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249Discussion

Valdueza et al., Neurosonology and Neuroimaging of Stroke: A Comprehensive Reference, Second Edition (ISBN 978-3-13-141872-2), copyright © 2017 Thieme Medical Publishers All rights reserved. Usage subject to terms and conditions of license.

lack of recanalization, a history of atrial ﬁ brillation, and a symptomatic ICH (Strbian et al 2013). Currently, oﬃ cial guidelines in the United States and Europe recommend intravenous thrombolysis within 4.5 hours of symptom onset, based on the results of the ECASS III study.

Improved recanalization rates and clinical outcomes were also reported for intra-arterial thrombolysis when compared with medical therapy with an antiplatelet agent. A meta-analysis compared the results of intravenous and intra-arterial thrombolysis within the posterior circulation. It demonstrated that recanalization rates were signiﬁ cantly better if intra-arterial thrombolysis was used instead of intravenous thrombolysis (65% versus 53%). However, survival rates did not diﬀ er signiﬁ - cantly between the two groups (45% versus 50%) and both groups had a similar proportion of good clinical outcome (24% versus 22%) (Lindsberg and Mattle 2006). Independent of the applied treatment strategy, the proportion of patients with a good clinical outcome was higher if recanalization had occurred (38% versus 2%). The Basilar Artery International Cooperation Study (BASICS) also found no evidence of superiority for intra-arterial thrombolysis over intravenous thrombolysis (Schonewille et al

2009).

In addition to the above-mentioned treatment regimens, a combination of therapies described as “bridging” therapy has been proposed for the posterior circulation. Bridging combines intra-arterial rt-PA, intravenous abciximab, and, if applicable, a balloon dilatation or stent placement. Compared with IV rt-PA alone, a study of 47 patients demonstrated similar recanalization rates (72% versus 68%), a better clinical outcome (34% versus 17%), and a signiﬁ cant lower mortality (38% versus 68%) for the combined treatment group (Eckert et al 2005).

As described above, a successful recanalization is closely related to the clinical outcome of the patient. A meta-analysis of 53 studies with reported recanalization rates calculated that a successful recanalization increases the chance of a good clinical outcome four- to ﬁ vefold while decreasing mortality accordingly (Rha and Saver

2007). Also, the previous thrombectomy studies demonstrated that patients with early recanalization perform better than those with delayed recanalization.

For these reasons, clinical research in recent years has predominantly focused on mechanical recanalization strategies, which can achieve high recanalization rates for all reported vessel segments.

First experiences with a new device for aspiration thrombectomy (the Penumbra system) were reported in 12 patients with acute BA occlusion who had previously received IV rt-PA thrombolysis. Thrombectomy was achieved in almost all cases while vessels remained o c c l u d e d i n 6 4 % o f t h e c o n s e r v a t i v e l y t r e a t e d p a t i e n t s (Roth et al 2011). Meanwhile, the more modern stent retrievers (Trevo, Solitaire) have yielded superior results compared with the coil-retriever (Merci) and the aspiration catheter (Penumbra). However, data concerning mechanical recanalization of the posterior circulation are scarce. Studies with negative results include either no patients with a vessel occlusions of the posterior circulation any (MR Rescue study) or only very few (IMS III: 2%, SYNTHESIS expansion: 8%). Criticism also arose concern-

ing study design as well as patient and device selection. The ﬁ rst and more recent studies with positive results for mechanical recanalization (ESCAPE, EXTEND IA, SWIFTPRIME, MR CLEAN) exclusively recruited patients with ischemic stroke of the anterior circulation. Studies analyzing mechanical recanalization of the posterior circulation are on their way and their results are eagerly anticipated (for fur ther informati on on mechanical th rombec tomy, see Case 10 and Chapter 6, “Technical Aspects of Mechanical Thrombectomy” under “Digital Subtraction Angiography”).

Medical secondary stroke prevention and treatment of

vascular risk factors in general do not diﬀ er from the con- cepts of the anterior circulation. Patients with a symptomatic stenosis in the vertebrobasilar vascular system (i.e., with a VA or BA stenosis >50%) have a threefold risk of recurrent stroke for within 90 days after stroke if compared with those without a detectable stenosis. Especially intracranial stenoses show an early relapse rate of up to 33% while early relapses in extracranial stenoses occur in only 16.2% (Gulli et al 2013).

In our patient, repetitive symptoms occurred during aspirin treatment. They were considered primarily hemodynamic on the basis of bilateral >50% V4-VA stenoses and a ﬂ uctuating blood pressure. Nonetheless, in view of the intracranial stenosis location dual antiplatelet therapy was initiated, adding clopidogrel which was continued for several years.

