Renal Masses

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Renal Masses

If there seems to be urinary obstruction indicated by dilatation of the renal pelvis and calices, try to find the level of the obstruction. The thickness of the renal parenchyma indicates the duration of the obstruction, a thin parenchyma giving the clue that it may have been present for a long time.

If there is marked atrophy of the kidney or focal attenuation of the renal parenchyma (a scar), investigation of the renal arteries is required.

Swelling of the renal parenchyma can be secondary to inflammation, diffuse infiltration with tumor cells, or vascular congestion, e.g., in lymphoma or renal vein thrombosis.

| Normal Renal Ultrasound (US) Scan_

Is the lesion cystic, solid, and/or fatty? Is the lesion solitary and/or unilateral? Is renal mobility on the psoas muscle restricted? Is there normal blood flow in the renal vein? Does the mass enhance following contrast injection in CT?

Is there para-aortic lymph node enlargement?

The Villain in the Kidney

Johnny Drip (54) has been generally unwell and so his local doctor is going through a comprehensive checkup with him. An abnormal finding on US made our colleague refer Mr. Drip for further investigation. Paul has a quick look at the renal US before establishing intravenous access (Fig. 10.2a). He later carefully examines the three-phase contrast-enhanced CT scan of the kidneys (Fig. 10.2b).

Three-phase CT Scan of the Kidney

This renal investigation consists of an unen-hanced scan, a scan during the arterial phase of contrast enhancement, and a scan during the parenchymal phase. Calcification is best seen without contrast. Hypervascular tumors, such as a renal cell carcinoma, are best demonstrated in the arterial phase; cysts are best seen in the parenchymal phase.

• What is Your Diagnosis?

Renal cyst: This common benign entity is found in approximately 30% of all elderly patients. It often occurs bilaterally and can be associated with hepatic cysts (Fig. 10.3). Simple renal cysts have a thin, smooth margin, have no internal echo on US, and are of water density on CT (less than 20 Hounsfield Units). They are predominantly found in the renal cortex, but can also protrude into the renal hilum, in which case they have to be distinguished from a dilated renal pelvis. Parapelvic renal cysts located in the renal sinus fat can also create the impression of hydro-nephrosis but are easily discernible from the actual renal pelvis on the excretory phase of a contrast-enhanced CT scan.

Any cystic structure that does not fulfill these criteria requires at least a follow-up or—depending on the findings and symptoms—immediate further work-up.

I The Case of Johnny Drip

Parapelvic Hydro
Fig. 10.2 Johnny Drip's US (a) and CT (b). What do you notice?

Polycystic kidneys: Polycystic kidney disease eventually leads to renal failure in adults, requiring hemodialysis or renal transplantation. Patients also frequently present with arterial hypertension. The cysts cause bulging of the renal outline and show different densities on CT, probably secondary to previous hemorrhage (Fig.10.4). In 30% of cases cysts are also found in the liver.

Horseshoe kidney: The horseshoe kidney, characterized by a partial fusion of the kidneys at the upper or lower pole, is a developmental anomaly associated with an increased risk for development of transitional cell carcinoma, Wilms tumor, and the rare renal carcinoid (Fig. 10.5). The "bridging" or so-called "isthmic" tissue can be mistaken for adenopathy or a mass on US.

I Renal Cyst

Fig. 10.3 This simple renal cyst has sharp margins (arrow), is of low density equivalent to water, and does not enhance after contrast administration. This patient also has a dilated renal pelvis. Differentiation from a parapelvic cyst is only possible with certainty after contrast accumulation in the renal pelvis.

Fig. 10.3 This simple renal cyst has sharp margins (arrow), is of low density equivalent to water, and does not enhance after contrast administration. This patient also has a dilated renal pelvis. Differentiation from a parapelvic cyst is only possible with certainty after contrast accumulation in the renal pelvis.

Renal abscess: Development of renal abscesses is possible in pyelonephritis (Fig. 10.6). Clinical signs and symptoms will point to the inflammatory nature of the lesion.

Angiomyolipoma: An angiomyolipoma is a hamartoma of the kidney (Fig 10.7). In 10% of cases it is associated with tuberous sclerosis. The angiomyolipoma is a benign lesion that contains varying amounts of blood vessels and fat. It often becomes symptomatic after hemorrhage into the tumor or perinephric space; occasionally hemorrhage can be quite extensive, requiring embolization or surgery.

