Megaureter: Symptoms, Types, Causes and Treatment

Megaureter is a medical term describing an abnormally dilated ureter—the muscular tube that carries urine from the kidneys to the bladder. While the word “megaureter” may sound dramatic, its implications are significant, particularly in children, where it is a leading cause of urinary tract obstruction and recurrent infections. With advances in prenatal imaging and a deeper understanding of the condition’s biology, today’s approach to diagnosis and management is more nuanced than ever. In this article, we’ll explore the symptoms, classification, causes, and modern treatment options for megaureter, drawing on the latest medical research and clinical consensus.

Symptoms of Megaureter

Recognizing the symptoms of megaureter is crucial for timely diagnosis and effective treatment. While many cases are discovered incidentally through imaging, especially in infants and children, others present with distinct clinical features that can impact quality of life and kidney health.

Main Symptom	Associated Features	Population Most Affected	Source(s)
Flank/abdominal pain	Acute pain crisis, Dietl’s crisis-like	Children, adults	1, 2
Urinary tract infection (UTI)	Febrile UTI, recurrent infections	Infants, children	2, 11, 12
Hematuria	Microscopic or visible blood in urine	Children, adults	2
Hydronephrosis	Detected via imaging	Infants (often prenatal)	3, 11, 13

Table 1: Key Symptoms

Flank/Abdominal Pain and Acute Pain Crisis

Pain, often in the flank or lower abdomen, is a common symptom and can sometimes present dramatically as an acute pain crisis. In children, these episodes may be severe enough to require emergency care, and are sometimes mistaken for other causes of abdominal pain. Acute pain is particularly associated with obstructive forms of primary megaureter and can lead to urgent interventions such as stenting or surgery for pain relief 1, 2.

Urinary Tract Infections

UTIs are a frequent complication, especially in infants and young children. These infections can be recurrent and may present as fevers without an obvious source. Febrile UTIs are especially concerning, as they can indicate underlying urinary tract obstruction or reflux, and signal the need for further investigation 2, 11, 12.

Hematuria

Blood in the urine—either visible (gross hematuria) or microscopic—can occur, particularly in older children and adults with megaureter. While hematuria is less common than pain or infection, its presence should prompt consideration of urinary tract malformations, including megaureter 2.

Hydronephrosis and Incidental Detection

With the rise of routine prenatal ultrasounds, many cases of megaureter are now detected in utero as hydronephrosis (swelling of the kidney due to urine buildup). These infants may be asymptomatic at birth, but ongoing monitoring is essential to detect any progression or complications 3, 11, 13.

Types of Megaureter

Understanding the different types of megaureter is fundamental for diagnosis and management. The classification is based on the underlying mechanism—whether it is due to intrinsic abnormalities of the ureter or secondary to issues elsewhere in the urinary tract.

Type	Defining Feature	Subtypes/Variants	Source(s)
Primary Megaureter	Ureteric abnormality at birth	Obstructed, refluxing, non-obstructed, refluxing-obstructed	4, 6
Secondary Megaureter	Caused by lower urinary tract disease	Neurogenic bladder, posterior urethral valves, prune belly syndrome	4, 5
Special Variants	Syndromic or complex forms	Megacystis-megaureter syndrome, ectopic megaureter	5

Table 2: Classification of Megaureter

Primary Megaureter

Primary megaureter refers to dilation caused by a congenital abnormality of the ureter itself, usually at the point where it enters the bladder (the vesicoureteric junction). It is further subdivided into:

• Obstructed: Urine flow is impaired due to a narrowed or non-functioning segment, often causing symptoms or kidney dysfunction.
• Refluxing: Urine flows backward from the bladder into the ureter (vesicoureteric reflux), leading to dilation.
• Non-obstructed, non-refluxing: The ureter is dilated, but without evidence of obstruction or reflux—sometimes considered a benign variant.
• Refluxing-obstructed: Both backward flow and obstruction are present 4, 6.

Secondary Megaureter

Secondary megaureter arises due to a problem lower down in the urinary tract, such as:

• Neurogenic bladder: Dysfunctional bladder muscle or nerve supply, often seen in spina bifida.
• Posterior urethral valves: Congenital obstruction in the urethra of boys.
• Prune belly syndrome: A rare syndrome with deficient abdominal muscles, urinary tract abnormalities, and undescended testes 4, 5.

The pathophysiology and management of secondary megaureter depend on the underlying disorder.

Special Variants and Syndromic Forms

• Megacystis-megaureter syndrome: Characterized by both a large bladder (megacystis) and dilated ureters, often representing an extreme form of reflux.
• Ectopic megaureter: The ureter does not insert into the bladder at the normal location and may be associated with duplicated kidneys 5.

Causes of Megaureter

Pinpointing the cause of megaureter requires an understanding of urinary tract development and the fine balance between urine flow and the function of muscular walls.

Cause	Mechanism	Population/Notes	Source(s)
Congenital defect	Embryopathy of ureteric bud/Wolffian duct	Infants, children	5, 7
Ureteral muscle anomaly	Abnormal smooth muscle or collagen	Primary megaureter	3, 7, 8
Distal obstruction	Narrowed/aperistaltic segment at bladder entry	Primary obstructed	3, 7
Vesicoureteric reflux	Malfunctioning valve at bladder-ureter junction	Refluxing megaureter	4, 6, 8
Secondary causes	Dysfunctional bladder or systemic disease	Secondary megaureter	4, 5

Table 3: Causes of Megaureter

Congenital and Developmental Factors

Megaureter often results from congenital anomalies in the development of the ureteric bud and Wolffian duct during fetal life. These embryologic disruptions can lead to improper formation of the ureter’s muscular wall or abnormal connections at the bladder, giving rise to obstruction or reflux 5.