The latter decision followed the results of the CHARISMA study (Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization Management and Avoidance) which included a total of 9,478 patients after myocardial infarction, ischemic stroke, or symptomatic peripheral arterial disease. The trial revealed a considerably lower rate of cardiovascular death, myocardial infarction, or stroke in the clopidogrel plus aspirin arm compared with the placebo plus aspirin arm (7.3% versus 8.8%) during a median follow-up of 27.6 months, while there was no signiﬁ cant diﬀ erence in the rate of severe bleeding (1.7% versus 1.5%; Bhatt et al 2007). Similar results were seen in the recently published CHANCE study (Clopidogrel in High-Risk Patients with Acute Non-disabling Cerebrovascular Events) which included 5,174 patients with minor stroke or TIA. A combination of clopidogrel and aspirin compared with aspirin alone showed a moderate superiority for the former in preventing of relapse incidents of all vascular territories (8.2% versus 11.7%) (Y. Wang et al 2013). The results of the SAMMPRIS study (Stenting and Aggressive Medical Management for Preventing Recurrent stroke in Intracranial Stenosis) add further arguments in favor of a temporary dual platelet inhibition therapy after minor stroke or TIA in patients with an intracranial stenosis (Chimowitz et al 2011) (for further reading, see also Case 5).

In our patient, balloon dilatation was performed in the left intracranial VA but a restenosis of the dilated vessel occurred. Restenosis has been reported in approximately one-third of cases after intracranial stenting (Jiang et al 2007, SSYLVIA Study Investigators 2004). Stenting seems not to be superior to balloon dilatation with respect to restenosis rates, but stroke rates at follow-up might be lower after stenting procedures. Furthermore,

250 Case 8 Basilar Artery Occlusion in Bilateral Intracranial V4 Vertebral Artery Stenosis

the periprocedural stroke risk is higher for intracranial VA stenosis and BA stenosis than for proximal VA stenosis (Eberhardt et al 2006). The SAMMPRIS study mentioned above showed a clear inferiority for the stent treatment of a symptomatic intracranial stenosis compared with aggressive medical therapy: 60 out of 451 patients included (13%) had a stenosis of the intracranial VA or the BA. Subgroup analysis reported a particularly high periprocedural stroke risk of 20.8% in BA stenosis compared with

6.7% in all other vessels. In the majority of cases, an occlusion of paramedian perforators was observed (Derdeyn et al 2013, Fiorella et al 2012). According to the current data, routine stenting or balloon dilatation of vessels in symptomatic stenoses of the posterior circulation cannot be recommended. According to the SAMMPRIS study, aggressive medical treatment with temporary dual platelet inhibition is the treatment of ﬁ rst choice. Whether a sec- ondary prophylactic interventional therapy in the vertebrobasilar artery might be another reasonable approach is currently being studied in the VIST trial (Vertebral artery Ischaemia Stenting Trial) and the VAST trial (Vertebral Artery Stenting Trial) (for further information on intracranial stenting, see also Case 5).

Angiologic and Anatomic Aspects

In our case, the transcranial color-coded sonography (TCCS) assessment of both intracranial V4-VA stenoses was uncomplicated. The cut-oﬀ for a 100% conﬁ dent de- tection of a >50% stenosis is >120 cm/s (Baumgartner et al 1999). Both VAs in our patient revealed systolic ﬂ ow velocities of around 170–180 cm/s, clearly above these cut-oﬀ values. There are no published data for a more detailed grading. In ultrasound examination, a ﬂ ow pro- ﬁ le analysis of pre- and poststenotic vessel segments can give valuable additional information. The extracranial VA proﬁ les in our patient revealed an increased pulsatility, pronounced on the left side, as well as a small left-sided retrograde ﬂ ow component. The BA itself did not show an obvious poststenotic ﬂ ow pattern. Taking this information into account, a hemodynamic relevant stenosis of at least 70% in the left V4-VA segment and a stenosis of 50–70% in the right V4-VA segment had to be assumed. In hemodynamic relevant stenoses of both VAs a clear poststenotic BA ﬂ ow pattern would

