Renal Biopsy in the Cat and Dog

Renal biopsy is a useful method of distinguishing between reversible and irreversible primary kidney disease. It can also be used to monitor response to therapy. However, it is essential to combine it with assessment of renal function: urine analysis and sediment examination; and a full Kidney 3-profile (which includes a urine protein:creatinine ratio to help distinguish pre-renal and renal disorders) would be appropriate.

Specific Indications for Renal Biopsy:

• Evaluation of severe proteinuria, especially in association with abnormal urine protein:creatinine (PCR) clearance ratios
  
  
• Investigation of renal disease in the young dog (cat). Juvenile or familial nephropathies are usually associated with a poor prognosis. In certain breeds, this diagnosis will be of relevance to littermates and breeding programmes.
  
  
• Evaluation of animals with suspected acute renal failure. Biopsy will help establish a diagnosis and prognosis and assist the clinician in deciding whether to start or continue intensive therapy, including peritoneal or other form of dialysis, to support the patient until renal function can be re-established.
  
  
• Post mortem to confirm the clinical diagnosis when owners will give permission for only minimal procedures.

Renal Biopsy Techniques

Surgical Biopsy via Laparotomy

• Incisional biopsy is indicated when the whole kidney is not involved or more sophisticated needle techniques are not available
• No specialised equipment is required
• A sharp incision is made through the renal capsule of the greater curvature of the kidney. A second, slightly curved incision adjacent to the first, will isolate a small wedge of cortical tissue, which is removed without crushing.
• The incision is closed with a mattress suture in the cortex and a continuous suture in the capsule.
• Any post-biopsy haemorrhage can be controlled before abdominal closure.
• Either kidney may be biopsied. The left is more accessible and is usually used, provided both kidneys are equally affected.

Keyhole finger technique

Used in dogs and cats where palpation and perabdominal immobilisation of the kidney are difficult.

• A small incision is made just ventral to kidney. A finger is inserted and used to hold the kidney against the abdominal wall. A biopsy needle is inserted into the kidney through an adjacent stab incision through skin and subcutis.
• Automatic tissue-core biopsy needles are preferred, but satisfactory biopsies can be obtained using a standard Trucut-14G needle.
• It is essential that the needle is advanced through the cortex parallel to the medulla. Insertion into the medulla where the major blood vessels and pelvis are located must be avoided.
• Finger pressure is applied to the kidney to control haemorrhage prior to abdominal closure.

The procedure is described in detail by Macdougall and Lamb (1996)—see references

Ultrasound guided percutaneous tissue core biopsy

• Increasingly used where ultrasound is available.
• A safe path for the needle is selected using ultrasound.
• The needle is inserted through a stab incision through skin and subcutis next to the transducer and its position is monitored as it is advanced.
• The needle may be placed in a guide attached to the transducer.
• Direct pressure over the biopsy site is used to control haemorrhage.

The procedure is described in detail by Macdougall and Lamb (1996)—see references

Percutaneous fine needle aspiration

• Indicated for suspect cystic lesions and differentiation of tumour (especially lymphosarcoma) from inflammatory disease.
• Provides no information on architecture and has limited value for most chronic, renal disorders.
• A 21-25G needle may be inserted into the left kidney when it is palpable and can be fixed against the abdomen. Otherwise, aspiration must be undertaken using a keyhole technique or ultrasound guidance. Ultrasound guidance is recommended where deep cystic lesions are suspected.

Management of the Renal Biopsy Patient

Pre-biopsy

• Full urinalysis to include PCR and semi-quantitative bacteriology. If a significant organism is isolated in significant numbers, an appropriate course of antibiotics can be given prior to or immediately after biopsy.
• Radiography or ultrasonography, if both kidneys are not readily palpable in the abdomen.
• A full biochemical and haematological work-up, including a coagulation profile with bleeding time, is advisable.

During biopsy:

• Appropriate intravenous fluid therapy to maintain urine production and reduce the risk of obstruction from any pelvic blood clots.

Post-biopsy:

• Evaluate for evidence of internal bleeding for up to 24 hours post biopsy.
• Monitor urine to determine the severity of post-biopsy haematuria and monitor renal function. Transient haematuria for up to three days is frequent and usually insignificant. Continue intravenous fluids if haematuria continues; this will help maintain urine output.
• Monitor plasma urea and creatinine and haematocrit daily.

Complications:

• Major complications (life-threatening haemorrhage from trauma to renal or adjacent vasculature; peritonitis from damage to a renal abscess or intestinal tract; possible dissemination of neoplasia) are rare.
• Minor complications (mild haemorrhage; localised infection; localised pain) are more common but can be managed appropriately.

Contra-Indications:

• Uncorrected severe coagulopathy. If suggested by history, clinical signs or abnormal bleeding or clotting times, must be confirmed by a full coagulation profile.
• Cavitating lesions are a contraindication for other than aspiration biopsy.

Handling the Biopsy Specimen:

• Biopsy specimens should be placed in 10% neutral buffered formalin as soon as possible.
• Tissue may be flushed from the needle with isotonic saline. If teasing from the needle is required, use a 25G needle to minimise damage.
• Tissue must be kept moist until placed in fixative, but avoid swabs as these can cause damage due to adhesion of the small samples.
• Incisional wedge biopsies should ideally be no more than 3 mm thick.
• Where, rarely, immunofluorescence is required, duplicate samples should be submitted in Michel's fixative (available on request).
• Please include a full history with related laboratory findings on blood and urine samples. This will aid interpretation.

Final Comments

In addition to reading this protocol, you are recommended to try out the technique on a cadaver prior to clinical biopsy. Dr. Dugald Macdougall will be pleased to give further advice.

Further Reading

Macdougall, D.F., and Lamb, C.R. (1996) Renal biopsy, BSAVA Manual of Canine and Feline Urology, edited by J.Bambridge and J.Elliot, chapter 12, p.148