Peritoneal Inclusion Cysts

A peritoneal inclusion cyst is a benign, non-neoplastic cystic lesion resulting from entrapment of peritoneal fluid within adhesions formed after previous pelvic surgery, infection, or endometriosis.

It occurs specifically in premenopausal women with functioning ovaries. The condition depends on ongoing physiological peritoneal fluid production by the functioning ovary, with adhesion-related mechanical trapping of that fluid.

It is an important, though relatively uncommon, cause of a pelvic mass. It requires careful clinical and radiological distinction from a genuine ovarian neoplasm, because management differs substantially.

Pathophysiology

• Normal peritoneal fluid is produced continuously by the functioning ovary as part of cyclical ovarian activity. It is ordinarily absorbed and cleared by the peritoneal mesothelial surface.
• Pre-existing pelvic adhesions (most commonly from previous pelvic surgery, pelvic inflammatory disease, or endometriosis) create a relatively enclosed, loculated space. This mechanically traps the continuously produced fluid, allowing progressive accumulation and cyst formation within the adhesion-bound space.
• Critically, the ovary itself is not the origin of the cystic structure. It is the ongoing source of fluid that becomes trapped within the surrounding peritoneal space.
• The ovary is therefore typically identified adjacent to, or partially incorporated within the wall of, the cystic structure, rather than the cyst arising from within the ovarian parenchyma. This distinction is sometimes subtle but is directly relevant to radiological interpretation and management planning.
• The condition characteristically does not occur without functioning ovarian tissue, because it depends on ongoing physiological peritoneal fluid production. It is not typically seen in postmenopausal women or in women who have undergone bilateral oophorectomy.

• The characteristic clinical context is a premenopausal woman with retained, functioning ovarian tissue and a history of previous pelvic surgery, pelvic inflammatory disease, or endometriosis, presenting with pelvic pain or a palpable pelvic mass.
• Symptoms, where present, include chronic or intermittent pelvic pain. Larger lesions cause a palpable abdominal or pelvic mass and pressure-related symptoms.
• A proportion of cases are identified incidentally on imaging performed for an unrelated indication, or during investigation for infertility, given the association with pelvic adhesive disease.
• The lesion may be unilateral or bilateral, and can vary in size and complexity on examination and imaging. Size and configuration reflect the pattern and extent of the underlying adhesive process.
• The underlying risk factors are shared, so specifically explore any coexisting history or ongoing symptoms of endometriosis, and any history of previous pelvic infection or surgery. This is relevant to diagnosis and to management of any ongoing contributing condition.

• Pelvic ultrasound is the standard initial imaging investigation. The characteristic appearance is a cystic structure with a complex, often multiloculated configuration conforming to the shape of the surrounding pelvic structures and adhesions.
• A genuine ovarian cyst arising within ovarian tissue is more typically rounded and spherical.
• The ovary is frequently identifiable at the periphery of, or partially incorporated within, the cystic structure. This is a characteristic and diagnostically valuable finding when clearly identified.
• Magnetic resonance imaging provides additional detailed characterisation. It more clearly delineates the relationship between the ovary and the surrounding cystic structure, and assesses the extent of associated pelvic adhesive disease, supporting more confident distinction from a genuine ovarian neoplasm.
• Diagnostic overlap with an ovarian neoplasm is possible, particularly where the relationship between the ovary and the cystic structure is not clearly delineated on imaging. Careful clinical correlation with the surgical, infective, or endometriosis-related history is an essential component of diagnostic assessment.
• Where diagnostic uncertainty persists despite full imaging, or any other concerning feature is present, diagnostic laparoscopy provides definitive clarification through direct visualisation of the relationship between the ovary and the adhesion-bound cystic structure. It also allows concurrent definitive surgical management where appropriate.

• Conservative management, comprising observation with periodic clinical and imaging surveillance, is appropriate for smaller, asymptomatic or minimally symptomatic lesions. The condition is benign and may resolve spontaneously or remain stable without active intervention.
• Symptomatic management, including simple analgesia for associated pelvic pain, provides relief for milder, ongoing discomfort not warranting more active intervention.
• Surgical management, typically via laparoscopic approach, comprises adhesiolysis (surgical division of the causative pelvic adhesions) together with drainage or excision of the cyst wall.
• Surgery is considered for larger, symptomatic lesions, or where diagnostic uncertainty persists and definitive clarification through direct visualisation and, where appropriate, histological assessment is required.
• The condition depends on the extent of pelvic adhesive disease. Recurrence following surgical treatment is recognised, particularly where extensive adhesive disease persists or reforms after adhesiolysis. Counsel patients realistically about this possibility as part of informed management planning.
• Manage any identified underlying contributing condition, including appropriate treatment of endometriosis where this is an ongoing factor, as a complementary component of management.
• Educate patients about the benign nature of this condition, its underlying mechanism, and its distinction from a genuine ovarian neoplasm. This underpins appropriately reassuring management of this uncommon, though important, cause of a pelvic mass in women with relevant risk factors.