1. health and fitness
2. disease

Radiology
Review
Marta Hernanz-Schulman,
MD
Index terms:
Infants, gastrointestinal tract
Pylorus, stenosis, 724.1431
Radiography, in infants and children,
70.1231
Review
Ultrasound (US), in infants and
children, 70.12981
Published online before print
10.1148/radiol.2272011329
Radiology 2003; 227:319 –331
Abbreviations:
IHPS ⫽ infantile hypertrophic pyloric
stenosis
UGI ⫽ upper gastrointestinal
examination
1
From the Department of Radiology
and Radiological Sciences, Vanderbilt
University Medical Center, MCN
D-1120, 21st Ave and Garland St,
Nashville, TN 37232. Received August
6, 2001; revision requested September 25; revision received February 22,
2002; accepted March 14. Address
correspondence to the author (email: [email protected]).
©
RSNA, 2003
Infantile Hypertrophic Pyloric
Stenosis1
Infantile hypertrophic pyloric stenosis is a common condition affecting young
infants; despite its frequency, it has been recognized only for a little over a century,
and its etiology remains unknown. Nevertheless, understanding of the condition
and of effective treatment have undergone a remarkable evolution in the 20th
century, reducing the mortality rate from over 50% to nearly 0%. The lesion is
characterized by gastric outlet obstruction and multiple anatomic abnormalities of
the pyloric antrum. The antropyloric muscle is abnormally thickened and innervated, and the intervening lumen is obstructed by crowded and redundant mucosa.
Recognition of the obstructive role of the mucosa led to discovery of effective
surgical treatment. Accurate clinical diagnosis in patients in whom a thickened
antropyloric muscle is not readily palpable can be difficult, resulting in delayed
diagnosis and can lead to emaciation and electrolyte imbalance, making the patient
a suboptimal surgical candidate. Current imaging techniques, particularly sonography, are noninvasive and accurate for identification of infantile hypertrophic pyloric
stenosis. Successful imaging requires understanding of anatomic changes that occur
in patients with this condition and plays an integral role in patient care. Accurate,
rapid, noninvasive imaging techniques facilitate rapid referral of vomiting infants
and prompt surgical treatment of more suitable surgical candidates.
©
RSNA, 2003
The lyf so short, the craft so long to lerne
Thassay so hard, so sharp the conquering.
Chaucer (1)
Infantile hypertrophic pyloric stenosis (IHPS) is a condition affecting young infants, in
which the antropyloric portion of the stomach becomes abnormally thickened and manifests as obstruction to gastric emptying. Typically, infants with IHPS are clinically normal
at birth; during the first few weeks of postnatal life, they develop nonbilious forceful
vomiting described as “projectile.” Gastric outlet obstruction leads to emaciation and, if
left untreated, may result in death. Surgical treatment is curative. The clinical diagnosis
hinges on palpation of the thickened pylorus, or “olive.” Abdominal palpation is accurate
but not always successful, depending on factors such as the experience of the examiner,
the presence of gastric distention, and a calm infant.
Although its etiology remains unknown, our understanding of the clinical manifestation and treatment of IHPS has undergone a remarkable evolution. In patients in whom
clinical examination is unsuccessful, modern imaging techniques are highly accurate in
facilitating the diagnosis. The radiologist, therefore, plays a key role in the initial care of
these infants and the appropriate surgical referral. It is important that the radiologist
understand the anatomic changes of the pyloric channel in affected infants as reflected by
imaging techniques.
The purposes of this review are to describe the imaging diagnosis of IHPS and to outline
the gross and histopathologic correlates of IHPS within the context of its historical
evolution and our current understanding of the lesion.
HISTORICAL PERSPECTIVE
IHPS is familiar to most pediatric practitioners and is the most common condition
requiring surgery in infants (2). Despite its frequency among Western populations in the
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northern hemisphere, it was virtually unknown prior to 1627, when a clinical description with survival was reported by
Fabricious Hildanus (1). Over the subsequent 2 centuries, only approximately
seven additional cases were described,
some without pathologic proof and of
doubtful origin (Table). At the German
Pediatric Congress in Wiesbaden in 1887,
Harald Hirschsprung (Fig 1) described
two infant girls with pathologically
proved IHPS, and his seminal article,
published in 1888 (3), triggered a profusion of scientific interest in the condition. By 1910, approximately 2 decades
later, 598 cases had been recognized.
Nevertheless, even as late as 1905, its existence was still occasionally doubted (1).
As we enter the 21st century, the etiology
of the condition remains elusive, yet
great strides have been made in the diagnosis and treatment of IHPS.
orifice and pyloric ring or sphincter. The
pyloric orifice marks the opening of the
stomach into the duodenum (Fig 2b).
EPIDEMIOLOGY
IHPS Anatomy
The incidence of IHPS is approximately
two to five per 1,000 births per year in
most white populations, although it varies with the geographic area and the time
period being reviewed (4,5). IHPS is less
common in India and among black and
Asian populations, with a frequency that
is one-third to one-fifth that in the white
population (6). The male-to-female ratio
is approximately 4:1, with reported ratios
ranging from 2.5:1 to 5.5:1 (7). There is a
familial link, but a hereditary propensity
to the development of IHPS is likely polygenic with no single locus accounting for
a greater than fivefold increase in the risk
to first-degree relatives (7). Male and female children of affected mothers carry a
20% and 7% risk of developing the condition, respectively, whereas male and female children of affected fathers carry a
risk of 5% and 2.5%, respectively. Probandwise concordance in monozygotic
twins is 0.25– 0.44, and that in dizygotic
twins is 0.05– 0.10 (8).
