS (transtemporal approach), left-sided insonation,
midbrain plane. Mildly raised flow velocities and slight turbulences
in the left proximalM1-MCA in a depth of58 mm (flow velocity: 141/
61 cm/s).
Fig. B14.10 TCCS (transtemporal approach), left-sided insonation,
midbrain plane. Normal Doppler signal and flow velocity in the left
middle M1-MCA in a depth of 50 mm (flow velocity: 111/42 cm/s).
Discussion
213
Discussion
Clinical Aspects
Here we present a very young patient who was transferred
to our hospital because of recurrent left-hemispheric TIAs
caused by a high-grade left carotid siphon stenosis. It
remained unclear whether the events were of embolic or
hemodynamic origin. The benign course of the recurring
events without development of a manifest ischemic stroke
could argue in favor of hemodynamic events. However,the
virtually normal MCA flow profiles, the absence of an
orthostatic component, normal blood pressure levels,
and the termination of recurrent symptoms after starting
of the antiplatelet medication argues in favor of the embolic event hypothesis.
Her first clinical event occurred at the age of 14, which
gave reason for an extended search of risk factors. No
classic vascular risk factors were found. A cardiac embolic
source was ruled out and investigations excluded vasculitis, chronic inflammatory disease, and thrombophilia. An
early stage moyamoya disease or FMD seemed possible
but could not be confirmed at that stage (for further discussion on moyamoya disease, see also Case 9, p. 171, and
for discussion on FMD, see Case 13, p. 204). Another differential diagnosis to consider in a young patient is an isolated vasospasm. However, the absence of migraine, lack of
clinical symptoms such as headaches or eye pain, and the
DSA findings, atypical for vasospasm, argue strongly
against this hypothesis. Furthermore, the stenosis remained unchanged over an observational period of more
than 1 week (time delay between MRA and transcranial
color-coded sonography [TCCS]). As there was no past
medical history concerning the use of illicit drugs or antidepressants, Call–Fleming syndrome characterized by a
reversible segmental cerebral vasoconstriction caused by
vasoactive sympathomimetic drugs also seemed unlikely
(Call et al. 1988, Noskin et al. 2006). Unfortunately, the
patient was lost to follow-up and the question of a persisting or transient stenosis cannot currently be answered.
Finally, an isolated atherosclerotic lesion also seemed unlikely because of the lack of risk profile, negative family
history and because of the patient’s young age. Therefore,
the exact etiology of the detected carotid siphon stenosis
remains unclear.
In typical cases with intracranial atherosclerotic processes the ICA and, in particular, the carotid siphon are
frequently affected. Akins and coworkers (1998) performed angiographic follow-up studies in 21 patients
with 45 intracranial arterial stenoses; 49 % of lesions affected the intracranial ICA with a stenosis greater than
50%. Compared with stenoses in the ACA, MCA, and PCA,
the ICA stenoses remained relatively stable without any
relevant progression over an observational period of 26.7
months. The authors assumed that a mild progression in
small-caliber vessels such as the ACA, MCA, and PCA resulted in a relatively greater narrowing as compared with a
large vessel as the ICA. Another interesting observation
was that the absence of extracranial atherosclerosis
seemed to be a risk factor for intracranial stenosis progression. The authors not only observed progression but
also regression of stenoses, the latter being attributed to a
presumed partial recanalization of intravascular thrombi
(Akins et al. 1998). The true incidence of an isolated stenosis of the carotid siphon is not known. In a larger angiographic study including 885 consecutive angiograms a
unilateral (71 patients) or bilateral (22 patients) isolated
carotid siphon stenosis of atherosclerotic origin was
present in 10.3 % of cases (Borozan et al. 1984). However,
in another study, a concomitant stenosis of the ipsilateral
proximal ICA was present in 14 of 15 cases (Wechsler et al.
1986).
A detailed discussion of treatment options in intracra-
nial stenoses can be found in Case 5 (p.149). Briefly, the
Warfarin-Aspirin Symptomatic Intracranial Disease (WASID) trial,which compared warfarin and antiplatelet agent,
did not demonstrate a superiority of anticoagulation in
patients with intracranial arterial stenoses. Therefore the
current standard therapeutic concept is the consequent
management of classic vascular risk factors in combination
with thrombocyte function inhibition.
