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Objectives: Gray scale median (GSM) analysis has been used to measure lipid content in carotid lesions. Previous studies have shown that a low GSM value is correlated with increased perioperative risk during carotid artery stenting (CAS). A comparative analysis of GSM values between patients with a primary stenosis (the “primary” group) and those with a post-carotid endarterectomy (CEA) atherosclerotic restenosis (the “post-CEA” group) was performed to determine if both groups are appropriate for GSM analysis.
Methods: Retrospective data was collected and analyzed from all patients undergoing CAS from November 2005 to August 2010. Data collected were: demographics, atherosclerotic risk factors, high risk criteria, ultrasound imagery, perioperative outcomes, and long-term outcomes. Patients who had pre-operative images amenable to gray scale analysis were identified as a sub-population for investigation. GSM values were calculated with Adobe Photoshop (v.CS4, San Jose, CA, USA) in the manner previously described in the literature.
Results: During the study period, 284 patients underwent 304 CAS procedures. The study population was comprised of 53 patients for whom GSM analysis was feasible. The study population was divided into one of the two groups mentioned above: the primary group (n=40, 75%) or the post-CEA group (n=13, 25%). The mean time from CEA to CAS reintervention for the post-CEA group was 7.3 years (range 0.5 to 15 years, σ=4.7). The two groups had the following characteristics:

	Primary (n=40)	Post-CEA (n=13)	p-value
Mean Age	72.2 (range 50 to 88, σ=9.5)	69.3 (range 55 to 86, σ=8.7)	0.31
Hypertensive	36 (90%)	9 (69%)	0.08
Coronary Artery Disease	16 (40%)	3 (23%)	0.33
CVA prior	13 (33%)	2 (15%)	0.31
Octogenarian	10 (25%)	2 (15%)	0.70
	Primary (n=40)	Post-CEA (n=13)	p-value
Mean GSM	43.8 (range 4 to 102, σ=23.6)	19.9 (range 0 to 53, σ=16.5)	0.0002
Perioperative Stroke	1 (2.5%)	0 (0%)	1.00
Perioperative Mortality	2 (5.0%)	0 (0%)	1.00
Combined Perioperative Complication	3 (7.5%)	0 (0%)	0.57
Mean Followup	280 days	412 days	0.20
Restenosis (>224 PSV)	4 (10%)	1 (7.7%)	1.00
>30 day Ipsilateral Stroke	1 (2.5%)	0 (0%)	1.00

The patients in each group were then further subdivided into low (<30) or high (>=30) GSM subsets. In the primary group, there were 10 patients (25%) in the low GSM subset and all perioperative complications occurred within this subset (n=3, 30%). This differed significantly from the patients in the high GSM subset (p=.0289). For the post-CEA group, there were 10 patients (77%) within the low GSM subset and there were no complications (n=0, 0%). There was no difference between the low GSM subset and high GSM subset in the post-CEA group (0 vs. 0 complications).
Conclusion: This study confirms that a low GSM value is associated with increased perioperative risk for primary stenosis but suggests that GSM analysis is less predictive for patients with post-CEA restensosis.