Gastrointestinal Imaging • Original Research

Lin et al.
Reasons for Nonvisualization of Appendix on Graded Compres-
sion Sonography

Gastrointestinal Imaging
Original Research

Anatomic Reasons for Failure to

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Visualize the Appendix With Graded

Compression Sonography: Insights
From Contemporaneous CT
Wilson Lin1 OBJECTIVE. The purpose of this study is to identify the anatomic locations of appendix-
R. Brooke Jeffrey 1 es on CT when graded compression sonography fails to visualize the appendix.
Angela Trinh1 MATERIALS AND METHODS. The study included 197 patients with suspected ap-
Eric W. Olcott 1,2 pendicitis whose appendixes were not visualized on graded compression sonography per-
formed with typically used transducers of at least 10 MHz, who underwent CT within 48
Lin W, Jeffrey RB, Trinh A, Olcott EW hours following graded compression sonography, and who had available either pathologic ex-
amination following surgery or 6-week follow-up if surgery was not performed. Appendixes
were retrospectively localized using four transverse quadrants (including the posteromedial
quadrant) centered on the ileocecal valve and projected vertically, the craniocaudal level rela-
tive to the iliac crests, and the depth of the appendix as measured from the surface of the skin.
Data were assessed using the Fisher exact test, t test, multinomial test, binomial distribution,
ANOVA, and linear regression.
RESULTS. Appendixes were most frequently located in the posteromedial quadrant (123
of 197 patients [62.4%]; 95% CI, 55.3–69.2%) at a statistically significantly greater frequency
than that expected by chance (p < 0.00001). Appendixes were located above the iliac crests
in 19.8% of patients (39/197; 95% CI, 14.5–26.1%) and at depths exceeding the penetration
of typical transducers of at least 10 MHz in 19.3% of patients (38/197; 95% CI, 14.0–25.5%).
All appendixes (95% CI, 98.1–100.0%) were located within the range of 6-MHz transducers.
CONCLUSION. Appendixes that are not visualized on graded compression sonography
are most frequently located in the posteromedial quadrant and are often located above the il-
iac crests or at depths too great for visualization with typically used transducers of at least 10
MHz. Accordingly, when the appendix is not visualized on graded compression sonography,
Keywords: appendicitis, diagnostic imaging, targeted scanning of the posteromedial quadrant and the region above the iliac crests, and
ultrasonography scanning with 6-MHz transducers, may enable visualization of the appendix and are recom-
DOI:10.2214/AJR.17.18059
mended additions to scanning protocols.

ompared with CT, graded com- Among these challenges, the location of

C
Received February 6, 2017; accepted after revision
March 1, 2017.
pression sonography offers sever- the appendix may be uniquely amenable to in-
Based on a presentation at the 2016 Radiological Society al advantages in the evaluation of novations in scanning methodology. For ex-
of North America annual meeting, Chicago, IL. patients with suspected appendi- ample, recent implementation of a three-step
citis, including the absence of both ionizing sequential positioning algorithm significant-
radiation and iodine-based contrast media as ly improved appendiceal visualization and
1
Department of Radiology, Stanford University School of
Medicine, 300 Pasteur Dr, H1307, Stanford, CA
94305-5105. Address correspondence to E. W. Olcott
well as lower cost [1–5]. However, the lower decreased the utilization of CT after graded
(eolcott@stanford.edu). rate of appendiceal visualization on graded compression sonography [9]. Nonetheless, ap-
compression sonography remains an ongoing pendiceal visualization rates of graded com-
challenge [1–10]. Nonvisualization of the ap- pression sonography remain inferior to those
2
Department of Radiology (114), Veterans Affairs Palo
Alto Health Care System, Palo Alto, CA.
pendix on graded compression sonography of CT, with the former ranging from 2.4% to
WEB may be considered an inconclusive finding greater than 70% and the latter ranging up to
This is a web exclusive article. and, as such, often leads to CT scanning, with 100% [2, 8, 14–19]. Accordingly, new meth-
its attendant radiation exposure, further de- ods that improve visualization of the appendix
AJR 2017; 209:W128–W138
lays, and additional costs [2, 5, 6, 11]. Known on sonography potentially can increase the
0361–803X/17/2093–W128 challenges for graded compression sonogra- utility of graded compression sonography in
phy include large body habitus, retrocecal ap- the evaluation of suspected appendicitis and
© American Roentgen Ray Society pendixes, and bowel gas [6, 9, 12–14]. decrease patients’ exposure to CT.