In our patient the general question of pathophysiologi-
cally justified therapy was raised. An interventional approach was dismissed because of the benign clinical course
and the unclear etiology of the lesion. Antiplatelet therapy
was initiated because of a reasonable benefit–risk ratio in
spite of the lack of clear evidence for an atherothrombotic
disease. The patient had initially been started on a combined aspirin and clopidogrel therapy. We changed this to
clopidogrel monotherapy based on the results of the Management of Atherothrombosis with Clopidogrel in HighRisk Patients with Recent Transient Ischemic Attack or
IschemicStroke(MATCH)studyatthattime.TheMATCH
study compared the efficacy of a combined aspirin plus
clopidogrel versus a clopidogrel plus placebo approach in
7599 patients after stroke or TIA. The combined approach
demonstrated a nonsignificant reduction ofmajor vascular
events, but at the same time it found a marked increase of
life-threatening bleeding complications (2.6 % vs. 1.3 %)
and major bleedings (Diener et al. 2004). In contrast with
these findings, a subanalysis of the Clopidogrel for High
Atherothrombotic Risk and Ischemic Stabilization Management, and Avoidance (CHARISMA) study including a
total of 9478 patients after myocardial infarction, ischemic
stroke, or symptomatic peripheral arterial disease revealed a considerably lower rate of cardiovascular death,
myocardial infarction, or stroke in the clopidogrel plus
aspirin arm than in the placebo plus aspirin arm: 7.3%
versus 8.8 % during a median follow-up of 27.6 months.
There was no significant difference in the rate of severe
bleeding:1.7%versus1.5%(Bhattetal.2007).
Degree of Neurosonologic Difficulty: Medium
Case 14 Isolated Carotid Siphon Stenosis
214
Angiologic and Anatomic Aspects
As intracranial stenotic processes are frequently found in
the ICA, and in particular within the carotid siphon, valid
diagnostic tools are required for exact evaluation of these
vessel segments. For routine ultrasound examination in
patients with TIA or stroke in the MCA territory and normal extracranial findings, it is essential to extend the
examination to the complete intracranial ICA as well as
the accessible MCA, i. e., the M1- and M2-MCA segments.
The intracranial ICA can be insonated via the transtemporal bone window using transcranial Doppler (TCD) or TCCS
(Bogdahn et al. 1990, Ley-Pozo et al. 1990). Because of the
restricted spatial orientation, the use of TCD is of limited
Degree of Neurosonologic Difficulty: Medium
value. If TCCS is applied and a patent transtemporal bone
window is present, the total intracranial ICA including the
proximal C6 and C5 segments, the carotid siphon as well as
the C1 and C2-ICA segments can be assessed using combined axial and coronal insonation planes (Eggers et al.
2007a, Jurgita et al. 2002). In cases of an absent transtemporal bone window, the transorbital approach using
TCD or TCCS can be considered if the restrictions concerning the used insonation energy are followed (Hu et al.1995,
Ley-Pozo et al.1990, Lindegaard et al. 1986, Schneider et al.
1991, Spencer and Whisler 1986).
Because of the often tortuous intracranial vessel course,
angle-corrected measurements of the carotid siphon are
usually not possible. Also, a turbulent flow pattern is frequent, even in the absence of any intracranial stenosis.
Whenever an obviously turbulent flow pattern and raised
flow velocities are seen, however, a stenosis should be
suspected. Our example also illustrates the importance of
a complete intracranial ultrasound assessment. The proximal M1-MCA segment demonstrated mildly raised flow
velocities (141/61 cm/s) and a turbulent flow which alone
could have been interpreted as a low-grade MCA stenosis.
However, in our case this profile alteration corresponded
to the transmitted stenotic signal from the carotid siphon
stenosis. Therefore, in any case of suspected MCA stenosis,
the pre- and poststenotic vessel segments (i.e. the M2MCA, C1/C2-ICA segment and carotid siphon) have to be
examined to avoid misinterpretation of findings and, as in
our example, to differentiate between isolated MCA and
distal ICA stenoses.
Because of its close anatomical proximity to the base of
the skull and its tortuous vessel course, the examination of
the carotid siphon is also difficult using other angiologic
methods. CTA clearly shows and separates soft from hard
plaques within any given ICA segment. Yet, post-process-
ing techniques, i. e., the widely used maximum intensity
projection, suffer from restriction due to the osseous
neighbourhood of vessel and bone at the skull base
(Woodckock et al. 1999). Quite recently, different scanner
vendors introduced digital subtraction software for CTA,
which presumably eliminates this limitation. MRA and the
frequently used TOF MRA is not limited by vessel calcification. However, as a flow sensitive method it is susceptible to artifacts, generated by the physiological turbulent
flow within the carotid siphon which might be amplified
by vessel elongation, a feature frequently seen with increasing age. Therefore, bilateral signal interruptions
within the carotid siphon are frequently found. In case of
a real underlying stenosis, the TOF MRA tends to aggravate
the degree of stenosis or even demonstrates complete
occlusion. Consequently, for skull base vessel assessment,
contrast-enhanced 3D FLASH MRA is superior to 3D TOF
MRA despite venous enhancement of the cavernous sinus
(Yang et al. 2002). In the presented case these artifacts
were not of relevance as little elongation was present in
our young patient and the clinical symptoms matched the
side of the pathological finding. Therefore, a stenosis was
beyond doubt. It was only the degree of stenosis that was
questioned as the conclusions of the various imaging
methods were initially contradictory.
