Clinical approach and laboratory evaluation of renal disease

Question 1

Purpose of the kidneys broadly.

Answer 1

Regulates volume and composition of extracellular fluid by forming urine.

Kidney disease includes:
- Decreased GFR - azotemia
- Damaged glomerular filtration barrier - proteinuria
- Tubular defects - altered urine/plasma composition, urolithiasis
- Endocrine function
- Blood pressure

Question 2

Polydipsia has been defined as water intake of how much in dogs and how much in cats?

Answer 2

Polydipsia has been defined as water intake >100 mL/kg/day in dogs and >50 ml/kg/day in cats.

Even if this threshold is not exceeded, observed increase in thirst may be significant.

Question 3

It is important to differentiate polyuria from pollakiuria, dysuria, or urinary incontinence, which are…

Answer 3

generally problems of the lower urinary tract rather than the kidneys.

polyuria = excessive or an abnormally large production or passage of urine

pollakiuria = abnormally frequent urination (with small volume)

Question 4

Ocular signs of hypertension, such as (3)

Answer 4

hyphema (blood in anterior chamber)
mydriasis (dilated pupil) &
blindness are more common in cats with CKD than dogs, even though prevalence is comparable.

Question 5

Dogs and cats with AKI often have a history of recent…

Answer 5

nonspecific signs (lethargy, inappetence).

Occasionally pets with AKI have a history of known toxin ingestion or of being given prescribed, potentially nephrotoxic, medications.

Weight loss can be a sign of more chronic kidney disease.

Question 6

Signs of uremia: (6+)

Answer 6

Nausea, vomiting,
lethargy, hypothermia,
oral mucosal and GI ulceration,
melena, encephalopathy, seizures.

The collection of clinical signs associated with severe azotemia is termed uremia.

Question 7

Azotemia =

Answer 7

Elevated concentrations of nitrogenous waste products such as BUN and serum Crea above the reference interval is termed azotemia.

Creatinine is a waste from protein and muscle breakdown.

Question 8

features of nephrotic syndrome? (2)

Answer 8

Edema and/or ascites are features of nephrotic syndrome but can also develop with overhydration in oligo-anuric dogs and cats.

Question 9

Main areas to pay especial attention to with a potential kidney disease patient during physical exam? (8)

Answer 9

kidney palpation
bladder size

hydration status
body condition

fibrous osteodystrophy or
pathologic fractures due to mineral & bone disorder from CKD

mm
BP

Question 10

The kidneys should be assessed for (3)

Answer 10

size, contour, and evidence of pain on palpation.

The kidneys of cats are easily palpated but in dogs they are often difficult to identify conclusively.

Question 11

The size of the bladder may be…

Answer 11

important:
a large bladder in a pet that urinated recently suggests PU,
bladder turgidity (= swollen or firm) may indicate obstruction, and
an empty bladder in a pet that has not urinated may indicate oliguria.

Question 12

Cats are particularly vulnerable to developing what? (2) with overhydration.

Answer 12

Cats are particularly vulnerable to developing pleural effusion and dyspnea with overhydration.

Question 13

Pets with CKD may be (insert non-specific sign)

Answer 13

in poor body condition.

Question 14

When CKD occurs in young growing animals, what type of sign may be present?

Answer 14

deformity of the maxilla and mandible (“rubber jaw” due to fibrous osteodystrophy) can occur, although this is uncommon.

Older animals occasionally suffer pathological fractures due to CKD-mineral and bone disorder (MBD).

Question 15

What non-invasive measurement should be taken in all kidney dz patients?

Answer 15

Blood pressure should be measured in all pets with kidney disease.

Fundic examination should also be performed, particularly when systolic pressure is >160 mmHg.

Question 16

Mucous membranes in CKD. (2)

Answer 16

Mucous membranes may be pale in CKD due to anemia.

Uremic ulceration of the oral mucosa and tongue tip necrosis can be present if azotemia is severe but does not differentiate between acute and chronic disease.

