Introduction
Background
Acute obstructive uropathy is a commonly encountered condition, occurring in both inpatient and outpatient settings. Unilateral obstruction to urinary outflow typically occurs, with little if any change in measured renal function in a healthy individual. However, the less common bilateral form results in measurable changes in kidney function.
Pathophysiology
In a normally functioning kidney, urine formed within the tubular system empties into the calyces, where pacemaker sites generate peristaltic activity to propel urine into the pelvis. Urine is conveyed into the ureter, where further peristalsis moves it in boluses into the bladder. The collecting system has a baseline pressure of 0-10 cm water, with peristaltic waves producing pressures in the range of 20-60 cm water.
In acute obstruction, the pressures within the collecting system and ureters above the point of obstruction can increase dramatically. Pressures in excess of 80 cm water may be generated. Intratubular pressure also is elevated, leading to progressive renal impairment in the face of continued obstruction. The kidney attempts to maintain excretory function by mechanisms for urine resorption, termed renal backflow. This includes pyelosinus backflow, the most important in acute obstruction. Urine extravasates from a rupture of a calyceal fornix into the perinephric spaces where it is resorbed, thus decompressing the collecting system. Pyelovenous (a unique pathway), pyelotubular, and pyelolymphatic backflow are other compensatory mechanisms.
The degree of obstruction is an important determining factor in the development of nephropathy, with impairment of function occurring in a more complete obstruction. Experiments conducted by Vaughan and Gillenwater on dogs revealed a direct relationship between the duration of obstruction and loss of renal function.1 Complete recovery of function occurred when the obstruction was relieved in 7 days. However, permanent loss of function was observed when the obstruction continued for 42-56 days.
Acute obstruction also produces alterations in blood flow, leading to ischemia. The renal capsule is a fixed container, and only with long-standing obstruction will the kidney significantly enlarge. Angiography may reveal slight splaying apart and compression of arteries. However, there is marked compression of the intrarenal veins, giving them a spidery appearance.
These effects are believed to be the result of interstitial edema secondary to increased hydrostatic pressure within the tubules. Other factors that are involved in the development of dysfunction include the health of the kidney preceding the insult, as well as coexisting illnesses. Of special significance is a superimposed infection that can cause a rapid deterioration in renal function.
Frequency
United States
Unilateral obstructive uropathy is predominantly the result of urolithiasis, which has an annual incidence of 1 in 1000. Approximately 12% of the population will develop calculi before age 70 years. The less common bilateral form has an estimated incidence of 1 in 10,000 in the general population.2
Ureteral injury occurs as a complication of gynecologic surgery in approximately 2% of patients. With abdominal radical hysterectomy, a 10-15% incidence rate has been reported.
Mortality/Morbidity
Morbidity is related to the etiology, degree, and duration of the obstruction. A stone that lodges in the urinary tract is associated with excruciating pain and discomfort. Concurrent infection may produce both localized sequelae such as perinephric abscess and systemic manifestations such as sepsis. Mortality can result from untreated superimposed infection. As the kidney has no pain receptors, it is only with pressure distention of the capsule, the site of the receptors, that pain is appreciated.
- The most common cause of acute obstructive uropathy is an impacted calculus. In 70% of patients, the level of obstruction is at the ureterovesical junction; in the remainder of patients, the ureteropelvic junction or mid ureter is the point where calculi tend to lodge. Most calculi (90%) contain calcium, combined with oxalate and/or phosphate. While metabolic disorders such as hyperparathyroidism can contribute to stone formation, idiopathic hypercalciuria occurs in approximately 50% of patients with stones. Magnesium ammonium phosphate (struvite) stones are the next most common type; they are observed most frequently laminated with calcium apatite. They form in the alkaline environment created by urease-splitting bacteria, especially Proteus species, and commonly produce the staghorn appearance of the pelvocalyceal system. Uric acid stones are less common, at least in the United States.
- Hyperuricemic conditions such as gout only account for a small minority of patients.3 An acidic environment is necessary for uric acid stones to form. These stones, along with the less common xanthine and matrix calculi, appear radiolucent on plain radiographs. Cystine stones are less opaque than calcium stones and may be difficult to demonstrate on plain radiographs.
- Intraluminal obstruction also may be the result of blood clots and mucosal edema. These may occur with passage of calculi but also can occur following instrumentation of the ureter, trauma, or anticoagulant therapy. Sloughed papillae secondary to papillary necrosis occasionally may cause symptoms and signs of acute obstruction. Less commonly, in patients with diabetes and in debilitated patients, fungal balls from Candida or Aspergillus may produce obstruction.
