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Received 15 May 2021 | Revised 20 June 2021 | Accepted 30 July 2021 | Published Online 9 Aug 2021

DOI: https://doi.org/xx.xxx/xxx.xx 
CMI JOURNAL 2 (3), 163−168 (2021) ISSN (O) 2694-4626 

CASE STUDY

Benign cystic mesothelioma: unknown cause of abdominal mass

N.Benjelloun 1∗        M.Salihoun 1        I.Serraj 1       M.Acharki 1       S.Sassi 2       K. Znati 2

Y. Bakali 3  |  F. Sabbah3 | N. Kabbaj 1

1Department of Gastroenterology
``EFD-HGE'', University Hospital
Ibn Sina Rabat, Morocco

2Department of Pathology,
University Hospital Ibn Sina,
Rabat

3Surgery Unit "Clinique
Chirurgical C", University
Hospital Ibn Sina, Rabat.

Abstract
Benign cystic mesothelioma (BCM) is a rare and benign disease that
arises from the peritoneal mesothelium. It occurs predominantly in
young to middle-aged women. The majority of cases were associated
with a history of abdominal or pelvic operation, an endometriosis,
and pelvic inflammatory disease. The etiopathogenesis is still unclear.
Malignant transformation is extremely rarewith only two cases reported
in the literature. Like the etiology, the name of this entity is also
controversial. Some authors prefer the term “peritoneal inclusion cyst”
instead of “benign multicystic mesothelioma” and argue that the term
mesothelioma should only be used when there is evidence of atypia.
Most cases of BCM are discovered incidentally. Others reflect sequela
of tumor mass effect. It appears intra-operatively as large, multi-
focal, cystic lesions in the peritoneal and pelvic cavity. Diagnosis is
achieved through surgical sampling with histopathological examina-
tion. Immunobiologically, BCM exhibits multiple small cystic spaces
with flattened lining containing calretinin positive cells without atypical
features, mitotic figures, or tissue invasion. Treatment includes cy-
toreductive surgery. We report on a 38-yearold woman who presented
an abdominal mass discovered incidentally. Laparoscopic exploration
revealed two cystic masses. The whole tumor was successfully excised
and histopathology revealed benign cystic peritoneal mesothelioma.
Keywords: cystic peritoneal mesothelioma, abdominal mass, la-
paroscopy

Copyright : © 2021 The Authors. Published by Medical Editor and
Educational Research Publishers Ltd. This is an open access article
under the CC BY-NC-ND license
(https://creativecommons.org/licenses/by-nc-nd/4.0/).

CMI JOURNAL 2 (3), 163−168 MEERP LTD 163

https://creativecommons.org/licenses/by-nc-nd/4.0/


1 INTRODUCTION

Benign cystic peritoneal mesothelioma
(BCM), a rare tumor, occurs mainly in
women in their reproductive age. The

pathogenesis of BCM is unclear and a controversy
regarding its neoplastic and reactive nature exists.
BCM is generally considered a benign process;
however, given the high rate of recurrence and
possible malignant transformation, close followup
is important. We would like to report a new case of
BCM associated with celiac disease.

2 CASE REPORT

We report the case of a 38-years-old women fol-
lowed in our unit for celiac disease. She was asymp-
tomatic and the systematic clinical examination
showed an isolated abdominal painless mass in the
left flank, measured approximately 20*30mm, fixed
at the profond plane.
The blood analysis showed normal findings,
leukocytes 5800/mm3, hemoglobin’s 13,2 g/dl,
and platelets 354.000/mm3. The biochemical test
results were as follows: C-reactive protein negative,
creatinine 0.83 mg/dl, with normal liver function.
The tumor marker tests; CEA and CA 19-9 were
negative. Abdominal ultrasonography showed two
well-limited rounded hypoechoic masses, measuring
2.54 * 3.20cm and 0.79 * 1.07cm in the left flank.
Abdominal computed tomography (CT) scan re-
vealed amesenteric lesion on the left flank, oval, well
limited, heterogeneous tissue and fluid, measuring
40 * 26mm (Figure 1), evoking a carcinoid tumor or
a gastrointestinal stromal tumor.

CT scan guided biopsy wasn’t done to avoide 
the dissemination of malignant cells. An 
exploratory laparoscopy which confirmed the 
presence of two masses measuring 4 cm and 2 cm 
next to the superior mesenteric axis. The 
intervention was converted to open laparotomy in 
order to resect those masses (Figure 2).

FIGURE 2: Operatory piece of mesenteric mass.

Supplementary information The online version of
this article (https://doi.org/xx.xxx/xxx.xx) contains
supplementary material, which is available to autho-
rized users.