W128 AJR:209, September 2017

 Reasons for Nonvisualization of Appendix on Graded Compression Sonography
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A
Fig. 1—24-year-old woman with suspected appendicitis. Images show method
used for localizing appendixes.
A, Transverse CT image shows anteroposterior and right-to-left orthogonal
boundaries (lines) centered on ileocecal valve, defining anterolateral,
anteromedial, posterolateral, and posteromedial quadrants.
B, Coronal CT image shows boundary (line) connecting most superior aspects of
iliac crests, demarcating regions superior and inferior to iliac crests.

For many years, graded compression so- the institutional review board at Stanford Univer- Additional scanning was performed by radiolo-
nography has been the first-line imaging mo- sity School of Medicine, in view of the retrospec- gists, as needed, for clarification of findings, as is
dality of choice at our institution for evaluating tive nature of the investigation. typical in our practice. The appendix was identi-
patients with suspected appendicitis. Sonog- fied as a blind-ending tubular structure associated
raphy is the modality preferred by the Ameri- Patient Selection with the cecal tip [2, 7, 14, 29, 31]. Final imaging
can College of Radiology for pediatric patients An institutional database was searched to iden- reports were generated by attending radiologists
[20] and has been proposed for adults in view tify patients who had undergone graded compres- with 5 years to more than 25 years of experience.
of concerns about radiation exposure associat- sion sonography and CT for suspected appendi-
ed with CT [1, 8, 11, 21–25]. On the basis of our citis between mid-October 2012 and mid-March Graded Compression Sonography
earlier experience, we elected to investigate po- 2015. Inclusion criteria were as follows: the ini- Graded compression sonography was per-
tential anatomic reasons for nonvisualization of tial imaging examination performed was appen- formed using Logiq 9 ultrasound equipment
the appendix and determine whether nonvisu- diceal graded compression sonography, the ap- (GE Healthcare). A three-step sequential posi-
alized appendixes are located in the deep pos- pendix was not visualized on graded compression tioning algorithm was used [9]. In this algorithm,
terior pelvis beyond the cecum or within the sonography, CT was performed within 48 hours of when the appendix was not visualized on initial
abdomen superior to the iliac crests (regions graded compression sonography and revealed the traditional scanning performed with the patient in
not specifically emphasized in our laboratory appendix, and reference standards were available, the supine position, the patient was placed in a 45°
or in much of the literature [7, 11, 26–31], al- including pathologic evaluation of resected speci- left posterior oblique position and was scanned
though they were identified in a previous study mens for patients treated with appendectomy and through the right flank to examine the retroce-
[32]), or are located at depths beyond the range 6-week follow-up for patients who did not undergo cal region. When the appendix still was not visu-
of the transducers of at least 10 MHz that are surgery. A total of 197 patients met these criteria. alized, the patient was returned to the supine po-
typically used in our laboratory. We sought to sition to undergo a second-look evaluation. We
evaluate these possibilities by evaluating pa- Scanning Technique typically use linear array transducers of at least
tients who underwent CT soon after appendi- All imaging studies were performed by li- 10 MHz for appendiceal studies performed in our
ceal graded compression sonography failed to censed CT technologists and one of six licensed laboratory. By agreement with our emergency
visualize the appendix. sonographers with at least 5 years of clinical expe- medicine and surgery departments, patients with
rience in graded compression sonography. These a body mass index (weight in kilograms divided
Materials and Methods technologists and sonographers were supervised by the square of height in meters) of 30 or more,
This study was HIPAA compliant. The require- by attending radiologists, fellows, and residents in or with peritoneal signs, were evaluated with CT
ment to obtain informed consent was waived by our body imaging and pediatric imaging sections. rather than sonography.

AJR:209, September 2017 W129

 Lin et al.

CT Review of CT Examinations al quadrant, anteromedial quadrant, posterolateral

Abdominopelvic CT was performed with colli- Each CT examination was retrospectively evalu- quadrant, and posteromedial quadrant (Figs. 1 and
mation of 0.625–1.25 mm using 16- or 64- MDCT ated by two independent reviewers, with discrep- 2). Localization also was performed craniocaudal-
scanners (LightSpeed VCT, GE Healthcare) with- ancies thereafter resolved by consensus. The po- ly, with the appendiceal tip identified as being lo-
out oral or rectal contrast medium. Adults re- sition of the appendix was defined by the location cated either superior or inferior to a line connecting
ceived 150 mL of iohexol contrast medium (Om- of the appendiceal tip because the blind-ended tip the most superior aspects of the iliac crests that di-
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nipaque 350, GE Healthcare) injected at a rate of 3 provides a recognizable and essential landmark for vide the pelvis from the abdomen [32, 33] (Fig. 1).
mL/s. Pediatric patients received 2 mL of contrast identifying the appendix [2, 7, 14, 29, 31] and is a Appendiceal tips lying on boundary lines were lo-
medium per kilogram of body weight, which was unique point in space that is identifiable on both calized using the immediately adjacent portion of
injected at a rate of 2 mL/s. Portal venous phase sonography and CT. Each tip was localized in the the appendix. Finally, appendiceal depth was de-
images of the abdomen and pelvis were recon- transverse plane to one of four quadrants demarcat- fined on axial images, with the use of the shortest
structed at a slice thickness of 1.25–5 mm with ed by straight lines centered on the ileocecal valve, distance from the tip to the skin surface without in-
sagittal and coronal reformations obtained at a extending anteroposteriorly and from right to left tervening osseous structures, reflecting the closest-
slice thickness of 2 mm. and projected vertically, including the anterolater- approach application of a sonographic transducer.