have been expected. Ultrasound assessment of the intracranial VA segment may be limited in patients who are uncooperative or have impaired neck mobility, or those with a large neck circumference. Furthermore, V4-VA segment elongations, frequently found in elderly people, might hinder unequivocal vessel identiﬁ cation and lead to confusion between VA and, for example, a prominent PICA. The quality of vessel insonation in our patient was poor. As the transforaminal insonation approach is not primarily limited by a bone window, insonation in our patient was most probably impaired by the known calciﬁ ed plaques, hindering long-segmented vessel visualization. Despite these limitations, ﬂ ow sig- nals in the stenosis were detectable, probably facilitated by the routine use of low insonation frequencies during transforaminal insonation and possibly inhomogeneities within the calciﬁ cations. If VA evaluation is diﬃ cult in the acute posterior stroke setting, delays should be avoided and further diagnostic steps (e.g., CTA or MRA) should be initiated; however, analysis of the intracranial VA and the transitional segment between the V3 and V4 segments may also be diﬃ cult with the latter two techniques. As seen in our patient, a distinct and long circumferential calciﬁ cation can hinder CTA to assess a V4-VA stenosis. In these cases, dual-energy CT might be advantageous, as reported for calciﬁ ed carotid stenoses (Uotani et al 2009). Also, the analysis of the axial source images or a combined approach with MRA may be of help (Hirai et al 2002). Compared with the gold standard DSA, time- of-ﬂ ight (TOF) MRA applied for the detection of intracranial VA stenoses demonstrates a lower diagnostic sensitivity and speciﬁ city (84% and 93% versus 74% and 82%) than for the detection of extracranial VA stenoses (92% and 96% versus 100% and 90%). Increasingly TOF-MRA is being replaced by contrast-enhanced MRA techniques. The latter show a better image contrast, require less time, and are therefore less susceptible to movement artifacts (Ersoy et al 2003). Compared with carotid artery analysis, contrast-enhanced MRA of the vertebrobasilar circulation is, however, less sensitive and speciﬁ c in detecting steno-occlusive processes (Yang et al 2005). In equivocal or conﬂ icting diagnostic constellations, catheter angiography may be required (for further information on assessment of intracranial stenoses, see also Case 5).

Case 9

Moyamoya Disease

251

Clinical Presentation

A 32-year-old white man was admitted after suﬀ ering a mild brachiofacial weakness, aphasia, and a homonymous hemianopia to the right side. He was a smoker. No further vascular risk factors were present. On admission, no sensorimotor deﬁ cit was detected but he had a right homonymous hemianopia and mild ﬂ uent aphasia (Na- tional Institute of Health Stroke Scale [NIHSS] score: 3).

Initial Neuroradiologic Findings

Immediately performed MRI demonstrated on d i ﬀ usion-weighted images a large acute territorial left occipital ischemia in the posterior cerebral artery (PCA) territory as well as a small territorial left parietal precentral infarction in the left middle cerebral artery (MCA) territory. FLAIR-weighted images unmasked a right frontal territorial infarction in the anterior cerebral artery (ACA) territory. Furthermore bilateral small internal border zone infarctions (BZI) and dilated leptomeningeal vessels pronounced on the left hemisphere were detected. Also, a moderate parietal accentuated hemiatrophy was seen on the right side. Contrast-enhanced MR angiography (ce-MRA) showed signs of bilateral distal carotid artery occlusion in otherwise normal extracranial brain-supplying arteries. The MCA and ACA were undetectable on both sides. Instead, multiple small vessels were seen. Otherwise, the insular and cortical branches appeared normal. Intracranial time-of-ﬂ ight (TOF) MRA was also suspicious for bilateral proximal MCA and ACA occlusion. However, on T2-weighted images both M1-MCAs could be depicted by their signal voids, indicating real ﬂ ow in these vessels (Fig. B9.1, Fig. B9.2, Fig. B9.3, Fig. B9.4). Because of the large infarcted areas no thrombolysis was performed.

Suspected Diagnosis

MCAs and ACAs, seen in the late arterial phase, showed regular contrast. In addition, a collateral leptomeningeal ﬂ ow was seen via the posterior communicating artery (PCoA) and dural anastomoses on the right side. Selective left vertebral artery (VA) ﬁ lling yielded a prominent right PCA and the suspicion of a left distal PCA occlusion. Similar to the anterior circulation, a network of small vessels indicating collateral pathways was seen in the area of the proximal PCA (Fig. B9.5, Fig. B9.6, Fig. B9.7, Fig. B9.8).

Conclusion

Moyamoya disease stage IV with acute left MCA and PCA territorial strokes in severe carotid-T pathology and left-sided PCA occlusion.

Clinical Course (1)

The neurologic deﬁ cits partially regressed and the patient was started on aspirin for secondary stroke prevention. For further occupational and physiotherapeutic treatment he was transferred to a rehabilitation center and an extracranial–intracranial (EC–IC) bypass was recommended to be performed after rehabilitation. A ﬁ rst detailed ultrasound examination was performed in the rehabilitation center.

Questions to Answer by Ultrasound Techniques

• Was there any evidence of pathologic vascular changes

in the cervical vessels?

