**5.2. Urological complications**

*5.1.3. Calcineurin Inhibitors (CNI) nephrotoxicity*

34 Current Issues and Future Direction in Kidney Transplantation

chronic rejection, ATN, or cyclosporine toxicity [56].

**Figure 7.** CNI toxicity. Spectral doppler evaluation with a mild elevatation of RI.

serum levels are described [52, 53].

CNI can cause renal vasoconstriction with ischemia. CNI toxicity is caused by afferent arteriolar vasoconstriction followed by a decrease in glomerular perfusion pressure and also by a tubulointerstitial injury independently from its vascular effects [51]. These physiological effects are similar between cyclosporine and tacrolimus. Monitoring the CNI serum levels is important to prevent the occurrence of nephrotoxicity and, on the other hand, to achieve the appropriate immunossupression. Moreover, nephrotoxicity of these drugs not related to their

When DGF occurs many experts prefer do not use CNI due to their possible detrimental effects in the ischemic damaged kidneys [54]. When creatinine level stabilizes without complete renal function recovery or when renal function deterioration occurs, a renal biopsy should be performed. Currently, no clinical findings are specific enough to differentiate allograft rejection from CNI nephrotoxicity. Imaging findings are also non-specific and superimposed with the other parenchymal complications. Cyclosporine toxicity may produce an enlarged kidney with increased cortical echogenicity and prominent medullary pyramids. On radio‐ nuclide images, acute cyclosporine toxicity resembles mild acute rejection, with depressed effective renal plasma flow and parenchymal retention [22, 45] Loss of the corticomedullary differentiation can be seen on MRI [55]. Findings should be correlated with cyclosporine levels. Sustained increasing in RI values (Figure 7), without a morphologic cause such as hydroneph‐ rosis, is indicative of graft dysfunction, but it´s non-specific and may be caused by acute or

The clinical setting of most UCs is that of a decrease in graft function. Because many of the complications are treatable, it is extremely important to make an early diagnosis and separate from rejection or ATN. The first reports concerning renal transplantation showed a prevalence of UC varying from 10% to 25%, with a mortality rate ranging from 20% to 30%. Nowadays, due to advances in immunosuppressive therapy combined with careful surgical technique the incidence of UC decreased, ranging from 1% to 8% [58, 59]. The majority of the UC are seen during the first month to six months after transplant. Ureteric obstruction and urine leak are the most common [22, 60].

#### *5.2.1. Obstructive uropathy*

The major causes of ureteral obstruction are ureteral ischemia, edema at the uretero-vesical anastomotic site, infection, extrinsic compression of the ureter by fluid collections, and ureteral kinking. Other relatively rare causes are stones, papillary necrosis, clots, fungi, pelvic fibrosis, and herniation of the ureter [61]. Early-onset obstruction of the ureter is secondary to kinks, clots, edema, inflammation, or a tight submucosal tunnel. Percutaneous treatment is the best treatment option. Late-onset obstruction is caused by fibrosis, ischemia, or periureteral masses or may be secondary to rejection [19]. The transplanted ureter is relatively prone to ischemia due to limited blood supply [22, 24, 50, 58]. A large majority of the ureteral strictures occur in the distal third of the ureter, usually secondary to ischemia [22, 58].

Sonography shows dilated renal pelvis and calyces and is useful to determine the site of ureteral obstruction (Figure 8). This is a nonspecific finding because it is also seen in cases of diminished ureteral tonus resulted from denervation of the transplant [62], mild dilated collecting system in rejection, vesico-ureteral reflux, and secondary to overdistended bladder. In the later condition, it's important to repeat the US with an empty bladder.

When highly echogenic, weakly shadowing masses are present in the collecting system, fungus balls should be considered, whereas low-level echoes may suggest pyonephrosis or hemo‐ nephrosis [63]. Other abnormalities of the collecting system include calculi and urothelial tumors. In some cases of acute obstruction an increased RI and PI may be present, however, again they are nonspecific findings [37, 64].