- Ureteral ligation is a well-recognized complication of abdominal and pelvic surgery, especially gynecologic interventions. In addition, distal ureteral ischemia may result during pelvic lymphadenectomy, as small blood vessels are stripped along with the lymphatics. Pelvic trauma, both penetrating and blunt, may produce obstruction to urine outflow from rupture of the ureter or compression from a retroperitoneal hematoma.4 Extrinsic compression from an abscess or inflammatory mass in patients with appendicitis, pancreatitis, or Crohn disease also has been reported.
Race
Stones are more common in whites, and in the United States, they are observed more frequently in the southeastern part of the country.
Sex
Urolithiasis occurs in a male-to-female ratio of 3:1. Iatrogenic ureteral injury, mainly ligation, is more common in women, as it is most frequently observed with gynecologic surgery. With the other etiologies, the relative incidence likely is variable.
Age
Renal calculi usually appear in the third decade, with a recurrence rate in untreated patients of 50% in 10 years.
Anatomy
The kidney is divided into a cortex and medulla. The renal pyramids are located within the medullary portion; they contain the loops of Henle and collecting ducts. At the apical portion of the pyramids, cone-shaped papillae convey urine from the distal collecting ducts into the minor calyx. The peripheral projection of a minor calyx termed the fornix produces the characteristic cup-shaped appearance.
The minor calyces are arranged into 3 groups: the upper, lower, and interpolar groups. Anterior and posterior calyces are found within each group. Approximately 4-6 minor calyces converge into a major calyx or infundibulum, which in turn forms the renal pelvis. The fat-containing renal sinus envelops the entire collecting system.
The pelvis tapers smoothly into the ureter at the ureteropelvic junction (UPJ). The ureter travels inferiorly along the psoas muscle, crossing over medially, anterior to the iliac bifurcation. It then descends posteriorly and laterally, inserting into the posteroinferior bladder wall at the level of the trigone. At the ureterovesical junction (UVJ), the ureter is most narrow; it also narrows at the UPJ, the area overlying the iliac bifurcation, and the point where the right ureter passes through the root of the mesentery.
Presentation
A patient with a calculus lodged in the urinary tract can present with acute, colicky flank pain that radiates to the groin.5 Initial management usually involves pain control and aggressive hydration. Patients generally are treated as outpatients unless a complicated course necessitates hospitalization.
With other causes of acute obstruction, no symptoms may be present. If bilateral obstruction is present, anuria or oliguria is the earliest indication. Often, especially in inadvertent ligation of a single ureter, no detectable change in urine output occurs. As a result, the obstruction remains unrecognized for 10-30 days postsurgery, at which time flank pain and fever alert the physician to this complication.
Related eMedicine topics:
Pregnancy and Urolithiasis
Diabetic Nephropathy
Hyperparathyroidism
Crohn Disease
Preferred Examination
The advent of helical CT has dramatically altered the diagnostic imaging approach to patients presenting with acute flank pain. Unenhanced helical CT has both a high sensitivity of 95-98% and a high specificity of 96-100% in detecting ureteral calculi in the acute setting.6,7,8,9 Both calcified and noncalcified calculi may be identified, along with the location and size of the stone. Secondary signs of obstructive uropathy, including hydronephrosis, perinephric and periureteral stranding, as well as ureterectasis, are well demonstrated on CT.10
Several recent reports compared unenhanced helical CT with intravenous urography (IVU), the established criterion standard in evaluating the genitourinary system.11,12 CT has been shown to be more sensitive in detecting and characterizing ureteral calculi and at least as sensitive in demonstrating the presence of obstructive uropathy.13 Additionally, CT may be performed rapidly, in approximately one third the time of an IVU study, and does not require the use of IV contrast material. The ability to diagnose noncalculus etiologies, as well as evaluate other intra-abdominal pathologies that may mimic renal colic, affords CT an invaluable advantage.
Levine et al reported the sensitivity of plain radiography in detecting ureteral calculi to be approximately 45% and recommended that noncontrast helical CT replace the kidneys, ureters, bladder (KUB) film as the initial and possibly only imaging study.9 While CT appears to have replaced plain radiography and IVU in the initial evaluation of acute flank pain, these modalities remain involved in the follow-up evaluation of stone disease, as well as surgical and interventional planning.
