The different types of abdominal wall hernias and their features are listed in Box 19.1. Abdominal wall hernias are generally easy to characterise as a cough impulse is usually present, the hernia may present in a characteristic position and it may be possible to reduce the hernia. To separate other masses found within the abdominal wall from masses within the abdominal cavity, ask the patient to contract the anterior abdominal muscles by lifting his or her head from the examining couch with hands behind head, or to straight leg raise both legs simultaneously while keeping the head on the bed. This may help to define the mass as follows:

• A mass within the abdominal cavity (the peritoneal cavity) will be made less distinct, less easy to palpate and may disappear altogether until the abdominal wall muscles are relaxed again.

Box 19.1 Causes of abdominal wall masses

Lumps that could occur anywhere on the body

These arise in the skin and subcutaneous fat and include:

• lipoma;

• sebaceous cyst; and

• neurofibroma.

Lumps specific to the anterior abdominal wall

• Paraumbilical: the neck of the hernia is just lateral to the umbilical scar. Usually present later in life.

• Epigastric: knuckle of extraperitoneal fat extrudes through a small linea alba defect, between xiphoid process and umbilicus. Usually small (under 2 cm), commonly irreducible, no cough impulse.

• Spigelian: rare. Found along linea semilunaris at lateral edge of rectus sheath. Usually a third of the way between the umbilicus and the pubis.

Divarication of the rectus muscles

• Supraumbilical elliptical bulging of attenuated linea alba between the recti when the patient strains. Not a true hernia and no cough impulse.

Figure 19.2 Unexpected palpable metastatic melanoma. Patient presented for assessment of dementia.

• A mass within the abdominal wall muscle layers becomes less easy to define when the abdominal wall muscles are contracted, but is less likely to disappear altogether than the type above.

• A mass that is within the abdominal wall but that is superficial to the abdominal wall muscles will be made more obvious when the abdominal wall muscles are contracted, as it is then palpated against the tightened abdominal wall muscles.

Retroperitoneal Masses

The retroperitoneal region is subdivided into five regions:

• a central column containing the great vessels and surrounding lymph nodes and the pancreas and duodenum overlying them;

• two lateral upper regions containing the kidneys and adrenals, plus the ascending colon on the right and the descending colon on the left; and

• two lateral lower regions that lie below the posterior brim of the pelvis and contain the right ureter and caecum on the right, and the left ureter and the lower descending colon on the left.

Palpation features of retroperitoneal masses

Retroperitoneal masses are fixed by their retroperitoneal attachments and do not move on palpation or with respiration. Retroperitoneal masses in the upper lateral regions may be ballotable on bimanual palpation. This sign is elicited by dipping the fingers of one hand into the renal angle while palpating the corresponding point on the anterior abdominal wall with the other hand. The mass is then held forward by pressure from the posterior hand and may be felt by the other hand palpating through the anterior abdominal wall.

The classic ballotable mass is an enlarged kidney. A mobile but normal right kidney is sometimes ballotable in thin patients. Other laterally placed masses, such as cancers of the ascending and descending colon, are rarely ballotable. Adrenal masses are not ballotable because they are situated above the posterior-inferior chest wall margin. An enlarged spleen is not ballotable. As the spleen enlarges, the lower pole of the spleen expands downwards and forwards into the abdomen while the upper pole remains covered by the posterior rib cage.

Masses in the central column are covered behind by the spine and the erector spinae muscles whereas masses in the lower lateral regions are protected by the pelvis.

Intraabdominal Masses

Site

On the basis of position (Fig 19.1), we can start to define the likely organ of origin of an intraabdominal mass as shown in Table 19.1. However, we cannot be certain of the organ of origin of a palpable mass on the basis of its position alone. Organs do not necessarily enlarge concentrically from a fixed point. The pattern of enlargement may be determined by surrounding structures, by retroperitoneal attachments and by the pathological process responsible for the organ enlargement. The liver, for example, is limited by the diaphragm along the superior surface and by the diaphragm and ribs along the lateral surface and so tends to enlarge downwards and inwards. The uterus and bladder are limited by the pelvic walls laterally and below and so tend to enlarge upwards in the midline. The kidneys, aorta and pancreas are retroperitoneal and limited behind by the posterior abdominal wall and so tend to expand from their original site in all directions except posterior. An enlarged segment of small bowel is usually not found in the upper reaches of the abdomen because the transverse mesocolon, the transverse colon and the greater omentum are attached to retroperitoneal tissues along a horizontal line at the level of the inferior border of the pancreas. These three organs tend to form a barrier restricting upward migration of small bowel masses.

Table 19.1 Organ of origin of intraabdominal masses by region

Right hypochondrium	Epigastrium	Left hypochondrium
Right lobe of liver	Stomach	Spleen
Gall bladder	Left lobe of liver	Pancreas^∗
	Pancreas^∗	Stomach
	Lymph nodes^∗
	Aorta^∗
Right lumbar region	Periumbilical	Left lumbar
Ascending colon^∗	Omentum	Descending colon^∗
Right kidney^∗	Transverse colon	Left kidney^∗
	Aorta^∗
	Retroperitoneal nodes^∗
Right iliac fossa	Hypogastrium	Left iliac fossa
Appendix	Bladder	Sigmoid colon
Caecum^∗	Uterus	Iliac aneurysm^∗
Iliac aneurysm^∗	Right and left ovary^∗	Left ovary^∗
Right ovary		Iliac nodes^∗
Iliac nodes^∗