In infants with IHPS, the pyloric ring is
no longer identifiable as a clearly definable separation between the normally
distensible pyloric antrum and the duodenal cap. Instead, a channel of variable
length (1.5–2.0 cm) corresponding to the
pyloric canal separates the normally distensible portion of the antrum from the
duodenal cap (Fig 3a). This channel is
characterized by thickened muscle,
which changes rather abruptly from the
normal 1-mm thickness in the distensible portion of the antrum to 3 mm or
more in the hypertrophied canal (12).
The muscle thickness may be greater
than 6 mm, with larger muscle usually
being present in larger and older infants
(12,13). The diameter of the canal lumen
is variable, ranging between 3 and 6 mm;
the canal lumen is filled with compressed
and redundant mucosa, presenting an
obstructed passage to the gastric contents
(Fig 3b) (15). The rigid antropyloric canal
is unable to accommodate the redundant
mucosa, which protrudes into the gastric
antrum. When viewed endoscopically,
the mucosa protrudes as a nipplelike projection (Fig 3c) (16), likened to a “cauliflower” by DeBacker et al (17).
ANATOMY
Normal Anatomy
The incisura angularis divides the stomach into a body to the left and a pyloric
portion to the right. The sulcus intermedius further divides the pyloric portion of
the stomach: the pyloric vestibule to the
left, denoted by an outward convexity of
the greater curvature, and the pyloric antrum or pyloric canal to the right (Fig 2a).
The pyloric antrum is approximately 2.5
cm in length and terminates at the pyloric
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Historical Perspective on Diagnosis of IHPS
Practitioner and Year
Fabricious Hildanus, 1627
Patrick Blair, 1717
Christopher Weber, 1758
George Armstrong, 1777
Hezikiah Beardsley, 1788
Michael Underwood, 1799
Thomas Williamson, 1841
Siemon-Dawosky, 1842
Harald Hirschprung, 1888
Various, 1910
Description
First reported clinical description with survival
Postmortem description, with lack of omentum, which was
believed to be related to cause of lesion
Postmortem description
Two cases, familial occurrence
First account in United States: Child died at age 5 years;
most likely a case of antral diaphragm
Postmortem description
Postmortem description
Postmortem description includes “hypertrophy of the
submucous cellular tissue”
Rigorous description of two proved cases
Descriptions of 598 cases
Source.—Reference 1.
CLINICAL PRESENTATION
The clinical presentation varies with the
length of symptoms. The infant presents
with a recent onset of forceful nonbilious
vomiting, typically described as “projectile.” The emesis consists of gastric contents, which may become blood tinged
Figure 1. Harald Hirschsprung (1830 –1916).
Dr Hirschsprung’s postmortem description of
two cases led to the recognition of IHPS by the
scientific community and ushered in the interest and research leading to our modern understanding and treatment of the condition. (Reprinted, with permission, from reference 2.)
with protracted vomiting, likely related
to gastritis. Initially intermittent, the frequency of vomiting increases to follow
all feedings. Since the child is unable to
achieve adequate nutrition, he or she exhibits a voracious appetite despite distention of the stomach. Starvation can exacerbate diminished hepatic glucoronyl
transferase activity, and indirect hyperbilirubinemia may be seen in 1%–2% of
affected infants. Vomiting of gastric conHernanz-Schulman
Radiology
Figure 2. (a) Schematic of gastric segmental anatomy. (Reprinted, with permission, from reference 9.) (b) Endoscopic photograph
of open pyloric sphincter. Arrow ⫽ open canal. (Reprinted, with permission, from reference 10.)
Figure 3. (a) Illustration of pyloric antrum in IHPS. Note circumferentially thickened muscle
(arrows). The lumen is shown as a narrowed canal, but the mucosa, which fills and obstructs the
lumen, is not illustrated. (Reprinted, with permission, from reference 11.) (b) Close-up view of
hypertrophied pylorus from specimen of infant dying of IHPS. Abnormally thickened antropyloric muscle stops abruptly at the duodenal cap (D) and antrum (A). Note thickened mucosa
within opened canal lumen curving from the antrum into the pyloric channel (curved arrows)
deep to muscle (M). (Reprinted, with permission, from reference 14.) (c) Endoscopic photograph
of pyloric sphincter in a patient with IHPS. Note mucosa (M) protruding into normal antrum,
occluding and obstructing the pyloric orifice. Compare with Figure 2b. (Reprinted, with permission, from reference 16.)
tents leads to depletion of sodium, potassium, and hydrochloric acid, which results
in hypochloremic alkalosis and sodium
and potassium deficits. Renal mechanisms
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ume conserve sodium at the expense of
hydrogen ions, leading to paradoxical aciduria. Weight loss may be extensive, and the
infant may be below birth weight at the
time of presentation to the radiologist.
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Weight loss and dehydration coupled
with an insatiable appetite lead to a characteristic facies, with a furrowed brow,
wrinkled appearance, and prominent
sucking pads, resembling an old man crying inconsolably and gnawing at his or
her fist. In emaciated infants, the distended stomach may be identifiable in
the hypochondrium, with active peristaltic activity visible through the thin abdominal wall (Fig 4).
