AJR 2000; 174:1559-1563
© American Roentgen Ray Society
Imaging of Peritoneal Inclusion Cysts
Kiran A. Jain1
1
Department of Radiology, University of California at Davis Medical Center,
4860 Y St., Ste. 3100, Sacramento, CA 95817.
Received July 20, 1999;
accepted after revision November 22, 1999.
Address correspondence to K. A. Jain.
Introduction
Although fairly common, peritoneal inclusion cysts are less well-recognized
entities on imaging of the female pelvis. Peritoneal inclusion cysts, also
known as peritoneal pseudocysts and inflammatory cysts of the pelvic
peritoneum, present with a variety of imaging appearances, which can be
confused with various adnexal masses of the female pelvis. A complex cystic
adnexal mass generates a long list of differential diagnoses, including
ovarian cancer. However, the confident diagnosis of peritoneal inclusion cysts
is possible if imaging findings are correlated with appropriate clinical
findings [1]. The correct
diagnosis allows conservative treatment, avoiding unnecessary surgery.
I describe the imaging appearances of peritoneal inclusion cysts. I also
discuss the differentiation of peritoneal inclusion cysts from other adnexal
masses.
Pathophysiology
The development of a peritoneal inclusion cyst depends on the presence of
an active ovary and peritoneal adhesions
[2]. The normal peritoneum
absorbs fluid easily. However, when the peritoneum becomes infected or
mechanically injured, its transport properties are changed and fluid
absorption is slower, causing a decrease in the clearance of ovarian fluid
[3].
Peritoneal fluid is predominantly formed by exudation from an active ovary.
The ovarian origin of the fluid is strongly supported by the higher
concentration of ovarian steroid hormones in peritoneal fluid than in plasma
[4,
5]. Additionally, inflammation
may cause exudate. These effects may result in the growth and persistence of
peritoneal inclusion cysts.
Peritoneal inclusion cysts represent a nonneoplastic reactive mesothelial
proliferation. They are also referred to as benign cystic mesotheliomas. The
lesions range in size from several millimeters in diameter to bulky masses
that may fill the pelvis and abdomen. Individual locules may be filled with
clear or yellow serous fluid, gelatinous fluid, or hemorrhagic gray pulplike
material [5].
Histopathologically, the locules are lined by one or several layers of flat
and cuboidal mesothelial cells, which occasionally form papillae. Typically,
blood vessels are visible in the mesothelial tissue
(Fig. 1). Occasionally, the
cuboidal cells undergo squamous metaplasia
[6]. Peritoneal inclusion cysts
have no malignant potential despite the occasional occurrence of
metaplasia.
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Fig. 1. —37-year-old woman with peritoneal inclusion cyst. Photomicrograph
shows locules of peritoneal inclusion cyst lined by one to several layers of
flat and cuboidal mesothelial cells (solid arrows). Note that blood
vessels are visible within mesothelial tissue (open arrows).
Occasionally, cuboidal cells can undergo squamous metaplasia; however,
peritoneal inclusion cysts have no malignant potential.
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Peritoneal fluid accumulation within adhesions appears as complex
multicystic adnexal masses on sonography. Peritoneal inclusion cysts are
adherent to the surface of the ovary but do not involve the ovarian parenchyma
[2].
Natural History
Most patients with peritoneal inclusion cysts present with pelvic pain or a
pelvic mass [1]. Peritoneal
inclusion cysts occur almost exclusively in premenopausal women with a history
of previous abdominal or pelvic surgery, trauma, pelvic inflammatory disease,
or endometriosis [1,
5]. Peritoneal inclusion cysts
tend to grow slowly as more fluid is secreted by the ovaries and not
reabsorbed by the peritoneum. Therefore, patients with a typical history and
suggestive presentation should be examined for peritoneal inclusion cysts.
Imaging Characteristics of Peritoneal Inclusion Cysts
Spider Web Pattern (Entrapped Ovary)
Peritoneal adhesions extend to the surface of the ovary and may distort the
ovarian contour but do not penetrate the ovarian parenchyma. When the
adhesions surround the ovary and fluid accumulates, complex cystic masses
form. The entrapped ovary appears like a spider in a web and may be mistaken
for a solid nodular portion of the tumor with surrounding septations.
Sometimes, the ovary may be eccentrically located to the adhesions
(Fig. 2).
