# 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.

![Sagittal T2-weighted MRI demonstrating a large submucosal fibroid distorting the endometrial cavity](images/uterine-fibroid-mri.jpg)

## 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.

![Transvaginal ultrasound demonstrating an endometrioma with homogeneous low-level echoes and ground-glass appearance](images/endometrioma-tvus.jpg)

## 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**.

![Coronal T2-weighted MRI showing a septate uterus with fibrous septum dividing the endometrial cavity](images/septate-uterus-mri.jpg)

## 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

1. Thomassin-Naggara I, et al. Ovarian-Adnexal Reporting and Data System (O-RADS) MRI. *Radiology*. 2020;296(3):672-686.
2. Reinhold C, et al. Uterine adenomyosis: endovaginal US and MR imaging features. *RadioGraphics*. 1999;19(suppl 1):S147-S160.
3. Sala E, et al. The role of MRI in staging endometrial and cervical carcinoma. *AJR Am J Roentgenol*. 2007;188(6):1726-1735.
4. ACR Appropriateness Criteria: Abnormal Uterine Bleeding. American College of Radiology, 2023.