A B

C D
Fig. 2—Appendiceal tips localized to each of four transverse quadrants in four patients. Boundaries (lines) centered on ileocecal valve, projected vertically, define
quadrants.
A, 63-year-old woman with suspected appendicitis. CT image shows appendiceal tip (arrow) in anterolateral quadrant.
B, 24-year-old woman with suspected appendicitis. CT image shows appendiceal tip (arrow) in anteromedial quadrant.
C, 37-year-old man with suspected appendicitis. CT image shows appendiceal tip (arrow) in posterolateral quadrant.
D, 85-year-old man with suspected appendicitis. CT image shows appendiceal tip (arrow) in posteromedial quadrant.

W130 AJR:209, September 2017

 Reasons for Nonvisualization of Appendix on Graded Compression Sonography

TABLE 1:  Sonographically Nonvisualized Appendixes, Stratified by Quadrant Where Appendix Was Located, Patient
Group, and Level of Appendix Relative to Iliac Crests
Location of Appendix pa
Patient Group, and Level of Appendix Anterolateral Anteromedial Posterolateral Posteromedial By Multinomial By Fisher
Relative to Iliac Crests Quadrant Quadrant Quadrant Quadrant Testb Exact Testc
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All levels
All patients (n = 197)
No. of patients 13 18 43 123 < 0.0001
Percentage of patients (95% CI) 6.6 (3.6–11.0) 9.1 (5.5–14.1) 21.8 (16.3–28.3) 62.4 (55.3–69.2)
p < 0.00001d
Patients with appendicitis (n = 31)
No. of patients 2 3 11 15 0.0015
Percentage of patients (95% CI) 6.5 (0.8–21.4) 9.7 (2.0–25.8) 35.5 (19.2–54.6) 48.4 (30.2–66.9)
p = 0.0056d
Patients without appendicitis (n = 166)
No. of patients 11 15 32 108 < 0.0001 0.21
Percentage of patients (95% CI) 6.6 (3.4–11.5) 9.0 (5.1–14.5) 19.3 (13.6–26.1) 65.1 (57.3–72.3)
p < 0.00001d
Level superior to iliac crests
All patients (n = 39)
No. of patients 11 10 5 13 0.32
Percentage of patients (95% CI) 28.2 (15.0–44.9) 25.6 (13.0–42.1) 12.8 (4.3–27.4) 33.3 (19.1–50.2)
p = 0.27d
Patients with appendicitis (n = 6)
No. of patients 2 2 2 0 0.74
Percentage of patients (95% CI) 33.3 (4.3–77.7) 33.3 (4.3–77.7) 33.3 (4.3–77.7) 0.0 (0.0–45.9)
p = 0.35d
Patients without appendicitis (n = 33)
No. of patients 9 8 3 13 0.10 0.11
Percentage of patients (95% CI) 27.3 (13.3–45.5) 24.2 (11.1–42.3) 9.1 (1.9–24.3) 39.4 (22.9–57.9)
p = 0.069d
Level inferior to iliac crests
All patients (n = 158)
No. of patients 2 8 38 110 < 0.0001
Percentage of patients (95% CI) 1.3 (0.2–4.5) 5.1 (2.2–9.7) 24.1 (17.6–31.5) 69.6 (61.8–76.7)
p < 0.0001d
Patients with appendicitis (n = 25)
No. of patients 0 1 9 15 < 0.0001
Percentage of patients (95% CI) 0.0 (0.0–13.7) 4.0 (0.1–20.4) 36.0 (18.0–57.5) 60.0 (38.7–78.9)
p = 0.00021d
Patients without appendicitis (n = 133)
No. of patients 2 7 29 95 < 0.0001 0.48
Percentage of patients (95% CI) 1.5 (0.2–5.3) 5.3 (2.1–10.5) 21.8 (15.1–29.8) 71.4 (63.0–78.9)
p < 0.00001d
Note—Please note that percentages may not total 100% because of rounding.
a All p values other than inequalities are presented to two significant digits after the decimal.
bMultinomial test with exhaustive enumeration was used to evaluate overall frequencies of appendixes in four quadrants across each row.
cThe Fisher exact test is a 2 × 4 comparison of the distribution of appendixes in four quadrants in patients with appendicitis versus patients without appendicitis.
d The null hypothesis is 25.0% distribution in each of the four quadrants.