Question 17

AKI vs CKD

Answer 17

AKI potentially reversible, CKD irreversible (>3months)

Despite permanent loss of functioning nephrons in CKD, remaining nephrons may hypertrophy and hyper-filtrate circulating blood.

Differentiating acute from chronic disease is usually based on history and physical exam.

Question 18

common features of CKD. (5)

Answer 18

Longstanding history of PU/PD,
weight loss due to poor appetite,
poor body condition, and
poor coat quality are common features of CKD.

Question 19

Diagnostic imaging can provide further information permitting objective assessment of

Answer 19

renal size and contour, together with evaluation for mineralization and loss of internal architecture, consistent with chronicity.

Question 20

Kidney size and shape may provide valuable clues to whether

Answer 20

the azotemia is acute (normal or enlarged size, normal shape, occasionally abnormal turgid feeling, evidence of pain)

or chronic (small and/or irregular in shape), especially in cats.

Question 21

Blood testing in possible kidney disease other than kidney values.

Answer 21

Nonregenerative anemia - CKD, (AKI)

Hyperkalemia - AKI, dogs with CKD that are fed renal diets

Question 22

Describe hematological changes in kidney disease.

Answer 22

Nonregenerative anemia may be present in CKD but anemia may also occur in pets with AKI, e.g., with overhydration, leptospirosis, or hypoadrenocorticism.

Hemorrhage or hemolysis can cause hypoxia/hypotension, which may serve as an inciting cause for AKI.

Anemia is not always caused by chronic disease, particularly regenerative anemias.

Question 23

Describe biochemical changes in kidney disease other than classic kidney values.

Answer 23

Hyperkalemia is most often associated with AKI and particularly with postrenal causes of azotemia.

Hyperkalemia may, however, develop in dogs with CKD fed “renal diets” especially if they are concurrently treated with angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (lower blood pressure and thus GFR).

Question 24

Urinalysis in kidney disease cases. (4)

Answer 24

Possibilities include:
Pyuria, bacteriuria, white cell casts e.g. pyelonephritis (acute/chronic)

Calcium oxalate monohydrate crystals in e.g. ethylene glycol poisoning

Euglycemic glucosuria in e.g. proximal tubular dysfunction (acute/chronic) (impaired reabsorption of GLU)

Large numbers of granular casts, renal epithelial tubular cell casts e.g. acute tubular necrosis

Question 25

ethylene glycol poisoning can cause the formation of what type of crystals? how?

Answer 25

Calcium oxalate monohydrate crystals in ethylene glycol poisoning. due to the metabolic breakdown of ethylene glycol into toxic metabolites, particularly oxalic acid. Oxalic acid is a dicarboxylic acid that can bind with calcium ions in the body. Oxalic acid binds with calcium ions in the bloodstream to form calcium oxalate. This calcium oxalate can crystallize in two main forms. These crystals can deposit in various tissues, particularly the kidneys. The formation of calcium oxalate crystals in the kidneys can lead to: Obstruction of renal tubules Acute tubular necrosis Acute kidney injury These crystals can appear in urine, and their presence is an important diagnostic clue in cases of ethylene glycol poisoning.

Question 26

high phosphorous to creatinine ratio is more suggestive of AKI, why?

Answer 26

As CKD progresses, phosphorous concentration increases gradually and proportionally to the decrease in kidney function (i.e., to the increase in serum creatinine concentration). Conversely, in AKI, since compensatory mechanisms are inactive, phosphorus concentration increases substantially compared with the increase in serum creatinine concentration. Thus, high phosphorous to creatinine ratio is more suggestive of AKI.

Question 27

Calcium values in AKI vs CKD.

Answer 27

Calcium concentration tends to be normal to low in animals with AKI, while in animals with CKD, calcium concentration tends to be normal to high. Yet, there are some exceptions to these trends. For example, grapes and raisins intoxication leading to AKI might be associated with hypercalcemia,5 and vitamin D intoxication results in hypercalcemia and AKI (i.e., hypercalcemic nephropathy).

