Chapter 6 THE ABDOMEN
The symmetry, size and shape of the abdomen varies considerably from breed to breed. In the bitch, the mammary glands are an important pre- and post-natal feature and in the pregnant bitch the topography may be altered and caesarean section required. This is carried out as for any abdominal laparotomy described below.
The abdomen has basically three regions; cranial abdominal, middle and caudal abdominal, with hyposplanchnic and xiphoid regions. The region is limited by the diaphragm, iliocostal line and pelvic brim. It contains a wide range of organ systems with plenty of opportunity for these to go wrong and require surgery. Many of these surgical interventions are carried out through a midline laparotomy anywhere along a line from the xiphisternum to the umbilicus, although most extend much further caudally than the umbilicus even in males where the penis deflected and the incision continued. This is along the linea alba (white line) and the incision here once through the skin can be accomplished with minimum bleeding, as this is the junction of the aponeuroses of the ventral abdominal musculature. The tissue or organ that requires surgery can then be brought to the exterior without damage to other structures and allows them to be kept moist. This site also produces a strong tissue for suturing.
An exploratory laparotomy is carried out to see what is going on and to possibly make a definitive diagnosis, otherwise this site may be used for: ovarohysterectomy (spaying) of the bitch, and for pyometra (uterus fills with a pus-like material), often in nulliparous, aged, and usually post-season bitches. This requires complete surgical removal. Likewise, ovarian cysts and tumours are similarly removed. The same site can also give good access for removal of intestinal neoplasia; enterotomies for foreign body removal such as bones, fish hooks or bouncing rubber balls; enterectomy for intussusception (bowel telescopes into bowel) with subsequent end-to-end anastomoses of the bowel after removal of necrotic portions. Gastric dilation and torsion can be approached through the same site. Here needle decompression to release gas is necessary and a stomach tube tightly in place will remove gas and fluid, and then the re-positioned stomach can be held in place by stitches. This midline ventral laparotomy can also be used for partial gastrectomy for tumours and for operations on the pylorus – particularly pyloric stenosis. Torsion of the spleen may be relieved and splenic tumours can also be removed via a midline ventral incision and good exposure of the kidneys is also achievable. The ventral midline approach also gives good exposure to repair rupture of the diaphragm. The midline laparotomy is used in some circumstances to inject into the intestinal veins for the purpose of portography so that the circulation through the liver can be visualized.
Portosystemic shunts are a not uncommon condition in the dog and require diagnosis by catheterization of the celiac or cranial mesenteric artery via the mesenteric vessels. Surgical correction of the shunt is the only specific treatment. Structures in the upper abdomen (kidneys, thoracolumbar vertebrae) can also be reached by flank laparotomy. This involves cutting the abdominal musculature along the direction of their fibers and therefore there is considerably more potential hemorrhage because the incisions run three ways in the muscle layers (exterior abdominal oblique, interior abdominal oblique and transverse). The exposure is not as good as in a straight midline incision. The other problem is that the ventral branches of the spinal nerves innervating the ventral abdomen, mammary and inguinal region run over the transverse muscles and they should be avoided.
Nowadays, many surgeons use the laparoscopic techniques to routinely spay bitches. Some people, particularly in former times, have always recommended ‘spaying’ bitches from the right flank as the left ovarian ligament is longer than the right and therefore the left ovary is more easily exteriorized for ligation across the abdomen. Lateral thoracolumbar fenestration for disc problems over the large iliocostal muscle is also a possibility. I have left the discussion of the urogenital system to a discussion of the pelvis, but the mammary glands are an important abdominal feature. They are a frequent site of both benign and malignant tumours requiring surgical incision of single glands or sometimes both complete lines of glands. Each has a good segmental blood supply which requires careful ligation. It is important to note the lymphatic drainage when tumours may be seeded or infection spread as the cranial glands drain to the axillary (possible palpable) and sternal lymph nodes (inside thorax) – caudal abdominal glands drain to both the cranial glands and caudal to the inguinal glands and the inguinal mammary glands to the inguinal (mammary) lymph nodes, which again may be palpable.
Laparoscopy using a fibroscope to investigate the abdominal contents can also be used through the ventral midline incision. Abdominocentesis, which is the withdrawal of fluid from the peritoneal cavity, can be performed at a site 1 to 2 cm caudal to the umbilicus. In younger animals, it may be necessary to repair a hernia at the umbilicus, and in these cases the falciform fat or even small intestine may fill the cavity of the umbilicus, possibly leading later to strangulated hernia.