In the evaluation of acute flank pain, ultrasound (US) is limited primarily to pregnant patients.14 While US demonstrates renal calculi, it is poor at detecting ureteral stones. Doppler sonography has been suggested as a method of indirectly determining obstruction by measuring the resistive index in renal arteries and evaluating the direction and magnitude of ureteral jets.15,16,17
In nuclear medicine, the passage of radionuclide agents through the urinary tract is monitored with a gamma camera. Outlines of the kidney and ureter are generated, and a point of obstruction may be evident. More importantly, it provides physiologic information regarding the function and dynamics of the urinary system. The technique of choice in the evaluation of obstruction is diuresis renography, which is performed with technetium-99m-labeled mercaptoacetyltriglycine (99m Tc-MAG3) in most centers.18,19
Diuresis renography is not performed routinely in acute ureteral colic, as CT usually provides the necessary information. However, it may be important in documenting return of renal function in patients for whom urologic intervention is required. Renography with Lasix is useful in determining whether pelvocalyceal system dilatation, often observed on a screening study such as US, is obstructive or nonobstructive in nature.
Ultrafast T1- and T2-weighted techniques such as spoiled gradient echo (T1) and single-shot fast spin echo (T2) have been reported to be highly sensitive and specific for determining the presence of both ureteral calculi and acute obstructive uropathy. However, as with US, in magnetic resonance urography (MRU), the degree of dilatation must be sufficient to use the native urine as a contrast agent.20
Limitations of Techniques
An inherent limitation of unenhanced helical CT is in providing functional information. The severity of obstruction may be inferred by the presence of perinephric stranding, which is believed to result from forniceal rupture or inflammation in the perirenal fat from high calyceal pressures. The absence of this finding, as well as the other signs of obstruction, does not exclude a significant obstruction.
Performing a contrast-enhanced CT may provide greater physiologic information by demonstrating an obstructive nephrogram and pyelosinus extravasation of contrast material. An important consideration in choosing this modality is the significant radiation dose to the patient, compared to an intravenous pyelogram (IVP). This disadvantage restricts its use, especially in pregnant and pediatric patients.
It has been reported that in patients with ureteral calculi, stone size alone determines initial treatment of patients, with no correlation found between severity of obstruction as suggested by CT and the decision to treat conservatively or perform an intervention. The authors therefore suggest that nonenhanced helical CT is adequate for the initial diagnosis and treatment of patients with stone disease.
Plain radiography and IVU have similar drawbacks, including lower sensitivity because of superimposition of bone and other calcified structures and obscuring bowel pattern. They are limited by stone size (<4 mm) and patient habitus. IVU, although providing both anatomic and physiologic information, has the added disadvantage of being time consuming and dependent on administration of contrast material, with its potential complications. It is also dependent on renal function, as the use of the test is greatly diminished when the serum creatinine concentration is elevated when the patient has both intrinsic renal disease and an acute obstruction.
US evaluates the ureters and detects calculi poorly. The accuracy of US in diagnosing obstruction in the setting of acute flank pain was found to be approximately 66%. This is directly related to the anatomic nature of the examination, which relies mainly on the presence of hydronephrosis to make the diagnosis. In early obstruction, up to 36 hours after onset, no dilatation of the collecting system may be present, and a false-negative study may result.
Doppler sonography is both operator dependent and time consuming. Determination of ureteral jets and the resistive index has not been adopted into widespread clinical use for acute obstruction because of technical limitations and questionable accuracy. Most pathologic processes decrease renal perfusion and thus increase the resistive index (RI).
Diuresis renography, a physiologically driven study, depends on renal function. If marked impairment of bilateral renal function is present, an indeterminate study results. In patients who are dehydrated, the expected response to the diuretic may not be evident, leading to an inconclusive study.
The use of MRU in the acute setting of flank pain also is limited. Studies comparing MRU to CT and IVU reveal that MRU misses small calculi and mild dilatation. In addition, it is time consuming and expensive and is limited to special situations, such as pregnant patients.
Differential Diagnoses
More on Obstructive Uropathy, Acute |
 Overview: Obstructive Uropathy, Acute |
| Imaging: Obstructive Uropathy, Acute |
| Follow-up: Obstructive Uropathy, Acute |
| Multimedia: Obstructive Uropathy, Acute |
| References |
| Next Page » |
References
Vaughan ED Jr, Gillenwater JY. Recovery following complete chronic unilateral ureteral occlusion: functional, radiographic and pathologic alterations. J Urol. Jul 1971;106(1):27-35. [Medline].
Kaya M, Boleken ME, Soran M, Kanmaz T, Yücesan S. Acute renal failure due to bilateral uric acid lithiasis in infants. Urol Res. Jun 2007;35(3):119-22. [Medline].
Bergman SM, Frentz GD, Wallin JD. Ureteral obstruction due to blood clot following percutaneous renal biopsy: resolution with intraureteral streptokinase. J Urol. Jan 1990;143(1):113-5. [Medline].
