Approach to Interpreting Pelvic Ultrasound (PUR USG)
Primary Imaging Technique
Pelvic ultrasound interpretation requires a combined transabdominal and transvaginal approach performed together whenever possible, as this provides both anatomic overview and high-resolution detail of pelvic structures. 1
Systematic Interpretation Framework
Step 1: Transabdominal Component
Perform this first to establish the overall pelvic anatomy 1:
- Bladder assessment: Optimal bladder filling occurs when the bladder dome sits just above the uterine fundus; underdistention limits visualization 1
- Uterine position and orientation: Note if the uterus is angled right or left of midline, as this guides subsequent imaging planes 1
- Adnexal overview: Identify high-positioned adnexa that may be distant from the transvaginal probe 1
- Free fluid detection: Assess for pelvic fluid collections in the broader field of view 1
Step 2: Transvaginal Component
Perform with an empty bladder for optimal imaging 1:
Uterine Evaluation
- Scan in two orthogonal planes (sagittal and coronal) by sweeping laterally to visualize the entire uterus, as it is often deviated to one side 1
- Trace from fundus to cervix to confirm you are imaging the uterus and not a gestational reaction from ectopic pregnancy 1
- Measure endometrial thickness and assess for structural abnormalities 2
- Identify fibroids and note their location, as they can cause significant pain 1
- Check for interstitial ectopic pregnancy: Any pregnancy within 5-7 mm from the myometrial edge is concerning 1
Adnexal Evaluation
- Scan each ovary completely in two planes (short and long axis) to visualize peripheral cysts and adjacent masses 1
- Assess ovarian size: Normal premenopausal ovary is <4 cm maximal dimension or <20 cm³ volume 1
- Evaluate for torsion signs 1:
- Enlarged ovary with central afollicular stroma and peripheral 8-12 mm follicles (74% of cases)
- Ovarian tissue edema (21% sensitive, 100% specific)
- Absence of intraovarian vascularity (52% sensitive, 91% specific)
Cul-de-sac Assessment
- Small to moderate fluid is normal depending on menstrual cycle phase 1
- Large amounts of fluid are abnormal: Echogenic fluid suggests blood or pus 1
- Perform "sliding sign" assessment: Real-time evaluation of organ mobility to detect adhesions 3
Fallopian Tube Evaluation
- Normal tubes originate from uterine cornua and may be difficult to visualize 1
- Distended tubes (hydrosalpinx, pyosalpinx) are more easily identified 1
- Look for tubo-ovarian abscess in suspected pelvic inflammatory disease 1
Step 3: Doppler Assessment
Color and spectral Doppler are standard components of pelvic ultrasound interpretation 1:
- Ovarian torsion: Absent or abnormal ovarian venous flow is 100% sensitive and 97% specific for abnormal venous flow 1
- Whirlpool sign: 90% of cases with this sign on ultrasound have confirmed adnexal torsion at laparoscopy 1
- PID diagnosis: Power Doppler showing hyperemia and lower pulsatility index discriminates PID from hydrosalpinx (100% sensitive, 80% specific) 1
- Twinkle artifact: 97.2% sensitive and 99% specific for detecting renal stones 1
Step 4: Documentation of Key Pathology
Ovarian Masses
Transvaginal ultrasound demonstrates 1:
- 83.3% sensitivity for ovarian torsion
- 88.2% sensitivity for hemorrhagic cysts
- 84% sensitivity for endometriotic cysts
- 58.3% sensitivity for tubo-ovarian abscess
- 62.5% sensitivity for dermoid cysts
Pelvic Inflammatory Disease
Specific ultrasound signs include 1:
- Wall thickness >5 mm in fallopian tubes
- Cogwheel sign (thickened tube with internal echoes)
- Incomplete septa within fluid collections
- Cul-de-sac fluid presence
- Bilateral adnexal masses (82% of PID cases vs. 17% of other diagnoses)
Ectopic Pregnancy
- Absence of intrauterine pregnancy with positive β-hCG
- Adnexal mass separate from ovary
- Free pelvic fluid (concerning for rupture if large volume) 1
Common Pitfalls to Avoid
- Don't skip transabdominal imaging: Information about bladder fullness, uterine position, and anatomic variations guides the transvaginal examination 1
- Don't assume normal arterial flow excludes torsion: 62% of patients with only abnormal venous flow (but normal arterial flow and grayscale appearance) had confirmed torsion 1
- Don't overlook nongynecologic pathology: Appendicitis, diverticulitis, and bowel obstruction can present as pelvic pain and may be identified on pelvic ultrasound 4
- Don't forget to assess kidneys: 5-10% of women with deep infiltrating endometriosis have ureteric involvement with silent hydronephrosis 3