Hydronephrosis

and Mikolaj Przydacz¹

(1)

Department of Urology, Jewish General Hospital, McGill University, Montreal, QC, Canada

Keywords

HydronephrosisVesicoureteral refluxObstructionUltrasoundComputed tomographyMagnetic resonance imagingIntravenous urogramVoiding cystographyPercutaneous nephrostomyUreteral stentingDouble J stent

Introduction

Hydronephrosis, a dilation of the renal collecting system (renal pelvis and/or calyces), may be diagnosed in patients suffering from neurogenic lower urinary tract dysfunction. One or both kidneys may be affected. If hydronephrosis coexists with a distension of the ureter, the presenting disorder can be termed hydroureteronephrosis. It is important to emphasize that hydronephrosis is an anatomic finding, not a functional diagnosis [1]. If not appropriately treated, this condition can lead to progressive kidney atrophy and functional failure. Parenchyma loss in patients with hydronephrosis is a long, gradual, pathologic process.

Pathophysiology

In patients with neurogenic bladders, significant hydronephrosis can result from either underlying urodynamic dysfunction or already developed complications. Therefore, a dilation of the renal collecting system can be caused by:

Urinary retention (detrusor underactivity or detrusor-sphincter dyssynergia) or primarily generated high bladder pressures (neurogenic detrusor overactivity, detrusor-sphincter dyssynergia, and/or decreased bladder compliance) when the antireflux mechanism of the ureterovesical junction becomes overwhelmed and the elevated pressures are eventually transmitted to the upper tracts (vesicoureteral reflux)
Obstruction of one or both ureters from stones, tumors, infection, urethral stricture, or detrusor thickening from fibrosis (with gradual remodeling of the ureteral orifices and progressive destruction of the bladder wall)
Other abnormalities also seen in the non-neurogenic population (e.g., congenital defects, injury, surgery, radiation therapy, prostatic hypertrophy, retroperitoneal fibrosis)

Diagnosis

Medical History and Physical Examination

Clinical presentation and reported symptoms vary, depending on whether the obstruction is acute or chronic, partial or complete, unilateral or bilateral, or even present or absent. Severity of hydronephrosis is related to the chronicity and degree of obstruction. Importantly, in patients without obstruction to urine flow, hydronephrosis may remain asymptomatic for a long time and the condition is detected on imaging for other reasons or during follow-up monitoring [2].

Rapidly developing obstruction of the renal collecting system often causes severe pain along the flank with radiation toward the ipsilateral groin or lower abdominal quadrant [2]. Nausea and vomiting may also occur. With underlying infectious pathology, patients may present with fever and blood or pus in the urine. When obstruction is subacute to chronic, symptoms may be absent or less intense and non-specific (e.g., dull discomfort).

Carefully conducted medical history should also rule out any possible causes of hydronephrosis not related to neurogenic bladder dysfunction.

Physical examination may not reveal hydronephrosis-related abnormalities but should be performed. Abdominal, pelvic, and genitourinary examinations should be conducted.

Laboratory Testing

If not already obtained by the referring physician , laboratory tests should be performed as soon as reasonably possible. These include:

blood chemistry—creatinine (with calculation of glomerular filtration rate, GFR), blood urea nitrogen, electrolytes (potassium, sodium, chloride, bicarbonate, phosphate, magnesium, calcium)
urinalysis/urine culture with sediment examination

Imaging

Ultrasound

Renal ultrasonography remains a first-line imaging modality in the evaluation of patients suspected of hydronephrosis because of its availability, low cost, safety, and lack of ionizing radiation [1]. Renal ultrasound has been found to be a highly sensitive and specific test for hydronephrosis in both the adult and pediatric population with reported sensitivity and specificity of this modality for hydronephrosis as >90% (Fig. 12.1) [2]. Nevertheless, no consensus exists regarding the standardized definition of hydronephrosis. In daily clinical practice, when a patient presents with hydronephrosis, it is usually classified as mild, moderate, or severe (Fig. 12.2) [3]. The proposed system of assessment includes four grades [4]:

Grade I (mild)—dilation of the renal pelvis without dilation of the calyces
Grade II (mild)—dilation of the renal pelvis with a few but not all calices
Grade III (moderate)—dilation of the renal pelvis with all calices
Grade IV (severe)—dilation of the renal pelvis with all calices and parenchymal atrophy

Fig. 12.1

Hydronephrosis of the right kidney . The renal collecting system is symmetrically dilated, including dilation of the renal calyces and central collecting system

