In a 27‑year‑old nulligravida with chronic menorrhagia and dysmenorrhea being evaluated for possible endometriosis, what is the appropriate initial diagnostic test?

Initial Diagnostic Study for Suspected Endometriosis

Transvaginal ultrasonography is the appropriate initial diagnostic study for this patient with suspected endometriosis. 1

Rationale for Transvaginal Ultrasound as First-Line Imaging

The American College of Radiology designates transvaginal ultrasound (TVUS) as the initial imaging modality for suspected endometriosis, assigning it the highest appropriateness rating among all imaging options. 1 This recommendation is particularly relevant for a 27-year-old woman presenting with chronic menorrhagia, dysmenorrhea, and infertility—the classic triad suggesting endometriosis. 2, 3

Key advantages of TVUS in this clinical scenario:

• TVUS demonstrates excellent performance for detecting deep infiltrating endometriosis (DIE), with sensitivity of 82.5% and specificity of 84.6%. 1, 4
• The examination is less invasive, generally painless, has no complications, and can effectively assess for structural causes of abnormal bleeding. 5
• TVUS allows evaluation of endometriomas, assessment of ovarian mobility, the "sliding sign" for pouch of Douglas obliteration, and detection of deep nodules in anterior and posterior compartments. 1, 6

Why Other Options Are Inappropriate

CA-125 (Option A)

CA-125 has no clinical utility for diagnosis of endometriosis. 1 While it may be helpful for monitoring clinical response in patients with confirmed extrauterine disease, it can be falsely elevated due to peritoneal inflammation or infection and should not be used as an initial diagnostic test. 1

CT Pelvis (Option C)

There is no relevant literature supporting the use of pelvic CT as the initial imaging modality for clinically suspected endometriosis. 7 CT has no role in standard endometriosis diagnosis. 1

MRI Pelvis (Option D)

While MRI is excellent for detecting deep endometriosis with sensitivity of 90.3% and specificity of 91%, it should be reserved as the next step if TVUS is inconclusive or for surgical planning, not as the initial diagnostic test. 1, 8 MRI is more expensive, less accessible, and the American College of Radiology recommends TVUS first. 1

Laparoscopy (Option E)

Laparoscopy with histologic confirmation is no longer required before initiating empiric treatment. 1 The diagnosis of endometriosis is fundamentally clinical and does not require surgical confirmation before starting therapy. 1 Surgery is now reserved for definitive treatment rather than diagnosis, particularly when first-line hormonal therapies are ineffective or contraindicated. 1, 2

Clinical Context and Diagnostic Approach

This patient's presentation is highly suggestive of endometriosis:

• Chronic dysmenorrhea and menorrhagia since teenage years are classic pain patterns associated with endometriosis. 1
• Infertility is present in approximately 50% of patients with endometriosis. 1
• The 8-month delay in conception despite regular intercourse warrants investigation. 2

The diagnostic algorithm should proceed as follows:

1. Perform transvaginal ultrasound (combined with transabdominal ultrasound to widen the field of view for urinary tract and bowel involvement). 1
2. If TVUS is inconclusive or shows findings requiring better anatomical detail, proceed to MRI pelvis without IV contrast. 1, 8
3. If imaging confirms deep infiltrating disease requiring bowel or urologic surgery, use these findings for surgical planning. 1
4. Initiate empiric hormonal treatment based on clinical diagnosis if the patient is not currently seeking pregnancy. 1, 2

Critical Pitfalls to Avoid

• Do not rely on standard TVUS alone for deep endometriosis—expanded protocols following the IDEA consensus approach are needed for optimal detection. 1, 6
• Do not assume negative imaging excludes endometriosis—superficial peritoneal disease is poorly detected by all imaging modalities. 1
• Do not delay treatment waiting for laparoscopic confirmation—the current imaging-first approach reduces morbidity by enabling better surgical planning and decreasing incomplete surgeries requiring reoperation. 1
• Remember that approximately 80% of women with endometriosis have superficial lesions, while 20% have deep infiltrating disease that requires preoperative mapping. 6

The correct answer is (b) Transvaginal ultrasonography.