Hyperechoic Medulla

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T3 Kidney

"g n Scan planes:

j^1 • Upper abdominal transverse scan (see p. 22)

.C • Lateral upper abdominal longitudinal scan (see p. 24)

n Sonographic anatomy and normal findings (Figs. 372 and 373):

• The kidneys are located in the retroperitoneum on the iliopsoas muscles. Their longitudinal axes point laterally downward at a divergent angle. They are tilted laterally, and their lower poles are directed forward.

• An imaginary line joining the bases of the medullary pyramids separates the cortical substance of the kidney from the medulla.

• The center of the renal ellipse (central echo complex, CEC) appears hyperechoic and consists of vessels, connective tissue, renal sinus fat, and the actual renal pelvis.

Fat Renal Pyramids Ultrasound
Fig. 372 Section through the kidney

n Normal values:

• Length 100-115 mm, width 50-70 mm, thickness 30-50 mm.

• Parenchyma: The parenchymal-pelvic ratio (ratio of the combined anterior and posterior parenchymal thickness to the CEC) is 1.7 up to 60 years of age and 1.1 after age 60.

n Note: Because of the position of the kidneys (see above), their size cannot be accurately determined. It tends to be underestimated, and their sonographically determined size is approximately 20 mm below the normal value. Unless the

Renal Parenchymal Graphs

longest renal dimension is accurately visualized, ultrasound measurements will be too low. n Scanning protocol:

• Patient generally supine. Left lateral decubitus occasionally used

• Right kidney: The right liver provides a good acoustic window for scanning the right kidney. The lower pole is occasionally obscured by the right colic flexure but is accessible to scanning from the posterior side.

• Left kidney: An acoustic window is not available for the left kidney. Scanning from the posterolateral side is advantageous as it avoids overlying gas in the colon and gastric fornix.

• Always scan the kidneys during inspiration and expiration to ensure that they are completely visualized (rib shadows and bowel gas are often troublesome) and move normally with respiration (i.e., are not fixed by perirenal abscesses).

• Both kidneys are systematically surveyed in longitudinal and transverse planes. n Scanning tips:

• If a kidney is not visualized, think of agenesis or nephrectomy. An ectopic kidney is often located in the lesser pelvis anterior to the iliac vessels. The possible causes of nonvisualization are listed below.

n Note: Take measurements to determine renal size. A visual estimate is often incorrect.

n Causes of large or small kidneys (see also Table 47, p. 267):

• Small kidneys: May be constitutional or may result from hypoplasia or ectopia, making the organs difficult to locate (Fig. 374).

Flanders Fig
Fig. 374a, b a Renal hypoplasia. The "absent left kidney" is probably a tiny hypoplastic kidney (cursors). b Malrotated kidney at a slightly ectopic location (cursors). The renal hilum is directed anteriorly 263
Acromegaly Pathway
a parenchymal band, b Acromegaly (cursors 138.1 mm)

• Large kidneys: May be constitutional or may result from duplex kidneys, unilateral aplasia, acromegaly, or compensatory enlargement of the remaining kidney after nephrectomy (Fig. 375).

n Causes of difficult visualization or nonvisualization:

• Ectopic kidney: Located along the path of its normal ascent, usually in the lesser pelvis near the iliac vessels; "lower abdominal mass" (see Fig. 376)

• Unilateral renal agenesis: Characterized by enlargement of the contralateral kidney

• Hypoplastic kidney: Careful inspection of the renal fossa in a close-up view should reveal a small kidney with normal-appearing parenchyma.

• Atrophic kidney: Shrunken kidney that displays abnormalities in its contours, internal echo pattern, or both

• Renal fusion anomaly: A bilateral "horseshoe kidney" initially appears as two normal kidneys, but the lower poles are found to be fused across the midline in the lesser pelvis.

Unilateral Fusion Kidney
Fig. 376a, b Empty right renal fossa, caused by a partial horseshoe kidney on the left side (K). AO = aorta, V = compressed vena cava, M = lumbar muscle, L = liver

Adrenal Glands n Scan planes:

• Upper abdominal transverse scan (right adrenal gland)

• Upper abdominal oblique scan (right adrenal gland)

• High flank scan (left adrenal gland)

• High upper abdominal transverse scan (left adrenal gland)

n Sonographic anatomy and normal findings (Figs. 377 and 378):

• The normal adrenal glands have a variety of ultrasound appearances, usually presenting a forked, Y, or triangular shape.

• The right adrenal gland is located between the upper pole of the kidney and the inferior vena cava. The left adrenal gland lies between the upper pole of the kidney and the aorta.