Corresponding Author: N.Benjelloun
Department of Gastroenterology ``EFD-HGE'', Univer-
sity Hospital Ibn Sina Rabat, Morocco

CMI JOURNAL 2 (3), 163−168 MEERP LTD 164

The postoperative outcome was uneventful and the 
patient was discharged after 2 days without 
compli-cations. Macroscopic examination revealed 
8 formations, which one of them was a cystic mass 
of 4,5 cm in major axis with a fleshy yellow wall, 
and the others correspond to a fibrosis tissues. 
Microscopic examination showed cystic mass 
bordered by a sim-ple cubic coating, deprived of 
atypia and resting on a fibrous wall with few cells 
and crossed by a fine capillary network (Figure 3).

FIGURE 1: CT images: sagi al and axial views of 
the mesenteric lesion.



BENIGN CYSTIC MESOTHELIOMA: UNKNOWN CAUSE OF ABDOMINAL MASS

FIGURE 3: Histopathology results: cysts lined by
cuboidal mesothelial cells.

At Immunohistochemistry the tumor cells were re-
active for calretinin (Figure 4), and non-reactive for
Ber-EP4 (Figure 5), consistent with benignmulticys-
tic peritoneal mesothelioma.

FIGURE 4: Immunohistochemically reac on for
Calre nin

3 DISCUSSION

BCM, also known as multilocular peritoneal 
inclu-sion cysts, is an uncommon lesion arising 
from the peritoneal mesothelium that covers the 
serous cavity [1].

It is a rare disease that occurs most often in 
young women with an average age of 37 
years and is associated with a history of prior 
abdominal surgery, endometriosis or 
inflammatory pelvic disease [1,2].

Until 2019, there are less than 200 documented cases
worldwide, and it accounts for approximately 3-5%
of the peritoneal mesotheliomas and the estimated
incidence is 2 for 1,000,000 per year [2].
This tumor was originally described by Plaut in 1928
as a cyst of the pelvis after being discovered by
accident during a surgery of uterine leiomyomas. In
1979,Mennemeyer and Smith first defined the lesion
as a « multicystic peritoneal mesothelioma » in a
27- year-old female with multicystic diffuse lesion
involving omentum, peritoneum, and pelvic viscera
[3].
The pathogenesis of BCM is controversial due to its
association with pelvic inflammatory disease (PID),
endometriosis, leiomyoma, and a history of previous
surgery, some authors believe that it has a possible
reactive etiology. One of the hypotheses states that
chronic peritoneal inflammation triggers the prolif-
eration and migration of peripheral mesothelial cells
and associated connective tissue, giving rise to these
cysts. Some authors have proposed a neoplastic ori-
gin based on a slow but progressive growth of the
lesions, a tendency to recur after surgical resection,
and high disease related mortality in advanced stages
[4,5]. A genetic and familial association of BCM has
been reported by a few studies [4].

CMI JOURNAL 2 (3), 163−168 (2021) MEERP LTD 165

FIGURE 5: Immunohistochemically reac on for
BerEP4.



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N.BENJELLOUN ET AL.

In addition, some studies suggest that female sex
hormones play a role in its pathogenesis. This hy-
pothesis is supported by the fact that BCM occurs
mainly in females of reproductive age [2]. It has
a strong predilection mostly for the surface of the
pelvic viscera and serosal surfaces of the intestine
and omentum or in the retroperitoneal space, spleen,
and liver [3].
Malignant transformation is extremely rare, with
only two cases reported in the literature, despite the
potential recurrence [3,4].
Mostly, BCM is asymptomatic and is often discov-
ered incidentally on imaging or during laparotomy
for other indication [4,6]. Typical symptoms include
abdominal distention, abdominal tenderness, ascites,
nausea, and constipation, urinary symptoms, and
dyspareunia [5,7].When it reaches large sizes, it may
present as a painful abdominal mass. In addition,
its presentation in the form of acute abdomen had
been reported [6]. Abdominal tenderness, abdominal
distention, and palpable abdominal or pelvic mass
may be present on physical examination [4].
On ultrasound BCM typically appears as a multicys-
tic, vascular mass without calcifications (Figure 6).
this aspect is named « spider in the web » [5,7].
CT scan typically shows a multicystic lesion with
density similar to blood (Figure 7). It is used to eval-
uate the location and the extent of the cystic mass,
where lesion appears as a low-density, multilocu-
lated, and thin-walled multicystic mass. However,
the results obtained by US and CT scans do not
differentiate BCM from other cystic mass [2].
The definitive diagnosis is histopathological. The
electron microscopy or immunohistochemistry can
assist diagnosis. Serum tumor markers such as
CA125, CEA, CA-15.3, CA-19.9, ferritin, 2- mi-
croglobulin are usually normals with one case re-
ported, with elevated CA-19.9 with regression after
surgical treatment [10,11].
The management protocol isn’t consensual. While
fine-needle aspiration could be used as a diagnostic
tool, in most cases this method is not informative.
Laparoscopy is the most accurate diagnostic method
since it allows visualization, biopsies of the sus-
pected tissue with intraoperative frozen section if
possible, though an invasive procedure [3,6].

