Cystic adnexal lesions

Naveed Ahmad, MD | Radiology Key | PDF

Key Concepts Summary

1. Pelvic Anatomy & Imaging Techniques

• Adnexa Composition: Includes the fallopian tubes, ovaries, and their ligamentous attachments.
• Ovaries: Normal premenopausal ovaries measure roughly $4 \times 3 \times 2$ cm. They contain T2-hyperintense physiologic follicles and T1-hypointense stroma.
• Blood Supply: The ovaries have a dual blood supply from the ovarian artery (aorta, L2) and uterine artery branches. The left ovarian vein drains into the left renal vein, while the right drains directly into the IVC.
• Imaging Modalities:
  • Ultrasound (US): First-line imaging tool (transvaginal preferred for high resolution).
  • MRI: Best for characterizing sonographically indeterminate masses (differentiating fat, blood, and fibrous tissue).
  • CT: Primarily used for staging malignancy rather than primary adnexal assessment.

2. Nonneoplastic Cystic Adnexal Lesions

• Functional/Follicular Cyst: Persistence of an unruptured Graafian follicle; thin-walled, anechoic, unilocular structure $>3$ cm.
• Corpus Luteum Cyst: Corpus luteum fails to regress; features a central avascular mass with a peripheral vascular “ring of fire” on Doppler and crenulated walls.
• Hemorrhagic Cyst: Bleeding into a cyst (often corpus luteum) featuring a characteristic lacy, cobweb, or fishnet pattern of fibrin strands.
• Endometrioma: Ectopic endometrial tissue appearing as a cyst with diffuse low-level ground-glass echoes on US. Demonstrates T1 hyperintensity and characteristic T2 shading (due to concentrated blood products/recurrent hemorrhage). Unlike teratomas, they do not lose signal on opposed-phase MRI.
• Hydrosalpinx & Pyosalpinx: Dilated fluid-filled fallopian tubes. The “waist sign” (indentations from endosalpingeal folds along opposing walls) is pathognomonic on US.
• Peritoneal Inclusion Cyst: Trapped pelvic fluid due to adhesions (prior surgery/PID), often wrapping around a normal ovary (“spider-in-a-web” appearance).
• Tuboovarian Abscess (TOA): Complex, thick-walled multilocular cystic inflammatory mass associated with PID, causing marked tenderness on transvaginal scanning.

3. Neoplastic Cystic Adnexal Lesions

• Mature Cystic Teratoma (Dermoid Cyst): Benign germ cell tumor containing mature fat, hair, and teeth. Sonographic signs include the “tip of the iceberg” sign, Rokitansky nodule (dermoid plug), and “dot-dash” hair pattern.
• Serous Cystadenoma: Most common benign epithelial ovarian neoplasm (4th–5th decade); typically thin-walled unilocular or multilocular cysts.
• Mucinous Cystadenoma: Large, multilocular benign epithelial tumors containing mucin, often presenting with a “stained glass” appearance on MRI due to varying fluid viscosities.
• Cystadenofibroma: Benign tumor with fibrous stroma, characterized by dark clumps of T1/T2 hypointense fibrous tissue.
• Borderline Ovarian Tumors: Low malignant potential, noninvasive tumors occurring younger (4th decade) featuring thin septations and papillary projections.
• Malignant Neoplasms (Serous/Mucinous Cystadenocarcinoma): Associated with thick septa ($>3$ mm), vascularized solid components, papillary projections, ascites, and peritoneal implants. Endometrioid and clear cell carcinomas are strongly linked to prior endometriosis.

Multiple-Choice Quiz

Question 1

A 32-year-old female undergoes a pelvic MRI for a complex left adnexal mass. The lesion shows high signal intensity on T1-weighted fat-suppressed images and profound low signal intensity (T2 shading) on T2-weighted images. It does not lose signal on opposed-phase imaging. Which of the following is the most likely diagnosis?

• A) Mature cystic teratoma
• B) Endometrioma
• C) Serous cystadenoma
• D) Hemorrhagic functional cyst

Answer: B) Endometrioma

Explanation: T2 shading is caused by recurrent and remote hemorrhage leading to high concentrations of protein and iron, which is a reliable discriminator for endometriomas. Unlike teratomas, endometriomas contain blood products rather than macroscopic fat, meaning they will not lose signal on fat-suppressed or opposed-phase sequences in the same manner as lipids.

Question 2

During a transvaginal ultrasound, a sonographer identifies a tubular, fluid-filled structure in the right adnexa. Closer inspection reveals small indentations from endosalpingeal folds along opposing walls, creating a characteristic “waist sign.” What is the pathognomonic diagnosis for this finding?

• A) Peritoneal inclusion cyst
• B) Paraovarian cyst
• C) Hydrosalpinx
• D) Tuboovarian abscess

Answer: C) Hydrosalpinx

Explanation: The “waist sign,” caused by inward indentations of the folds of the fallopian tube (endosalpingeal folds) along opposing walls, is pathognomonic for a dilated fluid-filled fallopian tube (hydrosalpinx).

Question 3

A 28-year-old woman presents with a right adnexal mass. Transvaginal ultrasound demonstrates a diffusely echogenic mass causing sharp beam attenuation and posterior acoustic shadowing that obscures deeper pelvic structures—a classic “tip of the iceberg” sign. A focal echogenic mural nodule (Rokitansky nodule) is also visible. What is the most definitive imaging feature to confirm this diagnosis on MRI?

• A) T2 shading and fluid-fluid levels
• B) Restricted diffusion within the fluid matrix
• C) Complete signal loss on fat-suppressed T1-weighted sequences
• D) Rim-enhancement following intravenous contrast administration

Answer: C) Complete signal loss on fat-suppressed T1-weighted sequences

Explanation: The clinical and sonographic features describe a mature cystic teratoma (dermoid cyst). The diagnostic confirmation on MRI relies on identifying macroscopic intracellular fat, which demonstrates high signal on T1 and subsequently drops out (loses signal) completely on fat-suppressed sequences.

Question 4

Which of the following sonographic or cross-sectional features is considered a reliable indicator of malignancy rather than benignancy in an adnexal cystic mass?

• A) Unilocularity with a thin, uniform wall (<3 mm)
• B) A “fishnet” or “cobweb” internal reticular pattern
• C) Presence of thickened (>3mm), vascularized septations and solid papillary projections
• D) A “stained-glass” appearance with varying fluid viscosities

Answer: C) Presence of thickened (>3 mm), vascularized septations and solid papillary projections

Explanation: According to standardized ultrasound criteria for evaluating adnexal masses, features suggestive of malignancy include increasing size, thickened (>3mm) and vascularized septa, solid components/papillary projections, and secondary signs like ascites or peritoneal implants. Thin walls, cobweb patterns (hemorrhagic cysts), and stained-glass multilocular cysts are typically benign.