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 Lin et al.

Relationship Between Depth Measurements Fig. 3—Scatterplot of

80

Graded Compression Sonography (mm)

on Graded Compression Sonography and CT depth of recognizable

Right External Iliac Artery Depth on

point of right external
Because graded compression sonography is per- iliac artery measured
formed under compression and CT is not, the depth with both CT and 60
measurements of the two modalities were related us- graded compression
sonography, with linear
ing linear regression. With a random sample of 40
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regression relating
patients (20 male patients and 20 female patients) measurements of two 40
chosen from among the 197 patients by use of sta- modalities. Circles
tistical software (Stata, version 14.1, StataCorp), the denote individual
patients, dashed line 20
distance from the anterior skin surface to a recog- denotes regression
nizable deep point along the right external iliac ar- line, and area outlined
tery was measured for each patient in side-by-side by black line denotes
95% CI. 0
evaluations of both modalities performed by one re-
20 40 60 80 100
viewer, with the conformation of the vessel as well Right External Iliac Artery Depth on CT (mm)
as the adjacent boney and muscular features used as
landmarks. Regression analysis was used to evaluate who recorded demographic information for each Results
relationships of appendiceal depth on graded com- patient. Final pathology reports following surgery The 197 patients who met the inclusion
pression sonography to depth on CT, producing the for patients who underwent appendectomy, and criteria included 42 male patients (age, 3–65
equation Y = mX + b, where Y denotes depth on grad- 6-week postpresentation chart reviews for patients years; mean, 21.9 years) and 155 female pa-
ed compression sonography, m denotes slope, X de- who did not undergo surgery, were used as diag- tients (age, 2–74 years; mean, 27.0 years).
notes depth on CT, and b denotes the y-intercept. Re- nostic reference standards to establish the pres- Of these patients, 13 male patients (31.0%;
gression analysis was also applied to sex, age, and ence or absence of appendicitis. 95% CI, 17.6–47.1%) and 18 female patients
diagnosis as revealed in the medical record. (11.6%; 95% CI, 7.0–77.7%) underwent ap-
Statistical Analysis pendectomy and had appendicitis as defined
Appendiceal Depth on Graded Compression Statistical analysis was performed using Stata by the pathologic reference standard. All pa-
Sonography and Transducer Penetration software, utilizing the exact binomial distribution tients who underwent appendectomy had ap-
Using the relationship that transducer penetra- to evaluate 95% CIs of proportions and appendi- pendicitis according to this reference stan-
tion in centimeters equals approximately 60 divided ceal frequencies in individual quadrants, the mul- dard, and no patients who were managed
by the frequency in megahertz [34], the regression tinomial exact test with exhaustive enumeration to without surgery presented with appendicitis
model was solved for the CT depth measurement compare overall four-quadrant distributions with- during follow-up.
corresponding to the lowest-frequency penetration in single groups, the 2 × 4 Fisher exact test to com-
of our typical transducers of at least 10 MHz. Pa- pare four-quadrant distributions between groups, Distribution of Appendixes Among Quadrants
tients whose appendiceal depths exceeded this val- one-way ANOVA with the Bonferroni method As shown in Table 1, the distribution of
ue were then identified. Similar computations were to adjust for multiple comparisons and a t test to appendixes among the four quadrants was
performed for 6-MHz transducers. compare depth measurements, and linear regres- statistically significantly nonuniform in the
sion to relate depth measurements between graded entire sample of 197 patients (p < 0.0001)
Review of Medical Records compression sonography and CT. Results with p < as well as in the 31 patients with appendi-
Electronic medical records were reviewed by 0.05, including those indicated by nonoverlapping citis (p = 0.0015) and the 166 patients with-
an individual not otherwise involved in the study 95% CIs, were considered significant. out appendicitis (p  < 0.0001). A significant
majority lay in the posteromedial quadrant
among all patients and those without appen-
TABLE 2:  Appendixes Not Visualized by Sonography, Stratified by Patient
Group and Level of Appendix Relative to Iliac Crests dicitis (with nonoverlapping 95% CIs be-
tween the posteromedial quadrant and each
Patient Group Superior to Iliac Crests Inferior to Iliac Crests pa of the other quadrants) and a nonsignificant
All patients (n = 197) majority was present in the posteromedi-
al quadrant of patients with appendicitis. In
No. of patients 39 158
all three patient groups (all patients, patients
Percentage of patients (95% CI) 19.8 (14.5–26.1) 80.2 (73.9–85.5) with appendicitis, and patients without ap-
Patients with appendicitis (n = 31) pendicitis), appendixes were significantly
No. of patients 6 25 more frequently located in the posteromedial
quadrant compared with the 25.0% rate ex-
Percentage of patients (95% CI) 19.4 (7.5–37.5) 80.6 (62.5–92.5)
pected by chance (p < 0.00001, p = 0.0056,
Patients without appendicitis (n = 166) and p < 0.00001, respectively); the null hy-
No. of patients 33 133 1.00 pothesis was that appendixes are distributed
Percentage of patients (95% CI) 19.9 (14.1–26.8) 80.1 (73.2–85.9) equally among the four quadrants. Overall
aBy four-quadrant distributions between patients
Fisher exact test (a 2 × 2 comparison of the presence or absence of appendicitis with the location of
the appendix superior or inferior to the iliac crests). The p value is presented to two significant digits with and without appendicitis did not differ
after the decimal. significantly (p = 0.21).

