The Renal Sinus, Pelvocalyceal System, and Ureter

Renal Sinus Lipomatosis

Fat is the largest single constituent of the renal sinus and it is readily visible with ultrasound (US), CT, and magnetic resonance imaging (MRI). Normally, the quantity of fat in the renal sinus gradually increases with age. Very little, if any, renal sinus fat is present at birth, whereas approximately 20% of total renal volume is due to renal sinus fat in the adult. With aging, fat proliferates in the renal sinus to compensate for atrophy of the renal parenchyma. Fatty proliferation that leads to mass effect on the intrarenal collecting system is usually referred to as renal sinus lipomatosis ( Box 5-1 ). This mass effect manifests radiographically as thinning and stretching of the infundibula resulting in a spidery appearance of the collecting system. Mass effect from renal sinus lipomatosis rarely leads to symptoms because calyceal obstruction does not result from simple sinus lipomatosis. While renal sinus lipomatosis is commonly seen in elderly individuals due to renal parenchymal atrophy, fatty proliferation can also be accelerated in patients with increased exogenous or endogenous steroids. In these patients, the volume of atrophied renal parenchyma is replaced with a similar volume of renal sinus fat. In the extreme, replacement lipomatosis occurs (see Box 5-1 ). This term describes massive renal sinus lipomatosis in association with severe parenchymal atrophy ( Fig. 5-6 ), usually the result of severe renal infection or vascular ischemia. Radiographically, replacement lipomatosis appears as a massive overgrowth of the renal sinus in association with marked thinning of the renal parenchyma. The proliferation of renal sinus fat, which is dispersed throughout the renal sinus, leads to attenuation and stretching of the collecting system without a dominant focal area of mass effect. This appearance is typical of replacement lipomatosis or extensive renal sinus lipomatosis and should not be confused with focal fat-containing neoplasms arising in the renal sinus.

Renal Sinus Cysts

Renal sinus cysts are common ( Box 5-2 ). True renal sinus cysts, also known as peripelvic cysts , are usually small and multiple, and they grow to insinuate themselves throughout the renal sinus in a distribution similar to that seen with renal sinus lipomatosis ( Fig. 5-7 ). These fluid-containing cysts are thought to be congenital, lymphatic in origin, and usually asymptomatic. Occasionally, these cysts can lead to focal hydronephrosis, which necessitates cyst drainage and sclerosis. With US, these water-containing structures may mimic hydronephrosis ( Fig. 5-8 ) because they often grow in parallel to the normal calyces and renal pelvis. With urography or excretory-phase CT, the extraluminal position of these cysts is readily apparent ( Fig. 5-8 ), which cannot be mistaken for hydronephrosis.

Parapelvic cysts are simple renal cysts arising in the medial renal parenchyma that protrude into the renal sinus. Despite their similar location in the renal pelvis, their origin appears to be different from that of peripelvic cysts. Parapelvic cysts, like other simple cysts of the renal parenchyma, are usually discrete, spherical, water-density masses ( Figs. 5-1 and 5-9 ). They are usually solitary or few in number, unlike peripelvic cysts. Diagnostically, parapelvic cysts should meet all the radiologic criteria for simple cysts elsewhere in the kidney. Unfortunately, because of their central location, it is often difficult to demonstrate the complete absence of internal echoes with US. Occasionally, CT or MRI may be necessary to confirm the benign nature of these lesions and to exclude a parenchymal neoplasm.

Less commonly, a urinoma may arise in the renal sinus. Urinomas are usually associated with ureteral obstruction secondary to stone disease with resulting collecting system rupture. Occasionally, renal sinus urinomas may result from trauma causing collecting system laceration. Extravasated urine usually diffuses throughout the renal sinus and into the perinephric space without causing a dominant uriniferous cyst. Occasionally a focal urinoma can develop, but spontaneous resolution usually occurs with adequate decompression of the urinary tract, and additional treatment is rarely required.

Renal Sinus Masses

Vasculopathic processes that involve the renal sinus include renal artery aneurysms and arteriovenous malformations. These lesions often arise in or protrude into the renal sinus, leading to mass effect. They are readily identifiable with CT, MRI, US, and conventional angiography. Endovascular treatment can be performed with catheter-introduced embolic materials to occlude aneurysms or vascular malformations.

