Ultrasound Characteristics of Functional Ovarian Cysts
Functional ovarian cysts typically appear on ultrasound as simple cysts less than 3 cm in diameter with smooth walls, or as thick-walled cysts with crenulated inner margins, internal echoes, and intense peripheral color Doppler flow in premenopausal women. 1
Defining Characteristics of Functional Cysts
Functional cysts are classified into two main types based on their ultrasound appearance 1:
- Follicular cysts: Simple cysts less than 3 cm in premenopausal women
- Corpus luteum cysts: Thick-walled cysts less than 3 cm that may have crenulated inner margins, internal echoes, and intense peripheral color Doppler flow
Corpus luteum cysts can sometimes appear as a hypoechoic region in the ovary with peripheral vascularity without a characteristic cystic component 1
Functional cysts are part of the O-RADS US classification system's "Physiologic Category" as they are consistent with normal ovarian physiology 1
Sonographic Features of Degenerating Functional Cysts
Degenerating functional cysts often show specific sonographic features including 2:
- Spider web-appearing or retracting clot within the cyst
- Peripheral vascularity around the cyst wall
- Hypoechoic internal debris or focal intracystic echogenicity
The presence of mural vascularity and spiderweb-appearing or retracting clot are particularly suggestive of functional cysts 1
Natural History and Follow-up
Most functional cysts in premenopausal women resolve spontaneously and will wax and wane over time 1, 2
Functional cysts typically reach maximum size at about 7 weeks of gestation with gradual diminution thereafter 3
Follow-up ultrasound can be performed to document resolution of functional cysts, confirming their benign nature 1, 2
Functional cysts that persist beyond the expected timeframe may require additional evaluation 1
Distinguishing from Other Cystic Lesions
Functional cysts must be differentiated from other cystic adnexal lesions based on their ultrasound characteristics 1:
- Simple cysts: Anechoic, well-circumscribed, round or oval with well-defined imperceptible wall and posterior enhancement
- Complicated cysts: Have most but not all elements of a simple cyst, may contain low-level echoes or intracystic debris
- Complex cysts: Have some discrete solid component, which may include thick walls, thick septa, and/or intracystic mass
The risk of malignancy in simple cysts is extremely low, particularly in premenopausal women (0% in women under 50 years in one large study) 1
Management Considerations
No additional management is required for simple cysts less than or equal to 5 cm in diameter in premenopausal patients 1
For cysts greater than 5 cm but less than 10 cm in premenopausal women, follow-up in 8-12 weeks is recommended to confirm their functional nature 1
The proliferative phase is the optimal time for reevaluation, allowing involution of functional cysts to occur following menstruation 1
Transvaginal ultrasound is the essential imaging modality for proper characterization of ovarian cysts, and color or power Doppler should be included 2
Common Pitfalls to Avoid
- Mistaking a degenerating cyst for a solid ovarian mass 2
- Confusing a hemorrhagic cyst with an endometrioma 2
- Unnecessary surgical intervention for a cyst that would resolve spontaneously 2, 4
- Failure to use color Doppler to differentiate true solid components from debris 2
By understanding the characteristic ultrasound findings of functional ovarian cysts, clinicians can avoid unnecessary interventions and provide appropriate follow-up for these benign, physiologic structures.