Benign multicystic mesothelioma (BMCM) of omentum and peritonium is a rare intra-abdominal lesion of unknown etiology. Incidence is more common in females of child-bearing age group. Rarity of this tumor and non-specific symptoms causes preoperative diagnostic dilemma. Precise diagnosis requires immunohistochemistry study. Despite of high recurrence rate, aggressive surgical excision is the treatment of choice. Our case report of BMCM is a rare as it was detected in a young male patient and there was involvement of omentum only.

1.
A rare omental tumor presenting as pelvic
mass - A case report

2. Case Report
A rare omental tumor presenting as pelvic
mass e A case report
Diwakar Sahu, Somak Das, Majid R. Wani, Prasanna K. Reddy*
Apollo Hospital, Greams Road, Chennai, India
a r t i c l e i n f o
Article history:
Received 24 July 2014
Accepted 29 July 2014
Available online xxx
Keywords:
Omental tumor
Benign multicystic mesothelioma
Mesothelioma
a b s t r a c t s
Benign multicystic mesothelioma (BMCM) of omentum and peritonium is a rare intra-
abdominal lesion of unknown etiology. Incidence is more common in females of child-
bearing age group. Rarity of this tumor and non-specific symptoms causes preoperative
diagnostic dilemma. Precise diagnosis requires immunohistochemistry study. Despite of
high recurrence rate, aggressive surgical excision is the treatment of choice. Our case
report of BMCM is a rare as it was detected in a young male patient and there was
involvement of omentum only.
Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.
1. Introduction
Primary omental tumors are very rare as compared to meta-
static tumors. Benign multicystic mesothelioma (BMCM) is a
rare form of tumor arising from cellular lining of abdominal
cavity. The most common site is the peritoneum followed by
uterus, ovary, bladder, rectum or retro-peritoneum. Incidence
is more common in females of child-bearing age (83%) and in
most cases, there will be an associated history of previous
abdominal surgery, pelvic inflammatory disease or endome-
triosis.1
Unlike pleural mesothelioma, peritoneal type is not
related to asbestos exposure.2
Pathogenesis is controversial
and two hypotheses have been proposed which are reactive
and neoplastic.1,3
Recurrence rate after surgery is reported
to be quite high (33e50%).4
BMCM usually presents with
symptoms due to pressure effects of massive lesion
including abdominal pain, fullness & distension. Definite
diagnosis is made with a combination of histopathology and
immunohistochemistry.5
2. Case report
A 19 year old male patient presented with a history of inter-
mittent mild abdominal pain since two years and fullness of
lower abdomen for last six months. On examination, an
abdominal lump of size 15 Â 12 cm was palpable occupying
the hypogastrium and extending into the pelvis. Consistency
was firm with smooth surface, ill defined margins and mini-
mal side to side mobility. Routine blood investigations showed
no obvious abnormality. Serum level of tumor markers
including CEA, CA19-9, AFP and CA-125 were within normal
limits. Ultrasound abdomen reported a large cystic anechoic
lesion with multiple internal septations. CT abdomen
revealed a diffuse cystic lesion in pelvis which was reaching
* Corresponding author.
E-mail address: drpkreddyapollo@gmail.com (P.K. Reddy).
Available online at www.sciencedirect.com
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Please cite this article in press as: Sahu D, et al., A rare omental tumor presenting as pelvic mass e A case report, Apollo
Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.07.017
http://dx.doi.org/10.1016/j.apme.2014.07.017
0976-0016/Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.