Most neoplasms involving the renal sinus do so by secondary invasion ( Box 5-3 ) because primary neoplasms of the renal sinus are rare. Renal parenchyma neoplasms such as renal cell carcinoma commonly extend into the renal sinus and lead to focal hydronephrosis or calyceal displacement. These lesions can be readily diagnosed with cross-sectional imaging, and their true site of origin is usually not in doubt. One tumor of particular interest is the cystic nephroma, also referred to as a multilocular cystic nephroma (MLCN). This tumor has a bimodal peak of incidence, occurring predominately in young male children and middle-aged women. This cystic lesion has numerous thick septa and it arises from the renal parenchyma. MLCN has a predilection to protrude and, in fact, to herniate into the renal sinus. This feature is characteristic of MLCN, although not truly diagnostic because the more common renal cell carcinoma occasionally mimics this appearance.

Renal sinus lymphoma is one of the more common renal manifestations of lymphoma. It usually spreads directly and contiguously from retroperitoneal lymph nodes. This solid neoplastic tissue infiltrates and replaces the normal constituents of the renal sinus ( Fig. 5-10 ), often with contiguous spread into the perinephric space. This situation is most common in patients with advanced non-Hodgkin lymphoma. Rarely lymphoma can primarily involve the ureter. This typically appears as marked concentric thickening of the ureteral wall. Even though the thickening can appear dramatic, obstruction is generally absent or minimal ( Fig. 5-11 ), in contrast to urothelial carcinomas that usually obstruct the ureter with a comparable degree of growth.

Finally, neoplasms arising primarily in the renal sinus are rare but include benign tumors such as angiomyolipoma, hemangioepithelioma, and teratoma, as well as tumors, both benign and malignant, arising from mesenchymal tissue. These mesenchymal tumors may originate from smooth muscle, fat, fibrous tissue, or nerve fiber. Radiographically, the characteristics of these tumors are often nonspecific. Mesenchymal tumors arising in the renal sinus appear identical to those arising elsewhere.

Congenital Anomalies

Congenital variants of the pelvocalyceal system and the ureter are common. Duplication anomalies are represented by a spectrum of findings. Mild anomalies include bifid renal pelvis and incomplete ureteral duplications. These anomalies, which are seen in up to 4% of the general population, develop when two or more ureteral buds form from the mesonephric duct. Incomplete ureteral duplication usually represents a clinically unimportant finding but, on occasion, yo-yo reflux can occur. Urine descending down one ureter refluxes up the second ureter during its relaxation phase of peristalsis. The yo-yo reflux can cause urinary infections and flank pain.

Complete ureteral duplications, two separate full-length ureters draining a single kidney, are substantially less common than incomplete duplications. However, the clinical significance of complete duplication anomalies is considerably greater than that of incomplete duplications. According to the Weigert-Meyer rule, the upper pole of the kidney drains through the ectopic ureter that inserts inferiorly and medially to the normal ureteral insertion point on the bladder, or it may have an extravesical insertion. This ectopic ureter often obstructs ( Figs. 5-13 and 5-14 ). The ureter draining the lower pole is usually normal in appearance and physiology but does have a higher incidence of vesicoureteral reflux ( Fig. 5-15 ).

In complete ureteral duplications, the ectopic ureter is associated with ureteroceles at the UVJ in one third of patients and result in obstruction of the ureter. It has been hypothesized that ureteroceles form as a result of a failure of the normal epithelial membrane to recanalize between the bladder and the ureter (Chwalla membrane). The ectopic ureterocele represents marked submucosal dilatation of the intramural ureter at the UVJ. The ureterocele is a dilated, spherical, urine-filled extension of the ureter protruding into the bladder lumen (see Figs. 5-13 and 5-14 ).

The ureterocele may cause distortion and obstruction of the other ipsilateral ureteral orifice. In addition, large ureteroceles may prolapse and obstruct the urethral orifice, leading to bladder outlet obstruction and bilateral ureteral dilatation. The obstructed pelvocalyceal system can push the lower pole calyces downward causing the drooping lily appearance of the unobstructed lower pole collecting system (see Fig. 5-15 ). Ectopic ureteroceles are seen predominantly in the female population; the female-to-male ratio is 4:1. Ectopic ureteroceles are rare in African Americans.