Question 28

one of the most commonly utilized modalities to differentiate AKI vs. CKD

Answer 28

Ultrasonographic examination The ultrasonographic appearance of the kidneys is affected by the etiology; however, typical ultrasonographic changes characterizing CKD include small kidneys with irregular margins, hyperechoic cortices and poor corticomedullary differentiation, whereas in AKI, the kidneys maintain normal architecture and often are enlarged with hyperechoic cortices. However, exceptions occur and in some etiologies of CKD the kidneys may be enlarged (e.g., amyloidosis, lymphoma, polycystic kidney disease, hydronephrosis) whereas in AKI the kidneys may have abnormal appearance (e.g., ethylene glycol intoxication).

Question 29

A less utilized ultrasonographic method to differentiate AKI from CKD is to

Answer 29

evaluate the parathyroid glands. Secondary renal hyperparathyroidism is an inevitable and early consequence of CKD, resulting in hypertrophy of the parathyroid glands, therefore should be present, at least in animals with advanced CKD, and absent in AKI. It has been shown that ultrasonographic examination of the parathyroid glands is helpful in differentiating AKI from CKD, yet identifying the parathyroid glands requires special skills.

Question 30

Discriminating prerenal from renal causes of azotemia can be aided by measuring

Answer 30

the urine specific gravity. If the USG is >1.030 in dogs or >1.035 in cats, azotemia is usually prerenal in origin, with certain caveats. Some cats with CKD retain urine concentrating ability (>1.035-1.040) despite azotemia.

Question 31

Prerenal azotemia is confirmed by

Answer 31

administering intravenous fluids (or reducing the dose of diuretics) and documenting the resolution or improvement in azotemia.

Question 32

If fluid is present in either the retroperitoneal or peritoneal cavity, a sample should be collected for analysis; if the creatinine concentration is...?

Answer 32

greater than twice that in the blood is consistent with urinary tract rupture. Since urine is a chemical irritant, nonseptic neutrophilic inflammation is common but the amount of associated hemorrhage and inflammation is variable.

Question 33

IRIS Grading of Acute Kidney Injury (AKI)

Answer 33

represents a continuum of renal injury from mild, clinically inapparent, nephron loss to severe acute renal failure. The IRIS AKI Grading scale (I-V) for dogs and cats is based on fasting blood creatinine determination and clinical parameters, such as urinary flow rate.

Question 34

IRIS Grading of Chronic Kidney Disease (CKD)

Answer 34

Staging of chronic kidney disease (CKD) is undertaken following the diagnosis of CKD in order to facilitate appropriate treatment and monitoring of the patient. Staging 1-4 is based initially on fasting blood creatinine, assessed on at least two occasions in the stable patient. The patient is then substaged based on proteinuria and systemic blood pressure. SDMA has also been included in staging criteria.

Question 35

the gold standard for assessing filtration and excretion kidney functions is

Answer 35

Direct assessment of GFR is the gold standard for assessing filtration and excretion kidney functions. Global GFR is the sum total of single nephron GFRs from both kidneys. Key factors determining GFR include oncotic and hydrostatic pressures of plasma and ultrafiltrate within Bowman’s space together with the capillary surface area for filtration and permeability. The result is the “ultrafiltration coefficient”.

Question 36

Markers of GFR have key characteristics: (5)

Answer 36

they must be freely filtered, not circulate bound to plasma proteins, not undergo reabsorption or be secreted by the tubules, and must not themselves alter GFR or be toxic to the kidneys.

Question 37

GFR can be beneficial for evaluating (3)

Answer 37

renal function in pets suspected to have non-azotemic kidney disease, screening for incipient renal disease (e.g., breeds with known juvenile or adult onset nephropathies), or before administration of potentially nephrotoxic medications where dose adjustment can be made. There is no reason for GFR assessment in pets with azotemic CKD, where creatinine is an appropriate marker.