Interestingly, the simultaneously performed DSA was
unable to clearly confirm the MRA diagnosis. Despite the
“state of the art” imaging in four different projection
planes, only a mild ICA stenosis could be suspected, which
would probablyhave been overlooked without knowledge
of the MRA findings. Subsequently, the clear ultrasound
finding of a high-grade carotid siphon stenosis was surprising as it corrected the DSA interpretation and confirmed the MRA finding. To date, DSA is considered to be
the method comprising the highest spatial resolution, correcting doubtful findings of the other methods almost
without any questioning. However, our example demonstratesthatitisalwaysvaluabletocombinefindingsofthe
available diagnostic techniques to avoid potential misdiagnoses. Interpretationof findings should critically imply the
strengths and weaknesses of each method. A typical
problem of the DSA technique is the limited number of
imaging planes, often restricted to the “routine” lateral
and posteroanterior view. However, this was not the
underlying reason in our case. We assume that here the
special anatomy of the carotid siphon and the distribution
of the diluted contrast agent within this vessel segment
was the main factor (for further discussion on evaluation of
intracranial stenoses see Case 5, p. 149).
Case 15
Near Occlusion of the Extracranial Internal Carotid Artery
215
Clinical Presentation
A 42-year-old Turkish woman presented following three
episodes of transient right-sided sensorimotor hemisyndromeandvisualdisturbanceinvolvingthelefteyethat
had started 4 days previously. Each episode lasted only a
few minutes.The patient had no known history of vascular
risk factors. On admission she was hypertensive. The neurological examination was normal. Initial laboratory examination showed a raised erythrocyte sedimentation
rate (ESR) (73 mm/hr, Westergren). Her C-reactive protein
(CRP) was within normal limits (3.9 mg/L).
Initial Neuroradiologic Findings
Cerebral magnetic resonance imaging (MRI) on the day of
admission demonstrated multiple signal abnormalities in
the left anterior cerebral artery (ACA), middle cerebral
artery (MCA), and in the posterior cerebral artery (PCA)
territory, as well as in the basal ganglia, consistent with
multiple ischemic lesions mainly of embolic origin, but an
internal border zone infarction (BZI) was also considered.
Intracranial time-of-flight (TOF) magnetic resonance angiography (MRA) showed no signal in the left internal
carotid artery (ICA) and left PCA, suggestive of an extracranial ICA and intracranial PCA occlusion (Figs.B15.1–
B15.3).
Suspected Diagnosis
Left hemispheric transient ischemic attacks (TIAs) and
multiple brain infarctions in left-sided extracranial ICA
and PCA occlusion, possibly caused by vasculitis.
Questions to Answer by Ultrasound
Techniques
• Was there evidence of occlusion or near occlusion of the
left ICA and/or occlusion of the left PCA?
• Were any of the other supraaortic vessels, such as the
common carotid artery (CCA) or subclavian artery (SA),
affected?
• Was the pathogenesis of the vascular disease atherosclerosis or vasculitis?
• What was the resulting intracranial collateral flow pattern?
Initial Neurosonologic Findings
Extracranial Duplex Sonography
B-mode imaging demonstrated bilateral atherosclerotic
changes, predominantly in the left carotid bifurcation.
There were no signs of arteritis. The left distal CCA
displayed a visual lumen reduction of < 40 % caused by a
homogeneous mildly hyperechogenic plaque (45 × 4mm).
Doppler spectrum analysis of the left proximal CCA revealed a mild high-resistance flow signal with increased
pulsatility. The left ICA showed a dramatically reduced
lumen with low flow velocities in all detectable segments
of 20/0 cm/s. The ipsilateral ECA showed increased diastolic, i. e., internalized blood flow. Assessment of the right
ICA and both vertebral arteries (VAs) was normal
(Figs. B15.4–B15.7).
Transcranial Duplex Sonography
The left carotid siphon presented markedly reduced flow,
similarly to the left extracranial ICA. The left M1-MCA
segment revealed a poststenotic flow pattern but normal
flow velocities (flow velocity: 115/75 cm/s). There was a
positive oscillation effect caused by submandibular oscillation of the extracranial contralateral ICA as well as by
oscillation of the ipsilateral eye bulb. A reversed flow and
poststenotic flow pattern was seen in the left A1-ACA
segment (flow velocity: 75/40 cm/s). The contralateral
A1-ACA segment and the ACoA had increased flow velocities that was interpreted as functional stenoses, indicative
of collateralization. The left P2-PCA segment also showed a
poststenotic flow pattern indicating its blood supply from
the right ICA via the ACoA and left PCoA (flow velocity: 46/
26 cm/s). Signalsin the right P2-PCA segment were normal
(flow velocity: 83/40 cm/s). The right ophthalmic artery
(OA) showed a normal orthograde flow (flow velocity: 25/
5 cm/s), whereas a raised internalized retrograde flow
signal was seen in the left OA (flow velocity: 70/35 cm/s)
(Figs. B15.8– B15.16).