Horseshoe Kidney


Article Author:
Joshua Kirkpatrick


Article Editor:
Stephen Leslie


Editors In Chief:
Kranthi Sitammagari
Mayank Singhal


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Trevor Nezwek
Radia Jamil
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes


Updated:
6/4/2019 7:42:36 PM

Introduction

Horseshoe kidneys are the most common fusion defect of the kidneys, but this still amounts to only about 0.25% of the population [1]. Initially described during autopsies by da Carpi performed in 1522, they are characterized by abnormalities in the position, rotation, and vascular supply of the kidney [2]. Horseshoe kidneys are identified as having functioning renal masses present on both sides of the vertebral column fused together with ureters that remain uncrossed from the renal hilum to the urinary bladder [3]. The isthmus connecting the two renal masses may be positioned in the midline or laterally resulting in asymmetric horseshoe kidney, 70% of which are left dominant, and consists of renal parenchyma in about 80% of cases with the remainder being composed of a fibrous band. In more than 90% of cases, fusion occurs at the lower pole, although fusion may occur at the upper pole in a minority of cases [4][5][6].

Etiology

Despite cases of familial clustering, no clear genetic cause has been described for horseshoe kidneys, although several etiological factors may contribute to their development [7]. These include abnormal migration of nephrogenic cells across the primitive streak, alterations in the intrauterine environment (with teratogenic drugs such as thalidomide, alcohol consumption and glycemic control causing an increase in incidence), and structural factors such as flexion/rotation of the caudal spine and narrowed arterial forks during migration [4][8][9][10]. Traditionally textbooks quote fusion as occurring between weeks four and six of development, although there is some evidence for later fusion, particularly when the isthmus is fibrous rather than renal parenchyma.

Epidemiology

The incidence of horseshoe kidney is approximately 1 in 500 in the normal population with a male preponderance of 2:1 [1][4]. The incidence is higher in those who present to urology clinics (1 in 304), and with some chromosomal disorders. These include Edward syndrome at approximately 67%, Turner syndrome at 14% to 20%, and Down syndrome at about 1% [11][12][13].

History and Physical

Horseshoe kidneys are often asymptomatic, and so are often identified incidentally. The presentation can otherwise be non-specific with one study showing that the two most common presenting complaints of in children with horseshoe kidney are with symptoms of a urinary tract infection or with abdominal pain [14].

The kidneys are normally located in the retroperitoneum between the transverse processes of T12 and L3 with the left kidney slightly more superior than the right. The upper poles are normally positioned slightly medially and posteriorly relative to the lower poles. Horseshoe kidneys are different in three main ways: location, orientation, and vasculature [2]. The horseshoe kidney's ascent is often quoted to be held back by the inferior mesenteric artery at L3 however, the horseshoe kidney can also be found lower in the abdomen and pelvis. During weeks six to eight of development, the renal ascent is coupled with a 90-degree medial rotation. Due to the isthmus, however, horseshoe kidneys experience malrotation, and consequently, the ureters need to either pass over the isthmus or down the anterior surface of the kidneys which can cause urinary drainage problems and stasis [15][16]. Horseshoe kidneys also show a greater variation in the origin and number of renal arteries and veins [4][16][6]. These are largely dependent on where during development ascent has terminated. In one study of 90 horseshoe kidneys, 387 arteries were identified [4]. Despite this, the normal intra-renal vascular segmental pattern remains, and the ligation or division of any of these arteries results in ischemic segmental renal necrosis due to their poor collateral arterial supply [17]. The incidence of renal vein anomalies in horseshoe kidneys is also high (23%)[4].

Evaluation

Horseshoe kidneys can be identified using most abdominal imaging modalities. The diagnosis of a horseshoe kidney is most commonly made using either ultrasound or intravenous urography [18]. CT and MRI are the best for demonstrating the anatomy and can detect accessory vasculature and surrounding structures [19][4][19][18]. It is also possible to identify horseshoe kidneys on plain radiography through visualization of the perinephric fat in association with an altered renal axis. The lower poles are positioned more medial than normal and because the kidneys sit lower in the abdomen than expected [18]. Nuclear medicine radionuclide renal scans can be helpful in differentiating true obstruction from passively dilated systems.

Treatment / Management

Shockwave lithotripsy for nephrolithiasis is less effective in horseshoe kidneys due to problems localizing the energy for pelvic stones and poor stone fragment clearance due to impaired renal drainage [20]. Larger renal stones, those greater than 2.5 cm, or those not allowing ureteroscopic approaches, can be removed via minimally invasive percutaneous surgery [21]. Pre-procedural imaging such as CT is essential during the workup for any surgery required. This is due not only to the highly variable nature of the blood supply but also the association of horseshoe kidneys with having a segment of colon posteriorly and the corresponding increases in risk of incidental bowel injury [22].