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Fig. 2. —23-year-old woman with Crohn's disease and peritoneal inclusion
cyst. Endovaginal coronal sonogram shows peritoneal inclusion cyst with spider
web pattern. Ovary (O) is eccentrically located to surrounding adhesions
(arrows).
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Peritoneal Inclusion Cyst Simulating Hydrosalpinx and Pyosalpinx
Peritoneal adhesions sometimes simulate a hydrosalpinx and entrap fluid in
an oblong loculation adjacent to the uterus
(Fig. 3A). Nodular mesothelial
tissue can project within the lumen, creating a classic cogwheel appearance
(Fig. 3B). The adhesions
extending partially within the fluid collection can be mistaken for the folded
appearance of the tube. Occasionally, peritoneal inclusion cysts can contain
echogenic fluid collection with a tubular configuration
(Fig. 4), simulating the
appearance of pyosalpinx; however, the patient is not severely symptomatic and
does not have a fever or a high WBC. Sometimes, adhesions extend across the
entire width of a fluid collection (Fig.
5) and are thus less likely confused with pyosalpinx.
Occasionally, the adhesions may be thick and polypoid in appearance
(Fig. 6).
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Fig. 3A. —35-year-old woman with Crohn's disease and peritoneal inclusion
cyst. Endovaginal coronal sonogram shows anechoic oblong fluid collection
adjacent to ovary. Note small nodular adhesions (arrows) protruding
in apparent lumen.
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Fig. 3B. —35-year-old woman with Crohn's disease and peritoneal inclusion
cyst. Coronal endovaginal sonogram shows typical cogwheel appearance of
peritoneal inclusion cyst similar to that of hydrosalpinx. Note nodular
projections (straight arrows) and normal ovary and follicles adjacent
to peritoneal inclusion cyst (curved arrows).
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Fig. 4. —28-year-old woman with history (1 year earlier) of prior pelvic
surgery and peritoneal inclusion cyst simulating pyosalpinx. Coronal
endovaginal sonogram shows tubular configuration of peritoneal inclusion cyst
filled with echogenic fluid simulates pyosalpinx. Adhesions (arrow)
extending in loculated fluid collection give appearance of a folded tube.
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Fig. 5. —33-year-old woman with peritoneal inclusion cyst and history (14
months earlier) of pelvic trauma and surgery. Sagittal endovaginal sonogram
shows adhesions (arrows) that extend across entire width of fluid
collection. This appearance is less likely confused with pyosalpinx.
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Fig. 6. —25-year-old woman with inflammatory bowel disease and peritoneal
inclusion cyst. Sagittal endovaginal sonogram shows irregularly shaped
peritoneal inclusion cyst with polypoid adhesion (arrow). This
appearance could be interpreted as a bowel appendage; however, lack of
peristalsis in this structure during real-time sonography clarified this
finding. Color Doppler imaging did not reveal vascularity.
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Peritoneal Inclusion Cyst Simulating Paraovarian Cyst
Sonographically, when peritoneal adhesions are not extensive, small fluid
collections contiguous with the adnexa may be mistaken for paraovarian cysts.
True or primary paraovarian cysts are not caused by adhesions and appear as
single or multiple cystic masses separate from the ovary in the broad
ligament. Identification of a normal ipsilateral ovary separate from the cyst
is helpful in diagnosing a paraovarian cyst
[7].
Peritoneal Inclusion Cyst Simulating Malignant Ovarian Neoplasm
Extensive adhesions can form irregular and thick septations and a complex
cystic mass difficult to differentiate from a malignant ovarian neoplasm
(Fig. 7A). Sometimes,
low-resistance flow can be detected within these septations, which is caused
by vessels inside mesothelial tissue (Fig.
7B) [8]. This
finding makes it difficult to distinguish a peritoneal inclusion cyst from a
malignant neoplasm. In such cases, it might be difficult or impossible to
detect the ovary. Sometimes, one of the loculi of a multiloculated peritoneal
inclusion cyst can contain old blood and may appear echogenic on sonography
(Fig. 8). This finding may be
suggestive of a neoplasm.
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Fig. 7A. —37-year-old woman with peritoneal inclusion cyst and history of
abdominal surgeries for Crohn's disease and colostomy. Sagittal endovaginal
sonogram reveals large irregular peritoneal inclusion cyst (arrows)
with thick septations, which looked suggestive of malignant neoplasm.