Question 38

R/UC is

Answer 38

Renal/Urinary Clearance (R/UC) of Markers the rate at which a filtered substance is cleared from a given volume of plasma by the kidneys into the urine, providing information about the amount of marker appearing in the urine per unit of time. Assessment of R/UC requires that the amount of substance, either exogenous or endogenous, is assayed both in the plasma and in the urine over a given time period, usually necessitating urinary catheter placement. Clearance markers include inulin, creatinine (endogenous/exogenous), and iohexol. Whereas R/UC of inulin has long been considered a gold standard, endogenous/exogenous creatinine or iohexol are more commonly used.

Question 39

Surrogate plasma/serum markers of GFR: (3)

Answer 39

urea, creatinine, SDMA. Only valid with steady state renal function. Isolated evaluation does not determine whether azotemia is prerenal/renal/postrenal, acute/chronic, reversible/irreversible.

Question 40

Evaluation of changes in BUN, serumCREA and SDMA:

Answer 40

Question 41

When can proteinuria be considered renal in origin.

Answer 41

If pre-renal (e.g., Bence Jones proteins which are a marker of multiple myeloma) and postrenal (lower urinary tract inflammation) causes are excluded, proteinuria can be considered renal in origin.

Question 42

Pre-renal proteinuria is a low-level proteinuria caused by

Answer 42

an overabundant filtered load of low molecular weight proteins that overwhelm the reabsorptive capacity of the proximal tubule (overload proteinuria). Examples of this include the presence of hemoglobin, myoglobin, and immunoglobulin light-chain monomers and dimers (Bence Jones proteins from neoplastic plasma cells) in the urine.

Question 43

Proteinuria should be evaluated in all pets with

Answer 43

CKD as part of the IRIS staging scheme. Proteinuria also may be further investigated if a positive result is obtained on a urine dipstick or if protein-losing nephropathy is a concern.

Question 44

Proteinuria is usually first assessed with a colorimetric biochemical reagent urine dipstick. Dipsticks have reasonable sensitivity (>80%), but poor specificity. If there is concern about proteinuria, further assessment with

Answer 44

a urine protein to creatinine ratio (UPCR) is warranted.

Question 45

The most common test for quantifying proteinuria is the

Answer 45

Urine Protein to Creatinine Ratio (UPCR) persistent values >0.4 in cats and >0.5 in dogs are considered abnormal. UPCRs >2.0 are strongly suggestive of underlying glomerular disease although other etiologies cannot be excluded without renal biopsy. Spot UPCR correlates well with 24-hour urine protein quantification. Considerable day-to-day individual variability in UPCR is reported, particularly in proteinuric pets. UPCR must change by 35% for patients with UPCR ∼12 and by 80% for those with UPCR ∼0.5 for this to reflect a true change in UPCR rather than day-to-day variability. Whereas 1 sample may be sufficient for dogs with UPCR <4.0, more than 2 samples should be checked when there is marked proteinuria (UPCR >4.0). They can be averaged to provide a credible assessment of proteinuria. Pooling an equivolume of urine from 3 samples (e.g., collected in a 48-hour period) is a more cost-effective and comparable way to evaluate proteinuria in pets with UPCR >4.0.

Question 46

Persistent proteinuria is common, affecting almost ?% of ?

Answer 46

almost 20% of elderly dogs.

Question 47

Proteinuria can be categorized as (3)

Answer 47

pre-renal/overflow, renal (glomerular or tubular), or post-renal. Interpretation of proteinuria should be made in the context of the sediment examination, as the presence of RBCs and WBCs is indicative of renal or post-renal issues and their absence may suggest renal origin (glomerulonephritis, amyloidosis). Pathological pre-renal causes of proteinuria include hemolysis (hemoglobin), rhabdomyolysis (myoglobin) or plasma cell cancers (immunoglobulins).

Question 48

Indications for renal biopsy/FNA. (3)

Answer 48

Persistent substantial proteinuria (UPCR >3.5) Proteinuria unresponsive to anti-proteinuric therapy Progressive decline in renal function despite therapy

Question 49

Contraindications for renal biopsy/FNA. (7)

Answer 49

IRIS stage 4 CKD Primary tubulointerstitial disease Hydronephrosis Pyelonephritis Hemostatic disorders Renal abscessation Little to gain with biopsy: amyloidosis, hereditary nephropathy

Question 50

Things to ensure take place pre renal biopsy. (4)

Answer 50

Proteinuria is persistent, renal Control of systemic hypertension Discontinue anti-thrombotic therapy Assessment of hemostasis

Question 51

What is a Low-risk alternative to biopsy with suspected inflammatory/neoplastic disease

Answer 51

FNA though is Rarely rewarding with glomerular disease.