Ureteral Muscle and Tissue Abnormalities

Histological studies reveal that primary megaureter, especially the obstructed type, often involves a segment near the bladder (the pre-vesical ureter) that has reduced smooth muscle, increased collagen, or abnormal nerve supply. This can result in poor peristalsis (muscular contractions), leading to functional obstruction and progressive dilation 3, 7, 8.

• Obstructed Megaureter: Marked by an increase in connective tissue, abnormal muscle cells, and sometimes increased cell death (apoptosis) in the affected segment 7, 8.
• Refluxing Megaureter: Characterized by a deficient muscular layer and fewer interstitial cells of Cajal (cells that help coordinate muscular contraction), leading to poor valve function and backward flow of urine 8.

Distal Obstruction and Aperistalsis

A classic cause of primary obstructed megaureter is a narrowed or non-contractile (aperistaltic) segment at the point where the ureter enters the bladder. This functional or anatomical blockage prevents urine from draining freely, causing upstream dilation and potentially harming kidney function 3, 7.

Vesicoureteric Reflux

In some cases, the valve that normally prevents urine from moving backward from the bladder into the ureter fails, resulting in vesicoureteric reflux. This can stretch the ureter and, over time, compromise the kidney 4, 6, 8.

Secondary Causes

Secondary megaureter is due to factors outside the ureter itself, most commonly:

• Bladder outlet obstruction (e.g., posterior urethral valves)
• Neuropathic bladder (e.g., from spina bifida)
• Systemic disorders (e.g., prune belly syndrome)

These conditions increase pressure in the bladder or lower urinary tract, leading to secondary dilatation of the ureter 4, 5.

Treatment of Megaureter

Treatment decisions for megaureter require careful consideration of the underlying type, severity, and impact on kidney function. Thanks to advances in imaging and a better understanding of the disease’s natural history, management has shifted towards a more individualized and often conservative approach.

Treatment Option	Indication	Notes/Outcomes	Source(s)
Observation	Mild, asymptomatic, stable cases	Many resolve or remain stable	3, 11, 13
Antibiotic prophylaxis	Infants with hydroureteronephrosis	Prevents UTI while under observation	11
Ureteral stenting	Acute pain crisis, severe obstruction	Temporary relief, bridge to surgery	1, 11
Surgical repair	Symptoms, declining renal function, severe/progressive hydronephrosis	Ureteral reimplantation, tapering, resection	1, 3, 11, 12
Treat underlying cause	Secondary megaureter	Manage bladder dysfunction, valves, etc.	4, 5

Table 4: Treatment Approaches

Conservative Management and Observation

Most cases of megaureter detected in infancy—especially those without significant symptoms or kidney dysfunction—can be managed conservatively. This involves regular monitoring with ultrasound and sometimes nuclear scans to assess kidney drainage and function. Many primary non-refluxing megaureters spontaneously resolve or remain stable, particularly when not associated with obstruction or infection 3, 11, 13.

• Antibiotic prophylaxis is often recommended in infants with hydroureteronephrosis to reduce the risk of UTIs during the observation period 11.

Indications for Surgical Intervention

Surgery is reserved for well-defined situations:

• Recurrent febrile UTIs
• Acute pain or pain crisis
• Progressive or severe hydronephrosis
• Decline in kidney function (e.g., differential renal function dropping below 40%) 1, 3, 11, 12

In such cases, timely intervention can prevent further kidney damage and resolve symptoms.

Surgical Techniques

Several surgical methods are available, tailored to the child’s age, the size of the ureter, and the specific type of megaureter:

• Ureteral reimplantation: The affected segment is removed, and the healthy part of the ureter is reimplanted into the bladder, often using an anti-reflux technique to prevent backward flow 3, 11, 12.
• Tapering or tailoring of the ureter: If the ureter is massively dilated, it may be surgically reduced in diameter (“tapered”) before reimplantation 3, 14.
• Temporary stenting: In infants or in acute situations (such as severe pain), a temporary ureteral stent may be placed to relieve obstruction until the child is older or definitive surgery can be performed 1, 11.
• Modifications and alternative approaches: Techniques have evolved, such as folding rather than resecting the ureter wall, to minimize injury and ensure better outcomes 14.

Management of Secondary Megaureter

When megaureter is secondary to an underlying problem—such as bladder dysfunction or posterior urethral valves—the primary focus is on correcting or managing that disorder. Only after the lower tract issue is addressed is further intervention on the ureter considered 4, 5.

Outcomes and Long-term Follow-up

Surgical repair, when indicated and properly performed, generally yields excellent outcomes in terms of symptom relief and preservation of kidney function. However, ongoing follow-up is needed, as some children may develop new issues such as reflux after surgery, or require additional interventions 12.

Conclusion

Megaureter is a complex but increasingly well-understood condition that spans a spectrum from benign anatomical variants to severe obstructive uropathy threatening kidney health. Advances in prenatal detection, imaging, and surgical techniques have transformed management, making individualized care and kidney preservation the central goals.

Key points:

• Megaureter often presents with pain, infection, hematuria, or is detected by imaging.
• It is classified as primary (intrinsic ureter abnormality) or secondary (due to lower urinary tract dysfunction), with further subtypes based on obstruction and reflux.
• Causes include congenital muscle/connective tissue anomalies, obstructive segments, reflux, or secondary pressure from bladder dysfunction.
• Most cases in infants can be managed with observation and infection prevention, but surgery is needed for symptomatic, progressive, or function-threatening disease.
• Long-term follow-up is vital to monitor for recurrence or complications, ensuring the best outcomes for patients.

By recognizing the varied presentations and tailoring treatment to each individual, healthcare teams can help children and adults with megaureter achieve healthy, active lives.