Antibiotic failure may point to missed pelvic mass. (Reserve Heparin for Very Large Thrombi).

VAIL, COLO. -- When a seemingly straightforward pelvic infection fails to respond to empiric broad-spectrum intravenous antibiotic therapy, think "pelvic mass," Dr. Ronald S. Gibbs said at a conference on obstetrics and gynecology sponsored by the University of Colorado.

Roughly 55% of cases of antibiotic failure in pelvic infections are due to an infected mass of some type, such as an abscess, septic pelvic thrombophiebitis, hematoma, or a retained placenta, said Dr. Gibbs, professor and chair of ob.gyn. at the university.

The three lesser causes of poor response to antibiotic therapy with clindamycin plus an aminoglycoside or a similarly broadspectrum regimen each account for about 15% of cases. These are the presence of resistant organisms; existence of another source of infection, such as pyelonephritis, pneumonia, or a catheter; or an infection that for no apparent reason fails initially to respond to appropriate antibiotic therapy but comes around with continued treatment and eventually is cured.

Given the likelihood that a woman whose infection has failed to respond to broad-spectrum antibiotics probably has an infected pelvic mass, it makes sense to routinely search for such a mass in nonresponders. Often, it can be felt during a pelvic examination. A pelvic mass may be missed if it's located retroperitoneally or behind the uterus, or if the patient is exquisitely tender.

Failure to detect a mass upon exam often triggers an imaging study Ob.gyns. can do this themselves using pelvic ultrasound, or a referral to a radiologist is in order.

Three therapeutic options exist when the diagnosis is a frank pelvic abscess or an infected pelvic mass believed to be on its way to becoming one. One is continued intravenous broad-spectrum antibiotic therapy. Although classic teaching holds ...