Comparative Anatomical, Ultrasonographical and Radiological studies of the biliary system of Rabbits and Domestic cats in Egypt

Under the prevailing overall Conditions of all veterinarians for the diagnosis of biliary diseases, application of surgical procedures and liver transplantation in Cats as carnivorous pet animal, and Rabbits as herbivorous pet animal and also as a human model in research. The present study was constructed on twelve native breeds of rabbits (Oryctolagus cuniculus) and eighteen adult domestic cats (Felis catus domesticus). We concluded that, in brief; the rabbit gall bladder was relatively small, fixed by several small hepato-cystic ducts to its fossa. The rabbit bile duct was formed commonly by the junction of the left hepatic duct and the cystic duct. The cystic duct was commonly fairly large, received the right hepatic duct that collected the right lobe in its route to enter the duodenum, the bile duct receives the branch of the caudate process of the caudate lobe. The present study revealed other four anatomic variations dealing with the shape and size of the feline native breed’s gall bladder from fundic duplication, bilobed, truncated fundus and distended rounded fundus. Commonly, the bile duct was formed by the triple convergence of the left and the right hepatic ducts with the cystic duct. However, in some exceptional cases a short common hepatic duct was formed. Sonographically, the normal gall bladder in rabbit appeared small, elongated with anechoic lumen bordered by right lobe laterally and quadrate lobe medially and has no visible wall, but in cat varied in conformation, bordered by the right medial lobe laterally and the quadrate lobe medially surrounded by echogenic wall.


INTRODUCTION
The biliary system comprised; the gall bladder, cystic duct, bile duct and hepatic ducts with its intrahepatic ramifications [1, 2].
The common hepatic duct was missing in rabbits, cats and dogs. In rabbits, two hepatic ducts were described; the left one drained both the left lobes and the quadrate lobe, then joined the cystic duct to form the bile duct which received the right duct, the latter drained the right and the caudate lobes. However, in feline and canine, the lobar hepatic ducts opened individually into the cystic duct [3]. In this respect, the absence of the common hepatic duct was also recorded in rabbit [4] and guinea pig [5] [6]. The common hepatic duct was formed in the rabbit by the confluence of the left and the right hepatic ducts at the ventral part of the liver porta. It received ramus omentalis and at the same level the cystic duct to form the bile duct. The latter duct received the ramus processus caudati through its course in the hepatoduodenal ligament [7].
In cats and dogs, 3-5 hepatic ducts opened separately in to the cystic duct which became the bile duct after the entrance of the last hepatic duct [8]; [9]; [10] and [11].
On the other hand, the cystic duct extended from the gall bladder to the first hepatic duct [1]. However, the cystic duct is an important landmark in that it distinguishes the otherwise continuous hepatic ducts from the bile ducts [2]. In cats, the bile duct was formed by the triple convergence of the left hepatic, the right hepatic and the cystic ducts [12].
In ruminants, the bile duct was formed by the union of the right and the left hepatic ducts, while the cystic duct opened into the right duct [13]; [14] and [15]. On the other hand, the right and left hepatic ducts joined to form a short common hepatic duct, which received the cystic duct and then after became the short and wide bile duct [16]; [10] and [17].
The rabbit gall bladder was long oval [7], cylindrical sac [3] or had elongated body with narrow neck [4]. It was embedded in its deep fossa at the middle of the visceral surface between right and quadrate lobes. It did not reach the liver ventral margin even when it was completely filled.
In carnivores, the gall bladder was sunk deeply between the right medial and quadrate lobes, just to the right of the median plane and opposite the eighth intercostal space. It was visible on the visceral as well as the parietal (diaphragmatic) surfaces and thus, in contact with the diaphragm [10] and [18]. However, the guinea pig gall bladder was rounded and extended to the liver ventral border, hanging freely and suspended by a single membrane from the liver [19]. Also, and in this respect, the pear-shaped gall bladder of ruminants was firmly attached to its fossa on the liver visceral surface, and protruded from its ventral margin [10].
The majority of the congenital abnormalities of feline gall bladder could be related to the failure of vacuolization of the solid gall bladder and bile duct diverticulum [20]. Three types of gall bladder abnormalities were recorded; a. Septated gall bladder, had a large lumen divided by septa inside, b. Bilobed gall bladder, with fundic duplication, body duplication where the two lobes opened by a single cystic duct to the bile duct, c. Duplex gall bladder, where the fundus, the body and cystic duct were formed as a couple (complete duplication) and they joined together at the bile duct

MATERIALS & METHOD
The present study was constructed on twelve (12) native breeds of rabbits (Oryctolagus cuniculus) and eighteen (18)

domestic cats (Felis catus domesticus)
which were adult apparently healthy of both sexes with average body weight; 2.800-3.500 Kg.

