Hydronephrosis describes hydrostatic dilation of the
renal pelvis and
calyces as a result of obstruction to urine flow downstream. Alternatively, hydroureter describes the dilation of the
ureter
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...
, and hydronephroureter describes the dilation of the entire
upper urinary tract (both the renal pelvicalyceal system and the ureter).
Signs and symptoms
The signs and symptoms of hydronephrosis depend upon whether the obstruction is
acute
Acute may refer to:
Science and technology
* Acute angle
** Acute triangle
** Acute, a leaf shape in the glossary of leaf morphology
* Acute (medicine), a disease that it is of short duration and of recent onset.
** Acute toxicity, the adverse eff ...
or
chronic, partial or complete, unilateral or bilateral. Hydronephrosis that occurs acutely with sudden onset (as caused by a
kidney stone
Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
) can cause intense pain in the flank area (between the hips and ribs) known as a
renal colic
Renal colic is a type of abdominal pain commonly caused by obstruction of ureter from dislodged kidney stones. The most frequent site of obstruction is the vesico-ureteric junction (VUJ), the narrowest point of the upper urinary tract. Acute ob ...
. Historically, this type of pain has been described as "Dietl's crisis". Conversely, hydronephrosis that develops gradually over time will generally cause either a dull discomfort or no pain. Nausea and vomiting may also occur. An obstruction that occurs at the urethra or bladder outlet can cause pain and pressure resulting from distension of the bladder. Blocking the flow of urine will commonly be prone to
urinary tract infection
A urinary tract infection (UTI) is an infection that affects part of the urinary tract. When it affects the lower urinary tract it is known as a bladder infection (cystitis) and when it affects the upper urinary tract it is known as a kidne ...
s which can lead to further development of stones, fever, and
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
or
pus in the urine. If complete obstruction occurs, a
postrenal kidney failure (obstructive nephropathy) may follow.
Blood tests may show impaired kidney function (elevated
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
or
creatinine
Creatinine (; ) is a breakdown product of creatine phosphate from muscle and protein metabolism. It is released at a constant rate by the body (depending on muscle mass).
Biological relevance
Serum creatinine (a blood measurement) is an importa ...
) or electrolyte imbalances such as
hyponatremia
Hyponatremia or hyponatraemia is a low concentration of sodium in the blood. It is generally defined as a sodium concentration of less than 135 mmol/L (135 mEq/L), with severe hyponatremia being below 120 mEq/L. Symptoms can be a ...
or
hyperchloremic metabolic acidosis.
Urinalysis
Urinalysis, a portmanteau of the words ''urine'' and ''analysis'', is a panel of medical tests that includes physical (macroscopic) examination of the urine, chemical evaluation using urine test strips, and microscopic examination. Macroscopic ...
may indicate an elevated
pH due to the secondary destruction of
nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ...
s within the affected kidney, which impairs acid excretion. Physical examination in a thin patient may detect a palpable abdominal or flank mass caused by the enlarged kidney.
Causes
Hydronephrosis is the result of any of several abnormal pathophysiological occurrences. Structural abnormalities of the junctions between the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
,
ureter
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...
and
bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...
that lead to hydronephrosis can occur during fetal development. Some of these congenital defects have been identified as inherited conditions, however, the benefits of linking genetic testing to early diagnosis have not been determined. Other structural abnormalities could be caused by injury, surgery, or radiation therapy.
The most common causes of hydronephrosis in children are anatomical abnormalities. These include
vesicoureteral reflux
Vesicoureteral reflux (VUR), also known as vesicoureteric reflux, is a condition in which urine flows retrograde, or backward, from the bladder into one or both ureters and then to the renal calyx or kidneys. Urine normally travels in one directio ...
,
urethral stricture
A urethral stricture is a narrowing of the urethra, the tube connected to the bladder that allows the passing of urine. The narrowing reduces the flow of urine and makes it more difficult or even painful to empty the bladder.
Urethral stricture is ...
