Obstetric and Gynecologic Imaging

What Is the Best Imaging to Characterize an Adnexal Mass Suspicious for Malignancy on Ultrasound?

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What Is the Best Imaging to Characterize an Adnexal Mass Suspicious for Malignancy on Ultrasound?

A 58-year-old postmenopausal woman is in your clinic to review her recent pelvic ultrasound, which was performed for vague bloating. The report describes a 7 cm complex right adnexal mass with solid components, thick septations, and internal vascularity on Doppler imaging. She has no acute pain, fever, or other urgent symptoms. The immediate clinical question is how to best characterize this suspicious finding to guide the next steps, which will likely involve a gynecologic oncology consultation and surgical planning. This article details the American College of Radiology (ACR) recommended imaging workflow for this specific scenario: an adult female with an adnexal mass suspicious for malignancy on ultrasound, without acute symptoms. For this presentation, the ACR rates MRI pelvis without and with IV contrast as Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance applies to adult women, both premenopausal and postmenopausal, who have already undergone an initial pelvic ultrasound that revealed an adnexal mass with features concerning for malignancy. These features include, but are not limited to, a solid component that is not hyperechoic, thick septations (>3 mm), evidence of blood flow within the solid component, papillary projections, or the presence of ascites. A key inclusion criterion is the absence of acute symptoms like severe pain, fever, or signs of hemodynamic instability, which would suggest a surgical emergency like ovarian torsion or a ruptured ectopic pregnancy and necessitate a different, more urgent evaluation.

This workflow is distinct from several related clinical situations. It does not apply to:

  • Initial imaging for a suspected mass: If a mass is suspected on physical exam but no imaging has been performed, the first step is typically pelvic ultrasound.
  • Indeterminate masses on ultrasound: For masses that lack overtly malignant features but are not clearly benign, a separate ACR workflow exists.
  • Likely benign masses: Follow-up imaging for simple cysts or other masses deemed likely benign on ultrasound follows different protocols depending on menopausal status.

This article is specifically for the crucial next step after ultrasound has already raised a high suspicion of malignancy, and the goal is definitive preoperative characterization.

What Diagnoses Are You Working Up in This Scenario?

When an adnexal mass appears suspicious on ultrasound, the primary goal of further imaging is to confirm or refute the suspicion of malignancy and characterize the lesion to guide management. The differential diagnosis is centered on identifying potentially cancerous growths while distinguishing them from complex benign mimics.

The most significant concern is an epithelial ovarian carcinoma. This is the most common type of ovarian cancer and the leading cause of death from gynecologic malignancy. Advanced imaging aims to identify features highly suggestive of this diagnosis, such as enhancing solid components, complex cystic areas, and evidence of local invasion or peritoneal spread, which profoundly impacts surgical approach and prognosis.

While less common, other primary ovarian malignancies must be considered. These include germ cell tumors (more frequent in younger, premenopausal women) and sex cord-stromal tumors. Each has distinct imaging characteristics that can sometimes be suggested by MRI, providing valuable preoperative information for the surgical team.

Another critical consideration is metastatic disease to the ovary. The ovaries are a common site for metastases, particularly from gastrointestinal (a “Krukenberg tumor”), breast, or endometrial cancers. Imaging may reveal bilateral solid masses or other features that suggest a non-ovarian primary, prompting a broader search for the original cancer.

Finally, several complex benign adnexal lesions can mimic malignancy on ultrasound. These include endometriomas, tubo-ovarian abscesses (though typically associated with acute symptoms), and hemorrhagic cysts. A key function of advanced imaging is to confidently identify the specific tissue characteristics of these benign mimics, potentially sparing the patient from overly aggressive surgery.

Why Is MRI of the Pelvis with Contrast the Recommended Study for This Presentation?

For characterizing an adnexal mass that is suspicious for malignancy on ultrasound, the ACR designates MRI pelvis without and with IV contrast as Usually Appropriate. This recommendation is based on MRI’s superior ability to evaluate the specific tissue composition and morphology of the mass, which is critical for differentiating malignant from benign etiologies.

MRI provides excellent soft tissue contrast, allowing for detailed assessment of the internal architecture of the mass. It can clearly delineate solid components, the thickness of septations, and the presence of papillary projections—all key indicators of malignancy. Furthermore, specific MRI sequences can identify fat (characteristic of a benign teratoma) or blood products (suggesting an endometrioma), helping to diagnose benign mimics with high confidence. The addition of intravenous contrast is crucial; the pattern and degree of enhancement within the solid components of a mass are strong predictors of malignancy. Malignant tissues typically demonstrate early, avid enhancement due to neovascularity.

In contrast, other imaging modalities are rated lower for this specific task:

  • CT pelvis without and with IV contrast is rated May be appropriate (Disagreement). While CT is excellent for detecting nodal metastases, peritoneal implants, and distant disease (staging), its soft tissue resolution is inferior to MRI for the primary task of characterizing the adnexal mass itself. It also involves significant ionizing radiation (RRL=☢☢☢☢ 10-30 mSv), whereas MRI has none (RRL=O 0 mSv).
  • FDG-PET/CT skull base to mid-thigh is rated Usually not appropriate for initial characterization. PET/CT is a powerful tool for staging known malignancies but has limited specificity in this initial diagnostic setting. Many benign conditions, such as inflammation or infection, can be FDG-avid, leading to false-positive results. Its role is in staging confirmed cancer, not in the primary diagnosis of a suspicious adnexal mass.

