Baylor University Medical Center Proceedings January 2014, Volume 27, Number 1 | Page 36

DISCUSSION
Mucocele of the appendix is a descriptive term that refers
to dilation of the appendiceal lumen as a result of mucin accumulation and is based on the gross or macroscopic appearance
of the appendix. Mucocele formation is most commonly caused
by epithelial proliferation, either benign or malignant. Much
less frequently, inflammatory or obstructive causes, to include
appendicitis and obstruction by a fecalith or appendicolith, are
the cause of mucocele formation.
Mucinous neoplasms of the appendix are classified on a
spectrum from benign to malignant based upon certain features during histologic examination. On the benign end of the
spectrum, there is the mucinous cystadenoma with no risk of
recurrence. On the malignant end of the spectrum is the mucinous adenocarcinoma with a very poor survival rate and a
high rate of metastases to lymph nodes and liver. In between
these disparate entities lie the mucinous neoplasms with low
and high rates of recurrence. There is controversy in using the
descriptors low and high rates of recurrence with mucinous
neoplasms, as the World Health Organization classifies both
in the term “low-grade mucinous neoplasm.” Many prefer to
use the descriptors because the risk of recurrence and associated
morbidity and mortality differ greatly between the two (1).
These intermediate-grade tumors are characterized by mucin
dissecting into or through the wall of the appendix with or
without epithelial cells. Extraappendiceal mucin with epithelial
cells characterizes the mucinous neoplasm with a high rate of
recurrence. This is the neoplasm of the appendix that is most
commonly the cause of pseudomyxoma peritonei, a complication characterized by noninvasive mucinous deposits throughout the peritoneum (Figure 2).
Mucoceles are frequently discovered incidentally, as most are
the result of a mucinous cystadenoma that causes no inflammation (2). When imaged with CT, a mucocele of the appendix
will typically manifest as homogenous hypoattenuating material
that has Hounsfield values similar to water filling the lumen
of the appendix. The presence of curvilinear calcification in
the wall of the appendix is highly suggestive of a mucocele
(3). The spatial resolution of CT usually allows for a confident
diagnosis of a dilated appendix. When extending into the pelvis of a woman, the appendix must be differentiated from the
right ovary and fallopian tube, as a cystic ovarian neoplasm,
tubo-ovarian abscess, and hydrosalpinx could have a similar
appearance. Additional differential diagnoses include enteric
duplication cyst, mesenteric cyst, and Meckel diverticulum.
Mucoceles are treated surgically, and the preoperative diagnosis aids in the planning of a careful mobilization and resection
to prevent peritoneal contamination. A right hemicolectomy
is frequently performed if a malignant cause is suspected based

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Figure 2. Coronal CT image of the abdomen and pelvis shows multiple lowdensity collections throughout the abdomen and pelvis causing mass effect on
adjacent organs, compatible with pseudomyxoma peritonei (white stars).

on imaging or on intraoperative frozen section (4). Right hemicolectomy was not performed in these cases because frozen
section analysis at the time of surgery showed no malignant
characteristics. Since the risk of developing an adenocarcinoma
of the colon is six times greater in patients with a mucocele than
in the general population, colonic surveillance is warranted in
these cases (5).
1.

2.
3.

4.
5.

Pai RK, Longacre TA. Appendiceal mucinous tumors and pseudomyxoma
peritonei: histologic features, diagnostic problems, and proposed classification. Adv Anat Pathol 2005;12(6):291–311.
Persaud T, Swan N, Torreggiani WC. Giant mucinous cystadenoma of
the appendix. Radiographics 2007;27(2):553–557.
Pickhardt PJ, Levy AD, Rohrmann CA Jr, Kende AI. Primary neoplasms
of the appendix: radiologic spectrum of disease with pathologic correlation. Radiographics 2003;23(3):645–662.
Dhage-Ivatury S, Sugarbaker PH. Update on the surgical approach to
mucocele of the appendix. J Am Coll Surg 2006;202(4):680–684.
Federle MP, Anne VS. Mucocele of the appendix. In Federle MP, ed. Diagnostic Imaging: Abdomen. Salt Lake City, UT: Amirsys, 2004:26–27.

Baylor University Medical Center Proceedings

Volume 27, Number 1