Fat-like adenoma. Adenoma (classification in Table 9.7) is a benign, well-circumscribed neoplasm of 1 cm or smaller. It is usually solitary. Papillary adenoma is the most common neoplasm of the epthelium of the renal tubules. It is found in 10% to 40% of specimens.13

Sonographically, adenoma appears hyperechoic. It has smooth margins. No reliable sonographic criteria are available ( 9.4 g,h).

Oncocytoma. Oncocytoma is also a slowgrowing tumor that is always benign. Its echogenicity varies from hyperto hypoechoic, but the presence of cystic parts excludes the diagnosis of an oncocytoma. In CEUS, an oncocytoma displays a slower uptake of contrast medium and an overall decidedly diminished vascularity (Fig. 9.75).

Fig. 9.75 Renal oncocytoma (CT, operation).

a Sharply circumscribed, very hypoechoic mass. Based on ultrasound morphology, the fine echogenic wall (arrows) is suggestive of a hemorrhagic cyst. N = kidney.

b Color Doppler shows subtle but constant vascularity, ruling out a cyst or abscess in favor of a solid mass.

Complex Structure

Abscess, Pyonephrosis

Xanthomatous Pyelonephritis

Hematoma, Intracystic Hemorrhage

Renal Cell Carcinoma, Cystic Renal Carcinoma, Malignant Lymphoma

Renal Trauma

In trauma, an irregular (hyperto anechoic) circumscribed transformation of the regular structure and an additional perirenal anechoic mass can be seen.

The most important information is the extent of viable renal tissue. CEUS adds to the color Doppler assessment with clear delineation of hematomas, and additional evidence for a persistent bleed (Fig. 9.70, Fig. 9.80).

Fig. 9.80 Extensive traumatic haematoma of the right kidney. Heterogeneous mass (arrows); band-shaped nonreflective marginal area dorsally (perirenal fluid collection). The extent of the destruction may be estimated in CEUS as the best diagnostic procedure. N = kidney.20

Hyperechoic Structure

Renal Abscess, Carbuncles

Hemorrhagic Cyst

Renal Cell Carcinoma

Angiomyolipoma

Scars

Angiomyolipomas are a common type of benign nonepithelial tumor. They contain thickwalled vessels, smooth muscle, and fatty tissue in varying proportions. In ultrasound they appear round or oval, smoothly defined, and mostly homogeneous and more hyperechoic than the renal sinus; but slightly less echogenic when containing only a small amount of fat or when hemorrhage is present. In harmonic imaging an incomplete shadowing sometimes presents (Fig. 9.84, Fig. 9.85). No intratumorous vessels are detectable in CDS except an entering vessel. In CEUS, a rapid enhancement and wash-out after 19 minutes is detectable.

The sensitivity and specificity of ultrasonography for typical angiomyolipomas can be as high as 85%, but the positive predictive value is

lower because of the small hyperechoic RCC. As result, some examinations require CT (Fig. 9.85b).

The tumor can be confidently diagnosed by the fat attenuation observed on CT, but this line of investigation is almost superfluous when typical ultrasound findings (also in color duplex and CEUS) are present. The accuracy of CT is compromised by an absence of fat in some tumors (< 10%). (Fig. 9.84, Fig. 9.85).

Multiple, bilateral angiomyolipomas occur in the setting of tuberous sclerosis (von Hip- pel–Lindau syndrome). This disease is frequently associated with clear-cell renal carcinomas, however, and so additional tests should be performed (Fig. 9.85a, Table 9.8).

Kidneys

Anomalies, Malformations Diffuse Changes Circumscribed Changes

Anechoic Structure

Hypoechoic or Isoechoic Structure

Complex Structure Hyperechoic Structure Echogenic Structure

Papillary Calcification

Interlobar and Arcuate Arteries

Bacterial Gas Bubbles

Parenchymal Calcification

Nephrocalcinosis, Medullary Sponge Kidney

Renal Tuberculosis, Putty Kidney

Pyelocaliceal Stone, Staghorn Calculus

Calcifications at the tips of the renal papillae are characteristic findings in analgesic nephropathy and diabetes mellitus. They appear only as echogenic flecks on ultrasound survey scans, where they often go undetected. They are easily detected and identified in strongly magnified views (Fig. 9.86).

