DOI:10.2214/AJR.07.3628
AJR 2008; 191:814-825
© American Roentgen Ray Society
Peritoneal Mesotheliomas: Clinicopathologic Features, CT Findings, and Differential Diagnosis
Ji Yeon Park1,
Kyoung Won Kim1,
Heon-Ju Kwon1,
Mi-Suk Park2,
Gui Young Kwon3,
Sun-Young Jun4 and
Eun Sil Yu3
1 Department of Radiology, Asan Medical Center, University of Ulsan College of
Medicine, 388-1, Pungnap 2-dong, Songpa-ku, Seoul 138-736, South Korea.
2 Department of Radiology, Yonsei University College of Medicine, Severance
Hospital, Seoul, South Korea.
3 Department of Pathology, Asan Medical Center, University of Ulsan College of
Medicine, Seoul, South Korea.
4 Department of Pathology, Hallym University Sacred Heart Hospital, Gyeonggi-do,
South Korea.
Received January 5, 2008;
accepted after revision March 30, 2008.
Address correspondence to K. W. Kim
(kimkw{at}amc.seoul.kr).
Abstract
OBJECTIVE. The objective of our study was to illustrate various CT
findings of peritoneal mesotheliomas, to review their clinicopathologic
features, and to discuss the differential diagnoses.
CONCLUSION. The clinicopathologic features of peritoneal
mesotheliomas vary among the subtypes such as malignant mesotheliomas, cystic
mesotheliomas, and well-differentiated papillary mesotheliomas, and
accordingly, there is a spectrum of CT appearances.
Keywords: CT • cystic mesothelioma • mesothelioma • oncologic imaging • papillary mesothelioma • peritoneum
Introduction
Mesotheliomas are rare neoplasms that arise from the mesothelial cells
forming the serosal membranes of body cavities. Second to the pleural cavity,
mesotheliomas commonly involve the peritoneal cavity, either solely or in
combination with pleural involvement.
Peritoneal mesotheliomas are characterized as one of three pathologic
subtypes: malignant mesothelioma, cystic mesothelioma, or well-differentiated
papillary mesothelioma [1]. The
clinicopathologic features of peritoneal mesotheliomas vary among these
subtypes, and their CT features vary as well
(Table 1).
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TABLE 1: Clinicopathologic Features, CT Findings, and Differential Diagnosis of
Subtypes of Peritoneal Mesotheliomas
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In this article, we present a review of peritoneal mesotheliomas. An
awareness of the diverse clinicopathologic features as well as the CT features
of peritoneal mesotheliomas may help radiologists to narrow the differential
diagnoses and may increase the chance for an accurate radiologic
diagnosis.
Malignant Peritoneal Mesothelioma
Most malignant peritoneal mesotheliomas occur in older men during the fifth
and sixth decades. The predominance in older men is possibly attributed to
their higher occupational asbestos exposure. In approximately half of the
reported cases, the patient has a history of asbestos exposure
[2,
3], and it has been reported
that malignant peritoneal mesotheliomas may be related to more prolonged and
heavy asbestos exposure than pleural mesotheliomas
[4]. Patients with malignant
peritoneal mesothelioma may present with mild vague symptoms including
abdominal pain, distention, anorexia, and weight loss. Because of these vague
symptoms, the disease is generally already advanced at presentation. The
prognosis is extremely poor even with multitechnique therapy.
Unlike many neoplasms, malignant peritoneal mesotheliomas tend to spread in
sheets of tissue over the parietal and visceral peritoneal surfaces and to
become confluent, thereby encasing the abdominal organs. Such extensive
lesions may be accompanied by ascites
[5]. The CT features of
malignant peritoneal mesotheliomas range from a "dry" appearance,
consisting of peritoneum-based masses (Fig.
1A,
1B), to a "wet"
appearance, consisting of ascites, irregular or nodular peritoneal thickening,
and an omental mass (Fig. 2A,
2B). Scalloping or direct
invasion of adjacent abdominal organs may also be seen. Associated calcified
plaques are uncommon in malignant peritoneal mesotheliomas in contrast to the
pleural counterpart [5].
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Fig. 1A —72-year-old woman with malignant peritoneal mesothelioma who
presented with incidentally detected perihepatic masses. Axial
contrast-enhanced CT scan shows low-attenuation masses in perihepatic space
(arrowheads) that indent lateral and inferior aspects of right
hepatic lobe.
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Fig. 1B —72-year-old woman with malignant peritoneal mesothelioma who
presented with incidentally detected perihepatic masses. Microscopically,
there was diffuse infiltration of pleomorphic epithelioid cells with frequent
mitosis. On immunohistochemical staining, tumor cells are positive
(brown) for calretinin, which is mesothelial cell marker (calretinin
immunostain, x400). Histopathologic diagnosis was malignant peritoneal
mesothelioma.
