31 Dissection of the Left Internal Carotid Artery C6 Segment

Dissection of the Right Internal Carotid Artery C6 Segment

Clinical Presentation

A 46-year-old woman was admitted with slight numbness and weakness in the left hand which began 5 days before presentation. At first, she felt only mildly affected and refused to seek medical attention. The day before symptom onset, she had suffered unusually severe right-sided headaches. She reported no trigger events and had no previous medical problems. She had no known vascular risk factors and, in particular, no history of migraine. Neurologic examination revealed a mild sensorimotor paresis of the left hand and reduced fine motor skills (National Institute of Health Stroke Scale [NIHSS] score: 2).

Initial Neuroradiologic Findings

Initial CT showed normal findings (not shown).

Suspected Diagnosis

Right-sided middle cerebral artery (MCA) ischemia in internal carotid artery (ICA) dissection.

Questions to Answer by Ultrasound Techniques

Is there a steno-occlusive lesion in the right anterior circulation?
Are there signs of ICA dissection?

Initial Neurosonologic Findings (Day 2)

Extracranial Duplex Sonography

Examination of the carotid and vertebral arteries (VAs) revealed normal results. No direct or indirect signs of a cervical artery dissection (CAD) were observed.

Transcranial Duplex Sonography

Normal flow signals were found in both M1-MCA and the detectable M2 segments as well as in the anterior (ACA) and posterior (PCA) cerebral arteries. The carotid siphon and carotid-T showed normal flow signals on both sides. An apparent difference was seen in the C6-ICA segment. The right ICA showed increased and nonturbulent flow with a flow velocity of 121/46 cm/s compared with 74/35 cm/s on the left side. Transforaminal examination of the VAs was normal (Fig. B31.1 and Fig. B31.2). No microembolic signals were detected during routine transcranial color-coded duplex sonography (TCCS) examination.

Follow-up Neuroradiologic Findings (Day 2)

Assuming a right-sided MCA ischemia caused by a right C6-ICA stenosis, MRI including time-of-flight angiography (TOF-MRA) was performed on the same day. MRI diffusion-weighted images revealed hyperintense signals in the right MCA territory, including the region of the hand knob (omega region). TOF-MRA showed a right C6-ICA tailoring and a hyperintense structure below the C6-ICA indicative of blood extravasation. Fat-suppressed T1-weighted images displayed a crescent-shaped wall hematoma. The right-sided A1-ACA segment and the right posterior communicating artery (PCoA) were not visible (Fig. B31.3, Fig. B31.4, Fig. B31.5).

Conclusion

Fragmented right-sided MCA infarction due to artery-to-artery embolism arising from C6-ICA stenosis caused by circumscribed spontaneous dissection.

Fig B31-6 shows a schematic of the patient’s extra-and intracranial brain-supplying arteries.

Clinical Course (1)

Anticoagulation was considered but not initiated. We decided against anticoagulation to avoid increasing the risk of secondary ICA occlusion at the dissection site, given the special anatomic cerebral arterial circle (circle of Willis) constellation and lack of collateral pathways on the right side. Therefore, secondary prevention with aspirin was started.

Follow-up Neurosonologic Findings (Day 120)

Transcranial Duplex Sonography

Normal flow parameters were found in all vessel segments including the right C6-ICA (not shown).

Fig. B31.1 TCCS (transtemporal approach), right-sided insonation, lower pontine plane. Non-angle-corrected increased but nonturbulent flow in the right C6-ICA (flow velocity 121/46 cm/s).

Fig. B31.2 TCCS (transtemporal approach), left-sided insonation, lower pontine plane. Normal (and lower) flow velocities on the unaffected left C6-ICA (flow velocity 74/35 cm/s).

Fig. B31.3 (A,B) MRI, diffusion-weighted image, axial plane. Hyper-intense signals in the right MCA territory (arrowhead) representing acute multiple small infarctions including the hand knob (arrow).