Figure 4. Infant with
IHPS. Note protruding rib
cage and scaphoid abdomen through which the
distended stomach and
prominent peristaltic activity can be seen. (Reprinted, with permission,
from reference 18.)
ETIOLOGIC CONSIDERATIONS
Despite the frequency of IHPS, our current familiarity with the condition, and
the success of modern surgical management, its etiology remains elusive. In the
search for an etiologic condition or
event, researchers have focused on findings associated with the condition, some
of which seem foolish from our more
sophisticated perspective. For example,
in 1717 the lack of omentum noted at
autopsy, which was likely a result of nutritional deprivation, led to a report that
this might be related to the cause of the
lesion. The identification of three of 11
cases as being children of physicians resulted in the condition being identified
as a disease “of the intellectual classes” in
1910. In 1917, Palmer suggested a link to
thymic hyperplasia (1,19), which he subsequently recanted.
During the past decade, advanced
techniques have been applied to examination of the hypertrophied muscle, with
some interesting results. It has been
found that, when compared with control
specimens, the muscular layer is deficient
in the quantity of nerve terminals (20),
markers for nerve-supporting cells (Fig
5a) (21), peptide-containing nerve fibers
(22,23), nitric oxide synthase activity
(24), messenger RNA production for nitric oxide synthase (25), and interstitial
cells of Cajal (26,27) and that it contains
increased insulin-like and platelet-derived growth factors (Fig 5b) (2) and increased expression of insulin-like growth
factor–I messenger RNA (28). It is postulated that this abnormal innervation of
the muscular layer leads to failure of relaxation of the pyloric muscle; increased
synthesis of growth factors; and subsequent hypertrophy, hyperplasia, and obstruction (29). An increased incidence of
IHPS in neonates receiving erythromycin
has been reported (30). The reason for
this remains unclear, although a prokinetic effect on gastric muscle contraction
is postulated.
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Figure 5. (a) Photomicrographs show immunocytochemical localization of D7, a marker for peripheral
Schwann cells, in pyloric muscle of a healthy patient (left) and of a patient with IHPS (right). Staining of
myenteric plexus (large arrow) is similar in both; however, there is a striking reduction in the intramuscular nerve fibers (small arrows) in the patient with IHPS. cm ⫽ circular muscle layer, lm ⫽ longitudinal
muscle layer. (Peroxidase technique; original magnification, ⫻100.) (Reprinted, with permission, from
reference 21.) (b) Photomicrographs show immunohistochemical peroxidase staining for platelet-derived
growth factor receptor in a healthy patient (left) and in a patient with IHPS (right). The muscle of the
healthy patient shows no evidence of immunoreactivity, whereas there is abundant staining in the muscle
of the patient with IHPS. (Original magnification, ⫻400.) (Reprinted, with permission, from reference 1.)
Hernanz-Schulman
Radiology
Figure 6. Longitudinal sonogram of the normal stomach, pyloric ring (cursors), and duodenum outlining the open pyloric ring in an
infant without IHPS. The distance between
cursors is 3.1 mm.
A variable degree of thickening of the
mucosa within the canal leading to obstruction of the lumen has also been described (15). The lumen of the canal is
wider than the normal pyloric ring (Fig
6), but it is obstructed and filled with
redundant mucosa. The mucosa filling
the canal typically equals or exceeds the
muscle thickness but at times may far
exceed it (Fig 7). In histologic descriptions of the mucosa, submucosal edema
and cellular infiltrates have been reported (15,31). Foveolar hyperplasia after
administration of prostaglandins has
been implicated in the development of
this condition (32). The hypergastrinemia hypothesis proposes that an inherited increase in the number of parietal
cells initiates a cycle of increased acid
production, repeated pyloric contraction, and delayed gastric emptying (33).
Development of IHPS after initiation of
feedings, increased postprandial gastrin
levels, markedly increased gastric acid secretion in infants with IHPS, and the induction of IHPS in puppies by means of
pentagastrin infusion (34) support this hypothesis. However, which if any of these
associated muscular and mucosal phenomena hold the key to initiation or development of the lesion remains uncertain.
Certain intriguing characteristics of
the development and resolution of IHPS
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Figure 7. Imaging-histopathologic correlation of exaggerated mucosal thickening that occurs in some infants with IHPS. Top left: Image
from upper gastrointestinal tract examination (UGI) shows a markedly widened pyloric channel with intervening mucosal filling defect
(arrows). Top right: Sonogram in same patient shows hypertrophied
mucosa (straight arrows) measuring approximately 8 mm protruding
into the gastric antrum (curved arrow). Arrowheads ⫽ thickened
pyloric muscle. (Reprinted, with permission, from reference 15.) Bottom: Histopathologic full-thickness biopsy specimen from another
patient shows thickened, hypertrophied, and edematous mucosa
(muc) and its relationship to the underlying hypertrophied musculature (MUS). (Reprinted, with permission, from reference 31.)
likely hold a key to the etiologic event(s) in
the initiation of IHPS. The condition is
seldom present at birth, but rather the
functional obstruction typically develops
in the first 2–12 weeks of life. Sonographic evaluation indicates that the
anatomy is also normal at birth (35). Relief of the obstruction by means of incision of the muscular layer leads to a relatively rapid involution of the muscle
and return of the anatomy to normal. As
early as 4 months after surgical treatment, assay results for nerve growth factor, interstitial cells of Cajal, and nitric
oxide synthase have returned to normal
levels, coincident with anatomic resolution of the lesion (27). Resuturing of the
muscle does not relieve the obstruction
and may result in surgical failure, as recognized by Ramstedt in 1911. If failure to
relieve the obstruction does not result in
death, the condition eventually resolves.
