Imaging findings of tubo-ovarian abscesses
On magnetic resonance imaging, an adnexal abscess is visualized as a fluid-containing mass with thick walls. Following contrast administration, the wall and surrounding inflamed soft tissues show avid enhancement on T1-weighted images (T1WI).
The contents of an abscess or pyosalpinx have specific features:
- Moderately hypointense signal on T2WI.
- Moderately hyperintense signal on T1WI (compared to urine signal), which is explained by the presence of tissue debris or hemorrhage elements.
- Marked diffusion restriction.
Differential diagnosis should include endometrioid cysts, ovarian tumors, abscesses of intestinal origin, and iatrogenic complications (e.g., following uterine perforation by an intrauterine device or oocyte retrieval in in vitro fertilization). When performing 18F-FDG PET/CT, inflammation can exhibit high metabolic activity, falsely mimicking a malignant neoplasm.
Venous system pathology: varices and thrombosis
Pelvic varices (Pelvic Varices) are characterized by dilation of the vessels of the ovarian plexus and broad ligament of the uterus. If the pathology is accompanied by chronic pelvic pain, it is referred to as pelvic congestion syndrome. This condition is typical for multiparous women of reproductive age and is often combined with varices of the vulva, buttocks, and lower extremities. Imaging criteria include a vein diameter of $\ge$ 4 mm, blood flow velocity of $\le$ 3 cm/s, and the presence of dilated arcuate veins within the myometrium.
Ovarian vein thrombosis occurs in the setting of recent childbirth, pelvic surgery, sepsis, or hypercoagulability. The pathology manifests with pain and fever, carrying a risk of pulmonary embolism.
- Ultrasound reveals an echogenic thrombus within the lumen.
- The method of choice is CT. It detects an expanded vessel with a hyperdense thrombus, a filling defect in the lumen, and stranding of the adjacent adipose tissue.
- MRI demonstrates the loss of the normal flowing blood "signal void" effect; the thrombus produces an intermediate signal on T2WI and a high signal on T1WI.
Specific syndromes and iatrogenic processes
Certain inflammatory conditions have recognizable radiological patterns:
- Fitz-Hugh-Curtis syndrome (Fitz-Hugh-Curtis Syndrome): axial CT scans of the upper abdomen reveal fat stranding and traces of free fluid near the liver capsule. The disease is associated with chlamydial infection.
- Actinomycosis and pyometra: T2WI visualizes an intrauterine device against the background of a complex thick-walled mass in the right adnexa (with high and intermediate MR signal) and a marked reaction of the surrounding adipose tissue.
Iatrogenic abscesses in the presence of an indwelling intrauterine device appear on CT as thick-walled, low-density fluid collections. On MRI, they demonstrate diffusion restriction and an intermediate signal on T2WI, while the device itself may be localized directly within the abscess cavity. Ultrasound-guided aspiration can be used to drain such collections (heterogeneous pus is evacuated through the vaginal wall using a hyperechogenic needle).
Benign cystic ovarian masses
Functional cysts include follicular cysts, corpus luteum cysts, and theca-lutein cysts. This is an extremely common pathology that is asymptomatic and often resolves spontaneously. Normal ovulation is accompanied by metabolic activity, which can yield a false-positive result on PET/CT.
Follicular cysts arise due to impaired reabsorption of a follicle that has not reached full development. Their sizes range from 3 to 8 cm. On ultrasound examination, these are thin-walled, hypoechoic, unilocular structures.
Briefly: answers to topical questions
What MRI features are characteristic of ovarian endometrioid cysts?
Ovarian endometrioid cysts on MRI are characterized by specific signal intensity changes caused by the presence of blood degradation products.
- Hyperintense signal — on T1WI.
- Low or variable signal — on T2WI.
- T2 shading sign (T2 shading sign) — indicates aged blood and helps differentiate from hemorrhagic cysts.
- T2 dark spot sign (T2 dark spot sign) — a well-defined hypointense focus on T2 within the cyst.
Fat suppression sequences (Fat suppression) improve the visibility of lesions.
How to differentiate a corpus luteum cyst from a follicular cyst on ultrasound?
Differential diagnosis of a follicular cyst and a corpus luteum cyst on ultrasound is based on evaluating the structure, echogenicity, and vascularity of the lesion.
| Sign | Follicular cyst (Follicular cyst) | Corpus luteal cyst (Corpus luteal cyst) |
|---|---|---|
| Structure | Unilocular (unilocular) lesion | May have a complex sonographic appearance due to internal hemorrhage |
| Wall | Thin-walled (thin walled) | Smooth walls, hypoechoic peripheral ring |
| Echogenicity | Hypoechoic (hypoechoic) | Iso- or hyperechoic, heterogeneous or homogeneous low-level internal echoes |
| Vascularity | Not described | Sometimes demonstrates increased peripheral vascularity |
To memorize the ultrasound criteria for pelvic varices, use the "4-3" formula: vein diameter $\ge$ 4 mm, and blood flow velocity $\le$ 3 cm/s.
Class and exam questions
Which diagnostic imaging modality is preferred for detecting ovarian vein thrombosis?
Contrast-enhanced computed tomography. It clearly visualizes the dilated vein, filling defect (hyperdense thrombus), and inflammatory stranding of the surrounding adipose tissue.
What does the content of a tubo-ovarian abscess look like on MRI?
The contents are characterized by a slightly hypointense signal on T2WI and a hyperintense signal on T1WI (due to debris or hemorrhage), as well as demonstrating marked diffusion restriction.
What else to study on this topic
- Differential diagnosis of tubo-ovarian abscess and endometrioma
- Ultrasound-guided methods for aspirating pelvic fluid collections
- Radiological semiotics of pelvic congestion syndrome
- Features of the MRI appearance of functional ovarian cysts
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