Normal Anatomy The Adrenal Glands

Fig. 377 Topography of the adrenal glands

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Fig. 377 Topography of the adrenal glands

Adrenal Gland Topography And Anatomy
Fig. 378a, b Normal right adrenal gland (arrows, AG) located between the kidney (K) and vena cava (VC)

"O n Scanning protocol:

§ n Note: Normal adrenal glands can be identified only by prolonged scanning with O high-resolution equipment. They are easier to image when they are enlarged

C . Right adrenal gland: High lateral upper abdominal transverse or oblique scan defining the renal upper pole and the inferior vena cava (the adrenal gland ^ should be between them), and an upper abdominal longitudinal scan in the

■g midclavicular line or anterior axillary line demonstrating the vena cava

<3 • Left adrenal gland: High flank scan through the lower pole of the spleen and the upper pole of the kidney, with the transducer angled medially toward the aorta.

C As on the right side, the gland can be identified between the aorta and renal

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upper pole in a high upper abdominal transverse scan.

n Size changes: Acute diffuse diseases are generally associated with renal enlargement due to inflammatory edematous swelling, whereas chronic diseases are marked by a decrease in renal size caused by loss of parenchyma. In chronic glo-merulonephritis and diabetic nephropathy, the kidneys do not shrink in size until the disease has progressed to the dialysis stage. n Echogenicity changes: Increased or decreased echogenicity reflects tissue changes at the histologic level (see Table 46).

Table 46 ■ Relationship between histologic change and renal echogenicity

Decreased echogenicity Increased echogenicity

Interstitial edema Leukocytic or tumor-cell infiltration

Hyaline or crystalline deposition Tubular atrophy Fibrosis or sclerosis n Diffuse renal changes with or without a change in size: see p. 267 and Table 47. n Circumscribed changes in the renal parenchyma: see p. 272 and Table 48. n Circumscribed changes in the renal pelvis or renal sinus: see p. 283 and Table 49. n Perirenal masses: see p. 292. n Adrenal glands: see p. 292.

10.2 Diffuse Renal Changes "§

Table 47 ■ Diffuse renal changes "o

Hypoechoic Hyperechoic "O

Enlarged or normal-sized kidneys ^

Acute renal failure, transient renal Acute renal failure (hyperuricemia, sepsis, p. 268) ,C insufficiency jg

Acute bacterial interstitial nephritis Diabetic nephropathy, early stage (see p. 269) (pyelonephritis, p. 268)

Renal vein thrombosis (p. 268) Acute glomerulonephritis (p. 269)

Renal myeloma, adrenal amyloidosis (p. 269), gouty nephropathy

Small or normal-sized kidneys

Hypoplastic kidney (p. 269) Chronic glomerulonephritis (p. 270)

Renal atrophy due to vascular Diabetic nephropathy (p. 270)

occlusive disease (p. 270)

Chronic pyelonephritis (p. 271) Analgesic nephropathy (p. 271)

n Acute renal failure or transient renal insufficiency (Fig. 379): Prerenal-cardio-vascular or postrenal.

• Sonographic findings:

- Parenchymal thickening with associated thinning of the CEC; renal sinus echo

- Decreased echogenicity

Fig. 379 Transient renal insufficiency in a patient with alcohol-related disease and diarrhea: Enlarged hypoechoic kidneys with swollen parenchyma and loss of corticomedullary differentiation. Length = 170 mm!

Poor Corticomedullary

n Acute bacterial interstitial nephritis = pyelonephritis (Fig. 380; emphysematous pyelonephritis, see Fig. 397, p. 278; acute suppurative pyelitis, see Fig. 412, p. 286)

• Thickened, hypoechoic, hazy parenchyma with a thinned sinus echo. A rim of fluid is often visible in the renal pelvis. Incipient abscess appears as a hypoe-choic zone.

• CDS: Perfusion defect with an increase in surrounding vascularity

Kidney Medulla Echo

Fig. 380 Acute pyelonephritis: Large, hypoechoic kidney with an obliterated sinus echo and a rim of fluid in the renal pelvis n Renal vein thrombosis (Fig. 381a, b):

• Hazy, hypoechoic renal echo pattern

• Evidence of venous thrombosis

• Tumor thrombosis is common (see Fig. 393e, p. 275)

• CDS: Veins not visualized. Absence of flow in the renal vein, reverse flow in arteries with a high RI; see Table 30, p. 193.