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Fig. 7B. —37-year-old woman with peritoneal inclusion cyst and history of
abdominal surgeries for Crohn's disease and colostomy. Sagittal endovaginal
sonogram reveals low-resistance arterial and venous flow in septations,
suggestive of neoplasm. However, mesothelial tissue of peritoneal inclusion
cyst contains blood vessels, which explains this finding.
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Fig. 8. —27-year-old woman with endometriosis and peritoneal inclusion cyst.
Coronal endovaginal sonogram reveals large multiloculated peritoneal inclusion
cyst (arrows). One locule contains echogenic fluid (e), which was old
blood.
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Occasionally, endometriosis is complicated by the formation of a peritoneal
inclusion cyst that causes progressive and severe adhesions around the lesion.
The thick walls of the cystic masses of endometriosis filled with low-level
echoes and surrounded by thick and irregular septations can have an appearance
similar to that of a malignant neoplasm
(Fig. 9). Occasionally, the
sonographic appearance of echogenic fluid is blood within the loculi of
peritoneal inclusion cysts
[1].
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Fig. 9. —45-year-old woman with endometriosis and peritoneal inclusion cyst.
Endovaginal sagittal left adnexal sonogram shows some normal ovarian
parenchyma with small follicles (arrow). Note small irregular
anechoic locule of peritoneal inclusion cyst (c) adjacent to ovary. Also note
small endometrioma (e) adjacent to ovary. This patient's cyst was mistaken for
neoplasm.
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Other imaging techniques, such as CT and MR imaging, can reveal peritoneal
inclusion cysts. MR imaging is useful in detecting pseudocysts because of its
high contrast resolution of soft tissues and multidimensional imaging
capabilities. Pseudocysts appear extremely irregular in shape and reflect the
invaginations of surrounding structures in the cyst wall because pseudocysts
have no true walls (walls are formed by surrounding organs)
[9]. On MR imaging, peritoneal
inclusion cysts have low signal intensity on T1-weighted images and high
signal intensity on T2-weighted spin-echo images, suggesting that the fluid is
serous (Fig.
10A,10B).
Occasionally, old blood in the loculi of peritoneal inclusion cysts can have
high signal intensity on T1-weighted images. Contrast-enhanced T1-weighted
images reveal pseudocysts with walls formed by surrounding anatomic structures
and not by cyst walls [9].
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Fig. 10A. —42-year-old woman with history (2 years earlier) of pelvic surgery,
Crohn's disease, and peritoneal inclusion cyst. Axial T1-weighted MR image
(TR/TE, 450/16) shows large low-signal-intensity fluid collection
(arrows) in pelvis.
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Fig. 10B. —42-year-old woman with history (2 years earlier) of pelvic surgery,
Crohn's disease, and peritoneal inclusion cyst. Axial fast spin-echo
T2-weighted fat-saturated MR image (4000/102) shows homogeneous
high-signal-intensity fluid collection (arrows) inside pelvis. No
septations or mural nodules were identified.
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Diagnosis
The diagnosis of peritoneal inclusion cysts should be suspected in the
right clinical setting. Preoperative diagnosis depends on the presence of
normal ipsilateral ovary with surrounding loculated fluid conforming to the
peritoneal space. Therefore, the extraovarian location of the lesion and
identification of a normal ovary enables definitive diagnosis. Stable imaging
appearance on follow-up sonography or MR imaging over a period of 6 months to
1 year is also helpful. Fluid can be seen to conform to the shape of the
peritoneal cavity with these imaging techniques. In the absence of these
findings, laparoscopy or surgery may be necessary in selected patients.
Finally, laparoscopy is useful in selected cases.
Treatment
The correct clinical diagnosis of peritoneal inclusion cysts is useful in
planning treatment. Conservative treatment should be considered for patients
with peritoneal inclusion cysts. After surgical resection, the risk of
recurrence is 30-50% [6].
Conservative treatment includes the use of oral contraceptives to suppress
ovulation, thus decreasing the formation of ovarian fluid trapped by adhesions
[5]; pain medication as needed;
and transvaginal fluid aspiration if symptoms from large collections exist.
Laparoscopic or surgical resection of adhesions is necessary only in selected
cases.
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Introduction
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