What types of ovarian cysts can be septated but have clear contents?

Septated Ovarian Cysts with Clear Contents

Septated ovarian cysts with clear (anechoic) fluid contents are most commonly benign functional cysts, serous cystadenomas, or paraovarian cysts, with the risk of malignancy being extremely low when septations are thin (<3 mm) and there are no solid components or papillary projections. 1

Primary Benign Entities

Functional Cysts

• Simple cysts with thin septations (<3 mm) are considered benign and represent the most common septated clear cyst type in premenopausal women. 1
• Multiple septations without papillary projections or solid components are unlikely to be malignant. 1
• These functional cysts often resolve spontaneously, particularly in premenopausal women. 1

Serous Cystadenomas

• Serous cystadenomas are the most common histologic diagnosis in surgically removed septated cystic ovarian tumors, accounting for approximately 59% of cases. 2
• These benign epithelial tumors characteristically present as unilocular or multilocular cysts with thin septations and clear fluid. 2
• They can occur in both premenopausal and postmenopausal women. 2

Mucinous Cystadenomas

• Mucinous cystadenomas represent approximately 10% of septated cystic ovarian tumors. 2
• These typically present as multilocular cysts with thin septations, though the fluid may be more echogenic than simple cysts. 2

Paraovarian Cysts

• Simple paraovarian cysts are extraovarian structures that can appear septated and contain clear fluid. 1
• Generally require no follow-up if simple, with optional 1-year follow-up in postmenopausal women based on diagnostic confidence. 1

Risk Stratification by Septal Characteristics

Low-Risk Features (O-RADS 2-3)

• Thin septations (<2-3 mm) without solid components or papillary projections carry minimal malignancy risk (<1-10%). 1
• In a large study of 2,870 septated cystic ovarian tumors, 79.7% had septal width <2 mm, with only one borderline malignancy and no invasive cancers detected. 2
• Smooth multilocular tumors with thin septations are classified as benign features in IOTA Simple Rules. 1

Size Considerations

• Septated cysts <5 cm in premenopausal women require minimal intervention, while those 5-10 cm warrant follow-up ultrasound in 8-12 weeks. 1
• In postmenopausal women, septated cysts >5 cm or those with elevated CA-125 should be evaluated surgically. 3

Management Algorithm by Patient Population

Premenopausal Women

• For septated cysts ≤3 cm with thin septations: no management required. 1
• For septated cysts >3 cm but <10 cm: follow-up ultrasound in 8-12 weeks during proliferative phase. 1
• If the cyst persists or enlarges, referral to ultrasound specialist or gynecologist, or MRI for further characterization. 1
• Color Doppler should be used to confirm absence of internal vascularity, which would suggest solid components rather than septations. 1

Postmenopausal Women

• Unilocular septated cysts <5 cm with thin septations and normal CA-125 may be followed conservatively with serial ultrasound. 3, 4, 5
• Septated cysts ≥5 cm or those with elevated CA-125 warrant surgical evaluation. 3
• Annual ultrasound surveillance is recommended for conservatively managed cysts. 1, 5
• Any interval change in morphology or development of vascular components requires referral to ultrasound specialist or MRI. 1

Critical Diagnostic Pitfalls to Avoid

Misidentification of Solid Components

• Use color or power Doppler to differentiate true septations from solid tissue—septations should be avascular. 1
• Hemorrhagic content with reticular pattern and retracting clot can mimic septations but will show concave margins and no internal flow. 1

Hydrosalpinx Misinterpretation

• Endosalpingeal folds in hydrosalpinx can be misinterpreted as complete septations or solid components. 1
• Look for tubular configuration and characteristic folding pattern to distinguish from true ovarian cysts. 1

Postmenopausal Hemorrhagic Cysts

• Hemorrhagic cysts should not occur in postmenopausal women—any such finding requires further evaluation by ultrasound specialist, gynecologist, or MRI. 1

Evidence-Based Malignancy Risk

In a prospective study of 1,319 women with 2,870 septated cystic ovarian tumors without solid areas or papillary projections, only one borderline malignancy (0.035%) was identified, with no invasive cancers detected over 7,642 follow-up years. 2 This confirms that septated cysts with clear contents and thin septations have extremely low malignancy potential and can be managed conservatively with ultrasound surveillance rather than immediate surgery. 2