Circumscribed Changes

Renal Cysts, Polycystic Kidney/Cystic Nephroma

Perirenal Cystic Masses

Lymph Cysts

Cystic Renal Cell Carcinoma, Intracystic Carcinoma

Papillary Necrosis, Cystic Degeneration of the Medullary Pyramids

Cavities

Abscess

Organized Hematoma

Urinoma, Seroma

Vascular Dilatations

Hydrocalices, Pyelectasis, Hydronephrosis

Cyst-like Metastases

Simple cysts (dysontogenic). Round, sharply circumscribed, anechoic masses located in or on the kidney and showing posterior acoustic enhancement can be confidently identified as primary (dysontogenic) cysts if, in addition to the usual cystic criteria, they show an absence of vascularity on color duplex scanning and there are no additional structural abnormalities in the affected kidney. Whether single or multiple, they represent tubular retention cysts that have resulted from dilatation of the Bowman capsule or proximal tubules. Consequently, they have a cyst wall that produces typical entrance and exit echoes in ultrasound but cannot always be directly visualized. Primary dysontogenic cysts display a typical location (Table 9.5; 9.2a–d).

Multiple cysts (dysontogenic). Kidneys that contain multiple cysts are usually of normal size. In contrast to a polycystic kidney, the renal cortex, medullary pyramids, and renal sinus are clearly defined. The multilocular cystic nephroma is to be considered as a special feature in earlyinfancy(age2 months–2 years).Itismostly unilateral and benign. It consists of irregular smallcystswithseptaeand showsno vascularity in CDS ( 9.2e, Fig. 9.72c,d, Fig. 9.9).9

Polycystic kidney disease (autosomal dominant polycystic kidney disease, ADPKD). This disease involves a polycystic malformation of the distal renal tubules, tubular epithelium, or tubular walls leading to a predominantly bilateral polycystic transformation of the kidneys. In ultrasound the kidneys are considerably enlarged and contain numerous cysts that completely alter the contours of the renal capsule and cause poor delineation of the renal borders. There is variable rarefaction of the parenchyma due to a combination of cyst compression, blooming effects, and interstitial fibrosis. Polycystic kidneys are commonly associated with cysts in the liver and other organs, and

ized septae are probably malignant ( 9.2a, Fig. 9.55). Lesions having this appearance require surveillance and possible surgery. The differential diagnosis should also include a hydatid cyst and, in young boys, multilocular cystic nephroma (benign cystic nephroma), which demonstrate in ultrasonography a complex renal mass with numerous anechoic cysts separated by echogenic septae.

Retention cysts due to scarring. Secondary retention cysts develop in one-third to one-half of all patients with chronic interstitial nephritis requiring dialysis. These cysts result from scarring of the renal tubules. Many of the cysts are misshapen and rather small, and most are related to the cortex ( 9.2 g, Fig. 9.37).

Hydatid cyst. Both the dog tapeworm (Echinococcus granulosus), which forms a primary cyst containing internal daughter cysts, and the fox tapeworm (Echinococcus multilocularis), in

Lymph Cysts

Parapelvic (peripelvic) lymph cysts. Parapelvic cysts generally represent lymph cysts, which have an epithelial lining. Projecting into the renal sinus, they present as flattened, usually elliptical cystic lesions. Generally these cysts are multiple.

When they are bilateral and show a fingerlike arrangement extending toward the renal hilum, they are classified as multiple parapelvic cysts or benign cystic lymphangioma. Between the elliptical, anechoic lesions tapering toward the hilum are hyperechoic, septum-like parti-

tions formed by the compressed sinus tissue and pyelocaliceal system ( 9.3a–h).10 Differentiation is required from renal pelvic dilatation due to a lower urinary tract obstruction, but the absence of ureteropelvic junction dilatation serves to exclude that condition. Occasionally there is no alternative to excretory urography for establishing a diagnosis. In the case of lymph cysts, the urogram will show sharply circumscribed impressions on the pyelocaliceal system ( 9.3 d).

Intrarenal or perirenal lymphoceles. Intrarenal or perirenal cystic lesions may also be lymphoceles, depending on the cause of the disease. They occur after surgery, in rejection episodes after renal transplantation, and also in chronic progressive renal diseases such as renal failure requiring dialysis. When they present as a perirenal mass, lymphoceles have an anechoic, cystic appearance. They may also contain septations ( 9.3e,f).

a and b Multiple parapelvic cysts on both sides: “benign cystic lymphangioma.”

a Right kidney (N): elliptical cysts radiating toward the hilum in a fan-shaped pattern. L = liver.

e Perirenal lymph cysts (arrows): small cysts, some showing a string-of-beads arrangement (varied at follow-ups). The patient presented clinically with severe right heart failure and erythrocytosis. N = kidney.

b Left kidney: a less obvious alignment toward the hilum.

f Postoperative lymphocele (C) following stone surgery with postoperative bleeding; very conspicuous medullary pyramids (arrows). Left nephrectomy. N = kidney.

c Parapelvic cysts, CDS: lack of interior vascularization, therefore no signs of tumor.10

g Parapelvine lymph cyst (Z) of the right kidney (N).

d Excretory urogram: multiple parapelvic cysts producing curved and smoothly margined impressions of the pyelocalyceal system.

h Parapelvic cyst (z) protruding from the right kidney (N; “extrapelvic cyst”).