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 Reasons for Nonvisualization of Appendix on Graded Compression Sonography

TABLE 3:  Depths of Appendixes Not Visualized by Sonography, Stratified by Patient Group and Quadrant Where
Appendix Was Located
Location of Appendix
Anterolateral Anteromedial Posterolateral Posteromedial
Patient Group All Quadrants Quadrant Quadrant Quadrant Quadrant pa
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All patients (n = 197)

Range 7–163 27–77 14–123 23–121 7–163
Mean (95% CI) 78.9 (75.1–82.7) 58 (48.8–67.2) 78.3 (63.7–92.9) 72.8 (65.2–80.4) 83.4 (78.5–88.2) 0.0034
Patients with appendicitis (n = 31)
Range 23–125 63–63 84–96 23–110 42–125
Mean (95% CI) 75.5 (67.2–83.9) 63.0 (63.0–63.0) 89.3 (74.2–104.5) 75.3 (55.3–95.2) 74.7 (63.4–86.0) 0.65
Patients without appendicitis (n =
166)
Range 7–163 27–77 14–123 42–121 7–163
Mean (95% CI) 79.5 (75.3–83.8) 57.1 (46.0–68.2) 76.1 (58.5–93.6) 71.9 (63.5–80.3) 84.6 (79.3–89.9) 0.0032
p = 0.45b p = 0.19b
Note—All depth measurements are expressed in millimeters.
a ANOVA with Bonferroni method to adjust for multiple comparisons. The p value is presented to two significant digits after the decimal.
bBy t test for the comparison of the appendiceal depth in patients with and without appendicitis. The p value is presented to two significant digits after the decimal.

Level of Appendixes Relative to Iliac Crests four quadrants was statistically significantly teromedial quadrant frequency that exceed-
As shown in Table 2, a statistically significant nonuniform for all three patient groups (p < ed the 25.0% rate expected by chance. Over-
majority of appendixes were located inferior to 0.0001, for each). For each patient group, most all four-quadrant distributions between patients
the iliac crests among all patients, patients with appendixes found below the iliac crests were with appendicitis and patients without appen-
appendicitis, and patients without appendicitis, located within the posteromedial quadrant, dicitis did not differ significantly whether the
as indicated by the nonoverlapping 95% CIs at a frequency that significantly exceeded the appendix was found above (p = 0.11) or below
between appendixes superior and appendixes 25.0% frequency expected by chance (for all (p = 0.48) the iliac crests.
inferior to the iliac crests for each of these three patients, p < 0.00001; for patients with appen-
patient groups. In addition, the presence or ab- dicitis, p = 0.00021; and for patients without ap- Depth of Appendixes on CT
sence of appendicitis was not associated with pendicitis, p < 0.00001). Above the iliac crests, Appendiceal depth on CT ranged from 7
location of the appendix superior or inferior to however, relatively few appendixes were pres- to 163 mm (mean, 78.9 mm) among the 197
the iliac crests (p = 1.00). ent and none of the three patient groups exhib- patients, and it did not differ significantly be-
As shown in Table 1, the distribution of ap- ited significant four-quadrant nonuniformity, a tween patients with appendicitis and patients
pendixes below the iliac crests among the majority in the posteromedial quadrant, or pos- without appendicitis (p = 0.45) (Table 3).