• Was there antegrade ﬂ ow detectable in the MCA and

ACA on both sides?

• Were the proximal PCAs also involved in the steno-

occlusive process?

• Could the collateral blood ﬂ ow be assessed?

Bilateral territorial and hemodynamic infarctions in bilateral severe steno-occlusive distal internal carotid artery (ICA) pathology compatible with moyamoya disease (MMD).

Conventional Angiography (Day 3)

Selective ICA contrast ﬁ lling demonstrated bilateral ter- minal ICA occlusion. Furthermore, a network of small capillary collateral vessels was visible in the region of the distal ICA and proximal MCA. The distal branches of both

Initial Neurosonologic Findings (Week 6)

Extracranial Duplex Sonography

B-mode and color-mode imaging revealed no atherosclerotic vascular changes. The lumen of both ICAs appeared reduced compared with the diameter especially of the right VA. Doppler spectrum analysis showed normal and symmetric ﬂ ow signals, but volume ﬂ ow measurements showed mildly reduced ﬂ ow in the ICAs and compensa- tory increased ﬂ ow in the VAs (Fig. B9.9 and Fig. B9.10).

252 Case 9 Moyamoya Disease

Fig. B9.1 (A,B) MR diﬀ usion-weighted image, axial plane. Hyperin- tense signals indicating acute territorial infarctions in the left PCA calcarine artery territory and left MCA prerolandic artery territories. Note the old right-sided ACA infarction (arrow) and the spared occipital pole (arrowhead). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.2 MR FLAIR image, axial plane. (A) Mild parietal atrophy on the right side. Note the dilated leptomeningeal vessels (arrowheads) indicating increased and delayed ﬂ ow. (B) Besides the post- central MCA infarction, small bilateral internal BZI can be seen (arrows). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.3 Contrast-enhanced MRA showing a steno-occlusive pathology in both distal ICAs. Instead of MCA and ACA main stems, multiple bilateral small vessels can be seen, but the i n s u l a r b r a n c h e s a p p e a r n o r m a l . N o t e t h e l a r g e d i a m e t e r o f the right VA, exceeding that of the right ICA. (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.4 (A) 3D TOF-MRA. Circle of Willis, coronal oblique maximal intensity projection (MIP). Absent ﬂ ow signal in the M1-MCA (arrows) and A1-ACA on both sides as well as in the left PCA (arrow). Note the ﬁ ne network-like collateral vessels surrounding the circle of Willis (arrowheads) (B) T2-weighted image, axial plane. In contrast to TOF-MRA, visible MCA signal voids indicate that both vessels remained open, even at its proximal site. Note that the T2-weighted images better delineate the multiple small collateral vessels surrounding the MCA, ACA, and PCA (arrowheads). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

253Initial Neurosonologic Findings (Week 6)

Fig. B9.5 DSA, right selective ICA injection, lateral view. The DSA

shows a right terminal ICA occlusion (dotted arrow). Collateral ﬂ ow derives in part from the PCA via the PCoA (arrowhead). Note the typical network-like anastomoses in the area of the proximal MCA, which itself is not visualized (arrows). Small dural anastomoses are also visible (arrowheads). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.7 DSA, left selective VA injection, posteroanterior view. (A) Early arterial phase: Suspected stenosis of both proximal PCAs (arrowheads). Similar to the anterior circulation, a ﬁ ne network can be seen surrounding both PCAs. (B) Late arterial phase: The right MCA territory is partially perfused by the PCA (arrow). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.6 DSA, right selective ICA injection, posteroanterior view. (A) Early arterial phase: No visible MCA but PCA leptomeningeal ﬁ lling through the PCoA (arrows). Note a dural anastomosis (arrowheads). (B) Late arterial phase with visible insular and leptomeningeal branches of the right MCA and both ACA. As retrograde ﬁ lling via the PCoA seemed unlikely, antegrade ﬁ lling via the proximal MCA and ACA in addition to the collateral network has to be assumed, even if the M1-MCA and A1-ACA are not directly visible. (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Lübeck, Germany.)

Fig. B9.8 DSA, left selective VA injection, lateral view. (A) Early a r t e r i a l p h a s e : B e t t e r d e l i n e a t i o n o f t h e ﬁ ne collateral network com- pared with the posteroanterior view (arrows). (B) The late arterial phase demonstrates the posterior pericallosal artery connecting via the pericallosal artery with the anterior circulation (arrowhead). (Courtesy of Prof. Schramm, Neuroradiological Department, University Hospital Schleswig-Holstein, Lübeck, Germany.)

