Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

KIDNEYS AND URETERS

Magnetic resonance imaging appears to have a role in evaluating posttransplant ureter complications. Similar to the bile ducts, MR images mimicking conventional urography are feasible. In patients with suspected urologic abnormalities, MR urography identifies dilated renal pelves and detects ureteral leaks and obstructions.

Ureteral obstruction develops secondary to postoperative edema, anastomotic stricture, kinking or compression by an extrinsic urinoma, hematoma, or lymphocele (Fig. 10.38). The ureteroneocystostomy is the most common site of obstructions. A ureter can be trapped in an obturator hernia. Because of denervation, posttransplant patients manifest obstruction simply by worsening renal function. With a stenosis, US or scintigraphy should detect any underlying hydronephrosis, but keep in mind that dilation is not always secondary to an obstruction.

Posttransplant ureteral obstructions are treated with ureteral balloon dilation and antegrade placement of nephroureteral stents; about two thirds of those with early obstruction are treated successfully, but the success rate decreases in those with late obstruction. Obstruction can also be relieved with a percutaneous nephrostomy. Only a minority of patients eventually require open surgery. In general, the survival of a renal graft in

patients who develop ureteral stenoses or fistulas is shorter than in those without these complications.

Most urinary extravasations occur at the ureteral anastomosis and result in a urinoma (Figs. 10.39 and 10.40). Some leaks are secondary to ureteral necrosis, presumably ischemic in origin, and are difficult to treat.

Ultrasonography detects most urinomas. Scintigraphy during the acute time period shows radiotracer activity in the urinoma.

A posttransplant leak is approached with a percutaneous nephrostomy and antegrade placement of a nephroureteral stent; leaks that do not heal require surgical repair.

Ureteral complications requiring reconstruction range from complete ureteral necrosis to long or multiple ureteral strictures. Most often with ureteral necrosis a part of the bladder is used as a substitute, although an artificial ureter has also been successfully employed.

Fluid Collections

Postoperative fluid collections are common and range from hematoma, seroma, urinoma, and lymphocele, to an abscess. Most small hematomas and lymphoceles resolve spontaneously.

Many of these fluid collections have a similar gray-scale US appearance, and fluid aspiration

KIDNEYS AND URETERS

is necessary to differentiate between them. A hematoma initially is hyperechoic,but gradually becomes hypoechoic and eventually anechoic.

A seroma, urinoma, and lymphocele are all hypointense on T1and hyperintense on T2weighted MRI. Significant urinomas usually require reoperation.

Lymphoceles develop from the disruption of pelvic lymphatics. They tend to become multiseptated. Therapy of these posttransplant lymphoceles includes open or laparoscopic marsupialization, percutaneous drainage, and percutaneous injection of a sclerotic agent. External drainage has a high failure rate, but percutaneous sclerotherapy using a povidoneiodine agent is a simple technique and has had considerable application; recurrent lymphoceles can be retreated percutaneously. Laparoscopic marsupialization with internal drainage is feasible, and effective therapy for posttransplant lymphoceles but is more invasive. Intraoperative US guidance is often helpful.

Stones

The frequency of urinary calculi in a transplanted kidney ranges up to 3%, a prevalence greater than in the general population. About half of these stones are composed of urate. Not all filling defects are stones. Blood clots, fungus balls, or sloughed papillae are also encountered.

Lymphoproliferative Disorder/Neoplasms

Renal transplant patients are immunosuppressed and, not surprisingly, are at an increased risk of developing neoplasms. Epstein-Barr virus infection is believed to be responsible for most of this increased risk. To put this issue in perspective, approximately 1% of renal transplant patients develop a lymphoproliferative disorder, considerably more than the general population. A retrospective Italian study found 15 cancers in 11 posttransplant patients, including skin cancers, Kaposi’s sarcomas, renal carcinomas, transitional cell carcinoma, and even colon cancer (141); the mean time of immunosuppression until tumor detection was 45 months, and, surprisingly, no lymphomas or female genital tract cancers were found.