A B
Fig. 4—38-year-old woman with appendicitis who was not included in sample of 197 patients. Sonographic images show value of sonography performed with 6-MHz
transducer after nonvisualization of appendix on sonography performed with 10-MHz transducer.
A, Initial gray-scale sonographic image obtained at 10 MHz shows no appendix within posteromedial quadrant.
B, Color Doppler image obtained at 6 MHz after image shown in A shows appendix (arrow) and vessels in posteromedial quadrant.
(Fig. 4 continues on next page)

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 Lin et al.

Fig. 4 (continued)—38- depth on graded compression sonography in

year-old woman with
univariate analysis or multivariate analysis
appendicitis who
was not included (for sex, p = 0.29 and p = 0.46, respectively;
in sample of 197 for age, p = 0.30 and p = 0.44, respectively;
patients. Sonographic and for diagnosis, p = 0.63 and p = 0.58, re-
images show value of
spectively), and were excluded from further
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sonography performed
with 6-MHz transducer calculations. Linear regression of depth on
after nonvisualization of graded compression sonography as a function
appendix on sonography
performed with 10-MHz
of depth on CT yielded a slope of 0.61 (95%
transducer. CI, 0.48–0.73), a y-intercept of −3.03 mm, p <
C, Gray-scale ultrasound 0.001, and R2 = 0.71 (Fig. 3).
image obtained at 6 MHz
permits measurement of
enlarged 9-mm appendix Appendiceal Depth on Graded Compression
(between calipers) in Sonography Versus Transducer Penetration
posteromedial quadrant. Using the relationship between transducer
penetration and frequency reported by Sza-
bo and Lewin [34], transducers of at least
C
10 MHz, such as those typically used in our
As evaluated with ANOVA (Table 3), all (p = 1.00, for each pairwise combination). Ap- laboratory, would penetrate to a maximum
patients and patients without appendicitis had pendiceal depth in the posteromedial quadrant depth of 60 mm. Substituting this value into
significant nonuniformity in mean appen- did not differ significantly between patients the linear regression model yielded an equiv-
diceal depth among the four quadrants (p = with appendicitis and patients without appen- alent CT depth of 103 mm.
0.0034 and p = 0.0032, respectively); these dicitis (p = 0.19) (Table 3). Appendiceal depths on CT exceeded 103 mm
findings reflected significant pairwise differ- in 38 of the 197 patients (19.3%; 95% CI, 14.0–
ences between the posteromedial quadrant and Relationship Between Depth Measurements 25.5%). As shown in Table 4, the distribution of
the anterolateral quadrant (and only between on Graded Compression Sonography and CT appendixes with a depth exceeding 103 mm was
the posteromedial quadrant and anterolater- In linear regression analysis of the subset statistically significantly nonuniform among the
al quadrant) for these two patient groups (p = of 40 randomly selected patients, depth mea- four quadrants for all patients and for patients
0.0070 and p = 0.0090, respectively). Patients surements on CT correlated significantly with without appendicitis (p < 0.0001 for both pa-
with appendicitis exhibited neither significant depth measurements on graded compression tient groups), with the posteromedial quadrant
nonuniformity among the four quadrants by sonography in both univariate (p < 0.001) and accounting for a statistically significant majority
ANOVA (p = 0.65) (Table 3) nor significant multivariate analysis (p < 0.001). Sex, age, and of appendixes in both patient groups (with non-
pairwise differences among the four quadrants diagnosis did not correlate significantly with overlapping 95% CIs between the posteromedi-

TABLE 4:  Appendixes Not Visualized by Sonography and Located at Depths Exceeding the Penetration of Transducers
of at Least 10 MHz, Stratified by Patient Group and Quadrant Where Appendix Was Located
Location of Appendix pa
Anterolateral Anteromedial Posterolateral Posteromedial By Multinomial By Fisher
Patient Group Quadrant Quadrant Quadrant Quadrant Testb Exact Testc
All patients (n = 38)
No. of patients 0 4 7 27 < 0.0001
Percentage of patients (95% CI) 0 (0.0–9.3) 10.5 (2.9–24.8) 18.4 (7.7–34.3) 71.1 (54.1–84.6)
p < 0.00001d
Patients with appendicitis (n = 5)
No. of patients 0 0 3 2 0.18
Percentage of patients (95% CI) 0.0 (0.0–52.2) 0.0 (0.0–52.2) 60.0 (14.7–94.7) 40.0 (5.3–85.3)
p = 0.60d
Patients with appendicitis (n = 33)
No. of patients 0 4 4 25 < 0.0001 0.046
Percentage of patients (95% CI) 0.0 (0.0–10.6) 12.1 (3.4–28.2) 12.1 (3.4–28.2) 75.8 (57.7–88.9)
p < 0.00001d
a All p values other than inequalities are presented to two significant digits after the decimal.
bMultinomial test with exhaustive enumeration was used to evaluate overall frequencies of appendixes in four quadrants across each row.
cThe Fisher exact test is a 2 × 4 comparison of the distribution of appendixes in four quadrants in patients with appendicitis versus patients without appendicitis.
d The null hypothesis is 25.0% distribution in each of the four quadrants.

