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ABDOMINAL ULTRASOUND
Hypertrophic pyloric stenosis (HPS)
HPS is a condition occurring in newborn infants
commonly about 6 weeks of age when the pyloric
muscle becomes hypertrophied and elongated,
restricting the passage of gastric contents, causing
projectile vomiting. Most infants with HPS are
found to have a hypochloraemic alkalosis and,
when seen in association with a palpable epigastric
mass the size of an olive on test feeding, the diagnosis
is clear without the need for ultrasonic imaging.
However, ultrasound is very successful in
demonstrating HPS in approximately 20% of
infants in whom the pyloric olive cannot be palpated.
26,27
The baby should be positioned comfortably right
side down and the stomach and pylorus identified
usually just to the right of the midline in the low epigastric
region. A small feed, of approximately 20–
30 ml of sugared water (preferable to milk as it does
not contain echoes which may obscure vital detail),
may be used to aid visualization of the gastric antrum
if the stomach is empty. A nasogastric tube may also
be used to administer clear fluid in a controlled way
providing that the gastric position of the tube is confirmed
prior to injection of the fluid. A small, highfrequency
linear or curved linear transducer is best.
The pylorus projects into gastric lumen and is
outlined by the fluid. HPS can be confirmed by the
demonstration of:
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Table 9.4
Wilms’ tumour
Neuroblastoma
Hepatoblastoma
Hepatocellular carcinoma
Rhabdomyosarcoma
Leukaemia
Lymphoma
Paediatric abdominal malignancies
thickened and elongated pyloric muscle
increased but ineffective peristalsis
failure of the pylorus to relax and open
Various figures have been quoted for muscle
thickness in hypertrophic pyloric stenosis ranging
from 2.5 to 5 mm but 3 mm is most commonly
accepted 28,29 (Table 9.5).
It must be stressed that the examination is
dynamic and measurements of muscle thickness
must be interpreted in conjunction with the observations
of gastric peristalsis and failure of the
pylorus to relax normally. Sensitivity and specificity
of 97% and 99% for the diagnosis of HPS have been
reported in expert hands (Fig. 9.14). If clinical suspicion
persists after a negative ultrasound, a repeat
examination after 1 or 2 days may be performed to
exclude an evolving pyloric stenosis.
Intussusception
Intussusception is the invagination of a segment of
bowel into the lumen of the adjacent bowel. It is a
common paediatric emergency, especially in
younger children aged 3 months to 3 years, and
tends to affect the ileocaecal region.
The child presents with abdominal pain, sometimes
with a palpable mass, vomiting or rectal bleeding.
Intussusception can result in bowel necrosis and
subsequently perforation requiring surgery.
The ultrasound appearances of bowel within
bowel are characteristic. In cross-section, the
bowel assumes a ‘doughnut’ configuration, with
concentric rings of bowel wall (Fig. 9.15). Dilated
loops of fluid-filled obstructed bowel may be
demonstrated proximal to the intussusception.
The use of ultrasound to diagnose this condition
is highly reliable, 30 reducing or eliminating the
need for contrast radiology.
An air enema is most commonly used to reduce
the intussusception using inflation pressures of up
to 120 mmHg. Hydrostatic reduction (that is,
with water/saline) under fluoroscopic or ultrasound
control is also an accepted treatment. 31
Table 9.5
Pyloric muscle dimensions
Normal
pylorus
Pyloric length < 15 ≥ 16
(mm)
Pyloric width < 11 ≥ 11
(mm)
Muscle thickness < 2.5 ≥ 3
(mm)
Hypertrophic
pyloric stenosis