peritoneal inclusion cyst

Peritoneal inclusion cysts, also known as peritoneal pseudocysts, are a type of cyst-like structure that appears in relation to the peritoneal surfaces and results from a non-neoplastic reactive mesothelial proliferation.


The nomenclature for this condition can be confusing due to the use of multiple interchangeable different synonyms (e.g. benign cystic mesotheliomas). Although there is still some debate on this matter, this article will refer to peritoneal inclusion cysts as those secondary to intra-abdominal inflammation with its fluid content originated from the ovarian stroma. Whereas the term mesothelioma will be reserved for true neoplasms, as discussed on the multicystic mesothelioma article.


Peritoneal inclusion cysts occur almost exclusively in premenopausal women with a history of previous abdominal or pelvic surgery, trauma, pelvic inflammatory disease, or endometriosis.

Clinical presentation

Most patients with peritoneal inclusion cysts present with pelvic pain or a pelvic mass. About 10% are discovered incidentally.


They are usually caused by the 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 millimeters in diameter to bulky masses that may fill the entire pelvis and abdomen. Pathologically, the cyst results from non-neoplastic, reactive cuboidal or flattened mesothelial proliferation.


Radiographic features

They typically appear as cystic masses with septations or loculated fluid collections within the pelvis.

  • large, ovoid or irregular, anechoic cyst is considered characteristic , but septations are not uncommon
    • size can vary from small localized 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 . 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 analogs, 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 .

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.

Differential diagnosis

On imaging, a peritoneal inclusion cyst can potentially mimic a :

If septated, also consider: