*5.2.2.1. Urinome / urinary leak*

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 urine volumes and sometimes, urine leakage from the wound.

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 diagnosis.

#### *5.2.2.2. Hematoma*

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

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

(A)

36 Current Issues and Future Direction in Kidney Transplantation

(B)

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,

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

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

round foci in the transplant renal parenchyma are the most frequent signs [43, 67].

diseases.

100% of stones.

abnormal position or condition of the stent.

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 performed.

**Figure 10.** Urinoma. Gray-scale US shows a simple fluid collection around the kidney, anechoic (\*). The biochemical

Imaging in Kidney Transplantation http://dx.doi.org/10.5772/55074 39

**Figure 11.** (A) Recent hematoma. Longitudinal US scan shows a complex, hyperechoic mass (\*) around the graft. (B)

Organizing hematoma. A complex collection (\*) around the graft with hiper-and hypoechoic areas.

analysis of the fluid after puncture revealed a high creatinine level.

(A)

(B)

**Figure 9.** Anomalous accumulation of the glomerular agent (99mTc-DTPA) above the renal pole compatible with a uri‐ noma. 99mTc-DTPA image showing accumulation of activity (arrow) outside the area of the kidney, ureter and bladder indicating urinary leakage.

#### *5.2.2.3. Abscess*

Abscess can be a complication of surgery, pyelonephritis or secondary to infections, urinomes, hematomas or lymphoceles. It can occur any time during the post transplant period. The appearance is the same as a hematoma, i.e. a complex collection. Parenchymal abscess manifests as a well defined hypoechoic mass on US, and nonenhancing, hypoattenuating collection on CT. On MR, it can show high signal intensity on DWI and peripheral enhancement after contrast media.

**Figure 10.** Urinoma. Gray-scale US shows a simple fluid collection around the kidney, anechoic (\*). The biochemical analysis of the fluid after puncture revealed a high creatinine level.

**Figure 11.** (A) Recent hematoma. Longitudinal US scan shows a complex, hyperechoic mass (\*) around the graft. (B) Organizing hematoma. A complex collection (\*) around the graft with hiper-and hypoechoic areas.

*5.2.2.3. Abscess*

indicating urinary leakage.

38 Current Issues and Future Direction in Kidney Transplantation

after contrast media.

Abscess can be a complication of surgery, pyelonephritis or secondary to infections, urinomes, hematomas or lymphoceles. It can occur any time during the post transplant period. The appearance is the same as a hematoma, i.e. a complex collection. Parenchymal abscess manifests as a well defined hypoechoic mass on US, and nonenhancing, hypoattenuating collection on CT. On MR, it can show high signal intensity on DWI and peripheral enhancement

**Figure 9.** Anomalous accumulation of the glomerular agent (99mTc-DTPA) above the renal pole compatible with a uri‐ noma. 99mTc-DTPA image showing accumulation of activity (arrow) outside the area of the kidney, ureter and bladder

### *5.2.2.4. Lymphocele*

Lymphoceles are lymph collection from the iliac lymphatic vessels of recipient or graft hilum that accumulates between the transplanted kidney and bladder. It results from surgical disruption of lymphatics and usually occur 4 to 8 weeks following transplantation [62, 70-72]. Usually these are small in size and asymptomatic; however, when large can cause hydro‐ nephrosis or lower extremity edema and may require drainage [33]. US shows an anechoic collection with fine septa within it, usually inferior to the region between the kidney and bladder (figure 12). Scintigraphy demonstrates a photopenic area which does not fill up with tracer on delayed images [73]. CT shows well defined round or oval collection of 0–20 HU. On MR images, an homogeneous and often minimal complex collection is depicted.

**•** Torsion: an extremely rare complication, more common in peritoneal location. It refers to rotation of the kidney transplant graft around its vascular pedicle resulting in vascular compromise and infarction [76]. On images the graft is with abnormal axis, enlarged,

Imaging in Kidney Transplantation http://dx.doi.org/10.5772/55074 41

**•** Rupture: a rare complication of uncertain etiology. Biopsy, acute rejection, ATN, vascular occlusion, trauma, rejection, and renal cell cancer development are proposed etiologies [78-80]. Sonographic findings are extrarenal and subcapsular collections, laceration or hematomas within the perinephric space [79]. CT shows dense clot and perinephric collection. Radionuclide scans show photopenic defect. MR shows clots and an hemorrhagic

Vascular complications (VC) after renal transplantation are the most frequent type following urological complications, seen in less than 10% [81]. Early VC includes renal artery or vein thrombosis, lesions to the iliac vessels and cortical necrosis. Delayed complications mainly include renal artery stenosis, arteriovenous fistula and rarely pseudo-aneurysm. They have a high associated morbidity and mortality. Although DSA remains the gold standard for vascular complications, US with Doppler is the screening method for assessing blood supply of a kidney graft [49, 82]. MRI with angiography (MRA) has been used more often to confirm US diagnosis of vascular abnormalities in renal transplants [31]. With this combination,

Usually occurs in the first week post transplantation. Renal artery and vein thrombosis are generally related to the position of the graft, to a long vessel, to surgical techniques (anasto‐ mosis of the arteries), or to compression, e.g. hematoma compressing the renal vein. Renal vein

Arterial thrombosis is rare in the early transplant period. US and MRI show complete absence of flow in the main transplant renal artery and intrarenal arteries, no flow in the parenchyma with CD or PD (Figure. 13), and no parenchymal perfusion detectable at MRI. MRI can also demonstrate absence of renal artery enhancement. Occlusion of a lobar artery or a pedicle artery leads to a focal well-defined area of infarct, which consequences are dependent to the extension of this area [25]. In the ischemic area, the renal cortex has appearance of a wedgebased hypoechoic mass with echogenic walls, and no signal on CD [31]. MRI can better delimitate the zone of infarct. MRI and CT show a non-enhancing area with enhancing capsule.

Renal vein thrombosis is a frequent cause of loss of the renal graft, occurring in 4-6% of the transplants in adults [83]. It´s a difficult diagnosis because it begins in the venules within the renal parenchyma, and initially, large veins remain normal [84]. Characteristic features of renal vein thrombosis include a dilated transplanted renal vein containing a thrombus with absent venous flow (Figure 15); lack of venous outflow that causes a very high resistance to arterial

radionuclides are scarcely used to evaluate graft vascular complications.

thrombosis can also be secondary to extent of a thrombus in the iliac vein.

Scintigraphy may also be used to confirm arterial occlusion (Figure 14).

hypoechoic and with poor enhancement [77].

perirenal collection.

**6.1. Vascular complications**

*6.1.1. Early vascular complications*

**Figure 12.** A minimal complex fluid collection around the graft extending to the pelvis, with fine septa, consistent with a lymphocele.

#### *5.2.3. Vesicoureteral reflux*

It seems to have a greater incidence in patients whom extravesical cystoureteral anastomosis was performed. However the clinical relevance is still not established, with a slightly increase in risk of infection. Cysto-uretrogram can easily make this diagnosis. Many technical modifi‐ cations has been proposed to reduce the vesicoureteral reflux and urine leakage like modified Lich-Gregoir technic [74].
