MRI Anatomy of Cystic Lesions
Magnetic resonance imaging is the primary method for the radiological evaluation of the structure and location of cystic vaginal lesions. To obtain a comprehensive diagnostic picture, T2-weighted images (T2WI) in the sagittal and axial planes are used (slices are positioned both cranially and caudally to the level of the pubic symphysis).
Key anatomical landmarks when reading pelvic tomograms include: the vagina (vagina), uterus (uterus), urinary bladder (bladder), rectum (rectum), and anus (anus).
Among typical cystic lesions, the following are distinguished:
- Gartner's duct cyst (Gartner's duct cyst): localized directly within the thickness of the vaginal wall, cranially (superiorly) to the pubic symphysis. On T2WI, it demonstrates a characteristic intermediate MR signal.
- Bartholin's gland cyst (Bartholin's cyst) and paraurethral gland cyst / Skene's duct cyst (Skene duct cyst).
- Urethral diverticulum and posterior cystocele. These conditions require careful differential diagnosis. The main distinguishing feature lies in the location of the ostium: a urethral diverticulum communicates with the middle third of the urethra, whereas a posterior cystocele communicates directly with the bladder cavity.
Imaging Follow-up After Sacrocolpopexy
During surgical correction of vaginal or uterine prolapse, sacrocolpopexy is frequently performed — suspension of the vaginal vault or uterine cervix to the sacral promontory (L5/S1 level) using an inverted Y-shaped mesh tape.
Normally on T2WI, the tape appears as a thin, hypointense (dark) band. However, MRI allows timely detection of several complications:
- Tape extrusion: penetration of the implant into the vaginal lumen is accompanied by inflammation, which manifests on MRI as local wall thickening and increased signal intensity on T2WI.
- Infectious complications: classical signs of inflammation are visualized. When reviewing tomograms, it is strictly mandatory to evaluate the L5/S1 vertebral bodies and intervertebral disc for discitis or osteomyelitis.
- Prolapse recurrence: may be associated with detachment of the tape from the L5/S1 promontory or compromise of its integrity.
Additionally, one should consider the risks of adhesive small bowel obstruction and internal hernia formation (especially with intraperitoneal placement of the implant). Tape erosions (occurring in 3–4% of patients, with a higher risk after total abdominal hysterectomy) are extremely difficult to differentiate on MRI.
Visualization of Fallopian Tubes and Uterine Cavity
In addition to assessing cysts and prolapse, diagnostic imaging (ultrasound and hysterosalpingography) is actively used to search for structural causes of infertility. Hysterosalpingography (HSG) is the primary tool for assessing fallopian tube patency.
Possible pathological findings on HSG:
- Hydrosalpinx: dilation of the tube without contrast spill from the ampullary region. Causes: pelvic inflammatory disease (PID), endometriosis, and postoperative adhesions.
- Occlusion: the tube may fail to fill with contrast completely or partially due to a myoma, polyp, mucus plug, or in the setting of PID. Selective catheterization is used to attempt to restore patency.
- Salpingitis isthmica nodosa (Salpingitis isthmica nodosa): a specific pattern of strictures and small diverticula (less than 1 cm) originating from the fallopian tubes. The condition is closely associated with genital tuberculosis and chronic PID.
HSG also reveals intrauterine filling defects: polyps and myomas (broad-based defects), as well as synechiae (linear defects). An extreme manifestation of the adhesive process is Asherman's syndrome (Asherman's syndrome), in which synechiae completely occlude the uterine cavity, causing amenorrhea.
Complications of Ovarian Stimulation and Ectopic Pregnancy
Patients undergoing IVF procedures are subject to specific risks that require monitoring via ultrasound.
Ovarian hyperstimulation syndrome (OHSS) is a potentially life-threatening complication of the luteal phase or early pregnancy. Due to the production of vasoactive substances, vascular permeability increases, leading to fluid shifts into the abdominal cavity (ascites) and hemoconcentration. Clinically, this manifests as abdominal distension, vomiting, and weight gain. Severe forms can be complicated by pleural effusion, thrombosis, shock, and renal failure. Enlarged ovaries in OHSS carry a high risk of torsion (reaching an incidence of 7.5%), which is extremely difficult to differentiate from OHSS itself.
