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Case Report
Torsion of the Appendix Secondary
to Appendiceal Mucocele
Gray Scale and Contrast-Enhanced
Sonographic Findings
Toshihide Hamada, MD, Keiichi Kosaka, MD, Naoya Shigeoka, MD,
Yoshimasa Hashimoto, MD, Masami Yamauchi, MD, Sonde Cho, MD,
Kuniharu Nakai, MD, Shohei Ishimaru, MD, Kenji Suenaga, MD
ucinous cystadenoma of the appendix, or the so-called appendiceal
mucocele, is a rare disease entity1 that has been infrequently diagnosed
before surgery or autopsy because of its lack of specific diagnostic features. With the development of cross-sectional imaging techniques,
including sonography and computed tomography, the number of reports describing
preoperatively diagnosed cases has increased.2–5
Most cases of this disease are clinically asymptomatic; however, on occasion, several
complications may be associated with it, such as intussusception and, in the case of
perforation, pseudomyxoma peritonei. Although mucoceles originating in the ovary
may occasionally be complicated by ovarian or adnexal torsion, the torsion of an
appendiceal mucocele is extremely rare. To our knowledge, 42 cases of torsion of the
vermiform appendix have been reported in the literature; of these, only 6 cases were
associated with an appendiceal mucocele.6–11
We hereby present a case of torsion of the appendix that occurred secondary to an
appendiceal mucocele that was diagnosed preoperatively by using gray scale and contrast-enhanced sonography. Preoperative gray scale sonography showed a targetlike
appearance at the base of the appendix that indicated the presence of this disease condition. In addition, contrast-enhanced sonography was useful in evaluating the viability of the appendiceal wall. We present the sonographic findings of mucinous
cystadenoma of the appendix with associated torsion and evaluate their correlation
with surgical and pathologic findings.
Case Report
Received July 20, 2006, from the Department of
Gastroenterology, Miyoshi Central Hospital, Miyoshi,
Hiroshima, Japan. Revision requested August 4,
2006. Revised manuscript accepted for publication
August 8, 2006.
Address correspondence to Toshihide Hamada,
MD, Department of Gastroenterology, Miyoshi
Central Hospital, 531 Higashisakeya, Miyoshi,
Hiroshima 728-8502, Japan.
A 79-year-old man was admitted to the emergency department of our hospital for abrupt onset of severe abdominal
pain approximately 1 hour after the occurrence of the
first symptoms. On clinical examination, his abdomen was
tender predominantly in the right lower quadrant; however, no signs of peritoneal irritation were elicited. The
laboratory findings included a white blood cell count of
10,600/mm3 with 89% neutrophils and a C-reactive protein level of 0.6 mg/L; the other findings were normal.
© 2007 by the American Institute of Ultrasound in Medicine • J Ultrasound Med 2007; 26:111–115 • 0278-4297/07/$3.50
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Torsion of the Appendix Secondary to Appendiceal Mucocele
We performed a sonographic assessment
immediately after obtaining the patient’s history
and conducting his physical examination. The
patient was not given oral water or other contrast
agents to distend the intestinal lumen before the
sonographic examination.
A gray scale scan showed the presence of a localized cystic lesion in the right lower abdomen
(Figure 1) that corresponded to the area of maximum tenderness. On sonographic examination,
the size of the lesion was observed to be approximately 6 × 3 cm. Sonography clearly showed a
complex structure with a targetlike appearance
that connected the blind-ended structure to the
cecum (Figure 2). The complex structure was seen
at the base of the cystic mass. On the longitudinal
gray scale scan of the cystic mass, the complex
structure was observed to have a targetlike appearance that revealed high, low, and high echogenicity from inside outward; this phenomenon is
similar to the “whirlpool sign” observed in cases of
ovarian and testicular torsion.12,13 No other luminal
structures, except for the terminal ileum, could
be detected extending from the cecum. Thus, we
identified the cystic structure as the appendix itself.