Instead of an inferomedial bladder insertion, the ectopic ureter may have an extravesical insertion of its caudal end. In female patients, the ectopic ureter often inserts into the bladder neck, the urethra, or directly into the vagina ( Fig. 5-16 ). Because these areas are chronically exposed to infection, fibrosis and stenosis often develop in the lower ureter and lead to hydro­nephrosis of the upper moiety. On the contrary, extravesical insertion of the ureter in female patients is frequently associated with chronic incontinence. Classically, extravesical ureter insertion in a female causes the triad of continuous urine leakage, abnormal voiding, and some degree of functional renal impairment. In male patients, the ureter never inserts inferiorly to the external sphincter, so it is protected from infection, and incontinence is rarely a symptom.

Another form of ureterocele is the orthotopic type. This is also known as a simple or adult-type ureterocele. Although thought to be a congenital anomaly, this asymptomatic ureterocele is usually only identified as an incidental, asymptomatic finding in adult patients. An orthotopic ureterocele is a cystic dilatation and invagination of the intramural segment of the ureter where it joins the bladder. The cause of orthotopic ureteroceles is unknown but it may be related to partial persistence of Chwalla membrane, an embryologic vestige. As ureteroceles grow, they are more commonly associated with complications. Ureteroceles larger than 2 cm in the greatest diameter are more likely to be associated with ureteral obstruction, and stone formation within the ureterocele. Radiographically, orthotopic ureteroceles have a bulbous appearance as they prolapse into the bladder lumen. Typically, this is described as a cobra-head or spring-onion appearance ( Figs. 5-17 and 5-18 ). It is easy to think of this anomaly as similar to a prolapsing hemorrhoid seen in the colon. A thin membrane representing the wall of the ureter and bladder mucosa surrounds the focally dilated lumen.

Radiographically, it is important to distinguish orthotopic ureteroceles from pseudoureteroceles. Pseudoureteroceles suggest underlying pathology such as infiltrating transitional cell carcinoma, or ureteral stone impaction. With an orthotopic ureterocele, the radiolucent line surrounding the ureterocele will be no thicker than 2 mm and will be uniform throughout. Irregularity or focal thickening of this radiolucent margin ( Fig. 5-19 ) suggests pathology and is indicative of a pseudoureterocele.

When evaluating congenital anomalies of the urinary tract, such as duplications, it is important to remember that up to one third of patients have a second coexisting significant congenital abnormality of the urinary tract. Duplication anomalies are frequently associated with strictures of the UPJ, in addition to the previously described ureteroceles, and refluxing UVJs.

Although duplication anomalies of some degree are seen commonly in everyday practice, other supernumerary anomalies of the ureter and pelvocalyceal system are distinctly uncommon. Triplication, tetrafication, and pentafication anomalies have all been described. Because of the rarity of these anomalies, little is known about their association with reflux, ureteroceles, and other urinary tract abnormalities. It is known that the Weigert-Meyer rule is violated in at least half the cases of triplication and greater supernumerary anomalies.

Another uncommon form of ureteral duplication occurs when incomplete development results in a congenital ureteral diverticulum. This most likely develops from a duplicated ureteric bud when one moiety fails to connect with the metanephric blastema, and as a result, a blind-ending segment of the ureter is connected to the otherwise normal ureter. Radiographically, the blind-ending ureter appears either saccular or cylindrical and it usually communicates with the normal ureter ( Fig. 5-20 ). Although this anomaly is of little clinical significance, the ureteral diverticulum can form a reservoir for relatively static urine, thereby increasing the risk of infection and stone disease.