Fig. 12.2

Hydronephrosis grading . Progressive dilation of the intrarenal collecting system and pyelocaliectasis with a progressive reduction of the renal cortical thickness (a). First grade with mild dilation of the intrarenal urinary tract (arrow) (b). Second grade with pyelocaliectasis and normal morphology of the renal calyx (c). Third grade with pyelocaliectasis and renal calyces with a balloon shape (d). Fourth grade with a progressive thinning of the renal parenchyma (arrow) (with permission from Quaia et al. [3])

As intra-observer variations in ultrasound assessment are well known, the results can vary significantly among clinicians. However, severe hydronephrosis can easily be diagnosed with characteristic ultrasound image consisting of collecting system dilation extended into renal parenchyma with cortical loss in long-standing cases. Ultrasound may also help in identifying potential causes of hydronephrosis, but its functionality is limited. Review of the literature revealed that ultrasound has a pooled sensitivity and specificity of 45% and 94%, respectively, for the detection of ureteric calculi, and 45% and 88%, respectively, for renal calculi [5]. It has also been demonstrated that ultrasound overestimates renal stone size compared to computed tomography, particularly for stones 5 mm or less.

Utilization of Doppler function with measurement of blood flow and resistance in the intrarenal arterial waveforms can also be used to assess the impact of hydronephrosis on renal function [6]. Doppler ultrasonography can help in differentiating between acute and chronic hydronephrosis [7, 8]. Ultrasonography with color Doppler function can also reliably identify ureteric jet dynamics in the bladder and help to distinguish between obstructive and non-obstructive hydronephrosis (Figs. 12.3 and 12.4) [9, 10]. Decreased frequency, duration, and peak velocity of ureteral jets indicate obstructive pathology [11]. Of note, this technique requires good hydration of the patient and is limited by the requirement of a normal contralateral collecting system for comparison [1]. Color flow Doppler ultrasound may also support and eventually replace voiding cystourethrogram in the detection of vesicoureteral reflux. When reflux is found in patients with neurogenic disorder, it further contributes to the development of hydronephrosis . The severity of vesicoureteral reflux has been most commonly reported using the classification of the International Reflux Study (Fig. 12.5) [12–14]:

Grade I: reflux into a non-dilated ureter
Grade II: reflux into the renal pelvis and calyces without dilation
Grade III: mild-to-moderate dilation of the ureter, renal pelvis, and calyces with minimal blunting of the fornixes
Grade IV: moderate ureteral tortuosity and dilation of the pelvis and calyces
Grade V: gross dilation of the ureter, pelvis, and calyces; loss of papillary impressions; and ureteral tortuosity

Fig. 12.3

(a) A strong left ureteral jet: pulsatile egress of urine into bladder gives the appearance of a fire-breathing dragon. (b) A strong left ureteral jet (arrows) in a patient with a left double pigtail ureteral stent. Note that the direction of the jet is slightly toward left of bladder and vertical, secondary to changes in the orientation of the orifice with the stent in place (with permission from Eshghi [10])

Fig. 12.4.

(a) Hydronephrosis on the right side with dilation of the renal pelvis due to acute ureteral obstruction . (b) Absence of right ureteral jet (arrow). (c) Presence of a strong left ureteral jet (arrow). (with permission from Eshghi [10])

Fig. 12.5

International Reflux Grading System (reprinted with permission from Cooper [14]. Macmillan Publishers Ltd: Nat Rev Urol. 2009)

It has been shown that color Doppler ultrasonography can diagnose all grade IV and V refluxes, almost 90% of grade III, more than 80% of grade II, and almost 60% of grade I [15].

Computed Tomography

Computed tomography (CT) of the abdomen helps to localize potential causes of hydronephrosis. CT scans without intravenous contrast medium provide a precise location of a ureteral calculus and has become the imaging modality of choice for patients suspected of having ureteral obstruction [1]. CT has a reported sensitivity of 96% for stone detection with a specificity and positive predictive value of 100% [16]. If renal function is normal, CT urography (without and then with contrast and delayed images of the urinary tract) should be considered in order to generate greater anatomic definition. Multidetector CT urography is now considered the imaging modality of choice for a comprehensive evaluation of the urinary tract (Figs. 12.6 and 12.7) [1, 17, 18]. In patients with contraindications for CT scan or when results from previous imaging methods are inconclusive, magnetic resonance imaging (MRI) should be considered. The reported sensitivity of MRI in diagnosing upper urinary tract obstruction is up to 100% [19] but clinicians should remember that MRI cannot directly detect a stone, which is a frequent cause of hydronephrosis in neurogenic patients (Fig. 12.8) [20]. The sensitivity of MRI for detecting stones has been reported to be 68.9–81% [21, 22]. Sensitivity can be improved up to 90–100% with gadolinium-enhanced excretory MRI [23].

