Spontaneous septic arthritis of the pubic symphysis mimicking acute abdomen: Diagnostic value of MRI

Septic arthritis of the pubic symphysis is an uncommon and frequently overlooked condition, typically occurring as a postoperative complication. Spontaneous cases without identifiable risk factors are exceptionally rare and may present with misleading clinical features, often mimicking acute abdominal, gynecological, urological, or hip-related conditions. We report the case of a 59-year-old woman with no prior medical or surgical history who presented with acute febrile hypogastric and suprapubic pain. Initial clinical and laboratory findings suggested a lower abdominal or pelvic inflammatory process, leading to diagnostic uncertainty. Computed tomography revealed inflammatory changes centered on the pubic symphysis, with symphyseal erosions and a retropubic/prevesical fluid collection. Magnetic resonance imaging further characterized the lesion, demonstrating bone marrow edema, soft tissue inflammatory involvement, and an ill-defined fluid collection with surrounding enhancement and caudal extension toward the proximal adductor and perineal soft tissues. Ultrasound-guided aspiration confirmed the diagnosis, yielding approximately 13 mL of purulent material positive for Staphylococcus aureus . Targeted antibiotic therapy resulted in rapid clinical improvement, with follow-up MRI showing marked regression of the collection and residual fluid-sensitive inflammatory changes. This case underscores the diagnostic challenge of spontaneous septic arthritis of the pubic symphysis and illustrates the value of cross-sectional imaging, especially MRI, for early characterization of disease extent, minimally invasive diagnostic confirmation, and post-treatment assessment.