Over the years, the sites of lymphoproliferative disorder involvement in renal trans-

plant patients have changed considerably; central nervous system involvement predominated initially, during the cyclosporine era thoracic and abdominal sites were more common, while isolated involvement of the transplanted kidney is now more evident. Currently lymphoproliferative disorders most often present as solitary or multiple tumors, often limited either to the allograft or allograft hilum (142); most are extranodal in location. Newer immunosuppression agents are evolving, and the type of neoplasms encountered in different studies reflects, in part, the immunosuppressive approach used.

Lymphoproliferation ranges from a nonspecific mild adenopathy to malignant lymphoma. B-cell non-Hodgkin’s lymphoma is most common, but other lymphomas are also encountered. In general, these lymphomas tend to be more aggressive than their counterparts in nonimmunosuppressed individuals.

Transplant patients develop renal cell carcinomas in the native kidneys and in the renal allograft and ovarian carcinomas. No significant relationship exists between the prevalence of renal cell carcinoma and the presence of acquired cystic kidney disease, patient age, type and duration of dialysis, or drugs used. Screening of the native kidneys appears reasonable in patients undergoing US of a renal allograft.

Those Australian and New Zealand Dialysis and Transplant Registry patients who had renal transplantation as a result of analgesic nephropathy were found to be at an increased risk of developing posttransplant transitional cell carcinomas of the upper urinary tracts compared to patients undergoing transplantation for other causes of renal failure (143); their tumors tend to be of a higher grade and stage, and they have a worse outcome than do other transplant patients. Screening with urinalysis and voided urine cytology does not appear to be reliable in detecting upper renal tract malignancies. Annual cystoscopy and retrograde ureteral catheterization with washings, brushings, and radiologic imaging were advocated in these patients. The patients should also be screened before transplantation.

Both bladder nephrogenic metaplasia and nephrogenic adenomas develop in these patients; these benign tumors, considered to be without malignant potential, have a relatively high relapse rate. Their long-term course in

these immunosuppressed patients is not clear.

The prevalence of cutaneous squamous cell carcinoma, basal cell carcinoma, cutaneous malignant fibrous histiocytoma, atypical fibroxanthoma, and Kaposi’s sarcoma is increased considerably over a control population. Among other tumors, basal cell epithelioma of the scalp, gastric adenocarcinoma, central nervous system lymphoma, breast carcinoma, and adenocarcinoma of the colon have been reported.

An annual abdominal US appears to have a role in detecting some neoplasms in asymptomatic renal allograft recipients. One should keep in mind, however, that US does not detect smaller tumors. Some evidence suggests that MR is superior in detecting lymphoproliferative disorders. Lymphomas appear as soft tissue tumors isodense to soft tissue on CT and hypodense postcontrast, isoor hypoechoic with US, and hypoto isointense on T1and hypointense on T2-weighted MRI and show minimal contrast enhancement. They are located in either renal parenchyma or renal hilum; at the latter location encasement of hilar vessels or excretory tract compression and obstruction is common. In the absence of therapy, calcifications suggest necrosis.

Infection

Bacterial allograft pyelonephritis leads to acute renal failure. Some patients also have superimposed acute rejection. Viral infections, such as with cytomegalovirus, are also associated with rejection. Therefore, in these patients both imaging and graft biopsy are necessary. A relationship between urinary tract infection and chronic rejection has been raised.

Especially in children, vesicoureteral reflux is a risk factor for pyelonephritis and graft dysfunction. Comparing voiding cystourethrography and contrast enhanced voiding US in adults with transplanted kidneys and suspected of reflux, US sensitivity and specificity for detecting reflux were 93% and 95%, respectively (144); agreement between the two studies was 95%.An antireflux reimplantation procedure is helpful in some of these children.

Tuberculous nephropathy is uncommon in renal transplant patients, even if they have had chest tuberculosis preoperatively (145).

ADVANCED IMAGING OF THE ABDOMEN

Some of these patients develop acute rejection and undergo steroid therapy. Also, a normal graft function does not exclude tuberculous infection.