It is important to remember: hemoperitoneum (free blood in the abdominal cavity) is not a symptom of OHSS. Its detection increases the probability of an ectopic pregnancy — the abnormal implantation of an embryo outside the endometrium. The incidence of ectopic pregnancy in IVF patients ranges from 2.1% to 8.6% (compared to 2% in the general population), and with concurrent tubal pathology, the risk increases up to 11%. In the overwhelming majority of cases (82%), ectopic pregnancy is localized precisely in the fallopian tubes.
Briefly: answers to topical questions
What types of cystic vaginal lesions are detected on MRI and what are their imaging features?
T2-weighted pelvic MRI reveals the following cystic lesions of the vagina and adjacent structures.
- Gartner's duct cyst (Gartner's duct cyst) — a cystic lesion with an intermediate MR signal, located within the thickness of the vaginal wall cranially to the pubic symphysis.
- Posterior cystocele (posterior bladder cystocele) — a cyst-like outpouching clearly communicating with the urinary bladder cavity.
- Urethral diverticulum (Urethral diverticulum) — a lesion communicating with the middle third of the urethra.
- Bartholin's cyst (Bartholin's cyst) — indicated by the red marker.
- Paraurethral gland cyst / Skene's duct cyst (Skene duct cyst) — indicated by the yellow marker.
What clinical and imaging manifestations are characteristic of severe ovarian hyperstimulation syndrome?
Severe ovarian hyperstimulation syndrome is characterized by pronounced systemic complications and a specific ultrasound appearance. Clinical manifestations include abdominal distension, nausea, vomiting, weight gain, as well as pleural effusion, intravascular fluid depletion (hemoconcentration), thrombosis, renal failure, and shock. Ultrasound imaging features include:
- Bilateral symmetrical ovarian enlargement (in severe cases $\ge$12 cm).
- Multiple peripheral thin-walled cysts/follicles with internal debris.
- Hyperechoic stroma due to edema and hemorrhage.
- Prolapse of enlarged ovaries into the iliac fossa.
- Presence of free fluid in the abdominal cavity (ascites) or pleural effusion.
What are the specific ultrasound features of tubal ectopic pregnancy?
Specific ultrasound signs of tubal ectopic pregnancy are based on the identification of a mass outside the uterine cavity. The main imaging signs include:
- Absence of an intrauterine gestational sac with a $\beta$-hCG level $\ge$ 2,000 mIU/mL.
- Presence of an adnexal mass located separately from the ovary (the most specific and sensitive sign).
- Visualization of a yolk sac or embryo within the mass.
- The 'tubal ring' / 'ring of fire' sign — a heterogeneous structure with a hyperechoic ring of increased vascularity.
- Echogenic free fluid in the abdominal cavity, indicating hemoperitoneum.
For differential diagnosis, apply the "ostium rule": if a cyst-like outpouching communicates with the urinary bladder cavity, it is a posterior cystocele; if it communicates with the middle third of the urethra, it is a urethral diverticulum.
Class and exam questions
Which MRI sequences provide the best visualization of vaginal cysts?
The optimal baseline for visualization is T2-weighted MRI of the pelvis in sagittal and axial projections.
What does a Gartner's duct cyst look like on MRI?
It is defined as a cystic lesion with intermediate MRI signal on T2-weighted images, located within the vaginal wall cranial to the level of the pubic symphysis.
What are the typical MRI signs of tape extrusion following sacrocolpopexy?
When the implant protrudes into the vagina, T2-weighted images show thickening of the organ wall and increased signal intensity, indicating localized inflammation.
What else to study on this topic
- Pathogenesis and imaging features of ovarian hyperstimulation syndrome (OHSS).
- The role of hysterosalpingography (HSG) in the differential diagnosis of fallopian tube occlusions.
- Nodular isthmic salpingitis: radiological patterns and association with pelvic inflammatory disease (PID).
- MRI features of sacrocolpopexy complications: assessment of the L5/S1 vertebral bodies.
- Asherman syndrome and the formation of intrauterine synechiae.
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