Horseshoe kidney overview: Difference between revisions
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==Classification== | ==Classification== | ||
Horseshoe kidney may be classified into three groups based on: | |||
# | # morphological appearance of fusion, | ||
# | # Site of the fusion, | ||
# | # Vascular supply or angiographic appearance of the vessels. | ||
==Pathophysiology== | ==Pathophysiology== | ||
Revision as of 03:27, 15 January 2019
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
Horseshoe kidney is the congenital disorder of kidneys in which the isthmus of both kidneys fuse together during embryonic development leading to appearance of "Horseshoe". It is the most common fusion defect of kidneys.
Historical Perspective
Before 1800 A.D. horseshoe kidney regarded as curiosity found only at postmortem examination.However with the advent of the roentgen rays and the intravenous pyelography the diagnostic possibilities to recognize the horseshoe kidney improved, which was later on aided by the ultrasound and computed tomography scan by which horseshoe kidney can be easily diagnosed.
Classification
Horseshoe kidney may be classified into three groups based on:
- morphological appearance of fusion,
- Site of the fusion,
- Vascular supply or angiographic appearance of the vessels.
Pathophysiology
Most people with horseshoe kidneys are totally asymptomatic and their kidneys function normally throughout their lives. About quarter of cases are found incidentally, usually during a CT scan due to some other problem. Nonetheless, there are lots of other patients who are predisposed to certain medical issues. These issues include:
- Ureteropelvic junction obstruction : It is the most common problem in horseshoe kidney. It is caused by crossing of ureter over the fused isthmus leading to its obstruction.
- Kidney Stones : Stones usually occur when there is obstruction leading to decreased urine output and stasis of urine which create environment for stone formation.
- Recurrent infections : Again due to stasis of urine, because stasis of urine create medium for bacterial growth
- Hydronephrosis : Basically it is caused by back-flow of urine due to obstruction of ureteropelvic junction.
- Increased incidence of certain cancers such as renal cell carcinoma, wilms tumor and carcinoid tumors.
Causes
During early fetal development, the kidneys are developed in the pelvis and then later they move upwards in abdomen. Sometimes due to unknown reason the lower ends of both kidneys fuse together forming a 'U' shaped single kidney. Although the exact cause is unknown, but there are two main theories. One theory suggests that during the fifth week of fetal development both kidneys are so close together leading to mechanical fusion of lower end of both kidneys. This kind of fusion creates the fibrous isthmus because it is made of connective tissue. Other theory suggests that posterior nephrogenic cells, which are the cells responsible for formation of kidney, migrate to wrong place leading to joining of lower end of both kidneys. This time it is called parenchymal isthmus because it is made of kidney cells.
The horseshoe kidney remains lower in abdomen than normal kidneys due to blockade caused by inferior mesenteric artery during its movement from pelvis to abdomen in 7-8 weeks of development.
Differentiating Horseshoe kidney from Other Diseases
There are other forms of kidney fusion defects. Usually they can be differentiated based on appearances on CT scan.
Epidemiology and Demographics
- It is fairly common condition with 1 case in every 500 live births.
- Males cases are twice more common than female cases.
- Although it has been seen in members of same families, but no any particular gene has been found to cause this disease.
Risk Factors and Associations
There are no particular gene discovered yet which are directly related to horseshoe kidney but it has been seen associated with other genetic disorders such as Turner syndrome and Edwards syndrome, further suggesting that it is linked to some genes.
Screening
There is no particular screening test for horseshoe kidney itself, although CT scanning or renal ultrasonography can be used to screen for the presence of stones, masses, or hydronephrosis.
Natural History, Complications, and Prognosis
- Hydronephrosis
- Renal stones
- Urinary tract infections
- Renal Cancer
Diagnosis
Diagnostic Study of Choice
Intravenous pyelography protocol computed tomography is the best initial test.
History and Symptoms
1 in every 3 patients remain asymptomatic throughout their lives. Other patients present with symptoms secondary to urinary tract infections, renal stones and obstruction. These symptoms include dysuria, flank pain and fever.
Physical Examination
Because the kidneys are lower in abdomen, a midline lower abdominal mass can be felt during physical examination.
Laboratory Findings
Urine routine (DR) and urine culture should be done to look for any sign of urinary infection and serum creatinine and electrolytes should be done to check the kidney function.
X-ray
X-ray may show renal outlines lower than in normal person, but other than that it is not that much useful.
Ultrasound
Renal Ultrasound can be used to look for presence of any stones, masses, obstruction or hydronephrosis.
CT scan
CT Scan with contrast is imaging technique of choice. CT Scan of abdomen and pelvis with and without contract is used to look for location of kidneys. It is accurate in determining the anatomical location and also help in differentiating the parenchymal from fibrous isthmus.
MRI
MRI is also helpful in diagnosing horseshoe kidney, and is used in conditions where CT Scan is not recommended or available. MRI is also costlier than CT Scan.
Other Imaging Findings
Other imaging studies such as nuclear imaging also called scintigraphy is available and helpful in diagnosis of horseshoe kidneys. This study also shows the functioning of kidneys and its isthmus.
Treatment
Medical Therapy
Symptomatic treatment for Urinary tract infection if associated.
Interventions
Surgery
If there is obstruction to urinary flow then it can be corrected surgically, although most people do not need surgery.