Table 1. The napkin-ring sign of the unstable and stable groups.

Variables	Unstable group	Stable group	P value
Patients	34	26	<0.01
Plaques	37	31
Napkin-ring sign
Yes (%)	33 (89.2)	7 (22.6)
No (%)	4 (10.8)	24 (77.4)