Computer analyzed histology of ischemic injury to the gut

Histopathologic alterations in the intestinal mucosa after ischemic injury have been extensively described in the literature, but these descriptions have primarily been qualitative in nature. The purpose of this study was twofold: (1) to establish parameters obtained by computerized digital image analysis that would be useful in identifying ischemic injury, and (2) to use these parameters to identify the critical period of intestinal ischemia producing measurable histopathologic change. Seventy male Sprague-Dawley rats weighing 80 to 150 g underwent various times of gut ischemic injury by vascular occlusion of the superior mesenteric artery and vein with a microaneurysm clamp. The clamp times were 0, 1, 20, 30, 40, 50, 60, 70, 80, and 90 minutes. Histological sections of the terminal ileum were quantitatively analyzed using Jandel Scientific's computerized morphometric image analysis system. Parameters studied were surface index (SI, surface length per linear unit of mucosa), average villous thickness (AVT), average villous height (AVH), and the number of villous cells/100 μm length (VC). Ischemic times of 1, 20, 30, and 40 minutes produced no measurable injury as compared with baseline ( P[40 minutes versus baseline] = SI, .60; AVT, .84; AVH, .93; VC, .09). At 50 minutes, SI and AVH showed a measurable change from baseline ( P[50 minutes versus baseline] = SI, .01; AVH, .02). Sixty minutes of ischemic time produced measurable change in all parameters ( P[60 minutes versus baseline] = SI, .007; AVT, .001; AVH, .002; VC, .007). Ischemic times beyond 60 minutes produced significant changes from baseline, but were not measurably different from that of 60 minutes ( P[90 minutes versus 60 minutes] = SI, .15; AVT, .89; AVH, .43; VC, .18). Interestingly, when each histological parameter was analyzed over time, the earliest measurable changes were noted in the SI and AVH between 40 and 50 minutes of ischemia. During this time period, there was a reduction in surface index ( P = .03) and average villous height ( P = .005) with a concomitant increase in the Chiu score ( P = .02). These results suggest that the critical period of ischemia producing significant histopathologic change without irreversible death lies within 40 to 50 minutes. Furthermore, morphometric analysis can be used with reliability in quantitatively evaluating the degree of gut ischemic injury, allowing a more objective and reproducible measurement of ischemic change.