Therefore, contrast-enhanced MRI offers the best balance of diagnostic accuracy and safety, providing the detailed anatomical and functional information needed to guide the gynecologic oncologist.

What’s Next After MRI of the Pelvis with Contrast? Downstream Workflow

The results of the contrast-enhanced pelvic MRI are a critical branch point in the patient’s management, directly informing the need for and type of subsequent intervention.

  • If the MRI confirms features of malignancy: A report detailing findings consistent with ovarian carcinoma (e.g., enhancing solid nodules, thick irregular septa, evidence of peritoneal spread) is the trigger for an urgent referral to a gynecologic oncologist. This specialist will typically proceed with surgical staging and debulking. The detailed information from the MRI is invaluable for preoperative planning, helping the surgeon anticipate the extent of the disease and plan the optimal surgical approach.
  • If the MRI confidently identifies a specific benign entity: If the MRI clarifies that the suspicious ultrasound findings were due to a benign lesion like an endometrioma or a fibroma, the management plan changes dramatically. Depending on the patient’s symptoms and the nature of the benign mass, the next step may be conservative management with follow-up imaging or a less extensive, fertility-sparing surgery performed by a general gynecologist rather than an oncologist.
  • If the MRI remains indeterminate: In the rare cases where even MRI cannot definitively distinguish between a benign and malignant process, the mass is typically managed as potentially malignant. This usually means proceeding with surgical evaluation by a gynecologic oncologist, who can perform an intraoperative frozen section to guide the extent of the surgery. The possibility of malignancy dictates a more aggressive approach to ensure the patient receives appropriate oncologic care if needed.

In all cases, the MRI report, often using a standardized system like the Ovarian-Adnexal Reporting and Data System (O-RADS) for MRI, provides a clear, actionable assessment that streamlines the patient’s path to the correct specialist and treatment plan.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup of a suspicious adnexal mass requires careful attention to detail to avoid common missteps. A primary pitfall is ordering a CT scan as the next step after a suspicious ultrasound for the purpose of mass characterization; MRI is the superior modality for this specific task. Another error is ordering an MRI without IV contrast, as contrast enhancement patterns are a vital piece of the diagnostic puzzle for assessing malignancy. Also, be cautious not to misinterpret elevated tumor markers like CA-125 in isolation; this marker can be elevated in many benign conditions (e.g., endometriosis, fibroids) and is not specific enough to diagnose cancer without corroborating imaging findings. Finally, failing to act on suspicious findings with an appropriate referral can lead to delays in diagnosis and treatment. If MRI findings are highly suspicious for malignancy, the necessary next step is an urgent consultation with a gynecologic oncologist.

Related ACR Topics and Tools

This article focuses on one specific clinical scenario. For a comprehensive overview of all related presentations and their corresponding imaging recommendations, please consult the parent topic article. The following resources can also help you apply appropriateness criteria and understand imaging protocols in your practice.

Frequently Asked Questions

Why not just go straight to surgery after a suspicious ultrasound?

While surgery is often the ultimate step, a preoperative MRI provides crucial information that optimizes the surgical plan. It can help differentiate malignancy from complex benign mimics, potentially avoiding a major oncologic surgery for a benign condition. For confirmed cancers, MRI helps the surgeon anticipate the extent of disease, plan for necessary resources (like a colorectal surgeon if bowel involvement is suspected), and counsel the patient more accurately.

Is MRI with contrast safe for a patient with kidney disease?

This is an important consideration. For patients with severe chronic kidney disease (e.g., eGFR < 30 mL/min/1.73m²), there is a risk of nephrogenic systemic fibrosis (NSF) with certain types of gadolinium-based contrast agents (GBCAs). However, newer macrocyclic GBCAs have a much lower risk profile. The decision to use contrast should be made in consultation with the radiologist, weighing the diagnostic benefit against the potential risk. An MRI without contrast may still provide valuable information but is less definitive.

Does the recommendation for MRI change if the patient is premenopausal versus postmenopausal?

No, for this specific scenario—an adnexal mass already deemed suspicious for malignancy on ultrasound—the ACR recommendation for contrast-enhanced MRI is the same for both premenopausal and postmenopausal women. While the underlying likelihood of malignancy is higher in postmenopausal women, the goal of definitive characterization remains the same, and MRI is the best tool for the job in either group.

What is the role of the O-RADS MRI score in this workflow?

The Ovarian-Adnexal Reporting and Data System (O-RADS) for MRI is a standardized scoring system that radiologists use to categorize the risk of malignancy of an adnexal mass, from O-RADS 1 (normal) to O-RADS 5 (high risk of malignancy). This score provides a clear, consistent, and actionable conclusion from the MRI report, helping to standardize the downstream referral and management pathway. An O-RADS 4 or 5 score strongly supports referral to a gynecologic oncologist.

If the MRI suggests metastasis to the ovary, what is the next step?

If the MRI findings are more suggestive of a metastasis (e.g., bilateral solid masses characteristic of a Krukenberg tumor) than a primary ovarian cancer, the clinical focus shifts to finding the primary tumor. The next steps would likely involve a broader imaging workup, such as a CT of the chest, abdomen, and pelvis to look for a primary cancer in the GI tract, pancreas, or breast, as well as relevant endoscopic procedures.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026