THE ANATOMICAL RECORD 297:663–669 (2014)
Anatomical Variations in the Aortic Bifurcation in New Zealand White Rabbits on Arteriography 1 RAMOS-PLA, MARIA TERESA BALASTEGUI,1,2 JUAN JOSE 3 MARIA DOLORES FERRER-PUCHOL, JOSE MARIA CARRILLO,1 SERGIO PEDRO MONTEAGUDO-FRANCO,4 ENRIQUE ESTEBAN,3 1,2 AND FERNANDO LISTE * 1 Department of Animal Medicine and Surgery, School of Veterinary Medicine, University CEU-Cardenal Herrera, C/Tirant Lo Blanc, 7. Alfara del Patriarca, Valencia 46115, Spain 2 Department of Veterinary Clinical Sciences, School of Veterinary and Biomedical Sciences, James Cook University, Douglas 4814, Queensland, Australia 3 Department of Radiology, La Ribera Hospital, Carretera de Corbera, Km 1, Alzira, Valencia 46600, Spain 4 Department of Radiology, School of Veterinary Medicine, University Alfonso X El Sabio, Avda. Universidad 1, Villanueva de la Ca~ nada, Madrid, Spain
ABSTRACT The radiologic anatomy of the aortic bifurcation in the rabbit has received little study but it is important as this anatomical area is widely used in atherosclerosis research. Thirty rabbits were used to study the aortic bifurcation and subsequent branching patterns on arteriography. Fifteen different arteries were identified. Mean arterial diameters of 2.88 6 0.7 and 2.27 6 0.55 mm were obtained for the aorta and external iliac arteries, respectively. The cranial and middle aspects at the seventh lumbar vertebra (L7) were the most frequent anatomical landmarks (53.3% of the cases) for aortic and common iliac bifurcations, respectively. The caudal aspect of L6 was the most frequent origin (50% of the cases) for the median sacral artery. Deep circumflex iliac arteries originated from common iliac arteries and not the abdominal aorta in the rabbit, showing anatomical asymmetry in 73.3% of the cases. No gender disparity was found in the anatomical location of any of the arteries of the study. Knowledge of normal vascular landmarks for the aortic bifurcation as well as anatomical variations should be helpful to future experimental C 2014 Wiley Periodicals, Inc. studies. Anat Rec, 297:663–669, 2014. V
Key words: arteriographic anatomy; rabbit; aortic bifurcation; iliac artery
The radiologic anatomy of the aortic bifurcation in the rabbit has received little study. A prior single report (G€othlin and Carter, 1969) on the pelvic angiography in female rabbits is available in the literature paying special attention to the uterine blood supply. Also, limited studies on arteriography for the abdominal aorta and lower limb of the rabbit have been reported (Singh et al., 1982; McNally et al., 1992). A description of the final branches of the abdominal aorta was recently performed in a post-mortem study (Daolio et al., 2011). C 2014 WILEY PERIODICALS, INC. V
Grant sponsor: Research project GV 007/39 of the Generalitat Valenciana, Valencia Government (Spain). *Correspondence to: Fernando Liste, Department of Veterinary Clinical Sciences, School of Veterinary and Biomedical Sciences, James Cook University, 1 Solander Drive, Douglas 4814 QLD, Australia. Fax: 161-747816174. E-mail: [email protected] Received 23 July 2013; Accepted 3 December 2013. DOI 10.1002/ar.22874 Published online 29 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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Arteriography is an important radiologic technique to show the normal arterial anatomy and identify signs of arterial disease. Rabbits are frequently used as experimental models to study cardiovascular diseases as they develop easily atheromatous lesions after feeding them with a cholesterolemic diet. Thus, selective arterial catheterization and angioplasty are often performed in these animals. Greater anatomical detail of certain regions is essential to safely guide a catheter into a given artery. In human atherosclerosis, the popliteal artery is used as an anatomical landmark for angioplasty of deep arteries of the limb and foot that are frequently injured with atheromas. Common and external iliac arteries in the rabbit are excellent models to perform experimental assays because they are relatively accessible and have a somewhat similar diameter compared to human distal popliteal arteries. A detailed knowledge of the arteriographic anatomy of the caudal abdominal aorta at its bifurcation site is not available in the rabbit. Hence, the radiographic anatomy of the aortic bifurcation in the rabbit as well as additional descriptions and measurements of main branching arteries is described in this report.
dle diaphysis. Each rabbit was identified with a numbered lead marker. The right external carotid artery was used for catheterization. Under aseptic conditions, a deep dissection of the ventral musculature of the neck was performed using a Seldinger technique (Seldinger, 1953) to catheterize the artery. To prevent thrombotic events, 25 IU of sodium heparin IV (RoviV) was injected. An 18G intravenous catheter (SafeletV Cath, NiproV) was introduced and advanced caudally a few centimetres into the carotid artery. After withdrawal of the plastic guide of the catheter, a hydrophilic wire guide (TerumoV, 0.035 in., 180 cm) was placed into the catheter. Then, the catheter sheath was removed leaving the wire inside. The wire was advanced through the carotid bifurcation and then directed towards the descending thoracic aorta. Finally, an introducer (Radiofocus IIV 4 Fr, TerumoV) was advanced into the artery using the wire as a guide and placed at the level of the base of the aortic arch X-ray under fluoroscopic guidance (BennettV, Technologies). Contrast arteriography was performed using Iohexol (Omnigraf 350V, Schering PloughV). A small volume of contrast was first introduced to test the correct position of the catheter under fluoroscopic guidance. Then, a 4 mL bolus of Iohexol was injected into the aortic lumen and a ventrodorsal radiograph taken near the end of the injection. Lateral projections were taken in three cases to obtain a three-dimensional vision of the pelvic area. R
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MATERIALS AND METHODS Animals The study was conducted on thirty 3-month-old New Zealand White rabbits (19 males, 11 females) with a weight of 3.17 6 0.08 kg. The experimental farm of the Department of Animal Science of the Polytechnic University of Valencia provided all animals. The protocol was performed in a period of 5 days. Animals were kept on cages in a room under controlled environmental conditions with the supervision of the Ethical Committee for animal experimentation of the CEU-Cardenal Herrera University. European Union guidelines for animal experimentation were also accomplished by following the 86/609/CEE rule.
