Porcine arteriogenesis based on vasa vasorum in a novel semi-acute occlusion model using high-resolution imaging

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.

Effect of vasa vasorum in cerebrovascular compensation: 2 case reports

Intracranial vasa vasorum (VV) are rare and develop predominantly in the proximal segments of the internal carotid artery (ICA) and vertebral artery (VA). The typical appearance of intracranial VV has not yet been reported in clinical practice. Although VV in the ICA have been found to re-institute the collateral flow, bypassing the obstructive segment, far less attention has been paid to the manner in which VV can connect the two ends of the obstructive segment through the plaque. In this study, we present two cases and discuss the positive effects of VV. In our first case, a patient with basilar artery (BA) occlusion and multiple infarcts in the posterior circulation territory received endovascular treatment. Digital subtraction angiography (DSA) showed the existence of VV, which originated from the proximal BA lumen, penetrated through the vessel wall, bypassed the obstructive segment, re-penetrated through the vessel wall, and reconnected to the distal BA lumen. Balloon angioplasty was performed, specifically avoiding the path of the VV, then the VV had disappeared in follow-up angiography. In our second case, a patient who had been diagnosed with occlusion in the initial segment of the left ICA two years ago suffered a stroke. DSA revealed that the VV collaterals penetrated directly through the plaque of obstructive site and reconnected to the distal vessel lumen, which caused low hemodynamic compensation. Angioplasty was performed directly following the VV path, then follow-up angiography showed the VV had disappeared. Arterial occlusion, including in the intracranial and extracranial artery, could trigger the occurrence of VV, which can improve downstream perfusion. VV also could play a role of signal light in endovascular treatment.

A Flow Dynamic Rationale for Accelerated Vascularized Composite Allotransplant Rejection

BACKGROUND

From 1996 to 2000, Diefenbeck et al. carried out six knee vascularized composite allotransplants. The allotransplants were composed of bone, soft tissue, and femoral vascular pedicle (25 to 40 cm). All rejected between 14 and 56 months. Failures were attributed to chronic rejection. In 2008, the Louisville team lost their fourth patient's hand transplant at 8 months. During the rejection workup, intraoperative findings noted a thickened arterial pedicle attributed to intimal hyperplasia with significant fibrotic perivascular tissue and a near "no-flow phenomenon." No cutaneous rejection was appreciated and failure was attributed to chronic rejection.

METHODS

Data were collected from two teams, one in Germany and the other in Louisville, Kentucky. The population under study consisted of the six knee and one hand transplants. The factor of interest was the long donor arterial pedicle. The outcome measurements were transplant survival time and histopathologic results.

RESULTS

There are only seven published vascularized composite allotransplant cases where a donor artery longer than 25 cm was used. This cohort represents a 100 percent accelerated failure rate. The cause of these losses remains unexplained. The donor arteries suffered from T-cell-mediated rejection and ischemia-induced media/adventitial necrosis.

CONCLUSIONS

We hypothesize that the donor artery rejected at an accelerated rate because of ischemia caused by disruption of the external vasa vasorum in conjunction with intimal hyperplasia induced by T-cell-mediated rejection that led to disruption of the Windkessel effect. Loss of this effect presented as intimal hyperplasia accelerated by ischemia causing an expedited transplant failure.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.