Transcranial Duplex Sonography

Despite good insonation conditions, the distal ICA could not be detected on both sides. Using color-mode imaging, a network of small arteries was visible in both perimesencephalic cisterns. Both M1-MCAs revealed a poststenotic ﬂ ow pattern, severely aﬀ ected on the right side and moderate aﬀ ected on the left side. Bilateral ﬂ ow velocities were markedly reduced. A similar ﬂ ow proﬁ le was observed in the right A1-ACA and no signal

could be depicted in the left A1-ACA. The left PCA was patent. Turbulent ﬂ ow and markedly raised ﬂ ow veloc- ities were observed in both P1/P2-PCA segments and also in cortical PCA branches, i.e., in the anterior temporal artery (ATA) and in the occipitotemporal artery (OTA). The ubiquity phenomenon in all accessible PCA segments was suggestive for increased collateral ﬂ ow but did not rule out the presence of additional stenoses (Figs. B9.11–B9.18; see also Video

B9 .1).

254 Case 9 Moyamoya Disease

ICA-R

Fig. B9.9 Extracranial duplex, longitudinal plane. The right ICA appears small showing a decreased blood volume ﬂ ow (BVF 210 mL/min).

M1-MCA-R

VA-R

Fig. B9.10 Extracranial duplex, longitudinal plane. The right V2-VA has a large diameter and an unusually high blood volume ﬂ ow (BVF 310 mL/min).

M1-MCA-L

Fig. B9.11 TCC S ( tran stem poral approa ch), ri ght-s ided in sona tion , midbrain plane. Severely poststenotic ﬂ ow pattern with a marked decreased ﬂ ow in the right M1-MCA (ﬂ ow velocity 21/16 cm/s). Note the color signals in the perimesencephalic cistern corresponding to the small collaterals seen in the T2-weighted MR image (arrow).

A1-ACA-R

Fig. B9.13 TCCS (transtemporal approach), right-sided insonation, midbrain plane. Severely poststenotic ﬂ ow pattern with a marked decreased ﬂ ow in the right A1-ACA (ﬂ ow velocity 19/14 cm/s).

Fig. B9.12 TCC S (trans temporal a ppro ach), left -sided i nson ation, midbrain plane. Moderate poststenotic ﬂ ow pattern with a decreased ﬂ ow in the left M1-MCA (ﬂ ow velocity 34/20 cm/s).

A2-ACA-R

Fig. B9.14 TCCS (t rans tempora l ap proach) , right-s ided inso nati on, midbrain plane. A poststenotic ﬂ ow signal can also be detected in the right A2-ACA (ﬂ ow velocity 25/20 cm/s).

255Clinical Course (2)

P1-PCA-R

Fig. B9.15 TCC S (tra nste mpor al app roac h), r ight- side d ins onati on, midbrain plane. A severely turbulent ﬂ ow signal with increased ﬂ ow velocity is detected in the right P1-PCA (ﬂ ow velocity 201/60 cm/s) assumed to present collateral ﬂ ow and a primary stenosis together.

ATA- L

P2-PCA-L

Fig. B9.16 TCCS (tra nste mpor al ap proach) , l eft -side d i nson atio n, midbrain plane. Turbulent ﬂ ow signal with increased ﬂ ow velocity (161/100 cm/s) in the proximal left P2-PCA, indicating collateral ﬂ ow (see below: increased ﬂ ow velocities in the left ATA and OTA) and probably also stenosis.

OTA-L

Fig. B9.17 TCCS (tran stemporal appro ach) , left -sid ed ins onati on, midbrain plane. Turbulent ﬂ ow signal with increased ﬂ ow velocity (111/60 cm/s) in the left ATA, a branch of the P2-PCA.

Conclusion

Bilateral carotid-T (accentuated on the right side) and proximal PCA pathology, with marked signs of leptomeningeal collateralization via both PCAs in angiographically conﬁ rmed moyamoya disease.

Clinical Course (2)

The angiographic ﬁ ndings of bilateral steno-occlusive ca- rotid-T processes including both proximal PCAs as well as the activated small-caliber collateral vessels were suggestive of moyamoya disease. The acute left-sided PCA occlusion which led to a large occipital PCA territorial infarction meanwhile reopened spontaneously. The bilateral BZIs indicated a severe hemodynamic compromise. Digital subtraction angiography (DSA) and transcranial color-coded duplex sonography (TCCS) both detected a more severe hemodynamic aﬀ ection of the right anterior circulation.

Fig. B9.18 TCCS (tran stemporal appro ach) , left -sid ed ins onati on, midbrain plane. Turbulent ﬂ ow signal with increased ﬂ ow velocity (76/47 cm/s) in the left OTA, a further branch of the P2-PCA.

A B

Fig. B9.19 (A) CTA, axial plane showing the donor vessel running through the trepanation defect (arrow). (B) Multislice CTA, v o l u m e - r e n d e r e d 3 D v i e w o f t h e l a t e r a l s k u l l o f a d i ﬀ erent patient to illustrate good patency of the STeA–MCA bypass.

256 Case 9 Moyamoya Disease

STeA-R

STeA-L

Fig. B9.20 Extracranial duplex, linear probe, color-mode and corresponding Doppler spectra. Top: Internalized right STeA ﬂ ow signal (31/17 cm/s) and decreased PI (0.7), compatible with a patent bypass. Bottom: Contralateral normal STeA with high pulsatility (PI = 2.2) and a ﬂ ow velocity 57/6 cm/s.

The mild sensomotoric hemiparesis and aphasia remitted completely and the hemianopia also partially regressed during rehabilitation. After hospital discharge, the patient was referred to the Neurosurgery Department and an EC–IC vascular bypass on the right side was planned and performed without complications. Postoperative cranial CT ruled out hemorrhagic complications. CT angiography revealed a patent bypass (Fig. B9.19) and the patient was sent back to rehabilitation. A second bypass was planned for the left hemisphere; however, the further course remained unknown as the patient was lost to follow-up.

Follow-up Neurosonologic Findings (3 Months)

Extracranial Duplex Sonography

Both superﬁ cial temporal arteries (STeAs) were studied. The left side showed a normal externa-like ﬂ ow signal with a high pulsatility of 2.2. The pulsatility of the right STeA was markedly decreased to 0.7 and now appeared like a parenchyma-related vessel. (Fig. B9.20).

Transcranial Duplex Sonography

The nonoperated left anterior and posterior circulation remained unchanged. On the right side, there was a marked improvement of the antegrade proximal M1-

MCA signal, revealing higher ﬂ ow velocities and a lower pulsatility. The distal MCA at the M1–M2 junction and one M2-MCA branch now revealed a retrograde ﬂ ow signal. Transient compression of the ipsilateral STeA led to an immediately cessation of the retrograde M2-MCA ﬂ ow. Flow velocities in the right PCA had decreased, obviously indirectly indicating a good bypass function (Fig. B9.21,

Fig. B9.22, Fig. B9.23, Fig. B9.24).

Final Diagnosis

Successful implantation of a right EC–IC bypass in severe moyamoya disease stage IV with recurrent territorial and hemodynamic brain infarctions.

Discussion

Clinical Aspects

This patient was a 32-year-old white man who attended medical treatment after a ﬁ rst stroke but who revealed symptomatic and asymptomatic territorial as well as hemodynamic brain infarction. Finally, severe MMD was diagnosed, based on angiographic ﬁ ndings of bilateral in- tracranial steno-occlusive pathology at the carotid-T and at the left PCA with typical small collateral vessels.

MMD was ﬁ rst described by Takeuchi and Shimizu in

1957 and is predominantly found in Japan (Kleinloog et al

2012). Between 6% and 12% of MMD cases are considered to be familial. The annual incidence in Japan is 0.35% per 100,000 inhabitants (Fukui and Kawano 1996). A recent review showed that the incidence of MMD in Japan is ~20–40 times higher than that in Taiwan and Iowa, USA, two times higher than that in Nanjing, China, and about ﬁ ve times higher than that in Hawaii. The relatively high incidence in Hawaii is most likely explained by the high proportion of people with Japanese and Chinese family backgrounds living there. Precise epidemiologic data for Europe are not available. Generally, young women seem to be more frequently aﬀ ected than men. The disease may manifest at any age. However, there are two peaks in presentation in those aged <10 years and between 30 and 40 years.

The course of the disease is usually characterized by a slow but progressive development of stenoses in the cerebral arterial circle (circle of Willis, CW), which is more accelerated in children. Also bleeding episodes are more common in the latter. Generally, the stenosed vessels are the ICA, MCA, and ACA, but the posterior circulation including the basilar and PCAs, as in our case, is more often involved than was considered previously. In a DSA study of 152 MMD patients, PCA vessels were aﬀ ected, showing stenosis or occlusion in 43%. The reported frequency of PCA involvement also increased with the extent of ICA lesions (Yamada et al 1995). A further study conﬁ rmed the high rate of steno-occlusive PCA lesions, describing PCA vessel involvement in 33% of 54 adult patients which also led to signiﬁ cantly more PCA territory infarctions (Hishikawa et al 2013). Involvement of the PCA also means that a potential collateral vessel cannot function and therefore the risk of TIA and/or cerebral infarction in both anterior and posterior circulation is increased (Kuroda et al 2002).