On the other hand, bypassing the obstruction may result in persistence of the
hypertrophied muscle for many years
(36). Thus, it is difficult to postulate that
the undeniable abnormalities of the muscular layer are congenital, given their
rapid resolution after relief of obstruction
and the absence of functional or anatomic abnormalities at birth. These facts
suggest that an obstructing event at the
gastric outlet may initiate a feedback cycle, resulting in obstruction that resolves
once the obstruction is relieved and normal gastric activity resumes.
At present, the etiologic events underlying the development of IHPS remain difficult to extricate from the multiplicity of
associated findings. Further investigation is
necessary to identify the pathophysiology
of IHPS, which could result in prevention
of the condition or identification of an effective nonsurgical treatment.
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Figure 8. Fluoroscopic image from UGI in a patient with IHPS. Contrast material courses through
the mucosal interstices of the canal, forming the
double-track sign (large arrowheads), with an additional central channel along the distal portion
(small arrowhead). Mass impression on the gastric antrum (arrow), best seen during peristaltic
activity, is termed the shoulder sign.
DIAGNOSIS
The diagnosis of IHPS is initially suggested by the typical clinical presentation. Palpation of the hard muscle mass,
or olive, is diagnostic but is often challenging and time consuming. In experienced hands and with adequate time and
preparation, abdominal palpation can be
successful in 85%–100% of infants (37).
However, increased reliance on rapid and
accurate imaging techniques has led to a
decline in this rate. For example, in a
study by Macdessi and Oates (38), palpation was successful in 87% of infants between 1974 and 1977 but in only 49%
between 1988 and 1991. Further, this is
not construed as being necessarily counterproductive, since the desired outcome
is rapid and accurate diagnosis (39). Palpation requires a calm infant with relaxed abdominal musculature, which is a
difficult accomplishment in these hungry babies. Sedation of infants has been
suggested to facilitate the examination
(18); given the ease of sonographic diagnosis, this does not seem indicated in a
child who may vomit while sedated. The
distended stomach may rise anterior to
the pylorus, rendering the examination
nondiagnostic unless the stomach is
evacuated by means of nasogastric drainage. In cases in which physical examination is unsuccessful, other methods must
be used to establish the diagnosis.
Several techniques involving insertion
of a nasogastric tube have been proposed
over the years. In 1913, Ramstedt indi324
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Figure 9. Sonograms demonstrate transducer sweep from esophagus to pylorus in a patient with
IHPS. Left: Transducer is placed transversely, below the xiphoid, allowing identification of the
esophagus (E) anterior to the aorta (A) at the gastroesophageal junction. Middle: Transducer is
swept in caudal direction to outline a distended, albeit gas-filled, stomach (S). Right: Gastroduodenal junction is shown bridged by the hypertrophied pylorus, with fluid-filled duodenal cap
(arrow). In this case, the pyloric mucosa is of the same echogenicity as gastric contents, which
could lead to a false impression of unimpeded gastric emptying. A ⫽ antrum.
cated that exploratory laparotomy was
preferable to undue delay in surgery in
infants in whom the diagnosis was uncertain (1). Hessa in 1912 and Howard in
1917 suggested insertion of a duodenal
catheter to help determine the degree of
gastric obstruction (1). Insertion of a nasogastric tube for assessment of the volume in the stomach is still occasionally
advocated today (40).
The roentgen ray was first applied to
the diagnosis of IHPS in 1903 by Ibrahim,
without success. Fluoroscopic techniques
were proposed by Abram and Strauss in
1918. By 1942, however, Mack (1) reported that “there is no universal agreement on the reliability of x-ray studies.”
Over the subsequent 4 decades, improvements in fluoroscopic equipment and
greater familiarity of radiologists with the
condition permitted the UGI (“barium
meal”) to become widely used in cases in
which palpation of the olive was unsuccessful at clinical examination.
In 1977, Teele and Smith (41) published
a report on five cases in which a correct
diagnosis was rendered after using articulated-arm B-mode sonography; this initiated a proliferation of articles on the sonographic diagnosis of IHPS. These articles,
coincident with the introduction of realtime capability and improvements in
equipment resolution aimed at defining
the measurements of the abnormal canal,
generated controversy regarding normal
and abnormal values and suggestions regarding various indices and signs to help
establish the diagnosis (42– 45). In 1988,
the author of an editorial (46) suggested
that the diagnosis should be made clinically by means of repeated attempts to palpate the olive, eschewing imaging techniques as time consuming and often
inaccurate. Authors of subsequent publications (40,47,48) have addressed the issue of
cost-effectiveness, suggesting that the use
of sonography does not justify the cost, as
compared with the cost of UGI. In 1994,
De Backer et al (17) proposed endoscopy as
the most expeditious and accurate method
for the diagnosis of IHPS.
