Para-ovarian cyst

A para-ovarian cyst (POC), also sometimes known as a para tubal cyst or a hydatid cyst of Morgagni ¹⁴, is a type of adnexal cyst that does not arise from the ovary. They account for ~ 10 - 20 % of adnexal masses ^3-4.

Epidemiology

They typically occur in women ~ the 3^rd to 4^th decades.

Clinical presentation

Most are asymptomatic, although patients with large lesions can present with pelvic pain.

Pathology

They usually occur around the broad ligament and arise from para-mesonephric, mesothelial, or mesonephric remnants. They are usually simple cysts (although some authors include para ovarian cystadenomas under the umbrella of para ovarian cysts and can complicate their definition).

Radiographic features

A para ovarian cyst is easier to recognise if the ipsilateral ovary is demonstrated to be separate from it. 

Pelvic ultrasound

They are typically thin-walled and smoothly marginated. They most often appear as unilocular 'simple' cysts (in ~ 66%) and rarely as multilocular ( ~ 4%). Depending on the definition used the cysts can show a variable number of papillary projections growing from the cyst wall (unilocular-solid cysts) in ~ 30% of cases ^ref. 

Pelvic MRI

Often seen located close to the ipsilateral round ligament and are often of homogenous signal intensity. 

In uncomplicated cases signal characteristics usually follow that of fluid ¹².

• T1 : low signal (can be high signal if complicated by haemorrhage)
• T2 : high signal

Other features include

• may show a beak sign ¹¹ : 

Treatment and prognosis

Large or symptomatic cyst often undergo surgical resection smaller asymptomatic ones are treated conservatively. 

For simple para-ovarian cysts with no suspicious features on ultrasound, follow-up recommendations are the same as for ovarian cysts. According to a consensus statement by the Society of Radiologists in Ultrasound ¹³ follow up is recommended for cysts that are:

• 5 to 7 cm in a woman of reproductive age, or
• 1 to 7 cm in a post-menopausal woman

Irrespective of age, cysts larger than 7 cm warrant further evaluation (with MRI) or surgical review.

Differential diagnosis

For an adnexal cystic lesion consider

• true ovarian cyst
• ovarian cystic neoplasm : typically has a solid component
• para ovarian cystadenoma : typically has a small solid nodule or septum
• pelvic peritoneal inclusion cyst