257Discussion

M1-MCA-R

Fig. B9.21 TCCS (transtemporal approach), right-sided insonation, midbrain plane. Antegrade ﬂ ow with a mild poststenotic ﬂ ow pattern in the right M1-MCA at a depth of 51 mm (ﬂ ow velocity 58/38 cm/s).

M1-MCA-R

Fig. B9.22 TCCS (t rans tempora l ap proach) , right-s ided inso nati on, midbrain plane. Retrograde ﬂ ow with a moderate poststenotic ﬂ ow pattern in the right M1-MCA at a depth of 44 mm (ﬂ ow velocity 42/28 cm/s).

P1-PCA-R

Fig. B9.23 TCCS (t rans tempora l ap proach) , right-s ided inso nati on, midbrain plane. Retrograde ﬂ ow in the distal right M1-MCA / prox- imal M2-MCA at a depth of 38 mm. Ipsilateral STeA compression leads to an abrupt and complete stop of the retrograde MCA ﬂ ow signal. At the same time, an increased ﬂ ow velocity was observed in the ipsilateral proximal M1-MCA (not shown). Duration of compression indicated by white dotted lines.

With an increasing burden of steno-occlusive lesions in the CW the typical basal and transdural collaterals appear as a network of intracerebral and extracerebral vessels. In DSA imaging they resemble fog or smoke-like structures, which gave the disease its name (moyamoya is Japanese for smoke or fog).

In macroanatomy, stenoses or occlusions are caused by an intimal thickening of the vessel. Histologic e x a m i n a t i o n s h o w s ﬁ brocellular thickening of the inti- ma with an increased number of smooth muscle cells, and marked undulation of the internal elastic lamina. Mural thrombi are frequently found within the stenosed regions, which are thought to be mainly responsible for the eccentric reduction of the vessel lumen (Hosoda et al 1997). Generally, no signs of atherosclerosis or inﬂ ammation are present (Takekawa et al 2004). The underlying pathomechanism remains unclear. A mixture of environmental factors like vessel wall stress, angio-

Fig. B9.24 TCCS (transtemporal approach), right-sided insonation, midbrain plane. A less turbulent ﬂ ow signal and lower ﬂ ow velocities in the right P1-PCA (ﬂ ow velocity 118/74 cm/s) after bypass surgery indicating a reduced demand to serve as a collateral vessel.

genesis-related factors, thrombogenic factors, and autoimmune processes seem to be included in this complex disease (Kuroda and Houkin 2008). But relevant genetic factors have also to be assumed, explaining the predominance among the Asian population and the reported inheritance in some families. Epidemiologic studies reported that up to 15% of patients in Japan have a familial form of moyamoya disease assumed to be autosomal dominant with incomplete penetrance (Baba et al 2008). In recent years a variety of gene loci have been related to moyamoya disease, especially 17q25 as a causative genetic lesion (Kamada et al 2011, Liu et al 2011, Roder et al 2010).

Clinically, MMD frequently manifests itself by reoccurring TIAs. Atypical reported symptoms are chronic headaches and focal or generalized epileptic seizures. In Asia, an increased incidence of intracranial bleeding has been reported as a further ﬁ rst manifestation of

258 Case 9 Moyamoya Disease

moyamoya in the adult population, in contrast to western countries, whereas TIAs prevail in the juvenile form. In Europe this diﬀ erence between age groups does not seem to exist. In our patient, only age and not gender or clinical presentation corresponded with the diagnosis of moyamoya disease.

Our patient revealed classical large territorial infarcts and BZI. In an analysis of 66 patients and 91 infarct lesions territorial infarctions with various patterns were the most common infarct type, seen in 78%, followed by multiple cortical dots in 8.8%, subcortical infarction in

7.7%, and BZI in 5.5%. Territorial infarctions may have a distinct appearance (gyral, honeycomb-like, atypical) compared with classical territorial lesions. Diﬀ erences may also be present between adult- and childhood-onset MMD. A classical territorial lesion was seen in 15.7% of patients with adult-onset MMD but only in 2.5% of patients with childhood-onset disease. Atypical and gyral territorial infarctions were seen in 48.9% and 80%, respectively (Cho et al 2011).

