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9

Diffuse Changes

■ Diffuse Changes

Large Kidneys

Kidneys

Anomalies, Malformations

 

 

 

 

 

 

Diffuse Changes

 

 

 

 

 

 

 

Large Kidneys

 

 

 

 

 

 

 

 

Small Kidneys

 

 

 

 

Hypoechoic Structure

 

 

 

 

Hyperechoic Structure

 

 

 

 

Irregular Structure

 

 

 

Circumscribed Changes

 

 

 

Fig. 9.18 Intrarenal vascular ectasia. Arteriovenous mal-

b Color duplex sonography (CDS) identifies the cystic

formation appears as an echo-free mass within the kid-

masses as ectatic intrarenal arterial vessels, probably

ney. L = liver; N = kidney.

arteriovenous malformations of the renal artery. (Doppler

a B-mode image demonstrates cystic masses in the renal

spectral analysis with resistance index determination

sinus echo (arrows).

yields additional information on the nature of the vascu-

 

lar ectasia.)

Constitutional/Acromegaly

Duplex Kidney, Single Kidney

Diabetic Nephropathy

Polycystic Kidney Disease

Acute Renal Failure, Shock Kidney

Septic–Toxic Kidneys

Acute Urinary Retention, Acute Outflow Obstruction

Renal Congestion Due to Heart Failure

Renal Vein Thrombosis

Acute Glomerulonephritis

Acute Pyelonephritis

AIDSand Heroin-induced Nephropathy

Amyloidosis/Paraprotein Kidney

Pyonephrosis

Renal Tumor

Renal Allograft, Allograft Rejection

Sonographic Determination of Renal Size

The sonographic estimation of renal size is unreliable. Whether a kidney appears large or small in ultrasonography depends very much on the selected field of view, i. e., an undersize kidney may appear large because it is displayed at a large scale, and vice versa (Fig. 9.19). For some examinations, then, it is necessary to measure at least the longi-

tudinal renal diameter and parenchymal thickness.

Anatomically, the adult kidney measures 1 cm over the sonographic diameter, 10–11.5 cm in length, 5–7 cm in width, and 3–4 cm in thickness. For physical reasons, radiographic measurements of the kidney add approximately 1.5 cm to its

The individual scatter of measurement is about

diameters divided by 2. Volume correlates

0.3–0.5 cm. The parenchymal thickness is in the

with age, or, even better, with body length.

range 13–18 mm; small kidneys have less than

Normal volumes range from 90 to 170 mL;

12 mm. For specific examinations, volume

small kidneys less than 80 mL, overlarge kid-

analysis is preferable: the product of the largest

neys more than 180 mL (Fig. 9.19).

longitudinal, transverse, and anteroposterior

 

length and 1 cm to its width. Sonographic measurements, by contrast, are slightly smaller than the true dimensions because the kidneys occupy planes that are angled laterally and anteromedially and do not coincide precisely with the planes used for routine scanning.

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9

Kidneys

Fig. 9.19 Subjective assessment of renal size.

a In a large field of view, the kidney (N) appears small in relation to the overall image.

b The kidney (N) appears larger in an enlarged view. According to measurements, this kidney is small but still within normal limits for the patient’s body size.

Constitutional/Acromegaly

Renal size is dependent on the patient’s constitution or body size. As a result, the renal dimensions may be greater or less than normal. Lengths from 9.6 to 13 cm may still be considered normal, depending on body size (Fig. 9.20). Nomograms plotted for children show a direct correlation with body size.

Fig. 9.20

b Enlarged kidneys in acromegaly (13.7 cm).

a Constitutionally large kidney (13.5 cm,

contralateral

13.0 cm) in a 47-year-old man with a height of 196 cm and body weight of 111 kg.