The BCM is characterized by solitary or multiple
cysts, with fine septa, multiloculated and filled with
serous fluid or blood. The size of lesions is few mil-
limeters to 30 centimeters. Themicroscopy shows up
multiple cystic spaces lined by cuboidal epithelium,
there is no atypia or mitosis, cysts are separated
by fibrous septa with areas of chronic inflammation
and proliferation stromal cells [9]. There have been
rare reports of transformation to low-grade malig-
nant mesothelioma, but it is generally classified as
a benign process [ 6,7].
The immunohistochemically study is important to
exclude possible mimic neoplasms cystic. Generally
positive markers include calretinin, D2-40, CK5/6
and WT-1, mesodermal markers present in epithe-
lia, especially the mesothelium. Markers MOC-31,
PAX8, BG8, Ber-EP4, B72.3, CEA, and CDX-2
are frequently negative. Most often used an epithe-
lial marker (cytokeratin), and CD34, an endothelial
marker that can also be used to exclude lymphan-
gioma or other suspected vascular neoplasms [9,7].
The differential diagnosis of BCM includes benign
and malignant cystic or multicystic abdominal tu-
mors such as cystic lymphangioma, endometriosis,
cystic forms of endosalpingiosis, cystic adenomatoïd
tumor, pseudomyxoma peritonei, malignant peri-
toneal mesothelioma. This last is a major differential
in the diagnosis of BCM, and distinguishing benign
and malignant mesothelioma is very crucial to pa-
tient care [4,10].
Due to its rarity, BCM treatment options remain an
area of controversy and there is no streamlined treat-
ment plan. Currently aggressive surgical resection is
the mainstay [10].
Alternative treatments such as hormonal therapy,
sclerotherapy, and potassium-titanylphosphate laser
vaporization have been proposed in the recent stud-
ies. Hormonal therapy with anti-estrogen drugs like
tamoxifen and GnRH agonist can be an alternative to
surgery in selected patients with estrogen-dependent
neoplasm, as they were showed to be associated
with a decrease in cyst volume. Laser vaporization
with potassium titanyl-phosphate laser were shown
to have a significant efficiency at penetrating the
tumor, but its therapeutic efficacy is still unknown.
Sclerotherapy consists of injecting povidone–iodine

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BENIGN CYSTIC MESOTHELIOMA: UNKNOWN CAUSE OF ABDOMINAL MASS

or ethanol through a catheter directly into the cyst
[2,11].
The treatment of choice for multicystic mesothe-
lioma is total surgical excision. Chemotherapy and
radiation therapy are generally not indicated, because
benign nature of this process. Some authors have
proposed heated intraperitoneal chemotherapy as a
possible treatment option, but there is inadequate
evidencebased research on this topic [11,12].
Although BCM is associated with a favorable prog-
nosis in a short term, because it is a completely
benign condition; in long term it has been described
about 50% after a period of 3 to 27 months (mean
32 months). There is a 40–55% recurrence rate in
female patients and a 33% recurrence rate in male
patients. No risk factors predicting the recurrence of
BCM have been identified yet [5,7,9].
There is evidence that malignant transformation
could occur. There are two cases described of malign
processing [7].
A long follow-up period is always necessary, al-
though there is still no consensus on when and what
additional tests should be ordered. Some authors
suggest that CT should be done every 3 months for
the first year after resection and then annually for the
next 5 years [4].

4 CONCLUSIONS

BCM is a rare benign neoplasm that is associated
with no well-defined symptoms, typical clinical, or
imaging data. The diagnosis remains unclear and the
definitive diagnosis requires histology and immuno-
histochemistry. BCM has a high risk of recurrence
and a significant potential of malignant transforma-
tion.

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How to cite this article: N.B., M.S., I.S., M.A., 
S.S., K.Z., Y.B., F.S., N.K. Benign cystic mesothe-
lioma: unknown cause of abdominal mass. Clinical 
Medicine Insights. 2021;163−168. https://doi.org/
xx.xxx/xxx.xx

MEERP LTD CMI JOURNAL 2 (3), 163−168 (2021) 168


	Introduction
	Case Report
	Discussion
	Conclusions
	References 