Patients with the characteristic moyamoya vasculopathy who have no known associated risk factors are deﬁ ned to have MMD. In a minority of patients, the vasculopathy occurs in association with other vessel -aﬀ ecting condi- tions, and these patients are categorized as having moyamoya syndrome. Given that moyamoya is a rare disease of unknown etiology, several focal and systemic diseases have to be excluded, including chronic meningitis, vasculitis, Down’s syndrome, neuroﬁ bromatosis type 1, dissec- tion, and sickle cell disease (for further reading on sickle cell disease see Case 43). In some middle-aged patients with atherosclerotic vascular disease, the latter may lead to a picture similar to the moyamoya ﬁ ndings. These patients, however, demonstrate additional macroangiopathic vessel wall changes in the extracranial brain-supplying arteries (Hinshaw et al 1976). As the fog-like collateral network can also be found in these patients, it has to be interpreted as an unspeciﬁ c compensatory reaction to a slowly progress- ing stenotic process. Finally, radiotherapy to the head and neck is strongly associated with moyamoya-like vasculopathy as a side eﬀ ect (Scott and Smith 2009).

MMD is a progressive disease. Its natural history in a North American adult cohort shows annual ischemic stroke and hemorrhage rates of 13.3% and 1.7%, respectively (Gross and Du 2013). Furthermore, disease progression was reported in 23.8% of adults in non-surgically-treated hemispheres, and in one-half of them it was symptomatic (Kuroda et al 2005). Mortality has been reported in the acute phase to be 2.4% in ischemic stroke and even 16.4% in the hemorrhagic variants (Yonekawa and Taub 1999).

To date, there is no medical treatment to stop the progression of moyamoya disease or reverse the intracranial arteriopathy. The aim of treatment strategies is to reduce symptoms and to prevent TIAs, recurrent strokes, and cognitive deterioration. It is unclear whether drug therapy improves outcome, although antiplatelet agents and anticoagulation are frequently used. The use of antiplatelet agents in the acute and symptomatic chronic phase in children and adults except for those presenting with hemorrhage is recommended (Research Committee on the Pathology and Treatment of spontaneous Occlusion

of the Circle of Willis 2012). There are strong indications from observational studies of large cohorts that surgical revascularization of the malperfused brain regions can reduce the risk of ischemic stroke and cognitive dysfunction by improving CBF in both children and adults (Abla et al 2013, Guzman et al 2009, Smith and Scott 2012). Examination of the cerebrovascular reactivity by CO or acetazolamide infusion using TCD or in patients with

inhalation

severe vessel diseases by acetazolamide infusion using xenon-CT or SPECT may be helpful in detecting patients at high risk and to identify candidates for bypass surgery.

Several surgical techniques are used. The most common is direct revascularization with an EC–IC bypass between the superﬁ cial temporal artery and a cortical MCA branch (STeA–MCA bypass) (for further information on EC–IC bypass, see Case 25). Indirect forms of revascularization are the placement of the STeA on the dura, muscle, or pia (encephaloduroarteriosynangiosis, encephalomyosynangiosis, or pial synangiosis). All approaches improve the perfusion of the poststenotic brain regions and are able to minimize or even to stop clinical events. The indirect approach is more frequently used in children and the direct approach in adults, as it was for our patient. Despite the clear results on the symptomatic hemisphere, there is no consensus on the indication for and timing of revascularization surgery in asymptomatic patients, or for the asymptomatic contralateral hemisphere in symptomatic patients, nor is there consensus on what type of revascularization surgery should preferably be performed (Pandey and Steinberg 2011).

A feature of particular clinical interest in our patient was the spontaneous remission of the homonymous hemianopia despite the large partial territorial ischemia in the perfusion area of the left calcarine artery. The MRI revealed a spared occipital pole and obviously also striate cortex which explained the visual restitution. Usually the irrigation area of the calcarine artery includes the visual cortex, but variants are often present and other cortical branches of the PCA, the parietooccipital artery and the occipitotemporal artery, may also contribute to the perfusion of the visual cortex in 20–35% and 3–22.5% of cases, respectively (Marinković et al 1987, Margolis et al 1971). Even the MCA may be involved in the supply of the medial occipital lobe but here usually a homonymous hemianopia sparing the macula is expected (McAuley and Russell 1979). For further reading on PCA branch anatomy, see Chapter 2, “Posterior Cerebral Artery” under “Special Arterial Anatomy and Ultrasound Anatomy;” for further reading on PCA stroke, see Case 6; for further reading on visual disturbances and stroke, see Case 38.

Angiologic and Anatomic Aspects

Diagnosis of MMD is based on morphologic vascular aspects depicted by the angiologic imaging methods. An additional diagnostic criterion is the bilateral occurrence of stenotic processes. In isolated unilateral cases, a moyamoya syndrome has to be postulated (Scott and Smith 2009). First-line techniques are the noninvasive CT and CTA as well as MRI and MRA. In suspected cases, these are followed by DSA. Conventional CT ﬁ ndings are variable and often unspeciﬁ c. They range from mild brain atrophy with frontal accentuation to multiple

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