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Diseases of the Ureter and Renal Pelvis
In the author’s surgical pathology practice at a large tertiary teaching medical center, the upper urinary tract specimens account for 5% to 10% of the genitourinary specimens. The major differences in clinical behavior and management between lesions of the upper and lower urinary tract include:
- 1.
Urothelial carcinoma of the upper tract is generally considered to be more aggressive than its counterpart in the lower tract, probably because of the thinner wall with less physical deterrence and late detection of the disease, which therefore is more advanced at presentation. Sixty percent of the cases are invasive on first diagnosis, compared with 15% in the bladder tumors.
- 2.
The muscular invasion by urothelial carcinoma, which is generally considered an indication for bladder resection (cystectomy), is not the only indicator for radical resection of the upper tract disease. Urothelial carcinoma in situ, noninvasive papillary urothelial carcinoma (either low-grade or high-grade), and urothelial carcinoma with lamina propria invasion may be subjected to radical resection in the upper urinary tract.
- 3.
The ureter is a small tubular structure, but it is important for transport of a large volume of urine daily. A benign lesion of the ureter, such as fibrosis or inflammation, without timely and appropriate treatment could obstruct the urinary outflow and subsequently lead to failure and loss of a vital organ (i.e., the kidney).
- 4.
A lesion of the renal pelvis, such as inflammation, abscess, or a tumor, may not only be mistaken for a renal parenchymal lesion but also may result in severe damages to the renal parenchyma and eventually in the loss of the kidney.
- 5.
A renal parenchymal lesion such as renal cell carcinoma may protrude into the renal pelvis, mimicking the renal pelvic lesion.
- 6.
The biopsy specimen obtained from endoscopy is often small and contains biopsy artifact that makes an accurate diagnosis challenging and occasionally impossible.
Anatomy and Histology
The upper urinary tract includes the ureters, renal pelvis, and calyces. The renal pelvis is a funnel-shaped structure that occupies most of the hilar region of the kidney ( Fig. 8-1 , A ). The renal pelvis, which connects to the ureter distally and branches into the renal calyces proximally ( Fig. 8-1 , B ), collects urine from the renal collecting duct system. The ureters are a pair of tubular structures that connect the renal pelvis to the bladder ( Fig. 8-1 , C ). The two ureteral openings within the bladder wall are the ureteral orifices. The upper tract is covered by urothelium ( Fig. 8-1 , A to C ), which is essentially the same as the urothelium that covers the bladder and is composed of umbrella cells and basal cells. The renal pelvis is surrounded by a layer of loose subepithelial connective tissue (lamina propria) and a couple of layers of smooth muscle (muscularis propria) that may be discontinuous in some areas ( Fig. 8-1 , A ). The visceral portion of the renal pelvis ( Fig. 8-1 , B, right ) that covers the renal papillae has scant subepithelial connective tissue and no muscularis propria, and the urothelium is continuous with the epithelia of the renal collecting ducts. The muscularis propria of the ureter consists of longitudinal inner and circular outer layers, which are not well separated. It is much thinner than the counterpart of the bladder ( Fig. 8-1 , C ).
Benign Nonneoplastic Lesions
Chronic Ureteritis and Pyelitis
Chronic ureteritis and pyelitis are characterized by lymphocyte-predominant chronic inflammatory infiltrates in the ureter and renal pelvis that can be caused by several different etiologies associated with or without obstruction. The obstruction of urinary outflow may be caused by calculi, fibrotic stenosis, and tumors in the upper tract; and benign prostatic hyperplasia, tumors, or other lesions in the lower tract. Nonobstructive etiology is related to irritation from calculi, tumors, catheterization or stents, or other instrumentation and surgical procedures. Hematogenous chronic ureteritis caused by systemic infections and progression from acute ureteritis and pyelitis is rare. Ureteritis caused by vesicoureteral reflux accounts for a subset of chronic ureteritis. Granulomatous ureteritis can be related to previous bacille Calmette-Guérin (BCG) treatment for superficial urothelial carcinoma of the upper urinary tract. Other causes of granulomatous inflammation, including previous biopsy (postbiopsy granuloma) or nonspecific (idiopathic) cause, are far less common in the upper tract than in the lower tract. Ureteritis may be present with or without pyelitis.
Clinical Features
Symptoms and signs of infection such as fever and flank pain may be present in the early phase. Urinary obstruction and hydronephrosis may be detected with imaging studies. The signs of renal failure are present in the late stage of the disease. In the case of ureteral carcinoma or calculi, the symptoms may be related to the presence and extent of the tumor and the location and size of the calculi.