Differential Diagnosis

The horseshoe kidney is one form of a renal fusion abnormality. The other two main types are crossed fusion renal ectopia and a fused pelvic kidney. In a crossed renal ectopia both kidneys are positioned on the same side of the body with one ureter crossing the midline to drain into the bladder while in a fused pelvic kidney there is one renal mass which is drained by two ureters that do not cross the midline [23].

Prognosis

An isolated finding of a horseshoe kidney is generally considered benign [3]. Horseshoe kidneys do however have an increase in frequency for some common renal cancers including transitional cell tumors (three to four times more common), Wilms tumor (twice as frequently), and an extremely large increase in very rare tumors such as carcinoid (62 to 82 times) [24][4][25][26][27][28].

Complications

About a third of all patients with horseshoe kidneys remain completely asymptomatic and are often found incidentally during imaging. The intrinsic anatomical defects present within horseshoe kidneys do however predispose individuals to a number of urological sequelae due to the associated ureteric obstruction and impaired urinary drainage [3][18]. Ureteropelvic junction obstruction (UPJ) is the most common abnormality associated with horseshoe kidneys, individuals are also predisposed to hydronephrosis, infection, vesicoureteral reflux [15][16][2]. One study showed that over half of the individuals who are symptomatic had either ureteropelvic junction obstruction or vesicoureteral reflux [14]. A recent meta-analysis suggested that 36% of patients with horseshoe kidney will develop nephrolithiasis at some stage [29]. Due to their ectopic position, horseshoe kidneys are also particularly susceptible to blunt abdominal trauma and can be compressed or fractured against the lumbar vertebrae [30].

Pearls and Other Issues

Symphysiotomy, or division of the fused isthmus, was previously recommended when doing a pyeloplasty in patients with a horseshoe kidney, but this has changed due to the increased risk of infection, fistulas, leakages, and bleeding [31]. It has also been noted that the kidneys return to their original location after such surgery, so symphysiotomy is no longer recommended.

Enhancing Healthcare Team Outcomes

Horseshoe kidneys are the most common fusion defect of the kidneys, but this still amounts to only about 0.25% of the population. Many professionals are not aware of the condition, its evaluation, or treatment. Due to its rarity, this condition is best evaluated and treated by an interprofessional team of specialty trained clinicians and nurses, and radiologists to achieve the best patient outcomes. The nursing urology specialty nurse should assist the clinician in educating the patient and family. [Level V]


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Horseshoe Kidney - Questions

Take a quiz of the questions on this article.

Take Quiz
Which of the following is not true of horseshoe kidneys?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the most common associated condition in patients with horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the most likely cancer in patients with a horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following occurs more commonly in patients with a horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
How is the diagnosis of horseshoe kidney usually made?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Once a horseshoe kidney is diagnosed, what is the radiological imaging study of choice for complete characterization?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
During surgery on an abdominal aortic aneurysm, a horseshoe kidney is discovered. What is the most appropriate management of this finding?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
In a horseshoe kidney, the fusion usually occurs at which location?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is the most common associated finding associated with a horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is the most common associated finding associated with a horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following is included in the recommended workup for horseshoe kidney?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A CT scan is done in a patient with vague abdominal pain. The radiologist highlights the area of importance. What is true about this condition?

(Move Mouse on Image to Enlarge)
  • Image 6935 Not availableImage 6935 Not available
    Image courtesy S Bhimji MD
Attributed To: Image courtesy S Bhimji MD



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Horseshoe Kidney - References