At Nuclear Medicine, in patients with early partial obstruction, good perfusion and prompt uptake of the radiotracer may be seen; however, in patients with functionally significant hydronephrosis, radioactivity is retained in the collecting system. Delayed images are useful for differentiating an obstructed ureter from a dilated but unobstructed ureter, since a nonobstructed system shows clearance into the bladder. Diuretic renography and conventional

*5.2.2. Perirenal collections*

collecting system obstruction.

*5.2.2.1. Urinome / urinary leak*

diagnosis.

performed.

*5.2.2.2. Hematoma*

In the early post transplant period, it is common to see fluid collections around the kidney in up to 50% cases. Common post-transplant fluid collections include urinome, hematoma, seroma, lymphocele, and abscess [33, 58, 62]. Rarely, they lead to a graft dysfunction or a

Imaging in Kidney Transplantation http://dx.doi.org/10.5772/55074 37

US is very useful to assess the presence and size of perinephric fluid collections; however, it is not very specific for further differentiation among different types of content. The posttransplant time interval may suggest the nature of collections. Fluid collections seen in the immediate postoperative period are usually hematomas or seromas [50]. All fluid collection are identified with US and although solid echoes or septations may suggest specific diagnosis, correlation with clinical findings helps to restrict differential diagnosis, occasionally puncture

Urinome occurs in up to 6% of transplant recipients [69] in the first weeks post-transplantation. It is believed to be caused by disruption of the vesicoureteric anastomosis or ischemic injury of the distal ureter [24]. It is normally preceded by increased abdominal pain, reduction in

US is essential in the evaluation of perirenal collections, including urinomes. It is the modality of choice for diagnosis and guiding puncture. A cystogram may show leakage from the bladder and an isotope scan is often helpful. These collections are expected to show increased activity on radionuclide MAG-3 (Tc99 mercaptoacetyltriglycine) scans while other fluid collections usually result in photopenic defects [33] (Figure 9). The appearance on US is of a homogeneous anechoic collection, with thin walls, usually without echoes (Figure 10). CT and MRI show a clear fluid collection. Diagnostic aspiration may be required to confirm the nature of the collection. A communication between the fluid collection and urinary tract is required for final

Hematomas are seen mostly in the early post operative period. The overall incidence of significant postoperative hematomas from renal transplant varies from 4 to 8% [70, 71]. They have a complex appearance, poorly defined wall with internal echoes (Figure 11 A and B). Clots and debris appear as dense areas in unenhanced CT scans. Ultrasound and CT define the collection, but differentiation from abscess is difficult. Radionuclide scans demonstrate photopenic collection adjacent to the kidney, which do not fill up in delayed images. MRI signal depends on the stage of hematoma. Aspiration and imaging guided drainage are

with biochemical analysis of the fluid are required to final diagnosis

urine volumes and sometimes, urine leakage from the wound.

**Figure 8.** (A) and (B) - Mild hydronephrosis presumably, secondary to a tight submucosal tunnel.

clearance times can be used in the assessment of urinary tract patency [65]. The anterograde urography usually depicts the site of obstruction. The combination of normal results from the Whitaker test and anterograde pyelography virtually excludes the presence of obstruction [66]. If necessary, MDCT allows accurate imaging of the entire course of ureteral and periureteral diseases.

In pyelonephritis, diffuse thickening of the urothelium in the renal pelvis and proximal ureter may be seen, but it´s also seen in rejection. At MRI, an absent renal fat sinus and decrease in corticomedullary differentiation, along with striated nephrogram and multiple nonenhancing, round foci in the transplant renal parenchyma are the most frequent signs [43, 67].

Renal stones may either form in the transplant kidney or be incidentally carried from the donor kidney. Because the kidney and ureter are denervated, these patients do not present with a typical colic pain. The incidence and risk factors for calculus are the same as for a native kidney [10], in some reports ranging from 0,4% to 1,0% [68]. Lithiasis can lead to further complications such as obstruction or infection. Small stones are missed in plain films, since the transplant kidney overlies iliac bone. Unenhanced MDCT is the gold standard as can detect virtually 100% of stones.

Occasionally, gas may be seen in the collecting system, usually introduced from external sources, such as catheter or occasionally from needle biopsy or, very rarely, from emphysem‐ atous pyelonephritis. Evaluation of the collecting system and bladder may also show an abnormal position or condition of the stent.