Interlobar andArcuate Arteries

Fig. 9.86 Medullary (papillary) (MP) calcification (arrows) with an acoustic shadow. Clinical presentation: neglected type 1 diabetes.

Small, vesicular, hood-like echogenic masses may be observed in the setting of emphysematous (bacterial gas-forming) pyelonephritis; the shadowed region usually obscures the abscess itself. These findings indicate an urgent need for treatment (immediate broad-spec- trum antibiotics or nephrectomy) due to existing or impending bacterial sepsis (Fig. 9.67,

Fig. 9.90).

Fig. 9.90 Hood-like bacterial gas collection (arrows) with associated reverberations. An actual abscess cannot be identified. Sepsis, emergency surgery, nephrectomy.

N = kidney.

Pyelocaliceal stones or staghorn calculi are easily diagnosed on ultrasound, which demonstrates the bright stone-surface echoes and associated shadows that are typical of stones and calcifications. Occasionally the stones are so small that their presence is revealed only by an acoustic shadow. This introduces a degree of uncertainty, as the shadowing focus may represent a vascular calcification.

Staghorn calculi in the renal pelvis may exhibit various shapes, depending on the orientation of the scan plane. If the scan is directed

through the greatest width of the renal pelvis, it will display a broad, hard linear echo with an equally broad acoustic shadow. But if the plane cuts portions of the stone in the calices, multiple echoes and acoustic shadows will be seen (Fig. 9.96, Fig. 9.97).

Some small stones may be missed within the bright reflections of the sinus echo complex. A helpful guide in these cases is the “twinkling artifact” seen in color duplex scanning. It consists of red and blue color artifacts appearing within the shadow cast by calcified

Tips, tricks, and pitfalls

Since most renal tumors found today are diagnosed in localities where ultrasound is commonly used, they are most often at a local operable stage. Therefore:

●The kidneys should be always investigated in case of abdominal scanning; what is the renal structure and the vascular architecture? Examination with magnification is called for.

●Renal tumors, renal calculi, infarction scars, cysts may be hidden: careful lamelliform examination of all kidney regions in two sectional planes including lateral decubitus position is indicated.

●Normal kidneys are movable.

–Pay attention to dynamic criteria (movement by respiration, normal movement by the iliopsoas muscles regarding also liver and spleen).

–Examine the patient in a standing position when nephroptosis is suspected.

●Parenchymal thickness correlates with age:

–In youth, the renal parenchyma is robust.

–In older people it is reduced, but to no less than 1.2 cm; values below this level indicate pathological changes through arteriosclerosis, scars, or renal artery stenosis (Fig. 9.98).

●Fusional, positional, and form variants (e. g., horseshoe or pelvic kidneys, lateral humpback, nodular formation) are not uncommon.

–In such findings a second ultrasound exam including CDS (in the case of regular vascularity) should be performed; otherwise, CEUS should be performed.

●Transplanted kidneys are denerved.

–A slight pyelectasis is a nearly normal finding. Pyelectasis also results from an ampullary renal pelvis, from fluid diuresis, and pathologically from highly inflamed pyelitis.

●Renal calculi are frequently not enveloped by fluid and therefore difficult to differentiate:

Look closely: does CDS show a “twinkling artifact”)?

Fig. 9.98 Small kidney with diminished parenchyma. Accidental finding. Clinically, general arteriosclerosis.

