What are some potential risks for renal biopsy associated with CRF?
Figure 3: A photograph illustrating infarction of the caudal pole of a dog's right kidney. A percutaneous needle biopsy containing
cortex and medulla was obtained from this kidney one week previously.
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Biopsy complications usually occur in inverse proportion to the experience of the individual performing this procedure. For
veterinarians who have not been formally trained in a specialty requiring these types of techniques, some extensive practice
is needed. Before attempting renal biopsy in a patient, individuals unfamiliar with the use of biopsy needles and techniques
should gain experience by obtaining samples from animals at the time of euthanasia or from cadavers. Familiarity with punch
biopsy needles may be gained initially by substituting apples or pears for kidneys. Careful attention to procedural detail
is essential if adequate biopsy samples are to be consistently obtained with minimal risk to patients.
Figure 4: Results of high-resolution angiography of the kidney of a normal young adult mixed-breed dog illustrating the arborizing
architecture of interlobar, arcuate and interlobular arteries. Confining renal biopsy tracts to the renal cortex will minimize
damage to larger vessels. (Angiogram courtesy of Dr. James W. Wilson.)
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Even when ultrasound-guided biopsies are performed by experienced individuals, they still can cause further renal damage.
In addition to mechanical trauma directly caused by advancing the needle through the renal parenchyma, varying degrees of
ischemia and infarction also occur secondary to disruption of blood perfusion through vessels damaged by biopsy needles. Because
renal arteries are end-arteries without collateral blood supply, sudden occlusion or transection of any portion of the arterial
tree will be followed by ischemia and infarction of parenchyma distal to the sites deprived of perfusion. Therefore, the overall
severity of damage caused by needle biopsy of the kidney depends primarily on the size and number of renal vessels through
which blood flow has been compromised. This mechanism (ischemia and infarction) may result in a significantly greater quantity
of damage to nephrons than mechanical damage along the biopsy tract directly caused by the needle.
Figure 5: Results of microangiography of a 1.5-mm slice of kidney obtained from a normal adult mixed-breed dog illustrating
afferent arterioles, glomeruli and some peritubular vessels. Note that larger arteries are not present in the renal cortex.
(Angiogram courtesy of Dr. James W. Wilson.)
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Damage to larger renal arteries, such as arcuate arteries located at the corticomedullary junction, may result in wedge-shaped
infarcts (which, in three dimensions, are cone-shaped; Figure 3). Because the kidneys of most cats are smaller than the kidneys
of most dogs, the risk of damaging larger renal arteries is greater in cats when standard punch biopsy needles are used. Likewise,
biopsy samples that contain tissue from the renal medulla are more likely to be associated with damage to larger vessels than
samples obtained from the renal cortex (Figures 4 and 5). For this reason, it is usually best to direct the long axis of the
biopsy needle so the biopsy tract is confined to the renal cortex (Figure 6). Even in those instances, however, linear infarcts
are likely to occur (Figures 7 and 8).
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