10 The Abdomen and Associated Digestive Organs

The abdominal cavity, the middle one of the three, is the largest of the body cavities. Exter­nally its anterior part merges with the thorax at the costal arch where, internally, it is separated from the thoracic cavity by the diaphragm. It is continuous posteriorly with the structures com­prising the pelvis; internally the demarcation line between the abdominal and pelvic cavities is formed by the brim of the pelvis, comprising the base of the sacrum dorsally, the iliopectineal lines laterally and the anterior border of the pubes ventrally.

Comparatively, the abdomen has a greater capacity in ruminant species than in the horse. The cavity of the abdomen, which is slightly compressed laterally, is ovoid in general form with its greatest axis extending from the con­cavity of the diaphragm to the pelvic inlet. The roof is formed by the upper part of the dia­phragm, the lumbar vertebrae and the lumbar muscles. The wall is comprised of the transverse and oblique abdominal muscles, the abdominal tunic, the upper, anterior parts of the ilia, the parts of the posterior ribs which extend below the attachment of the diaphragm and the costal cartilages of the retrosternal ribs. The floor consists of the xiphoid cartilage of the sternum, the two recti muscles, the aponeuroses of the transverse and oblique abdominal muscles and the abdominal tunic. The anterior boundary is formed by the diaphragm, the convexity of which projects forward limiting the size of the thoracic cavity.

The abdominal cavity is lined by a thin serous membrane, the peritoneum, which is continued to a somewhat variable extent into the pelvic cavity. The peritoneum is reflected from the inter­nal surface of the abdominal cavity on to the visceral organs, which are thereby covered to a greater or lesser extent.

Alimentary Tract Dysfunction

Some of the primary functions of the alimen­tary tract, including prehension, mastication and deglutition of food and water, have already been considered. Other major activities, such as digestion, absorption and excretion, which are the normal functions of the stomach and intes­tines, must now receive consideration. The sig­nificance of these functions, which are related to stabilizing the internal environment of the ani­mal, can be realized by appreciating that almost without exception all its nutritional and func­tional requirements are processed by the diges­tive tract.

Alimentary tract dysfunction is an expression of derangement of one or more of the following: motility, secretion, digestion, absorption. In cli­nical diagnosis the primary consideration should be to recognize which of these functions is or are deranged.

Gastrointestinal motility, consisting of peri­staltic movements and segmentation movements, and of which sphincter tone is an important component, depends upon balanced functioning of the sympathetic and parasympathetic nervous systems, together with that of the intrinsic nerve plexuses. Imbalance of the autonomic nerves, which can result from stimulation or damage to any of the component parts, is manifested by hypermotility or hypomotility. The change in the pattern of motility may be widespread or segmental in extent. Hypermotility causes diar­rhoea; hypomotility is responsible for constipa­tion. In segmental hypermotility there may be a reversal of the normal downward gradient from the stomach to the rectum, so that retroperistalsis is produced, proceeding to vomition.

Abnormalities of motility lead to distension of the stomach and/or intestine because of ineffec­tive eructation of gas (more likely when gas accumulates rapidly), occlusion of the tract lumen by obstruction or displacement, or en­gorgement on solid or liquid foods. Overdisten-sion of the gastrointestinal tract causes pain with reflex spasm and increased motility of adjoining segments. The distension is exaggera­ted because it leads to increased secretion of fluid into the lumen of the affected part.

Secretory dysfunction by the alimentary tract is a rare event in large animals. Recognizable syndromes arising from defective gastric and pancreatic secretion occur occasionally in dogs and cats.

Digestion is dependent on both the secretory and the motor functions of the alimentary tract. In herbivorous animals the activity of the microflora (in the forestomach compartments of rumi­nant species, or the caecum and colon of equine species) plays a significant role in the digestion of cellulose and nitrogenous substances. Impair­ment of microbial digestion can result from dietary imbalance, inadequate food, inappetance, derangement of ruminal pH or oral administra­tion of antibiotics or specific antibacterial drugs in ruminant animals.

The absorptive functions of the intestinal tract will be impaired to a variable degree by hyper­motility or by damage to the mucous membrane. These two states not infrequently coexist, but significant degrees of damage to the mucosa may occur, without hypermotility, in some forms of intestinal helminth infestations.