Renal lymphoma: Lymphoma can also be found in the kidney and present as a well-circumscribed mass that takes up contrast less avidly than the renal parenchyma (Fig. 10.8). With successful treatment it will regress with residual scarring.

I Polycystic Kidneys

I Polycystic Kidneys

Kidney Mutiple Cacification

Fig.10.4 In polycystic kidney disease, multiple cysts gradually replace the renal parenchyma. These cysts can contain calcification and can become hyperdense on CT after hemorrhage or display an internal hematocrit level. Additionally, several hepatic cysts, which are commonlyassociated with renal cysts, are noted in this patient.

Fig.10.4 In polycystic kidney disease, multiple cysts gradually replace the renal parenchyma. These cysts can contain calcification and can become hyperdense on CT after hemorrhage or display an internal hematocrit level. Additionally, several hepatic cysts, which are commonlyassociated with renal cysts, are noted in this patient.

I Renal Cyst j Horseshoe Kidney j Horseshoe Kidney

Horseshoe Abscess
Fig. 10.5 In a horseshoe kidney a tissue bridge ("isthmus," arrow) is seen anterior to the aorta. There is inferior and medial displacement of both kidneys. The isthmus often has its own arterial blood supply arising from the distal aorta or common iliac arteries.

j Renal Abscess j Renal Abscess

Renal Parenchyma

Fig. 10.6 A hypodense subcapsular mass with a fluid center is demonstrated in the left kidney during the parenchymal (ne-phrographic) phase, i.e., the phase of most intense contrast enhancement by the renal parenchyma.

j Angiomyolipoma of the Kidney

Horseshoe Abscess

Fig. 10.7 This patient presented with severe acute flank pain. A left perirenal hematoma (arrows) is demonstrated on CT. Foci of fat density, characteristic of angiomyolipoma, are clearly visible within the hematoma. This kidney had to be surgically removed; sometimes acute bleeding from an angiomyolipoma can be stopped by the interventional radiologist embolizing the main feeding vessel to the tumor.

Renal cell carcinoma: Eighty percent of all solid renal tumors are renal cell carcinomas (Fig. 10.9a). They are predominantly found in the elderly. Any solid lesion in the kidney represents a malignant neoplasm until proven otherwise, unless there are definite benign features such as internal fat (Fig. 10.9b). Suspicion of renal cell carcinoma always warrants surgery, as tissue biopsy is contraindicated.

Renal cell carcinoma is often very vascular and can contain areas of calcification and necrosis; occasionally it can be predominantly cystic. There is a tendency for vascular invasion by the tumor, growing into renal veins, and sometimes also extending into the inferior vena cava, even up to the right atrium.

Lymph node metastases are first found in the para-aortic lymph nodes at level of the renal vein/caval junction. Metastases are also tend to be very vascular. In cases of planned surgical removal of metastases, prior radiologi-cally guided embolization may be a useful adjunct.

Perirenal hematoma: Perirenal hematoma can be post-traumatic, especially in patients with abnormal blood clotting, but it can also happen spontaneously or after minor trauma (Fig. 10.10).

j Renal Lymphoma

Fig. 10.6 A hypodense subcapsular mass with a fluid center is demonstrated in the left kidney during the parenchymal (ne-phrographic) phase, i.e., the phase of most intense contrast enhancement by the renal parenchyma.

j Angiomyolipoma of the Kidney

Renal Lymphoma

Fig. 10.8a In this patient with histologically proven lymphoma, both kidneys are affected. There seems to be bilateral focal swelling of the parenchyma and decreased parenchymal contrast enhancement. Under therapy there was complete remission of this lymphoma. b In this patient with lymphoma, abnormal perirenal tissue is seen bilaterally. Both kidneys are affected in this case, too.

Fig. 10.7 This patient presented with severe acute flank pain. A left perirenal hematoma (arrows) is demonstrated on CT. Foci of fat density, characteristic of angiomyolipoma, are clearly visible within the hematoma. This kidney had to be surgically removed; sometimes acute bleeding from an angiomyolipoma can be stopped by the interventional radiologist embolizing the main feeding vessel to the tumor.

