Clinical Practice Guideline



Developed for the

Aerospace Medical Association

by their constituent organization

American Society of Aerospace Medicine Specialists


Overview: The diagnoses that will be discussed in this clinical practice guideline include medullary sponge kidney, horseshoe kidney, autosomal dominant polycystic kidney disease, congenitally absent or atrophic kidney, and congenital obstruction of the ureteropelvic junction (UPJ).  The kidneys and urinary tract are host to more survivable congenital abnormalities than any other system of the body.  Most abnormalities either present early in life with mass, infection or decreased renal function, or remain silent to be discovered incidentally later in life.  The most common reasons for discovery of silent cystic and congenital abnormalities of the urinary tract include microscopic hematuria, urinary tract infection, stone formation and investigation of unrelated problems such as during cardiac catheterizations.


Medullary Sponge Kidney

Medullary sponge kidney is a condition which is usually an incidental finding during imaging of the abdomen, commonly by IVP.  A significant number of patients with medullary sponge kidney are asymptomatic, and their condition is never diagnosed.  As a result, the true incidence of the condition is unknown.  Among patients undergoing intravenous urography for various indications, 1 in 200 was found to have medullary sponge kidney.  In most cases the renal function is normal.  The principal finding is dilated intrapapillary collecting ducts and small medullary cysts, which range in diameter from 1 to 8 mm and give the cross-sectioned kidney the appearance of a sponge; some describe the appearance as that of small brushes or “bouquets of flowers”.  Although many cases are asymptomatic, it may present with renal colic from stones, urinary tract infection or gross hematuria.  Symptoms rarely occur prior to age 20.  It is the complications of medullary sponge kidney, calculus formation and infection that require management.  It is estimated that medullary sponge kidney is found in up to 20% of stone patients and that more than 70% of patients with medullary sponge kidney will develop stones.  Treatment includes antibiotics for acute pyelonephritis and thiazides and potassium citrate to prevent stone formation.  Patients with medullary sponge kidney frequently have a renal calcium leak, which can lead to secondary hyperparathyroidism and hypercalcemia in addition to nephrolithiasis.


Horseshoe Kidney

The horseshoe kidney is probably the most common of all renal fusion anomalies, occurring in 0.25% of the population.  It should not be confused with asymmetrical or off-center fused kidneys, which may give the impression of being horseshoe shaped.  The anomaly consists of two distinct renal masses lying vertically on either side of the midline and connected at their respective poles (usually the lower poles) by a parenchymatous or fibrous isthmus that crosses the midplane of the body.  Horseshoe kidneys are frequently associated with other congenital anomalies, including skeletal, cardiovascular and central nervous system defects, as well as other genitourinary anomalies such as hypospadias, undescended testes, bicornuate uterus and vaginal anomalies.  The male to female ratio is approximately 2:1.  The most common associated finding in these patients is UPJ obstruction, which occurs in up to 35% of patients.  For many patients, the horseshoe kidney remains asymptomatic, and the horseshoe kidney is an incidental finding during radiological examination.  Symptoms, when present, are usually due to obstruction, stones, or infection.  In children, urinary tract infection is the most common presenting symptom.  Aviators with horseshoe kidney pose no threat to flight safety.  However, if there is recurrent stone formation, infection, or discomfort, the risk of severe pain in flight due to a stone and the need for frequent treatment of these complications may compel the flight surgeon to ground the flyer and refer for treatment.


Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease is the most common form of polycystic disease and occurs in about 1 in 800 live births.  There may be associated abnormalities in the liver, pancreas, brain, arterial blood vessels, or a combination of these sites (liver cysts develop in up to 80% of these patients).  Affected patients have numerous fluid-filled cysts in the kidneys which may become hemorrhagic, and the cysts may also be the site of pyogenic infection.  Patients often present with hypertension, hematuria, polyuria, and flank pain, and are prone to recurrent urinary tract infections and renal stones.  The development of hypertension signifies that the disease is progressing and should be treated aggressively with target blood pressure levels of 130/80 mm Hg or lower.  There are currently no treatments that have been demonstrated to slow the formation of cysts or disease progression.  Because so many patients with polycystic kidney disease will develop hypertension, the diagnosis should be considered, especially in younger aviators who are hypertensive but are otherwise healthy.  At what point in the course of the disease (the period from the onset of signs and symptoms to the occurrence of severe uremia) an aviator should be permanently disqualified from flying must be judged on an individual basis in close cooperation with a specialist in renal disease.  The early presence of mild anemia or proteinuria should not pose a threat to flight safety, but when renal impairment increases or the patient has frequent discomfort or urinary tract infections requiring treatment, continued flight duties become problematic.  In particular blood pressure must be carefully monitored and controlled.


