5 Left M1 Middle Cerebral Artery Stenosis

Left M1 Middle Cerebral Artery Stenosis

Clinical Presentation

A 29-year-old woman was admitted to a district general hospital. Four weeks prior, she had developed a first-time mild aphasia and right-sided sensory hemisyndrome but had not paid attention to her symptoms. She was a heavy smoker (15 cigarettes/day) and took an oral contraceptive but no other drugs or vasoactive medication. She reported no headaches during the time until presentation and there was no history of migraine. Her mother had suffered from stroke aged 24 years. On admission, her National Institute of Health Stroke Scale (NIHSS) score was 2.

Initial Neuroradiologic Findings

MRI of the brain revealed a fragmented left frontoparietal ischemic lesion in the middle cerebral artery (MCA) territory. There was gadolinium enhancement in the infarcted areas, consistent with a partial subacute territorial MCA infarction. Intracranial 3D time-of-flight MR angiography (TOF-MRA) showed an isolated left proximal high-grade M1-MCA segment stenosis with reduced or absent M2-MCA signals and a mild right M1-MCA and A1-segment anterior cerebral artery (ACA) stenosis. A prominent left posterior cerebral artery (PCA) signal was considered as an indirect sign of collateral PCA flow activation (Fig. B5.1 and Fig. B5.2).

Suspected Diagnosis

Subacute left MCA territory ischemia caused by artery-to-artery embolism in high-grade left proximal M1-MCA stenosis and suspected contralateral M1-MCA and A1-ACA stenoses.

Conventional Angiography (Day 2)

Because of the unclear underlying vessel processes digital subtraction angiography (DSA) was performed. Segmental high-grade narrowing of the proximal left M1-MCA segment was confirmed. The distal course of the vessel was normal. The contrast filling of the left-sided distal MCA branches was mildly delayed in comparison with branches of the ipsilateral ACA. Late arterial phase images showed mild leptomeningeal collateralization via the ACA. The right M1-MCA appeared mildly narrowed. The posterior circulations showed no abnormalities (Fig. B5.3 and Fig. B5.4).

Clinical Course

During the patient’s hospital stay the clinical symptoms improved. Thrombophilia, vasculitis, Fabry’s disease, and an autoimmune etiology were excluded. A normal transesophageal echocardiogram and a 24-hour electrocardiogram (ECG) made a cardiac cause unlikely. Dual antiplatelet treatment with aspirin and clopidogrel was started and after 6 months switched to aspirin alone. After a clinical uneventful time of 2 years she presented for follow-up control. She was still smoking but no longer took the contraceptive pill. Clinically, a mild sensory aphasia and memory deficits remained. On MRI, no acute ischemic lesions were detected but a mild, parietal accentuated left-sided hemiatrophy had developed. TOF-MRA revealed no progress of reported vessel abnormalities (not shown).

Questions to Answer by Ultrasound Techniques

Were there vessel wall changes in the extracranial brain-supplying arteries?
Were the grades of stenoses still comparable to the initial DSA results?
If yes, what was the grade of the left proximal M1-MCA stenosis?
Where there signs of collateral flow activation?
Could the mild contralateral M1-MCA and A1-ACA stenoses be confirmed?

Initial Neurosonologic Findings

Extracranial Duplex Sonography

B-mode imaging revealed no atherosclerotic vascular changes. Doppler spectrum analysis showed normal and symmetric flow signals in both carotid and vertebral arteries.

Transcranial Duplex Sonography

Doppler spectrum analysis revealed an increased flow velocity reaching 328 cm/s peak systolic flow in the left proximal M1-MCA segment at a depth of 50 mm. A severe poststenotic flow pattern was detected in both visible M2-MCA branches. The right M1-MCA revealed a mild turbulent flow signal with increased flow velocities (222/106 cm/s). Both A1-ACA had increased flow velocities (left A1-ACA 157/72 cm/s, right A1-ACA 153/74 cm/s). On the left side the cause could either be stenosis or collateral flow activation. Reviewing MRA and DSA finally ruled out stenosis. On the right side, the raised A1-ACA flow was assumed to indicate a stenosis. The left P2-PCA showed a mild increased flow velocity (82/30 cm/s) which was considered to be caused by collateral flow activation. The right PCA and the vertebrobasilar arteries showed normal flow signals (Figs. B5.5–B5.12).

