| Koshima et al first reported harvesting infra-abdominal tissue based on the musculocutaneous perforators given off from the deep inferior epigastric artery through the rectus abdominus to reconstruct the tissue defects of the mouth floor and inguinal region in1989, which ushered in the era of the perforator flap. The perforator flap confirms to the reconstructive principle of "minimal morbidity at the donor site, greatest aesthetics at the recipient site"Increasingly sophisticated surgical approach requires deeper understanding into the anatomy and physiology of vessels. In1987, Taylor performed elaborate anatomical study on the cutaneous vasculature of human and other mammal animals, defining the anatomical territories of composite blocks of tissue supplied by source arteries as "angiosomes". Neighboring discrete angiosomes are linked by anastomotic vessels, most in the form of Choke anstomotic vessels (gradually diminishing in diameter). With the prevalent use of perforator flaps in clinics, the concept of angiosome is further divided. Saint-cyr carried out thorough study on perforator flap using static and dynamic CTA, putting forward the terminology of "perforasome" summing up the morphological characteristics of "perforasome":adjoining perforasomes communicated with each other through direct and indirect linking vessels. Preferential filling of perforasomes occurs within perforators of other adjacent source arteries first, followed by perforators of other adjacent source arteries.Since the cutaneous perforator is often small in diameter, its anatomical territory is often small too, which often make it unable to cover large defects caused by trauma, tumor ablation and congenital malformation restoration if only the anatomical territory is included. Through detailed study of the cutaneous vasculature, Cormack divided the cutaneous territory into three levels when a large flap is harvested:the anatomical territory(the territory directly nourished by the branches of a perforator), the potential territory(the territory immediately neighboring the anatomical territory), and the dynamic territory(the territory immediately neighboring the dynamic territory). When a large extended flap is harvested, the demarcation between the necrotic tissue and the viable tissue often appear at the Choke zone between the potential territory and the dynamic territory.Extended flaps have been frequently harvested in clinics for coverage of large-sized tissue defects. In order to guarantee the survival of the tissue volume as large as possible, delay measure has been commonly adopted. Animal experiments have elucidated that improvement of tissue survival by delay approach is attributable to the dilation of Choke vessels. Then we come to two ways the body develops to respond to ischemia:one is the dilation of existing vessels, termed as arteriogenesis, the other one is neovascularization, which can be subdivided further into angiogenesis (formation of new vessels by sprouting from existing vessels) and vasculogenesis (in situ formation of new vessels by recruitment of bone marrow-derived endothelial progenitor cells). The three forms of biological behaviors of vessels are independent from each other, but are complementary and overlapping to each other. They are now front and center in the field of vascular biology. Breakthroughs on the fundamental research of them stand a good chance of changing the strategy in ischemia prevention and treatment. The knowledge built up on the Choke vessels previously has mainly been two-dimensional, static and non-physiological, due to the limitation of methods available in the early stage. In recent years, the development of medical science and technology and biological technology has spawned numerous new methods for study of vascular morphology. Zhang et al and Tang et al found out during their study on perforator flaps using radiography that digital data obtained from CT scanning of the human body perfused with contrast medium can be imported into the personal computer, with which vessels of tiny caliber can be located, calibrated and reconstructed in three dimensions, heralding the study of perforator flaps in three-dimensional and digital ways. However, X-ray angiogram bears in itself an obvious drawback, namely, it cannot be used to study vessels in vivo for a long period. This limitation can be circumvented using rodents implanted with a dorsal skinfold chamber. The dorsal skinfold chamber allows researchers to continuously monitor the vascular behaviors in vivo. Moreover, when a positive phenomenon is observed, the experimented can be terminated, and the tissue can be harvested for bio-molecular tests. In previous investigations on Choke vessels with the angiogram, the Choke arteries are the focus while the Choke veins are always left out largely because of the difficulty in perfusing venous system evenly with contrast medium due to the existence of venous valves. However, venous drainage problems have contributed in a