Circumscribed Changes in the Renal Parenchyma

Table 48 • Circumscribed changes in the renal parenchyma

Anechoic

Hypoechoic

Isoechoic

Echogenic, hyperechoic

Simple cysts (p. 272)

Metastases (p. 276)

Bulge, lobulation

Renal cell carcinoma

(see p. 278)

(p. 279)

Polycystic kidneys

Malignant

Parenchymal

Angiomyolipoma

(p. 273)

lymphoma

bands (p. 278)

(p. 279)

(see p. 276)

Secondary cysts (p. 274)

Renal adenoma

Hematoma

Scars (p. 280)

(see p. 277)

(p. 279)

Renal infarction (p. 281)

Atypical or complicated

Abscess, carbuncle

Renal cell carci-

Medullary nephrocalci-

cysts (p. 274)

(p. 277)

noma (p. 279)

nosis (p. 281)

Obstructive pyelocaly-

Oncocytoma

Cortical nephrocalci-

ceal ectasia (p. 275)

(p. 278)

nosis (see p. 282)

Cystic renal cell

Vascular calcification,

carcinoma (p. 276)

parenchymal calcifica-

tion (p. 283)

Benign cystic lymphangioma (p. 275) Lymphocele (p. 275) Tuberculosis (p. 275) Intracystic hemorrhage (p. 275)

Hematoma (p. 275)

n Simple cysts (Bosniak type I, Fig. 388): dysontogenetic cysts = tubular retention cysts

• Classification by location:

- Subcapsular (perirenal) cysts

- Cortical cysts

- Parapelvic cysts of the renal sinus (generally lymphatic cysts, but occasionally tubular retention cysts projecting into the central echo complex)

• Classification by number:

- Solitary

- Multiple

• Sonographic criteria:

- Anechoic

- Smooth margins with a thin wall and lateral edge shadowing

- Round shape; parapelvic cysts may also have a flattened or oval shape 272 - Distal acoustic enhancement a

Sonograpghic Images Parapelvic Cysts

"O

Fig. 388a-d Simple renal cysts (C). a Perirenal (subcapsular, "extrarenal") cyst. b Cortical cyst. Arrow: orthograde projection of the renal capsule. c Parapelvic cyst. d CDS of parapelvic cysts shows absence of internal vascularity (this excludes a tumor). K = kidney

- A fine, echogenic capsule can often be identified in an orthograde projection (entry and exit echoes). n Polycystic kidneys (adult type polycystic kidney disease, see Fig. 389):

• Clinical features: autosomal dominant mode of inheritance. Renal swelling, hypertension, and slowly progressive renal failure starting at about 40 years of age. Often accompanied by a cystic liver. The pediatric form becomes symptomatic at an early age.

Complex Renal Cysts Images

Fig. 389a, b Differentiation of polycystic kidney from multiple renal cysts. a Multiple renal cysts: The kidney is normal-sized with definable parenchyma. Arrow: parapelvic cysts. b Polycystic kidney: The kidney is enlarged and poorly defined with little evidence of residual parenchyma. A central echo complex is not visualized

Fig. 389a, b Differentiation of polycystic kidney from multiple renal cysts. a Multiple renal cysts: The kidney is normal-sized with definable parenchyma. Arrow: parapelvic cysts. b Polycystic kidney: The kidney is enlarged and poorly defined with little evidence of residual parenchyma. A central echo complex is not visualized

"O • Sonographic criteria:

§ - Small or large cystic masses, or a combination of both, permeating both kid-

O neys

"¡3 - Significant renal enlargement jj - Little identifiable parenchyma

- Absence of the CEC and loss of corticomedullary differentiation ^ n Secondary cysts (Fig. 390):

nd • Occurrence: secondary to an underlying renal disease such as nephritis, renal a abscess, parenchymal scarring, diabetic nephropathy, or renal tuberculosis ey • Sonographic criteria: C - Usually have a noncircular shape

- Often located near scar tissue

- Cystic degeneration of medullary pyramids

- Evidence of inflammatory renal disease

Pictures Analgesic Nephropathy
Fig. 390a, b Secondary cysts. a Secondary cysts (C) in analgesic nephropathy (decreased renal size, cursors). b Cavernous cysts (C) in renal tuberculosis with calcifications (arrows) and acoustic shadows (S). K = kidney

n Atypical or complicated cysts (Bosniak types II and III): Figs. 391, 392, 393c.

