Improving risk stratification of indeterminate adnexal masses on MRI: What imaging features help predict malignancy in O-RADS MRI 4 lesions?

Abstract

Purpose: Ovarian-Adnexal Reporting and Data System (O-RADS) MRI uses a 5-point scale to establish malignancy risk in sonographically-indeterminate adnexal masses. The management of O-RADS MRI score 4 lesions is challenging, as the prevalence of malignancy is widely variable (5-90%). We assessed imaging features that may sub-stratify O-RADS MRI 4 lesions into malignant and benign subgroups.

Method: Retrospective single-institution study of women with O-RADS MRI score of 4 adnexal masses between April 2021-August 2022. Imaging findings were assessed independently by 2 radiologists according to the O-RADS lexicon white paper. MRI and clinical findingswere compared between malignant and benign adnexal masses, and inter-reader agreement was calculated.

Results: Seventy-four women (median age 52 years, IQR 36-61) were included. On pathology, 41 (55.4%) adnexal masses were malignant. Patients with malignant masses were younger (p = 0.02) with higher CA-125 levels (p = 0.03). Size of solid tissue was greater in malignant masses (p = 0.01-0.04). Papillary projections and larger solid portion were more common in malignant lesions; irregular septations and predominantly solid composition were more frequent in benign lesions (p < 0.01). Solid tissue of malignant lesions was more often hyperintense on T2-weighted and diffusion-weighted imaging (p ≤ 0.03). Other imaging findings were not significantly different (p = 0.09-0.77). Inter-reader agreement was excellent-good for most features (ICC = 0. 662-0.950; k = 0. 650-0.860).

Conclusion: Various MRI and clinical features differed between malignant and benign O-RADS MRI score 4 adnexal masses. O-RADS MRI 4 lesions may be sub-stratified (high vs low risk) based on solid tissue characteristics and CA-125 levels.

Keywords: Adnexal mass; MRI; Malignancy; O-RADS; Ovary.

Figure 1.

Flowchart showing patient selection process

Figure 2.

58-year-old woman with O-RADS MRI 4 adnexal mass demonstrating papillary projection confirmed as malignant. (A) Axial T2-weighted imaging shows T2 isointense left adnexal mass (solid arrow) with overall size 4.3 × 3.9 cm and 4.3 × 3.2 cm and size of papillary projection (arrowhead) 2.8 × 2.1 cm and 2.1 × 1.9 cm, by readers 1 and 2, respectively. Cystic component (*) is unilocular with simple fluid. (B-C) Papillary projection is hyperintense on diffusion-weighted imaging (B) and measures 1.254 and 1.335 × 10⁻³ mm²/s (by readers 1 and 2) on the apparent diffusion coefficient (ADC) map (C). ADC of the cystic component measures 2.210 and 2.220 × 10⁻³ mm²/s, by readers 1 and 2, respectively. (D) On post-contrast MRI, papillary projection enhances avidly but slightly less than the outer myometrium (broken arrow). After hysterectomy and bilateral salpingo-oophorectomy, the adnexal mass was pathologically confirmed as a serous borderline serous tumor.

Figure 3.

42-year-old woman with O-RADS MRI 4 adnexal mass containing a larger solid portion (not categorized as other types of solid tissue) confirmed as malignant. (A) Axial T2-weighted imaging shows T2 isointense left adnexal mas (solid arrow) with overall size 6.8 × 6.3 cm and 5.8 × 4.0 cm and size of larger solid portion (arrowhead) 6.5 × 5.4 cm and 5.1 × 3.5 cm, by readers 1 and 2, respectively. Cystic component (*) is multilocular (3–10 septae) with non-simple fluid. (B-C) Larger solid portion is hyperintense on diffusion-weighted imaging (B) and measures 1.021 and 1.014 × 10⁻³ mm²/s (by readers 1 and 2) on apparent diffusion coefficient (ADC) map (C). ADC of cystic component measures 1.987 and 2.023 × 10⁻³ mm²/s (by readers 1 and 2). (D) On post-contrast MRI, papillary projection enhances mildly less than the outer myometrium (broken arrow). After hysterectomy and bilateral salpingo-oophorectomy, the adnexal mass was pathologically confirmed as metastasis from endometrial cancer (broken polygon).

Figure 4.

70-year-old woman with O-RADS MRI 4 adnexal mass demonstrating irregular septation confirmed as benign. (A) Axial T2-weighted imaging shows T2 hypointense left adnexal mass (solid arrow) with overall size 6.7 × 4.2 cm and 6.9 × 3.7 cm and size of irregular septation (arrowhead) 4.4 × 3.2 cm and 3.6 × 2.4 cm, by readers 1 and 2, respectively. Cystic component (*) is multilocular (>10 septae) containing non-simple fluid (not shown). (B-C) Irregular septation is hyperintense on diffusion-weighted imaging (B) and measures 0.865 and 1.099 × 10⁻³ mm²/s (by readers 1 and 2) on apparent diffusion coefficient (ADC) map (C). ADC of cystic component measures 2.278 and 2.313 × 10⁻³ mm²/s (by readers 1 and 2). (D) On post-contrast MRI, irregular septation enhances moderately and less than outer myometrium (broken arrow). After bilateral salpingo-oophorectomy, adnexal mass was pathologically confirmed as serous cystadenofibroma.

Figure 5.

75-year-old woman with O-RADS MRI 4 adnexal mass manifesting as a solid (>80%) lesion confirmed as benign. (A) Axial T2-weighted imaging shows heterogenous T2 hyperintense right solid mas (solid arrow) measuring 2.3 × 2.1 cm by reader 1 and 2.2 × 1.9 cm by reader 2. (B-C) Mass is hyperintense on diffusion-weighted imaging (B) and measures 0.926 and 0.927 × 10⁻³ mm²/s (by readers 1 and 2) on apparent diffusion coefficient map (C). (D) On post-contrast MRI, mass enhances heterogeneously, with some areas equal to and others less than the outer myometrium (broken arrow). After hysterectomy and bilateral salpingo-oophorectomy, adnexal mass was pathologically confirmed as ovarian fibroma.