Fig. 12.6

Bilateral moderate hydronephrosis of patient after spinal cord injury (difficult patient positioning). There is also marked diffuse thickening of the bladder wall: (a, b) coronal view, (c, d) sagittal view

Fig. 12.7

Neurogenic bladder with bilateral vesicoureteral reflux . Coronally reconstructed CT image shows the bilaterally dilated ureters (arrows) due to vesicoureteral reflux and diffuse wall thickening of the bladder (with permission from Sung and Sung [18])

Fig. 12.8

Excessive signal intensity of urine. (a) Static-fluid MR urography (single-shot thick slab fast spin-echo sequence) shows the hydroureteronephrosis. The dilated ureter terminates just before the ureterovesical junction. However, no filling defects are seen within the ureter. (b, c) Thin section T2-weighted fast spin-echo images document the dilated pelvis and ureter and a small stone with low signal intensity in the distal ureter (arrow in b) (with permission from Pozzi Mucelli [20])

Other Techniques

Intravenous urogram (excretory urography) is useful for assessing the anatomical location of the obstruction (Fig. 12.9). In past decades considered the imaging modality of choice for evaluating urinary tract obstruction , including urolithiasis, it has now been widely replaced by CT scans. The utility of intravenous urograms is also limited in patients with renal insufficiency. However, it may still be considered in individuals with contraindications for increased radiation exposure. Cystogram/voiding cystogram constitutes the present-day gold standard approach to reflux detection (Fig. 12.10) [12]. Voiding cystourethrogram is also obtained to exclude anatomical abnormalities such as posterior urethral valves and bladder neck obstruction. Vesicoureteral reflux may also be revealed by videourodynamics (Fig. 12.11). Antegrade (the injection of contrast into the upper collecting system through a percutaneous approach) or retrograde (the injection of contrast into the upper collecting system through a cystoscopic approach) ureterograms may be considered during further work-up.

Fig. 12.9

Intravenous urography. Images showing different views of hydronephrosis of the left kidneys

Fig. 12.10

Cystogram (contrast bladder filling phase) with vesicoureteral reflux : (a) bilateral, (b) unilateral

Fig. 12.11

Videourodynamics with vesicoureteral reflux

Treatment

The primary approach to treatment of hydronephrosis in patients suffering from neurogenic bladder is proper management of the underlying urodynamic pathology [24]. Appropriate therapeutic measures should transform a high-pressure system to a low-pressure reservoir, thus subsequently treating diagnosed hydronephrosis. Studies have shown that intra detrusor injections of botulinum toxin A have a positive influence on vesicoureteral reflux and renal pelvis dilation in patients with neurogenic detrusor overactivity [25–28]. New onset or worsening of pre-existing vesicoureteral reflux after botulinum toxin injections have not been currently reported [24]. Treatment of obstructed hydronephrosis focuses on the removal of the obstruction, and specific treatment depends on the cause of the obstruction and where the obstruction lies. The renal parenchyma thickness is a predictor of the ability to recover renal function despite the introduced treatment [29]. However, renal drainage might become necessary. Indications for kidney drainage include: rising creatinine, pyelonephritis (febrile infection), and intractable pain [30, 31]. Immediate (emergency) kidney drainage should specifically be considered if obstruction involves a solitary functioning kidney or both kidneys simultaneously, when hydronephrosis is accompanied by fever and/or complicated by undrained infection, as well as in patients presenting with symptoms of acute renal failure (oliguria/anuria, nausea, vomiting, pedal edema, and altered sensorium) and/or electrolyte imbalance and acidosis. [1, 32].

Drainage

Kidney drainage is necessary to relieve pain and prevent renal deterioration. It may serve as a temporary measure (before a definitive procedure for underlying cause of hydronephrosis) or permanent solution. In cases of obstructive pathology, hydronephrosis may persist after relief of the obstructing cause.

Treatment involves percutaneous nephrostomy tubes and ureteral double J stents. Both methods have been demonstrated to be equally effective in relieving an obstructed collecting system with similar complication rates [33]. The choice of drainage depends on the indication for the procedure, the patient’s medical condition, the patient’s individual anatomy, and preferences of both patient and physician [34].

Percutaneous Nephrostomy

Percutaneous nephrostomy may be used to drain the upper urinary tract collecting system when obstruction occurs at an intrarenal location, at the ureteropelvic junction, or anywhere in the ureter [34]. The general scheme of this technique is to place a needle (trocar) and nephrostomy tube through the skin into the collecting system of the upper urinary tract (Fig. 12.12) [35]. Advantages of percutaneous nephrostomy include: