A pelvic abscess is loculated purulent material in the pelvic cavity and develops as a complication of either gastrointestinal or urogenital infection or surgical procedures. It can present with mild symptoms or life-threatening peritonitis. Imaging studies help to diagnose the condition while microbiological studies are required to identify the causative organism.
A pelvic abscess represents the penultimate stage of a pelvic cavity infection . It can occur spontaneously in Crohn's disease  but is usually secondary to infections and surgeries in the abdominopelvic region. Acute diverticulitis with perforation of the colon has been reported to be the commonest cause of pelvic abscess  while other causes are a pelvic inflammatory disease (PID), obstetric/ prostate/ colon surgeries, Crohn's disease and appendicitis. Risk factors for pelvic abscess include diabetes mellitus, immunodeficiencies, malignancies, and pregnancies.
Although immunosuppressed patients and the elderly present few or no symptoms , most patients present with constitutional symptoms of anorexia, high-grade fever, asthenia, nausea, and vomiting. Irritation of the peritoneum or neighboring organs can cause bilateral lower quadrant abdominal pain, diarrhea, prostration, increased frequency of urination, dysuria, foul-smelling vaginal discharge, vaginal bleeding, and dyspareunia. Non-specific flank pain or limp may be the initial presentation in cases with involvement of the psoas muscle by a pelvic abscess .
If the abscess ruptures, then clinical features of peritonitis such as severe abdominal guarding and rigidity are noted. Fistulous tracts leading from the abscess cavity into the affected part of the intestine  occur in patients with Crohn's disease and this is associated with severe abdominal pain and a palpable swelling . One-third of these patients also have rebound tenderness .
Unless diagnosed and treated emergently, a ruptured pelvic abscess with peritonitis can be life-threatening.
Clinical suspicion, a thorough history, along with pelvic and rectal examination help to recognize pelvic abscesses in a majority of the patients . Bimanual palpation may elicit tenderness in either the cul-de-sac or adnexal region in pelvic abscess secondary to PID.
Routine laboratory tests such as a complete blood count and inflammatory markers may reveal leukocytosis and elevated erythrocyte sedimentation rate. Serological tests for autoimmune conditions, syphilis, and human immunodeficiency virus are performed based on clinical findings. A cervical swab is required to identify chlamydial or gonorrheal infection while urinalysis may detect pus cells.
The gold standard test for diagnosing a pelvic abscess is an abdominopelvic ultrasonogram which (US) is performed initially as it can differentiate between an abscess and appendicitis while a transvaginal ultrasound, in cases with PID, helps to confirm and localize the abscess.
Computed tomography (CT) with contrast or magnetic resonance imaging (MRI) are indicated in post-operative patients or patients with Crohn's disease or malignancies suspected to have enteric fistulae. CT with contrast (enterography) provides information regarding the severity of bowel inflammation and a concomitant fistula .
Imaging may show a thickened abscess wall in a chronic abscess  or an ill-defined border in case of a mass or a phlegmon . US guided or CT guided aspiration of the purulent material from the pelvic abscess should be sent for microbiological staining, culture, and antibiotic sensitivity testing in all cases.