Peritoneal inclusion cyst (PIC) (also known as a peritoneal pseudocyst and benign cystic mesothelioma) is a type of cyst-like structure that appears in relation to the peritoneum and results from a non-neoplastic reactive mesothelial proliferation.
Most patients with peritoneal inclusion cysts present with pelvic pain or a pelvic mass. About 10% are discovered incidentally.
They are usually caused by accumulation of ovarian fluid that is contained by a peritoneal adhesion. The development of a peritoneal inclusion cyst depends on the presence of an active ovary and peritoneal adhesions. The normal peritoneum absorbs fluid easily. However, the absorptive capacity of the peritoneum is greatly diminished in the presence of mechanical injury, inflammation and peritoneal adhesions.
Peritoneal inclusion cysts range in size from several millimetres in diameter to bulky masses that may fill the entire pelvis and abdomen. Pathologically, the cyst results from non-neoplastic, reactive mesothelial proliferation.
- previous abdominal trauma
- previous pelvic inflammatory disease
- previous abdominal surgery
They typically appear as cystic masses with septations or loculated fluid collections within the pelvis
- large, ovoid or irregular, anechoic cyst is considered characteristic 1, but septations are not uncommon
- size can vary from small localised collections up to large cystic masses which occupy the entire pelvis and lower abdomen
- invagination of the surrounding structures into the cyst
- lack of a discrete limiting wall
- no mural nodularity
- minimal internal debris
Other features in relation to the ovary include:
- spider web pattern (from an entrapped ovary)
May be seen as a loculated fluid collection conforming to the peritoneal space with a normal ipsilateral ovary within it or in the wall 5. Septations within the loculated fluid can also be encountered.
The location of the ovary with respect to the cysts is clearly demonstrated on MRI. They tend to appear as irregular cystic masses. Signal characteristics are:
- T1: hypointense
- T2: hyperintense
- T1 C+ (Gd): enhancing cyst walls
Treatment and prognosis
Conservative treatment (use of GnRH analogues, oral contraceptives to suppress ovulation, pain medication) is the first line of treatment. Image-guided transvaginal fluid aspiration and sclerotherapy have been attempted with partial success 8.
Surgical resection of adhesions is necessary only in selected cases. After surgical resection, the risk of recurrence is 30-50%. Peritoneal inclusion cysts have no malignant potential despite the occasional occurrence of metaplasia.
On imaging, a peritoneal inclusion cyst can potentially mimic a 2:
- paraovarian cyst
- appendiceal mucocoele: may cause pseudomyxoma peritonei if ruptured, but is separated from ovary
If septated, also consider:
- malignant cystic ovarian neoplasm
Editorial board note
At the time of writing we are not sure how much of a overlap there is with this entity and multicystic mesothelioma. If you are an expert on this we would love your help.
- 1. Kim JS, Lee HJ, Woo SK et-al. Peritoneal inclusion cysts and their relationship to the ovaries: evaluation with sonography. Radiology. 1997;204 (2): 481-4. Radiology (abstract) - Pubmed citation
- 2. Jain KA. Imaging of peritoneal inclusion cysts. AJR Am J Roentgenol. 2000;174 (6): 1559-63. AJR Am J Roentgenol (full text) - Pubmed citation
- 3. Brown DL, Dudiak KM, Laing FC. Adnexal masses: US characterization and reporting. Radiology. 2010;254 (2): 342-54. doi:10.1148/radiol.09090552 - Pubmed citation
- 4. Guerriero S, Ajossa S, Mais V et-al. Role of transvaginal sonography in the diagnosis of peritoneal inclusion cysts. J Ultrasound Med. 2004;23 (9): 1193-200. J Ultrasound Med (full text) - Pubmed citation
- 5. Jeong YJ, Kim S, Kwak SW et-al. Neoplastic and nonneoplastic conditions of serosal membrane origin: CT findings. Radiographics. 28 (3): 801-17. doi:10.1148/rg.283075082 - Pubmed citation
- 6. Yaegashi N, Yajima A. Multilocular peritoneal inclusion cysts (benign cystic mesothelioma): a case report. J. Obstet. Gynaecol. Res. 1996;22 (2): 129-32. - Pubmed citation
- 7. Moyle PL, Kataoka MY, Nakai A et-al. Nonovarian cystic lesions of the pelvis. Radiographics. 30 (4): 921-38. doi:10.1148/rg.304095706 - Pubmed citation
- 8. Jeong JY, Kim SH. Sclerotherapy of peritoneal inclusion cysts: preliminary results in seven patients. Korean J Radiol. 2 (3): 164-70. Korean J Radiol (link) - Free text at pubmed - Pubmed citation
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