Renal cell carcinoma. Cystic RCC is a rare form of renal carcinoma which can be inferred when more than 50% of the lesion is cystic (clear-cell carcinoma) (see Table 9.6). It shows a predominantly anechoic, cystic structure with more or less pronounced solid components. Foci of necrobiotic tumor liquefaction are common, especially in tumors of long duration.

CEUS allows the characterization of renal cystic lesions as benign or malignant at least as accurately as contrast-enhanced CT. It is more sensitive than CT in detecting enhancement of the cystic wall, septa, and solid components11 (Fig. 9.57, Fig. 9.78).

Intracystic carcinoma. Another type of cystic renal tumor is renal carcinoma that arises inside a cyst. Because intracystic carcinoma is extremely rare, it does not justify regular sonographic or CT follow-ups in patients with known cysts (Fig. 9.58).

Papillary necrosis and caliceal cysts most commonly develop in a setting of purulent or nonpurulent interstitial chronic nephritis. They present as small cystic lesions projecting toward the calices.

In advanced diabetic nephropathy, it is not uncommon to find cystic degeneration of the medullary pyramids, which exhibit classic cystic features. Often they are located next to very hypoechoic medullary pyramids that may eventually undergo complete cystic transformation. The medullary pyramids disappear in the dialysis stage, often to be replaced by multiple small, secondary cysts that were once pyramids (Fig. 9.59, 9.1 d).

Fig. 9.59 Cystic mass in the area of a medullary pyramid. Color Doppler shows no vascularity. Diabetes mellitus. Probably the cystic transformation of a medullary pyramid. N = kidney.

Cavities

Hematogenous spread of renal tuberculosis gives rise to cortical tubercles that descend into the tubules, papillae, and associated calices where they form ulcer cavities.

These cavities have a cystic appearance in ultrasound. While a purely cavernous-cystic process cannot be recognized sonographically as a tuberculous cavity, the late stage is additionally marked by the formation of scars and calcifications. This combination allows for a presumptive sonographic diagnosis (Figs. 9.60, 9.93, 9.94).

Fig. 9.60 Old cavernous (?) medullary pyramids that have undergone secondary cystic transformation (arrows). Ultrasound shows irregular, echo-free masses with a hyperechoic rim projected at the site of the medullary pyramids (see also Fig. 9.93). Patient had a known history of spinal tuberculosis.

Whereas fresh hematomas appear as echogenic, heterogeneous masses in ultrasound (see below), older hematomas appear increasingly hypoechoic to anechoic. Besides circumscribed parenchymal destruction, hematomas usually produce a subcapsular mass caused by the subcapsular extravasation of blood. This mass presents sonographically as perirenal fluid (Fig. 9.62). Color Doppler shows decreased perfusion in areas of renal contusion, while it shows an absence of perfusion in a hematoma.

The history and clinical presentation give additional information on the cause of these cystic lesions. Equivocal cases should be evaluated by CT, which is superior to ultrasound for this type of examination.

Fig. 9.62 Perirenal, elliptical echo-free mass (arrows): urinoma, hematoma following renal trauma. N = kidney.

Certain sectional planes through distended calices in obstructive pyelocaliceal dilatation can create the impression of multiple renal cysts. In this case an oblique longitudinal scan, preferably from the posterior (ureter) side, will demonstrate the cystic enlargement of the calices.

Hydrocalices and hydronephrosis are seen in association with ureteral obstructions. Hydrocalices may also be congenital or secondary to caliceal stones or nephrocalcinosis (Fig. 9.64,

Fig. 9.65; see also Fig.11.10).

Fig. 9.65 Cyst combined with obstructive caliceal and pelvic ectasia. N = kidney.

a Transverse ultrasound scan through the left kidney: cyst (Z), pyelectasis (P).

b Excretory urogram: curved medial and lateral indentations in the upper portions of the calices. Renal pelvic indentation and congestion due to subpelvic obstruction (by a tumor?).

Fig. 9.64 Obstructive caliectasis. N = kidney.

a Scan through the calices, which resemble cysts (Z) in this plane.