When a 3.5-MHz convex probe was used, the
space inside the cystic lesion was observed to be
hypoechoic without definite internal echoes
(Figure 1). On the other hand, when a 7-MHz linear probe was used, multiple echogenic layers,
similar to an onion skin, were visualized, particularly at the margins of the structure (Figure 3). In
contrast to severe appendicitis, no collection of
free fluid or a consequent hyperechoic zone was
present adjacent to this structure.
To evaluate the viability of the appendiceal wall,
we first performed conventional Doppler imaging;
however, only a few signals were depicted on the
appendiceal wall, and the whirlpool sign was not
evident at the base of the appendix, the region
where the targetlike appearance was observed on
gray scale sonography. Consequently, to obtain
more detailed hemodynamic information, we conducted contrast-enhanced intermittent Doppler
sonography (flash echo imaging) after the administration of Levovist (Schering AG, Berlin, Germany)
at a concentration of 300 mg/dL. The focus point
was set as close to the structure as possible. The
imaging parameters were set as follows: mechanical index, 1.6; dynamic range, 60 dB; velocity
range, 53.7 cm; and high-pass Doppler filter cutoff, 290 Hz. Unlike conventional Doppler imaging,
contrast-enhanced Doppler sonography clearly
depicted Doppler signals along the entire wall of
the appendix (Figure 4).
On the basis of the above-mentioned findings,
the preoperative sonographic diagnosis of this
condition was that of an appendiceal mucocele,
which was suspected to have undergone torsion
without any necrotic change. The patient
underwent emergency surgery, after which we
found an appendiceal mucocele with a 180°
anticlockwise twist at its base; the appendix was
congested but revealed no severe ischemic
changes (Figure 5). Thus, an appendectomy was
performed. Pathologically, the specimen was
confirmed as mucinous cystadenoma of the
appendix (Figure 6). The surgical and pathologic
findings corresponded well with the gray scale
and contrast-enhanced sonographic findings.
Figure 1. Longitudinal sonographic scan (with a 3.5-MHz convex probe) of the appendix shows a large cystic mass with few
internal echoes and a surrounding thin wall.
Figure 2. Longitudinal sonographic scan at the base of the
appendix shows the targetlike appearance (arrows).
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Hamada et al
Figure 3. High-resolution gray scale sonogram (with a 7-MHz linear probe) of the swollen appendix. On both the longitudinal (A)
and axial (B) views of the appendix, echogenic layers, similar to an onion skin, were visualized in part of the cavity.
Mucinous cystadenoma of the appendix, the
so-called appendiceal mucocele, is a rare disease entity that is found in 0.2% to 0.3% of
appendectomies.1 In addition, appendiceal
torsion is also an extremely rare disease condition, and, to our knowledge, only 42 cases
have been reported. Of these, only 6 cases
with appendiceal torsion secondary to an
appendiceal mucocele have been reported to
date6–11; this is the seventh case report of this
Val-Bernal et al14 reported that the direction
of appendiceal rotation is more frequently
anticlockwise, which was in agreement with
that of our case. In addition, they reported that
the degree of rotation in the cases reported
with this disease entity varied from 270° to
1080° (mean, 580°). In our patient, the degree
of rotation of the appendix was 180°, which is
the least degree of rotation observed among
the cases reported to date.
J Ultrasound Med 2007; 26:111–115
The sonographic features of an appendiceal
mucocele have been well described by Caspi et
al.5 They have stated that a sonographically layered cystic mass, which they named the “onion
skin sign,” in the right lower quadrant of the
abdomen in the presence of a normal ovary
Figure 4. Contrast-enhanced Doppler sonogram shows clearly
that intramural perfusion exists in the entire wall of the appendix
and its twisted base.
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Torsion of the Appendix Secondary to Appendiceal Mucocele
Figure 5. Enlarged appendix secondary to appendiceal mucocele with a 180° anticlockwise twist in its base.
strongly suggests the diagnosis of appendiceal
mucocele; this agreed with our findings,
although our patient was male. We could easily
diagnose the cystic mass with the multiple
echogenic layers as an appendiceal mucocele.
There are only a few case reports of patients
who underwent preoperative sonography for
appendiceal torsion; however, to our knowledge,
no reports have shown the sonographic appearance of appendiceal torsion itself. Here, we
describe the sonographic appearance of this disease condition.
