Differential Diagnosis for a 16-year-old girl with left lower quadrant abdominal pain
- Single most likely diagnosis
- Ovarian cyst rupture or torsion: The presence of a 3-cm cyst on the left ovary with several subcentimeter cysts, tenderness over the left adnexa, and a small amount of free fluid in the posterior cul-de-sac on ultrasound suggests that the patient may have experienced a rupture or torsion of an ovarian cyst. The patient's symptoms of sudden onset left lower quadrant pain and the absence of other obvious causes support this diagnosis.
- Other Likely diagnoses
- Functional ovarian cyst: The patient's age, symptoms, and ultrasound findings could also be consistent with a functional ovarian cyst, which is a common cause of pelvic pain in young women. However, the presence of free fluid and significant adnexal tenderness makes ovarian cyst rupture or torsion more likely.
- Pelvic inflammatory disease (PID): Although the patient is sexually active and using condoms with spermicide, PID is still a possible diagnosis, especially given the adnexal tenderness. However, the absence of fever, cervical motion tenderness, and other symptoms makes this less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Ectopic pregnancy: Despite a negative urine pregnancy test, ectopic pregnancy must be considered in any sexually active female with abdominal pain, especially if there is a possibility of a false negative test. The patient's symptoms and ultrasound findings do not strongly suggest ectopic pregnancy, but it cannot be entirely ruled out without further evaluation.
- Appendicitis: Although the patient's pain is in the left lower quadrant, appendicitis can occasionally present with pain in this location, especially if the appendix is retrocecal. The absence of rebound tenderness and other symptoms makes this less likely, but it should still be considered.
- Ovarian torsion: While mentioned under the single most likely diagnosis, ovarian torsion is a do-not-miss diagnosis due to its potential for severe consequences if not promptly treated.
- Rare diagnoses
- Endometriosis: Although endometriosis can cause chronic pelvic pain, it is less likely to cause acute, severe pain like the patient is experiencing. However, it could be considered if other diagnoses are ruled out.
- Adnexal tumor: The presence of a cyst on the ovary could raise concern for an adnexal tumor, but the patient's age and ultrasound findings make this less likely.