Sedation and Anesthesia All anesthetic protocols were performed according to previously described methods (Flecknell, 1996, pp. 159–187). Rabbits were sedated via intramuscular injection with xylazine (XylagesicV 2%, CalierV, 3 mg/ kg), ketamine (ImalgeneV 1000, MerialV, 20 mg/kg), and morphine (Morphine 2%, BraunV, 0.2 mg/kg). Induction was performed intravenously with propofol (Propofol LipuroV, BraunV, 3 mg/kg). A surgical plane of anesthesia was then induced and maintained either with a continuous infusion rate (15 mL/hr) of propofol or isofluorane (IsobaVetV, Schering PloughV) as needed. R
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Image Analysis A digital radiology unit (Regius Model 110, Konica Minolta Medical and GraphicV, Japan) was used to store images in DICOM format on Efilm PACS software (MergeV Healthcare, 2011). The aortic bifurcation was used as an anatomical landmark to measure arterial diameters. Measurements for diameters of abdominal aorta and external iliac arteries were calculated 1 cm cranial and caudal to the bifurcation, respectively. The external iliac artery was measured on the right side. R
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Statistical Analysis Results were expressed as mean 6 SD. Mean values were compared using the Student t test and the Kruskal–Wallis nonparametric test. P < 0.05 was considered significant.
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Aortic Arteriography Animals were positioned on the X-ray table on dorsal recumbency and kept stable in the X-ray beam using sandbags. Both femurs were placed perpendicularly to the coxal bone keeping the coxofemoral joint on a neutral position. X-ray beam collimation was restricted to the pelvic area with the iliac wings and ischia as cranial and caudal palpable anatomical landmarks, respectively. Both femurs were also included at the level of the mid-
RESULTS Ventrodorsal pelvic arteriograms were obtained in 30 rabbits, resulting in an excellent opacity of the caudal abdominal aorta, aortic bifurcation, and subsequent arterial branches on both hindlimbs. Main arterial branches at the aortic bifurcation and common iliac trunk were easily identified in all cases following transcarotideal arteriography. Table 1 shows the values for internal diameters of the aorta and external iliac arteries measured from the pelvic ventrodorsal arteriography. Mean arterial diameters of 2.88 6 0.7 and 2.27 6 0.55 mm were obtained for the
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TABLE 1. Dimensions of Caudal Abdominal Aorta and External Iliac Arteries on Ventrodorsal Arteriography Total (N 5 30) Males (N 5 19) Females (N 5 11) P
Aorta
External iliac artery
2.88 6 0.70 2.68 6 0.58 3.22 6 0.78 0.07
2.27 6 0.55 2.12 6 0.48 2.52 6 0.60 0.09
Mean 6 SD of internal diameter values (mm) of the caudal abdominal aorta and right external iliac arteries in rabbits when measured on a ventrodorsal pelvic arteriography.
Fig. 1. Ventrodorsal radiographic projection of the pelvic area in a rabbit after transcarotideal arteriography indicating the anatomy of most arterial branches at the aortic bifurcation. L: Left. 1: A. aorta abdominalis. 2: A. lumbal, ramus dorsalis. 3: A. circumflexa ilium profunda. 4: A. iliaca communis. 5: A. iliaca externa. 6: A. iliaca interna. 7: A. circumflexa femoris lateralis. 8: A. sacralis mediana. 9: A. profunda femoris. 10: A. femoralis. 11: A. glutea caudalis. 12: A. circumflexa ilium profunda, ramus cranialis. 13: A. pudenda interna. 14: A. saphena. 15: A. poplitea.
aorta and external iliac arteries, respectively. No differences for gender were noted for the aorta or the external iliac arteries (P > 0.05). Figures 1 and 2 depict the arteriographic anatomy of the aortic bifurcation and pelvic region in the rabbit, showing most arterial branches at the aortic bifurcation and thigh. Origins and branching variations for main arteries are shown in Table 2. Fifteen different arteries were identified in all ventrodorsal projections: aorta, lumbar dorsal, deep circumflex iliac, common iliac, external and internal iliacs, deep
Fig. 2. Right lateral radiographic projection of the pelvic area in a rabbit after transcarotideal arteriography indicating the anatomy of most arterial branches at the aortic bifurcation. L: Left. 1: A. aorta abdominalis. 2: A. lumbal, ramus dorsalis. 3: A. circumflexa ilium profunda. 4: A. iliaca communis. 5: A. iliaca externa. 6: A. iliaca interna. 7: A. circumflexa femoris lateralis. 8: A. sacralis mediana. 9: A. profunda femoris. 10: A. femoralis. 11: A. glutea caudalis. 12: A. circumflexa ilium profunda, ramus cranialis. 13: A. pudenda interna. 14: A. saphena. 15: A. poplitea.
TABLE 2. Origins of Different Aortic Branches in Rabbits from Ventrodorsal Pelvic Arteriography
Anatomical location Cranial L6 Middle L6 Caudal L6 L6–L7 Intervertebral space Cranial L7 Middle L7 Caudal L7
Sex
Median sacral artery
Aortic bifurcation site
Right deep circumflex artery
Left deep circumflex artery
Common iliac trunk bifurcation site
# $ # $ # $ # $ # $ # $ # $
1 2 5 6 12 3 1 – – – – – – –
– – – – 2 2 4 4 11 5 2 – – –
– – – – 2 – – 1 4 4 9 5 4 1
– – 1 – 1 1 1 3 9 5 7 2 – –
– – – – 1 – – – 2 3 9 7 7 1
Expressed in number of individuals per location; N 5 30; # 5 19, $ 5 11.