Congenitally Absent or Atrophic Kidney

The congenital absence of a kidney occurs in approximately 1 in 1200 live births.  Males predominate in a ratio of 1.8:1.  The absent kidney is most often from the left side.  Even though the anomaly is more common in males, associated anomalies are more common in females; about 30% of females with a congenitally absent kidney have an abnormality of the internal genitalia.  In general, there are no specific symptoms heralding an absent kidney.  The diagnosis should be suspected during a physical examination when the vas deferens or body and tail of the epididymis is missing or when an absent, septate, or hypoplastic vagina is associated with a unicornuate or bicornuate uterus.  There is no clear-cut evidence that patients with a solitary kidney have an increased susceptibility to other diseases.  In general, the absence of a kidney is not a contraindication to flight duties as long as the remaining kidney is functioning normally and there is no evidence that its continued normal function is being threatened by underlying disease.


Congenital Obstruction of the Ureteropelvic Junction

The diagnosis of UPJ obstruction results in a functionally significant impairment of urinary transport from the renal pelvis to the ureter.  Although most cases are probably congenital, the problem may not become clinically apparent until much later in life.  Congenital UPJ obstruction most often results from intrinsic disease.  A frequently found defect is the presence of an aperistaltic segment of the ureter, perhaps similar to that found in primary obstructive megaureter.  UPJ obstruction may also result from acquired lesions.  In children, vesicoureteral reflux can lead to upper tract dilatation with subsequent elongation, tortuosity, and kinking of the ureter.  In older children or adults, intermittent abdominal or flank pain, especially during periods of increased hydration or urine production, at times associated with nausea or vomiting, is a frequent presenting symptom.  UPJ obstruction may not become apparent until middle age or later.  Hematuria, either spontaneous or associated with otherwise relatively minor trauma, may also be an initial symptom.  Laboratory findings of microhematuria, pyuria, or frank urinary tract infection might also bring an otherwise asymptomatic patient to the urologist.  Radiographic studies should be performed with a goal of determining both the anatomic site and the functional significance of an apparent obstruction.  Excretory urography remains a reasonable first-line option for radiographic diagnosis.  Intravenous pyelography is performed less commonly now, and a CT Urogram may be a helpful initial study.  Ultrasonography is also a useful modality.  If UPJ obstruction is suspected, a MAG3 lasix renal scan (nuclear medicine diuretic renography) should be ordered to assess differential renal function and the degree of obstruction.


Contemporary indications for intervention for UPJ obstruction include the presence of symptoms associated with the obstruction, impairment of overall renal function or progressive impairment of ipsilateral function, development of stones or infection, or rarely, causal hypertension.  The primary goal of intervention is relief of symptoms and preservation or improvement of renal function.  Open operative intervention for UPJ obstruction has historically provided a widely patent, dependently positioned, and well-funneled UPJ.  In addition, the option to reduce the size of the renal pelvis is readily available with this approach.  Although the procedure has stood the test of time with a published success rate of 95%, several less invasive alternatives to standard operative reconstruction are available.  The advantages of endourologic approaches include a significantly reduced hospital stay and postoperative recovery.  However, the success rate does not approach that of standard open or laparoscopic pyeloplasty; the success rate has often been less than 70%, and these procedures are declining in popularity.  With the refinement of robotic-assisted and laparoscopic techniques, the robotic-assisted laparoscopic pyeloplasty has now supplanted both endourologic and open repairs, enjoying the same high degree of success as open repairs.


Aeromedical Concerns: Depending on the underlying condition, a number of symptoms may occur which could impair flying performance and mission completion.  These include flank pain, renal stones, urinary urgency, frequency and dysuria, fever, malaise, and subtle declines in general health and mental clarity.  With some conditions, pyelonephritis may occur that can lead to cortical scarring and potentially compromise renal function.  In addition, these conditions may require close subspecialty follow-up incompatible with worldwide flying duties.


Medical Work-up: For all aviators requesting a waiver, the following information is required before a disposition can be made.  Discuss how the condition was discovered, all associated symptoms, treatments initiated, and any side effects.  Document the GU exam and results of all imaging tests.  Laboratory analysis is to include: urinalysis, BUN, creatinine and all other tests that the particular condition requires.  Need a careful assessment of renal function and mention of presence or absence of stone disease.  Finally, a consultation report from urology and/or nephrology is required.