General Clinical Examination

Diseases of the digestive system are of fre­quent occurrence in domestic animals and, with the development of even more intensive produc­tion methods, or their wider application, may increase in incidence still further. Because many of the organs concerned, more particularly those situated within the abdominal cavity, are of relatively large size and are inaccessible, recog­nition of the situation and nature of any disease process is usually more difficult to establish than when other parts of the body are involved. As a consequence, it is necessary to give careful consideration to all aspects of behaviour associa­ted with digestive function. In this context, atten­tion has already been directed to such features as physical condition, appetite for food and fluid, the oral cavity, deglutition and vomiting. Furthermore, the enquiries made when the his­tory was being elicited included consideration of the excretory functions of the intestine, as indi­cated by the volume and character of the faeces. Correlating the history and behavioural signs with the clinical findings, and assessing the in­formation so obtained on the basis of the distur­bances of function mentioned earlier will assist diagnosis.

The clinical examination of the abdomen con­sists of external examination, comprising inspec­tion, palpation, percussion and auscultation, and internal examination, which includes rectal exploration, exploratory puncture, peritoneoscopy and, in small animals, radiography.

Inspection provides an opportunity to assess the relative size of the abdomen and determine the presence of localized conditions. In the upper part of the flank, in the normal abdomen, it is usual to note a depression in the so-called paralumbar fossa or 'hunger hollow'. This is particularly obvious in ruminant species, includ­ing cattle and goats, and is slightly larger on the right side than on the left. Undulating move­ments, corresponding to the motility of the underlying rumen, may be observed on the left side.

The abdomen may appear distended, of normal size or reduced in capacity. An increase in the size or circumference of the abdomen (Fig. 135) occurs from varying causes, including advanced pregnancy, flatulence, distension of the rumen or stomach, tumours of the liver, spleen, lymph nodes, etc., diseases of the uterus (hydrometra, pyometra, etc.), urinary retention and accumu­lation of fluid in the peritoneal cavity (ascites, ruptured bladder, exudative peritonitis). In gaseous distension, the increase in size is more or less uniform, although in ruminal bloat the distension is greatest over the left flank. When gaseous distension of the intestine is severe the affected loops of bowel may cause distinctive bulging in the flank region.

In advanced pregnancy, and when there is fluid accumulation, the distension is most notice­able in the dependent part of the abdomen, the paralumbar fossae being considerably deepened. Fetal movements may be observed through the abdominal wall in advanced pregnancy—on either side in the mare and on the right side in the cow. Ruminal movements are often quite obvious by their influence on the left flank, but the frequency and quality of the movements are not readily assessed by inspection. If fluid is free in the peritoneal cavity, changes in the posture of the animal alter the position of the fluid, the altered conditions being appreciated by means of percussion, which reveals, by the production of a non-resonant sound, that the fluid always gravitates to the most dependent part. When the fluid causing abdominal distension is enclosed in a sac, or a hollow organ, percussion indicates that changes in posture have no influence on its relative position.

The degree of abdominal distension associated with faecal or urinary retention is, even in extreme cases, of moderate degree only. Enlarge­ment of the abdomen caused by neoplasia involving the spleen, liver, ovary or other organ is generally only recognized in the advanced stages, and then usually only in the dog and cat. With tumours, more particularly when superficial structures are involved, hernias, abscesses and haematomas, there may be a frankly localized swelling (Fig. 136). Oedematous swelling of the ventral abdomen occurs in congestive heart failure, acute gangrenous mastitis, infectious equine anaemia, rupture of the penile urethra due to obstructive urolithiasis or malapplication of a crushing type castrator, and as an expression of hypoproteinaemia in the terminal stages of pregnancy, particularly in young mares and heifers.

A decrease in the circumference of the abdo­men, resulting in a tucked-up, 'herring-gutted' or gaunt appearance, is observed in prolonged mal­nutrition, in many chronic diseases with reduced appetite and in diseases associated with prolong­ed, severe dehydration (enteritis) or marked disturbance of the tissue fluid balance of the body, notably subacute grass sickness of horses (Fig. 137). Note should also be taken of any change in the anatomical conformation of the bony prominences such as 'knocked-down' hips —a possible indication of calcium or phosphorus deficiency (Fig. 138).

External palpation of the abdomen provides limited information in the horse. Its object is to ascertain the size and shape of the various organs, the character of the intestinal contents and the detection of any pain focus. As a rule horses intensify the tone of the abdominal musculature during the examination and this together with the thickness of the abdominal wall, prohibits deep palpation of the abdomen. The whole hand, or closed fist, should be placed firmly in contact with the abdomen and held in place until a degree of muscular relaxation occurs, and then either a firm punch or jab applied for the purpose of detecting superficial pain. When deep-seated pain is suspected a firm, even application of pressure is required. This examination is made on both sides.

