Several reports have addressed the need for radiologists to be
clear and pertinent in their interpretation or reporting of
radiologic procedures.1-5 Imprecise or poorly understood reports
can adversely affect the workup and management of patients.
Plain abdominal radiography (PAR) is one of the more frequently
requested examinations in emergency medicine. In our experience,
emergency physicians frequently utilize the term "nonspecific
abdominal gas pattern" in their preliminary interpretations when,
in fact, they mean that the bowel gas pattern is normal.6 A recent
survey of community-based teaching hospital radiologists showed
that 70% of the radiologists used this term;7 65% of these
radiologists considered the phrase to mean "normal or probably
normal," 22% interpreted this as "cannot tell if normal or
abnormal," and 13% use this term to mean that findings are abnormal
but it cannot be determined if it is due to mechanical obstruction
or adynamic ileus." Of the rererring physicians in the same survey
who received the report, 44% defined it as "normal"; 51% delined it
as "normal or abnormal"; and 5% defined it as abnormal,
representing either mechanical obstruction or adynamic ileus. It is
obvious that the term has a wide range of meaning, both for
radiologists and referring clinicians. At one extreme, it appears
to signify a normal condition; whereas at the other extreme it is
perceived as a pathologic state, such as obstruction. Few other
radiologic interpretations have more consistent disagreement about
their meaning, both among radiologists and between radiologists and
referring clinicians.
Prior communications have called for the abandonment of the term
"nonspecific abdominal gas pattern,7,8 and yet the term continues
to be used. It is pertinent to consider why this is so. Is it
because radiologists and emergency physicians do not read the
literature, or is it because a "nonspecific" intestinal gas pattern
really exists? My experience suggests that there is a group of
patients whose abdominal radiographs do not fit the definition of
"normal", "probable small bowel obstruction", or "definite small
bowel obstruction" gas patterns. As there is no applicable
alternative recommendation, there is likely to be difficulty in
"ignoring" or abandoning this interpretation. How does one report
this intestinal gas pattern and what are its clinical
implications?
A recent report of a blinded analysis of plain film abdominal
examinations in the diagnosis of small bowel obstruction (SBO) by
experienced gastrointestinal radiologists showed a sensitivity of
66%.9 This report differed from other studies in that the PAR
patterns were defined and a follow-up for every defined
interpretive category was given. In this report, 62% of the
patients clinically suspected of SB0 were in fact not obstructed.
Of "normal'' plain film interpretations, 21% had low grade SBO. Of
the so-called "abnormal but nonspecific'' plain film
interpretations, 13% had low grade and 9% had high grade SBO. The
investigators defined the latter pattern as a borderline or
slightly dilated (2.5 cm to 3 cm) small bowel with more than two
air-fluid levels. Of the "probable" SBO plain film interpretations,
37% had low grade SBO and 16% had high grade SBO. Of the "definite"
SBO interpretations, 26% had low grade SBO and 23% had high grade
SBO; 13% had complete SBO. This report clearly showed that there is
a pattern which is neither normal nor fits the categories of
probably or definitely obstructed. Gammill and Nice recognized this
pattern to mean ileus (i.e., the small bowel is unable to push
fluid along).10 Indeed, the word "ileus" means stasis and does not
differentiate between mechanical and nonmechanical causes. Our
acceptance of the term "ileus" to mean an adynamic etiology when in
fact it simply means stasis that can result from any cause may be
part of the problem.
The interpretation "nonspecific abdominal gas pattern" should be
avoided. I propose the term "mild small bowel stasis." However, if
the term nonspecific abdominal gas pattern is used, it should be
qualified as abnormal and should be followed by a specific
recommendation for further workup. This interpretation satisfies a
group of plain film findings that does not fit the normal and
definitely abnormal categories, but may still have clinical
implications.9 Based on the current literature, the various
intestinal gas patterns are defined as follows:
1. A "normal" intestinal gas pattern is defined as either an
absence of small intestinal gas (without abnormal increase in
abdominal density or loss of soft tissue planes) or the presence of
gas within a few (3 to 4) variably shaped small intestinal loops
measuring less than 2.5 cm in diameter. In addition, there is a
normal gas and/or fecal distribution in a nondistended colon.
2. "Mild small bowel stasis" (abnormal but nonspecific pattern)
is defined as those cases demonstrating single or multiple loops of
borderline or slightly dilated small intestine (2.5 cm to 3 cm)
with 3 or more air-fluid levels on upright or decubitus films.
There is no disproportionate distention of the small intestine
relative to the colon. Gas and/or feces are present in a
nondistended colon. The term is used to indicate an abnormal gas
distribution, but does not allow distinction between mild reflex or
adynamic ileus and mechanical obstruction. Some of the patients in
this category have low grade obstruction and are difficult to
diagnose clinically, and others may have reflex or reactive ileus
secondary to a variety of processes, e.g. trauma, critical illness,
or urinary tract calculus. Some may be related to
medication-induced hypoperistalsis and air swallowing.10
3. A "probable" SBO pattern is defined as unequivocally dilated
multiple gaseous and/or fluid-filled loops of small intestine with
a moderate amount of colonic gas, but the degree of distention of
small intestine relative to the colon is insufficient to make a
definite diagnosis. Air-fluid levels are generally present, but
there is an element of uncertainty in diagnosing SBO.
4. A "definite" SBO pattern is defined as abnormal and clearly
disproportionate gaseous and/or fluid distention of small bowel
relative to the colon (or other segments of small intestine).
Air-fluid levels are evident, and the diagnosis of SBO is
considered unequivocal.
The use of a precise definition of plain film intestinal
patterns will enable radiologists to prevent misunderstandings with
referring clinicians, and allow us to make more cost effective
recommendations for further work-up in suspected SBO.11 The
radiologic report should include a recommendation for further
imaging if this is needed, so that erroneous application of
radiologic resources, which can increase the cost of work-up and
management, is avoided. An algorithm is proposed for additional
imaging in the work-up of patients with suspected intestinal
obstruction (figure 1). This is based on the acknowledged
limitations of PAR,9 the value of CT in the emergent
situation,12,13 and the problem-solving ability of enteroclysis in
the subacute or chronic setting.11,14 The recommendations given are
based not on firm scientific evidence, but on continuing clinical
radiologic observations over the last decade.9,11-17 As the value
of other imaging modalities are established, their use can be added
to the recommendations. The role of radiology has undergone
significant changes in the last decade with the use of CT,
enteroclysis, and the rebirth of the long decompression
table.18
Radiologists must understand each other if we expect other
physicians to understand us. The lack of a definition of the
meaning of the various terms used in plain film interpretation has
resulted in confusion and has prevented meaningful comparison of
different reports. A careful analysis and clear reporting of the
plain film is crucial to prevent erroneous application of imaging
resources and clinical mismanagement. The "misleading" patterns in
intestinal obstruction appear to be largely plain film
misinterpreations, miscommunication, and the use of undefined
terms. Our reports should be concise and as precise as
possible.
"Nonspecific abdominal gas pattern" is an interpretation whose
time should have been long gone. lt serves no useful purpose and
deserves permanent burial.
Acknowledgement:
The author would like to thank Frederick M. Kelvin, MD, for his
advice and Fran Shaul for secretarial assistance.
This editorial is reprinted with permission from Maglinte DDT:
Nonspecific abdominal gas pattern: An interpretation whose time is
gone (editorial). Emerg Radiol 3:93-95, 1996.
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