Q: What is the usual cut off point in size to consider immediate drainage for renal abscess and perirenal abscess respectively? 


Answer: 5 cm and 3 cm respectively

Though both starts as tissue necrosis due to infection, renal and perinephric abscess are two different processes, at least in terms of location, which may make managements little different. A renal abscess is a walled-off cavity inside the kidney, and the perinephric abscess is relatively a liquefied substance lying between the renal capsule and Gerota’s fascia. 

Renal abscesses can be managed conservatively until the size is about 5 cm, but perinephric abscesses should be drained relatively early at around 3 cm. This is just a rule of thumb, as smaller abscesses may require percutaneous or surgical interventions if antibiotics remain ineffective.

This leeway is due to the reason that renal abscess usually responds well to a proper antibiotic regimen, as well as drainage can be relatively difficult. Also, as perinephric abscesses do not communicate with the collecting system, there is no other way to obtain culture/microorganism except direct intervention to tailor proper antibiotics.


References:

1.  Lee SH, Jung HJ, Mah SY, Chung BH. Renal abscesses measuring 5 cm or less: outcome of medical treatment without therapeutic drainage. Yonsei Med J 2010; 51:569.

2. Dalla Palma L, Pozzi-Mucelli F, Ene V. Medical treatment of renal and perirenal abscesses: CT evaluation. Clin Radiol 1999; 54:792.

3. Coelho RF, Schneider-Monteiro ED, Mesquita JL, et al. Renal and perinephric abscesses: analysis of 65 consecutive cases. World J Surg 2007; 31:431.

4. Meng MV, Mario LA, McAninch JW. Current treatment and outcomes of perinephric abscesses. J Urol 2002; 168:1337.