Duplex Kidney, SingleKidney

Duplex kidney. One of the most common types of renal enlargement involves duplex kidneys, whose sonographic features are described above. Their shape in ultrasound resembles that of a pretzel. The longitudinal diameter may be normal or increased up to 15 cm, with a normal width. The overall thickness may be increased if the duplicated kidneys are ar-

ranged side by side (Fig. 9.21), creating a tu- mor-like appearance. The moieties can be distinguished from a tumor by color Doppler sonography, which shows a normal duplex vascular pattern.

Single kidney. A single kidney undergoes compensatory physiological enlargement in re-

sponse to contralateral hypoplasia or aplasia, contralateral nephrectomy, a nonfunctioning opposite kidney, or a renal allograft (Fig. 9.22).

Fig. 9.21 Large duplex kidney with multiple parenchymal

Fig. 9.22 Renal aplasia.

b Compensatory enlargement of the right kidney

bands.

a Absent left kidney, empty renal fossa below the spleen

(12.3 cm, cursors).

 

(MI) on the left side. F = fatty tissue; M = musculature; S =

 

 

shadow.

 

330

9

Diffuse Changes

is why early detection at the hyperperfusion stage critically influences the prognosis. Other criteria of diabetic nephropathy are not present in stages I and II, and the only sign of hyperperfusion is an elevated creatinine clearance rate in excess of 120 mL/min.

Sonographic features. In ultrasound, the renal parenchyma is thickened and often shows increased sonodensity. The medullary pyramids appear bulky and less echogenic than the adja-

Fig. 9.23 Stage IV diabetic nephropathy with a large kidney (N, 12.1 cm) and proteinuria. Long history of type II diabetes mellitus. Six months later, persistent diarrhea and reversible decompensation with creatinine of 8 mg/ dL. MI = spleen.

cent parenchyma, which often but not always shows increased echogenicity. The kidney should therefore be measured in patients evaluated for diabetic nephropathy. It is not until an advanced stage, when the patient requires hemodialysis, that the kidney shrinks in size and

Fig. 9.24 Diabetic nephropathy. Large kidney (N, 12.5 cm) with prominent hypoechoic medullary pyramids (arrow). L = liver.

shows obvious structural changes. Other signs of diabetic nephropathy are swollen, hypoechoic medullary pyramids. In advanced stages (Mogensen stages IV–V, here with manifest renal failure), the parenchyma shows increased echogenicity (Fig. 9.23, Fig. 9.24).

Polycystic Kidney Disease

Besides multiple anechoic lesions and ill-de- fined borders, polycystic kidneys are conspicuous by their enormous enlargement due to the mass effect of the cysts (Fig. 9.8).

Acute Renal Failure,Shock Kidney

In the setting of acute renal failure and renal shock or severe hypovolemia, ultrasound usually shows an increased parenchymal volume and a decrease (or increase) in echogenicity with enlargement of the kidneys and consequent narrowing of the sinus echo complex (Fig. 9.25).

Fig. 9.25

a Acute prerenal renal failure. Creatinine 8.2 mg/dL (al- cohol-related disease, persistent vomiting and diarrhea). The kidney is greatly enlarged (16.1 cm) with a hypoechoic, ill-defined structure.

b Sepsis, alcohol-related disease, kidney (N) enlarged to 13.0 cm. Renal echogenicity is slightly decreased. The medullary pyramids are swollen and very hypoechoic.

L = liver.

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9

Kidneys

Septic–Toxic Kidneys

Renal enlargement also occurs occasionally in

Fig. 9.26 Septic–toxic kidneys with renal failure: greatly

sepsis. The kidneys tend to show increased

enlarged kidney (N) with parenchymal swelling. The me-

dullary pyramids are markedly enlarged and hypoechoic.

echogenicity, probably due to a suppurative

 

leukocytic reaction to septicopyemic foci in

 

the organs. The reaction may also be a result

 

of dehydration (Fig. 9.26).

 

Acute Urinary Retention, Acute Outflow Obstruction

In this situation as well, the kidneys often react with enlargement and decreased echogenicity due to interstitial edema. The medullary pyramids may show signs of conspicuous swelling. Often the bladder is greatly distended. The sonographic renal changes are the same as those seen in renal congestion resulting from heart failure.

