Figure 5.20. coronal reformat image from a non-contrast ct demonstrates a left proximal mid ureteric calculus (arrow) causing renal obstruction.

multiplanar reformats (Fig. 5.23) as well as detailed 3-D images. This facility is particularly useful for surgical planning in those patients with complex stone disease being considered for percutaneous nephrolithotomy or ureteroscopy.

Renal Cystic Disease

Benign Renal Cysts

Benign or “simple” renal cysts are common and may be seen in at least 50% of the population over the age of 60. The majority are situated in the renal cortex and are usually asymptomatic although larger cysts can enlarge leading to pressure symptoms. Occasionally, benign cysts become infected resulting in sepsis or undergo hemorrhage giving rise to flank pain. Symptomatic cysts can often be managed by radiologically guided percutaneous drainage.

On ultrasound, simple cysts are unilocular anechoic structures with associated posterior acoustic enhancement (Fig. 5.24). On CT they can be recognized as rounded non-enhancing homogenous fluid density structures. Renal cysts are not usually identifiable IVU, however larger cysts can result in lobulation of the renal outline or distortion the renal collecting system.

Table 5.4. nonobstructive renal and nonrenal causes of flank pain

nonobstructive renal causes of flank pain

•Acutepyelonephritis

•Renaltumor

•Renalhemorrhage

•Renalinfarction

•Renalveinthrombosis

nonrenal causes of flank pain

•Appendicitis

•Diverticulitis

•Pelvicinflammatorydisease

•Cholecystitis

•Aorticaneurysm

Parapelvic renal cysts arise adjacent to the renal pelvis resulting in extrinsic compression of the renal collecting system.They tend to contain lymphatic fluid and are usually asymptomatic. On ultrasound they can be seen as rounded anechoic structures situated in the renal medulla.

Occasionally, parapelvic cysts can give rise to diagnostic confusion on ultrasound and on unenhanced CT as their appearance can be difficult to distinguish from hydronephrosis. On IVP, they may result in distortion and stretching of the pelvicalyceal system. Definitive diagnosis

Figure 5.23. coronal ct urography image demonstrating the presence of renal calculi within the left lower pole calyx.there is generalized left renal cortical atrophy.

can be made by CT urography, which opacifies the collecting system and allows the cysts to be identified separately (Fig. 5.25).

Complex Renal Cysts

Complex renal cysts demonstrate atypical features that may warrant follow-up or consideration of surgical removal. Atypical features include, increased wall thickness, nodularity, septations, calcification, or internal contents not typical for simple fluid. Complex renal cysts are usually evaluated by CT. MRI can also help further characterize complex cysts and may be useful as a supplementary test.

Figure 5.25. ct urography: Para pelvic cysts are seen as homogenous low attenuation structures adjacent to the opacified pelvicalyceal system.

The Bosniak classification, which is based on CT appearances is used to categorize renal cysts in increasing order of complexity and radiological concern (Table 5.5 and Fig.5.26).Bosniak category

Upper Tract Infective and

Inflammatory Disease

Most patients with urinary tract infections do not require imaging investigations. However, imaging may be appropriate in those patients with severe recurrent infections to identify any underlying renal tract abnormality. Ultrasound is a useful first-line test to assess renal morphology and is frequently used to investigate patients with recurrent UTIs. IVU or CT urography may also be helpful in identifying any underlying upper tract abnormality.

Chronic pyelonephritis results in renal scarring, atrophy, and distortion of the renal calyces and is readily appreciated on ultrasound or CT.

Urosepsis: In this situation it is important to distinguish between pyelonephritis, which is treated medically from other causes of urosepsis such as,pyonephrosis,renal abscess,and emphysematous pyelonephritis, which may require surgical or radiological intervention.

Acute Pyelonephritis can be diffuse or focal. Characteristic changes on ultrasound include swelling of the kidney, reduced echogenicity as a result of parenchymal edema, and diminished vascularity. However, ultrasound is a relatively insensitive test for the assessment of acute pyelonephritis and may underestimate the severity of the disease.