Kluger Y, Altman GT, Deshmukh R. Acute obstructive uropathy secondary to pelvic hematoma compressing the bladder: report of two cases. J Trauma. Sep 1993;35(3):477-8. [Medline].
Haddad MC, Sharif HS, Shahed MS. Renal colic: diagnosis and outcome. Radiology. Jul 1992;184(1):83-8. [Medline].
Smith RC, Verga M, McCarthy S. Diagnosis of acute flank pain: value of unenhanced helical CT. AJR Am J Roentgenol. Jan 1996;166(1):97-101. [Medline].
Smith RC, Verga M, Dalrymple N. Acute ureteral obstruction: value of secondary signs of helical unenhanced CT. AJR Am J Roentgenol. Nov 1996;167(5):1109-13. [Medline].
Dalrymple NC, Verga M, Anderson KR. The value of unenhanced helical computerized tomography in the management of acute flank pain. J Urol. Mar 1998;159(3):735-40. [Medline].
Levine JA, Neitlich J, Verga M. Ureteral calculi in patients with flank pain: correlation of plain radiography with unenhanced helical CT. Radiology. Jul 1997;204(1):27-31. [Medline].
Fielding JR, Fox LA, Heller H. Spiral CT in the evaluation of flank pain: overall accuracy and feature analysis. J Comput Assist Tomogr. Jul-Aug 1997;21(4):635-8. [Medline].
Smith RC, Rosenfield AT, Choe KA. Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology. Mar 1995;194(3):789-94. [Medline].
Sourtzis S, Thibeau JF, Damry N. Radiologic investigation of renal colic: unenhanced helical CT compared with excretory urography. AJR Am J Roentgenol. Jun 1999;172(6):1491-4. [Medline].
Mostafavi MR, Ernst RD, Saltzman B. Accurate determination of chemical composition of urinary calculi by spiral computerized tomography. J Urol. Mar 1998;159(3):673-5. [Medline].
Swanson SK, Heilman RL, Eversman WG. Urinary tract stones in pregnancy. Surg Clin North Am. Feb 1995;75(1):123-42. [Medline].
Hill MC, Rich JI, Mardiat JG. Sonography vs. excretory urography in acute flank pain. AJR Am J Roentgenol. Jun 1985;144(6):1235-8. [Medline].
Laing FC, Jeffrey RB Jr, Wing VW. Ultrasound versus excretory urography in evaluating acute flank pain. Radiology. Mar 1985;154(3):613-6. [Medline].
Tublin ME, Dodd GD 3rd, Verdile VP. Acute renal colic: diagnosis with duplex Doppler US. Radiology. Dec 1994;193(3):697-701. [Medline].
Kletter K, Nurnberger N. Diagnostic potential of diuresis renography: limitations by the severity of hydronephrosis and by impairment of renal function. Nucl Med Commun. Jan 1989;10(1):51-61. [Medline].
Taylor A. Radionuclide renography: a personal approach. Semin Nucl Med. Apr 1999;29(2):102-27. [Medline].
Hussain S, O''Malley M, Jara H. MR urography. Magn Reson Imaging Clin N Am. Feb 1997;5(1):95-106. [Medline].
Traubici J, Neitlich JD, Smith RC. Distinguishing pelvic phleboliths from distal ureteral stones on routine unenhanced helical CT: is there a radiolucent center?. AJR Am J Roentgenol. Jan 1999;172(1):13-7. [Medline].
Blake SP, McNicholas MM, Raptopoulos V. Nonopaque crystal deposition causing ureteric obstruction in patients with HIV undergoing indinavir therapy. AJR Am J Roentgenol. Sep 1998;171(3):717-20. [Medline].
Merrilees DA, Kennedy-Smith A, Robinson RG. Obstructive uropathy as the etiology of renal failure in ovarian hyperstimulation syndrome. Fertil Steril. Jul 10 2007;[Medline].
Beige J, Kreutz R, Rothermund L. [Acute renal failure: pathophysiology and clinical management]. Dtsch Med Wochenschr. Nov 2007;132(48):2569-78. [Medline].
Miklovicova D, Cervenova O, Cernianska A, Jancovicova Z, Dedik L, Vasilenkova A. Long-term follow-up of renal function in patients after surgery for obstructive uropathy. Pediatr Nephrol. Feb 20 2008;[Medline].
Karam AR, Birjawi GA, Sidani CA, Haddad MC. Alternative diagnoses of acute appendicitis on helical CT with intravenous and rectal contrast. Clin Imaging. Mar-Apr 2007;31(2):77-86. [Medline].
Further Reading
Keywords
acute hydronephrosis, acute obstructive nephropathy, renal calculi, nephrolithiasis/urolithiasis, urinary obstruction
