Transvaginal Ultrasound (TVUS) is the Most Appropriate Next Step
In a 28-year-old woman with right lower quadrant pain and an inconclusive transabdominal ultrasound, transvaginal ultrasound (TVUS) should be performed next before proceeding to CT imaging. This approach follows the American College of Radiology appropriateness criteria for reproductive-age women presenting with pelvic pain manifesting as right lower quadrant symptoms 1.
Rationale for TVUS Before CT
The ACR rates pelvic TVUS as "appropriate" (rating 5) for women with pelvic pain that manifests as right lower quadrant symptoms, indicating it should be the first-line imaging study in this population 1.
In peri- or postmenarchal women, a pelvic ultrasound following an equivocal appendix ultrasound may identify alternative causes of pelvic pain or potentially identify an appendix located in the pelvis 2.
TVUS avoids unnecessary ionizing radiation exposure while still allowing accurate assessment of both gynecologic emergencies and the appendix 1.
Combined transabdominal and transvaginal ultrasound achieves 97.3% sensitivity and 91% specificity in adult women when performed by experienced operators 3.
Why Not CT Immediately?
Performing CT as the initial study in young women exposes them to unnecessary ionizing radiation; the ACR specifically recommends TVUS first to avoid this risk 1.
CT identifies gynecologic pathology in approximately 21.6% of alternative diagnoses among patients presenting with abdominal pain, but many of these can be detected with TVUS without radiation 1.
When to Proceed to CT After TVUS
If TVUS does not provide a definitive diagnosis (i.e., is nondiagnostic or equivocal) but clinical suspicion for appendicitis remains, proceed directly to contrast-enhanced CT of the abdomen and pelvis with IV contrast only (no oral contrast) 1.
CT demonstrates 91% sensitivity and 98% specificity for appendicitis following equivocal ultrasound 2.
A staged algorithm of ultrasound followed by CT when needed achieves 99% sensitivity and 91% specificity for acute appendicitis 2, 1.
Why Not Diagnostic Laparoscopy or Open Appendectomy?
Clinical determination of appendicitis is notoriously poor, with negative appendectomy rates as high as 25% when relying on clinical assessment alone without imaging confirmation 1.
Preoperative imaging reduces the negative appendectomy rate to 1.7-7.7%, significantly improving patient outcomes 1.
A 2014 Cochrane review demonstrated that diagnostic laparoscopy increases the rate of definitive diagnoses and reduces negative appendectomy rates in women of childbearing age, but it should be reserved for cases where imaging remains inconclusive after both TVUS and CT 1.
Critical Pitfalls to Avoid
Do not skip TVUS and proceed directly to CT in reproductive-age women with inconclusive transabdominal ultrasound, as this exposes patients to unnecessary radiation when gynecologic pathology may be the cause 1.
Do not proceed to surgery without imaging confirmation, as the absence of rebound tenderness and relatively mild leukocytosis (12.5) suggest this patient may not have classic appendicitis 1.
Recognize that fever is absent in approximately 50% of appendicitis cases, so its absence does not exclude the diagnosis 1.