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Fig. 4. Detail of a ventrodorsal radiographic projection of the aortic bifurcation at the level of the L6–L7 intervertebral space in a rabbit after transcarotideal arteriography. 1: A. aorta abdominalis. 2: A. circumflexa ilium profunda. 3: A. iliaca communis. 4: A. iliaca interna. 5: A. sacralis mediana.
Fig. 3. Detail of a ventrodorsal radiographic projection of the caudal lumbar area in a rabbit after transcarotideal arteriography. Paired symmetrical lumbar dorsal arteries (A and B) are seen at L5 and L6 vertebral segments. 1: A. aorta abdominalis. 2: A. circumflexa ilium profunda.
femoral, median sacral, medial circumflex femoral, femoral, caudal gluteal, and pudendal arteries. Lumbar dorsal arteries follow a segment pattern and can be seen coming off the aorta between middle aspects of the vertebral bodies. They show a dorsal direction, reaching the dorsolumbar musculature (Fig. 3). The most caudal portion of the abdominal aorta ended into a bifurcation that gives off the right and left common iliac arteries (Fig. 4). The aortic bifurcation was more frequently seen arising from the level of the cranial aspect of L7 (53.3% of rabbits). However, some anatomical variations were identified in this study. Thus, the aortic bifurcation arose from the level of the L6–L7 intervertebral disc spaces in 26.7% of cases. Rarely, caudal aspects of L6 (13.3%) or middle aspects of L7 (6.7%) were also identified as origin of the aortic bifurcation. The right and left common iliac arteries were short, giving off a further bifurcation around the middle aspect or caudal and lateral aspect of L7. The common iliac bifurcation was more frequently seen arising from the middle aspect of L7 (53.3%), followed by the caudal aspect of L7 (26.7%). Some anatomical variations with respect to the common iliac bifurcation were also noted in this study. Thus, the caudal (26.7%) or cranial (16.7%) aspects of L7 or rarely the caudal aspect of L6 (3.3%) also were noted as anatomical locations for the common iliac bifurcation in our study. The bifurcation from the common iliac arterial trunk produced the external and internal iliac arteries, which were located close to the iliac body and sacrum, respectively. The external iliac artery advances ventrally and
medially with respect to the iliac wing but never was observed to enter the pelvic girdle. After issuing the deep femoral artery, external iliac artery becomes the femoral artery (Fig. 5). The deep femoral artery was directed caudally towards the ventral and lateral aspect of the ischium. The femoral artery emits the lateral femoral circumflex artery at the level of the acetabulum, which advances cranial and distal with respect to the lateral aspect of the thigh. The femoral artery was directed caudally towards the caudal and medial aspect of the thigh. Conversely, the dorsal and medial branch of the common iliac trunk is the internal iliac artery. This vessel advances caudally close the mid sacral axis inside the pelvic girdle and gives off dorsally and laterally the caudal gluteal artery to supply the gluteal musculature. After this branch, the internal iliac artery continues caudal and lateral towards the ischial body as the pudendal artery (Fig. 6). The median sacral artery was considered the continuation of the abdominal aorta and was located along the spinal axis (Figs. 1 and 6). This artery presented a primary branching pattern coming off the abdominal aorta most frequently at the caudal aspect (50% of the cases) or middle aspect (36.7%) of L6, and then tapered caudally towards the coccygeal vertebrae. However, it could also be seen arising at the cranial aspect of L6 (10%) and rarely at the L6–L7 intervertebral space (3.3%). The deep circumflex iliac arteries were seen most frequently coming off the common iliac artery at the level of L7 (Fig. 7). However, the right deep circumflex iliac artery had a more caudal origin in the common iliac trunk compared to its left contralateral in most rabbits from our study. The right branch originates at the level of L7 in 90% of the cases and the left branch only in 76.7% of the rabbits. The right deep circumflex artery most frequently originates from the common iliac trunk at the level of the middle body of L7 (46.7% vs. 30% for
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Fig. 5. Detail of a ventrodorsal radiographic projection of the right coxofemoral joint after transcarotideal arteriography. R: Right. 1: A. iliaca externa. 2: A. circumflexa femoris lateralis. 3: A. profunda femoris. 4: A. femoralis. 5: A. pudenda interna.
the left branch). The left deep circumflex artery originates from the cranial aspect of L7 in 46.7% of the cases and only in a 26.7% in the case of the right branch. Some right branches originate as caudally as the caudal aspect of L7 (16.7%). No deep circumflex arteries on the left side were seen at this level. More left branches were seen originating at the level of the L6–L7 intervertebral disc space compared to the right (10% vs. 3.3%). Left branches could be seen originating from the common iliac trunk as cranially as the middle aspect of L6 (3.3%). No deep circumflex arteries in the right side
Fig. 6. Detail of a ventrodorsal radiographic projection of the right coxal bone after transcarotideal arteriography. 1: A. circumflexa ilium profunda. 2: A. iliaca interna. 3: A. iliaca externa. 4: A. glutea caudalis. 5: A. pudenda interna. 6: A. sacralis mediana. 7: A. profunda femoris. 8: A. femoralis.
were seen at this level. The symmetry for the origin of deep circumflex arteries was only seen in eight cases (26.7%, five males and three females).