Failed Transplant

Failed renal allografts are usually left in situ and the patient then undergoes either dialysis or retransplantation. Most of these failed kidneys are asymptomatic and gradually shrink in size, and a number eventually calcify. Some develop fatty infiltration and become hydronephrotic, findings detectable with imaging.Acute enlargement of a failed transplant should suggest an infarct and hemorrhage.

Other Complications

Torsion of an intraperitoneal renal transplant should be suspected if abnormal perfusion is associated with a change in renal axis.

Occasionally acute tubular necrosis develops in a newly transplanted allograft kidney following unrelated surgery; Tc-99m-MAG3 scintigraphy detects focal acute tubular necrosis.

Not all pain in these patients is related to a transplant; right lower quadrant pain in renal transplant patients can be secondary to acute appendicitis and related conditions.

Post–Bone Marrow Transplant

Acute renal failure developed in roughly 25% of bone marrow transplant patients, most often occurring during the first month after transplantation. This complication occurs primarily in allogenic bone marrow transplantation. The etiologies for such failure tend to be multifactorial and include nephrotoxicity, liver venoocclusive disease, and others.

Nephrectomy

An arteriovenous fistula of the renal pedicle is a rare complication of nephrectomy, at times developing years after a nephrectomy. Turbulent blood flow in the fistula often results in a bruit. With time, the artery feeding a fistula and draining vein dilate and collateral vessels develop. Doppler US should detect these fistulas.

KIDNEYS AND URETERS

Conduits

An ileal conduit is formed after a cystectomy. A not uncommon complication is an ureteroileal stricture. These strictures are amenable to dilation with a balloon catheter, followed by stenting with a double-J stent, with good results. Stents can be inserted through urinary diversion stomas.

Major ureteroileal reflux of a Kock pouch is an occasional complication, and these patients undergo an antireflux ureteroileal implantation. Follow-up of these patients is with a retrograde study to detect any reflux.

An adenocarcinoma within an ileal conduit is a recognized but rare complication years later.

If necessary, a ureteral defect is replaced by an interposed ileal loop (ureteroileoplasty), thus preserving ureter continuity. Several studies suggest that such ileal interposition is a safe and effective procedure.

Some of the complications encountered after ureterosigmoidostomy are pyelonephritis, hyperchloremic metabolic acidosis, incontinence, and a late development of anastomotic colon carcinoma.

A patient with a ureterocutaneostomy developed a squamous cell carcinoma at the stomal site; presumably chronic infection and irritation of the indwelling catheter were factors in carcinoma formation.

Examination and Surgical

Complications

Biopsy

Needle tract seeding after percutaneous biopsy occurs with numerous neoplasms, including even a Wilms’ tumor, and some investigators do not perform pretreatment needle biopsies of renal tumors in children for fear of needle tract tumor seeding.

More hemorrhage, arteriovenous and arteriocaliceal fistulas, and other complications are encountered when renal biopsy is performed with a 14-gauge needle rather than when an 18gauge needle is used. Also, percutaneous renal biopsy can lead to a subcapsular hematoma and hypertension.

An arteriovenous fistula is probably more common than suspected after a renal biopsy. Fistulas also develop secondary to renal surgery. Some fistulas manifest with hematuria (Fig. 10.41), but many patients are asymptomatic. A rare fistula leads to renal ischemia or even hypertension. Some are associated with a pseudoaneurysm.

Color Doppler US readily detects these fistulas and is useful in follow-up. Eventually, most fistulas tend to resolve. If needed, a fistula is treated by superselective angiographic embolization, including transcatheter coil occlusion. Usually such embolization results in limited renal parenchymal loss. Postocclusion hypertension is uncommon.

