georgee.lees,dvm,ms,diplomateacvim; annebahr,dvm,ms ... · • ask the expert: renal...

Procedures Pro / NAVC Clinician’s Brief / April 2010 ............................................................................................................................................................................67

PerformingRenal Biopsy

Performing a renal biopsy requires select-ing a suitable method of approaching orlocating the target kidney and choosing

a device or method to retrieve the tissue.Ultrasonography-guided needle biopsy tech-niques are commonly used and are generallysatisfactory when the expected changes arelikely to be diffusely distributed in the cortex(as for acute kidney injury and most glomeru-lar disorders).

BIOPSY NEEDLESA variety of automated biopsy devices thatprocure satisfactory specimens when used properly are available commercially. The diameter anddepth of penetration (ie, length of throw) of the needle should be appropriate for the size of the tar-get, which can be assessed directly with ultrasonographic guidance.

When the cortex is thin (because the animal is small or because of the effects of disease), use of ashort-throw needle (eg, 11-mm throw, 7-mm specimen notch) is recommended to help keep thebiopsy tracts entirely within the cortex, even if taking a few more samples is necessary to obtain suffi-cient tissue.

If the samples are intact (not fragmented) and handled carefully, the cores provided by 18-gaugeneedle biopsy devices generally are satisfactory for most purposes. Nonetheless, all other things beingequal, larger-diameter needles (eg, 16-gauge) yield more informative samples and are preferable whenthey can be used safely.

Pro cedu re s P ro U R O L O G Y / N E P H R O L O G Y

George E. Lees, DVM, MS, Diplomate ACVIM;Anne Bahr, DVM, MS, Diplomate ACVR; &

Mary H. Sanders, RVT; Texas A&M University

C O N T I N U E S

Operators should haveextensive practice inaspiration and biopsyof other organs andmasses before attempt-ing kidney biopsybecause there is littlemargin for error.

AUTHORINSIGHT

Use a dissecting microscope with 20× to 40× magnification toassess the tissue composition of each biopsy core retrieved.

PATIENT POSITIONINGThere are several different combinations of patient positions, scanning angles, needledirections, and aspects of the kidney to be biopsied that can be used successfullydepending on operator preferences. The approach should minimize the possibility ofinadvertent damage to the major renal vessels in the hilus because this can lead to acatastrophic outcome, such as fatal hemorrhage.

Some prefer to perform a biopsy of the right kidney because it typically is less mobile(ie, held in place against the liver) than the left kidney; however, others prefer the leftkidney because of its more caudal and superficial location.

TECHNIQUEA biopsy guide attached to the scanning probe to direct the needle biopsy device isthe safest method, but some people prefer to use a “freehand” technique in which theprobe and biopsy device are not connected to one another and can be manipulatedindependently until the operator is certain that the needle is positioned optimally.This latter method requires excellent hand–eye coordination and extensive operatorexperience.

Pro cedu re s P ro CONT INUED

68 ............................................................................................................................................................................NAVC Clinician’s Brief / April 2010 / Procedures Pro

WHAT YOU WILL NEED

Shown here is the top of a mobile cart used at Texas A&M University to help process renalbiopsy specimens. The cart is readily taken to the site in the hospital (eg, surgery or ultra-sound suite) wherespecimen collectionis planned.

The dissecting micro-scope (or some othersuitable means ofmagnification andgood illumination) isused to assess speci-men content. Theforceps have no teethand are suitable fordelicate manipula-tion of the samples.The syringe contain-ing sterile saline andfitted with a 25-gauge needle irri-gates the specimens after collection. The ice bucket (or a nearby refrigerator) helps keep thefixative for electron microscopy chilled. The rest of the items displayed are provided in renalbiopsy kits that are available from centers that perform comprehensive pathologic evaluations.

Ultrasonography-guided needle biopsy ofthe kidney should beperformed under gen-eral anesthesia to allowsufficient control overpatient discomfort andmotion, including res-piratory motion, dur-ing the procedure.

AUTHORINSIGHT

STEP BY STEP RENAL BIOPSY

The cortex of the kidney is the proper target for all renal biopsy procedures for2 important reasons, the first of which is safety. Biopsy needle tracts that crossthe corticomedullary junction are associated with risk for damaging the largevessels (eg, arcuate arteries) that are located there, possibly causing both excesshemorrhage and greater dam-age to the renal parenchymaas a result of ischemia orinfarction of the regionserved by the damaged vessel.

Second, the renal cortex isthe primary tissue of interestfor almost all indications forkidney biopsy. Indeed, allglomeruli are in the cortex,and a renal biopsy for evalua-tion of glomerular disease isinadequate if it does not con-tain a large enough sample ofcortical tissue.

STEP 1

Correct

Incorrect

The lateral cortex (if imaging is done in a ventrodorsalposition) or the dorsal cortex (if imaging is done in alateral position) is often the best area from which toobtain samples based on the availability of ultrasono-graphic windows and ability to position the biopsydevice appropriately. These areas also are distant fromthe hilus, which minimizes the risk for damaging themajor vessels located there.