Congenital abnormalities of the ureter, which typically result in hydronephrosis or ureteral dilatation, include congenital strictures, retrocaval ureter, primary megaureter, prune-belly syndrome, and vesicoureteral reflux. When hydroureteronephrosis is detected, attention should be directed to identify the cause of dilatation. A search should be made to define the transition point from dilated ureter to normal ureter. Congenital strictures of the ureter are the most common congenital anomalies of the ureter. These fibrotic strictures may develop at any site along the course of the ureter ( Fig. 5-21 ), but the vast majority develops near the UPJ and at the UVJ. In fact, UPJ obstruction is the most common cause of fetal hydronephrosis. The etiology of these strictures is unclear. However, it has been postulated that in utero ureteral ischemia leads to the formation of a focal stricture. The degree of hydroureteronephrosis varies, as does the clinical significance of these strictures. The most extreme form of UPJ stricture results in a nonfunctioning, hydronephrotic form of multicystic dysplastic kidney. Milder forms of UPJ stricture often go unnoticed until adulthood. Typical symptoms of a UPJ stricture are flank pain, hematuria, infection, or stone disease. The delayed presentation of UPJ stricture in an adult is common. This is thought to be due to gradual worsening of UPJ scarring due to intermittent subclinical inflammation or due to increased urine production with growth. Anomalous accessory renal arteries crossing and compressing the UPJ cause approximately 5% of UPJ strictures. The diagnosis of UPJ stricture caused by a crossing artery is of clinical significance because surgeons generally select open pyeloplasty repair over percutaneous endopyelotomy in these situations. An anomalous vessel can be confirmed with CT ( Fig. 5-22 ). The diagnosis of nephrolithiasis associated with a UPJ stricture is also clinically significant. The combination of these two abnormalities encourages clinicians to choose percutaneous nephrolithotomy and endopyelotomy for treatment. In these cases, renal calculi can be removed and endopyelotomy can be performed percutaneously during the same procedure.

The frequency of multiple coexistent urinary tract anomalies is again an important concept when a UPJ stricture is detected. Up to 25% of patients with congenital UPJ obstruction will have a contralateral congenital urinary tract anomaly. Frequently associated anomalies include contralateral multicystic dysplastic kidney and contralateral UPJ obstruction. Detection of these contralateral anomalies may be greatly significant and may affect treatment. For example, detection of a multicystic dysplastic kidney opposite to a UPJ stricture may lead to more aggressive treatment of the UPJ stricture.

Other abnormalities of the ureter can be classified into several groups according to radiologic pattern. These are abnormalities of ureteral course or caliber, and filling defects. Similar abnormalities can be seen in the renal pelvis and calyces.

Deviations of the Ureter

The ureter may be deviated medially or laterally, and deviation can occur along its entire course or segmentally. Abnormalities of ureteral course are rarely due to primary ureteral disease but usually result from abnormalities extrinsic to the ureter. In most cases a definitive diagnosis of the underlying pathology cannot be made without cross-sectional imaging techniques. When ureteral deviation is visualized by retrograde pyelography, CT or MR scanning is usually indicated to further evaluate the adjacent retroperitoneal structures.

Upper Ureter Medial Deviation

Some patterns of ureteral deviation are characteristic and indicative of a single diagnosis, and therefore negate the need for further evaluation. For example, abrupt medial deviation of the upper segment of the right ureter with a course resembling a fishhook, with the medial portion located medial to the adjacent verte­bral pedicle, is diagnostic of a retrocaval ureter ( Fig. 5-23 and Box 5-4 ). This is readily detectable with CTU or MRU if the course of the ureter is carefully traced.

In another typical pattern, both ureters are medially deviated in their midsegments, usually at the L3 to L5 level, with associated hydronephrosis and ureteral narrowing ( Figs. 5-24 and 5-25 ). This pattern is typical of retroperitoneal fibrosis. Unfortunately, medial deviation of the ureter occurs in only approximately one half of retroperitoneal fibrosis cases, and it alone is not diagnostic of this disease. In addition, retroperitoneal fibrosis can involve one ureter and spare the contralateral ureter. Cross-sectional imaging is often helpful to confirm the abnormality or guide biopsy in these patients.

Lower Ureter Medial Deviation

Symmetric medial deviation of the pelvic ureters associated with fat proliferation in the pelvis is typical of pelvic lipomatosis ( Fig. 5-26 ), which is an idiopathic process in most cases. It is more commonly seen in young, African-American men, and it can lead to bilateral hydroureteronephrosis. It usually causes extrinsic compression of the bladder resulting in the characteristic pear- or tear-shaped bladder ( Fig. 5-27 ). Often, the rectum is also involved, and concentric narrowing and straightening of the rectosigmoid colon may occur. These patients often have difficulties with voiding and recurrent urinary tract infections. Cystitis glandularis is a premalignant bladder lesion that is associated with pelvic lipomatosis.