Fig. 381a, b Renal vein thrombosis. a Acute renal vein thrombosis in septic pyelonephritis: Enlarged kidney (K, cursors) with a hazy, hypoechoic structure and patchy-streaky hypoechoic transformation of the central echo complex. C = atypical cyst. b Spectral analysis shows an extremely high RI of 0.96

n Acute renal failure:

• With massive hyperuricemia (Fig. 280): echogenic parenchyma

• With sepsis: large, echogenic kidneys

• With diabetic nephropathy (Fig. 382a):

- Enlargement, sometimes massive

- Hyperechoic parenchyma

- Hypoechoic medullary pyramids

Medullary Nephrocalcinosis Differential

Fig. 382a-d Increased renal echogenicity. a Diabetic nephropathy: Large kidney (12.5 cm) with prominent hypoechoic medullary pyramids (arrow). b Subacute glomerulonephritis: Increased cortical echogenicity with very hypoechoic medullary pyramids (arrows). c Renal myeloma, renal insufficiency: Basically the same features as in a, with an echogenic parenchyma and hypoechoic medullary pyramids (arrows; K = kidney). d Gouty nephropathy: Increased echogenicity of the medullary pyramids reflects the precipitation of uric acid in the tubules (arrows; S = acoustic shadows). Patient presented with ubiquitous gouty tophi, hyperuri-cemia, and mild renal function impairment. Differential diagnosis: medullary nephrocalcinosis, medullary sponge kidney (tuberulosis)

n Diabetic nephropathy, early stage (Mogensen stage I-IV; Fig. 382a):

• Increase in renal volume

• Hyperechoic parenchyma

• Prominent hypoechoic medullary pyramids n Acute glomerulonephritis (Fig. 382b): Clinical signs include fever, somnolence, weakness, oliguria, and hypertension.

• Laboratory findings: elevated creatinine, erythrocyturia, proteinuria

• Sonographic fndings:

- Marked renal enlargement due to parenchymal swelling

- Consequent narrowing of the CEC

- Increased echogenicity

- Prominent hypoechoic medullary pyramids n Renal myeloma, renal amyloidosis, gouty nephropathy (Fig. 382c):

• Significant increase in echogenicity

• Prominent hypoechoic medullary pyramids n Hypoplastic kidney (see Fig. 374a, p. 263): small kidney with normal parenchymal echogenicity 269

Hypoechoic Renal Parenchyma

Fig. 383 Hypoplastic kidney (K) due to renal artery stenosis: Small kidney with parenchymal thinning. Patient presented clinically with severe hypertension. S = faint acoustic shadow n Renal atrophy due to vascular occlusive disease (Fig. 383): Small kidney, usually showing loss of parenchyma p CDS with determination of RI values (see p. 193)

n Chronic glomerulonephritis (predialysis, dialysis; Fig. 384): Kidneys are not decreased in size until the dialysis stage.

• Increased echogenicity

• Loss of corticomedullary differentiation

• Hypoechoic cystic or ill-defined medullary pyramids

Kidney Medulla Calcification Echo

Fig. 384 Chronic glomerulonephritis (IgA nephropathy requiring dialysis): Small kidney (cursors) showing increased echogenicity, loss of cortico-medullary differentiation, and a hazy internal echo pattern n Diabetic nephropathy (Fig. 385):

• Renal size is not decreased until the dialysis stage

• Parenchymal thinning

• Increased parenchymal echogenicity

• Hazy parenchyma with irregular contours

• Loss of corticomedullary differentiation

• Loss or cystic transformation of the medullary pyramids

• CDS: Loss of regional vascularity

• End stage: Calcification (optional), secondary cysts (optional), loss of parenchyma

Diabetic Nephrology Graphics

Fig. 385a, b Diabetic nephropathy at the dialysis stage. a Small kidney ¡j?

(K, 91.8 mm long) shows increased echogenicity. Arrow: Medullary pyramid with a patchy echo pattern. L = liver b CDS prior to dialysis shows very little vascularity

Fig. 385a, b Diabetic nephropathy at the dialysis stage. a Small kidney ¡j?

(K, 91.8 mm long) shows increased echogenicity. Arrow: Medullary pyramid with a patchy echo pattern. L = liver b CDS prior to dialysis shows very little vascularity n Chronic pyelonephritis (Fig. 386):

• Kidneys often remain normal in size for years and do not shrink until the advanced stage.

• Focal echogenic scarring and thinning of the parenchyma accompanied by hypoechoic areas of hypertrophy

• Possible calyceal cysts, renal pelvic abscess n Analgesic nephropathy (Fig. 387):

• Irregular, ill-defined contours, poor delineation, irregular parenchymal echogenicity

• Echogenic papillary microcalcifications

• Possible secondary retention cysts due to inflammation and scarring m

Fig. 386 Decreased renal size in pyelonephritis (83.9 mm, cursors): Foci of parenchymal thinning due to scarring, producing a wavy surface contour. C = flat cyst. Fine-needle aspiration of a suspected abscess p adrrenal epithelium

Fig. 387 Analgesic nephropathy (K). Harmonic imaging shows marked parenchymal thinning with a hazy internal echo pattern and fine calcifications projected over the papillary tip (arrows). Secondary cyst (C)

Parenchymal Echo Pattern

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Responses

  • gracie
    What is hyperechoic parenchymal echopattern with cortico medullary accentuation?
    3 years ago

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