Functional cysts: follicular and corpus luteum cysts
Follicular cysts are often asymptomatic and do not require treatment as they typically resolve spontaneously. On MRI, they demonstrate low signal on T1-weighted images and high signal on T2-weighted images.
Corpus luteum cysts (corpus luteal cysts) develop after ovulation. A potential complication is internal hemorrhage, creating a complex sonographic appearance.
- Clinically, a persistent cyst may present with localized pain and delayed menstruation.
- On ultrasound, they may exhibit increased peripheral vascularity.
- To differentiate from ectopic pregnancy, a β-hCG test is used (it is negative) along with visualization of a hypoechoic peripheral ring.
The evolution of hemorrhagic cysts changes over time:
- Acute stage: iso- or hyperechoic internal signals, smooth walls.
- Subacute stage: clot retraction, "shimmering" sign of gelatinous contents.
- Late stage: formation of fibrin strands resembling a "fishing net" or "web" (without blood flow on color Doppler).
Theca lutein cysts are less common, frequently bilateral, and develop due to excessive beta-hCG (e.g., in molar pregnancy or ovulation induction). They can be complicated by torsion or hemorrhage.
Polycystic ovary syndrome (PCOS)
To diagnose PCOS (Polycystic Ovaries) according to the Rotterdam criteria, two of the three features are required: oligo-/anovulation, hyperandrogenism, and polycystic ovarian morphology on ultrasound.
Ultrasonic criteria for polycystic ovaries (suffices to identify in one ovary):
- Presence of 12 or more follicles measuring 2–9 mm.
- Increased ovarian volume ≥10 cm³.
The examination is best performed transvaginally. It is important to consider the phase of the cycle: follicles ≥10 mm or a corpus luteum increase ovarian volume; in such cases, the ultrasound is repeated at the beginning of the next cycle.
Epithelial tumors
Arise from the surface epithelium.
Serous cystadenomas are the most common. Typically, they are large, anechoic unilocular cysts (on ultrasound) with low MRI signal on T1-weighted images and high signal on T2-weighted images. In 20% of cases, they affect both ovaries. When a fibrous component is present, they are termed cystadenofibromas.
Mucinous cystadenomas (15–25% of all ovarian tumors) contain thick mucus. They are frequently multilocular with thin septations. On MRI (T2-weighted images), the locules may show varying signal intensity ("stained glass effect") due to the differing protein content of the mucin within each individual locule.
Brenner tumors (Brenner tumours) are rare, small, solid epithelial neoplasms.
Germ cell and stromal tumors
Germ cell tumors originate from germ layers and are typical in women under 30. The most frequent variant is mature cystic teratomas (dermoid cysts).
On ultrasound, dermoids appear varied: from cysts with an echogenic node to structures with acoustic shadowing from sebum and hair. They may demonstrate a fluid-fluid level. On MRI, a specific sign is the loss of high signal on fat-suppressed sequences. Potential complications include torsion, rupture, and rarely, malignant transformation (most commonly into squamous cell carcinoma within the Rokitansky nodule).
Stromal tumors include fibromas and thecomas:
- Fibromas are solid, showing low signal on T1- and T2-weighted MRI. They are occasionally associated with ascites and pleural effusion (Meigs syndrome).
- Thecomas frequently occur in postmenopause; they are solid and unilateral. They may produce estrogen, triggering endometrial hyperplasia.
Briefly: answers to topical questions
What are the ultrasound and MRI features of an endometrioid ovarian cyst?
The ultrasound and magnetic resonance features of an endometrioid cyst (endometrioma) depend on the presence of blood degradation products.
Ultrasound features:
- Endometriomas are cystic masses with diffuse homogeneous low-level echoes (low-level echoes).
- With repeated hemorrhages, fluid-fluid or fluid-debris levels may form with a dependent hyperechoic component.
MRI features:
- T1-weighted images — high (hyperintense) signal.
- T2-weighted images — low or intermediate signal.
- T1-weighted fat-suppressed images (FST1W) — high signal.
- Contrast-enhanced T1-weighted images (CET1W) — high signal.
What types of epithelial ovarian tumors exist according to the histological classification?
According to histological classification, epithelial tumors account for about 90% of all ovarian neoplasms and are divided into several types.
- Serous tumors (serous) — the most common (50%), can be cystadenomas or cystadenofibromas.
- Mucinous tumors (mucinous) — account for 20%, often multilocular.
- Endometrioid tumors (endometrioid) — account for 20%.
- Clear cell tumors (clear cell) — account for 10%.
- Undifferentiated tumors (undifferentiated) — occur in 1% of cases.
- Transitional cell or Brenner tumors (Transitional cell or Brenner tumours) — rare, usually small and solid.
What tumor markers are used for the differential diagnosis of benign and malignant ovarian masses?
For the differential diagnosis of ovarian tumor processes, the levels of specific tumor-associated antigens are determined in the blood.
The following tumor markers are used:
- CA-125 — the primary marker used in risk assessment algorithms.
- HE4 — used in combination with CA-125 as a more accurate indicator of malignancy.
- CA 19-9 — an additional antigen.
- CEA — carcinoembryonic antigen.
- β-hCG — human chorionic gonadotropin.
- ROMA test — used in comprehensive diagnostics.
Most of these markers are non-specific and may be elevated in non-neoplastic conditions. To improve accuracy, HE4 and CA-125 levels are used in the Risk of Ovarian Malignancy Algorithm (ROMA).
Class and exam questions
How to distinguish a corpus luteum cyst from an ectopic pregnancy?
Key differences include a negative pregnancy test and the presence of a hypoechoic peripheral rim in a corpus luteum cyst.
What are the MRI features of mucinous cystadenomas?
They are characterized by the "stained glass" sign—a multilocular structure where each locule has its own signal intensity due to varying protein concentrations in the mucin.
How to reliably confirm a dermoid cyst on MRI?
Use a fat suppression technique (T1-FS): the high signal from the fatty component of the cyst should decrease (be suppressed).
What masses can mimic ovarian cysts?
Paraovarian cysts, peritoneal inclusion cysts, lymphoceles, and hematomas. The main distinguishing feature is the visualization of a normal ovary separate from the lesion.
What else to study on this topic
- MRI contrast enhancement patterns of adnexal masses (simple cyst, hemorrhagic cyst, endometrioma).
- Differential diagnosis of solid ovarian tumors and subserous leiomyoma.
- Complications of teratomas: acute and chronic rupture, malignant transformation.
- Imaging findings in Meigs and Gorlin syndromes.
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