Investigation of the stomach and duodenum
Flexible
endoscopy
Amongst all of the methods used to investigate
and image the stomach and duodenum, flexible endoscopy is now the ‘gold
standard’. The original gastroscopes were fibre-optic (Hirschowitz), but now
most use a solid-state camera mounted at the instrument’s tip (Figs 51.5).
The main
Flexible
endoscopy is more sensitive than conventional radiology in the assessment of the
majority of gastroduodenal conditions. This is particularly the case with peptic
ulceration, gastritis and duodenitis. In upper gastrointestinal bleeding
endoscopy is far superior to any other investigation and in most circumstances
is the only imaging required. Although in Japan double-contrast barium meals
performed by very experienced radiologists are able to detect quite small
gastric cancers, endoscopy is far superior in most centres and also allows
biopsies to be taken.
Although
fibre-optic endoscopy is a safe and commonly used investigation, it is important
that all personnel undertaking this procedure are adequately trained and that
resuscitation facilities are always available. Although the morbidity and
mortality associated with upper gastrointestinal endoscopy is extremely low,
it is not without hazard. Careless and rough handling of the endoscope during
intubation of a patient may result in perforations of the pharynx and oesophagus.
Any other part of the upper gastrointestinal tract may also be perforated. An
inadequately performed endoscopy is also dangerous as a serious condition may be
overlooked. This is particularly the case in respect of early and curable
gastric cancer, the appearances of which may
Upper
gastrointestinal endoscopy is normally carried out under sedation usually with
incremental doses of diazepam or midazolam until the patient is adequately
sedated. Midazolam is often preferred for its amnesic effect. Sedation is of
particular concern in the case of gastrointestinal bleeding as it may have a
more profound effect on the patient’s cardiovascular stability. It has now
become the standard to use pulse oximetry to monitor patients during upper
gastro intestinal endoscopy, and nasal oxygen is often also administered.
Opiates are not usually necessary, although they are commonly used for
endoscopic retrograde cholangiopancreatography (ERCP). Buscopan is useful to
abolish duodenal motility for examinations of the second and third parts of the
duodenum. Examinations of this type ate best carried out using a side-viewing
endoscope such as is used for
ERCP
Some
patients are relatively resistant to sedation with benzodiazipenes, particularly
those who are accustomed to alcoholic beverages. Increasing the dose of benzodiazipenes
in these patients may not afford any useful sedation but merely make the patient
more restless and confused. Such patients are sometimes better endoscoped fully
awake using a local anesthetic throat spray and a narrow-gauge endoscope.
Whatever the circumstances, it is important that resuscitation facilities are
available including agents that reverse the effects of benzodiazipenes, such as
flumazenil.
The
technology associated with upper gastrointestinal endoscopy is continuing to
advance. Instrumentation is now available in many centres which allows both
endoscopy and endoluminal ultrasound to be performed simultaneously (see later).
Intervention via the endoscope is also developing rapidly. A variety of
haemostatic measures is used in the treatment of bleeding ulcers such as
injection with various substances, diathermy, heater probes and lasers. These
approaches appear to have utility in the treatment of bleeding ulcers,
although good controlled trials in this area are not abundant. There is no good
evidence that such interventional procedures at the moment work in patients who
are bleeding from very large vessels, such as the gastroduodenal artery or
splenic artery.
Contrast
radiology
Upper gastrointestinal radiology is not used
as much as in previous years as endoscopy is a more sensitive investigation for
most gastric problems. There is, however, a number of circumstances where the
barium meal is of great value and augments the value of endoscopy. These include
large hiatus hernias of the rolling type and chronic gastric volvulus where it
may be difficult for the endoscopists to determine exactly the anatomy or,
indeed, negotiate the deformity to see the
Ultrasonography
Standard ultrasound imaging can be used to
investigate the stomach, particularly in patients with neoplasia. Thickening of
the gastric wall can be seen in malignancy, some assessment made of local
invasion, and liver and peritoneal disease is often detected. However, used,
conventionally, it is less sensitive than other modalities. By contrast,
endoluminal ultrasound and laparoscopic ultrasound are probably the most
sensitive techniques available in the preoperative staging of gastric cancer. In
endoluminal ultrasound the transducer is usually attached to the distal tip of
the instrument. However, devices have been developed which may be passed down
the biopsy channel, albeit with poorer image quality. Five layers (Fig.
51.7) of
the gastric wall may be identified on endoluminal ultrasound and the depth of
invasion of a tumour can be assessed with exquisite accuracy (90 per cent
accuracy for the ‘T’ component of the staging). Enlarged lymph nodes can
also be identified and the technique’s accuracy in this situation is about 80
pet cent. Finally, it may be possible to identify liver metastases not seen on
axial imaging. Laparoscopic ultrasound is also a very sensitive imaging
modality, especially when combined with the laparoscopy (see later). It is one
of the most sensitive methods of detecting liver metastases from gastric cancer.
An additional use of ultrasound is in the assessment of gastric emptying. Swallowed contrast is utilised which is designed to be easily seen using an ultrasound transducer. The emptying of this contrast is then followed directly. The accuracy of the technique is similar to that of radioisotope gastric emptying studies (below).
