Prune Belly Syndrome Imaging

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Prune belly syndrome typically occurs in boys with a thin or lax abdominal wall; such laxity is variable in severity. The prostatic urethra is long and dilated as a result of prostatic hypoplasia. Some patients have a utricle diverticulum from the urethra; a large, vertically oriented, thick-walled bladder; a urachal remnant from the dome of the bladder; and tortuous and dilated ureters. Varying amounts of hydronephrosis and varying degrees of renal dysplasia are seen. All have cryptorchidism.

The amniotic fluid volume may be normal or decreased in neonates with prune belly syndrome. The presence of oligohydramnios may account for some of the accompanying findings of the extremities. ^{[1, 2, 3]} See the images below.

The etiology of prune belly syndrome is not fully understood. The thinness of the abdominal wall has been attributed to hydronephrosis. The distended urinary system is thought to interfere with the normal descent of the testes. However, some patients with severe hydronephrosis do not have the same disorder of the abdominal wall. Cryptorchidism usually is not seen in patients with distended bladders of other etiology. ^{[4, 5]}

Prune belly syndrome is a rare anomaly seen in 1 in 35,000-50,000 live births. The genetic origins remain unclear. ^{[6, 7, 8]}

To confirm prune belly syndrome, radiography is used to evaluate the abdomen and chest initially. For urinary tract evaluation, renal US and voiding cystourethrography are performed. For fragile neonates and for infants with severe reflux and retention, these simple diagnostic studies may be much more threatening than they are for the normal baby. The use of prophylactic antibiotics and the need to act upon the study results should be weighed before proceeding indiscriminately.

Some diagnosticians assess renal function by performing a technetium-99m (^99m Tc) dimethylsuccinic acid (DMSA) renal scan. DMSA is a cortical agent; DMSA renal scans provide information about both the appearance and function of the kidneys.

Radiographic findings in prune belly syndrome are as follows:

Chest: Hypoplastic lungs, flaring of the lower ribs secondary to the distended abdomen is seen (see image below).

Abdomen: Diffusely distended flanks are seen. Masslike areas in the abdomen represent a hydronephrotic urinary tract (see image below).

Kidneys: Dilated, clubbed, and dysplastic calyces are seen. Renal parenchyma often is hyperechoic on US, which shows poor development and differentiation of the calyces. Often, small cysts are seen in the subcapsular cortex.

Ureters: Ureters are markedly dilated and tortuous, with involvement more severe distally. Usually, refluxing ureters are seen (see image below).

Bladder: The bladder is vertical and trabeculated, with a urachal remnant at the dome. The base of the bladder is triangular, with a relaxed internal sphincter (see image below).

Urethra: A wide, long posterior urethra is seen, along with a utricular remnant. The posterior urethra may be triangular in appearance as a result of the absence of the posterior lobe of the prostate. Corporal absence may result in megalourethra of the anterior urethra, giving it a fusiform appearance (see image below).

Cryptorchidism: The testes are in the abdomen or inguinal canals. Often, the testes appear hypoplastic, although they may be of normal size.

For those who have access to nuclear radiology, a scan using a cortical agent such as^99m Tc DMSA is useful in assessing renal function. Radiopharmaceuticals that are excreted by tubular secretion such as^99m Tc mercaptoacetyltriglycerine (MAG-3) or glomerular filtration such as diethylenetriamine pentaacetic acid (DTPA) may be helpful in visualizing the kidneys and collecting systems.

The radiographic appearance is virtually always characteristic of prune belly syndrome.

Findings of prune belly syndrome on CT include a broad flabby-appearing abdomen, absence of the musculature of the abdomen, hydronephrosis, and tortuous dilated ureters and bladder. ^[9]

See the image below.

Sonography of the kidneys shows diffusely hyperechoic parenchyma, small parenchymal cysts, clubbed dysplastic calyces, and markedly tortuous ureters; these findings are sufficient to make the diagnosis of prune belly syndrome. The increased echogenicity of the parenchyma is an indicator of underlying dysplasia of the renal tissue during early differentiation and maturation. The bladder is usually large and thick-walled. Angled outlet views may show the dilated prostatic urethra, which is difficult to differentiate from posterior urethral valves by sonography alone ^{[10, 11, 12, 13, 14]}

See the images below.

On US, prune belly syndrome has a characteristic appearance.

Although a firm diagnosis may usually be made on the basis of the combination of the clinical examination and US findings, in cases in which abdominal thinning is mild, the diagnosis may be less certain. In such cases, a voiding cystourethrogram may reveal the characteristic urethral appearance.

The diagnosis of prune belly syndrome is made in utero using ultrasound (US). In the neonate, the diagnosis is made on the basis of characteristic clinical findings. The diagnosis should be suspected in the fetus when US imaging reveals a characteristic enlarged bladder, dilated ureters, and an abnormal abdominal wall. However, the same constellation of US findings can signal posterior urethral valves with severe hydroureteronephrosis; thus, as a cautionary measure, the diagnosis should not be declared with certainty for either condition.

Megacystis-microcolon syndrome may have an appearance that is almost identical to that of prune belly syndrome; however, in megacystis-microcolon syndrome, the bladder is smoother and larger than in prune belly syndrome. Megacystis-microcolon syndrome has a marked female preponderance.

Renal cortical scanning is extremely useful for infants with borderline renal function. DMSA renal scanning indicates the degree of renal functional impairment and demonstrates focal areas of decreased or absent function.

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Byon M, Kim GJ. Prune-belly syndrome detected by ultrasound in the first trimester and the usefulness of vesicocentesis as a modality of treatment. Obstet Gynecol Sci. 2013 Jul. 56(4):265-8. [Medline]. [Full Text].

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Beverly P Wood, MD, MSEd, PhD Professor Emerita of Radiology and Pediatrics, Division of Medical Education, Keck School of Medicine, University of Southern California; Professor of Radiology, Loma Linda University School of Medicine

Beverly P Wood, MD, MSEd, PhD is a member of the following medical societies: American Academy of Pediatrics, Association of University Radiologists, American Association for Women Radiologists, American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Radiological Society of North America, Society for Pediatric Radiology

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

John Karani, MBBS, FRCR Clinical Director of Radiology and Consultant Radiologist, Department of Radiology, King’s College Hospital, UK

John Karani, MBBS, FRCR is a member of the following medical societies: British Institute of Radiology, Radiological Society of North America, Royal College of Radiologists, Cardiovascular and Interventional Radiological Society of Europe, European Society of Radiology, European Society of Gastrointestinal and Abdominal Radiology, British Society of Interventional Radiology

Disclosure: Nothing to disclose.

Prune Belly Syndrome Imaging

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