A. The Anatomical study: -
The used animals were euthanized by lethal dose of Diazepam at 10 mg/kg intravenously through the external jugular vein. The experiments were conducted by the international ethical standards set by the institutional animal care and use committee (Vet. CU. IACUC) VetCU1111201808. Three rabbits and nine cats were anatomically dissected freshly for gall bladder morphology then fixed by 10% neutral buffered formalin. For cast study, six rabbits and nine cats were injected with colored latex neoprene into the major duodenal papilla and then fixed by freezing or neutral buffered formalin overnight, further dissection occurred and then transferred to concentrated HCL and left for three days.
The specimens were photographed using Olympus digital camera SP-600UZ 12 mega pixel. The anatomical nomenclature used in this study was in accordance with the Nomina Anatomica Veterinaria 2017 (6 th edition).

B. The Ultrasonographical and Radiological study: -
Concerning the Ultrasound examination, we evaluated 6 live animals; 3 each animal species, by using two devices according to availability at the time of study; B-mode scan (Pie medical) and doppler device (EXAGO, Echo control medical, France) with a linear multifrequency transducer using a frequency of 5-7.5 MHz in rabbits and 7.5 MHz in cats. These animals were later used as specimens for the radiological examination of the biliary duct system using the radiographic device (Fisher imaging, Chicago, USA). The animals were euthanized as mentioned before and injected by lead oxide dissolved in turpentine oil into the major duodenal papilla in both animals to obtain X-ray films.

A. Anatomical study: -
The present investigation in the rabbit, showed a relatively small and elongated gall bladder (Figs 1,2,3/f) with nearly rounded fundus and narrow neck. It was situated and fixed in the gall bladder fossa on the middle of the liver visceral surface, bordered medially by the quadrate lobe and laterally by the right lobe. several small ducts entered the fundus and the corpus of the gall bladder as hepatocystic ducts, were demonstrated during the dissection process of the injected specimens. In addition to their drainage to the parenchyma of the gall bladder fossa, they served as a means of fixation in its highest position and did not permit it to reach the liver ventral margin (Fig. 1, 2A,B/f).
It must be noted that the common hepatic duct was missing in the most (common) of rabbit liver specimens. The bile duct ( It was worthy to note that the biliary system of the native breed cats presented considerable variations in size, shape and position of the gall bladder as well as the manner of terminations of the hepatic ducts and the formations of the bile duct. In the most common investigated cat livers, the gall bladder was relatively large, situated more superficially in the gall bladder fossa, between the right medial lobe laterally and the quadrate lobe medially and did not reach the liver ventral margin and did not appear on the hepatic parietal surface (Figs. 5A,B,C&11A/g). It was curved pear-shaped with broad fundus, slightly concave hepatic surface, slightly convex gastric surface and folded neck (Figs. 5D,E&9B/g) connected with tortuous cystic duct. In two investigated liver specimens, the gall bladder appeared oval in shape ( During the present investigation on cat liver, four different variations in its shape were observed; A. The gall bladder was relatively small, partly appeared on the liver visceral surface, enveloped completely by the quadrate lobe and presented only a small impression on the right medial lobe. its broad fundus ( Fig.7A/g) was divided by a sagittal groove (Duplex fundus) and each portion showed several small notches externally, appeared on the liver parietal surface ( Fig.7C/g) as the gall bladder fossa in such case was too deep. Internally, there was no septa dividing the fundus or corpus (Fig.7B).
B. The gall bladder was fairly large and long to reach, nearly, the level of the liver ventral borders where they appeared on the parietal aspect ( Fig. 8) The animals were positioned in dorsal recumbency and a 5-7.5 MHz and a 7.5 MHz linear multifrequency transducer was used for rabbit and cat, respectively. The sonographic approach was transabdominal percutaneous epigastric.