DISCUSSION The purpose of this study was to characterize anatomically the aortic bifurcation as this area is frequently
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used as a location for catheter placement in atherosclerosis research assays. In such assays, rabbits are usually positioned on dorsal recumbency. In this study, lateral arteriograms were also taken in a few cases for the purpose of study completion. Figure 8 shows the aortic bifurcation in a rabbit from a fresh specimen after intraarterial injection of latex. An identical anatomical pattern can be observed when compared to the arteriograms (Figs. 1 and 2). The aortic bifurcation pattern changes according to species. This is shown in Fig. 9, which depicts different patterns of aortic bifurcation in humans and domestic animals. In ruminants, carnivores, and swine, the aorta bifurcates into the external iliac arteries and then follows caudally before giving finally off the internal iliac branches. In equine, a different pattern has been described, in which the aorta gives off immediately the external and internal iliac arteries without a common iliac trunk (Barone, 1996, pp. 362–385). Like humans, the aortic bifurcation in the rabbit divides into two short common iliac trunks before giving off the external and internal iliac arteries. In all cases, the median sacral artery acts as a continuation of the abdominal aorta. In this study, the cranial aspect of L7 was the most fre-
Fig. 7. Detail of a ventrodorsal radiographic projection of the aortic bifurcation after transcarotideal arteriography showing the main lateral branches in a rabbit. L: Left. 1: A. aorta abdominalis. 2 and 3: A. circumflexa ilium profunda. 4: A. iliaca communis.
Fig. 8. Ventrodorsal image of the aortic bifurcation from a rabbit after arterial injection of a solution of Neoprene latex 450 colored with red pigment. Image courtesy of Dr. A.L. Filadelpho. Previously published on “Estudo dos ramos sacrais da aorta abdominal do Coelho. 2011. Rev. Cient. Elect. Med. Vet., 17.”
Fig. 9. Diagram depiction of different anatomical branching patterns of the aortic bifurcation in humans and domestic mammals.
ARTERIOGRAPHIC ANATOMY IN RABBITS
quent (53%) anatomical landmark for the aortic bifurcation in both males and females, followed by the intervertebral space at L6–L7. Five rabbits had sacralization of L7. These individuals showed a most cranial origin for the aortic bifurcation, at the caudal aspect of L6 or L6– L7 the intervertebral space. Similar differences at the aortic bifurcation site have been found in humans (Chithriki et al., 2002). Differences in size of some arteries between human female and males independently of their body surface area and body mass index have been reported in the literature (Minami et al., 2007). In this study, no differences in body weight were found between male and females and no gender disparity for size was detected in any of the arteries. The uterine artery has been described previously on arteriography as a distended vessel coming off the internal iliac artery in pregnant does (Carter et al., 1968). However, this branch was not visible in this study where rabbits were not allowed to mate. Unlike the dog and the horse (Barone, 1996, pp. 362– 385), deep circumflex iliac arteries arise from the common iliac arteries and not the abdominal aorta as in the rabbit. These arteries supply the broad abdominal musculature migrating laterally and showing an almost perpendicular disposition with respect to the abdominal aorta. An asymmetry for deep circumflex arteries in this study was found in 73.3% of the cases, with the right branch having a more caudal origin from the common iliac trunk with respect to its left contralateral. In humans, it was reported that about 66% of individuals had asymmetrical deep circumflex arteries (Penteado, 1983). Dogs present also an asymmetrical distribution with these branches, with the right branch more cranial with respect to the left branch (Evans, 1993, pp. 659– 660). However, cats present the opposite pattern, with the right deep circumflex artery being more caudal with respect to the left (Geraldo et al., 2013). Non-symmetrical anatomic variations of different parts of the body including systemic vasculature have been described during the early development of the foetus (Zaidi, 2011). During vasculogenesis, angioblasts are attracted towards the midline by guidance cues thought to emanate from the endoderm (Hogan and Bautch, 2004). Once the angioblasts have reached the embryonic midline, they form aggregates and tube formation commences. Ventral and dorsal sprouting are then initiated which will give rise to segmental arteries. Molecular signaling pathways regulate the endothelial tip cells at the beginning of the angiogenic sprout and synchronize cellular oscillations to achieve regular formation of somite boundaries and symmetry (Hellstrom et al., 2007). Thus, asynchronous cellular oscillations might lead to vascular asymmetry in some individuals as happens in deep circumflex arteries in rabbits.
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In summary, in the rabbit it was possible to identify at least fifteen major vessels on a ventrodorsal projection of the pelvic girdle with arteriography. Both aortic and common iliac bifurcations were more frequently located on the cranial and middle aspects of L7 while the median sacral artery arises from the caudal aspect of L6. Deep circumflex arteries were frequently asymmetrical. Knowledge of the normal anatomy and variations in the anatomy of the aortic bifurcation in the rabbit will be useful for future studies.
ACKNOWLEDGEMENTS The authors thank Dr. A.L. Filadelpho for his help in this manuscript.
