A 57-year-old male was hospitalized 5 days after the occurrence of a right hemiparesis and speech disturbance. The patient had undergone bilateral carotid thrombendarterectomy 5 years before the accident, without any further follow-up. Underlying conditions were hypertension, diabetes and hyperlipoproteinemia.

On admission, the patient had motor aphasia, right facial nerve palsy and right pyramidal palsy. Brain computed tomography revealed an ischemic lesion in the left parietooccipital area. Carotid duplex scan showed 30% stenosis of the left internal carotid artery with a fibrolipid plaque of uneven surface on the posterior wall of the carotid bifurcation, partly spreading into the internal carotid artery. The patient was discharged with clopidogrel 75 mg and simvastatin 20 mg daily.

The 6-month follow-up carotid duplex scan showed a mobile floating ridge-shaped plaque on the posterior wall of the left common carotid artery around 25 mm below the bifurcation with obstruction of 30% \[[Figure 1a](#F1){ref-type="fig"}\]. On the next 6-month control, carotid duplex scan proved the enlargement of the plaque, which was now grown into the lumen, while another small lesion located diametrically on the wall of the carotid artery was also present. The stenosis was less than 50% \[[Figure 1b](#F1){ref-type="fig"}\]. Given the non-significant stenosis and the fact that the patient had been asymptomatic, the conservative treatment was continued. Six months later, the two plaques were conjoined, forming a membranous plaqe dividing the lumen of the common carotid artery \[[Figure 1c](#F1){ref-type="fig"}\]. Magnetic resonance angiography confirmed double lumen of the common carotid artery \[[Figure 1d](#F1){ref-type="fig"}\]. The patient was still asymptomatic.

![(a) Duplex scan on first follow-up after discharge: longitudinal brightness-modulated (B-mode) scan shows a mobile floating plaque. (b) Follow-up duplex scan 6 months later: transverse power Doppler flow image (PDFI) scan shows incomplete division of lumen. (c) Follow-up duplex scan 6 months later: transverse PDFI scan shows completely divided lumen. (d) Magnetic resonance time of flight angiography shows divided lumen of common carotid artery](AIAN-15-347-g001){#F1}

Mobile floating carotid plaques are uncommon, with an estimated prevalence of one in 2000,\[[@ref1]\] and usually originate from degenerated atherosclerotic flaps, intimal dissection flaps, post-trauma or ruptured plaque.\[[@ref2][@ref3]\] As such plaques are unstable and associated with higher risk of embolic cerebrovascular events, carotid endarterectomy could be the best treatment option.\[[@ref3][@ref4]\]

In contrast to dissection, double lumen only rarely occurs in atherosclerotic carotid disease. There is a possibility that a channel dissects through the atherosclerotic plaque, forming a second lumen, as described in the case series of ACSCEPT trialists.\[[@ref5]\]

We described evolution of a ridge-shaped mobile carotid plaque that gradually divided the lumen of the common carotid artery. Most probably, tearing of the fibrous cap of the plaque occurred during endarterectomy. As the tearing enlarged, it became mobile and embolized causing ischemic stroke. Further on, the plaque grew as a mobile ridge-shaped mass eventually dividing the carotid lumen.

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