The abdominal musculature is much less tense in cattle, and palpation over the rumen in the left flank yields much useful information concerning motility and the amount and consistency of the rumen contents. Large tumours, or extensive areas of mesenteric or omental fat necrosis situa­ted near the abdominal wall, and in advanced pregnancy parts of the fetus may be recognized by this means. In cattle in lean condition the upper right border of the liver, when the organ is enlarged, may be detectable by palpation behind the upper part of the right costal arch. A pain reaction may be elicited generally over the abdomen in peritonitis, and over the upper half of the last 3 or 4 ribs, on the right side, in various forms of subacute and acute hepatitis. In trau­matic reticuloperitonitis, the existence of a pain­ful lesion can often be demonstrated by applying firm, upward pressure in the hypogastric region at the point where the diaphragm is attached to the upper surface of the xiphoid cartilage (Fig. 139), whereupon the animal arches its back slightly, moves sideways, kicks and groans. Palpation of the abdominal wall is painful also in rumenitis and in inflammatory conditions of other abdominal organs.

In sheep and pigs, a suitable degree of relaxa­tion of the abdominal musculature to permit palpation can not be obtained; in the latter species, the thickness of the abdominal wall is a further obstacle. Both species will, however, evince a pain reaction to palpation of any part of the abdomen in peritonitis.

Palpation of the abdomen is most satisfactorily performed in the dog and cat by reason of it being possible to identify many of the intra-abdominal organs. The examination should be made with the animal standing on a table with a non-slip surface; muscular tension is greatly increased and is difficult to overcome if the animal is apprehensive by reason of uncertain footing. If the dog is too large, or it is considered undesirable to place it on a table, the examina­tion is made with it on the floor, the clinician sitting on a stool behind, and slightly to one side. During palpation, both hands, with the fingers firmly extended together, are placed one on each side of the abdomen, the thumb of each hand pointing upwards (Fig. 140). Gentle pressure is applied and then gradually increased until the tension of the muscles disappears and the under­lying organs can be identified. The procedure should be applied in a methodical manner over the whole area of the abdomen. Generally speaking, the gentler the palpation, the more readily the organs can be recognized and the more expeditiously the examination is made.

In obese animals abdominal palpation is un­rewarding and in those with a nervous disposition it may be resented. A long period of continuous gentle palpation may prove successful, otherwise administration of a sedative or tranquillizing drug may be required. In such circumstances it must be appreciated that the animal may not react when pressure is applied over a pain focus. Abdominal pain occurs in a variety of inflam­matory conditions including peritonitis, hepati­tis, splenitis, nephritis, lymphadenitis, etc. Its presence is indicated by greater than usual ten­sion of the abdominal musculature which is suddenly greatly increased when the painful area is approached. Observation of the animal may have revealed that the back is arched, and that it made voice sounds indicating pain when defaecating or urinating and during palpation.

Undulation ('fluid wave') can be demonstrated by a combination of percussion and palpation when the peritoneal cavity contains a large volume of fluid, as in ascites, exudative peritoni­tis, and rupture of the urinary or gall-bladder. For the dog and cat, the palm of one hand is placed firmly against the side of the abdomen, and the opposite side is percussed at various levels with the fingertips of the other hand. The impact of any wave currents produced in the fluid by the finger taps is detected when they impinge on the palm of the hand that is applied to the abdominal wall. In large animals an assistant is required to generate the wave currents by strong percussion. A combination of finger percussion and auscultation may be employed for the detection of fluid motion in place of the more orthodox method. Wave motion of this type can be demonstrated only when there is sufficient volume of fluid present, and it does not completely fill the peritoneal cavity.

Percussion of the abdomen generally provides limited information of diagnostic value. It is, however, possible to distinguish areas where the percussion note is loud or tympanic, from those where it is dull, and thus determine whether the underlying structure is a gas-filled portion of the alimentary tract, or a solid organ. A dull sound is obtained over the impacted stomach or intes­tine, over the spleen and liver, over neoplasms and where there is an accumulation of fluid in the peritoneal cavity. In the last condition, the upper margin of the dull area is horizontal and, if the posture of the animal is changed, the dull­ness is always located at the most dependent part of the abdomen.