A. Anatomical study:
The present study revealed that the rabbit gall bladder was relatively small, elongated in shape with a rounded fundus and narrow neck. It was positioned high in its fossa on the liver visceral surface between the right and the quadrate lobes and was fixed to the hepatic parenchyma by several small hepato-cystic ducts, thus it did not reach the liver ventral margin even when it was completely filled. In all investigated specimens, it did not appear on the liver parietal surface. A result which was in accordance with the description of [7], [3] and [4] in the same animal.
The results of our studies on the cat gall bladder revealed that in most specimens, it was relatively large, oval or slightly curved pear-shaped, situated more superficially in its fossa between the quadrate and right medial lobe and neither reach the liver ventral margin nor the parietal surface. In this respect, the canine gall bladder was embedded within the liver and appeared on the visceral and parietal surfaces [32]; [10] and [18].
On the other hand, our investigations on the same examined cat livers, revealed four different shapes and sizes of the gall bladders. In one case, the gall bladder was relatively small pear-shaped with duplex fundus, without any internal septa. In second case, the liver gall bladder was bilobed; had duplex fundusm duplex corpus with single small neck. The previous results were reported as congenital abnormalities by It must be noted that, the liver investigated specimen of bilobed gall bladder revealed that the right lobe presented two small buds connected together. A condition which was not recorded in relevant references. Our results on cat liver was documented by [20] in that the variety of the cat gall bladder shap vacuolization of the solid gall bladder and bile duct diverticulum during development .
Concerning the extrahepatic biliary tract, the most common pattern of rabbit bile duct formation investigated in the present study, by the junction of the left hepatic duct with the cystic duct. The left duct drained both left lobes and quadrate lobe as well as the papillary process of the caudate lobe, while the right hepatic lobe was drained by its own right hepatic duct which opened into the cystic duct about its middle in its route to enter in the formation of the bile duct. The bile of the caudate process of the caudate lobe was collected by two branches that merged and opened directly into the bile duct.
The absence of the common hepatic duct in the rabbit most examined specimens was in accordance with the description of In the rabbit investigated specimens, the caudate process of the caudate lobe was drained by its own branch that entered directly into the bile duct. A result which was in agreement with [7] in the same animal and also in ruminants The biliary ducts drained the caudate and the right lateral lobes entered the bile duct directly was observed by [9] in prairie dog and in domestic animals [18]. Similar observation was also recorded in the present study on some cat livers. However, in most examined specimens the two ducts merged to form what could be named right accessory hepatic duct. However, the present study revealed, in exceptional cases, that caudate process branch entered separately the bile duct while the right lateral lobar branch entered in the formation of the right hepatic duct by joining the right medial lobar branch.
The entrance of the bile and pancreatic ducts into the duodenum either individually as in the investigated rabbit specimens or ended together as observed in the cat specimens were in accordance with [7] and [3] in the rabbit as well as in the cat

B. Ultrasonographical study:
The ultrasonographic study on the rabbit's liver was performed using a linear multifrequency transducer with a working frequency range from 5 to 7.5 MHz, In rabbit, the right medial hypo-chondral sagittal scan, identifying the

CONCLUSION:
The rabbit gall bladder was relatively small in all investigated liver specimens.
It was positioned high and fixed by several small hepato-cystic ducts to its fossa. The rabbit bile duct was formed commonly by the junction of the left hepatic duct and the cystic duct. The former one drained both left lobes and quadrate lobe as well as the papillary process of the caudate lobe. the cystic duct was, commonly fairly large, received the right hepatic duct that collected the right lobe in its route to enter the duodenum, the bile duct receives the branch of the caudate process of the caudate lobe.
It must be noted that, in some of the investigated specimens, the rabbit gall bladder was connected by a thin and small cystic duct, with the right hepatic duct which joined the left one to form a short common hepatic duct.
The relatively large, oval or slightly curved pear-shaped cat gall bladder were commonly investigated. It was situated more superficially on the middle of the liver visceral surface and neither reached the ventral margin nor appeared on its parietal surface. In addition, the present study revealed other four anatomic variations dealing with the shape and size of the feline, native breed, gall bladder from fundic duplication, fundic duplication with body duplication (Bilobed), truncated fundus and distended rounded fundus. In all these different forms, the gall bladder appeared partially on the hepatic diaphragmatic surface. There was no relation between the shape of the gall bladder and the mode of the hepatic ducts' terminations in felines. Commonly, the bile duct was formed by the triple convergence of the left and the right hepatic ducts with the cystic duct. However, in some exceptional cases a short common hepatic duct was formed, by the union of the previous two hepatic ducts, and merged with the cystic duct forming the bile duct. In the present study, the caudate process branch and the right lateral branch, each drained its respective hepatic portion. Commonly, these two branches merged to form a single duct that could be named right accessory hepatic duct which entered the "original" right hepatic duct of the right medial lobe.
The sonographic investigation of the gall bladder was mainly confined to the left medial hypochondriac, middle xyphoid and right medial hypochondriac epigastric region. The normal gall bladder in rabbit appeared small, elongated with anechoic lumen bordered by right lobe laterally and quadrate lobe medially and has no visible wall, but in cat varied in conformation, bordered by the right medial lobe laterally and the quadrate lobe medially surrounded by echogenic wall.

ACKNOWLEDGMENT:
We would like to express our great appreciation to professor doctor Salah         quadrate and right lobes appeared and outlined by green, yellow and red dots, respectively-with characteristic C/S appearance of anechoic vena hepatica lobi sinistri medialis without echogenic wall (green arrow) and anechoic ramus lobi sinistri medialis portal vein with echogenic wall (yellow arrow). Noted the small elongated anechoic gall bladder with a red arrow pointed at the cystic duct and a blue arrow pointed at the echogenic diaphragm.