What are the distinguishing characteristics of the four fluid collections?

Hematoma: commonly seen within 24 hours of surgery, hyperechoic on ultrasound, increased attenuation on CT (~50 HU), pain, hematocrit drop

Abscess: develops within weeks, complex fluid collection on ultrasound or CT, fever

Urinoma: develops during the first month, hydronephrosis may or may not be present, hot on Tc-99m MAG3

Lymphocele: occurs 5 to 6 weeks after surgery, low attenuation on CT, linear septations seen on ultrasound in 80% of patients