Postoperative fluid collections like abscess, hematoma, lymphocele, and urinoma can be identified on US, but it cannot reliably differentiate between them. Sometimes an US examination may not demonstrate the extent of the collection and a noncontrast CT may be required. If large, these collections can lead to hydronephrosis; compression of the renal vein, leading to RVT; or compression of femoral vessels, leading to lower-extremity swelling or deep venous thrombosis. Large hematomas may lead to Page kidney. The time frame in which the collection is discovered has some prognostic ability since urinomas, hematomas, and abscesses occur in the early postoperative period, whereas lymphoceles occur weeks to months after surgery. Lymphoceles more often have septa than other collections, and hematomas tend to have higher echogenicity. In order to differentiate these entities, aspiration is usually required, and this is commonly performed with US guidance. Hydronephrosis can also be easily identified with US; however, it should be interpreted in correlation with biochemical data since reflux can give a similar appearance as well [27]. Urine leak may appear as a fluid collection on US, but an isotope scan would be more helpful [23]. Leaks are definitively diagnosed by aspiration of the collection with measurement of creatinine. Since ATN and acute rejection cannot be diagnosed with US and serum creatinine is insensitive for detecting early graft pathology, US-guided biopsy is the standard method for the diagnosis of rejection and evaluation of immunosuppression. The complication rate from renal transplant biopsies is low, with a reported rate of 0.4% to 1% graft loss in approximately 2500 biopsies [28]. Contrast-enhanced US (CEUS) has been used by some investigators to evaluate graft perfusion both in large arteries and within the cortex. Schwenger et al [29] found that patients with CAN had significantly lower blood flow values quantified by CEUS compared to patients without CAN.
Renal Transplant Dysfunction. Postoperative fluid collections like abscess, hematoma, lymphocele, and urinoma can be identified on US, but it cannot reliably differentiate between them. Sometimes an US examination may not demonstrate the extent of the collection and a noncontrast CT may be required. If large, these collections can lead to hydronephrosis; compression of the renal vein, leading to RVT; or compression of femoral vessels, leading to lower-extremity swelling or deep venous thrombosis. Large hematomas may lead to Page kidney. The time frame in which the collection is discovered has some prognostic ability since urinomas, hematomas, and abscesses occur in the early postoperative period, whereas lymphoceles occur weeks to months after surgery. Lymphoceles more often have septa than other collections, and hematomas tend to have higher echogenicity. In order to differentiate these entities, aspiration is usually required, and this is commonly performed with US guidance. Hydronephrosis can also be easily identified with US; however, it should be interpreted in correlation with biochemical data since reflux can give a similar appearance as well [27]. Urine leak may appear as a fluid collection on US, but an isotope scan would be more helpful [23]. Leaks are definitively diagnosed by aspiration of the collection with measurement of creatinine. Since ATN and acute rejection cannot be diagnosed with US and serum creatinine is insensitive for detecting early graft pathology, US-guided biopsy is the standard method for the diagnosis of rejection and evaluation of immunosuppression. The complication rate from renal transplant biopsies is low, with a reported rate of 0.4% to 1% graft loss in approximately 2500 biopsies [28]. Contrast-enhanced US (CEUS) has been used by some investigators to evaluate graft perfusion both in large arteries and within the cortex. Schwenger et al [29] found that patients with CAN had significantly lower blood flow values quantified by CEUS compared to patients without CAN.