LITERATURE CITED Barone RA. 1996. Anatomie compar ee des animaux domestiques. Tome V. Angiologie. Paris: Vigot. p 362–385. Carter AM, G€ othlin J, Bengtsson LP. 1968. Effect of vasopressin on the uteroplacental circulation: an angiographic study in the rabbit. J Reprod Fert 17:419–426. Chithriki M, Jaibaji M, Steele RD. 2002. The anatomical relationship of the aortic bifurcation to the lumbar vertebrae: a MRI study. Surg Radiol Anat 24:308–312. Daolio M, De Marchi PN, Pinto JRC, Guazzelli J, Schimming BC, Matheus SMM, Filadelpho AL. 2011. Estudo dos ramos sacrais da aorta abdominal do coelho. Rev Cient Elect Med Vet, n umero 17. Evans HE, editor. 1993. Miller’s anatomy of the dog. Philadelphia: WB Saunders. p 659–660. Flecknell PA. 1996. Laboratory animal anaesthesia. A practical introduction for research workers and technicians. New York: Academic Press. p 1. Geraldo B, Pinto JRC, Schimming BC, Guazzelli J, Filadelpho AL. 2013. Contribuic¸~ ao ao estudo anat^ omico dos ramos sacrais da aorta abdominal do gato (Felis catus). Rev Cient Elect Med Vet, n umero 20. G€ othlin J, Carter AM. 1969. Pelvic angiography in the female rabbit. Invest Radiol 4:45–49. Hellstrom M, Phng L, Gerhardt H. 2007. VEGF and Notch signaling. The Yin and Yang of angiogenic sprouting. Cell Adh Migr 1: 133–136. Hogan KA, Bautch VL. 2004. Blood vessel patterning at the embryonic midline. Curr Top Dev Biol 62:55–85. McNally MA, Small JO, Mollan RAB, Wilson DJ. 1992. Arteriographic study of the rabbit lower limb. Anat Rec 233:643–650. Minami T, Eisen LA, Berger JS, Sekiguchi H, Mayo PH, Narasimhan M. 2007. Gender disparity in radial and femoral arterial size: an ultrasound study. Intensive Care Med 33:552–553. Penteado CV. 1983. Anatomosurgical study of the superficial and deep circumflex iliac arteries. Anat Clin 5:125–127. Seldinger SI. 1953. Catheter replacement of the needle in percutaneous arteriography; a new technique. Acta Radiol 39:368–376. Singh AP, Singh GR, Sharma DN, Nigam JM, Bhargava AK. 1982. Arteriographic anatomy of the abdominal aorta in the goat, dog, pig and rabbit. Vet Radiol Ultrasound 23:279–281. Zaidi ZF. 2011. Body asymmetries: incidence, etiology and clinical implications. Aust J Basic Appl Sci 5:2157–2191.
Anatomical Variations in the Aortic Bifurcation in New Zealand White Rabbits on Arteriography 1 RAMOS-PLA, MARIA TERESA BALASTEGUI,1,2 JUAN JOSE 3 MARIA DOLORES FERRER-PUCHOL, JOSE MARIA CARRILLO,1 SERGIO PEDRO MONTEAGUDO-FRANCO,4 ENRIQUE ESTEBAN,3 1,2 AND FERNANDO LISTE * 1 Department of Animal Medicine and Surgery, School of Veterinary Medicine, University CEU-Cardenal Herrera, C/Tirant Lo Blanc, 7. Alfara del Patriarca, Valencia 46115, Spain 2 Department of Veterinary Clinical Sciences, School of Veterinary and Biomedical Sciences, James Cook University, Douglas 4814, Queensland, Australia 3 Department of Radiology, La Ribera Hospital, Carretera de Corbera, Km 1, Alzira, Valencia 46600, Spain 4 Department of Radiology, School of Veterinary Medicine, University Alfonso X El Sabio, Avda. Universidad 1, Villanueva de la Ca~ nada, Madrid, Spain
ABSTRACT The radiologic anatomy of the aortic bifurcation in the rabbit has received little study but it is important as this anatomical area is widely used in atherosclerosis research. Thirty rabbits were used to study the aortic bifurcation and subsequent branching patterns on arteriography. Fifteen different arteries were identified. Mean arterial diameters of 2.88 6 0.7 and 2.27 6 0.55 mm were obtained for the aorta and external iliac arteries, respectively. The cranial and middle aspects at the seventh lumbar vertebra (L7) were the most frequent anatomical landmarks (53.3% of the cases) for aortic and common iliac bifurcations, respectively. The caudal aspect of L6 was the most frequent origin (50% of the cases) for the median sacral artery. Deep circumflex iliac arteries originated from common iliac arteries and not the abdominal aorta in the rabbit, showing anatomical asymmetry in 73.3% of the cases. No gender disparity was found in the anatomical location of any of the arteries of the study. Knowledge of normal vascular landmarks for the aortic bifurcation as well as anatomical variations should be helpful to future experimental C 2014 Wiley Periodicals, Inc. studies. Anat Rec, 297:663–669, 2014. V
Key words: arteriographic anatomy; rabbit; aortic bifurcation; iliac artery
The radiologic anatomy of the aortic bifurcation in the rabbit has received little study. A prior single report (G€othlin and Carter, 1969) on the pelvic angiography in female rabbits is available in the literature paying special attention to the uterine blood supply. Also, limited studies on arteriography for the abdominal aorta and lower limb of the rabbit have been reported (Singh et al., 1982; McNally et al., 1992). A description of the final branches of the abdominal aorta was recently performed in a post-mortem study (Daolio et al., 2011). C 2014 WILEY PERIODICALS, INC. V
Grant sponsor: Research project GV 007/39 of the Generalitat Valenciana, Valencia Government (Spain). *Correspondence to: Fernando Liste, Department of Veterinary Clinical Sciences, School of Veterinary and Biomedical Sciences, James Cook University, 1 Solander Drive, Douglas 4814 QLD, Australia. Fax: 161-747816174. E-mail: [email protected] Received 23 July 2013; Accepted 3 December 2013. DOI 10.1002/ar.22874 Published online 29 January 2014 in Wiley Online Library (wileyonlinelibrary.com).
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BALASTEGUI ET AL.
Arteriography is an important radiologic technique to show the normal arterial anatomy and identify signs of arterial disease. Rabbits are frequently used as experimental models to study cardiovascular diseases as they develop easily atheromatous lesions after feeding them with a cholesterolemic diet. Thus, selective arterial catheterization and angioplasty are often performed in these animals. Greater anatomical detail of certain regions is essential to safely guide a catheter into a given artery. In human atherosclerosis, the popliteal artery is used as an anatomical landmark for angioplasty of deep arteries of the limb and foot that are frequently injured with atheromas. Common and external iliac arteries in the rabbit are excellent models to perform experimental assays because they are relatively accessible and have a somewhat similar diameter compared to human distal popliteal arteries. A detailed knowledge of the arteriographic anatomy of the caudal abdominal aorta at its bifurcation site is not available in the rabbit. Hence, the radiographic anatomy of the aortic bifurcation in the rabbit as well as additional descriptions and measurements of main branching arteries is described in this report.