Pathology Features
Gross Findings
Chronic ureteritis is characterized by the thickening of the ureteral wall and roughness of the mucosal surface ( Fig. 8-2 , A ). The ureter proximal to the involvement, the renal calyces, and the renal pelvis may be dilated. Stones may be seen. In the late stage of the disease, renal cortical scarring or thinning may be prominent.
Microscopic Findings
Chronic ureteritis and pyelitis is characterized by varying degree, but predominantly lymphocytic inflammatory infiltrates ( Fig 8-2 , B ). Occasionally granulomatous inflammation can be seen in the renal pelvis ( Fig. 8-2 , C ) or ureter and is often related to the BCG treatment for superficial urothelial carcinoma in the upper urinary tract.
Prognosis and Treatment
The prognosis depends on the etiology. In most cases, removal of the primary insult, such as a calculus, suffices. In other cases, severe unabating ureteritis may lead to loss of the kidney.
Lithiasis (Renal and Ureteral Calculi)
When urine becomes oversaturated, the crystal material deposits to form a nucleation of the stone (calculus), which continues to grow to a significant size and to cause obstruction. In most cases, the grossly recognizable calculi are located in the renal pelvis or calyces.
Clinical Features
Small calculi may pass through the urinary tract without causing symptoms. Calculi larger than 2 to 3 mm may be lodged in the renal calyces, renal pelvis, or ureter. Typical presentation includes severe flank pain (renal colic) associated with nausea, vomiting, and fever. Red blood cells, crystals, and casts may be seen on urine examination. Urine culture results may be positive if the calculi are associated with bacterial infection. Imaging studies are diagnostic.
Pathology Features
Gross Findings
Calculi can be of variable sizes and shapes ( Fig. 8-3 , A ). Large staghorn calculi can be found in the renal pelvis ( Fig. 8-3 , B ). Sometimes, numerous sand-like stones can block the ureteral lumen ( Fig. 8-3 , C ). Hydronephrosis and hydroureter are present if calculi are large and obstructive.
Microscopic Findings
Calculi are not subjected to histologic analysis; rather they are often sent for chemical analysis for their composition. Microcalcification and calcium oxalate crystals seen microscopically in the kidney parenchyma are not considered to be nephroliths. Changes associated with lithiasis, such as acute and chronic pyelonephritis, ulceration, and fibrosis, can be seen in the renal pelvis or ureter. Urothelial atypia, either flat or papillary, associated with lithiasis can be surprisingly severe and may be confused with low-grade urothelial carcinoma.
Prognosis and Treatment
Medical treatment includes alkalization of urine and administration of diuretics. Extracorporeal shockwave lithotripsy and ureteroscopic extraction can remove the calculi should symptomatic calculi fail to pass spontaneously. Nephrectomy may be necessary if noninvasive procedures fail.
Hydronephrosis and Hydroureter
Hydronephrosis and hydroureter are conditions of pathologic dilation and distension of the renal pelvis and calyces and ureter caused by downstream urinary outflow obstruction.
Clinical Features
The common lesions that cause hydronephrosis and hydroureter are calculi, tumors, overlying vessels, inflammation and scarring in the upper urinary tract; and bladder dysfunction in adults; ureteral orifice obstruction by tumor and ureteral and urethral developmental anomalies in infants; and obstruction of the prostatic urethra by benign prostatic hyperplasia in the lower tract.
The urinary obstruction can be complete or partial. Hydronephrosis and hydroureter can be unilateral or bilateral. Imaging studies can provide diagnostic information.
Early on, renal function is preserved. However, renal failure and end-stage kidney disease ensue in the advanced stage.
Pathology Features
Gross Findings
Dilated renal pelvis and calyces, or hydronephrosis, can be focal or severe, with or without dilation of the ureter (hydroureter) ( Fig. 8-4 , A ). Renal parenchyma is compressed and atrophic in the late phase of the disease. The associated conditions such as calculi or tumors may be observed in the renal pelvis or in downstream organs.
Microscopic Findings
The renal pelvis and ureter typically show chronic inflammation, edema, and fibrosis ( Fig. 8-4 , B ). The surface urothelium is often attenuated and may be denuded. Reactive changes are often present. In advanced stage, the renal parenchyma displays end-stage changes that include thyroidization and glomerulosclerosis.
Prognosis and Treatment
Identification and treatment of the causal condition such as stones, chronic pyelonephritis, benign prostatic hyperplasia, or carcinoma is important. Unilateral hydronephrosis and hydroureter have a better prognosis if the obstruction can be corrected surgically. Drainage with a catheter can provide temporary relief.