Catheter and Stent Related

Minor complications of ureteral catheters and stents include hematuria, dysuria, frequency, and flank and suprapubic pain. Major complications encountered are initial catheter malposition, obstruction, stent migration or fracture, necrosis, erosion into adjacent structures, and ureterovascular fistula. Some stents break spontaneously; others are associated with stone formation. A broken stent usually can be removed either by ureteroscopy or by using a percutaneous approach. An uncommon complication is a knot forming in a ureteral catheter. A stiff guidewire advanced through the catheter lumen aids in untying such a knot. Rarer complications include a pelvic abscess and even septic hip arthritis. Blood clots and debris can obstruct the lumen, although flow is often both inside and around a stent. The risk of obstruction is decreased by using a large-bore catheter. Being foreign bodies, they lead to urinary infection and encrustation (Fig. 10.42). Encrustation is minimized by high fluid intake, treating infections vigorously, and routine catheter exchange. Both proximal and distal J-loops minimize but do not prevent stent migration either proximally or distally. Because stents are radiopaque, their position is generally verified with conventional radiography. Computed tomography establishes catheter patency indirectly by revealing an interval decrease in hydronephrosis. If necessary, a voiding cystogram establishes patency because most catheters will reflux. Other tests of catheter

KIDNEYS AND URETERS

patency include Doppler US detection of urinary jets and measurement of the resistance index with Doppler US. Nuclear renography, often combined with a diuretic agent, evaluates patency in an appropriate clinical setting.

Because urethral catheters positioned with a distal tip in the bladder result in reflux, their use is inappropriate if additional reflux is detrimental.

Stent erosion into an adjacent vessel is favored by ischemia—often due to either prior radiation therapy or extensive surgery.

Most ureteral stents are retrieved cystoscopically. Occasionally it is necessary to retrieve a stent using a percutaneous fluoroscopic approach. Some stents remain in place for a number of years and become encrusted. The initial approach to such a chronic stent should be an IV urogram to evaluate renal function and identify any obstruction. With no significant encrustation, stent extraction under fluoroscopic control is generally successful. With encrustation, ESWL can be successful. With a fixed proximal J-curved stent percutaneous removal may be successful.

Vascular Complications

Significant hematuria occasionally develops after an invasive percutaneous renal procedure. Angiography should detect any underlying vascular injury and, if necessary, transarterial embolization with Gelfoam, steel coils, or other material performed.

A rare complication of renal angioplasty is acute pulmonary edema.

Nephrectomy

Either a transabdominal or retroperitoneal approach is used during laparoscopic radical nephrectomy. The incidence of complications and the need for conversion to open surgery decreases with experience. These complications range from access site complications, such as hernia formation and hematoma, to vascular injury, splenic laceration, adrenal injury, and pneumothorax.

Computed tomography reliably identifies postoperative bleeding, urinary leak, or obstruction in these patients.

Nephrostomy

The most common indication for percutaneous nephrostomy is renal collecting system obstruction; an occasional nephrostomy is performed to bypass a ureteral fistula. These common procedures are associated with few serious complications. Transient hematuria is common after the procedure. Occasional hemorrhage requires transfusion. Rare complications include gallbladder puncture and peritonitis and air embolism.

While palliative percutaneous nephrostomy does decompress a more distal malignant obstruction, whether it improves quality of life in patients with an unresectable cancer is another question.

Related to Other Abdominopelvic Surgery

One complication of gynecologic surgery is iatrogenic ureteral injury. The risk of ureteral injury is about 10 times greater during an abdominal hysterectomy than during vaginal surgery; some of these injuries are relatively asymptomatic and lead to a silent kidney loss.

A rare complication is a bladder or ureteroacetabular fistula, often a result of extensive pelvic surgery.

An occasional surgical scar shows uptake of Tc-99m–methylene diphosphonate (MDP).

Ureteroscopy

Possible complications of ureteroscopic calculi removal are perforation, stricture, and even ureter avulsion. Avulsion of the lumbar ureter is related to both ureteroscope and Dormia catheter manipulation. During an iatrogenic ureteral perforation a calculus can be pushed into the retroperitoneum alongside the ureter. Such paraureteral calculi should not result in a subsequent stricture.

Contrast Nephropathy

According to the Contrast Media Safety Committee of The European Society of Urogenital Radiology, hemodialysis and peritoneal dialysis