Abdominal mass

A 29 year old man was admitted as an emergency in the general surgical ward with one day history of right iliac fossa pain. He also had past history of on and off right iliac fossa pain.

On admission he was apyrexial; blood pressure and pulse were normal. Abdominal examination showed non-distended abdomen and tenderness in the right iliac fossa.

An ill defined mass was palpable in the right iliac fossa. Bowel sounds were normal. Laboratory investigations showed slightly raised blood urea and serum creatinine.

Other blood counts and inflammatory markers were normal. An ultrasound scan and ointravenous ureterogram (IVU) identified a congenital anomaly. Subsequently, a computed tomography scan was arranged (fig 1). He had a mercapto acetyl triglyceride renogram, which showed split renal function of 35% on the right side.

Fig 1: Computed tomograph
of the pelvis

Questions

1. What is the congenital anomaly identified in fig 1?
2. What is the incidence and sexual distribution of the pelvic kidney?
3. Name the common anomalies which can be associated with pelvic kidney.
4. What does the radiograph of the kidney, ureter, and bladder show in fig 2?

Fig 2: Radiograph of the kidney,
ureter, and bladder

Answers

1. Fig 1 shows grossly hydronephrotic right side pelvic kidney.
2. The incidence of pelvic kidney in an average is 1 in 900 and there is no difference in incidence between sexes.
3. Pelvic kidney is usually associated with genital anomalies--in males hypospadias, duplication of urethra, and undescended testis; in females bicornuate uterus, rudimentary or absent uterus, and duplication of vagina.
4. The kidney, ureter, and bladder x ray in fig 2 shows the ureteric stent placed in the right pelvic kidney ureter to relieve the acute pelvi ureteric junction obstruction.

Discussion

A pelvic kidney occurs when the mature kidney fails to reach to its normal location in the renal fossa and remains in the pelvis. The incidence in an average is 1 in 900. Incidence between sexes is not significantly different, but left sided is favoured slightly over right.

Embryology

The permanent functioning adult kidneys develop from the metanephric mesoderm (which provides the excretory unit) and the ureteric bud (which gives rise to collecting system). The pronephros and mesonephros (primitive kidneys) are present during the intrauterine life and will regress in utero.

The ureteric bud develops from the distal portion of the mesonephric duct and comes into contact with the metanephric mesenchyme (fig 3) at the end of the fourth week of gestation. Subsequently the bud dilates forming the primitive renal pelvis and splits to form major calyces. p>

Fig 3: Development
of the uretic bud

Initially the metanephric kidneys lie in the pelvis. As the caudal part of the embryo grows away from the kidneys the kidneys progressively occupy their normal adult position. As the kidneys ascend they rotate medially, and this process of migration and rotation completes by the end of the eighth week of gestation.

Ureteral bud maldevelopment, defective metanephric tissue, and maternal illnesses and teratogenic causes may prevent the migration of the kidneys and lead to pelvic kidneys. Other ectopic sites of the kidneys are lumbar or thoracic.

Associated anomalies

Pelvic kidney is often found with genital anomalies, but cardiovascular and skeletal anomalies are also common. In females pelvic kidney usually associates with bicornuate uterus, rudimentary or absent uterus, and duplication of vagina. Among males undescended testis, duplication of urethra, and hypospadiasis are the most common.

Clinical presentation

Most pelvic kidneys are clinically asymptomatic and usually is a coincidental finding. Others present at any age with vague abdominal pain secondary to obstructed stone or urinary tract infection.

Differential diagnosis

1. Appendicitis--this is most often misdiagnosed in cases of right pelvic kidney
2. Ovarian pathology in females
3. Abdominal mass--hydronephrotic collecting system due to obstruction of pelviureteric or ureterovescical junction.

Investigations

1. Ultrasonography, nephrotomography during excretory urogram are usually diagnostic and are the first choices of investigations. Computed tomography with contrast will be useful to identify the site of ectopic kidneys in difficult cases.
2. Renal scintigraphy studies will be useful in difficult cases and for more detailed study of the anatomy and function of the kidneys. These are divided into dynamic and static studies.

Dynamic studies

In dynamic studies, the function of the kidneys are assessed--for example mercapto acetyl triglyceride (MAG3) renogram. Technetium labelled MAG3 is injected and the emissions from the kidneys are recorded for analyses of time-activity curves.

In a normal kidney renogram the time-activity curve comes down to normal after an initial peak. This fails to happen in an obstructed system (such as the obstructed pelvic kidney in fig 4)

Static studies

Static studies provides detailed imaging of the kidneys--for example, scans in which technetium labelled dimercaptosuccinic acid is injected and accumulates in the kidneys for several hours. This gives a complete renal outline. Static studies are useful in identifying ectopic kidneys.

Treatment

Treatment is usually symptomatic. Surgical intervention with ureteric stenting or pyeloplasty is needed when patients present with acute pelviureteric junction obstruction.

R Gudena senior house officer,
Email: gudenar@msn.com

E K N Ahiaku consultant urologist, Ysbyty Gwynedd, Bangor


studentBMJ 2004;12:393-436 November ISSN 0966-6494