Other abdominal diagnostic techniques include liver biopsy. This used to be done from the left side of the abdomen to avoid damage to the right-sided gall bladder, large vessels and bile ducts at the hilus of the liver, i.e. dog is in right lateral recumbency after fasting, as it is not easy with a full stomach. To take just liver cells, it is possible to carry out a fine-needle biopsy in the 10th intercostal space on the right hand side, at the level of the costochondral junction. Nowadays, many surgeons tend to do this using ultrasound or laparoscope.
The last area that may require surgery is the inguinal region, with incisions over the inguinal canal to repair either an inguinal hernia or to search for a retained testicle somewhere between the internal inguinal ring and the caudal pole of the kidney from where in embryological terms the testicle originates before its traverse to the scrotum.
The vaginal process of the peritoneum in males exits from the inguinal region through the deep and superficial inguinal rings; 80% of female dogs also have a peritoneal vaginal process. The round ligament of the uterus passes through the inguinal canal and is contained within the vaginal process, and the canal itself is filled with connective tissue.
In ‘open’ castration of the dog, the parietal layer of the vaginal tunic is incised and thus the potential space of the peritoneal cavity is invaded.
Surgery of the bladder for removal of bladder stones or debris is also carried out through a caudal midline intervention with the incision avoiding the dorsal bladder surface where the ureters enter the bladder. Removal of kidney or ureteric stones may also be required.
Fig. 6.1 Surface features of the abdomen and hip: left lateral view. The bony ‘landmarks’ that are palpable around the borders of the abdomen are shown in this figure. In a normal standing position the femur and its covering thigh muscles obscure the rear end of the abdomen. The caudal border of the abdomen is marked by the tuber coxae dorsolaterally and the pubis ventrally. The inguinal ligament, marking the caudal border of the muscular abdominal wall, is palpable between these two points in the fold of the groin (see also Fig. 6.67 of the abdomen in ventral view).
Fig. 6.2 Skeleton related to the abdomen: left lateral view. The palpable bony features shown bordering the abdomen in the surface view on Fig. 6.1 are colored green for reference. It should be noted that caudal to the large thoracic outlet (bounded by the xiphoid cartilage of the sternum, the costal arches and floating ribs) the abdominal wall is entirely muscular. The considerably restricted pelvic inlet, bounded by the sacrum above and pelvic bones bilaterally, marks the caudal boundary of the abdomen.
Fig. 6.3 Radiograph of the abdomen: left lateral view. The normal features of the abdomen and its contents are shown in this picture. The position and appearance of the viscera do vary considerably with the amount of fat present. The animal used for this radiograph was actually obese, the contrast made possible by its fat clarifying soft tissue to some extent.
Fig. 6.4 Radiograph of the abdomen: lateral view, 20 minutes after oral administration of barium. Barium can be seen highlighting the stomach and duodenum. Rugal folds are visible in the gastric fundus. Irregularities on the ventral aspect of the descending duodenum represent regions of mucosal thinning over submucosal lymphoid accumulations.
Fig. 6.5 Radiograph of the abdomen: lateral view, 45 minutes after oral administration of barium. Barium can be seen highlighting the stomach and small intestine. The small intestines occupy the centre of the abdomen.
Fig. 6.6 Radiograph of the abdomen: ventrodorsal view, 45 minutes after oral administration of barium. Barium can be seen highlighting the stomach and small intestine. The small intestines occupy the centre of the abdomen.
Fig. 6.7 Radiograph of the abdomen: lateral view, 4 hours after oral administration of barium. The barium can be seen highlighting parts of the jejunum and ileum, the caecum and the colon.
Fig. 6.8 Radiograph of the abdomen: ventrodorsal view, 4 hours after oral administration of barium. The barium can be seen highlighting parts of the jejunum and ileum, the caecum and the colon.
Fig. 6.9 Radiograph of the abdomen: ventrodorsal view, 5 minutes after intravenous injection of water-soluble iodine-containing contrast medium. The contrast medium can be seen highlighting the kidney parenchyma, the renal pelves and parts of the ureters. Ureters are rarely highlighted by continuous contrast columns in the normal dog due to their peristaltic movements. The bladder has been filled with air as part of the contrast study to enable greater visualization of the ureters.
Fig. 6.10 Radiograph of the abdomen: ventrodorsal view, 15 minutes after intravenous injection of water-soluble iodine-containing contrast medium. The bladder has been filled with air to highlight the ureterovesical junctions.
Fig. 6.11 Superficial fascia of the abdomen and hip: left lateral view. The skin has been removed displaying the superficial fascia, a thick subcutaneous covering of loose connective tissue rich in elastic fibers and usually containing variable quantities of fat. The cutaneous muscle of the trunk, located in the superficial fascia, extends cranioventrally and converges into the axilla. It is absent from the skin over the rump and thigh.