, and
stenosis. The most common cause of hydronephrosis in young adults is
kidney stone
Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
s. In older adults, the most common cause of hydronephrosis is
benign prostate hyperplasia (BPH), or
intrapelvic neoplasm
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s such as
prostate cancer.
Compression of one or both ureters can also be caused by other developmental defects not completely occurring during the fetal stage such as an abnormally placed vein, artery, or tumor. Bilateral compression of the ureters can occur during
pregnancy
Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occur ...
due to enlargement of the
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
. Changes in hormone levels during this time may also affect the muscle contractions of the bladder, further complicating this condition.
Sources of obstruction that can arise from other various causes include kidney stones,
blood clots or
retroperitoneal fibrosis
Retroperitoneal fibrosis or Ormond's disease is a disease featuring the proliferation of fibrous tissue in the retroperitoneum, the compartment of the body containing the kidneys, aorta, renal tract, and various other structures. It may present wi ...
.
The obstruction may be either partial or complete, and can occur anywhere from the
urethral meatus
The urinary meatus, (, ) also known as the external urethral orifice, is the opening of the urethra. It is the point where urine exits the urethra in both sexes and where semen exits the urethra in males. The meatus has varying degrees of sensiti ...
to the
renal calyces
The renal calyces are chambers of the kidney through which urine passes. The minor calyces surround the apex of the renal pyramids. Urine formed in the kidney passes through a renal papilla at the apex into the minor calyx; two or three minor c ...
. Hydronephrosis can also result from the retrograde flow of urine from the bladder back into the kidneys (
vesicoureteral reflux
Vesicoureteral reflux (VUR), also known as vesicoureteric reflux, is a condition in which urine flows retrograde, or backward, from the bladder into one or both ureters and then to the renal calyx or kidneys. Urine normally travels in one directio ...
), which can be caused by some of the factors listed above as well as
compression of the bladder outlet into the
urethra
The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra c ...
by
prostate enlargement
Benign prostatic hyperplasia (BPH), also called prostate enlargement, is a noncancerous increase in size of the prostate gland. Symptoms may include frequent urination, trouble starting to urinate, weak stream, inability to urinate, or loss o ...
or
fecal impaction
A fecal impaction is a solid, immobile bulk of feces that can develop in the rectum as a result of chronic constipation.
A related term is fecal loading which refers to a large volume of stool in the rectum of any consistency. Fecal impaction is ...
in the
rectum (which sits immediately behind the prostate), as well as abnormal contractions of bladder
detrusor muscle
The detrusor muscle, also detrusor urinae muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to stor ...
s resulting from neurological dysfunction (
neurogenic bladder Neurogenic bladder dysfunction, or neurogenic bladder, refers to urinary bladder problems due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination. There are multiple types of neurogenic bladde ...
) or other muscular disorders.
Pathophysiology
Hydronephrosis is caused by obstruction of urine before the renal pelvis. The obstruction causes dilation of the
nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ...
tubules and flattening of the lining of the tubules within the kidneys which in turn causes swelling of the renal calyces.
Hydronephrosis can either be
acute
Acute may refer to:
Science and technology
* Acute angle
** Acute triangle
** Acute, a leaf shape in the glossary of leaf morphology
* Acute (medicine), a disease that it is of short duration and of recent onset.
** Acute toxicity, the adverse eff ...
or
chronic. In acute hydronephrosis full recovery of kidney function is seen. However, with chronic hydronephrosis, permanent loss of kidney function is seen even once obstruction is removed.
Obstruction that occurs anywhere along the upper urinary tract will lead to increased pressure within the structures of the kidney due to the inability to pass urine from the kidney to the bladder. Common causes of upper tract obstruction include obstructing stones and
ureteropelvic junction
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epith ...
(UPJ) obstruction caused by intrinsic narrowing of the ureters or an overlying vessel.
Obstruction occurring in the lower urinary tract can also cause this increased pressure through the reflux of urine into the kidney. Common causes include bladder dysfunction (such as
neurogenic bladder Neurogenic bladder dysfunction, or neurogenic bladder, refers to urinary bladder problems due to disease or injury of the central nervous system or peripheral nerves involved in the control of urination. There are multiple types of neurogenic bladde ...