significant proportion to the complications seen in flap surgery. Consequently, it is of equal importance to study both the Choke arteries and the Choke veins, which can be achieved by adopting the dorsal skinfold chamber model. Finally, previous studies focuses on morphological studies of the Choke vessels, while mechanism underlying the Choke vessels dilation has been rarely explored.This project aims to do investigation in the following fields:①perform thorough anatomical study on the infra-abdominal region employing systematic angiograms. layered dissection, materialized interactive medical image control system, providing morphological basis for designing of extended flap in this region;②document the time sequence of microvascular events after extended flap elevation using dorsal skinfold chamber:③HE staining was used to detect the condition of the infiltration of inflammatory cells around the Choke vessels3days after flap elevation, and semi-quantification of the expression of MCP-1, ICAM-1, MMP-2and VEGF3days after flap elevation were carried out using immunohistochemistry, providing a preliminary investigation into the mechanism underlying Choke vessels expansion.Methods:1.10fresh cadavers were used for this study. On each cadaver, the femoral arteries were dissected out above the inguinal ligament, and two small cuts were made at the femoral arteries, one for each, respectively. The femoral arteries were then cannulated proximally and distally with the catheters of right size. Eight cadavers were perfused with gelatin-lead oxide compound, and two with red latex. The eight cadavers perfused with gelatin-lead oxide compound were subject for spiral CT scanning, and the data obtained were saved in the format of DICOM, which were then imported to the software of Mimics. Three-dimensional reconstruction of the abdominal vasculature was performed. Then the10cadavers underwent layered dissection, mainly in the abdominal region; layers of integument, muscle were all subject for X-ray angiogram. The amount, course, caliber, anastomosis the perforators from the deep inferior epigastric artery, the distributing pattern of the superficial epigastric artery and the inneration the inferior abdomen were the focuses of the investigation.2.30male SD rats were executed by cannulated exsanguination through the carotid artery, after which the gelatin-lead oxide compound were perfused through the small cannulation. Then, dissection were performed beginning from the abdominal midline, and the perforating sites, courses, branches, distributing patterns and anastomosis of the cutaneous arteries were investigated. The integuments were dissected free and spread on the cupboard for X-ray angiogram. A dorsal skinfold chamber mode was designed. The chamber consists of two main frames with their base bent outside with an angle of45’, a lid, four screws and four nuts. According to the previous anatomical outcome, a three-territory axial flap based on the iliolumar perforator was harvested on one side of the dorsum of the rat’s skin and sutured back in situ; the chamber was mounted with the observation collar aligned with the Choke zone between the iliolumbar perforator and the posterior intercostal artery. A whole layer of skin with the same size of the observation chamber was removed on the non-flap side of the dorsum. A total of12rats were subjected for this procedure.10were put under the stereoscopic microscope for observation of the morphological change every12h continuously for8d; Evans blue was injected into the other two rats via the tail veins for observation of the microcirculation after flap elevation.3.10SD rats were equally divided into two groups. The rats in one group underwent flap elevation as what has been described in the second chapter; The rats in the other group serve as the control group.3days after flap elevation, blocks of skin tissues were taken from the Choke zones between the iliolumbar perforator and the posterior intercostal perforator from all rats, labeled and stored in centrifugal tubes containing9%paraformaldehyde. The tissues then went through paraffin embedding and section. The sections were stained by two methods:one group of section were subject to HE staining for observation of the aggregation of polymorphous inflammatory cells, and the other group of sections were subject to immunostaining for detection of the expression of the following cytokines:MCP-1, ICAM-1. MMP-2and VEGF. Outcomes:1. The deep inferior epigastric artery bifurcates into a lateral branch and a medial branch in the middle1/3of the rectus abdominus. which give off a lateral row of perforators and a medial row of perforators, respectively. These perforators perforate through the rectus abdominus and the anterior sheath, and supply the middle portion of the abdominal integument. The medial row perforators with an average number of3.1±0.7and an average diameter of0.69±0.11mm were located in the medial1/3of the rectus abdominus, whose branches in the fascia are