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Incidental Adnexal Mass (ACR CT/MRI)

Guided recommendation from the ACR Incidental Findings Committee white paper on adnexal masses detected on CT or MRI (Patel et al., JACR 2020). Answer the questions; an optional paste box pre-selects what it can.

Applies to an incidentally detected adnexal mass >1 cm in a woman after menarche. Does not apply if: already characterized by US/MRI, stable in size & appearance for ≥2 years, the patient is at high genetic risk for ovarian cancer, or the mass is symptomatic. When menopausal status is unknown, use age 50 as the surrogate (<50 → premenopausal; ≥50 → postmenopausal). Once a mass is characterized on ultrasound or MRI, score it with the O-RADS calculator.

Encodes the ACR Incidental Findings Committee adnexal mass algorithm (Fig 1, Table 1). Recommendations, not standard of care: deviate as the imaging and patient warrant.

Parses size and a few keywords (simple, hemorrhagic, endometrioma, dermoid, pre/postmenopausal) to pre-select below — always review.

Algorithm definitions & thresholds

Mass categories

Simple-appearing cyst: round/ovoid fluid-density (CT, −10 to 20 HU on multiple ROIs) or fluid-signal (MR) mass with smooth, imperceptible or thin wall, no solid component and no septation. Characteristic features: a non-simple mass with imaging features allowing a confident specific diagnosis (Table 1). Uncertain: features that do not allow a confident diagnosis.

Characterization quality (simple cysts)

Limited assessment: consistent with simple cyst but limited by low SNR, artifact, no IV contrast, or incomplete coverage. Fully characterized by MR: T2-weighted images, pre- and post-contrast T1-weighted images, and complete coverage in ≥2 planes.

Simple-appearing cyst <10 cm — no-follow-up size thresholds (Fig 1)

Premenopausal: ≤5 cm (≤7 cm if fully characterized by MR). Postmenopausal: ≤3 cm (≤5 cm if fully characterized by MR). Above threshold (but <10 cm): US follow-up in 6–12 months if not fully characterized; US to characterize if assessment is limited. Simple-appearing cyst ≥10 cm → US or MR to characterize.

Table 1 — characteristic entities

Hemorrhagic cyst: premenopausal ≤5 cm no further imaging, >5 cm US to characterize; postmenopausal US or MRI to characterize. Para-ovarian cyst, peritoneal inclusion cyst, simple hydrosalpinx, ovarian fibroma, uterine leiomyoma: further imaging usually unnecessary; clinical management. Endometrioma, dermoid: usually managed by gynecology, may require periodic imaging. Suspected malignancy: US or MRI to characterize.

Patel MD, Ascher SM, Horrow MM, et al. Management of Incidental Adnexal Findings on CT and MRI: A White Paper of the ACR Incidental Findings Committee. J Am Coll Radiol 2020;17:248–254. Figure 1 and Table 1.