• Atypical: extrarenal extension

• Septation, calcification, intracystic hemorrhage; echinococcal cyst: single or septated cyst, hyperechoic wall

• Vascularized septa: cystic renal carcinoma (Bosniak type IV)

Anechoic Cyst Kidney
absence of vascularity and a well-defined echogenic wall. b Atypical cysts (C) with septa-like internal structures and bulging contours (arrow) p requires 274 cytohistologic evaluation!
Atypical Hemorrhage
Fig. 392a, b Complicated cyst with internal hemorrhage. a Anechoic clotted blood (arrows in b) within the cyst (C), which is still identifiable. SP = spleen, K = kidney. b CDS: no detectable vascularity. This excludes a cystic tumor
Echogenic Flecks Within Renal Parenchyma
Fig. 393a, b Cystic renal cell carcinoma. a Renal cell carcinoma (T) with cystic regressive changes and areas of intralesional hemorrhage (H). K = kidney b Cystic renal cell carcinoma (T, H). CDS: predominantly cystic mass. Only the peripheral vascular rim marks the outlines of a solid tumor

n Obstructive pyelocalyceal ectasia (see Fig. 408, p. 285):

• Multiple oval or triangular anechoic masses

• Dilatation of the renal pelvis

• Dilatation of the ureteropelvic junction n Multiple parapelvic cysts ("benign cystic lymphangioma"): see Fig. 407, p. 284:

• Hypoechoic

• Complex internal echo pattern. n Lymphocele:

• Atypical round or angular anechoic mass

• Frequently, past history of urologic surgery n Tuberculosis (see Fig. 390b; Fig. 405c, p. 282):

• Area of parenchymal cavitation

• Cystic renal pelvic mass (dilated calyces, clean cavities)

• Late changes include atrophy or calcification n Intracystic hemorrhage (see Fig. 392):

• Cystic shape can still be recognized

• Echogenic or complex internal echo pattern

• Possible moving echoes

n Cystic renal cell carcinoma (cystic RCC, Fig. 393):

• Clinical features: cystic component > 50% (note: never oncocytoma)

• Histology: carcinoma that has undergone small-cell or papillary pseudocystic transformation

• Differential diagnosis: intratumoral hemorrhage, tumor liquefaction, cyst-associated carcinoma, and intracystic hemorrhage

^ • Sonographic criteria:

"O - Round or oval masses, anechoic or hypoechoic (intratumoral hemorrhage or

O necrosis)

- Tumor can still be recognized in many cases C - Tumor occurrence in cysts is controversial.

• Heterogeneous hyper- or hypoechoic mass with indistinct margins

• Anechoic or complex perirenal mass

• Hypoechoic parenchymal area with a normal organ contour, suggesting a contusion (= hypoperfused area)

• CDS: absence of color flow signals

Fig. 394a, b Traumatic renal hematoma. a Mixed hypoechoic-hyperechoic echo pattern with a bulging contour (C) and a thin fluid rim surrounding the kidney (K). b Parenchymal contusion (hypoechoic to anechoic area of intraparenchymal hemorrhage, arrows). K = kidney. Patient had a history of ladder-related and riding injuries n Metastases (see Fig. 416, p. 287): The primary tumor may be in the breast, bronchi, stomach, bowel, or kidney.

• Sonographic appearance: Round or oval mass of low echogenicity n Malignant lymphoma (Fig. 395):

• Round or oval hypoechoic mass (low-grade lymphoma)

• Large mass with a complex pattern of low-level internal echoes (high-grade lymphoma)

Fig. 395 High-grade non-Hodgkin lymphoma (T) of the kidney: extensive hypoechoic to complex mass with tumor nodules, also a branched anechoic pattern signifying pyelectasis (P)

n Renal adenoma (Fig. 396):

• Round, hypoechoic mass with smooth margins

• Complex internal echo pattern due to regressive changes

• Occasionally hyperechoic

• CDS: internal vascularity

Echogenic Hemorrhagic Cyst
Fig. 396a, b Renal adenoma. a Intensely hypoechoic mass with smooth margins. The fine echogenic wall (arrows) closely resembles a hemorrhagic cyst. b CDS: subtle but constant vascularity excludes a cyst or abscess in favor of a solid mass

n Abscess (due to suppurative pyelonephritis); carbuncle (due to hematogenous spread of staphylococci):