Fig. 6.12 Cutaneous muscle of the trunk and cutaneous nerves of the abdomen and cranial thigh: left lateral view. Limited cleaning of the superficial fascia has exposed the cutaneous muscle of the trunk. It has been cut into and partially removed from the caudodorsal abdomen and loin, a procedure which has exposed two lateral series of cutaneous nerves with accompanying cutaneous vessels.
Fig. 6.13 Superficial structures of the abdomen – cutaneous nerves: left lateral view. The remaining superficial fascia has been cleaned from the trunk along with most of the cutaneous muscle. On the underside of the abdominal wall the glans of the penis and its enclosing prepuce are suspended by a fold of skin. This fold has been removed from the left side exposing the preputial muscle radiating caudally into the prepuce, and the preputial components of the external pudendal vessels extending cranially from the inguinal region (see also Figs 6.14, 6.46 and 6.101).
Fig. 6.14 Abdominal wall (1). External abdominal oblique muscle after removal of the hindlimb: left lateral view. Removal of the left hindlimb exposes the overall extent of the muscular abdominal wall. The latissimus dorsi and pectoral muscles have also been removed from the thorax which exposes the origin of the external oblique muscle. The caudal limit of the muscular abdominal wall, the inguinal ligament, is visible on the surface of the iliopsoas muscle. Ventrally the aponeurosis of the external oblique forms a major component of the external layer of the rectus sheath (see also Figs 6.69–6.71).
Fig. 6.15 Abdominal wall (2). Internal abdominal oblique muscle: left lateral view. The external oblique has been removed except where it forms part of the external layer of the rectus sheath. Here it is inseparable from the underlying aponeurosis of the internal oblique (see also Figs 6.69–6.71). The pelvic tendon of the external oblique has also been removed, in consequence the inguinal canal is completely opened on its cranial and lateral aspects. Cranially the contribution of the aponeurosis of the internal oblique to both deep and superficial layers of the rectus sheath is exposed. This relationship is shown to advantage in the next few figures and in Figs 5.16–5.19.
Fig. 6.16 Abdominal wall (3). Internal abdominal oblique muscle and rectus sheath: left lateral view (1). Reflection of the cranial part of the rectus abdominis muscle from the thorax exposes the costal cartilages and the fleshy origin of the rectus from costal cartilage 9. The position internally of the costodiaphragmatic line of pleural reflection (broken line) demonstrates the caudal-most extent of the thoracic cavity and therefore penetration caudal to this line will enter the abdomen.
Fig. 6.17 Abdominal wall (4). Internal abdominal oblique muscle and rectus sheath: left lateral view (2). Further reflection of the rectus muscle has been accomplished after severance of its fleshy attachment to costal cartilage 9. The costal arch is now displayed and the intercostal/interchondral spaces are completely cleared of intercostal musculature. Caudal to the costodiaphragmatic line of pleural reflection (broken line), diaphragmatic muscle is attached to the internal surfaces of costal cartilages except that of rib 13 whose costal cartilage remains free.
Fig. 6.18 Abdominal wall (5). Transverse abdominal muscle and nerves of the abdominal wall: left lateral view. The internal oblique muscle has been cut through longitudinally close to its origin from the thoracolumbar fascia, and from its association with the inguinal ligament. The muscle is reflected ventrally and is left hanging down from the ventrolateral aspect of the abdomen. The rectus abdominis has also been reflected away from the transverse abdominal aponeurosis stretching the nerves which enter it dorsally. In the upper part of the abdominal wall, caudal to rib 13, a rudimentary rib 14 is visible. This extra rib is only cartilaginous and has fascial connective tissue attachments to both internal oblique and transverse muscles.
Fig. 6.19 Abdominal wall (6). Rectus abdominis muscle and rectus sheath external layer: left lateral view. The internal oblique muscle has been almost completely removed. Only the ventral part of its aponeurosis remains on the surface of the rectus abdominis muscle where it forms the external layer of the rectus sheath together with the aponeurosis of the external oblique. The two are inseparably fused down to the linea alba in the midventral line. The rudimentary rib 14 has been removed and the series of nerves entering the upper part of the abdominal wall are displayed on the surface of the transverse muscle (see also Fig. 6.72).
Fig. 6.20 Abdominal wall (7). Rectus abdominis muscle and rectus sheath internal layer: left lateral view. Severing of the caudal part of the transverse abdominal aponeurosis where it contributed to the external layer of the rectus sheath has allowed the rectus abdominis muscle to be reflected ventrally away from the underlying transverse muscle and aponeurosis. The dorsal surface of the rectus is exposed with the terminations of abdominal wall nerves entering it in series. The internal layer of the rectus sheath is represented here by the aponeurosis of the transverse muscle, except caudal to the caudal iliohypogastric nerve branch where it consists solely of transverse fascia (see also Figs 6.72 and 6.101).
