Isolated pelvic fluid in males on outpatient magnetic resonance imaging examinations: differences in incidence based on age

Determine the incidence and amount of isolated pelvic fluid in males, stratified by age, on outpatient pelvic magnetic resonance imaging (MRI) examinations performed for lower back or extremity pain. After institutional review board approval, 161 pelvic MRIs performed on males for musculoskeletal or neurologic indications over an 18-month period were retrospectively reviewed for isolated pelvic fluid by 2 radiologists. Patients with a potential etiology for the fluid were excluded. Volume and maximal 2-dimensional measurements of fluid were calculated. Statistical analysis included logistic regression, Wilcoxon rank-sum, and χ tests. Twenty (44.4%) of 45 patients 5 to 29 years old, 5 (10%) of 50 patients 30 to 49 years old, and 4 (6.1%) of 66 patients older than 50 years had isolated pelvic fluid (P < 0.001). Mean volume of fluid was 2.5 mL; 97% (28/29) had less than 10 mL. Mean maximal 2-dimensional measurement was 2.1 cm; 93% (27/29) had less than 6 cm(2). Isolated fluid is greater than 7 times more common on outpatient pelvic MRIs in males younger than 30 years compared with men older than 49 years. Fluid rarely exceeded 10 mL or 6 cm(2).