Residency · Residency · Diagnostic Radiology
Female Pelvic Imaging: Uterine and Ovarian Pathology
Introduction
Female pelvic imaging relies on a multimodality approach including transvaginal ultrasound (TVUS), MRI, and CT to evaluate uterine and ovarian pathology. TVUS remains the first-line modality for most gynecologic complaints, with MRI serving as the definitive problem-solving tool for characterization and staging.
Imaging Modalities
Transvaginal ultrasound is first-line for abnormal uterine bleeding, pelvic pain, and adnexal masses. Transabdominal ultrasound complements TVUS for large masses extending beyond the pelvis. Pelvic MRI provides superior soft tissue contrast for tumor staging, characterization of indeterminate masses, and Mullerian anomalies. CT has a limited role in primary gynecologic evaluation but is essential for staging known malignancies and detecting metastatic disease.
Uterine Pathology
Leiomyomas (Fibroids)
| FIGO Type | Location | Description |
|---|---|---|
| 0 | Submucosal | Pedunculated, intracavitary |
| 1 | Submucosal | <50% intramural |
| 2 | Submucosal | >=50% intramural |
| 3 | Intramural | Contacts endometrium, 100% intramural |
| 4 | Intramural | Entirely within myometrium |
| 5 | Intramural | Subserosal, >=50% intramural |
| 6 | Subserosal | <50% intramural |
| 7 | Subserosal | Pedunculated |
Leiomyomas are the most common uterine neoplasm, found in up to 70-80% of women by age 50. On MRI they appear as well-circumscribed, low T2 signal masses due to smooth muscle and collagen content. They are classified by the FIGO system as submucosal (types 0-2), intramural (types 3-5), or subserosal (types 6-7). Degenerative changes include hyaline, cystic, red (hemorrhagic in pregnancy), and calcified types. Submucosal fibroids are the most common cause of abnormal uterine bleeding among fibroids.
Adenomyosis
Adenomyosis represents ectopic endometrial glands and stroma within the myometrium. On MRI, findings include a thickened junctional zone (>12 mm is diagnostic) and T2 low-signal myometrial thickening with interspersed bright foci. On ultrasound, the myometrium appears heterogeneous with myometrial cysts, ill-defined hypoechoic areas, and venetian blind shadowing. Both diffuse and focal forms exist, and focal adenomyosis (adenomyoma) can mimic a fibroid.
Endometrial Carcinoma
| T Stage | Description |
|---|---|
| T1a | <50% myometrial invasion |
| T1b | >=50% myometrial invasion |
| T2 | Cervical stromal invasion |
| T3 | Serosal or adnexal involvement |
Endometrial carcinoma is the most common gynecologic malignancy and presents with postmenopausal bleeding. On ultrasound, endometrial thickness >4 mm in postmenopausal women warrants biopsy. MRI staging classifies T1a as less than 50% myometrial invasion, T1b as 50% or more invasion, T2 as cervical stromal invasion, and T3 as serosal or adnexal involvement. Deep myometrial invasion on MRI is identified by disruption of the low-signal junctional zone with tumor signal extending into the outer myometrium.
Ovarian Pathology
Functional Cysts
Follicular cysts are simple, thin-walled, and anechoic, typically less than 3 cm but capable of reaching 5 cm. Corpus luteum cysts have a thick, crenulated wall with peripheral vascularity ("ring of fire" on Doppler) and may contain internal hemorrhage. Most resolve spontaneously within 1-2 menstrual cycles.
Endometrioma
Endometriomas show homogeneous low-level echoes on ultrasound (the "ground glass" appearance). On MRI, they are T1 hyperintense with T2 shading (progressive signal loss on T2) and show the "light bulb" sign on T1 fat-saturated sequences. They are bilateral in 30-50% of cases and associated with deep infiltrating endometriosis.
Mature Cystic Teratoma (Dermoid)
Dermoids are the most common ovarian neoplasm in reproductive-age women. They contain fat, hair, sebaceous material, and sometimes calcification (teeth, bone). On ultrasound, they appear as an echogenic mass with posterior acoustic shadowing (tip-of-the-iceberg sign), dermoid plug, and fat-fluid level. On MRI, fat signal is confirmed by signal dropout on fat-saturated sequences.
Ovarian Malignancy
Risk factors include age, BRCA mutations, nulliparity, and endometriosis (for clear cell and endometrioid subtypes). Suspicious features include solid enhancing components, thick septations (>3 mm), papillary projections, peritoneal implants, ascites, and lymphadenopathy. The O-RADS scoring system standardizes risk stratification of adnexal masses on ultrasound and MRI.
Mullerian Duct Anomalies
The septate uterus is the most common anomaly, with a normal fundal contour and an internal septum dividing the cavity; it carries the highest rate of pregnancy loss. The bicornuate uterus has a fundal cleft greater than 1 cm with two separate horns. The unicornuate uterus has a banana-shaped cavity and may have a rudimentary horn. MRI is the gold standard for classification using the updated ASRM system.
Key Clinical Pearls
Always report fibroid FIGO classification (submucosal vs intramural vs subserosal) as it determines the treatment approach. On MRI, the junctional zone is the key landmark for assessing myometrial invasion in endometrial carcinoma. O-RADS provides a standardized risk score for adnexal masses, and O-RADS 4-5 lesions warrant surgical referral. An endometrioma with a solid enhancing nodule should raise concern for endometriosis-associated malignancy (clear cell or endometrioid carcinoma).
References
- Thomassin-Naggara I, et al. Ovarian-Adnexal Reporting and Data System (O-RADS) MRI. Radiology. 2020;296(3):672-686.
- Reinhold C, et al. Uterine adenomyosis: endovaginal US and MR imaging features. RadioGraphics. 1999;19(suppl 1):S147-S160.
- Sala E, et al. The role of MRI in staging endometrial and cervical carcinoma. AJR Am J Roentgenol. 2007;188(6):1726-1735.
- ACR Appropriateness Criteria: Abnormal Uterine Bleeding. American College of Radiology, 2023.