Computerised
tomography (CT) scanning and magnetic resonance imaging (MRI)
The resolution of the CT scanners is
continuing to improve and this form of axial imaging is of increasing value in
the investigation of the stomach, especially gastric malignancies (Fig.
51.8).
The presence of gastric wall thickening associated with a carcinoma of any
reasonable size can be easily detected by CT but the investigation lacks
sensitivity in detecting smaller and curable lesions. It is much less accurate
in ‘T’ staging than endoluminal ultrasound. Lymph node enlargement can be
detected and, based on the size and shape of the nodes, it is possible to be
reasonably accurate in detecting nodal involvement with tumour. However, as with
all imaging techniques, it is limited. Microscopic tumour deposits in lymph
nodes cannot be detected when the node is not enlarged and, by contrast, lymph
nodes may undergo reactive enlargement but not contain tumour. These problems
apply to all imaging techniques. The detection of small liver metastases is
improving, although in general terms metastases from gastric cancer are less
easy to detect using CT than those, for instance, from colorectal cancer. This
is because metastases from gastric cancer may be of the same density as liver
and may not handle the intravenous contrast any differently. MRI scanning does
not at present offer any specific advantage in assessing the stomach, although
it has a higher sensitivity for the detection of gastric cancer liver metastases
than conventional CT imaging.
Laparoscopy
This technique is now well used in the
assessment of patients with gastric cancer. Its particular value is in the
detection of peritoneal disease that is difficult by any other technique, unless
the patient has ascites or bulky intraperitoneal disease. Its main limitation is
in the evaluation of posterior extension but other techniques are available to
evaluate posterior
Gastric
emptying studies
These are useful in the study of gastric dysmótility
problems, particularly those that follow gastric surgery. The principle of the
examination is that a radioisotope-labelled liquid and solid meal are ingested
by the patient and the emptying of the stomach is followed on a gamma camera.
This allows the
proportion of activity in the remaining in the
stomach to be assessed numerically, and it is possible to follow liquid and
solid gastric emptying independently (Fig. 51.9).
In the past tests of gastric acid secretion
were frequently performed, particularly by surgeons. Recent advances, however,
have made these tests virtually redundant except in the context of physiological
and pharmacological studies. Part of the interest in these tests related to the
higher levels of gastric acid secretion commonly found in patients with duodenal
ulcer disease (see later).
Traditionally,
basal and maximal acid output is measured. A nasogastric tube is passed into the
stomach, the basal secretion collected over 1 hour and the acid output in
millimoles calculated. To obtain the maximal acid output intramuscular injection
of the gastrin analogue pentagastrin is given at a dose of 6 pg/kg body weight
and the secretions are collected over the ensuing hour. The maximal acid output
is calculated as the peak 15-minute collection multiplied by 4 or twice the peak
30-minute collection in two consecutive collections.
A
wealth of data exists on the acid outputs in a whole range of populations.
Ultimately, the peak acid output is related to the parietal cell mass; larger
stomachs produce more acid. Although traditionally patients with duodenal ulcers
do secrete more acid than normal, there is considerable overlap between normal
and duodenal ulcer populations. Patients with gastric ulcers produce acid at
approximately normal levels. In a patient with a gastrinoma the basal acid
output is unusually high and there may be little response to pentagastrin, the
parietal cell mass already being near maximally stimulated by the gastrin
produced by the tumour. It is now known that other nongastrin peptide products
also may result in the Zollinger—Ellison syndrome.
The
insulin test was previously beloved of gastric surgeons, particularly those
interested in the quality of vagotomy. The test was originally described by
Hollander and involves the induction of hypoglycemia in a postvagotomy patient
using an intravenous soluble dose of insulin of 0.2 units/kg body weight.
Gastric acid secretion is then measured in the 2 hours following insulin
injection. The theoretical basis of the test is that the hypoglycaemia
stimulates the hypothalamic nuclei inducing a parasympathetic response. If the
vagus is intact to any degree this is reflected in a rise in gastric acid
secretion. Various criteria are used to determine whether a test is positive or
not. Distinction is often made between an ‘early’ positive test, thought to
mean that a substantial vagal innervation remains, and a ‘late’ positive
test, the significance of which is less clear. Although in these tests they did
correlate to some degree with ulcer relapse following vagotomy, their use in
patient management was always limited as they are performed postoperatively
and therefore could not influence patient management. In this respect the
intraoperative Grassi test may have been a more useful method of controlling the
quality of vagotomy. However, all of these tests are virtually redundant as
vagotomy is now uncommonly performed on the elective situation.
24-hour
intragastric pH monitoring
Studies of this type became very popular
during the 198 Os, particularly in the investigation of new gastric
antisecretory agents. The pH within the stomach is measured over a 24-hour
period either by the passage of a nasogastric tube and regular aspiration or by
placing a radiotelemetry capsule on a tether within the stomach and monitoring
the pH with an externally worn aerial. The median daytime, night-time or 24-hour
intragastric pH can thus easily be calculated and, by converting the pH to
hydrogen ion concentration, the median intragastric acidity over various periods
can be studied. This latter manoeuvre allows the percentage reduction in acidity
produced by a pharmacological agent to be measured (the step of converting pH to
hydrogen ion concentration is obviously vital as pH is a logarithmic scale).
Although of great physiological and pharmacological interest, these tests have
little clinical relevance.
Measurement of
plasma gastrin