3. upto umbilical level with thin septations with no significant
enhancement after contrast [Fig. 1]. No infiltration into
bladder, sigmoid colon & small bowel was reported and
impression of lymphangioma of lower half of omentum was
made. So, based on CT scan finding, strongly favoring a benign
tumor, patient was posted for surgery. During laparotomy, a
large 20 Â 16 cm multi-loculated mass involving the lower half
of omentum was found [Fig. 2]. It was adherent to anterior
abdominal wall, urinary bladder & sigmoid colon and con-
sisted of multiple locules or cysts (1e5 cm in diameter) with a
thin translucent wall and clear watery content. The tumor
was occupying almost whole of the pelvis and there was no
infiltration into bladder or colonic wall. Adhesions were
released & complete excision of tumor was done [Fig. 3]. His-
topathological examination was suggestive of a multicystic
lesion, lined by clusters of mesothelial cell, with abundant
eosinophilic cytoplasm & hobnail appearance [Fig. 4]. So,
diagnosis of a benign multicystic lesion was made with
possibility of benign multicystic mesothelioma and omental
lymphangioma. Subsequently, immunohistochemistry (IHC)
was done for confirmation which showed positive staining for
cytokeratin, calretnin, CK7 and WT1. Also, staining was
negative for CD31, CD34 and CK20. Ultimately based on IHC,
diagnosis of benign multicystic omental mesothelioma was
made.
Post operative recovery of the patient was uneventful and
after six months of surgery, there are no signs of recurrence or
any complications.
3. Discussion
Mesothelioma arises from the epithelial and mesenchymal
component of the mesothelium. Omentum is composed of
two layers of mesothieal cells and most of tumors arising from
it, including BMCM, are mesenchymal in nature. Benign
multicystic mesotheioma involving the peritonium was first
described in 1979 by Mennemeyer and Smith.6
As mentioned,
Fig. 1 e CT scan showing multicystic lesion involving omentum.
Fig. 2 e BMCM of omentum. Fig. 3 e Specimen of BMCM.
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Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.07.017

4. it occurs mainly in women of child-bearing age but cases of
BMCM have been reported in children and adults. Pathogen-
esis is mainly inflammatory in origin as tumor microscopi-
cally reveals inflammatory features and there will be history
of endometriosis or PID and abdominal surgery. In view of the
progressive growth pattern, large tumor size and tendency to
recur after surgery, some authors consider that origin of
tumor is neoplastic.1,4
According to inflammatory origin the-
ory, chronic irritation causes peritoneal reaction in form of
entrapment of mesothelial cells, leading to reactive prolifer-
ation and multiple cyst formation.4
Role of female sex hor-
mones has been implicated in its pathogenesis as it is more
common in females and few case reports show ER & PR
expression.7
Grossly, BMCM is characterized by multiple cysts filled
with mucinous or clear fluid ranging from several mm to
>20 cm in diameter. Few cases of malignant transformation
have been reported and it is characterized by destructive
growth with infiltration of the entire omentum or adjacent
organs, cellular atypia and increased mitotic count.1,4,8
Preoperative diagnosis is often difficult. CT scan is the most
useful diagnostic modality and BMCM is characterized by
well-defined, low-attenuation mass with non-enhancing
septa. Also, it gives information regarding involvement of
adjacent organs and cyst's contents, thus helps to determine
feasibility of resection.9
Definite diagnosis is made with the
combination of histopathology and immunohistochemistry.
Histopathology will show multicystic lesion lined by a single
layer of cuboidal cells of mesothelial origin along with septa-
tions containing fibromuscular stroma and inflammatory
cells. Immunohistochemistry will demonstrate positive
staining for mesothelial origin markers like calretinin, cyto-
keratin, CK7 and WTA.1,5
The differential diagnosis include lymphangioma, pseu-
domyxoma peritonei and carcinomatosis peritonei. Lym-
phangioma intimately resembles BMCM and usually
characterized by a large, thin-walled and muliloculated cystic
mass. Content of lymphangioma cyst is predominantly
chylous (but may be serous or hemorrhagic). Microscopic ex-
amination shows cystic spaces lined by a single layer of flat-
tened endothelial cells and stroma contains smooth muscle
and aggregates of lymphocytes.10
IHC is positive for CD31þ,
CD34þ and factor VIIIþ.1
Recurrence is very low after surgery.
Treatment option for BMCM is complete and aggressive
surgical excision including cytoreductive surgery with peri-
tonectomy. Continuous hyperthermic peritoneal perfusion
with cisplatin or doxorubicin and peritonectomy has also
been described.1,5,7
There are reports of use of tamoxifen and
GnRH analogs (e.g leuprolide) to reduce cyst volume and cyst
growth but results are variable.7
Due to relatively high recur-
rence rates of BMCM, follow-up imaging is advised, especially
after incomplete surgical excision. Prognosis is excellent with
very low mortality.4
To conclude, benign multicystic mesothelioma of omen-
tum is a very rare benign tumor, which is seldom diagnosed
on preoperative imaging. Diagnosis requires histological &
immunohistochemistry evaluation. Treatment consist of
aggressive complete surgical excision.
Conflicts of interest
All authors have none to declare.
r e f e r e n c e s
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Fig. 4 e HPE showing multicystic lesion lined by
mesothelial cell.
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Please cite this article in press as: Sahu D, et al., A rare omental tumor presenting as pelvic mass e A case report, Apollo
Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.07.017

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