CURRENT CONSIDERATIONS
It is clear that for a diagnostic study to
become the imaging modality of choice,
it must be demonstrated to be, above all,
accurate; further, the procedure should
be noninvasive and should be able to be
performed quickly so that results will be
available immediately, without delay in diagnosis. The examination must allow unequivocal differentiation between normal
Hernanz-Schulman
Radiology
Technique and Imaging Findings
UGI Studies
Figure 10. Sonograms demonstrate transducer sweep from esophagus to pylorus in a patient
without IHPS. Left: The esophagus (E) is seen anterior to the aorta (A), allowing identification of
the caudal gas-filled viscus to the left as the stomach (S). Right: Normal empty antrum (A) is seen
adjacent to the duodenal cap (D).
Figure 11. Sonograms in a patient with IHPS. (a) Longitudinal sonogram shows anterior thickened
muscle (cursors). Double layer of crowded and redundant mucosa fills the channel and protrudes into
fluid-filled antrum (arrow). D ⫽ fluid-filled duodenal cap. (b) Cross-sectional sonogram shows circumferential muscular thickening (cursors) surrounding the central channel and filled with mucosa (M).
and abnormal conditions. At present, there
are two valid and successful methods for
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the imaging diagnosis of IHPS, the UGI
and sonography.
Abnormal study.—In patients with IHPS,
there is failure of relaxation of the prepyloric antrum, typically described as
“elongation” of the pyloric canal. The
canal is outlined by a string of contrast
material coursing through the mucosal
interstices, termed the string sign; or by
several linear tracts of contrast material
separated by the intervening mucosa (Fig
8). The latter is termed the double-track
sign. This sign demonstrates the intervening redundant mucosa outlined as a
filling defect by the contrast material; it
was reported as specific for IHPS by Haran
et al in 1966 (49) and, therefore, may aid
in differentiation from pylorospasm. Interestingly, the fact that the redundant
mucosa in the canal is responsible for the
filling defect between the channels of
contrast material was not recognized by
the authors in the illustration included in
the original article.
UGI is performed with the infant in
the right anterior oblique position, to facilitate gastric emptying. The examination can be successfully accomplished
with the child drinking from a bottle;
these infants are usually very hungry and
will drink with little effort. Insertion of a
nasogastric tube is not necessary; however, emptying of an overdistended
stomach may help to prevent vomiting,
if needed. Fluoroscopic observations include vigorous active peristalsis resembling a caterpillar and coming to an
abrupt stop at the pyloric antrum, outlining the external thickened muscle as an
extrinsic impression, termed the shoulder sign. Luminal barium may be transiently trapped between the peristaltic
wave and the muscle, and this is termed
the tit sign. Eventual success of gastric
peristaltic activity will propel contrast
material through the pyloric mucosal interstices, with the appearance as either
the string sign or the double-track sign,
although at times more than one layer of
contrast material may be appreciated in
the mucosal filling defect (Fig 8).
Normal study.—On the normal study,
the prepyloric antrum is widely distensible between normal peristaltic waves,
and the thin pyloric ring can be seen
bridging the prepyloric antrum and duodenal cap. Fluoroscopic observations are
important, since antral peristalsis may
transiently simulate an elongated and abnormal canal.
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Sonography
Equipment.—The examination should
be performed with high-frequency transducers. We use a linear transducer operating between 6 and 10 MHz, adjusted to
the size of the infant and the depth of the
pylorus. Because the pylorus rises anteriorly with positioning of the patient, the
transducer frequency may be adjusted for
greater detail while achieving adequate
penetration to the pyloric channel. A sector transducer may be helpful in certain
cases, as discussed later.
Abnormal study.—Sonographic examination demonstrates the thickened prepyloric antrum bridging the duodenal bulb
and distended stomach. In infants with
IHPS, the stomach is distended to a variable degree. This gastric distention in a
vomiting infant is the first sign available
to the examiner that there is a gastric
outlet obstruction. Positioning of the patient by using gravity allows the examination to proceed, with the focus on
identifying the duodenal cap and its connection to the stomach. Because the variable gastric distension is likely to displace
the gastroduodenal junction, the search
for the pylorus may prove difficult. It is,
therefore, best to begin at a specific site of
constant location. We begin by placing
the transducer transversely below the xiphoid process, identifying the esophagus
as it enters the abdomen anterior to the
aorta at the diaphragmatic crus. Caudal
movement of the transducer allows identification of the gastric fundus, and continued caudal motion subsequently allows
definition of the gastric body, antrum, and
duodenal cap, regardless of displacement
or position and whether or not IHPS is
present (Figs 9, 10).
If the stomach is filled with gas, placement of the patient in a right anterior
oblique position permits fluid to gravitate to the antrum for adequate evaluation. On the other hand, if the stomach is
markedly distended the duodenal cap
may be displaced caudally and medially,
rendering the pylorus extremely difficult
to access. In such cases, if the patient is
slowly moved toward the supine and
even the left posterior oblique position,
the pylorus will be able to rise anteriorly
for optimal examination. Use of these
simple gravity-aided maneuvers eliminates the need for placement of nasogastric tubes to evacuate the stomach or for
additional drinking of fluid to further distend an already overtaxed system, thus
markedly shortening the duration of the
examination. Demonstration of the pylorus is achieved by identifying the duode326
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Figure 12. Longitudinal sonograms obtained within a few minutes of each other show peristaltic activity and changes in pyloric anatomy in a patient with IHPS. Note the shorter canal in
image on left and subsequent elongation coincident with peristaltic activity in image on right.