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Fig. 2A —43-year-old woman with malignant peritoneal mesothelioma who
presented with abdominal distention. Axial contrast-enhanced CT scan shows
diffuse irregular thickening (arrowheads) of parietal peritoneum up
to 1.5 cm in thickness. Large amount of ascites is also noted.
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Fig. 2B —43-year-old woman with malignant peritoneal mesothelioma who
presented with abdominal distention. At level of lower abdomen, CT scan shows
multiple masses (arrowheads) involving greater omentum.
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When a patient with malignant peritoneal mesothelioma has no history of
asbestos exposure, differentiating a typical wet type of malignant peritoneal
mesothelioma from peritoneal carcinomatosis, serous surface pap illary
carcinoma, lymphomatosis, and tuberculosis may be difficult on the basis of CT
findings alone. These more commonly seen entities are still in the
differential diagnoses, and malignant peritoneal mesothelioma is predominantly
a diagnosis of exclusion. However, several investigators have reported that
the amount of ascites is disproportionately small in relation to the degree of
tumor dissemination in malignant peritoneal mesotheliomas compared with
peritoneal carcinomatosis. The incidence of liver metastasis and
lymphadenopathy is also higher in peritoneal carcinomatosis
(Fig. 3).
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Fig. 3 —55-year-old man with peritoneal carcinomatosis from stomach
cancer who presented with abdominal distention. Axial contrast-enhanced CT
scan shows omental cakes (long arrows), peritoneal nodules
(arrowheads), and massive ascites. Peritoneal thickening is less
severe, and amount of ascites is disproportionately large compared with
malignant mesothelioma. Metastatic liver nodule (short arrow) is also
noted.
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Serous surface papillary carcinoma is a rare primary tumor of the
peritoneum. Unlike malignant peritoneal mesothelioma, it is found
predominantly in elderly women and postmenopausal women (Fig.
4A,
4B). Diffuse retroperitoneal
and mesenteric lymph adenopathy and the lack of omental involvement should
raise the suspicion of lymphomato sis (Fig.
5). The diagnosis of tuberculous peritonitis is favored when there
is smooth peritoneal thickening, mesenteric lymphadeno pathy with central
necrosis, ascites with high attenuation, and combined with splenomegaly.
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Fig. 4A —67-year-old woman with serous papillary carcinoma of
peritoneum who presented with abdominal distention. Coronal contrast-enhanced
CT scan shows huge omental masses (arrowheads) and large amount of
ascites.
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Fig. 4B —67-year-old woman with serous papillary carcinoma of
peritoneum who presented with abdominal distention. On photograph of gross
specimen, cut surface of multiple omental masses is heterogeneous, whitish
yellow with multifocal hemorrhage and necrosis
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Fig. 5 —75-year-old man with peritoneal lymphomatosis who presented
with abdominal distention. Axial contrast-enhanced CT scan shows huge
conglomerated lymphadenopathy (arrows) in mesocolon and small amount
of ascites. Retroperitoneal lymphadenopathy (arrowheads) is also
noted posterior to left renal vein.
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Rarely, malignant peritoneal mesotheliomas appear as a solitary mass
[2]; it may be misdiagnosed as
a visceral tumor on CT if it occurs at the visceral peritoneum and involves an
adjacent organ (Fig. 6A,
6B,
6C). Malignant peritoneal
mesothelioma may also occasionally have a cystic appearance
[6] (Fig.
7A,
7B,
7C).
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Fig. 6A —56-year-old man with malignant peritoneal mesothelioma that
masqueraded as exophytic liver mass. Axial contrast-enhanced CT scan obtained
during arterial phase shows large lobulated mass (asterisk) with
heterogeneous contrast enhancement in right anterior subphrenic space invading
liver. Small amount of ascites is also noted.
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Fig. 6B —56-year-old man with malignant peritoneal mesothelioma that
masqueraded as exophytic liver mass. Axial contrast-enhanced CT scan obtained
during portal venous phase also shows large lobulated mass (asterisk)
with heterogeneous contrast enhancement in right anterior subphrenic space
invading liver.
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Fig. 6C —56-year-old man with malignant peritoneal mesothelioma that
masqueraded as exophytic liver mass. High-power photomicrograph shows
pleomorphic epithelioid cells with frequent mitosis (H and E, x400).
Tumor cells were positive for calretinin (not shown). Histopathologic
diagnosis was malignant peritoneal mesothelioma.
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Fig. 7A —10-year-old boy with malignant peritoneal mesothelioma who
presented with abdominal distention. Axial contrast-enhanced CT scan shows
huge cystic lesion (asterisk) with thick-walled septa replacing right
lobe of liver and extending from hepatic hilum.