References

Schiappacasse G,Aguirre J,Soffia P,Silva CS,Zilleruelo N, CT findings of the main pathological conditions associated with horseshoe kidneys. The British journal of radiology. 2015 Jan;     [PubMed]
Stroosma OB,Scheltinga MR,Stubenitsky BM,Kootstra G, Horseshoe kidney transplantation: an overview. Clinical transplantation. 2000 Dec     [PubMed]
Crawford ES,Coselli JS,Safi HJ,Martin TD,Pool JL, The impact of renal fusion and ectopia on aortic surgery. Journal of vascular surgery. 1988 Oct     [PubMed]
Bhattarai B,Kulkarni AH,Rao ST,Mairpadi A, Anesthetic consideration in downs syndrome--a review. Nepal Medical College journal : NMCJ. 2008 Sep     [PubMed]
    [PubMed]
O'Hara PJ,Hakaim AG,Hertzer NR,Krajewski LP,Cox GS,Beven EG, Surgical management of aortic aneurysm and coexistent horseshoe kidney: review of a 31-year experience. Journal of vascular surgery. 1993 May     [PubMed]
    [PubMed]
Stein RJ,Desai MM, Management of urolithiasis in the congenitally abnormal kidney (horseshoe and ectopic). Current opinion in urology. 2007 Mar     [PubMed]
Rais-Bahrami S,Friedlander JI,Duty BD,Okeke Z,Smith AD, Difficulties with access in percutaneous renal surgery. Therapeutic advances in urology. 2011 Apr     [PubMed]
    [PubMed]
Rubio Briones J,Regalado Pareja R,Sánchez Martín F,Chéchile Toniolo G,Huguet Pérez J,Villavicencio Mavrich H, Incidence of tumoural pathology in horseshoe kidneys. European urology. 1998     [PubMed]
Huang EY,Mascarenhas L,Mahour GH, Wilms' tumor and horseshoe kidneys: a case report and review of the literature. Journal of pediatric surgery. 2004 Feb     [PubMed]
Pitts WR Jr,Muecke EC, Horseshoe kidneys: a 40-year experience. The Journal of urology. 1975 Jun     [PubMed]
Chopra P,St-Vil D,Yazbeck S, Blunt renal trauma-blessing in disguise? Journal of pediatric surgery. 2002 May     [PubMed]
Boatman DL,Kölln CP,Flocks RH, Congenital anomalies associated with horseshoe kidney. The Journal of urology. 1972 Feb     [PubMed]
Natsis K,Piagkou M,Skotsimara A,Protogerou V,Tsitouridis I,Skandalakis P, Horseshoe kidney: a review of anatomy and pathology. Surgical and radiologic anatomy : SRA. 2014 Aug     [PubMed]
Cook WA,Stephens FD, Fused kidneys: morphologic study and theory of embryogenesis. Birth defects original article series. 1977     [PubMed]
Glodny B,Petersen J,Hofmann KJ,Schenk C,Herwig R,Trieb T,Koppelstaetter C,Steingruber I,Rehder P, Kidney fusion anomalies revisited: clinical and radiological analysis of 209 cases of crossed fused ectopia and horseshoe kidney. BJU international. 2009 Jan     [PubMed]
David RS, Horseshoe kidney: a report of one family. British medical journal. 1974 Dec 7     [PubMed]
Solhaug MJ,Bolger PM,Jose PA, The developing kidney and environmental toxins. Pediatrics. 2004 Apr     [PubMed]
Friedland GW,de Vries P, Renal ectopia and fusion. Embryologic Basis. Urology. 1975 May     [PubMed]
Mandell GA,Maloney K,Sherman NH,Filmer B, The renal axes in spina bifida: issues of confusion and fusion. Abdominal imaging. 1996 Nov-Dec     [PubMed]
Cereda A,Carey JC, The trisomy 18 syndrome. Orphanet journal of rare diseases. 2012 Oct 23     [PubMed]
Ranke MB,Saenger P, Turner's syndrome. Lancet (London, England). 2001 Jul 28     [PubMed]
Lallas CD,Pak RW,Pagnani C,Hubosky SG,Yanke BV,Keeley FX,Bagley DH, The minimally invasive management of ureteropelvic junction obstruction in horseshoe kidneys. World journal of urology. 2011 Feb     [PubMed]
GLENN JF, Analysis of 51 patients with horseshoe kidney. The New England journal of medicine. 1959 Oct 1     [PubMed]
    [PubMed]
    [PubMed]
Neville H,Ritchey ML,Shamberger RC,Haase G,Perlman S,Yoshioka T, The occurrence of Wilms tumor in horseshoe kidneys: a report from the National Wilms Tumor Study Group (NWTSG). Journal of pediatric surgery. 2002 Aug     [PubMed]
Kölln CP,Boatman DL,Schmidt JD,Flocks RH, Horseshoe kidney: a review of 105 patients. The Journal of urology. 1972 Feb     [PubMed]
Pawar AS,Thongprayoon C,Cheungpasitporn W,Sakhuja A,Mao MA,Erickson SB, Incidence and characteristics of kidney stones in patients with horseshoe kidney: A systematic review and meta-analysis. Urology annals. 2018 Jan-Mar     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of PA-Hospital Medicine. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for PA-Hospital Medicine, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in PA-Hospital Medicine, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of PA-Hospital Medicine. When it is time for the PA-Hospital Medicine board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study PA-Hospital Medicine.