Following abdominoperineal resection, the pelvic ureters will lie more medial than normal ( Fig. 5-28 ). There is loss of the normal lateral curvature of the ureteral course in patients following this form of surgery. Typically, upon entering the pelvis, the ureters course directly inferior to the bladder. A history, or radiographic evidence, of substantial previous abdominal surgery is usually evident.

Upper Ureter Lateral Deviation

Unilateral lateral deviation of the upper two thirds of the left ureter is often due to abdominal aortic aneurysm ( Fig. 5-29 ). Atherosclerotic calcifications of the aorta are often seen in association with this type of deviation. Focal lateral deviation of the upper left ureter in a young man suggests lymph node metastases from a testicular carcinoma ( Figs. 5-30 and 5-31 ). These neoplasms typically spread through lymphatics. A primary path of lymphatic drainage of the left testicle parallels the left testicular vein and empties to nodes near the left renal vein. Bilateral deviation of the upper ureters is most commonly due to hypertrophy of the psoas muscles ( Fig. 5-32 ) and usually occurs in muscular young men. The enlarged muscles are often visible on an abdominal radiograph and on CT. This form of deviation is asymptomatic and incidentally detected. If the psoas muscle is wider than 8 cm from the edge of a vertebral body to its lateral edge, at the upper edge of the iliac bone, then psoas hypertrophy is likely to be the cause of ureteral deviation. Often the pelvic ureters are also medially deviated in these muscular individuals because of large iliacus and obturator internus muscles, with resulting displacement of the ureters. An alternative cause of this pattern of ureteral deviation is massive lymphadenopathy. Massive retroperitoneal and pelvic lymphadenopathy causes lateral deviation of the upper ureters and medial deviation of the lower ureters ( Fig. 5-33 ). It is typically seen in patients with lymphoma or chronic leukemia. Another typical pattern of ureteral deviation is seen after mobilization and peritonealization of the ureters as treatment for retroperitoneal fibrosis. In these patients, the ureters exhibit marked lateral deviation ( Fig. 5-34 ) in association with other postsurgical findings (i.e., surgical clips or wire sutures). In this surgery, the ureters are dissected away from the retroperitoneal fibrotic process, mobilized laterally, and wrapped in peritoneum or omentum to protect them from further involvement with the retroperitoneal disease.

Lower Ureter Lateral Deviation

Several other conditions are associated with deviations that have a typical radiographic pattern. Focal lateral deviation of the ureter at the level of the upper sacrum ( Fig. 5-35 ) is usually due to aneurysm of the iliac artery. A common site of bladder diverticulum is just inferior to the UVJ. A diverticulum in this specific location is often referred to as a Hutch diverticulum . When large, these diverticula will deviate the ureter. Typically, this leads to focal medial deviation of the ureter ( Fig. 5-36 ) as it nears the UVJ. This is usually a unilateral process. Segments of the ureter may herniate leading to typical deviation patterns. Ureteral hernias are in general more common in middle-aged men, and are usually unilateral involving the right ureter only. With ureterosciatic herniation, the ureter deviates laterally into the greater sciatic foramen ( Fig. 5-37 ). This leads to a focal lateral deviation of the ureter in the pelvis. Inguinal and femoral herniation of the ureter also occurs. With inguinal herniation, the ureter in the pelvis focally deviates inferiorly ( Fig. 5-38 ) into the inguinal canal. Femoral hernias have a similar appearance, but the herniation occurs in a more lateral location. Ureteral herniation may be asymptomatic, and these hernias often go unrecognized unless surgical repair is undertaken. In some cases, ureteral hernias cause ureteral obstruction.

The other causes of ureteral deviation have nonspecific findings radiographically. The presence of one of these nonspecific forms of deviation should prompt a CT scan of the abdomen and pelvis to establish a definitive diagnosis or to exclude significant retroperitoneal disease.

Abnormalities of Ureteral Caliber

Caliber abnormalities of the ureter encompass both dilatation and narrowing. Causes of ureteral dilatation and narrowing are summarized in Boxes 5-5 and 5-6 . Obviously, some overlap occurs between these two classes of abnormalities because ureteral narrowing often leads to obstruction with dilatation. However, ureteral dilatation can be seen without associated ureteral obstruction ( Box 5-7 ), in which case it may be due to mechanical distention from intraluminal mass, diminished tone of the ureteral musculature, or increased intraluminal volume in the ureter. The ureter may be universally or segmentally dilated.