• Nonhomogeneous hypoechoic mass

• Possible gas bubbles (empyematous pyelonephritis, Fig. 397)

Pyelectasis Image

Fig. 397a, b Suppurative, empyematous pyelonephritis. a Extensive gas bubbles (arrows). The kidney (K) is partially obscured by reverberations (R). b Scan 2 weeks later shows a demarcated abscess (arrows), still accompanied by gas bubbles (young, poorly managed diabetic patient; changes resolved in response to intensive conservative therapy). L = liver

Fig. 397a, b Suppurative, empyematous pyelonephritis. a Extensive gas bubbles (arrows). The kidney (K) is partially obscured by reverberations (R). b Scan 2 weeks later shows a demarcated abscess (arrows), still accompanied by gas bubbles (young, poorly managed diabetic patient; changes resolved in response to intensive conservative therapy). L = liver n Oncocytoma (adenoma): no reliable sonographic criteria

• Usually hypoechoic

• Smooth margins

• CDS: internal vascularity n Lateral bulge in the renal contour, fetal lobulation (Fig. 398):

• Bulge in the lateral renal contour not associated with thinning of the parenchyma n Parenchymal bands (parenchymatous extensions or hypertrophic renal columns):

• Tissue band passing from parenchyma to parenchyma through the central echo complex, often multiple

• Tumor-like parenchymal thickening (often creates a hypoechoic appearance)

• Signs of duplex kidney are common (surface notching, long narrow or enlarged kidney, duplicated renal pelvis)

Fig. 398a, b Isoechoic bulges in the renal contour (arrows). a Lateral bulge, b Fetal lobulation. Note the concomitant thickening of the parenchymal border 278 in the direction of the renal sinus. K = kidney

Renal Fetal Lobulation

Fig. 399a-d Bulges in the renal contour. a In a duplex kidney. b Associated with renal cell carcinoma (T). The tumor appears as a largely isoechoic mass that creates a bulge in the normal parenchymal outline. c CDS: slight peripheral vascularity and a tumor-feeding vessel associated with an echogenic tumor (T) of the upper renal pole. d Advanced neoplasm, marked by a tumor thrombus (TH) in the renal vein and vena cava with minimal lateral residual flow in the vena cava (arrow). K = kidney, CY = renal cyst n Hematoma (see Fig. 394a, p. 276): variable internal echo pattern ranging from hyperechoic (very fresh) to hypoechoic (clotted blood) n Renal cell carcinoma (adenocarcinoma, hypernephroid carcinoma): Fig. 399a-d

• Isoechoic, hypoechoic, or echogenic (small tumors)

• Bulge in the renal contour

• Occasional cystic liquefaction or calcification (20%)

• Frequent invasion of the renal vein or vena cava

• CDS: internal or peripheral vascularity n Renal cell carcinoma (RCC; Fig. 399c):

• Approximately 30% of hyperechoic tumors are RCCs

• Echogenic tumors are usually small

• CDS: internal or peripheral vascularity n Angiomyolipoma (Fig. 400): benign mesenchymal tumor composed of fat, muscle, and atypical vessels with thickened walls

• Round mass with smooth margins

• Intensely hyperechoic ("white tumor")

• Little or no bulge in the renal contour

• Size: 1 cm to 3-5 cm. Rapid enlargement suggests liposarcoma

"O

Fig. 400a, b Angiomyolipoma: echogenic tumor with smooth margins (arrow) causing an almost imperceptible bulge in the renal contour. a B-mode image. C = small anechoic cyst. b CDS: short segment of a peripheral vessel but no detectable internal vascularity n Note: Tumors < 3 cm require differentiation from renal cell carcinoma. • CDS: little if any vascularity; no more than one intratumoral vessel n Scars (pyelonephritic, embolic, atherosclerotic, inflammatory; Figs. 401 and 402): often detected incidentally. The etiology of many renal scars cannot be determined.

Renal Parenchyma

Fig. 401a-d Scar tissue in the renal parenchyma. a Pyelonephritic scars (arrows) with cystic calyceal ectasia (C). b Plaque-like scar (arrows) in the kidney (K) resulting from vascular embolism. The patient also presented clinically with cerebral infarction (both are often embolic and secondary to mitral stenosis, as in this case). c Atherosclerotic scar following a long history of hypertension.