There is failure of relaxation of the pyloric channel, and persistent obliteration of the lumen. Also
note that on the left image, the gastric contents and pyloric mucosa have similar echogenicity,
falsely suggestive of unimpeded passage of gastric contents through the canal. A ⫽ antrum, D ⫽
duodenal cap, arrows ⫽ outer muscular layer.
nal cap, distended stomach, and intervening pyloric channel.
In patients with IHPS, the muscle is hypertrophied to a variable degree, and the
intervening mucosa is crowded, thickened
to a variable degree, and protrudes into
the distended portion of the antrum (the
nipple sign; Fig 11a) (12,16,50) and can
be seen filling the lumen on transverse
sections (Fig 11b). The length of the hypertrophied canal is variable and may
range from as little as 14 mm to more
than 20 mm. The numeric value for the
lower limit of muscle thickness has varied in reports in the literature, ranging
between 3.0 and 4.5 mm. In our experience and in that of others (51), the actual
numeric value is less important than the
overall morphology of the canal and the
real-time observations. The antropyloric
canal, as part of the stomach, is a dynamic structure, and it is seen undergoing changes in both length and width
during many examinations (Fig 12). The
intervening mucosa can often be observed sliding within the canal, usually as
a wave of gastric peristalsis washes over
the hypertrophied channel.
The unequivocal diagnosis of IHPS is
made by identifying the hypertrophied pylorus; in these patients, the muscle thickness, although variable during the examination, will be 3 mm or more throughout
the examination. The intervening lumen
is filled with crowded and redundant mucosa, best seen on transverse sections or
on longitudinal sections through the
center of canal (Fig 13), and gastric peristaltic activity at all times fails to distend
this preduodenal portion of the stomach.
Normal study.—A negative study hinges
on an unequivocal diagnosis of a normal
pyloric ring and a distensible antropyloric portion of the stomach, which rule
out IHPS. The examination is similar to
that described for an abnormal study,
with identification of the esophagus,
body, and antrum of the stomach and
hence the duodenal bulb (Fig 10). The
duodenal bulb is separated from the gastric antrum by the pyloric ring, and the
appearance is analogous to that seen at a
normal UGI (Fig 14). There is, therefore,
no overlap between the length and dimensions of the normal pyloric ring and
those of the abnormal hypertrophied
Hernanz-Schulman
Radiology
Figure 13. Longitudinal sonograms of hypertrophied pylorus in a patient with IHPS. Left: On
image obtained off center, the maximum width of the canal lumen and intervening mucosa
(arrowheads) cannot be identified. Right: Image obtained through the central portion of the canal
outlines full diameter of channel (arrowheads).
11% have been reported (12). As with
sonography, the experience and skill of
the examiner are important to achieve
the most accurate results (54).
Sonography provides direct information on the anatomy of the pyloric canal;
there is no need to wait for gastric contents to exit through the narrowed channel; therefore, the diagnosis can be made
rapidly, without the need for the patient
to drink additional contrast material and
for the examiner to await gastric emptying. There is no radiation exposure. Use
of gravity-aided maneuvers permits rapid
examination in all infants, without manipulation of gastric contents. Identification of the pylorus, whether the study
proves to be positive or negative and regardless of gastric distention, can be
made rapidly by following the stomach
from the gastroesophageal junction to
the duodenal cap during one transverse
sweep of the transducer. The examination can be performed accurately in a
very short time with an accuracy approaching 100% (12). Sonography is operator dependent, and the learning curve
is steep. However, once technical proficiency has been achieved, sonography is
the most expedient diagnostic examination for this condition.
Pitfalls
Figure 14. Normal correlative anatomy. Sonogram (left), illustration (middle), and fluoroscopic
image from UGI (right) show the normal pyloric ring (arrows) and the proximity of the duodenal cap
(D) to the relaxed antropyloric portion of the stomach, bridged by the pyloric ring. See also Figure 2a.
A ⫽ antrum. (Middle image adapted and reprinted, with permission, from reference 52.)
antropyloric canal. As in the UGI, realtime observations are important (53)
since antral peristalsis may transiently
simulate IHPS (Fig 15).
Comments
There are several options for evaluation of a vomiting infant. The first option
is to perform a clinical examination. In a
calm infant and with experienced hands,
this is successful in the majority of cases,
the findings are diagnostic of IHPS, and
no further imaging is required. In patients in whom the olive is not readily
palpable, however, maneuvers such as
placement of nasogastric tubes to evacuate the stomach and sedation of the infant do not seem justifiable when noninvasive and successful diagnostic tools are
available.
Endoscopy has been advocated by
some investigators (17) as a successful
tool in the diagnosis of IHPS. DemonstraVolume 227
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tion of the cauliflower- or nipplelike projection of the mucosa is characteristic in
patients with IHPS (Fig 3c). However, the
invasiveness and expense of this procedure do not seem to justify its use when
other diagnostic methods are available.