W134 AJR:209, September 2017

 Reasons for Nonvisualization of Appendix on Graded Compression Sonography

Fig. 5—26-year- in the posteromedial quadrant within the

old woman with
deep posterior pelvis, at frequencies statisti-
appendicitis and
periappendiceal cally significantly greater than that expected
abscess who was not by chance, whether appendicitis was present
included in sample of 197 or not. Additionally, sonographically nonvi-
patients. Sonographic
sualized appendixes were found above the il-
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image obtained at 6 MHz

shows appendix (long iac crests in 19.8% of patients and were pres-
arrow) in posteromedial ent at depths beyond the range of our typical
quadrant, cecum,
abscess, and focal loss
transducers of at least 10 MHz in 19.3% of
of submucosal layer at patients. No significant differences were evi-
appendiceal tip (short dent between normal appendixes and those
arrow) immediately with appendicitis with respect to quadrant lo-
after nonvisualization
of appendix on initial cation, craniocaudal level relative to the iliac
sonography performed crests, or depth from the skin.
at 10 MHz. Our findings were obtained from evalua-
tions of living patients who were undergoing
noninvasive imaging, and thus they may reflect
in vivo relationships in ways that previous sur-
gical or postmortem studies have not [35, 36].
To our knowledge, this is the first study to uti-
lize contemporaneous CT to evaluate potential
al quadrant and each of the other quadrants) at increased to 100 mm [34], and the equivalent anatomic reasons for nonvisualization of the
frequencies significantly greater than the 25.0% depth on CT would have increased to 169 mm appendix on graded compression sonography.
expected by chance for both patient groups (p < in the regression model. This increased pen- We employed orthogonal transverse and cra-
0.0001, for both groups). Although compari- etration would have been sufficient to reach niocaudal planes to accomplish localization,
son of the overall four-quadrant distributions the appendixes of all 197 patients in the sam- using four quadrants centered on the ileocecal
between patients with and without appendici- ple (100.0%; 95% CI, 98.1–100.0%), which valve in the transverse plane as well as the lev-
tis was of borderline statistical significance (p = ranged in depth from 7 to 163 mm on CT. el of the iliac crests in the coronal plane, with
0.046), caution is in order because very few pa- the appendiceal tip serving as the unique point
tients with appendicitis had appendixes deeper Discussion for appendiceal localization. In doing this, we
than 103 mm. On CT performed shortly after grad- sought to produce straightforward, rigorous or-
If 6-MHz transducers been used instead of ed compression sonography, a statistically thogonal data that could be correlated between
transducers of at least 10 MHz, penetration on significant majority (62.4%) of sonographi- CT and graded compression sonography; the
graded compression sonography would have cally nonvisualized appendixes were found region of the ileocecal valve is generally vis-

A B
Fig. 6—27-year-old woman with appendicitis who was not included in sample of 197 patients. Sonographic images show value of scanning above iliac crests after
nonvisualization of appendix below iliac crests.
A, Initial transverse gray-scale sonographic image shows iliac artery and vein (arrows) but no appendix in region below iliac crests.
B, Transverse gray-scale sonogram obtained after image in A shows appendix (arrows) adjacent to psoas muscle in region above iliac crests.

AJR:209, September 2017 W135

 Lin et al.

Fig. 7—10-year-old ed a regression model associating depth on CT

boy with appendicitis with depth on graded compression sonography.
who was not included
in sample of 197 Because appendixes were not visible on graded
patients. Sonographic compression sonography in our patient sample,
image shows enlarged we evaluated the depth of vascular structures
appendix (arrow) above
visible on both CT and graded compression
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iliac crests immediately

