Pictorial Essay Imaging of Peritoneal Inclusion Cysts Kiran. Jain1 lthough 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. 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 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. 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]. dditionally, inflammation may cause exudate. 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). Received July 20, 1999; accepted after revision November 22, 1999. 1 Department of Radiology, University of California at Davis Medical Center, 4860 Y St., Ste. 3100, Sacramento, C 95817. ddress correspondence to K.. Jain. JR 2000;174:1559 1563 0361 803X/00/1746 1559 merican Roentgen Ray Society JR:174, June 2000 1559
Jain Fig. 3. 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., 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). 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. dhesions (arrow) extending in loculated fluid collection give appearance of a folded tube. 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. 4 5 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. 1560 JR:174, June 2000
Imaging of Peritoneal Inclusion Cysts 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. 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 Fig. 7. 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., 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. 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). 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. 3). Nodular mesothelial tissue can project within the lumen, creating a classic cogwheel appearance (Fig. 3). 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 WC. 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). 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. 7). Sometimes, low-resistance flow can be detected within these septations, which is caused by vessels inside mesothelial tissue (Fig. 7) [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. JR:174, June 2000 1561
Jain 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. 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. lso note small endometrioma (e) adjacent to ovary. This patient s cyst was mistaken for neoplasm. Fig. 10. 42-year-old woman with history (2 years earlier) of pelvic surgery, Crohn s disease, and peritoneal inclusion cyst., xial T1-weighted MR image (TR/TE, 450/16) shows large lowsignal-intensity fluid collection (arrows) in pelvis., xial fast spin-echo T2-weighted fat-saturated MR image (4000/102) shows homogeneous high-signalintensity fluid collection (arrows) inside pelvis. No septations or mural nodules were identified. 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]. Other imaging techniques, such as CT and MR imaging, can reveal peritoneal inclusion 1562 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. 10). Occa- sionally, old blood in the loculi of peritoneal inclusion cysts can have high signal intensity on T1-weighted images. Contrast-enhanced T1weighted images reveal pseudocysts with walls formed by surrounding anatomic structures and not by cyst walls [9]. Diagnosis The diagnosis of peritoneal inclusion cysts should be suspected in the right clinical setting. Preoperative diagnosis depends on the JR:174, June 2000
Imaging of Peritoneal Inclusion Cysts 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. fter 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. References 1. Sohaey R, Gardner TL, Woodward PJ, Peterson CM. Sonographic diagnosis of peritoneal inclusion cysts. J Ultrasound Med 1995;14:913 917 2. Kim JS, Lee HJ, Woo SK, Lee TS. Peritoneal inclusion cysts and their relationship to the ovaries: evaluation with sonography. Radiology 1997;204:481 484 3. Hoffer F, Kozakewich H, Colodny, Goldstein DP. Peritoneal inclusion cysts: ovarian fluid in peritoneal adhesions. Radiology 1988;169:189 191 4. Maathuis J, Van Look PF, Michie E. Changes in volume total protein and ovarian steroid concentrations of peritoneal fluid throughout the human menstrual cycle. J Endocrinol 1978; 76:123 133 5. Komickx PR, Renaer M, rosens I. Origin of peritoneal fluid in women: an ovarian exudation product. r J Obstet Gynaecol 1980;87:177 183 6. Ross MJ, Welch WR, Scully RE. Multilocular peritoneal inclusion cysts (so-called cystic mesotheliomas). Cancer 1989;64:1336 1346 7. Kim JS, Woo SK, Suh SJ, Morettin L. Sonographic diagnosis of paraovarian cysts: value of detecting a separate ipsilateral ovary. JR 1995; 164:1441 1444 8. Schneider V, Partridge JR, Gutierrez F, Hurt WG, Maizels MS, Demay RM. enign cystic mesothelioma involving the female genital tract: report of four cases. m J Obstet Gynecol 1983;145:355 359 9. Kurachi H, Murakami T, Nakamura H, et al. Imaging of peritoneal pseudocysts: value of MR imaging compared with sonography and CT. JR 1993;160:589 591 JR:174, June 2000 1563