Question 52

Coagulation status should be evaluated in (3)

Answer 52

Protein-losing nephropathy: up to 89% of dogs with PLN are hypercoagulable, but there is no association with serum albumin, UPCR, or AT activity. All dogs and cats with PLN are at risk for thrombotic complications. AKI: Pets with AKI are at risk for thrombosis and/or bleeding disorders. Extracorporeal therapy: Coagulation status is an integral part of managing any pet receiving extracorporeal therapies for renal disease. (Extracorporeal therapy involves drawing blood from a patient, processing it in some way and then returning it to the patient = dialysis)

Question 53

urine specific gravity or USG is defined as

Answer 53

The ratio of the weight of a volume of liquid to the weight of an equal volume of distilled water. Measured using a refractometer, dipsticks aren't reliable for this even though the sticks have USG on them.

Question 54

Isosthenuria = Hyposthenuria = Hypersthenuria = give numbers

Answer 54

Isosthenuria 1.008-1.015, urine has about the same solute concentration as the glomerular filtrate and plasma. Hyposthenuria <1.008, active tubular dilution Hypersthenuria > 1.015

Question 55

Normal urine concentrating ability develops at what age in kittens and puppies?

Answer 55

from 8 weels of age in kittens and 4 w in puppies

Question 56

Normal USG in Dog: Cat:

Answer 56

Dog: 1.015- 1.050 Cat: 1.030-1.060

Question 57

Dehydration/prerenal azotemic USG values: Dog: Cat:

Answer 57

Dog: >1.030 Cat: >1.040 A dog or cat with normal renal function that is dehydrated or has prerenal azotemia should have maximally concentrated urine (USG >1.030 in dogs, >1.040 in cats) as part of physiologic conservation of blood volume.

Question 58

For cats and dogs with either AKI or CKD, identifying what value supports a renal etiology?

Answer 58

USG, identifying sub-maximally concentrated urine together with azotemia supports a renal etiology.

Question 59

Isosthenuria (USG 1.008-1.012) is seen in (3)

Answer 59

health, AKI, and CKD and implies the kidneys are neither concentrating nor diluting tubular filtrate.

Question 60

Hyposthenuria (USG <1.008) indicates

Answer 60

active dilution in the tubules and, therefore, non-renal causes of PU/PD should be investigated.

Question 61

The WDT can be used to

Answer 61

Water Deprivation Test (WDT) used to test tubular response to arginine vasopressin (AVP) in pets with PU/PD after all causes have been excluded apart from nephrogenic or central diabetes insipidus and psychogenic PD. Some suggest that the WDT never be performed, due to attendant risks. Any dog or cat that is azotemic or has a prerenal azotemia and inappropriately dilute urine (USG <1.030) has already failed a WDT and should never have further water restriction.

Question 62

Renal glucosuria indicates

Answer 62

Tubular dysfunction. Glucosuria in a euglycemic dog or cat is indicative of altered renal tubular function, called renal glucosuria, and can be either a single or complex renal tubular disorder. In the latter, increased excretion of other molecules (e.g., amino acids, phosphate, bicarbonate and electrolytes) may occur and the disorder can be either inherited (e.g., Fanconi syndrome) or acquired.

Question 63

Acid-Base Evaluation and Urine pH

Answer 63

Evaluation of acid-base status via blood gas analysis can be important in managing pets with either CKD or AKI where metabolic acidosis is common. In addition, renal tubular acidosis is a rare group of disorders that leads to metabolic acidosis. Urine pH usually reflects total body acid-base and may be influenced by diet, time of day, and disease. Interpretation of urine pH in the context of current blood gas, electrolyte, and bicarbonate may help identify renal tubular acidoses and paradoxical aciduria in vomiting.