The UGI provides indirect information
regarding the status of the antropyloric
canal based on the morphology of the
canal lumen as outlined by contrast material. Because of this fact, failure of relaxation of the antropyloric canal, also
known as pylorospasm, may be difficult
to differentiate from IHPS. The examination may be time consuming, particularly in infants with high-grade obstruction, because it necessitates awaiting the
passage of contrast material through the
obstructed canal. Fluoroscopy time and,
therefore, radiation exposure may be prolonged. The reported sensitivity of UGI
for the diagnosis of IHPS is approximately 95%, but error rates as high as
Inability to visualize the pylorus.—In patients with IHPS, the most common reason for inability to visualize the pylorus
is gastric overdistention. As discussed earlier, this leads to displacement of the pylorus dorsally by the overdistended stomach. By following the course of the
stomach from the esophagus and slowly
turning the patient supine and toward
the left, the pylorus can rise anteriorly.
The junction of stomach and duodenum
can then be identified, and the hypertrophied pylorus can be recognized.
In patients without IHPS, an excessive
amount of gas may be present distal to
the stomach and may obscure the gastric
antrum, particularly when the stomach is
decompressed and overlaid by the transverse colon. In these patients, imaging
with a sector transducer, with caudal angulation toward the stomach through
the left lobe of the liver, allows access to
the antroduodenal junction. Placement
of the infant in the right side down position permits fluid in the stomach to
enter the antrum and definition of the
normal pyloric ring bridging the distensible antrum and duodenal cap.
Borderline measurements.—Thickening
of the antropyloric canal may be a tranInfantile Hypertrophic Pyloric Stenosis
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sient phenomenon due to peristaltic activity or to pylorospasm. Typically, in patients without IHPS the muscle does not
measure more than 3 mm in thickness at
any given point in time. Relaxation of
the antropyloric canal is denoted by a
change from the rigid linear morphology
of the canal to areas of relaxation that
permit pockets of fluid within the lumen.
In some patients without IHPS, the stomach is empty and the antrum is collapsed.
If documentation of an open distended
antrum is desired, a small amount of
fluid may be fed to these infants. Within
a few minutes, the normal fluid-filled antrum can be documented (Fig 16).
As is the case on UGI images, real-time
observation for a few minutes usually
clarifies the problem (53). Patients in
whom the antropyloric canal relaxes to a
normal morphology do not have IHPS.
Patients in whom the muscle is 2–3 mm
thick and does not relax throughout the
examination warrant careful monitoring
and follow-up examination, particularly
if they are at the younger end of the age
spectrum at the time of presentation
(12,43). UGI in these patients will not
help clarify the diagnosis further, and the
results may erroneously suggest fully developed IHPS (12). At present, however,
neither the cause nor the evolution of
IHPS are known. It is, therefore, uncertain whether a young infant in whom the
antropyloric canal fails to relax completely will go on to develop IHPS requiring surgery or whether these changes will
be arrested and resolve without sequelae.
In our experience (12) and that of others
(43), these patients in whom measurements are equivocal form a small minority of infants at presentation, and the
condition in few of them advances to
fully developed IHPS.
VOMITING INFANT:
DIFFERENTIAL DIAGNOSIS
AND IMAGING ALGORITHM
Patients with bilious vomiting do not
have IHPS and are not directed to an initial sonographic evaluation. UGI is the
study of choice in a child with bilious
vomiting. In patients with malrotation,
inversion of the normal relationship of
the superior mesenteric artery and vein
may be observed at sonography. This
finding is not constant, and, when encountered, UGI is necessary for confirmation of the diagnosis (55).
Patients with nonbilious vomiting typically have IHPS or reflux. Other conditions that can manifest with nonbili328
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May 2003
Figure 15. Peristaltic changes in antropyloric anatomy on normal sonographic study. Left:
Antropyloric channel is closed during peristaltic activity. Right: Distal antrum (A) is fully relaxed.
Arrows ⫽ pyloric ring, D ⫽ duodenal cap.
Figure 16. Sonogram of normal pylorus before (left) and after (right) ingestion of a small
amount of fluid. Left: The stomach is empty. Note that the pyloric channel and stomach have a
similar appearance and the anatomy of the pylorus is difficult to delineate. Right: The infant has
been given a small amount of fluid to fill the stomach. Prepyloric antrum (A) distends normally
and is immediately adjacent to the duodenal cap. D ⫽ duodenum.
ous vomiting include pylorospasm, hiatal hernia, and preampullary duodenal
stenosis.
IHPS can be diagnosed or excluded by
using sonography. Pylorospasm is more
easily demonstrated with sonography
than with UGI because of the ability with
the former to detect and measure the
muscle thickness (12). Hiatal hernia is
uncommon in infants and can be detected easily at UGI (56). However, herniation of the gastric fundus can also be
identified along the esophageal hiatus
during sonography. Preampullary duodenal stenosis is rare among the population
of infants with nonbilious vomiting. At
sonography, a normal pyloric ring bridges
the distensible antrum to a dilated duodenal cap. In these patients, UGI may be
performed for confirmation of this diagnosis (Fig 17).
Thus, infants presenting with nonbilious vomiting should be directed to
undergo sonography if IHPS is a considHernanz-Schulman
Radiology
Figure 17. Preampullary duodenal stenosis. (a) Sonogram in vomiting infant demonstrates a distensible antropyloric canal (A). However, there is
a consistent gas shadow to the right of the pyloric ring, resembling a very dilated duodenal cap (D). This led to suspicion of preampullary duodenal
stenosis and referral for UGI. (b) Initial UGI image of stomach shows gas-filled dilated duodenum (D). (c) UGI image obtained with patient prone
shows normal pylorus (arrow) and dilated proximal duodenum (D).