280 d Parenchymal scar (arrow) with calcification and a distal acoustic shadow (S)

Fig. 402 Atherosclerotic surface indentations in the kidney, with areas of parenchymal thinning and rarefaction

• Pyelonephritic: irregular echogenic surface indentations, possible calcifications. The presence of calyceal cysts confirms the presumptive diagnosis.

• Embolic: frequently triangular in shape. Other lesions may appear as plaquelike indentations or an area of parenchymal thinning.

• Atherosclerotic: wavy surface with foci of parenchymal thinning between the "bulges" (normal tissue)

• Mild form: echogenic periphery of the medullary pyramids n Renal infarction (Fig. 403):

• Acute: wedge-shaped area of increased echogenicity

• CDS: avascular segment

Fig. 403a-c Fresh renal infarction. a Scan shows increased echogenicity at the upper pole of the right kidney. b Magnified view. c CDS: the wedge-shaped avas-cular area (arrows) confirms the infarction n Medullary nephrocalcinosis (Fig. 404): may be caused by hypercalcemia ortubu-lar acidosis (i.e., an excess of calcium)

• Medullary sponge kidney: congenital malformation with patchy calcifications and cystic ectasia of the collecting ducts

- Radiograph: bouquet or rosette pattern

• Sonographic criteria:

- Calcification of renal parenchyma and medullary pyramids, possible kidney stones

- Frequent secondary calcification

- Conspicuous echogenic areas in place of the medullary pyramids

- Possible pyelocalyceal ectasia and congestion (obstructing stone)

Appendicitis Pyelocalyceal Medullary

Fig. 404a, b Medullary nephrocalcinosis. a Cause is tubular acidosis: echogenic calcifying medullary pyramids (arrows) with obstructive pyelocalyceal ectasia (E) of the kidney (K) due to recurrent kidney stones. b Pronounced medullary nephrocalcinosis: small atrophic kidney with a band of residual parenchyma and hypere-choic areas, some with acoustic shadows (S) projected over the medullary pyramids (arrows)

n Cortical nephrocalcinosis (Fig. 405): parenchymal calcifications due to degenerative changes:

• Small flecks of calcification: e.g., vascular calcification in the setting of malignant hypertension or pseudoxanthoma elasticum

• Disseminated renal calcification: e.g., in hyperparathyroidism, tuberculosis, or renal atrophy requiring dialysis

Tubular Calcifications Dialysis

Fig. 405a-c Cortical nephrocalcinosis. a Fine flecks of calcification (vessels) in pseudoxanthoma elasticum ("starry sky"). b End stage of cortical nephrocalcinosis: flocculent calcifications (arrows), no staghorn calculus. The patient presented clinically with renal atrophy and type II diabetes mellitus requiring dialysis. F = fat capsule, K = kidney, S = shadow. c "Putty kidney" or "mortar kidney," representing the end stage of renal tuberculosis: diffuse calcifications and acoustic shadows (S) (K; cursors). L = liver

Fig. 405a-c Cortical nephrocalcinosis. a Fine flecks of calcification (vessels) in pseudoxanthoma elasticum ("starry sky"). b End stage of cortical nephrocalcinosis: flocculent calcifications (arrows), no staghorn calculus. The patient presented clinically with renal atrophy and type II diabetes mellitus requiring dialysis. F = fat capsule, K = kidney, S = shadow. c "Putty kidney" or "mortar kidney," representing the end stage of renal tuberculosis: diffuse calcifications and acoustic shadows (S) (K; cursors). L = liver

Calcified Arcuate Arteries

n Vascular calcification (interlobar or arcuate arteries):

• Echogenic tramlines

• Absence of internal echoes n Parenchymal calcification (Fig. 406; Fig. 390b, p. 274; Fig. 401d, p. 280): common; many cases have an indeterminate cause (e.g., calcified cyst or hematoma, postinflammatory, tuberculosis)

Tram Lines Kidney

"O

Fig. 406a, b Parenchymal calcification. a Hyperechoic mass in the renal parenchyma (arrow), suspicious for angiomyolipoma. b CDS with a high PRF: "twinkling" artifact indicates calcifications or kidney stones. K = kidney

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