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Fig. 7B —10-year-old boy with malignant peritoneal mesothelioma who
presented with abdominal distention. Low-power photomicrograph shows several
foci of solid aggregations of tiny nests of mesothelial cells in visceral
peritoneum of liver. (H and E, x40)
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Fig. 7C —10-year-old boy with malignant peritoneal mesothelioma who
presented with abdominal distention. Photomicrograph shows variably thickened
fibrous cystic walls with lining mesothelial cells (H and E, x40). On
electron microscopy (not shown), there were glandular arrangements of plump
epithelial cells with large irregular nuclei and prominent nucleoli. Luminal
surfaces of epithelial cells showed well-developed, long, and slender
microvilli. Based on histopathologic and electron microscopic findings,
diagnosis of malignant peritoneal mesothelioma with cystic change was
made.
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Cystic Mesothelioma
Cystic mesotheliomas are rare and occur predominantly in young to
middle-aged women [7]. In
contrast to malignant peritoneal mesothelioma, this tumor has no association
with asbestos exposure, but it is commonly associated with a history of
previous abdominal surgery or pelvic inflammatory disease
[8]. Involvement of the pelvic
region is characteristic [5].
These tumors are believed to be hormone-sensitive, and some investigators have
reported a reduction in tumor volume and clinical improvement in patients
treated with hormonal therapy
[9].
Pathologically, cystic mesothelioma typically consists of multiple
grapelike clusters of mesothelium-lined cysts, although it may be unilocular
as well [5]. CT features vary
according to the gross morphologic appearance of this tumor, which appears as
a multilocular cystic mass (Fig.
8A,
8B,
8C), multiple unilocular
thin-walled cysts, or a unilocular cystic mass (Fig.
9A,
9B). Major radiologic
differential diagnosis of cystic mesothelioma is cystic lymphangioma. Cystic
lymphangioma primarily affects younger patients, with almost the same
distribution between sexes and no regional predilection (Fig.
10A,
10B). On the contrary, cystic
mesothelioma shows a strong predilection for the pelvis. Abdominal
presentation of this tumor is generally secondary to extension from the pelvis
[8].
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Fig. 8A —25-year-old woman with multilocular cystic mesothelioma who
presented with amenorrhea and abdominal pain. Axial contrast-enhanced CT scan
shows variably sized, thick-walled, multiloculated cystic masses
(arrowheads) in mid abdomen.
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Fig. 8B —25-year-old woman with multilocular cystic mesothelioma who
presented with amenorrhea and abdominal pain. On photograph of gross specimen,
multilocular cystic sticky appearance of peritoneal mass is seen. Cysts
contained serous fluid.
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Fig. 8C —25-year-old woman with multilocular cystic mesothelioma who
presented with amenorrhea and abdominal pain. Low-power photomicrograph shows
multilocular cysts lined by fibrous walls of variable thicknesses (H and E,
x40). Cells lining cysts were positive for cytokeratin (not shown).
Histopathologic diagnosis was cystic mesothelioma.
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Fig. 9A —54-year-old woman with unilocular cystic mesothelioma who
presented with palpable mass in right lower quadrant. Axial contrast-enhanced
CT scan shows huge well-defined unilocular lesion (asterisk)
displacing liver, pancreas, and duodenum.
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Fig. 9B —54-year-old woman with unilocular cystic mesothelioma who
presented with palpable mass in right lower quadrant. Tumor cells are positive
for calretinin, which is mesothelial cell marker (calretinin immunostain,
x200). Histopathologic diagnosis was cystic mesothelioma.
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Fig. 10A —42-year-old man with cystic lymphangioma who presented with
abdominal distention. Axial contrast-enhanced CT scan shows multilocular
cystic mass (asterisk) in left upper abdominal cavity.
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Fig. 10B —42-year-old man with cystic lymphangioma who presented with
abdominal distention. On photograph of gross specimen, oligolocular cystic
mass is seen in peripancreatic adipose tissue. In contrast to cystic
mesothelioma, which shows strong predilection for pelvis, cystic lymphangioma
has no regional predilection.
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Other differential diagnoses are cystic epithelial neoplasms of the ovaries
and endometriosis. Although the typical grapelike multilocular or multiple
unilocular cystic appearance favors the diagnosis of cystic mesothelioma,
there may otherwise be considerable overlap that does not permit reliable
differentiation. Thick-walled cysts, thick internal septa, and
high-attenuation internal debris favor the diagnosis of endometriosis. Rarely,
pseudomyxoma peritonei may resemble cystic mesotheliomas.
Cystic mesothelioma tends to recur locally, with reported recurrence rates
of approximately 50% after surgical resection
[7]. Moreover, although
researchers generally agree that cystic mesothelioma is benign with no
metastatic potential, malignant transformation of cystic mesothelioma has been
documented [10] (Fig.
