Evolution of a “falx lunatica” in demarcation of critically ischemic myocutaneous tissue

Abstract

Using intravital microscopy in a chronic in vivo mouse model, we studied the demarcation of myocutaneous flaps and evaluated microvascular determinants for tissue survival and necrosis. Chronic ischemia resulted in a transition zone, characterized by a red fringe and a distally adjacent white falx, which defined the demarcation by dividing the proximally normal from the distally necrotic tissue. Tissue survival in the red zone was determined by hyperemia, as indicated by recovery of the transiently reduced functional capillary density, and capillary remodeling, including dilation, hyperperfusion, and increased tortuosity. Angiogenesis and neovascularization were not observed over the 10-day observation period. The white rim distal to the red zone, appearing as "falx lunatica," showed a progressive decrease of functional capillary density similar to that of the necrotic distal area but without desiccation, and thus transparency, of the tissue. Development of the distinct zones of the critically ischemic tissue could be predicted by partial tissue oxygen tension (Pt(O(2))) analysis by the time of flap elevation. The falx lunatica evolved at a Pt(O(2)) between 6.2 +/- 1.3 and 3.8 +/- 0.7 mmHg, whereas tissue necrosis developed at <3.8 +/- 0.7 mmHg. Histological analysis within the falx lunatica revealed interstitial edema formation and muscle fiber nuclear rarefaction but an absence of necrosis. We have thus demonstrated that ischemia-induced necrosis does not demarcate sharply from normal tissue but develops beside a fringe of tissue with capillary remodeling an adjacent falx lunatica that survives despite nutritive capillary perfusion failure, probably by direct oxygen diffusion.

Selective blockade of endothelin-B receptor improves survival of critically perfused musculocutaneous flaps

“…The absence of signs of angiogenesis, which should be visible after ∼day 3, might be due to desiccation of the tissue within the chamber. The transitory zone of demarcation between the perfused area of the flap proximally and the necrotic area distally adjacent revealed an increased microvascular stasis, arterio-venular dilation, and hence tortuosity but no signs of angiogenesis, representing a zone of compromised blood perfusion as previously shown [22].…”

“…Accordingly, only after ET-B-receptor blockade capillary perfusion was found improved during the first days after flap elevation. In fact, the values of FCD after ET-B-receptor blockade were in the range of the physiologic values of intact tissue within dorsal skinfold chamber preparations [18,22]. Assessment of FCD after blockade of the ET-A receptor or both the ET-A and ET-B receptor revealed that the late recovery of aBF was not anymore capable of improving capillary perfusion.…”

Gender-specific ischemic tissue tolerance in critically perfused skin

“…The critically perfused zone of demarcation of a flap consists of an area with a rarefaction of perfused capillaries that dilate in order to increase the exchange surface of O 2 between vessels and interstitial tissue, i.e., to increase O 2 conductance [2]. These scarce microvessels may not serve as an adequate nutritional supply to the tissue but only function as "thoroughfare" channels, as described for .…”

“…Insufficiency of the microcirculation on the other hand may lead to irreversible tissue damage due to persistent ischemia and hypoxia, which untreated will result in wound breakdown [1] and compromised tissue survival, including surgical accesses with extensive undermining or randomly perfused remote areas of the critically perfused flap tissue [2,3].…”

The dorsal skinfold chamber: A versatile tool for preclinical research in tissue engineering and regenerative medicine

“…Analyses of the microcirculation and partial oxygen tension in different zones of the myocutaneous flap revealed that the critical ischaemia-induced necrosis does not demarcate sharply from the adequately perfused tissue at the flap basis (Harder et al, 2005a). Between the two zones a fringe of tissue with vascular remodelling develops a distally adjacent falx lunatica lacking nutritive www.ecmjournal.org…”