Question 64

What pathology may cause alkaline urine.

Answer 64

Urinary tract infections (UTIs) with urease-producing bacteria (e.g., Staphylococcus aureus, Proteus) cause alkaline urine.

Question 65

What type of diets acidify and what types alkalinize urine?

Answer 65

High protein diets acidify while vegetable or cereal-based diets alkalinize urine. Urine obtained after a meal is often alkaline due to gastric acid secretion.

Question 66

Hematuria originating in the kidney is associated with (3)

Answer 66

nephrolithiasis, pyelonephritis, and is occasionally idiopathic. RBC casts on UA confirm a renal origin of hematuria.

Question 67

Pyuria refers to the presence of increased white blood cells (WBCs) in urine. Pyuria cannot be used to determine

Answer 67

source: whether inflammation is in the lower or upper urinary tract (e.g., pyelonephritis) unless WBC casts are identified, or the sample has been obtained by pyelocentesis.

Question 68

Transitional epithelial cells are derived from

Answer 68

urothelium and are typically smaller with tapered ends (caudate cells) when originating from the renal pelvis or they may form epithelial cellular casts, which are indicative of renal injury.

Question 69

Bacteria on UA should always be linked to

Answer 69

presence or absence of clinical signs referable either to the upper or the lower urinary tract to differentiate pyelonephritis from subclinical bacteriuria or sporadic bacterial cystitis. Bacteria in urine obtained from the renal pelvis is indicative of pyelonephritis.

Question 70

Crystalluria is seen with

Answer 70

some alterations in tubular function. They may be indicative of stone type in pets with nephrolithiasis.

Question 71

Cylindruria implies

Answer 71

kidney damage because casts are typically formed within the ascending limb of the loop of Henle and the collecting duct, where tubular flow rates are slowest. Rare hyaline or granular casts may be normal in dogs and cats, but high numbers of cellular casts are always abnormal. Casts can be classified as hyaline, granular, waxy, fatty, cellular (epithelial, WBC, RBC), may contain crystals and/or microorganisms, or can be mixed in origin.

Question 72

Rarely, parasitic ova from

Answer 72

Stephanurus dentatus, Capillaria plica, Capillaria felis, or Dioctophyma renale may be identified in urine. Microfilariae of Dirofilaria immitis may rarely be observed in canine urine sediment.

Question 73

Review summary of renal biomarkers. Biomarkers of GFR typically lag behind

Answer 73

kidney injury biomarkers. Use of biomarkers allows earlier identification of AKI and may lead to earlier diagnosis and treatment.

Question 74

Describe Urinary Enzymes

Answer 74

Enzymes are located on the brush border and in intracellular locations within tubular cells. Since enzymes are usually medium- to high-molecular-weight proteins (>100 kDa), enzyme activity identified in urine is most likely of renal origin. Knowledge of the location of urinary enzymes within the nephron and alteration in either urine enzyme concentration or activity can be used to indicate either damage or an alteration in activity of cells from that region of the tubule. Urine gamma glutamyl transferase (GGT)/creatinine ratio has been used for the monitoring of gentamicin nephrotoxicosis.

Question 75

Describe Radiography for kidney disease. (3)

Answer 75

Renal size Contour Radiopaque calculi

Question 76

Describe CT for kidney disease. (2)

Answer 76

Focus of interest: renal pelvis, ureter Masses

Question 77

Describe U/S for kidney disease.

Answer 77

US can provide important anatomical information about kidney size, shape, and internal architecture. Diffuse renal enlargement with relatively normal internal renal architecture may occur with compensatory hypertrophy, AKI of various causes, amyloidosis, lymphoma, portosystemic shunts, and acromegaly. Small kidneys are found with congenital renal hypoplasia or dysplasia, chronic end-stage renal disease of many etiologies, and as a sequela of chronic ureteral obstruction. Renal cortex thickness may be a better indicator of CKD than total renal dimensions. Diffuse increase in cortical echogenicity is a nonspecific indicator of renal disease and only weakly correlates with histologic findings. Lack of corticomedullary definition is also a nonspecific finding commonly associated with CKD, whatever the underlying etiology.