11A,
11B,
11C).
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Fig. 11A —54-year-old woman with malignant transformation of cystic
mesothelioma who presented with palpable mass in left lower quadrant. Axial
contrast-enhanced CT scan shows large thin-walled cystic mass
(asterisk) in left lower quadrant.
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Fig. 11B —54-year-old woman with malignant transformation of cystic
mesothelioma who presented with palpable mass in left lower quadrant. Axial
contrast-enhanced CT scan obtained 5 years after A shows large
lobulated mass with both cystic and solid compartments in left lower quadrant
invading retroperitoneum and posterior abdominal wall. Malignant
transformation of preexisting cystic mass is suggested.
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Fig. 11C —54-year-old woman with malignant transformation of cystic
mesothelioma who presented with palpable mass in left lower quadrant. Partial
excision of mass was performed. On photograph of gross specimen, multiple
omental masses and nodules without hemorrhage or necrosis are seen.
Microscopically, there was diffuse infiltration of pleomorphic epithelioid
cells with frequent mitosis (not shown). Histopathologic diagnosis was
malignant peritoneal mesothelioma.
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Well-Differentiated Papillary Mesothelioma
Well-differentiated papillary mesothelioma is a rare subtype of peritoneal
mesothelioma. Unlike malignant peritoneal mesothelioma, well-differentiated
papillary mesothelioma predominantly affects women of reproductive age who
lack a history of asbestos exposure
[11]. Well-differentiated
papillary mesothelioma is usually found incidentally at surgery performed for
other indications. Most well-differentiated papillary mesotheliomas have been
reported to behave in a benign or indolent fashion, but it is generally
considered a low-grade malignancy
[12,
13]. Although extensive
debulking surgery or chemotherapy is not warranted because of the indolent
nature of the disease, long-term follow-up is required because of the
potential of well-differentiated papillary mesothelioma to progress to true
malignant peritoneal mesothelioma
[12].
Pathologically, well-differentiated papillary mesothelioma is characterized
by uniform, coarse, or branching papillae covered by a single layer of
mesothelial cells with only slight cellular atypia
[10]. The size of
well-differentiated papillary mesothelioma ranges from less than 1 cm to more
than 3 cm [13].
Well-differentiated papillary mesothelioma has rarely been described in the
radiology literature, most likely because of its lack of specific radiologic
features. Well-differentiated papillary mesotheliomas may present with plaque
calcification that diffusely involves the visceral and parietal peritoneum
without the presence of a significant associated soft-tissue mass
[14]. However, when these
tumors present with nonspecific CT findings, such as peritoneal thickening,
multiple peritoneal nodules, omental infiltration, and ascites (Figs.
12A,
12B,
12C,
12D and
13A,
13B), differentiating
well-differentiated papillary mesothelioma from tuberculous peritonitis,
serous surface papillary carcinoma, or peritoneal carcinomatosis is difficult
on the basis of CT findings alone. Moreover, CT may not enable us to
sensitively detect well-differentiated papillary mesotheliomas given that more
than half of the reported well-differentiated papillary mesotheliomas are
smaller than 1 cm [13].
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Fig. 12A —58-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. Axial contrast-enhanced
CT scan shows massive ascites and nodular omental infiltration. There were no
significantly enlarged lymph nodes and no definite bowel wall thickening (not
shown).
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Fig. 12B —58-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. Photograph of gross
specimen shows multiple small nodules (orange) scattered in
omentum.
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Fig. 12C —58-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. Low-power
photomicrograph shows papillary growth pattern in fibrovascular core, which is
lined by single layer of cuboidal epithelial cells (H and E, x40).
Histopathologic diagnosis was well-differentiated papillary mesothelioma.
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Fig. 12D —58-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. On follow-up 1 year
after A–C, axial contrast-enhanced CT scan shows ill-defined
enhancing mass involving peritoneal surface of lower abdomen and anterior
abdominal wall. Massive ascites is also noted.
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Fig. 13A —56-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. Axial contrast-enhanced
CT scan shows thickened, "smudged" greater omentum
(arrowheads) and massive ascites.
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Fig. 13B —56-year-old woman with well-differentiated papillary
mesothelioma who presented with abdominal distention. On photograph of gross
specimen, multiple nodules and thickening of greater omentum are seen.
Histopathologic diagnosis was well-differentiated papillary mesothelioma.
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Conclusion
The clinicopathologic features of peritoneal mesotheliomas vary among the
subtypes such as malignant mesotheliomas, cystic mesotheliomas, and
well-differentiated papillary mesotheliomas, and accordingly, there is a
spectrum of radiologic appearances.
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Abstract
Introduction