) and urethral obstruction (such as posterior urethral valves in male infants) or compression (such as from prostatic hypertrophy in older male adults).
In pregnancy, dextrorotation (rotation to the right) of the uterus can cause compression on the right ureter, thus making hydronephrosis more common in right kidney than left kidney. Besides, hormones such as oestrogen, progestrerone, and
prostaglandin can cause ureter dilatation, thus causing hydronephrosis despite the absence of visible obstruction along the urinary tract.
Diagnosis
![Phydronephrosisfromstone](https://upload.wikimedia.org/wikipedia/commons/7/7b/Phydronephrosisfromstone.png)
Prenatal diagnosis is possible,
and in fact, most cases in pediatric patients are incidentally detected by routine screening ultrasounds obtained during pregnancy. However, approximately half of all prenatally identified hydronephrosis is transient, and resolves by the time the infant is born, and in another 15%, the hydronephrosis persists but is not associated with urinary tract obstruction (so-called non-refluxing, non-obstructive hydronephrosis). For these children, regression of the hydronephrosis occurs spontaneously, usually by age 3. However, in the remaining 35% of cases of prenatal hydronephrosis, a pathological condition can be identified postnatally.
Diagnostic workup depends on the age of the patient, as well as whether the hydronephrosis was detected incidentally or prenatally or is associated with other symptoms. Blood tests (such measurement of creatinine) are typically indicated, though they must be interpreted cautiously. Even in cases of severe unilateral hydronephrosis, the overall kidney function may remain normal since the unaffected kidney will compensate for the obstructed kidney.
Urinalysis is usually performed to determine the presence of blood (which is typical for kidney stones) or signs of infection (such as a positive leukocyte esterase or nitrite). Impaired concentrating ability or elevated urine pH (distal renal tubular acidosis) are also commonly found due to tubular stress and injury.
Imaging studies
Imaging studies, such as an
intravenous urogram
Pyelogram (or pyelography or urography) is a form of imaging of the renal pelvis and ureter.
Types include:
* Intravenous pyelogram – In which a contrast solution is introduced through a vein into the circulatory system.
* Retrograde pyelogram ...
(IVU),
renal ultrasonography
Renal ultrasonography (Renal US) is the examination of one or both kidneys using medical ultrasound.
Ultrasonography of the kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most ...
,
CT, or
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
, are also important investigations in determining the presence and/ or cause of hydronephrosis. Whilst ultrasound allows for visualisation of the ureters and kidneys (and determine the presence of hydronephrosis and / or hydroureter), an IVU is useful for assessing the anatomical location of the obstruction.
Antegrade or retrograde pyelography will show similar findings to an IVU but offer a therapeutic option as well. Real-time ultrasounds and
Doppler ultrasound
Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of a ...
tests in association with
vascular resistance
Vascular resistance is the resistance that must be overcome to push blood through the circulatory system and create flow. The resistance offered by the systemic circulation is known as the systemic vascular resistance (SVR) or may sometimes be cal ...
testing helps determine how a given obstruction is effecting urinary functionality in hydronephrotic patients.
[Kay, Robert, M.D. "Evaluation of Hydronephrosis in Children" in ''Urology Secrets'', 2nd Ed. by Resnick & Novick; 1999, Hanley & Belfus]
In determining the cause of hydronephrosis, the location of obstruction can be determined with a Whittaker (or pressure perfusion) test, wherein the collecting system of the kidney is accessed
percutaneous {{More citations needed, date=January 2021
In surgery, a percutaneous procedurei.e. Granger et al., 2012 is any medical procedure or method where access to inner organs or other tissue is done via needle-puncture of the skin, rather than by using ...
ly, and the liquid is introduced at high pressure and constant rate of 10ml/min while measuring the pressure within the
renal pelvis. A rise in pressure above 22 cm H
2O suggests that the urinary collection system is obstructed. When arriving at this pressure measurement, bladder pressure is subtracted from the initial reading of internal pressure. (The test was first described by Whittaker in 1973 to test the
hypothesis
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
that patients whose hydronephrosis persists after the
posterior urethral valves have been
ablated usually have ureters that are not obstructed, even though they may be
dilated.)