dle diaphysis. Each rabbit was identified with a numbered lead marker. The right external carotid artery was used for catheterization. Under aseptic conditions, a deep dissection of the ventral musculature of the neck was performed using a Seldinger technique (Seldinger, 1953) to catheterize the artery. To prevent thrombotic events, 25 IU of sodium heparin IV (RoviV) was injected. An 18G intravenous catheter (SafeletV Cath, NiproV) was introduced and advanced caudally a few centimetres into the carotid artery. After withdrawal of the plastic guide of the catheter, a hydrophilic wire guide (TerumoV, 0.035 in., 180 cm) was placed into the catheter. Then, the catheter sheath was removed leaving the wire inside. The wire was advanced through the carotid bifurcation and then directed towards the descending thoracic aorta. Finally, an introducer (Radiofocus IIV 4 Fr, TerumoV) was advanced into the artery using the wire as a guide and placed at the level of the base of the aortic arch X-ray under fluoroscopic guidance (BennettV, Technologies). Contrast arteriography was performed using Iohexol (Omnigraf 350V, Schering PloughV). A small volume of contrast was first introduced to test the correct position of the catheter under fluoroscopic guidance. Then, a 4 mL bolus of Iohexol was injected into the aortic lumen and a ventrodorsal radiograph taken near the end of the injection. Lateral projections were taken in three cases to obtain a three-dimensional vision of the pelvic area. R
R
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MATERIALS AND METHODS Animals The study was conducted on thirty 3-month-old New Zealand White rabbits (19 males, 11 females) with a weight of 3.17 6 0.08 kg. The experimental farm of the Department of Animal Science of the Polytechnic University of Valencia provided all animals. The protocol was performed in a period of 5 days. Animals were kept on cages in a room under controlled environmental conditions with the supervision of the Ethical Committee for animal experimentation of the CEU-Cardenal Herrera University. European Union guidelines for animal experimentation were also accomplished by following the 86/609/CEE rule.
Sedation and Anesthesia All anesthetic protocols were performed according to previously described methods (Flecknell, 1996, pp. 159–187). Rabbits were sedated via intramuscular injection with xylazine (XylagesicV 2%, CalierV, 3 mg/ kg), ketamine (ImalgeneV 1000, MerialV, 20 mg/kg), and morphine (Morphine 2%, BraunV, 0.2 mg/kg). Induction was performed intravenously with propofol (Propofol LipuroV, BraunV, 3 mg/kg). A surgical plane of anesthesia was then induced and maintained either with a continuous infusion rate (15 mL/hr) of propofol or isofluorane (IsobaVetV, Schering PloughV) as needed. R
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Image Analysis A digital radiology unit (Regius Model 110, Konica Minolta Medical and GraphicV, Japan) was used to store images in DICOM format on Efilm PACS software (MergeV Healthcare, 2011). The aortic bifurcation was used as an anatomical landmark to measure arterial diameters. Measurements for diameters of abdominal aorta and external iliac arteries were calculated 1 cm cranial and caudal to the bifurcation, respectively. The external iliac artery was measured on the right side. R
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Statistical Analysis Results were expressed as mean 6 SD. Mean values were compared using the Student t test and the Kruskal–Wallis nonparametric test. P < 0.05 was considered significant.
R
Aortic Arteriography Animals were positioned on the X-ray table on dorsal recumbency and kept stable in the X-ray beam using sandbags. Both femurs were placed perpendicularly to the coxal bone keeping the coxofemoral joint on a neutral position. X-ray beam collimation was restricted to the pelvic area with the iliac wings and ischia as cranial and caudal palpable anatomical landmarks, respectively. Both femurs were also included at the level of the mid-
RESULTS Ventrodorsal pelvic arteriograms were obtained in 30 rabbits, resulting in an excellent opacity of the caudal abdominal aorta, aortic bifurcation, and subsequent arterial branches on both hindlimbs. Main arterial branches at the aortic bifurcation and common iliac trunk were easily identified in all cases following transcarotideal arteriography. Table 1 shows the values for internal diameters of the aorta and external iliac arteries measured from the pelvic ventrodorsal arteriography. Mean arterial diameters of 2.88 6 0.7 and 2.27 6 0.55 mm were obtained for the
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TABLE 1. Dimensions of Caudal Abdominal Aorta and External Iliac Arteries on Ventrodorsal Arteriography Total (N 5 30) Males (N 5 19) Females (N 5 11) P
Aorta
External iliac artery
2.88 6 0.70 2.68 6 0.58 3.22 6 0.78 0.07
2.27 6 0.55 2.12 6 0.48 2.52 6 0.60 0.09
Mean 6 SD of internal diameter values (mm) of the caudal abdominal aorta and right external iliac arteries in rabbits when measured on a ventrodorsal pelvic arteriography.
Fig. 1. Ventrodorsal radiographic projection of the pelvic area in a rabbit after transcarotideal arteriography indicating the anatomy of most arterial branches at the aortic bifurcation. L: Left. 1: A. aorta abdominalis. 2: A. lumbal, ramus dorsalis. 3: A. circumflexa ilium profunda. 4: A. iliaca communis. 5: A. iliaca externa. 6: A. iliaca interna. 7: A. circumflexa femoris lateralis. 8: A. sacralis mediana. 9: A. profunda femoris. 10: A. femoralis. 11: A. glutea caudalis. 12: A. circumflexa ilium profunda, ramus cranialis. 13: A. pudenda interna. 14: A. saphena. 15: A. poplitea.
aorta and external iliac arteries, respectively. No differences for gender were noted for the aorta or the external iliac arteries (P > 0.05). Figures 1 and 2 depict the arteriographic anatomy of the aortic bifurcation and pelvic region in the rabbit, showing most arterial branches at the aortic bifurcation and thigh. Origins and branching variations for main arteries are shown in Table 2. Fifteen different arteries were identified in all ventrodorsal projections: aorta, lumbar dorsal, deep circumflex iliac, common iliac, external and internal iliacs, deep
Fig. 2. Right lateral radiographic projection of the pelvic area in a rabbit after transcarotideal arteriography indicating the anatomy of most arterial branches at the aortic bifurcation. L: Left. 1: A. aorta abdominalis. 2: A. lumbal, ramus dorsalis. 3: A. circumflexa ilium profunda. 4: A. iliaca communis. 5: A. iliaca externa. 6: A. iliaca interna. 7: A. circumflexa femoris lateralis. 8: A. sacralis mediana. 9: A. profunda femoris. 10: A. femoralis. 11: A. glutea caudalis. 12: A. circumflexa ilium profunda, ramus cranialis. 13: A. pudenda interna. 14: A. saphena. 15: A. poplitea.