Renal Congestion Due to Heart Failure

The fluid build-up that occurs in severe congestive heart failure leads to swelling and increased echogenicity of the renal parenchyma secondary to edema and hemorrhage. This swelling is another cause of renal enlargement (Fig. 9.27).

Renal VeinThrombosis

Acute renal vein thrombosis also leads to en-

●

A broadened renal vein that contains intra-

largement and unilateral hypoechoic swelling

 

luminal echoes and is devoid of color flow

of the parenchyma (Fig. 9.28). The diagnosis is

●

A high resistance index (RI, after Pourcelot:

supported by:

 

(Vmax − Vmin)/Vmax in the intrarenal renal ar-

 

 

teries

Fig. 9.27 Acute prerenal renal failure: enlarged kidneys (13.0 cm), hypoechoic parenchyma, and swollen, hypoechoic medullary pyramids (arrows).

●Reverse flow (hard, negative systolic signal in the renal artery)

Fig. 9.28

b Respective renal vein and caval thrombosis.

c Spectral analysis in renal vein thrombosis indicates an

a Renal vein thrombosis secondary to suppurative pyeli-

 

extremely high resistance index of 0.96.

tis. The kidney is greatly enlarged to 14.2 cm (cursors)

 

 

with a hazy, irregular hypoechoic structure.

 

 

332

Fig. 9.29 Acute IgA nephritis: slightly enlarged, swollen kidney (N) with prominent medullary pyramids (arrows).

A different picture is seen with severe acute

 

septic pyelonephritis, in which one or both

 

kidneys are enlarged and generally show a de-

 

crease in parenchymal echogenicity. Often

 

there are accompanying abscesses, pyonephro-

 

sis, or merely circumscribed anechoic to hyper-

 

echoic lesions in the parenchyma, renal pelvis,

 

or renal sinus representing abscesses or in-

 

fected, purulent urine. Swelling of the renal

 

pelvic walls is also occasionally

seen

 

(Fig. 9.30). Other characteristic findings are ur-

 

othelial thickening to more than 2 mm and

 

hypoechoic foci in the parenchyma

(see

 

Fig.11.1, p. 381).

Fig. 9.30

b CDS shows inflammatory hypervascularity.

 

a Acute septic pyelonephritis: slightly enlarged kidney

 

with swollen, hypoechoic parenchyma. The sinus echo has largely disappeared. Focal abscess (arrows).

AIDSand Heroin-induced Nephropathy

As in other forms of renal enlargement, these

heightens the contrast with the unchanged,

cases show increased cortical echogenicity that

hypoechoic medullary pyramids.

Amyloidosis/Paraprotein Kidney

The sonographic changes in amyloidosis are like those seen in AIDS-related and heroin-re- lated nephropathy and acute glomerulonephritis. These conditions are not distinguishable by their sonographic features (Fig. 9.31,

Fig. 9.50).

 

Fig. 9.31

b Paraprotein kidney (lymphoplasmacytic immunocy-

 

a Amyloidosis of the kidney (AA—amyloid with general-

toma with Bence Jones proteinuria). Enlarged kidney (N)

 

ized amyloid deposits in Mediterranean fever). Intensive

shows slightly increased echogenicity relative to the liver

 

hyperechoic kidney (N). L = liver.

(L). The medullary pyramids (arrows) are markedly swol-

 

 

len and show patchy low echogenicity due to protein-

 

 

filled tubules, with the formation of hyaline casts in the

 

 

distal tubules (creatinine 3.0 mg/dL).

Pyonephrosis

 

 

If the purulent collection in the renal pelvis

largement. The affected kidney has a tumor-

ically indistinguishable from a large tumor

takes up the entire central echo complex, the

like appearance and is in fact sonomorpholog-

(Fig. 9.76; 11.3 g–i, p. 394).

pyonephrotic mass leads to overall renal en-

 

 

9

Diffuse Changes

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