Sonography plays an important role in the evaluation of patients with right lower quadrant (RLQ) pain. This article addresses diagnostic considerations for RLQ pain, with a focus on evaluation of patients with possible appendicitis. The author details relevant sonographic techniques and findings leading to a definitive diagnosis.
is a Professor of Diagnostic Radiology and the Chief of
Diagnostic Ultrasound at the University of California, Davis
Medical Center, Sacramento, CA.
Evaluation of acute right lower quadrant (RLQ) pain has
undergone an evolution over the past decade. Previously, evaluation
focused on history, physical examination, and laboratory results.
Plain radiographics were utilized in select patients, while the use
of sonography was limited to patients with possible pelvic
etiologies of pain. More recently, sonography and computerized
tomography (CT) have played a larger role in evaluation of these
patients. Much of the attention in evaluation of RLQ pain is to
diagnose or exclude appendicitis. A list of diagnostic
consideration for RLQ pain may be divided into the 3 "Gs"¡ªie,
gastrointestinal, gynecological, and genitourinary (Table 1). Much
of the focus of this article will be on evaluation of patients with
Why image possible appendicitis?
It is necessary to decide why we would need to use imaging to
evaluate patients with RLQ pain suspected of acute appendicitis. In
most patients with classical findings of appendicitis, imaging is
not necessary. Imaging may delay operation and thus increase the
possibility of developing complications of acute appendicitis, such
as perforation. However, in many cases, the diagnosis of acute
appendicitis is not so straightforward. Thus, the differential
becomes quite large (Table 1). Prior to use of imaging, it was
common practice to perform appendectomies on a number of patients
who had normal appendixes. This is a so-called false-positive
laparotomy. Traditionally, a false-positive laparotomy rate of
approximately 20% has been accepted. Therefore, 1 of 5 patients
with suspected acute appendicitis had, in fact, a normal appendix
at operation. However, with imaging, the false-positive rate has
dropped to ¡Ü6% in a number of studies.
In addition to preventing unnecessary surgery, imaging can
reduce intervention time, thus reducing potential complications,
procrastination-induced expenses, and medical costs.
Finally, imaging is obviously important in establishing a correct
diagnosis. For instance, in a series by Poortman,
41 of 199 patients (21%) with suspected acute appendicitis had an
alternative diagnosis at surgery. This was nearly equally divided
into a gynecologic and a gastrointestinal etiology of symptoms
Why not image with CT in all patients?
The imaging literature generally reports an increase in
sensitivity of CT compared with ultrasound in evaluation of
patients with suspected acute appendicitis. For instance, in an
early article by Balthazar,
he reported sensitivity of CT to be 90%, compared with the
sensitivity of sonography of 76% in diagnosing acute appendicitis.
Others have shown a general increased sensitivity of CT compared
with ultrasound in diagnosing appendicitis. However, in a recent
article by Poortman,
the sensitivities of CT and sonography were approximately equal at
76% and 79%, respectively. Noncontrast CT was reported to have been
used in this study, while other studies would favor use of
iodinated contrast-enhanced CT. Furthermore, in select patient
populations in which ultrasound is performed by individuals with
experience in appendicular sonography, there are very high reported
sensitivities of ultrasound for diagnosing appendicitis.
Baldisserotto et al
reported sensitivity and specificity of compression and
noncompression sonography to be 98.5% and 98.2%, respectively. This
study was in a pediatric population aged 6 months to 12 years.
Therefore, there are advantages of both sonography and CT; some of
these are listed in Table 3.
In reviewing Table 3, there is little doubt that, whenever
possible, sonography should be used rather than CT. The
disadvantages of CT include its expense and the high radiation
dose. Radiation dose is especially problematic in the pediatric
population. However, a major disadvantage of sonography is the
limited ability of ultrasound to be used in the adult patient,
especially those who are overweight or obese. This, unfortunately,
includes a large segment of the U.S. population. Thus, this segment
of the population is best examined by CT. Finally, operator
dependence is a major factor in utilizing CT as opposed to
ultrasound. While CT technique is automated and nearly "foolproof,"
the same cannot be said about sonography. Precise technique must be
used when performing ultrasound to evaluate the RLQ for possible
appendicitis. "Practice makes perfect," and if the examiner
performs an RLQ ultrasound only once a month, the advantage goes to
CT. Therefore, sonography should ideally be used in the initial
evaluation of the pediatric patient, in women of childbearing age,
and for thin men. On occasion, both CT and ultrasound may be used
What is the best sonographic technique?
While there are many variations of techniques for evaluation of
a patient with RLQ pain, I prefer initial use of a screening
ultrasound followed by graded compression sonography. The initial
screening examination is performed with a sector scanner (3 to 5
MHz) to get the "lay of the land." It is important not to focus
only on the diagnosis of appendicitis, but to remember the 3 "Gs"
(Table 1). A 4-MHz sector probe will be helpful to diagnosis
genitourinary and etiologies, such as nephrolithiasis or renal
obstruction (Figure 2). A sector probe can also diagnose some
gynecological abnormalities, including possible ovarian pathology,
such as a hemorrhagic cyst (Figure 3; Table 3). Thus, scanning
should include a brief evaluation from the right upper quadrant to
the pelvis. Patients with possible renal obstruction or
cholecystitis may be diagnosed with a sector probe (Tables 1 and 2;
Figure 2). Also, gynecological abnormalities, such as ovarian
cysts, may be visualized (Figure 3).
