A giant mucinous cystadenocarcinoma of the appendix: a case report and review of the literature

A previously healthy 63-year-old woman presented with a chief complaint of abdominal
distention. She denied abdominal pain, nausea, or constipation. She also did not have
any relevant medical history. Her abdomen was remarkably distended but was soft and
nontender. Blood test indicated slight anemia of hemoglobin (10.2 g/dL; normal range,
11.6–14.8 g/dL) and increased levels of the carcinoembryonic antigen (CEA) and cancer
antigen 19-9 (CA19-9) to 406.1 ng/mL (normal range, 0–5.0 ng/mL) and 66 U/mL (normal
range, 0–37.0 U/mL), respectively. The CA-125 level was normal.

Contrast-enhanced computed tomography (CT) showed a well-encapsulated, unilocular
cystic mass with focal mural calcification. It occupied her entire abdomen from just
below the diaphragm to the pelvis, and it measured 40.2 cm in length (Fig. 1). Magnetic resonance imaging (MRI) demonstrated a cystic mass with high signal intensity
on T2-weighted images and intermediate signal intensity on T1-weighted images (Fig. 2). These imaging studies also showed a dendritic structure protruding into the cavity,
and the feeding artery originated from a branch of the ileocecal artery. Extrinsic
obstruction due to the giant mass was identified on colonoscopy, but the orifice of
the appendix remained intact. Based on these results, our preoperative diagnosis was
a large neoplastic mucocele of the appendix.

Fig. 1. Contrast-enhanced computed tomography showed a well-encapsulated, unilocular cystic
mass which occupied the entire abdomen from just below the diaphragm to the pelvis.
Arrow showed a dendritic structure protruding into the tumor cavity

Fig. 2. Magnetic resonance imaging demonstrated a giant unilocular cystic mass with high signal
intensity on T2-weighted images (a) and intermediate signal intensity on T1-weighted images (b)

Laparotomy showed the enlarged appendix, which occupied the entire abdomen. A mucinous
deposit was not found in her abdominal cavity, and the ovaries were grossly normal
bilaterally. Even though the cyst adhered strongly to the abdominal wall due to inflammation,
ileocecal resection was performed uneventfully.

The cystic mass contained about 7000 mL of serous fluid. The levels of CEA and CA19-9
in the fluid were 57,905 ng/mL and 1380 U/mL, respectively. Macroscopically, a cross-section
of the mass showed a cystically dilated lumen containing mucin, and the portion protruding
from the appendiceal lumen looked like a villous tumor (Fig. 3). The histopathological diagnosis was a mucinous adenocarcinoma with a low-grade
mucinous neoplasm that had invaded the wall into the subserosa (Fig. 4). Regional lymph node metastasis was not detected. The levels of CEA and CA19-9 were
within normal range 3 months postoperatively, and the patient has had recurrence-free
survival for 5 years.

Fig. 3. a A cross-section of the mass showed a cystically dilated lumen with the portion protruding
from the appendiceal lumen (arrow). b A magnified view of the dendritic structure which appeared as a villous tumor

Fig. 4. a Microscopical view of the tumor showed a mucinous adenocarcinoma, and a low-grade
mucinous neoplasm is intermingled (hematoxylin and eosin stain, ×20). b Adenocarcinoma is observed to invade the subserosa of the appendix (hematoxylin and
eosin stain, ×50)

Discussion

We report a rare case of a giant appendiceal mucocele caused by mucinous cystadenocarcinoma,
which occupied the entire abdomen of an adult woman.

An appendiceal mucocele is a morphologic entity referring to the distention of the
appendicular lumen due to the accumulation of mucus. It has been a long time since
it was first described by Rokitansky 3], but the terminology for appendiceal mucocele has not been agreed on 4]. Mucoceles of the appendix have been classified into four types: (1) a simple mucocele
or retention cyst resulting from obstruction of the appendiceal outflow, (2) mucosal
hyperplasia, (3) a benign mucinous cystadenoma, and (4) a mucinous cystadenocarcinoma
5], 6]. A mucinous cystadenocarcinoma is the second most common etiology after mucinous
cystadenoma, and it accounts for 11 to 20 % of cases of appendiceal mucoceles.

