Ovarian simple cyst is a thin-walled benign cystic lesion containing clear serous fluid, originating from functional or retention mechanisms. It is the most common ovarian lesion in premenopausal women, with most being functional cysts (follicular or corpus luteum). On ultrasound, it presents as an anechoic, thin-walled lesion with posterior acoustic enhancement. Cysts less than 3 cm are considered physiological and require no follow-up. In postmenopausal women, simple cysts >1 cm carry clinical significance but the vast majority remain benign.
Age Range
15-50
Peak Age
30
Gender
Female predominant
Prevalence
Very Common
Ovarian simple cysts form when the follicle fails to rupture during ovulation and continues to grow (follicular cyst) or from fluid accumulation during normal follicular development. The cyst wall consists of a single layer of granulosa or theca cells and lacks vascularity — hence the thin, smooth wall appearance on ultrasound with no Doppler wall vascularity. The contents are low-protein serous transudate — causing anechoic appearance on ultrasound and water density (0-20 HU) on CT. On MRI, the cyst shows T1 hypointense and markedly T2 hyperintense signal because free water has a long T2 relaxation time. Posterior acoustic enhancement results from the cyst fluid transmitting sound waves without attenuation — making tissues deep to the cyst appear brighter than normal.
The triad of anechoic internal structure, thin smooth wall (<3 mm), and posterior acoustic enhancement on ultrasound is the signature finding of simple cyst. When all three are present, diagnosis is definitive and no further imaging is needed. Absence of any component (internal echoes, thick wall, no enhancement) increases the probability of complicated cyst or solid lesion.
Completely anechoic (black) internal structure on ultrasound. No internal echoes, debris, or septation. Round or oval shaped, well-defined.
Report Sentence
A ___ x ___ mm anechoic, thin-walled, well-defined cystic lesion is seen in the right/left ovary, consistent with a simple cyst.
Prominent posterior acoustic enhancement (through-transmission) deep to the cyst. Tissues distal to the cyst appear brighter (more echogenic) than normal.
Report Sentence
The lesion demonstrates posterior acoustic enhancement, consistent with cystic nature.
Imperceptible or <3 mm thin, smooth wall. No nodularity, papillary projection, or wall thickening. No septa.
Report Sentence
The cyst wall is thin and smooth, without solid component, septation, or papillary projection.
No flow detected within or in the wall of the cyst on color Doppler. No ring of fire pattern. Cyst is completely avascular.
Report Sentence
No vascular flow is detected within or in the wall of the cyst on color Doppler examination.
Markedly hyperintense homogeneous signal isointense to CSF on T2-weighted sequences. Direct MR evidence of fluid content.
Report Sentence
The lesion shows markedly hyperintense signal isointense to CSF on T2-weighted sequences, consistent with simple fluid content.
Hypointense (low signal) homogeneous appearance on T1-weighted sequences. High T1 signal excludes simple cyst diagnosis (suggests blood or protein).
Report Sentence
The lesion shows hypointense signal on T1-weighted sequences, with no evidence of hemorrhagic content.
Water-density (0-20 HU) thin-walled, well-defined cystic lesion on CT. No enhancement.
Report Sentence
A ___ x ___ mm water-density (___ HU) thin-walled cystic lesion is seen in the left/right adnexal region, consistent with a simple cyst.
Criteria
Results from failure of dominant follicle to rupture. Usually 3-8 cm in size. In premenopausal women, typically unilateral.
Distinct Features
Completely anechoic, thin-walled, shows spontaneous regression within 1-3 menstrual cycles. Size decrease or disappearance on follow-up US confirms diagnosis.
Criteria
Located separate from ovary, within broad ligament. Arises from Wolffian duct remnants. Demonstration separate from normal ovary is diagnostic.
Distinct Features
Normal ovary is seen separately (split sign positive). No size change with menstrual cycle. Usually unilateral, thin-walled.
Criteria
Simple cyst detected in postmenopausal woman. <1 cm insignificant, 1-7 cm annual follow-up, >7 cm consider surgery.
Distinct Features
Functional cyst is not expected without hormonal stimulation. If simple cyst features are complete, malignancy risk is very low (0.3%). Surgery recommended if size >7 cm or atypical features present.
Distinguishing Feature
Hemorrhagic cyst shows reticular/fishnet pattern (fibrin strands) and internal echoes. Simple cyst is completely anechoic. On MRI, hemorrhagic cyst is T1 hyperintense (methemoglobin), simple cyst is T1 hypointense.
Distinguishing Feature
Corpus luteum cyst shows thick, irregular (crenulated) wall and ring of fire pattern on Doppler (intense peripheral vascularity). Simple cyst is thin-walled and avascular.
Distinguishing Feature
Serous cystadenoma is usually >5 cm and may contain thin septa. Larger than simple cyst and does not regress with menstrual cycle. Even a thin septum excludes simple cyst diagnosis.
Distinguishing Feature
Endometrioma shows homogeneous low-level internal echoes (ground glass appearance) — simple cyst is anechoic. On MRI, endometrioma shows T1 bright + T2 shading, simple cyst shows T1 hypointense + T2 markedly hyperintense.
Urgency
surveillanceManagement
conservativeBiopsy
Not NeededFollow-up
6-monthIn premenopausal women, simple cysts ≤3 cm are physiological and need no follow-up. 3-5 cm simple cysts are followed with control US at 6-12 weeks — most regress spontaneously. For >5 cm cysts, MR characterization may be considered. In postmenopausal women, <1 cm simple cyst is insignificant, 1-7 cm annual US follow-up, >7 cm consider surgery. When typical simple cyst features (anechoic + thin wall + posterior enhancement) are complete, malignancy risk is negligible.
Ovarian simple cysts are usually asymptomatic and incidentally discovered. Functional cysts are physiological in reproductive age. Follow-up is recommended for cysts >5 cm. In postmenopausal women, simple cysts have low neoplastic potential but require follow-up.