A colleague in private practice asked my opinion about the likely benefit of obtaining an ultrasound-guided percutaneous needle
biopsy of the kidney of a 15-year-old spayed female domestic shorthaired cat. He said evaluation of a serum chemistry profile,
hemogram and urinalysis revealed findings (isosthenuria, intrarenal azotemia, hypoproliferative anemia, acidemia, hyperphosphatemia)
consistent with idiopathic chronic renal failure (CRF). No evidence of bacterial urinary tract infection was noted. The cat's
systolic blood pressure was increased. The cat's owners requested the veterinarian pursue additional diagnostics, especially
if they could help in devising a treatment for the renal failure and prolong the cat's life.
Ultrasonographic evaluation of the cat's kidneys by a board-certified radiologist revealed that both kidneys were reduced
in size. Uroliths were not observed. An advantage of ultrasonography is the biopsy needle can be guided into portions of the
kidney so as to minimize the risk for damage to large renal vessels and the renal pelvis. In addition, the kidney can be scanned
for evidence of significant post-biopsy hemorrhage.
The consulting radiologist, who had considerable experience with ultrasound-guided percutaneous needle biopsies of the kidney,
was willing to perform this procedure if requested to do so. Are the probable benefits associated with needle biopsy of this
cat's kidneys likely to outweigh the risks associated with the procedure?
Why and when should percutaneous renal biopsies be performed?
Information obtained by renal biopsy may confirm, support or eliminate diagnostic probabilities formulated on the basis of
the history, physical examination, laboratory data and radiographic or ultrasonographic evaluation. The results of biopsy
may be very helpful in formulating prognoses and treatment plans for some diseases, including protein-losing glomerulopathy
and acute or subacute renal failure (Table 1; Figure 1).
Figure 1: A photomicrograph of a renal cortex section of a 15-year-old neutered male domestic shorthaired cat's right kidney.
The cat developed signs of renal failure eight to 10 days ago. Notice the extensive accumulations of neutrophils in the tubulointerstitium.
These biopsy results indicate this suppurative nephritis potentially is reversible.
In cases in which renal biopsy permits establishment of a specific diagnosis, knowledge of the etiology facilitates formulation
of a specific therapy designed to eliminate or control the underlying cause of renal disease. Although the specific therapy
may not alter existing lesions, it may prevent further damage to nephrons and adjacent structures. In situations in which
the light microscopic, immunofluorescence or electron microscopic changes do not indicate a specific diagnosis, the character
and distribution of lesions may allow one to determine whether the disease process is likely to undergo partial or complete
resolution, remain static or become progressive and irreversible. Such information may be especially helpful when evaluating
patients with acute renal failure associated with declining renal function and/or oliguria despite appropriate specific and
supportive therapy. In some patients, properly performed serial biopsies of the kidney also may be used to monitor therapeutic
efficacy, morphologic resolution of the disease or progression of renal disease.
In the current state of knowledge, however, biopsies are usually of little value to patients with CRF associated with kidneys
of reduced size (Figure 2). Once the disease process has progressed to this state of chronicity, it typically follows an irreversible
and progressive course, ultimately leading to uremia and death. In this situation, biopsy results are unlikely to provide
information that would alter the long-term prognosis or the therapeutic plan. Results of a renal biopsy would not alter treatment,
which consists primarily of supportive therapy designed to modify or eliminate abnormalities that occur secondary to altered
renal function. Irrespective of the underlying cause, supportive therapy of CRF is usually formulated to minimize retention
of metabolic wastes and alterations (deficits and excesses) in fluid, electrolyte, acid-base, endocrine and nutrient balance.
Figure 2: A photomicrograph of a section of a renal biopsy obtained from a 14-year-old spayed female Siamese cat with renal
failure. This cat had severe hypoproliferative anemia and bilateral reduction in renal size—changes consistent with CRF. In
this case, since the clinical presentation suggested that a specific finding on biopsy would not alter therapy, nor provide
prognostic information, the procedure was not justified.