Question 78

Kidney measurement using U/S.

Answer 78

In dogs, the relationship between body weight and renal length is not linear, making it difficult to determine if kidneys are increased or decreased in size. Methods for indexing renal length to the aortic diameter, or to the length of vertebral body L5, are described but are not widely used. Normal renal length in cats is about 3.0 to 4.5 cm (5 cm is not usually worrisome).

Question 79

Focal renal Lesions on U/S

Answer 79

Usually easy to identify with US, include cysts with round to oval contours, echo-free contents, thin walls, and strong distal acoustic enhancement. Single, simple cysts are usually an incidental finding. Multiple small cyst-like lesions may be seen throughout the cortex and medulla with end-stage kidney disease. Multiple small cysts limited to the cortex or cortico-medullary junction may be seen with familial forms of glomerulocystic disease. Autosomal dominant polycystic kidney disease (PKD) is commonly found in Persian and related cat breeds, and occasionally in dogs. If cystic lesions have thick or irregular walls, internal septations, or if the contents are not completely anechoic, then other disorders, such as hematoma, abscess, and tumor should be considered.

Question 80

Solid Masses on renal U/S

Answer 80

Solid masses are often neoplastic and may be hypoechoic, isoechoic, or hyperechoic to the surrounding renal parenchyma, or may have a mixed pattern. The appearance of most solid masses is non-specific and aspiration cytology or biopsy is required for identification. Granulomas or calcified hematomas or abscesses are potential differential diagnoses for this type of lesion but are much less common. An acute renal infarct may initially appear isoechoic or hypoechoic and could be confused with a mass lesion, but more typically these are diagnosed long after the original insult, resulting in hyperechoic wedge-shaped lesions that are widest toward the outer surface of the kidney.

Question 81

Describe Subcapsular or Perirenal Fluid on U/S

Answer 81

Fluid surrounding the kidney may be difficult to localize. Small volumes of fluid may be urine, blood, transudate, or exudate. Such fluid may be seen with urine leakage, AKI, ureteral obstruction, renal abscessation, hemorrhage or neoplasia. Presence of a large volume of anechoic fluid is likely to represent a perinephric pseudocyst which is more common in cats than dogs and usually in cats with CKD. They may be unilateral or bilateral. Hypoechoic subcapsular thickening mimicking fluid accumulation is a relatively common appearance of renal lymphoma in cats.

Question 82

Describe Medullary Rim Sign on U/S

Answer 82

Sometimes a distinct hyperechoic line is present parallel to the corticomedullary junction: the so-called medullary rim sign. The significance of this line has been debated. It may be a normal finding in both dogs and cats. A diffuse band of hyperechoic tissue within the inner medulla has been reported in some dogs with acute leptospirosis.

Question 83

Describe Pyelectasia U/S

Answer 83

In normal dogs and cats, urine cannot be visualized within the renal pelvis; however, mild pyelectasia may be visible during diuresis. Pyelectasis is a dilation of the renal pelvis. This may be asymmetric. The differential diagnosis for renal pelvic dilation therefore includes all polyuric renal diseases, as well as obstructive lesions and possibly pyelonephritis. U/S changes are not always present in dogs or cats with pyelonephritis; however, changes that have been reported, in addition to pyelectasia, include increased echogenicity of the medulla and/or renal cortex, and hyperechogenicity of the mucosal lining of the renal pelvis. When the reason for pelvic dilatation is uncertain, U/S-guided percutaneous antegrade renal pyelography may be useful to identify an obstruction.

Question 84

Describe Pulsed-Wave Doppler Examination

Answer 84

Examination of blood flow in the interlobar or arcuate arteries can be used to measure its velocity and to calculate the resistive index (RI). RI may increase with many tubulointerstitial renal disorders (acute and chronic), ureteral obstruction, and renal allograft rejection. In clinical practice there are many limitations to the interpretation of RI since it may also be affected by sedation and non-renal disorders.