Introduction

Renal pelvic dilatation, or better known as Pyelectasis, is a condition in fetuses in which too much urine builds inside the centre fetus’s kidney, the renal pelvis, and so causes it to expand in size, dilatation.¹

This buildup occurs when there's a blockage within the tubes known as the ureters, which stops urine from moving smoothly from the kidneys to the bladder. Sometimes, it can also happen if urine leaks backwards from the bladder into the kidneys, a condition known as urinary reflux.

It also has other names depending on the location of the urine buildup, such as pelviectasis, pelvocaliectasis or caliectasis.²

Pyelectasis is typically diagnosed through an ultrasound scan during pregnancy. 

What is an Ultrasound scan?

An ultrasound scan, or a sonogram, is a safe, non-invasive imaging technique that uses high-frequency sound waves (hence ultrasound) to look at internal structures to look at a developing fetus, or a person’s abdominal, pelvic, muscular, and cardiovascular organs.³

Ultrasound is a very good way to look at the anatomy of the fetus during the second trimester, which is around 13-28 weeks of pregnancy. Renal/kidney problems account for 20% of all birth defects.^4,5 However, 1-3% of fetuses are diagnosed with Pyelectasis through ultrasound imaging within the second trimester, with fluid buildup found in the renal pelvis of the fetus.^6,8

Pyelectasis can be diagnosed when the renal pelvis measures a certain size from the front to the back, which is larger than normal.

One diagnostic criterion for if Pyelectasis is present is if the renal pelvis exceeds 7mm before 28 weeks, 8mm at or after 28 weeks, and 10mm at or after 32 weeks of pregnancy, which is outside the normal size range of the renal pelvis.⁹

Fortunately, Pyelectasis for the most part does not harm the fetus, and most cases (~96%) get better on their own during pregnancy or soon after the fetus is born, which can be monitored by additional ultrasound imaging after birth,¹⁰ looking to check for any swelling in the small collecting tubes of the kidneys, the tubes that carry urine from the kidney to the bladder, how the kidney tissue looks, the appearance of the bladder, and any cases of unexplained low amniotic fluid.¹¹

The likelihood of developing kidney issues after birth is increased if:

• The swelling is more significant
• The swelling worsens during pregnancy
• Both kidneys are involved

When pyelectasis is identified before birth, particularly if it is the sole concern, known as isolated pyelactasis, it does not necessarily indicate a specific problem, such as urine leaking from the bladder into the kidneys.^10–12

Research indicates that when a fetus has pyelectasis along with other birth defects or specific ultrasound signs, there’s a higher chance of genetic abnormalities, especially trisomy 21, better known as Down syndrome.^13,14

What is Down syndrome?

Down syndrome (DS) or trisomy 21 is a genetic condition to the presence of an additional copy of chromosome 21, which is an anomaly called aneuploidy, in which there are additional or missing chromosomes in the cells.

Down syndrome is the most common chromosomal abnormality occurring in humans and has the most common aneuploidy that is caused by trisomy 21.^15,16

This extra copy of chromosome 21 alters development and affects many parts of the body, especially within muscles, bones, the nervous system, and the heart and blood vessels.¹⁷

DS is the most common genetic condition that causes intellectual disabilities in addition to other symptoms, manifestations, and associated birth defects.¹⁸

These include:

• Neurodevelopmental: Language disorders, developmental delay
• Cardiovascular: Heart defects present at birth 
• Musculoskeletal: Short stature and decreased muscle tone 
• Sensory: Hearing loss, sight problems
• Respiratory: Breathing issues
• Autoimmune: Thyroid disease, Coeliac disease, and Alopecia

Despite these physical health manifestations that may result from DS, when people with DS have sufficient support and services, they can lead perfectly happy and healthy lives.¹⁷ Adults with DS who are employed report that they are happy with their jobs when their needs are met.¹⁹

How is DS diagnosed?

DS can be diagnosed by a combination of ultrasound scans and blood tests during pregnancy²⁰.

The DS aneuploidy occurs during a disruption in cell division known as "nondisjunction." This error leads to an embryo having three copies of chromosome 21 instead of the usual two. Before or at the moment of conception, a pair of chromosomes 21s in either the sperm or the egg do not separate properly.²¹ The cause of this cell division error is unknown. 