Although a scan plane that includes both the cortex andmedulla often makes the kidney easy to recognize, aplane that includes only the cortex (in which the biopsytract will be confined) is recommended for renal biopsy.The kidney typically is visualized in a sagittal or dorsalplane, after which the operator should fan the scanplane so that only the cortex remains in the plane inwhich the biopsy needle will be placed.

STEP 2

When the scan plane and direc-tion of needle placement havebeen identified, a small stab inci-sion is made through the skin atthe entry point to minimizedulling of the biopsy needle beforeit is advanced through the bodywall to the kidney.

In addition, and before activationof the biopsy device, it often isnecessary to advance the biopsyneedle tip into the capsule of thekidney (especially when biopsy ofthe left kidney is being performed)to minimize movement of the kid-ney away from the biopsy instru-ment when it is activated.

STEP 3

In general, it is best to collect atleast 2 cortical cores if each is > 10mm long. When the cores areshorter than 10 mm each, 3 coresare usually required. Needle biopsycores do not need to be cut intosmaller pieces except as needed tosubdivide them for separate evalua-tions.

STEP 4

AUTHORINSIGHT

Specimens shouldbe kept moist(never placed ondry sponges) withphysiologic salinesolution andmanipulated verygently (withoutgrasping them withforceps) as they arecollected, assessed,processed, andplaced in fixativeor preservative.

C O N T I N U E S



The renal tissue corecan be retrieved fromthe needle biopsy deviceby using a gentle flow ofsterilized normal salinesolution through a 25-gauge needle to washthe specimen onto theglass slide. Using thistechnique prevents thesterile biopsy needlefrom touching the glassslide. After the speci-men is retrieved, vigor-ous flow of saline can beused to dislodge tissue

tags that remain in the specimen notch before the biopsy needle is reused toobtain an additional core.

STEP 5

Visual assessment of the composition of needle biopsy tis-sue cores to verify that they contain glomeruli (ie, that thesamples to be submitted for evaluation are cortical tissue) isan important, often overlooked step. This is best accom-plished with a low level of magnification (10–40×), such ascan be achieved with good illumination and a dissectingmicroscope, ocular loupe, or hand-held lens.

With such magnification, several aspects of the appearanceof core biopsy specimens help differentiate the cortex from

the medulla. One is that glomeruli often can be seen incortical tissue as small spherical structures or merely asspherical disruptions in the surrounding pattern of tubules.However, even when individual glomeruli are not recog-nized, the cortex can usually be distinguished from themedulla on the basis of the general architecture of the tis-sue: tubules in cortical tissue are convoluted (they appearjumbled) (Figure A), whereas those in the medulla arestraight and parallel with one another (Figure B).

STEP 6

A B

AUTHORINSIGHT

Assess the tissue content ofthe cores to verify that satis-factory samples have beenobtained before ending thebiopsy procedure.


Samples needed for electron microscopic examination or immunos-taining must be appropriately processed and placed into the properfixatives and preservatives when tissue specimens are first obtained.

Figure A shows the recommended ways to subdivide renal biopsycores for light microscopic (LM), transmission electron microscopic(TEM), and immunofluorescence (IF) evaluations under the follow-ing conditions: (1) the cores are not examined with sufficient mag-nification to allow direct assessment of their composition, (2) thecores are verified to be composed of cortex and 2 long (> 10 mm)cores are available, and (3) the cores are verified to be composed ofcortex and 3 short (< 10 mm) or fragmented cores are available.

Figures B through D show division of a needle biopsy core into 2portions for separate evaluations (one for TEM evaluation and theother for IF microscopic evaluation) after examination with suffi-cient magnification to verify that the core is composed entirely ofcortical tissue.

STEP 7

A

C O N T I N U E SIF = immunofluorescence; LM = light microscopic; TEM = transmission electron microscopic

B

C

D

1 2 3



Centers that perform renal biopsyevaluations provide kits containingthe materials and instructionsneeded to obtain, process, and sub-mit satisfactory renal biopsy speci-mens to their laboratories. Forfurther information on renal biopsykits and the evaluation process, seeEvaluation of Renal Biopsy Sam-ples (October 2009, page 67).

STEP 8

IF = immunofluorescence; LM = light microscopic; TEM = transmission electron microscopic

WEDGE BIOPSIESNeedle biopsy devices also can be used with other aiming methods, includ-ing manual palpation (such as in cats), laparoscopy, and a keyhole or fullyopen celiotomy. However, when surgeons use biopsy needles to obtainspecimens of thekidney during aceliotomy, theyoften direct thedevices too deeply.This problem isavoided if a wedgebiopsy sample isobtained. In addi-tion, wedge biop-sies are better forevaluating renalchanges that arenot uniformlydistributed in thecortex, as oftenis the case inanimals withjuvenile-onsetrenal diseases.

A comprehensive collection ofarticles on renal biopsy havebeen featured in Clinician's Brief:

• Ask the Expert: RenalBiopsy—When & Why,October 2009, page 26

• Diagnostics: Evaluation ofRenal Biopsy Samples,October 2009, page 67

• A Picture is Worth 1000Words: Renal Biopsy Stains,January 2010, page 27

Articles available atcliniciansbrief.com

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