Diagnostic Ultrasound - Abdomen and Pelvis

Peritoneal Inclusion Cyst
TERMINOLOGY
Abbreviations
• Peritoneal inclusion cyst (PIC)
Synonyms
• Peritoneal pseudocyst
• Benign cystic mesothelioma
• Inflammatory cysts of pelvic peritoneum
• Benign encysted fluid
• Multilocular inclusion cyst
Definitions
• Not true ovarian cyst
• Peritoneal or ovarian fluid trapped by peritoneal adhesions
IMAGING
General Features
• Best diagnostic clue
○ Normal ovary surrounded or displaced by fluid
containing septations
• Location
○ Adnexal
– Unilateral 65%
– Bilateral 35%
○ Midline if large
• Size
○ Variable
• Morphology
○ Lacks true wall
○ Boundaries defined by pelvic structures
○ Displaces structures without invasion
Ultrasonographic Findings
• Grayscale ultrasound
○ Irregular cystic lesion: Unilocular or multilocular
○ Soft and deformable
○ Lacks mass effect
– Passive lesion conforming to shape of pelvis
□ Lateral border from pelvic sidewall
○ Anechoic content
– Echoes with hemorrhage or proteinaceous debris
○ Variable number and thickness of septa (in 81%)
– Fine septations most common
□ Mobile with transducer pressure
□ "Flapping sail" sign
– Thick septations with nodules possible
○ Intact ovary present
– Entrapped ovary
□ Ovary surrounded by fluid and septations
□ "Spider in web" appearance
– Displaced ovary
□ External/adjacent to PIC
□ Along pelvic sidewall
□ Stuck to pelvic organ
– Distorted ovary
□ May lose normal contour
□ Pulled by adhesions but intact
• Color Doppler
○ Blood flow can be seen in septations, especially if thick
CT Findings
• Multiseptated pelvic fluid collection
• Mass respects pelvic structure boundaries
○ Pelvic sidewall as lateral boundaries
○ Bladder, bowel, uterus, fallopian tubes serve as
boundaries
• Thin septations not seen by CT
○ Mass appears unilocular
• Thicker septations resolved by CT
○ May enhance
• Associated ovary often not seen
• Useful for large PIC and for excluding malignant peritoneal
disease
MR Findings
• Simple fluid characteristics
○ Low signal on T1
○ High signal on T2
• Blood products sometimes present
○ High signal on T1
• Enhancement helps define borders and septa
○ Walls of PIC formed by surrounding structures
– Pelvic walls, pelvic organs, bowel loops
○ No true cyst wall
• MR may help find intact ovary if not seen by ultrasound
Nonvascular Interventions
• Therapeutic or diagnostic aspiration using transabdominal
or transvaginal approach
Imaging Recommendations
• Best imaging tool
○ Transvaginal ultrasound first-line to localize ovary and
exclude signs of malignancy
○ MR most useful if PIC is large and normal ovaries cannot
be found using ultrasound
○ CT may be suggestive but less sensitive at locating
ovaries
• Protocol advice
○ Suspect diagnosis in right clinical setting
– Premenopausal patient with history of multiple pelvic
surgeries
○ Look for otherwise normal ovary surrounded by
septated fluid collection
– May be displaced to periphery of mass
– Consider MR to find ovary
○ Use transvaginal probe to displace pelvic structures
– PIC is not invasive
○ Exclude solid components to differentiate from cancer
DIFFERENTIAL DIAGNOSIS
Ovarian Cystic Neoplasm
• Cystadenoma/cystadenocarcinoma
• Separate normal ovary not seen
• Unilocular or multilocular
• Papillary projections, solid nodules
• Thicker or irregular septa
• ± ascites, ± calcification
• Mass effect on adjacent structures
Diagnoses: Female Pelvis
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