centered around the perforator stems and communicate with their counterparts at the contralateral side. The lateral row perforators with an average number of3.3±0.8and an average caliber of0.73±0.13mm were located at the lateral1/3of the rectus abdominus, who course in the abdominal fascia laterally for some distance and communicate with the superficial epigastric artery and the posterior intercostal (or subcostal) artery, and do not have branches transverse across the abdominal midline. Three patterns of the superficial epigastric artery were found:single stem and single branch, single stem and double branches, double stems. The superficial epigastical artery is1.2±0.6mm in diameter,88±29mm in pedicle length and supply a territory of113±34cm2. The donor site of the deep inferior epigastric artery perforator flap is innervated mainly by nerves ranging from T10to T12. The sensory branches of the intercostal nerves are closely associated with the perforators;85.1%of the perforators with caliber greater than0.5mm has accompanying sensory nerves. The stems of T10, T11and T12course anterior across the two branches of the deep inferior epigastric artery, with the convergence points located at13.1±6.3mm above the umbilicus.14.8±8.6mm and41.4±10.1mm below the umbilicus, respectively.2. The gross anatomy and plain-film angiogram show that the dorsal rat’s integument is innervated by three perforators. They are the iliolumbar artery perforator, one of the perforators of the posterior intercostal artery and the thoracodorsal artery perforator from the head to the tail. The three-territory axial flap based on the iliolumbar artery developed a necrotic rate of38.8±5.9%, with the demarcation between viable tissue and necrotic tissue appearing often at the second zone. After extended flap elevation, both Choke arteries and Choke veins underwent diameter dilation and tortuosity increase, but most distinctive changes occurred on the tiny venules communicating between the Choke veins. These venules initiated diameter dilation60±11h after flap elevation, with the trend continuing until4.5±0.4d after flap elevation; Then, the venules started to diminish in diameter gradually and eventually vanished. No neovascularization of any form was discovered through the whole observant period, and some arterioles with no function gradually vanished after flap elevation, leading to the decrease of vascular density. Through injection Evans blue via the tail vein, complete process of microcirculation can be captured.3. Three days after flap elevation, the polymorphous inflammatory cells around the enlarged Choke vessels increased in number, and MCP-1, ICAM-1, MMP-2immunoreactive cells at and around the Choke vessels also increased. The difference is statistically significant(P<0.05). The immunoreactive cells of VEGF in two groups did not show significant differences(P>0.05).Conclusions:1. when one of the lateral row perforators is chosen as the vascular pedicle. Zone I and II of the deep inferior epigastric artery perforator flap are oriented laterally; when one of the medial row perforators is chosen as the vascular pedicle, zonei and II are midline-centered, so is the whole flap. When the sensory branches of the intercostal nerves are isolated from the main stems without any hurt imposed, then the perforator flap can be made possible as a sensible flap without damage to the function of the abdominal musculature. The main stems of T10, T11, and T12travels anterior across the deep inferior epigastric artery, which should be paid with due attention when intramuscular dissection was performed to avoid injury to the nerves. The superficial epigastric artery flap can be thinned, has a reliable blood supply and afflict no injury to abdominal musculature. Consequently, when the tissue volume needed for reconstruction does not exceed the abdominal midline, the superficial epigastric artery flap should be preferential choice.2. The dorsal skinfold chamber is novel method for investigation of Choke vessels, whose greatest advantage resides in its allowance for chronic, in-vivo observation of Choke vessels. After flap elevation, both Choke arteries and Choke veins underwent diameter dilation. The Choke arteries dilation resembles what has been described in the literature, while the expansion of the Choke veins has rarely been reported in literature. With this experiment, we take the opinion that in the early stage after flap elevation, venous drainage is mainly through by-pass way, while in the late stage, incompetent valves become the main route. Evans blue can serve as a sensible blood tracer for investigation of hemodynamics.3. Choke vessels dilation is the form of arteriogenesis occurring in skin tissue. The increase of shear fluid stress is the main reason behind the dilation. Inflammatory cells, particularly the monocytes and macrocytes play important roles in Choke vessels dilation. Ischemia may not be necessary driven factor. |
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