In our patient, sonography showed a targetlike
appearance at the base of the appendix that was
similar to that seen in cases of ovarian and testicular torsion12,13; this is known as the whirlpool
sign. The targetlike appearance was visualized on
gray scale sonography as high, low, and high
Figure 6. Resected appendix with appendiceal mucocele filled
with gelatinous material. Pathologic examination revealed mucinous cystadenoma of the appendix.
echogenicity from the inner to the outer layers. A
comparison of these results with the surgical
findings showed that they corresponded to the
inner luminal echo, the appendiceal wall, and
the fatty connective tissue adjacent to the
appendix, such as the mesoappendix, respectively. The sonographic appearance described above
led us to suspect this disease condition preoperatively. In addition, there was no free fluid adjacent to the appendix suggestive of perforation;
nevertheless, the patient had severe abdominal
pain. From these sonographic findings, we first
suspected torsion of the appendix, which thereby progressed to ischemia of the appendix. To
evaluate the viability of the appendix, we first performed conventional Doppler imaging, which
showed hyperemia at the base of the appendix;
however, few color signals were observed in the
major portion of the appendiceal wall. To obtain
more detailed information on the hemodynamics of the bowel wall, we subsequently conducted contrast-enhanced Doppler imaging. We
observed clear enhancement not only at the
base of the appendix but also in the entire wall of
the appendix, where the conventional Doppler
imaging had depicted few Doppler signals. The
surgical and the pathologic findings were almost
in agreement with those of the contrastenhanced sonography.
We believe that the discrepancy between the
findings of the conventional Doppler imaging
and the contrast-enhanced Doppler imaging are
a result of the fundamental sensitivity of these
investigating modalities. Conventional Doppler
sonographic imaging is considered to be inadequate for detecting subtle Doppler shifts, such as
circulation in minute vessels perfusing the bowel
wall. In recent years, the significance of contrastenhanced sonography has been discussed in
several reports,15–18 and it has increased in importance in the evaluation of transmural bowel wall
perfusion. Particularly, the use of Levovist combined with the flash echo mode for Doppler
imaging (ie, loss of correlation image) has been
attracting attention for the evaluation of minute
visceral perfusion. Because of Doppler frequency
shifts that are produced by bubble collapse, this
imaging technique facilitates the detection of
minute vessels independent of the blood flow
velocity. Therefore, compared with conventional
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Hamada et al
Doppler imaging, contrast-enhanced Doppler
sonography appears to be more appropriate for
evaluating bowel viability.
On the basis of the sonographic findings, a representative differential diagnosis of this disease
condition includes an appendiceal abscess and
suppurative appendicitis. We suppose that
the sonographic findings best discriminating
between these diseases would be as follows.
Appendiceal mucocele does not involve circumferential inflammation adjacent to the distended
appendix, unless it is complicated by inflammatory changes or rupture. On the other hand, an
appendiceal abscess and suppurative appendicitis are generally accompanied by surrounding inflammatory changes such as the
thickening of adjacent fat tissue and free fluid
collection. In our patient, sonography showed
few changes adjacent to the distended appendix,
except at the base of the appendix where the torsion had occurred. In addition, an appendiceal
abscess does not have a wall structure, whereas
appendiceal mucocele does have a wall.
If the patient is female, this disease condition
can mimic torsion of ovarian mucocele. These
disease conditions can be distinguished from
each other on sonography if we can determine
whether the lesion extends from the cecum or
from the uterine adnexa; however, if the twisted
lesion is extremely complex, its sonographic
identification might be difficult. Fortunately, it
was relatively easy in our case.
In conclusion, we have reported an extremely
rare case of appendiceal mucocele with torsion
that was assessed preoperatively by gray scale and
contrast-enhanced Doppler sonography. On gray
scale sonography, the targetlike appearance was
useful in identifying appendiceal torsion. In addition, in our case, contrast-enhanced sonography
was particularly useful for preoperative evaluation
of the appendiceal viability after torsion.
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