The sounds produced by the functional mo­tility of the intra-abdominal portion of the diges­tive tract are detected by auscultating over the wall of the abdomen. When examining the larger animals in this way, the clinician should face caudally and run the hand along the dorsal part of the neck over the withers and back and down over the abdominal wall, pressing lightly, to prepare the animal for the application of the stethoscope. When the instrument has been applied to the abdominal wall (Fig. 141) it is necessary to listen for at least 30 seconds because the motility sounds (borborygmi) are not con­tinuous at any one point, but occur at intervals of from 10 to 20 seconds or longer. Normal peristaltic and segmentation sounds have gurg­ling, murmuring or rumbling characteristics. They are often loud enough to be audible some distance away from the animal. The type of sound reflects the character of the intestinal contents, which may be solid, semi-solid, liquid or gaseous, and the pattern of motility. According to the frequency of the sounds, motility is described as active, sluggish, infrequent or absent. The activity of the rumen and reticulum, which can be investigated by means of palpation and auscultation, will be considered during the de­tailed examination of the abdomen in the rumi­nant species.

Rectal Examination

Rectal examination is the process of palpating the interior of the pelvis and posterior abdomen by means of a hand or finger introduced into the rectum through the anus. For aesthetic and hygienic reasons, a shoulder-length rubber or plastic glove or a finger-stall should be worn. In large animals, the examination may necessarily involve introducing the whole length of the arm into the rectum. The protective glove or finger­stall should be thoroughly lubricated with soap, bland oil, petroleum jelly or a suitable proprie­tary obstetrical cream; some of the last have the advantage of being readily removable, even in cold water. This last is of no account in the case of disposable plastic items. Suitable restraint should be used which, in the horse, may consist of lifting up a foreleg or applying a twitch. For obviously fractious horses more effective safe­guards, consisting of side lines, service hobbles or stocks, are essential. Rectal examination in cattle can usually be performed with the animal tied in a stall and further restrained by an assistant standing against one side and holding the tail.

The prepared, glove-covered hand is intro­duced through the anal sphincter by extending the fingers, which are held together to form a cone with the thumb directed towards the base of the middle finger. The tone of the anal sphincter is reduced by gentle insertion of the fingers, and the hand is then inserted with a rotatory move­ment. Many horses resent this action but once the hand passes beyond the anal sphincter, manipulations which do not engender pain, cause no resentment. Force must be avoided, and forward pressure applied with considerable cau­tion. When the animal strains, no resistance must be offered; the arm should relax immedi­ately and allow itself to be pushed backwards by the mounting intra-abdominal pressure, as otherwise it is likely that the intestinal wall will be perforated. This catastrophe is invariably fatal in the horse. Palpation is performed with the open hand, the extended fingers being maintained in close apposition, or with the closed fist. If, on introducing the hand, the rectum is found to be filled with faeces these should be removed before proceeding.

Irrespective of whether a protective glove is worn or not, it is advisable to clip the fingernails quite short and, as a further safety measure, to fill the free edges with soap. In all cases, to avoid soiling the clothing, and in the interests of personal hygiene and disease control, the clini­cian should don a sleeve protector and a rubber apron or gown, which can be washed and dis­infected immediately after use (Fig. 142; see also Fig. 172, p. 246).

To reduce excessive straining during rectal examination the following expedients can be adopted: enemas of lukewarm water; elevating the animal's head; applying pressure with the thumbs in the lumbar region; administering a sedative or tranquillizing drug; induction of low epidural anaesthesia.

In small animals, rectal exploration involves the same principles as in the larger species. It is obvious that, with this method of examination the information obtained in the large animals is much more extensive than that obtainable from the small species in which, at best, only the pelvic inlet is reached with the finger. The deficiencies of rectal examination in the small animal are, however, more than made good by the results obtained from external abdominal palpation.

General Anatomical Considerations

At this point in the clinical examination pro­cedure it is expedient to consider the anatomical character and topographical arrangement and relationships of the organs and viscera situated within the abdominal cavity in the different species of domestic animals. Some of the im­portant organs are the stomach, intestines, liver, spleen and their supporting structures the omentum and mesentery, in which are situated the associated lymph nodes, as well as the kidneys, uterus and pancreas. The bladder, when disten­ded with urine, extends for a variable distance into the abdomen. Externally, in male animals of all the domestic species, with the exception of the cat, the prepuce, accommodating the free portion of the penis when retracted, is situated in the posterior part of the ventral abdomen. The testes in the stallion, bull and ram are situated in the inguinal region of the abdomen, as is the mammary gland in the mare, cow and ewe. In the sow, bitch and female cat the mammary glands, which vary in number, form two rows parallel to and a short distance away from the midline of the ventral abdomen.

The anatomical relationships, and in certain instances the physiological function of the organs within the abdominal cavity vary as between the different species of domestic animals. The difficulties in clinical diagnosis that arise from these factors become obvious during the physical examination, and are increased by the limiting influence of the abdominal wall and, in some species, the large size of the organs.