Reactive Urothelial Changes
Similar to the urinary bladder, reactive urothelial changes such as von Brunn nests and cystitis cystica et glandularis occur in the upper urinary tract in response to acute or chronic stimuli. Most cases with these reactive urothelial lesions are asymptomatic. Some patients may have nonspecific symptoms and signs that include microscopic hematuria, mild pain, and infection. Other patients may have symptoms that are associated with such inciting conditions as carcinoma and calculi.
Most of these lesions are not grossly visible. Occasionally, small erythematous, granular, and opaque mucosal areas can be seen. Rarely papillary or dome-shaped mass lesions are visible on cystoscopy. Histologic features of reactive epithelial changes are identical to those lesions in the bladder. Florid von Brunn nests that comprise numerous solid nests of urothelial cells with minimal cytologic atypia in the lamina propria are occasionally observed ( Fig. 8-5 ). Squamous metaplasia, keratinizing or nonkeratinizing type, and intestinal metaplasia are also seen occasionally.
These reactive urothelial lesions per se are benign and necessitate no treatment, although underlying etiology should be sought and dealt with.
Fibroepithelial Polyp of the Ureter and Renal Pelvis
Fibroepithelial polyp of the upper tract is a benign urothelium-lined polypoid mesenchymal proliferation of uncertain etiology. It may occur at any age, but it is the most common benign polypoid lesion of the ureter in children. It is slightly more common in males, with a 3:2 male-to-female ratio. It frequently involves the upper ureter but may occur anywhere along the urinary tract from renal pelvis to urethra. The presenting symptoms depend on the location but commonly include hematuria and urinary tract infection. This lesion is benign, and complete excision is curative.
Grossly, the lesion is a polypoid firm mass that ranges from 0.5 mm to 12 cm. Microscopically, it is composed of a loose fibrovascular stroma with overlying benign urothelium in a finger-like or polypoid architecture ( Fig. 8-6 ). The urothelium may show squamous metaplasia, glandular differentiation, and denudation. The stroma shows variable degree of fibrosis, smooth muscle, and vasculature proliferation. Degenerative atypia may be seen in both epithelium and stroma. Polypoid ureteritis and pyelitis can mimic the fibroepithelial polyp but are usually associated with marked inflammation and edema. Benign urothelial papillomas show urothelia proliferation forming papillae with thin and delicate fibrovascular cores. The stroma is not prominent.
Ureteropelvic Junction Obstruction
Ureteropelvic junction obstruction is a clinical condition defined by the obstruction of the urinary outflow from the renal pelvis to the proximal ureter as a result of blockage at the ureteropelvic junction.
Clinical Features
Most cases are sporadic. The condition affects patients of any age. In children, it remains the most common cause of hydronephrosis; it affects 1 in 1000 to 2000 newborns, predominantly boys. The left side is more likely to be affected, but bilateral involvement is reported in 30% of cases. Etiologically, defects in muscularis are seen in 75% of cases. Other causes include extrinsic compression by aberrant renal vessels and abnormally high ureteral insertion.
In adults, ureteropelvic junction obstruction is most often unilateral, and it affects females preferentially. Calculi, inflammation, scarring from prior surgery, and tumors are among the most common causes.
Patients often have periodic abdominal and flank pain and urinary tract infection. Rarely, massive hydronephrosis has been reported. Five to 20% of affected children also have other urologic malformations.
Pathology Features
Gross Findings
The ureteropelvic junction is narrowed and has a funnel-shaped appearance. The pelvic and ureteral mucosa in the proximity of the obstruction site may be edematous. Valve-like intraluminal protrusion of edematous mucosa or muscularis may be seen.
Microscopic Findings
There is segmental attenuation or absence of smooth muscle, which is replaced by fibrosis (see Fig. 8-7 ). Because of the fibrosis, the ureteral lumen or the renal pelvic space is distorted (see Fig. 8-7 , A ). The urinary tract proximal to the obstruction displays prominent mucosal edema and muscular hyperplasia.
Prognosis and Treatment
Therapy should be aimed at correction of the underlying etiology, with conservative treatment and prophylactic antibiotics for cases with moderately decreased renal function. Surgical intervention is indicated for patients with significant loss of renal function or cases suspicious for neoplastic conditions.
Idiopathic Retroperitoneal Fibrosis
Idiopathic retroperitoneal fibrosis is an inflammatory and fibrosing disease of unknown etiology that involves retroperitoneal structures including the kidney and the ureter.
Clinical Features
This disease has a wide age range with a peak in the 4th to 6th decades. Men are affected more frequently than women. Most symptoms are nonspecific, including flank and abdominal pain. The symptoms of ureteral obstruction can be quite severe. Imaging studies show poorly defined mass lesions around the kidney or proximal ureter. Recently, this disease has been reported with patients with immunoglobulin G (IgG) 4–related fibrosing diseases.
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