Figure 5.26. (a–d) series of ct images showing various renal cysts. image (a) shows a non-complex homogenous (Bosniak 1) renalcyst.image(b)demonstratesacystcontainingfineseptations

(Bosniak 2 lesion).cyst containing coarse calcification and soft tissue component (c) in keeping with a Bosniak 3 cyst. image (d) demonstrates a malignant cystic mass (Bosniak 4 lesion).

Figure 5.27. (a) axial and (b) coronal ct images demonstrate diffuse abnormal enhancement and swelling of the left kidney with soft tissue stranding in the perinephric fat.appearances are

CT features of acute pyelonephtitis include patchy or wedge shaped low attenuation poorly enhancing areas within the renal parenchyma and swelling of the affected kidney often with inflammatory changes in the perinephric fat13 (Fig. 5.27).

Renal abscess can arise secondary to severe pyelonephritis or may be associated with underlying stone or cystic disease. On ultrasound renal abscess can be recognized as a thick walled cystic structure, which may contain echogenic fluid indicating internal debris.

CT typically demonstrates a thick walled enhancing fluid containing structure (Fig. 5.28).

Figure 5.28. thick walled fluid collection demonstrated in the upper pole of right kidney (white arrow) in patient with swinging pyrexia and leucocytosis, appearances indicate renal abscess.

in keeping with acute pyelonephritis.note also the presence of a small left renal calculus (arrow).

The presence of gas within a renal fluid collection is virtually diagnostic for abscess.

Renal abscesses can be treated with antimicrobial therapy but percutaneous drainage may be necessary if conservative measures fail.

Emphysematous Pyelonephritis is a rare lifethreatening condition in which there is severe renal infection resulting in gas formation within the renal parenchyma.The vast majority of cases (90%) are seen in diabetic patients. CT readily demonstrates abnormal renal enhancement and presence of gas in the renal parenchyma which is diagnostic for emphysematous pyelonephritis (Fig. 5.29). Nephrectomy is indicated if conservative measures fail.

Pyonephrosis: Pus in an obstructed renal collecting system can lead to life-threatening sepsis and is a urological emergency. Urgent decompression of the kidney either by nephrostomy drain or ureteric stent is indicated.

Pyonephrosis commonly occurs in kidneys obstructed by ureteric calculi although can occur secondary to any cause of renal obstruction. Ultrasound typically demonstrates hydronephrosis, which in the context of flank pain and pyrexia strongly suggests the diagnosis of pyonephrosis. Echogenic fluid within the collecting system or sedimented debris representing purulent material within the renal pelvis is also sometimes a feature (Fig. 5.30).

Xanthogranulomatous pyelonephritis (XPN) is an inflammatory renal condition associated with chronic urinary tract infection (usually caused

Figure 5.29. (a, b) ct scan images in a patient with poorly controlled diabetes and pyrexia of unknown origin. Pockets of gas are present in the renal parenchyma (white arrow) and perinephric space (yellow arrows) which confirm the diagnosis of

emphysematous pyelonephritis. the patient was successfully treated with antibiotics and ureteric stent insertion. images courtesy of mr. nigel Boucher (consultant Urological surgeon, chesterfield royal lnfirmary).

Figure 5.30. Ultrasound in a patient with loin pain and fever shows a severely hydronephrotic kidney with an obstructing calculus at the pelvi-ureteric junction (yellow arrow). Echogenic fluid is identified in the collecting system in keeping with pyonephrosis.

by E. Coli or Proteus species). Histologically, the kidney is infiltrated by lipid laden macrophages, which destroy the normal renal parenchyma. Clinical features include flank pain and pyrexia. The condition is usually unilateral, more common in women and can be focal or diffuse.

CT usually demonstrates renal enlargement with replacement of normal renal parenchyma by areas of low attenuation of xanthomatous tissue (Fig. 5.31). Associated stone formation, usually of the staghorn type is seen in up to 80% of cases. Extrarenal extension of XPN into the perinephric fat, Gerotas fascia, and adjacent psoas muscle is a common feature.

Figure 5.31. Xanthogranulomatous pyelonephritis ct scan demonstrates an enlarged inflamed kidney. multiple renal calculi and abnormal parenchymal enhancement is shown. note extension of infection into the perinephric fat (arrow).

