Teaching Case

A 30-year-old female patient underwent laparotomy for endometriosis. Six months later, she presented with recurrent lower abdominal pain. Per-vaginal examination revealed a 4-5 cm cystic mass localised mainly at the left adnexa.

Ultrasound images of the pelvis revealed an irregular, anechoic, cystic lesion containing septations; the ovary was not seen (Fig. 1). Abdominopelvic CT followed and showed a cystic adnexal mass with a normal ovary eccentrically located in the collection (Fig. 2a-d).
Routine haematological and biochemical investigations were normal.
Based on the existence of a cystic mass without clearly defined walls, encircling a normal-appearing ovary, in a young female with history of pelvic surgery a diagnosis of peritoneal inclusion cyst was made and the patient was managed conservatively. The patient improved clinically after one month.

Peritoneal inclusion cysts (PIC), present with a variety of imaging representations that may be confounded with various adnexal masses.
A complex cystic adnexal mass refers to a long list of differential diagnoses, including ovarian cancer. Yet, imaging findings will confirm diagnosis of PIC if they are correlated with appropriate clinical findings [1]. The correct diagnosis allows conservative treatment, preventing unnecessary surgery.
The development of a PIC relies on the existence of an active ovary and peritoneal adhesions [2].
When the peritoneum is infected or mechanically injured, its properties of transport are modified and fluid absorption is slower, leading to a decrease in the clearance of ovarian fluid [3].
The higher concentration of ovarian steroid hormones in peritoneal fluid than in plasma support the ovarian origin of the fluid [4, 5]. Furthermore, inflammation may cause exudate.
Most women with PICs present with pelvic pain or a pelvic mass [1].
PICs occur almost exclusively in premenopausal women; the most common peritoneal insults are endometriosis, pelvic inflammatory disease, previous abdominal or pelvic surgery, and trauma.
Ultrasound, CT or MRI typically show cystic masses with septations or loculated fluid collection within the pelvis but no enhancing solid component. The ovaries are usually normal or entrapped by but clearly separate from cystic locules. The entrapped ovary appears like a spider in a web and may be mistaken for a solid nodular portion of the tumour with surrounding septations. Sometimes, the ovary may be eccentrically located to the adhesions [6, 7].
Haemorrhage occasionally may be seen within a cyst; the cyst will show attenuation higher than that of simple fluid at CT, hypersignal at T1-weighted MR imaging, and hyposignal at T2-weighted MR imaging [8].
The correct clinical diagnosis of peritoneal inclusion cysts is helpful in planning treatment. Conservative treatment should be considered for patients with peritoneal inclusion cysts. It includes the use of oral contraceptives to suppress ovulation, pain medication as needed; and transvaginal fluid aspiration if symptoms from large collections exist. Laparoscopic or surgical resection of adhesions is required only in selected cases [6].