after nonvisualization sonography, performed regression analysis on
of appendix on initial these data, and then applied the results to ap-
sonographic image
of region below iliac
pendixes. This analysis revealed that 38 of 197
crests. appendixes (19.3%) were located at depths ex-
ceeding the penetration expected of the trans-
ducers of at least 10 MHz that we typically use
in our laboratory, with a statistically significant
majority of these located in the posteromedi-
al quadrant. Importantly, parallel analysis in-
dicates that 6-MHz transducers would reach
all the appendixes of our 197 patients. Accord-
ingly, although modern scanning benefits from
high-frequency high-resolution images that
show features such as mural hyperemia, hy-
ible on both modalities, and the iliac crests are In addition, the deep posterior pelvis beyond perechoic periappendiceal fat, and fine mural
visible on CT and are palpable during graded the cecum is an area not previously empha- anatomy, findings that are essential in the sono-
compression sonography. sized during evaluations in our laboratory or graphic evaluation of appendicitis [6–8, 25, 26,
This design represents a departure from in much of the previous literature [7, 11, 26– 29, 37, 38], a role clearly exists for lower-fre-
earlier reports that addressed surgical, post- 31]. In our sample, some of the appendixes in quency scanning as well.
mortem, and sonographic subjects, utilized the posteromedial quadrant and posterolateral On the basis of our findings, we encour-
more qualitative categories such as “splenic quadrant could be considered retrocecal in lo- age specific practical modifications to recent
or post-ileal,” “pelvic,” and “midpelvic,” and cation; however, definitions of retrocecal loca- graded compression sonography protocols,
variably intermixed transverse and cranio- tion are not uniform in the literature, and the such as the three-step algorithm reported by
caudal components of location [32, 33, 35, reported frequencies of retrocecal appendixes Chang et al. [9]. First, we propose having both
36]. Moreover, our subjects all had suspected vary widely (e.g., from 26.5–28.6% in stud- higher-frequency (at least 10 MHz) and low-
appendicitis with sonographically nonvisual- ies using graded compression sonography to er-frequency (6 MHz) transducers connected
ized appendixes and underwent contempora- 65.28% in large autopsy studies and 20.2–74% at the outset of each examination. Should the
neous CT, characteristics that may differen- in postmortem and surgical studies [32, 33, 35, appendix not be visualized with typical scan-
tiate them from subjects in earlier reports yet 36]. Although the preponderance of appendix- ning performed with transducers of at least 10
currently characterize these individuals as a es found in the posteromedial quadrant in our MHz, we suggest, first, targeted scanning of
clinically important and diagnostically chal- study could reflect the anatomy of the popula- the posteromedial quadrant and, second, pal-
lenging group of patients. tion in general, this is uncertain given the sub- pation of the iliac crests and targeted scanning
The preponderance of appendixes in the pos- stantial variability that exists in the literature of the region above them. Should the appen-
teromedial quadrant evident in our results may regarding appendiceal positions. dix still remain unseen, we suggest toggling
reflect several factors. First, anteriorly located Our results revealed that a substantial pro- to the lower-frequency transducer already
appendixes (those located in the anterolateral portion of appendixes that were not visualized connected and again addressing the postero-
or anteromedial quadrant) are closer to the skin sonographically were located above the iliac medial quadrant and the region above the il-
than are posteriorly located appendixes (those crests (19.8%), a region not routinely empha- iac crests. Once the appendix is visualized at
located in the posterolateral or anteromedial sized in our typical graded compression so- lower frequency, the sonographer can toggle
quadrant), as evidenced by their significantly nography examination or in much of the pre- back and use the higher-frequency transduc-
lesser mean depth. Additionally, as opposed vious literature [7, 11, 26–31]. These results er; the sonographer may then find it possible
to the posterolateral quadrant, the posterome- parallel those of previous studies. For exam- to visualize the appendix and generate high-
dial quadrant likely affords a tapering acoustic ple, appendixes were found above the iliac er-resolution images. These maneuvers spe-
window during the left posterior oblique step crests in 21.4% of patients with abdominal cifically address the 62.4%, 19.8%, and 19.3%
of the three-step sequential positioning algo- pain who underwent noncompressive sonog- of the nonvisualized appendixes found in the
rithm that we use [9]; the acoustic beam likely raphy [33], in 14.3% of patients with appen- posteromedial quadrant, above the iliac crests,
narrows as it passes behind the cecum before dicitis, and in 6.8% of patients without ap- and at depths exceeding the typical range of
reaching the posteromedial quadrant. Also, we pendicitis who underwent compressive and transducers of at least 10 MHz, respectively.
found that a statistically significant majority noncompressive sonography [32]. Figures 4 and 5 show the value of scanning
of appendixes in the posteromedial quadrant To evaluate appendiceal depth during grad- the posteromedial quadrant with a 6-MHz
were located beyond the range of the transduc- ed compression sonography and compare it transducer after nonvisualization of the ap-
ers of at least 10 MHz that we routinely use. with transducer penetration, we first generat- pendix with a 10-MHz transducer, and Fig-

W136 AJR:209, September 2017

 Reasons for Nonvisualization of Appendix on Graded Compression Sonography

ures 6 and 7 show the value of scanning above corroborate these findings and to evaluate role of abdominal wall thickness and appendiceal
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