Teaching Case

A 16-year-old girl presented to our emergency department complaining of abdominal pain without fever. Physical examination revealed an abdominal mass.

Abdominal US showed a large cystic lesion that determined mass effect on the abdominal organs and right hydroureteronephrosis (Fig. 1). No ascites.
CE-CT imaging confirmed a well-defined mass (20x9x26 cm LLxAPxCC) that presented homogeneous hypodense content (Fig. 2). No septations, wall nodules or solid components were found. The pyelographic phase (obtained 30 min after i.v. contrast) showed no communication with the urinary tract (Fig. 3). Due to the lesion dimensions and the almost complete absence of intrabdominal fat, establishing the exact origin of the cyst was difficult at CT.
The patient underwent MRI to establish the possible gynaecological origin.
On MRI (Fig. 4), the unilocular cyst was hypointense on T1w images and hyperintense on T2w images, in accord with a likely serous fluid content. The left ovary was stretched and dislocated posteriorly by the mass, with no certain cleavage plane in between. No imaging features of malignancy were depicted at MRI.
Our diagnosis was directed towards a benign cystic lesion of the left adnexa.

Paraovarian cysts compose 10-20% of the adnexal masses [1] and may be normally found in woman between the 2nd and 4th decade. These cysts arise from the mesosalpinx, the part of the broad ligament that extends from the ovary to the uterine tube [2]. Embryologically, paraovarian cysts originate from remnants of the Wolffian duct. Frequently they are asymptomatic but if the cyst is large it can cause abdominal pain.
The possible rare complications include rupture, torsion, and haemorrhage.

Commonly, the radiological presentation is a simple unilocular cyst that can be separated from the ipsilateral ovary. Multilocular paraovarian cysts are rare (4%). Pelvic ultrasound is often sufficient for diagnosis, especially in small lesions. Follow-up can be done using pelvic ultrasound: it is recommended in cysts that measure 5 to 7 cm during the reproductive age and in cysts that measure 1 to 7 cm in the postmenopausal period. However, in doubtful cases or in larger cysts (> 7 cm) MRI is extremely recommended [3].

Pelvic MRI helps to determine the origin of the lesion and to demonstrate the fluid content of the cyst, showing low signal intensity on T1WI and high signal intensity on T2WI. If the cyst is complicated by haemorrhage, it may present high signal intensity on T1WI and have thick walls [1].

Moreover, MRI is useful for the differential diagnosis revealing the presence of malignant features such as solid component, wall thickness (>3mm), multiple septations, ascites and pelvic organ invasion [2, 4].

Smaller and asymptomatic paraovarian cysts are treated conservatively, unlike symptomatic ones that are surgically resected.
In our case, the patient underwent laparoscopic surgery and the cyst was completely removed with ovarian preservation.