Background: Peritoneal free fluid can indicate an underlying disease process; however detection of minimal peritoneal free fluid in healthy children is not uncommon.
Objective: To assess the significance of incidental peritoneal free fluid within healthy children by MRI and its relation to physiological changes during puberty.
Materials and methods: This prospective study was performed on 32 healthy volunteers (20 boys) between the ages of 8 years and 13 years, with consecutive follow-ups every 8-10 months for an average of 3 years. Body mass index (BMI) z-score, pubertal status, C-reactive protein and sex hormone concentrations were assessed prior to MRI studies. We reviewed a total of 120 pelvic MRI studies (61 boys) and measured the quantity of peritoneal free fluid. For statistical analysis we used linear mixed-model accounting for within-patient correlations.
Results: The mean ± standard deviation volume of peritoneal free fluid was 4.7±5.7 mL in girls and 1.9±3.1 mL in boys, with a maximum volume of 25 mL and 17 mL, respectively. The prevalence of peritoneal free fluid was significantly higher in girls (91%) compared to boys (67%; P=0.0035). In 15% of the girls and 3% of the boys the fluid was greater than 10 mL. The mean volume of peritoneal free fluid in the fourth stage of puberty was higher and significantly different from the mean volume in the first stage of puberty (P=0.01).
Conclusion: Among healthy pubescent children, the prevalence of peritoneal free fluid is significantly higher in girls. The volume of peritoneal free fluid can reach volumes greater than 10 mL during normal puberty, especially in the fourth stage, and can be assumed normal in the absence of active disease.
Keywords: Children; Magnetic resonance imaging; Normal values; Pelvis; Peritoneal free fluid; Pubertal stage.