Imaging of Upper Urinary Tract

Obstruction

There are many causes for obstruction of the upper urinary tract, which can occur at any level between the pelvi ureteric junction and bladder. Causes can be divided into intrinsic pathology arising within the renal tract or extrinsic (Table 5.6). Hydronephrosis, dilatation of the pelvicalyceal system is the main imaging feature of renal obstruction. Depending on the

underlying etiology renal obstruction may lead to a gradual or acute deterioration in renal biochemistry.

Ultrasound has a sensitivity of almost 100% for the detection of hydronephrosis, which is easily appreciated as dilatation of the renal pelvis and calyces (Fig. 5.32) and is commonly performed as a first-line test in suspected renal obstruction.14 Hydronephrosis, however, does not always indicate obstruction and is sometimes seen in well-hydrated patients and in those with bladder distension. Para pelvic cysts (Fig. 5.33), extra renal pelvis, and prominent renal vasculature can mimic hydronephrosis potentially leading to a false positive diagnosis

Figure 5.32. hydronephrotic kidney demonstrated by ultrasound. the renal cortical thickness is preserved in keeping with acute obstruction.

Figure 5.33. Parapelvic cysts: commonly misinterpreted as hydronephrosis. the presence of noncommunicating anechoic areas with separating septations representing the walls of the cysts helps differentiate this appearance from hydronephrosis.

of renal obstruction. Cortical atrophy is usually seen in chronic obstructive uropathy.

Obstructing pelvic masses may be visible on ultrasound; however, the retroperitoneal structures are frequently obscured by overlying bowel gas and alternative imaging tests are often necessary to demonstrate the underlying obstructing pathology.

Delayed contrast excretion, a dense nephrogram, and hydronephrosis are the principal IVU features of acute obstruction (Fig. 5.34). Associated hydroureter may also be evident depending on the level of obstruction. Obstructing ureteric calculi and ureteric can often be identified. However, extrinsic causes of renal obstruction cannot in most cases be diagnosed by IVU. Absence of renal excretion is seen in cases of severe acute obstruction or chronic obstructive uropathy.

Unenhanced CT has a high sensitivity for the detection of renal calculi and is the most accurate imaging modality for investigation of suspected obstructing ureteric calculi10. CT urography can readily demonstrate obstructing ureteric tumors as well as extrinsic abdominal or pelvic masses. Hydronephrosis with associated reduced parenchymal enhancement and cortical atrophy are features of chronic obstructive uropathy (Fig. 5.35).

MRI is useful for the assessment of patients with renal obstruction in those patients with renal impairment or iodine contrast allergy. MRI is particularly valuable for the diagnosis

Figure 5.34. iVU image demonstrating a right PUJ obstruction.

and evaluation of pelvic masses and is superior to CT for the local staging of bladder and prostate tumors. Heavily T2-weighted sequences are utilized to demonstrate the degree and level of ureteric obstruction15 (Fig. 5.36). The main disadvantage of MRI is its inability to adequately demonstrate obstructing ureteric calculi.

Management of Acute Renal

Obstruction

Urgent decompression of the upper renal tracts is indicated in patients with renal obstruction resulting in acute renal failure or urosepsis. This can be achieved by percutaneous nephrostomy tube (Fig. 5.37) or ureteric stent insertion.

Percutaneous renal drainage via a nephrostomy tube involves the insertion of a catheter into the kidney under imaging guidance and results in rapid decompression of the collecting system.

Typically the procedure is performed under local anasthesia. Complications are uncommon but include renal hemorrhage, sepsis, and inadvertent damage to surrounding organs. Nephrostomy drains can be left in situ until definitive treatment of the underlying cause of obstruction is dealt with.

Ureteric stents provide internal drainage of the upper tracts and are usually inserted retrogradely via a cystoscope. The main advantages over nephrostomy tubes are patient convenience as external drainage bags are not needed and avoidance of trauma to the renal parenchyma with less risk of hemorrhagic complications. The procedure is usually performed under general anasthesia. Retrograde stent insertion may be difficult or impossible in patients with extensive pelvic malignancy, in these patients antegrade ureteric stent insertion via a nephrostomy track may be feasible.