The anterior abdominal wall extends from the lower costal margin down to the iliac crests, inguinal ligaments and the symphysis pubis. However, the abdominal cavity passes up behind the rib cage under the diaphragm, to the level of the fourth intercostal space, and down into the pelvis to the pelvic diaphragm, formed by the levator ani muscles. The anterior and lateral aspects of the abdominal wall are formed of the three layers of flat abdominal wall muscles (table 1) that contain and compress the abdominal contents (defecation, micturition, coughing and parturition) and participate in respiratory movements, and flexion and rotation of the trunk. Posteriorly, the wall is formed by the erector spinae muscles, with the psoas and quadratus lumborum lying within the cavity (page 86, table 2).
Table 1 Muscles of the anterior abdominal wall
Table 2 Muscles of the posterior abdominal wall
The abdominal cavity is lined by parietal peritoneum, which is reflected from the posterior wall around the gut and abdominal organs as the visceral peritoneum. Sensation from the parietal peritoneum (usually due to inflammation), is appreciated directly over it, whereas that of the visceral peritoneum, may be referred to its dermatome of derivation (e.g. sensation from under the diaphragm is referred to the tip of the shoulder and that of the small gut to the umbilicus).
For descriptive and recording purposes, the anterior abdominal wall is divided by two horizontal and two vertical lines, into nine regions (figure 15). The horizontal lines are the subcostal and transtubercular and the vertical lines pass through the midinguinal point and cross the costal margin at the ninth costal cartilage. From above downwards, the nine regions are: centrally, the epigastric, umbilical and suprapubic, and, on each side, the hypochondral, lumbar and iliac. Each lumbar region extends laterally and posteriorly into the loin.
Figure 15 Abdominal planes
1. Vertical line through midinguinal point
3. Transpyloric plane
4. Right and left hypochondria
5. Subcostal line
7. Lumbar regions
8. Transtubercular line
9. Right and left iliac fossae
Another useful landmark is the horizontal transpyloric plane, midway between the suprasternal notch and the symphysis pubis. It crosses the body of the second lumbar vertebra, passes through the pylorus, just above the hilum of the right kidney and just below the hilum of the left kidney (figure 16). In clinical practice it is also common to refer to the four quadrants of the abdomen (upper, lower, right, left) when describing the location of abnormal signs.
Figure 16 Abdominal viscera
7. Left (splenic) flexure of colon
9. Second part of duodenum
10. Right (hepatic) flexure of colon
11. Duodenojejunal flexure
12. Transverse colon
13. Ascending colon
14. Descending colon
15. Terminal ileum
18. Sigmoid colon
Abdominal pain is a common symptom and, in view of the large number of possible causes, it can present difficulty of diagnosis (table 3). A detailed history of the pain is essential. The symptom is often specific to a diseased organ and specific pathologies, as considered below. No attempt is made to provide a detailed pathway for the investigation of all types of abdominal pain, but the differential diagnosis is considered in each area and selected tables, including extra-abdominal causes of abdominal pain (table 4).
Table 3 Acute abdominal pain
Table 4 Non- abdominal causes of abdominal pain
The site of the pain is often helpful in diagnosis. Epigastric pain may be related to diseases of the stomach and duodenum, and is often related to meals; weight loss is a particular feature of gastric as well as other intra-abdominal neoplasms. Gastroenteritis may produce central abdominal pain and tenderness, and may be accompanied by vomiting and diarrhea. The causes of dysphagia are considered in table 5 and figure 17 is an example of one of these disorders.
Biliary pain is commonly in the right hypochondrium and radiates through to the interscapular region. Subphrenic inflammatory irritation, such as an abscess, can present with referred pain to the tip of the shoulder.
Small gut pain is characteristically around the umbilicus and may be colicky in nature, as in intestinal obstruction, and associated with distension, vomiting and constipation. The commonest cause of intestinal obstruction is adhesions, but examine the hernial orifices routinely, and specifically whenever obstruction is present.
Appendicular pain often starts centrally, at the umbilicus, before moving to the right iliac fossa. Severe central abdominal pain radiating through to the back may be due to acute pancreatitis, or ruptured and dissecting abdominal aortic aneurysms. In the latter, check for the loss of one or both femoral pulses.
Table 5 Dysphagia
Pain and tenderness in the left iliac fossa may be due to diverticulitis or other large bowel pathology. Alteration in bowel habit in middle age and later life must be considered as due to cancer until proved otherwise. Gynecological problems, such as dysmenorrhea, salpingitis, ruptured ovarian cyst, ectopic pregnancies and the complications of pregnancy usually present with lower abdominal, often suprapubic, pain.
Renal pain is typically in the lumbar region but may radiate to the inguinal region and scrotum, as can incipient or obstructed hernias. The diagnosis of abdominal pain is further complicated, by radiating pain from the chest or a nerve root, and referred pain from other conditions, extra-abdominal causes are considered in table 4.
Vomiting occurs in many abdominal conditions. Examine its contents to detect the smelly and undigested food or pyloric obstruction, or the feculent brown fluid of intestinal obstruction. When associated with diarrhea the vomiting may be due to gastroenteritis. Gastrointestinal hemorrhage may have no abnormal abdominal symptoms or signs, but a full history and examination are essential in its differential diagnosis. A full small gut history and examination is essential in the differential diagnosis of malabsorption.