Fig. 10.8a In this patient with histologically proven lymphoma, both kidneys are affected. There seems to be bilateral focal swelling of the parenchyma and decreased parenchymal contrast enhancement. Under therapy there was complete remission of this lymphoma. b In this patient with lymphoma, abnormal perirenal tissue is seen bilaterally. Both kidneys are affected in this case, too.

a a Renal cell carcinoma

Calcified Pelvic Mass

a Renal cell carcinoma

Fig. 10.11 In this child (vertebral epiphyses are not calcified yet) urinary diversion of both kidneys was attempted via external percutaneous catheters (nephrostomy). This caused bilateral leakage from the renal pelvis, resulting in a perirenal fluid (urine) collection. Each renal pelvis shows calcification.

Renal Parenchyma

Fig. 10.9 a There is a large mass (arrow) demonstrated in the right kidney, which seems to be hypodense compared to the contrast-enhanced renal parenchyma. This tumor, formerly known as a hypernephroma, is highly vascularized. The next step is to ascertain that the renal vein is not invaded by viable tumor thrombus and to check the lymph node status in the renal hilum as well as para-aortic and pericaval nodes. Another important anatomical landmark is the perirenal (Gerota's) fascia, which can be invaded or broken through by more locally advanced tumors. b This lesion proved to be a renal adenoma (arrow). Renal adenomas are difficult to differentiate radiologically from renal carcinomas and are for that reason treated like carcinomas until proven otherwise.

Fig. 10.9 a There is a large mass (arrow) demonstrated in the right kidney, which seems to be hypodense compared to the contrast-enhanced renal parenchyma. This tumor, formerly known as a hypernephroma, is highly vascularized. The next step is to ascertain that the renal vein is not invaded by viable tumor thrombus and to check the lymph node status in the renal hilum as well as para-aortic and pericaval nodes. Another important anatomical landmark is the perirenal (Gerota's) fascia, which can be invaded or broken through by more locally advanced tumors. b This lesion proved to be a renal adenoma (arrow). Renal adenomas are difficult to differentiate radiologically from renal carcinomas and are for that reason treated like carcinomas until proven otherwise.

I Perirenal

Hematoma

Fig. 10.10 On the unenhanced CT scan there is a very heterogeneous left perirenal mass that displaces the kidney anteriorly. The dense parts of the mass represent recently coagulated blood. The cause of hemorrhage in this patient was extracorporeal shock wave lithotripsy (ESWL) administered in an attempt to fragment renal calculi.

Fig. 10.10 On the unenhanced CT scan there is a very heterogeneous left perirenal mass that displaces the kidney anteriorly. The dense parts of the mass represent recently coagulated blood. The cause of hemorrhage in this patient was extracorporeal shock wave lithotripsy (ESWL) administered in an attempt to fragment renal calculi.

Fig. 10.11 In this child (vertebral epiphyses are not calcified yet) urinary diversion of both kidneys was attempted via external percutaneous catheters (nephrostomy). This caused bilateral leakage from the renal pelvis, resulting in a perirenal fluid (urine) collection. Each renal pelvis shows calcification.

I Tumors of the Renal Pelvis

I Tumors of the Renal Pelvis

Fig. 10.12 A tumor of the renal pelvis is easily overlooked in the early contrast phase. Only when the collecting system is completely filled with contrast is the tumor of the renal pelvis (arrow) easily detected. Remember to use wide window/level settings when assessing the contrast-filled renal pelvis on CT, otherwise you may miss a small mural lesion in the ocean of white contrast.

Fig. 10.12 A tumor of the renal pelvis is easily overlooked in the early contrast phase. Only when the collecting system is completely filled with contrast is the tumor of the renal pelvis (arrow) easily detected. Remember to use wide window/level settings when assessing the contrast-filled renal pelvis on CT, otherwise you may miss a small mural lesion in the ocean of white contrast.

Urinoma: Urinoma can develop after trauma to the renal pelvis or the ureter (Fig. 10.11). The distinctive feature of a urinoma is a mostly perirenal fluid collection with density equivalent to water. When a stone obstructs the ureter, a calix can spontaneously rupture, decompressing the renal pelvis into the perinephric space, forming a urinoma.

Tumor of the renal pelvis: Transitional cell carcinoma of the renal pelvis is much less common than renal cell carcinoma. It arises from the urothelium; even small lesions can become symptomatic because of hematuria. On CT it is best demonstrated in the late contrast phase on wide window settings, when it is seen as a filling defect in the otherwise contrast-filled renal pelvis (Fig. 10.12).

/ The main role for imaging in renal pelvis tumors is staging of the disease.

I Perirenal

Hematoma

I Wilms

Tumor

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