Figure 18. Surgical photograph of Ramstedt
pyloromyotomy. Thickened pyloric muscle
has been divided, and forceps outlines the internal bulging mucosal lining. (Photograph
courtesy of R. Cywes, MD.)
eration. If the patient has IHPS, the appropriate surgical referral is made rapidly
and accurately. If the sonogram delineates a normal pylorus, a search for other
causes, as described above, may allow
identification of preampullary duodenal
stenosis or hiatal hernia. UGI may be performed if further evaluation for these
conditions is warranted. UGI or scintigraphy can be performed to assess reflux if
documentation is clinically needed prior
to institution of appropriate therapy.
TREATMENT
The treatment of IHPS has undergone
an impressive evolution punctuated by
landmark surgical innovations and paralleled by remarkable decline in patient
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mortality. Nonsurgical treatment has
been directed toward maintenance of adequate nutrition until the condition is
overcome, manipulations directed at the
pylorus, and pharmacologic agents. In
1627, Hildanus advocated “nutrient enemas” consisting of broth, egg yolk, and
sugar. In the late 19th and early 20th
centuries, enema solutes included breast
milk and Ringer solution. In 1880, gastric
lavage was advocated as the first standard
treatment in infants with “gastric dilatation”; lavage was believed to help by reducing gastric acidity. In 1901, irradiation of the thymus was advocated, with
few adherents; in 1929, irradiation of the
pylorus was recommended. Local applications of heat and various types of poultices were also attempted. Pharmacologic
management was begun in 1904 and included administration of atropine, belladonna, opium, and cocaine. Thickened
foods were also advocated by many,
probably because of their success in the
treatment of vomiting patients with severe reflux but who were unlikely to have
had IHPS. Contemporary explanations
for the success of this form of medical
management included the belief that the
hypertrophied stomach would more successfully propel the thickened food
across the obstruction, that it was more
difficult to vomit this material, and that
it had a protective effect on the gastric
mucosa (1).
Surgical management was begun in
1892. Initial curative attempts consisted
of gastroenterostomy, with the first survival reported in 1898. Lobker would admit the mother to the hospital and insist
that she lie in bed with the lower part of
her body uncovered, cradling the infant
through the surgical and postoperative
period. The initial surgical attempt directed at the pylorus itself was attempted
by Nicoll and consisted of crude forceps
dilatation of the lumen, accessed via a
gastric incision, to burst up the thickened pyloric ring by forcible overstretching “with a screwing motion” with forceps (57). Although the initial operation
performed in 1899 was successful, subsequent complications included hemorrhage and perforation. Pyloroplasty became the procedure of choice in the 1st
decade of the 20th century and was applied by Dent, Heineke, Mikulicz, Nicoll,
Fredet, and Weber, with variations on the
theme of incising and resuturing the pyloric muscle (1). In 1911, Conrad Ramstedt performed his first operation for
IHPS, and, having difficulty resuturing
the muscle, did not complete the process.
The operation was successful but not
without a protracted course of continued
vomiting. In his next patient, Ramstedt
decided not to suture the muscle, because
“one gained the impression that the stenosis had not entirely been overcome,
and that the mucosa, perhaps as a result
of the transverse closure, was folded in
the pylorus, causing additional obstruction” (58). The Ramstedt procedure divides the hypertrophied muscle, leaving
the intact mucosa bulging through the
incision (Fig 18) and, whether performed
via abdominal incision or at laparoscopy
(59), remains the standard of surgical
treatment today.
Mortality for patients with IHPS reInfantile Hypertrophic Pyloric Stenosis
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flects one of the great success stories in
modern medicine. The mortality rate in
patients undergoing gastroenterostomy
was 53%; that for pyloroplasty was 40%.
In the United States prior to 1904, the
mortality rate was 100%. Within 10 years
of the advent of the Ramstedt procedure,
published mortality rates for this operation had decreased to 10%; this rate further diminished to 2% by 1931 and is
well below that value today (1). These
declining numbers are no doubt the result not only of a successful operation
but also of increased acceptance of the
operation by the medical community,
leading to earlier surgical referral, and of
earlier diagnosis with successful imaging
techniques. In the initial years of experimental surgical treatment, medical management was not considered a failure until the child had lost over 30% of his or
her body weight. The question was
“Should the child be saved by surgery or
from surgery?” (60). Today, IHPS is not
considered to be a life-threatening disease. However, when discussing a mortality rate of 2%, Harold Mack (1) defined it
as nothing short of “a miracle.”
5.
6.
7.
8.
9.
10.
11.
12.
13.
SUMMARY
This discussion has focused on a review
of the detailed anatomic changes that result in the development of IHPS within
the historical perspective of the evolution of our understanding and treatment
of the lesion. Particular emphasis has
been placed on successful imaging techniques. Imaging findings have been correlated to the anatomic, histologic, endoscopic, and surgical anatomy.
The recognition, diagnosis and treatment of IHPS has culminated in remarkable diagnostic and therapeutic success,
in which radiologists have played an important role. Radiologists are in a unique
position to observe the changes that occur in the antropyloric junction in vivo
and to contribute to the eventual unraveling of the etiology of this complex entity.
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