Graded compression should include use of a linear array or
curved linear array probe with a frequency from 6 to 9 MHz. I find
that starting at the common femoral vessels and scanning cephalad
is useful (Figures 4 and 5). It is important to have moderate probe
pressure to compress the lumen of normal bowel. Also important is
to observe peristalsis, which identifies a structure as a normal
loop of bowel, rather than the appendix. A 3- to 4-MHz sector
scanner is not appropriate for examining the appendix, since it
does not allow significant resolution to identify the
characteristic features of the bowel or appendix (Figure 6). It is
also important when using a high-resolution linear array probe to
concentrate on visualization of structures just deep to the
abdominal musculature. The proper focal zone should be used, and
the area of interest should be magnified to exhibit the region of
interest. In thin or pediatric patients, the appendix is usually
superficial and, therefore, the focal zone should be kept at no
greater than 3 to 4 cm.
Self-localization of pain by the patient is important. Ask the
patient where his or her pain is located and concentrate on that
region. I find localization of the region of pain with the
ultrasound probe is very important. This is analogous to an
ultrasound Murphy's sign in the gallbladder. Pain should direct the
examination to the area of tenderness, where the abnormality may be
Finally, in women, if a diagnosis is not made by the general
survey examination or the compression technique, endovaginal
sonography may be use-ful.
This may be helpful to diagnose an infiamed appendix located in the
pelvis or gynecological etiologies of pain (Figure 7). Because
gynecological abnormalities are often a cause of RLQ pain,
endovaginal sonography should always be performed whenever
What are sonographic findings of acute appendicitis?
Helpful sonographic findings in diagnosing acute appendicitis
include a blind-ending, noncompressible, fiuid-filled tubular
structure with a diameter >6 mm (Table 4; Figure 8). In
addition, whenever even small amounts of free fiuid are noted in
the RLQ, this should raise the suspicion of a possible pathologic
process, including appendicitis. Free fiuid and increased
mesenteric echogenicity may occur later in the course of
appendicitis. The increased echogenicity of the mesentery can be
easily overlooked. This is similar to the mesenteric stranding
identified on CT. Finally, increased color fiow may be seen in the
wall of the appendix (Figure 9). However, this finding is lost with
The perforated appendix
If the diagnosis of appendicitis is overlooked, acute
appendicitis may progress to gangrenous appendicitis. Sonographic
features of gangrenous appendicitis include increasing echogenicity
of the mesentery, free fiuid in the RLQ, and eventual loss of
appendicular color fiow. Eventually, the appendix may rupture. The
infiammation may be walled off in the RLQ as a focal abscess. In
other situations, fiuid may spread through the abdomen, but it most
commonly spreads into the pelvis. Sonographically, an appendicitis
abscess appears as a thick-walled, fiuid-filled structure. There
may be a "dirty" shadow if air is present in the abscess.
Sonography can be used to guide drainage of complications of
appendicitis. For instance, ultrasound can be used to guide
drainage of an RLQ appendiceal abscess (Figure 10). Commonly, we
are called upon to drain fiuid collections in the pelvis that are
complications of acute appendicitis, including pelvic abscess.
These pelvic abscesses may be drained via the transrectal route.
Complete aspiration alone has been curative in many pelvic
Catheters may be placed using combined sonography and fiuoroscopy
with the guide wire exchange technique. Alternatively, the trocar
technique with a small-diameter catheter has been advocated by some
(Figure 11). Cure rate of trans-rectal or endovaginal drainage of
pelvic abscesses is >85%.
What are the alternative diagnoses to consider?
Differential diagnoses for RLQ pain are listed in Table 1. While
review of all these diagnoses is beyond the scope of this article,
at least one diagnosis must be mentioned briefiy. Mesenteric
adenitis is a diagnosis that is easily confused with appendicitis
in children. Mesenteric adenitis may be secondary to a diffuse
gastrointestinal infiammatory process and, perhaps, should be more
correctly called mesenteric adenitis-enteritis. The sonographic
hallmark of this entity is enlarged mesenteric nodes (approximately
1 cm), which are both tender and hypervascular (Figure 12).
Remember that these infiamed mesenteric nodes refiect
gastrointestinal infiammation. Usually, the appendix is not
involved with mesenteric adenitis, which is most commonly a
self-limiting process. Mesenteric adenitis may be associated with
hypervascularity of the surrounding mesentery or infiammation and
thickening of the terminal ileum. This diagnosis should be kept in
mind when examining the pediatric patient with RLQ pain.
Other diagnoses must also be considered in patients with RLQ
pain. Some gastrointestinal etiologies may not be diagnosed by
sonography (Table 2). However, most gynecological etiologies of RLQ
pain may be identified sonographically. This can include anything
from a ruptured or hemorrhagic ovarian cyst (Figure 3) to an
ovarian abscess from pelvic infiammatory disease. Therefore, in
female patients, an endovaginal scan should almost always be
Sonography can be used in the initial evaluation of right lower
quadrant pain in pediatric patients, women of childbearing age, and
for thin males. Precise technique and concentration on graded
compression sonography using a linear or curved linear probe is
necessary to properly identify the infiamed appendix. However,
other etiologies of right lower quadrant pain should be considered
and are easily diagnosed with sonography.