TABLE 2. Origins of Different Aortic Branches in Rabbits from Ventrodorsal Pelvic Arteriography
Anatomical location Cranial L6 Middle L6 Caudal L6 L6–L7 Intervertebral space Cranial L7 Middle L7 Caudal L7
Sex
Median sacral artery
Aortic bifurcation site
Right deep circumflex artery
Left deep circumflex artery
Common iliac trunk bifurcation site
# $ # $ # $ # $ # $ # $ # $
1 2 5 6 12 3 1 – – – – – – –
– – – – 2 2 4 4 11 5 2 – – –
– – – – 2 – – 1 4 4 9 5 4 1
– – 1 – 1 1 1 3 9 5 7 2 – –
– – – – 1 – – – 2 3 9 7 7 1
Expressed in number of individuals per location; N 5 30; # 5 19, $ 5 11.
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Fig. 4. Detail of a ventrodorsal radiographic projection of the aortic bifurcation at the level of the L6–L7 intervertebral space in a rabbit after transcarotideal arteriography. 1: A. aorta abdominalis. 2: A. circumflexa ilium profunda. 3: A. iliaca communis. 4: A. iliaca interna. 5: A. sacralis mediana.
Fig. 3. Detail of a ventrodorsal radiographic projection of the caudal lumbar area in a rabbit after transcarotideal arteriography. Paired symmetrical lumbar dorsal arteries (A and B) are seen at L5 and L6 vertebral segments. 1: A. aorta abdominalis. 2: A. circumflexa ilium profunda.
femoral, median sacral, medial circumflex femoral, femoral, caudal gluteal, and pudendal arteries. Lumbar dorsal arteries follow a segment pattern and can be seen coming off the aorta between middle aspects of the vertebral bodies. They show a dorsal direction, reaching the dorsolumbar musculature (Fig. 3). The most caudal portion of the abdominal aorta ended into a bifurcation that gives off the right and left common iliac arteries (Fig. 4). The aortic bifurcation was more frequently seen arising from the level of the cranial aspect of L7 (53.3% of rabbits). However, some anatomical variations were identified in this study. Thus, the aortic bifurcation arose from the level of the L6–L7 intervertebral disc spaces in 26.7% of cases. Rarely, caudal aspects of L6 (13.3%) or middle aspects of L7 (6.7%) were also identified as origin of the aortic bifurcation. The right and left common iliac arteries were short, giving off a further bifurcation around the middle aspect or caudal and lateral aspect of L7. The common iliac bifurcation was more frequently seen arising from the middle aspect of L7 (53.3%), followed by the caudal aspect of L7 (26.7%). Some anatomical variations with respect to the common iliac bifurcation were also noted in this study. Thus, the caudal (26.7%) or cranial (16.7%) aspects of L7 or rarely the caudal aspect of L6 (3.3%) also were noted as anatomical locations for the common iliac bifurcation in our study. The bifurcation from the common iliac arterial trunk produced the external and internal iliac arteries, which were located close to the iliac body and sacrum, respectively. The external iliac artery advances ventrally and
medially with respect to the iliac wing but never was observed to enter the pelvic girdle. After issuing the deep femoral artery, external iliac artery becomes the femoral artery (Fig. 5). The deep femoral artery was directed caudally towards the ventral and lateral aspect of the ischium. The femoral artery emits the lateral femoral circumflex artery at the level of the acetabulum, which advances cranial and distal with respect to the lateral aspect of the thigh. The femoral artery was directed caudally towards the caudal and medial aspect of the thigh. Conversely, the dorsal and medial branch of the common iliac trunk is the internal iliac artery. This vessel advances caudally close the mid sacral axis inside the pelvic girdle and gives off dorsally and laterally the caudal gluteal artery to supply the gluteal musculature. After this branch, the internal iliac artery continues caudal and lateral towards the ischial body as the pudendal artery (Fig. 6). The median sacral artery was considered the continuation of the abdominal aorta and was located along the spinal axis (Figs. 1 and 6). This artery presented a primary branching pattern coming off the abdominal aorta most frequently at the caudal aspect (50% of the cases) or middle aspect (36.7%) of L6, and then tapered caudally towards the coccygeal vertebrae. However, it could also be seen arising at the cranial aspect of L6 (10%) and rarely at the L6–L7 intervertebral space (3.3%). The deep circumflex iliac arteries were seen most frequently coming off the common iliac artery at the level of L7 (Fig. 7). However, the right deep circumflex iliac artery had a more caudal origin in the common iliac trunk compared to its left contralateral in most rabbits from our study. The right branch originates at the level of L7 in 90% of the cases and the left branch only in 76.7% of the rabbits. The right deep circumflex artery most frequently originates from the common iliac trunk at the level of the middle body of L7 (46.7% vs. 30% for
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Fig. 5. Detail of a ventrodorsal radiographic projection of the right coxofemoral joint after transcarotideal arteriography. R: Right. 1: A. iliaca externa. 2: A. circumflexa femoris lateralis. 3: A. profunda femoris. 4: A. femoralis. 5: A. pudenda interna.