Fig. B5.1 MR diffusion-weighted (b=1,000) image (A) and T1-weighted image after gadolinium administration (B), axial plane. Mild signal increase in the left MCA territory in the left frontoparietal cortex and corresponding contrast enhancement, compatible with a subacute territorial MCA ischemia. (Courtesy of S. Paris, A. Heiniche, and A. Recker, Radiologische Praxis am Evangelischen Krankenhaus Herzberge, Berlin, Germany.)

Fig. B5.2 3D TOF-MRA, coronal maximal intensity projection (MIP). Markedly reduced flow signal in the proximal left M1-MCA (arrows) with a short gap at its origin (arrow), suggesting a high-grade stenosis. Note also the irregularities in the mid part of the right M1-MCA (large arrowhead) and A1-ACA (short arrowhead). Note also the prominent flow signal in the periphery of the left PCA (arrowheads) indicating leptomeningeal collateral flow. (Courtesy of S. Paris, A. Heiniche, and A. Recker, Radiologische Praxis am Evangelischen Krankenhaus Herzberge, Berlin, Germany.)

Fig. B5.3 DSA, left ICA injection, posteroanterior view (A) and left anterior oblique view (B). Severe short-segmental narrowing of the proximal MCA (arrow). The contrast filling of the left-sided distal MCA branches is mildly delayed in comparison to the distal branches of the ipsilateral ACA (arrows) indicating a hemodynamic significance of the M1-MCA stenosis. (Courtesy of Dr. Langhoff, Angiologische Abteilung, Evangelischen Krankenhaus Herzberge, Berlin, Germany.)

Fig. B5.4 DSA, right ICA injection, posteroanterior view (A) and right anterior oblique view (B). A mild stenosis is seen in the mid part of the right M1-MCA (arrowhead) as well as in the mid part of the A1-ACA (arrow). (Courtesy of Dr. Langhoff, Angiologische Abteilung, Evangelischen Krankenhaus Herzberge, Berlin, Germany.)

Fig. B5.5 TCCS (transtemporal approach), left-sided insonation, midbrain plane, color-mode image. Using the standard pulse repetition frequency (PRF) settings adjusted for normal flow velocities, the image would suggest the wrong diagnosis of a mid-part M1-MCA occlusion (arrow).

Fig. B5.6 TCCS (transtemporal approach), left-sided insonation, midbrain plane. Reducing the PRF for better visualization of vessel with low flow velocities, more distal parts of the left M1-MCA become visible. Doppler spectra analysis revealed a stenosis in the left mid M1-MCA with an intrastenotic flow velocity of 328/220 cm/s in a depth of 50 mm. Note the severe turbulent flow impairing the measurement of the true systolic and diastolic flow.

Fig. B5.7 TCCS (transtemporal approach), left-sided insonation, midbrain plane. Marked poststenotic flow pattern in the left frontal (anterior) M2-MCA branch at a depth of 40 mm.

Fig. B5.8 TCCS (transtemporal approach), left-sided insonation, midbrain plane. Marked poststenotic flow pattern in the left parietal (posterior) M2-MCA branch at a depth of 39 mm.

Conclusion

High-grade left proximal M1-MCA segment stenosis of hemodynamic relevance (>70%) with leptomeningeal collateral flow via the left ACA and PCA. In addition, mild right M1-MCA and A1-ACA stenosis of ~50%.

Fig. B5.13 shows a schematic of the patient’s extra-and intracranial brain-supplying arteries.