Although luminal dilatation is mild (up to 1 cm) in retention mucocele and hyperplasia,
mucinous cystadenoma and cystadenocarcinoma often exhibit marked distention 7]. We searched PubMed for publications on mucoceles of the appendix with the keywords
“giant” and “large,” and there have been about 50 cases reported from 1919 to 2015.
The median diameter was 13 cm, and the largest mucocele ever reported was 40 cm in
diameter, which was caused by a mucinous cystadenoma 8]. The majority of these giant mucoceles were caused by mucinous cystadenomas, whereas
cystadenocarcinomas were the cause of only a few cases 9]–14]. Therefore, the present case is rare in two respects: it is the largest mass among
all types of appendiceal mucoceles, and it is a giant mucocele caused by a cystadenocarcinoma.

A mucocele is usually diagnosed by an abdominal CT scan. The typical finding of an
appendiceal mucocele is a low attenuated, well-encapsulated, thin-walled cystic mass
in the right lower quadrant. Mural calcification is seen in less than 50 % of cases
6]. MRI demonstrates a mass with intermediate signal intensity on T1-weighted images
and homogeneous high signal intensity on T2-weighted images 15], 16]. An enhancing nodule in the mucocele wall is suggestive of a cystadenocarcinoma.
In the present case, the dendritic structure within the cystic cavity was a clue to
suspect malignancy.

However, the precise preoperative distinction between a cystadenoma and cystadenocarcinoma
is often difficult 17], 18]. The tumor marker level is insufficient for an accurate diagnosis, because it is
still unclear whether there is a difference in the serum or cystic fluid of CEA and
CA19-9 levels between cystadenomas and cystadenocarcinomas 19], 20].

The boundary between cystadenomas and cystadenocarcinomas is ambiguous even in a pathological
study. The term “mucinous tumor of low malignant potential” 21] or “low-grade appendiceal mucinous neoplasm” 22] was introduced to describe intermediate grades between cystadenomas and cystadenocarcinomas
23]. Furthermore, various subclassifications have been proposed according to the presence
of acellular peritoneal mucin deposits or extra-appendiceal neoplastic epithelium
21], 22].

The Peritoneal Surface Oncology Group International recently reported the consensus
for classification and pathologic reporting 24]. It argues that the term “cystadenoma” should no longer be used as a diagnostic term
with regard to the appendix. Mucinous adenocarcinoma is defined as a mucinous tumor
with infiltrative invasion. Mucinous neoplasm with low-grade cytologic atypia is classified
as low-grade appendiceal mucinous neoplasm (LAMN) regardless of its associated features.
The term “high-grade appendiceal mucinous neoplasm” was proposed for lesions with
low-grade architectural features similar to LAMN but with high-grade cytologic features.

The operative strategy is also changing. It was the standard concept, and it still
is in many facilities, that if the histological diagnosis is hyperplasia or cystadenoma,
appendectomy is the definite treatment, but if it is a cystadenocarcinoma, resection
should be combined with right colectomy 25], 26]. However, appendectomy combined with excision of all the mesoappendiceal fat can
be adequate in patients with a cystadenocarcinoma in the absence of mesenteric adjacent
organ or peritoneal involvement 27], 28]. Obviously, right hemicolectomy is advised if tumor clearance is required.

Formerly, an appendiceal mucocele was considered an indication for open surgery, but
now, many surgeons think that laparoscopic appendectomy is a reasonable choice when
treating a mucocele of the appendix 29]. However, extreme care is imperative to avoid underestimating the extent of the disease
and prevent iatrogenic rupture and dispersion of mucus or epithelial cells into the
peritoneal cavity during the surgical procedure. In the current case, we converted
to open ileocecal resection to achieve curative operation without causing intraoperative
rupture.