[
Kay recommends that a ]neonate
An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
born with untreated in utero
''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albin ...
hydronephrosis receive a renal ultrasound within two days of birth. A renal pelvis greater than 12mm in a neonate is considered abnormal and suggests significant dilation and possible abnormalities such as obstruction or morphological abnormalities in the urinary tract.[
The choice of imaging depends on the clinical presentation (history, symptoms and examination findings). In the case of ]renal colic
Renal colic is a type of abdominal pain commonly caused by obstruction of ureter from dislodged kidney stones. The most frequent site of obstruction is the vesico-ureteric junction (VUJ), the narrowest point of the upper urinary tract. Acute ob ...
(one sided loin pain usually accompanied by a trace of blood in the urine) the initial investigation is usually a spiral or helical CT scan. This has the advantage of showing whether there is any obstruction of flow of urine causing hydronephrosis as well as demonstrating the function of the other kidney. Many stones are not visible on plain X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
or IVU but 99% of stones are visible on CT and therefore CT is becoming a common choice of initial investigation. CT is not used, however, when there is a reason to avoid radiation exposure, e.g. in pregnancy.
For incidentally detected prenatal hydronephrosis, the first study to obtain is a postnatal renal ultrasound, since as noted, many cases of prenatal hydronephrosis resolve spontaneously. This is generally done within the first few days after birth, although there is some risk that obtaining an imaging study this early may miss some cases of mild hydronephrosis due to the relative oliguria of a newborn. Thus, some experts recommend obtaining a follow-up ultrasound at 4–6 weeks to reduce the false-negative rate of the initial ultrasound. A voiding cystourethrogram
In urology, voiding cystourethrography (VCUG) is a frequently performed technique for visualizing a person's urethra and urinary bladder while the person urinates (voids). It is used in the diagnosis of vesicoureteral reflux (kidney reflux), am ...
(VCUG) is also typically obtained to exclude the possibility of vesicoureteral reflux or anatomical abnormalities such as posterior urethral valves. Finally, if hydronephrosis is significant and obstruction is suspected, such as a ureteropelvic junction (UPJ) or ureterovesical junction (UVJ) obstruction, a nuclear imaging study such as a MAG-3 scan is warranted.
File:BilateralHydroMark.png, CT scan of bilateral hydronephrosis due to a bladder cancer
File:Hydronephrosis.png, Massive hydronephrosis as marked by the arrow.
File:UOTW 10 - Ultrasound of the Week 1.webm, Renal ultrasonography
Renal ultrasonography (Renal US) is the examination of one or both kidneys using medical ultrasound.
Ultrasonography of the kidneys is essential in the diagnosis and management of kidney-related diseases. The kidneys are easily examined, and most ...
of hydronephrosis[
File:UOTW 10 - Ultrasound of the Week 3.webm, Stone causing hydronephrosis][
File:UOTW 10 - Ultrasound of the Week 2.webm, Stone causing hydronephrosis][
File:UOTW 10 - Ultrasound of the Week 4.webm, Urine jets]
File:CT of peripelvic cysts with non-contrast and urography.jpg, Peripelvic renal cyst
A renal cyst is a fluid collection in or on the kidney. There are several types based on the Bosniak classification. The majority are benign, simple cysts that can be monitored and not intervened upon. However, some are cancerous or are suspicio ...
s may look like hydronephrosis on non-contrast CT (left image). However, CT urography (at right) reveals non-dilated calyces and pelvises.