References

[1]Banholzer P, Haslbeck M, Mehnert H. Sonographische Größenveränderungen der Nieren bei Typ-I-Diabetes als Früherkennungsmethode der diabetischen Nephropathie. Ultraschall Med 1988;9:255–259

[2]Mogensen CE. Diabetes mellitus and the kidney. Kidney Int 1982;21(5):673–675

[3]Jinzaki M, Ohkuma K, Tanimoto A, et al. Small solid renal lesions: usefulness of power Doppler US. Radiology 1998;209(2):543–550

[4]Bönhof JA, Meairs SP, Wetzler H. Duplexund Farbdoppler-sonographische Kritrien von Nierenarterien-Stenosen. Ultraschall Klin Prax 1990;5:187

[5]Klauser A, Pallwein L, Frauscher F, Helweg G, Peschel R, Debus J. Die Wertigkeit des farbdopplersonographischen „Twinkling-Arte- fakts“ in der Diagnostik der Nephrolithiasis. 24th Dreiländertreffen der ÖGUM, DEGUM, SGUM. Vienna 2000

[6]Farrelly C, Delaney H, McDermott R, Malone D. Do all non-calcified echogenic renal le-

sions found on ultrasound need further evaluation with CT? Abdom Imaging 2008;33(1):44–47

[7]Mostbeck G, Derfler K, Walter R, Herold Ch, Mallek R, Tscholakoff D. Sonographie bei terminaler Niereninsuffizienz—ätiologische Rückschlüsse? Ultraschall Med 1988;9(6): 250–254

[8]Hricak H, Cruz C, Romanski R, et al. Renal parenchymal disease: sonographic-histologic correlation. Radiology 1982;144(1):141–147

[9]Deeg KH, Gerdemann C, Weingärtner K, Seitz

G. Sonographic diagnosis of an unusual case of multilocular cystic nephroma mimicking polycystic kidney disease. Ultraschall Med 2008;29(Suppl 5):264–267

[10]Schmidt G, Ed. Ultrasound Thieme Clinical Companions. New York: Thieme, 2007

[11]Piscaglia F, Nolsøe C, Dietrich CF, et al. The EFSUMB Guidelines and Recommendations on the Clinical Practice of Contrast Enhanced Ultrasound (CEUS): update 2011 on non-hep- atic applications. Ultraschall Med 2012; 33(1):33–59

[12]Takebayashi S, Aida N, Matsui K. Arteriovenous malformations of the kidneys: diagnosis and follow-up with color Doppler sonography in six patients. AJR Am J Roentgenol 1991;157(5):991–995

[13]Lopez-Beltran A, Scarpelli M, Montironi R, Kirkali Z. 2004 WHO classification of the renal tumors of the adults. Eur Urol 2006; 49(5):798–805

[14]Mostofi FK, Davis CJ. Histological Typing of Kidney Tumours. 2nd ed. Berlin: Springer, 1998

[15]Ascenti G, Zimbaro G, Mazziotti S, Gaeta M, Settineri N, Scribano E. Usefulness of power Doppler and contrast-enhanced sonography in the differentiation of hyperechoic renal masses. Abdom Imaging 2001;26(6): 654–660

[16]Hofmann R, Schütz R, Leyh H, Braun J. Sonographischer Nachweis von Nierenvenenund Vena-cava-Thrombosen beim Adenokarzinom der Niere. Ultraschall Med 1985;6: 312–315

[17]Snyder ME, Bach A, Kattan MW, Raj GV, Reuter VE, Russo P. Incidence of benign lesions for clinically localized renal masses smaller than 7 cm in radiological diameter: influence of sex. J Urol 2006;176(6 Pt 1):2391–2395, discussion 2395–2396

[18]Remzi M, Memarsadeghi M. Der kleine, zufällig entdeckte Nierentumour. Aggressionspotential und Abklärung [Small incidental renal tumors. Evaluation and biological parameters]. Urologe 2007;46:478–484

[19]Lau DM, Siegel MJ. Pediatric abdominal masses. In: Bluth EI, Arger PH, Benson CB, Ralls PW, Siegel MJ, eds. Ultrasound. 1. ed. New York: Thieme, 2000: 425

[20]Schmidt G, Görg C. Kursbuch Ultraschall . 5. ed Stuttgart: Thieme, 2008

[21]Smith AD, Remer EM, Cox KL, et al. Bosniak category IIF and III cystic renal lesions: outcomes and associations. Radiology 2012; 262(1):152–160

[22]Schmidt G. Differential Diagnosis in Ultrasound Imaging. Stuttgart: Thieme, 2006