the left branch). The left deep circumflex artery originates from the cranial aspect of L7 in 46.7% of the cases and only in a 26.7% in the case of the right branch. Some right branches originate as caudally as the caudal aspect of L7 (16.7%). No deep circumflex arteries on the left side were seen at this level. More left branches were seen originating at the level of the L6–L7 intervertebral disc space compared to the right (10% vs. 3.3%). Left branches could be seen originating from the common iliac trunk as cranially as the middle aspect of L6 (3.3%). No deep circumflex arteries in the right side
Fig. 6. Detail of a ventrodorsal radiographic projection of the right coxal bone after transcarotideal arteriography. 1: A. circumflexa ilium profunda. 2: A. iliaca interna. 3: A. iliaca externa. 4: A. glutea caudalis. 5: A. pudenda interna. 6: A. sacralis mediana. 7: A. profunda femoris. 8: A. femoralis.
were seen at this level. The symmetry for the origin of deep circumflex arteries was only seen in eight cases (26.7%, five males and three females).
DISCUSSION The purpose of this study was to characterize anatomically the aortic bifurcation as this area is frequently
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used as a location for catheter placement in atherosclerosis research assays. In such assays, rabbits are usually positioned on dorsal recumbency. In this study, lateral arteriograms were also taken in a few cases for the purpose of study completion. Figure 8 shows the aortic bifurcation in a rabbit from a fresh specimen after intraarterial injection of latex. An identical anatomical pattern can be observed when compared to the arteriograms (Figs. 1 and 2). The aortic bifurcation pattern changes according to species. This is shown in Fig. 9, which depicts different patterns of aortic bifurcation in humans and domestic animals. In ruminants, carnivores, and swine, the aorta bifurcates into the external iliac arteries and then follows caudally before giving finally off the internal iliac branches. In equine, a different pattern has been described, in which the aorta gives off immediately the external and internal iliac arteries without a common iliac trunk (Barone, 1996, pp. 362–385). Like humans, the aortic bifurcation in the rabbit divides into two short common iliac trunks before giving off the external and internal iliac arteries. In all cases, the median sacral artery acts as a continuation of the abdominal aorta. In this study, the cranial aspect of L7 was the most fre-
Fig. 7. Detail of a ventrodorsal radiographic projection of the aortic bifurcation after transcarotideal arteriography showing the main lateral branches in a rabbit. L: Left. 1: A. aorta abdominalis. 2 and 3: A. circumflexa ilium profunda. 4: A. iliaca communis.
Fig. 8. Ventrodorsal image of the aortic bifurcation from a rabbit after arterial injection of a solution of Neoprene latex 450 colored with red pigment. Image courtesy of Dr. A.L. Filadelpho. Previously published on “Estudo dos ramos sacrais da aorta abdominal do Coelho. 2011. Rev. Cient. Elect. Med. Vet., 17.”
Fig. 9. Diagram depiction of different anatomical branching patterns of the aortic bifurcation in humans and domestic mammals.
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quent (53%) anatomical landmark for the aortic bifurcation in both males and females, followed by the intervertebral space at L6–L7. Five rabbits had sacralization of L7. These individuals showed a most cranial origin for the aortic bifurcation, at the caudal aspect of L6 or L6– L7 the intervertebral space. Similar differences at the aortic bifurcation site have been found in humans (Chithriki et al., 2002). Differences in size of some arteries between human female and males independently of their body surface area and body mass index have been reported in the literature (Minami et al., 2007). In this study, no differences in body weight were found between male and females and no gender disparity for size was detected in any of the arteries. The uterine artery has been described previously on arteriography as a distended vessel coming off the internal iliac artery in pregnant does (Carter et al., 1968). However, this branch was not visible in this study where rabbits were not allowed to mate. Unlike the dog and the horse (Barone, 1996, pp. 362– 385), deep circumflex iliac arteries arise from the common iliac arteries and not the abdominal aorta as in the rabbit. These arteries supply the broad abdominal musculature migrating laterally and showing an almost perpendicular disposition with respect to the abdominal aorta. An asymmetry for deep circumflex arteries in this study was found in 73.3% of the cases, with the right branch having a more caudal origin from the common iliac trunk with respect to its left contralateral. In humans, it was reported that about 66% of individuals had asymmetrical deep circumflex arteries (Penteado, 1983). Dogs present also an asymmetrical distribution with these branches, with the right branch more cranial with respect to the left branch (Evans, 1993, pp. 659– 660). However, cats present the opposite pattern, with the right deep circumflex artery being more caudal with respect to the left (Geraldo et al., 2013). Non-symmetrical anatomic variations of different parts of the body including systemic vasculature have been described during the early development of the foetus (Zaidi, 2011). During vasculogenesis, angioblasts are attracted towards the midline by guidance cues thought to emanate from the endoderm (Hogan and Bautch, 2004). Once the angioblasts have reached the embryonic midline, they form aggregates and tube formation commences. Ventral and dorsal sprouting are then initiated which will give rise to segmental arteries. Molecular signaling pathways regulate the endothelial tip cells at the beginning of the angiogenic sprout and synchronize cellular oscillations to achieve regular formation of somite boundaries and symmetry (Hellstrom et al., 2007). Thus, asynchronous cellular oscillations might lead to vascular asymmetry in some individuals as happens in deep circumflex arteries in rabbits.
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In summary, in the rabbit it was possible to identify at least fifteen major vessels on a ventrodorsal projection of the pelvic girdle with arteriography. Both aortic and common iliac bifurcations were more frequently located on the cranial and middle aspects of L7 while the median sacral artery arises from the caudal aspect of L6. Deep circumflex arteries were frequently asymmetrical. Knowledge of the normal anatomy and variations in the anatomy of the aortic bifurcation in the rabbit will be useful for future studies.
ACKNOWLEDGEMENTS The authors thank Dr. A.L. Filadelpho for his help in this manuscript.
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