Grading
The Society of Fetal Ultrasound (SFU) has developed a grading system for hydronephrosis, initially intended for use in neonatal and infant hydronephrosis, but it is now used for grading hydronephrosis in adults as well:
* Grade 0 – No renal pelvis dilation. This means an anteroposterior diameter of less than 4 mm in fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
es up to 32 weeks of gestational age
In obstetrics, gestational age is a measure of the age of a pregnancy which is taken from the beginning of the woman's last menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Su ...
and 7 mm afterwards. In adults, cutoff values for renal pelvic dilation have been defined differently by different sources, with anteroposterior diameters ranging between 10 and 20 mm. About 13% of normal healthy adults have a transverse pelvic diameter of over 10 mm.
* Grade 1 (mild) – Mild renal pelvis dilation (anteroposterior diameter less than 10 mm in fetuses) without dilation of the calyces nor parenchymal atrophy
* Grade 2 (mild) – Moderate renal pelvis dilation (between 10 and 15 mm in fetuses), including a few calyces
* Grade 3 (moderate) – Renal pelvis dilation with all calyces uniformly dilated. Normal renal parenchyma
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
* Grade 4 (severe) – As grade 3 but with thinning of the renal parenchyma
Treatment
Treatment of hydronephrosis focuses upon the removal of the obstruction and drainage of the urine that has accumulated behind the obstruction. Therefore, the specific treatment depends upon where the obstruction lies.
Acute obstruction of the upper urinary tract is usually treated by the insertion of a nephrostomy
A nephrostomy is an artificial opening created between the kidney and the skin which allows for the urinary diversion directly from the upper part of the urinary system (renal pelvis).
An urostomy is a related procedure performed more distally a ...
tube. Chronic upper urinary tract obstruction is treated by the insertion of a ureteric stent
A ureteral stent (pronounced you-REE-ter-ul), or ureteric stent, is a thin tube inserted into the ureter to prevent or treat obstruction of the urine flow from the kidney. The length of the stents used in adult patients varies between 24 and 30&nb ...
or a pyeloplasty
Pyeloplasty is performed to treat an uretero-pelvic junction obstruction if residual renal function is adequate.
This revision of the renal pelvis treats the obstruction by excising the stenotic area of the renal pelvis or uretero-pelvic juncti ...
.
Lower urinary tract obstruction (such as that caused by bladder outflow obstruction secondary to prostatic hypertrophy) is usually treated by insertion of a urinary catheter
In urinary catheterization a latex, polyurethane, or silicone tube known as a urinary catheter is inserted into the bladder through the urethra to allow urine to drain from the bladder for collection. It may also be used to inject liquids used ...
or a suprapubic catheter. Surgery is not required in all prenatally detected cases.
Prognosis
The prognosis of hydronephrosis is extremely variable and depends on the condition leading to hydronephrosis, whether one (unilateral) or both (bilateral) kidneys are affected, the pre-existing kidney function, the duration of hydronephrosis (acute or chronic), and whether hydronephrosis occurred in developing or mature kidneys.
Permanent kidney damage can occur from prolonged hydronephrosis secondary to compression of kidney tissue and ischemia.
For example, unilateral hydronephrosis caused by an obstructing stone will likely resolve when the stone passes, and the likelihood of recovery is excellent. Alternately, severe bilateral prenatal hydronephrosis (such as occurs with posterior urethral valves) will likely carry a poor long-term prognosis
Prognosis (Greek: πρόγνωσις "fore-knowing, foreseeing") is a medical term for predicting the likely or expected development of a disease, including whether the signs and symptoms will improve or worsen (and how quickly) or remain stabl ...
, because obstruction while the kidneys are developing causes permanent kidney damage even if the obstruction is relieved postnatal.
Hydronephrosis can be a cause of pyonephrosis
Pyonephrosis (Greek ''pyon'' "pus" + ''nephros'' "kidney") is an infection of the kidneys' collecting system. Pus collects in the renal pelvis and causes distension of the kidney. It can cause kidney failure.
Cause
Pyonephrosis is sometimes a c ...
, which is a urological emergency.
References
{{Nephrology
Kidney diseases
Nephrology