Fig. 6.21 Abdominal wall (8). Transverse abdominal muscle and diaphragm: left lateral view. The transverse abdominal muscle is exposed in its entirety after removal of the rectus abdominis muscle and the nerves of the abdominal wall. The costal part is seen arising from the internal face of the costal arch interdigitating with fibers of the diaphragm immediately caudal to the costodiaphragmatic line of pleural reflection. The lumbar part emerges from beneath the iliocostalis lumborum. The extensive aponeurosis ventrally provides the internal lamina of the rectus sheath and extends down to the linea alba (see also Figs 6.70, 6.72). The caudal border of the transverse muscle does not extend to the caudal end of the abdominal wall.
Fig. 6.22 Abdominal wall (9). Transverse fascia: left lateral view. The transverse abdominal muscle has been carefully removed and the transverse fascia lining the internal face of the abdominal wall is exposed. This clear layer supports the parietal peritoneum internally and blends with the iliac fascia on the iliopsoas muscle and with the pelvic fascia at the pelvic inlet ventrally. Cranially the transverse fascia is continued onto the rear surface of the diaphragm medial to the costal arch.
Fig. 6.23 Abdominal viscera in situ (1). After removal of the abdominal wall: left lateral view. Removal of the transverse fascia and the closely applied parietal peritoneum opens the peritoneal cavity and exposes jejunal coils. Several areas where fat is deposited beneath the peritoneum are apparent; viz. great mesentery associated with the jejunal coils, around the kidney (perirenal fat), and in the falciform ligament ventrally (see also Figs 6.74 and 6.75 for fat deposits in the abdomen). Also visible in the great mesentery are clearly defined opaque strips which represent afferent lymphatic channels. Compare this view with equivalent views from the right (Fig. 6.47) and ventrally (Fig. 6.73).
Fig. 6.24 Abdominal viscera in situ (2). After removal of the abdominal wall and diaphragm: left lateral view. The left half of the diaphragm has been removed, the cut edge of the diaphragmatic cupola in the midline now indicates the most cranial extent of the abdominal cavity. The costal arch is left in place and the position of the costodiaphragmatic line of pleural reflection is still indicated by the broken line in advance of it. Compare this view with equivalent views from the right side (Fig. 6.48) and ventrally (Fig. 6.76).
Fig. 6.25 Viscera of the cranial abdomen in situ after removal of the abdominal wall, ribs and diaphragm: left lateral view. At the cranial end of the abdomen the remaining ribs and costal arch have been removed. The spleen is abnormally enlarged following barbiturate narcosis, and extends right down to the belly floor in the xiphoid region (see also Figs 6.77, 6.78 in ventral view, Figs 6.88–6.90 in caudal view, and Figs 6.96, 6.97 in section).
Fig. 6.26 Descending colon: left lateral view (1). The transverse and much of the descending part of the colon have been exposed following removal of the deep layer of the greater omentum and a number of jejunal coils. The colon in this specimen is somewhat enlarged and appears sacculated. For a more ‘normal’ appearance see Fig. 6.61 from a right medial view and Figs 6.80 and 6.82 from a ventral view. Dorsal to the colon the left kidney is exposed further by removal of perirenal fat. In the caudal abdomen the iliacus component of the iliopsoas muscle has been removed, and the psoas major has been additionally trimmed as far cranially as the tuber coxae.
Fig. 6.27 Descending colon: left lateral view (2). More jejunal coils have been removed from the ventral abdomen and the cut ends are clearly displayed. The jejunum has actually been severed close to its commencement at the duodenojejunal flexure which is visible immediately ventral to the initial part of the descending colon. Caudally, removal of more of the psoas major and the flattened tendon of the psoas minor muscle has exposed the most caudal extent of the descending colon as it enters the pelvis. Removal of the iliopsoas muscle has also exposed both internal and external iliac vessels, a medial iliac lymph node and the quadratus lumborum muscle.
Fig. 6.28 Left kidney and mesocolon: left lateral view. The descending colon has been removed except for its terminal part dorsal to the bladder. Cranially, the cut surface of the transverse colon is clearly observed immediately cranial to the duodenojejunal flexure (its position is shown to advantage in section in Fig. 6.97). Extending caudally from the transverse colon, below the kidney, the fat infiltrated mesocolon and its cut edge are visible. Medial to the duodenojejunal flexure and caudal to the transverse colon the mesenteric root is just exposed. The relationship of structures to the root is shown to advantage in ventral view (Figs 6.80, 6.81) and in section (Figs 6.98, 6.99).