Final Diagnosis

Ischemic brain infarction in the left MCA territory by artery-to-artery embolization caused by a left-sided hemodynamically relevant high-grade M1-MCA stenosis. Contralateral asymptomatic moderate M1-MCA and A1-ACA stenoses of unknown origin.

Discussion

Clinical Aspects

The patient is a 31-year-old woman with a left-sided proximal high-grade M1-MCA stenosis with subsequent cortical ischemic brain infarction in the MCA territory. Because of her young age and lack of any extracranial arterial macroangiopathy, a primary intracranial stenosis with artery-to-artery embolism was considered. However, a confident differentiation between a fixed stenosis, a fresh local thrombus, a partially reopening embolus vasospasm, or a reversible vasoconstriction was not possible in the former acute state. The hypothesis of fixed stenoses could then be confirmed during the follow-up assessment 2 years later because the vascular status had remained unchanged.

Fig. B5.9 TCCS (transtemporal approach), left-sided insonation, midbrain plane. Raised flow velocities in the left A1-ACA (157/72 cm/s) without turbulence. Because of the high-grade ipsilateral M1-MCA stenosis and the normal DSA findings, the increased flow velocity was considered to indicate leptomeningeal collateral flow to the MCA territory.

Fig. B5.10 TCCS (transtemporal approach), left-sided insonation, midbrain plane. Increased flow velocities in the left P1/P2-PCA (82/30 cm/s), indicating leptomeningeal collateral flow to the MCA territory.

Fig. B5.11 TCCS (transtemporal approach), right-sided insonation, midbrain plane. Right M1-MCA with intrastenotic flow velocity of 222/106 cm/s at a depth of 50 mm. Note that the flow is not turbulent. No poststenotic flow pattern was seen in the downstream segments (not shown).

Fig. B5.12 TCCS (transtemporal approach), right-sided insonation, midbrain plane. Increased flow velocities in the left A1-ACA (153/74 cm/s) with a moderate turbulent flow pattern. In contrast to the contralateral side, a moderate stenosis had to be assumed as no high-grade M1-MCA or PCA stenosis was present.

The clinical course and follow-up investigations are often of paramount importance to clarify the stroke etiology. In our patient, the stable clinical and neurosonologic findings over several years were suggestive of fixed high-grade left-sided MCA stenosis and also moderate right-sided A1-ACA and M1-MCA stenoses. The permanence of the stenoses and also the absence of headaches typical of reversible cerebral vasoconstriction syndrome (RCVS) ruled this diagnosis out (for further reading of RCVS, see Case 36). As expected at her age, even considering her smoking, assessment of the extracranial brain-supplying arteries did not demonstrate any atherosclerosis. A cardiac embolic source, thrombophilia, vasculitis, or autoimmune disease could not be found. A hereditary cause was considered because of her mother suffering from stroke as a young adult but was not confirmed by genetic or metabolic tests. Cannabis use was considered as a known cause of multifocal intracranial stenoses reported in the literature (Wolffet al 2011, 2014) but was convincingly denied by the patient, as was the use of other illicit drugs. The moderate contralateral M1-MCA and A1-ACA stenoses argued against an intracranial dissection (for further reading, see Case 21 and Case 24). Because of the bilateral affection of vessel segments near the carotid T, a moyamoya-like disease was discussed, but finally considered unlikely because of the atypical asymmetry and the bilateral sparing of the distal ICA (for further reading, see Case 9). No migraine history was present, ruling out migraine-related vessel pathology (for further reading, see Case 22).

Finally, an intracranial atherosclerosis was discussed, which may also occur as isolated findings in the white population, and treatment tailored to this diagnosis (platelet inhibition and statin) was given for secondary stroke prevention (for further reading on intracranial stenosis, see also Chapter 5, “MCA Stenosis” under “Intracranial Pathology,” Case 25, and Case 44; for further reading on stroke in young people, see Case 6).