The use of tPA in pediatric abdominal abscesses is poorly defined. The indications are somewhat subjective and the dosage guidelines vary between institutions. Some studies have suggested that it be administered at, or soon after, the time of drainage if the ultrasound appearance of the collection is complex and/or septated, or if the initial aspirated contents are thick and viscous. Both criteria are difficult to accurately define and implement. In many instances, when there is minimal ongoing drainage despite follow-up ultrasound appearances suggesting a significant residual collection, tPA is administered several days following the initial procedure.