As stated above, DS can result in various health issues and birth defects, such as Pyelectasis.

If pyelectasis is found on an ultrasound, it can slightly increase the likelihood of the baby having Down syndrome, but most babies with pyelectasis do not have it. 

In most cases, if there are no unusual blood test results or other ultrasound findings, pyelectasis is usually just a normal part of how the baby is developing.²²

Severity of Pyelectasis

Although most cases of Pyelectasis improve on their own, there are different levels of severity to consider. However, because of the many definitions that come under Pyelactasis, and different healthcare providers and studies come up with their own size of the renal pelvis to consider it to be Pyelactasis, so there is not a lot of standardisation about its definition, let alone the grading of severity.^12,23,27

Pyelectasis has often been compared to hydronephrosis in fetuses, which refers to the kidney swelling due to a buildup of urine, which can also affect children and adults. 

Whilst Pyelectasis is specific to the renal cavity, hydronephrosis refers to the buildup inside the kidney in general, these terms are used interchangeably and also have varying degrees of severity.²⁸

In this case, we will be looking at Mild, Moderate, and Severe Pyelectasis AND Hydrophrenosis.

Several studies use the definitions of the severity of pyelectasis by size of the renal pelvis, with mild (5–9.9 mm), moderate (10–15 mm), and severe (>15 mm).^29,30

Mild

Mild Pyelactasis and Hydrophrenosis refers to the majority of cases, where the kidney is larger than what is considered normal, is harmless and tends to go away on its own.^24,28

Moderate

Moderate tends to be slightly larger than the lesser mild form, although this one does also go away on its own. However, with its enlarged size, it is more likely to have complications, the most common of which is a Urinary Tract Infection (UTI).³¹

UTIs are fairly common and can happen to people at different times in their lives. These infections mainly affect the bladder, kidneys, and other parts of the urinary system. Although they can cause discomfort and pain, they usually go away after a few days with or without antibiotics.³²

Furthermore, some moderate cases lead to blockage at the point where the pelvis connects to the ureter (PUI), in which surgery was needed to help resolve the blockage to prevent any permanent damage to the kidneys, which occurred in a quarter of cases in one particular study.²⁵

Severe

Severe hydronephrosis and pyelectasis are considered to be very problematic as it has much more severe blockage and cause the kidney to ‘balloon’ because of its large size in comparison to its mild and moderate forms.^22,31

Similar to moderate pyelectasis, severe pyelectasis can also cause UTIs and PUI blockage, in which one study found that 60% of fetal patients needed surgery in order to prevent kidney damage.²⁵

Regardless of surgery intervention or severity, frequent ultrasound check-ups and antibiotics can be used to check on the fetal patient’s kidneys.³³

Summary

Pyelectasis is a condition where urine collects in the fetal kidney's central area before birth. It usually occurs due to a blockage or backflow of urine. Doctors diagnose it using ultrasound scans, and they use size measurements to determine how serious it is. Most of the time, it gets better on its own without treatment.

How it's diagnosed

An ultrasound shows if the kidney’s central part is larger than 7mm before 28 weeks of pregnancy, larger than 8mm at 28 weeks or later, or larger than 10mm after 32 weeks. It is fairly common, affecting about 1-3% of pregnancies, and usually is not harmful. But, if the swelling gets bigger or does not get smaller, it may increase the chance of kidney problems.

What it’s linked to

Pyelectasis by itself usually does not mean there is a more serious problem. However, if there are other abnormalities or conditions, like Down syndrome, the risks are higher. Pyelectasis has been associated with Down syndrome, which happens when chromosomes don’t divide properly during cell formation.

Having Down syndrome can cause developmental delays, heart issues, and other health concerns. While physically there are differences, many people with Down syndrome live healthy, fulfilling lives with sufficient support.

Whilst there is no universal definition for the degree of severity or confirmed sizes of Pyelectasis, some studies have made their own definitions by the degree of severity.

Different levels of severity: 

• Mild (5-9.9mm): The most common, usually fixes itself, and doesn’t cause serious problems
• Moderate (10-15mm): Slightly larger swelling, may increase risk of urinary tract infections, and some may need surgery
• Severe (>15mm): Larger blockage, kidneys may become swollen like a balloon, and there’s up to a 60% chance that surgery will be needed