Aeromedical Disposition:


Air Force: According to AFI 48-123 each of the congenital urinary anomalies noted above are disqualifying for all flying classes in the US Air Force.  After careful evaluation, most of these conditions can be considered for a waiver.


Army: Congenital Urinary Anomalies are generally disqualifying for aviation duties according to AR 40-501 Standards of Medical Fitness.  The aeromedical concerns are the same as those articulated in the USAF Clinical Guidelines.  An exception to policy for initial flight applicants is rarely granted; however a waiver is possible for rated aviators in most cases provided adequate renal function and no symptoms are present.  Waiver consideration hinges on a nephrology evaluation with adequate imaging appropriate to the condition, and normal renal function.


Navy: A waiver is possible if renal function is normal and the aviator remains asymptomatic.


1. Nephrology consultation is required, together with confirmation by CT scan or MRI that there is no coexisting berry aneurysm.

2. Annual submission with 24 hour urine collection for determination of creatinine clearance is required.


Civilian: Medullary Sponge Kidney: Since there is a predisposition to renal stones with this condition medical certification will generally not be granted. 

Horseshoe Kidney:  Asymptomatic horseshoe kidney is allowed and likely no routine follow up is required.

Polycystic Kidney Disease:  Once this condition begins to manifest the airman is placed on an authorization for special issuance.  This will require routine status reports and renal function studies yearly for first- and second-class airmen and every other year for third-class. 

Congenital UPJ Obstruction: Symptoms and diagnosis of this condition will require the airman to have correction prior to permitting medical certification. 


Waiver Experience:


Air Force: AIMWTS search revealed a total of 55 cases submitted with a diagnosis of polycystic kidney, horseshoe kidney, atrophic or congenitally missing kidney, medullary sponge kidney, congenital obstruction of ureteropelvic junction, and other miscellaneous congenital kidney or ureteral obstructions.  There were 2 FC I/IA cases, 32 FC II cases, 21 FC III cases and 0 identified as FC IIU or UAS cases.  There were at total of four disqualifications; one was a FC II pilot with severe polycystic disease that progressed to a kidney transplant and the other three disqualifications were initial FC III cases with active disease and could not be initially certified.


Army: Over a recent two year period there were 1,741 unique rated aircrew encounters filed in the Army Aeromedical Epidemiological Data Repository.  Among these there were no cases congenital urinary tract anomalies.


Navy: Not available at this time


Civilian: The FAA does not maintain statistical data for these conditions. 


ICD 9 codes for congenital urinary anomalies


Absence of kidney


Polycystic Kidney


Medullary Sponge Kidney


Other specified cystic kidney disease


Unspecified obstruction of renal pelvis and ureter


Atrophic kidney


Horseshoe kidney




Glassberg KI.  Renal Dysgenesis and Cystic Disease of the Kidney.  Ch. 114 in Wein: Campbell-Walsh Urology, 9th ed., Saunders, 2007.


Chu JY, Yan MT, and Lin SH.  Recurrent pyelonephritis as a sign of ‘sponge kidney’.  Cleve Clin J Med, 2009; 76:479-80.


Bauer SB.  Anomalies of the Upper Urinary Tract.  Ch.113 in Wein: Campbell-Walsh Urology, 9th ed., Saunders, 2007.


Irshad A, Ackerman S, and Revenel J.  Horseshoe Kidney (Radiology).  eMedicine,, , 1 Mar 2010.


Allen RC.  Horseshoe Kidney.  Horseshoe Kidney (GU).  eMedicine,, 9 Dec 2008.


Rayman RB, Hastings JD, Kruyer WB, et al.  Clinical Aviation Medicine, 4th ed.  New York; Professional Publishing Group, Ltd.  2006, pp. 282-84.


Grantham JJ.  Autosomal Dominant Polycystic Kidney Disease.  N Eng J Med, 2008; 359:1477-85.


Wilson PD.  Polycystic Kidney Disease.  N Eng J Med, 2004; 350:151-64.


Hsu THS, Streem SB, and Nakada SY.  Management of Upper Urinary Tract Obstruction.  Ch. 38 in Wein: Campbell-Walsh Urology, 9th ed., Saunders, 2007.




Prepared by Dr. Dan Van Syoc