KIDNEY BIOPSY RENAL TRANSPLANT BIOPSY

Native kidney biopsy
Histology is frequently required in order to direct further management of diffuse renal disease. Biopsy of solid renal masses is rarely performed as the diagnosis of renal cell or transitional cell carcinoma is usually clear from imaging. Biopsies are still performed however in those patients who are not having surgery to confirm the diagnosis; this is often required prior to chemotherapy or new therapeutic regimes. Biopsy of the native kidney is performed in the majority of centres under ultrasound guidance. Contraindications to biopsy include hydronephrosis, which may be more appropriately treated with catheterization or nephrostomy, or small kidneys, that is < 8 cm longitudinal axis (these appearances being indicative of chronic renal impairment). Kidneys > 9 cm can potentially be biopsied; however other factors, including cortical thickness, age, clinical history and the requirement for definitive diagnosis will all have a bearing on whether biopsy is performed or not. Hydronephrosis and kidney size are easily assessable with a prebiopsy scan.

In most cases the biopsy is performed with the patient prone over a small bolster to maximize access to the kidney. The shortest route, avoiding adjacent structures, is selected; subcostally, traversing the cortex of the lower pole and avoiding the collecting system and major vessels is recommended. With ultrasound guidance, either kidney may be chosen and accessibility will vary between patients. The depth of penetration and angle of approach are carefully assessed. Biopsy is normally with a 16G needle.

The patients cooperation is required with suspending respiration at the crucial moment. This avoids undue damage to the kidney as the needle is introduced through the capsule. The needle should be positioned just within the capsule prior to biopsy so that the maximum amount of cortical tissue is obtained for analysis, as the throw of the needle may be up to 2 cm.

Renal transplant biopsy
Biopsy is a valuable tool in the postoperative management of the transplant patient, enabling the cause of graft dysfunction to be identified, in particular differentiating acute tubular necrosis from acute rejection. Ultrasound guidance is essential in order to reduce complications such as haematoma, vascular damage (which may result in arteriovenous fistula or pseudoaneurysm formation) and laceration of the renal collecting system. A single-pass technique, using the spring-loaded biopsy gun with a 16-gauge needle, is usually sufficient for histological purposes; however two passes are often required so that electron microscopy and immunofluorescence can also be perfomed. The procedure is well tolerated by the patient and the complication rate low, at less than 5%.

A full scan of the kidney is first performed to highlight potential problems, for example perirenal fluid collections, and to establish the safest and most effective route. The transplanted kidney lies in an extraperitoneal position and the chosen route should avoid puncturing the peritoneum, to minimize the risk of infection. Unlike the native kidney, the upper pole of the transplanted kidney is usually chosen to avoid major blood vessels and the ureter, which pass close to the lower pole.

The biopsy aims to harvest glomeruli, and the chosen route should therefore target the renal cortex. An angle is chosen to include the maximum thickness of cortex and, where possible, avoid the renal hilum.