- Email: [email protected]
Urinary Tract
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C h a p t e r
4 4
Urinary Tract
III RENAL SONOGRAPHY Normal Sonographic Anatomy Penninck and co-workers reported the sonographic appearance of the kidneys in three normal horses and a single case of a calcified renal adenoma.1 As in pet animals, the renal cortex of the horse appears relatively bright compared with the medulla but relatively dark compared with the nearby spleen. The deep renal interior is composed of an anechoic pelvis and pelvic recesses, interspersed with echogenic foci corresponding to intrapelvic fat and fibrous tissue. Unlike that of the dog and cat, the equine kidney has a distinctly triangular shape featuring rounded corners.
Renal Biopsy Percutaneous renal biopsy is ideally performed with sonographic assistance. Barratt-Boyes and co-workers have reported their experience obtaining renal biopsies (primarily right-sided) from seven normal horses using both full sonographic guidance and preprocedural renal localization.2 Sonographic localization followed by “blind biopsy” was preferred over constant sonographic surveillance because it required fewer people. The preferred route to the lateral aspect of the right kidney was a transverse approach through the 17th intercostal space. Biopsy of the left kidney proved potentially more hazardous, twice requiring penetration to access underlying kidney.
Renal Dysplasia Ramirez and co-workers reported the sonographic appearance of renal dysplasia in a 3-month-old Quarter Horse colt.3 548
Ectopic Ureter Congenital and acquired ureteral ectopia has been described in foals.4,5 Blikslager and co-workers described the sonographic and urographic appearance of bilateral ectopic ureter in an incontinent 7-week-old Appaloosa filly.6 Urography was performed under anesthesia, using 300 ml of diagnostic organic iodine solution (Renografin 76, Amfac, Shawnee Mission, Kansas 66203). Distal ureteral contrast was enhanced by catheterizing the bladder, removing as much of the urine as possible and replacing it with air. Films were made at 5, 15, and 40 minutes post injection. The collecting systems of both kidneys were dilated, along with their respective ureters. The bladder failed to opacify, but contrast was observed in the vagina, strong circumstantial evidence of ureteral displacement, which necropsy later confirmed. Tomlinson and co-workers described the use of percutaneous ultrasound-guided pyelography to diagnose hydronephrosis and ectopic ureter in a 3-week-old filly.7
Renal Calculi (Nephrolithiasis, Kidney Stones) Wooldridge and co-workers described the sonographic appearance of renal dysplasia in a 2-year-old Quarter Horse, leading to hydronephrosis, hydroureter, renal and ureteral calculi, and eventually renal failure.8 Ehnen and co-workers described renal and ureteral obstruction caused by kidney stones.9 Common clinical signs in the eight horses included weight loss, poor performance, and decreased appetite. Diagnosis was made with a combination of sonography and rectal palpation. As might be anticipated, the obstructed ureters were urine distended. When identified, the ureteral stones appeared as discrete echogenic objects.
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CHAPTER 44 III Urinary Tract
Hydronephrosis The most common cause of acquired hydronephrosis in horses is nephrolithiasis or ureterolithiasis. Less often, hydronephrosis is caused by infection, tumor, postinflammatory adhesion, or injury related to surgery. Congenital ureteral ectopia is usually associated with hydronephrosis and often infection. Jones and co-workers reported unilateral hydronephrosis in a 4-month-old foal hospitalized because of hematuria. Transabdominal sonography revealed an enlarged, hydronephrotic right kidney, but the ureter and retroperitoneal cavity could not be identified.
Nephritis Kisthardt and co-workers reported the sonographic appearance of pyelonephritis in seven horses initially seen because of hematuria.10 One or more of the following sonographic abnormalities characterized renal infection: ∑ ∑ ∑ ∑ ∑ ∑
Decreased length Increased echogenicity Abnormal contour Poor or absent corticomedullary junction Dilated or distorted renal pelvis and pelvic recesses Focal hypoechoic or hypoechoic cortical defects
549
repeated on the opposite kidney, which showed leakage of contrast from a dilated proximal ureter. After ureteral repair and relocation, postoperative urine leakage, and infection, the foal eventually recovered. The histologic appearance of the resected portion of the left ureter was considered consistent with ureteritis, although there was no proof of infection. The authors did not speculate about how the proposed ureteritis was able to develop so rapidly after birth or whether this might have been an in utero infection.
Umbilical Evagination of the Urinary Bladder Textor and co-workers reported the displacement of the urinary bladder into the umbilicus in an 8-hourold Standardbred filly; this was diagnosed sonographically14 (Box 44-1).
Ruptured Urinary Bladder Bladder rupture in adult horses has been attributed to a variety of causes, including (1) dystocia in the mare, (2) urethral obstruction due to calculi, (3) urethral hematoma, (4) structural weakening subsequent to surgery, (5) infectious perforation related to umbilical infection, (6) torn bladder adhesions, (7) blunt trauma, and (8) iatrogenic rupture: overdistension during endoscopy or catheter perforation (Figure 44-1).16
Bladder Tumor Renal Carcinoma (Renal Adenocarcinoma) Ramirez and Seahorn described the sonographic appearance of a renal carcinoma in a 15-year-old Tennessee Walking Horse mare.11 The tumor appeared as a large, eccentric, relatively hyperechoic mass protruding from the caudal pole. Other than some distortion at the junction between the tumor and kidney, the latter appeared sonographically normal, with a discrete cortex and medulla. In their discussion, the authors point out that renal tumors occur rarely in horses and do not show any gender preference. Renal carcinomas develop in the polar cortex within the tubular epithelium and gradually expand, often leading to adhesions. The tumor eventually spreads via the lymph or blood systems to the regional lymph nodes and lungs. The presence of renal carcinoma is often signaled clinically by polyuria and polydipsia combined with an abnormal urine/creatinine ratio. There is no cure.12
Ureteral Stenosis Morisset and co-workers reported a case of congenital ureteral stenosis in a 2-day-old foal with uroperitoneum.13 Sonographically, the left renal pelvis appeared dilated, but retrograde urography failed to determine the cause. Guided by ultrasound, diagnostic iodine solution was injected directly into the left renal pelvis (unilateral antegrade urography), eventually revealing distal ureteral stenosis. The procedure was
Lymphosarcoma. Sweeney and co-workers described a large pelvic lymphosarcoma that infiltrated the wall of the urinary bladder, obstructing a ureter and causing hydronephrosis. The tumor also invaded the uterus.17 The renal lesion was detected with transabdominal ultrasound; the bladder lesion was identified using rectal sonography. Adrenal Glands. Johnson described pheochromocytoma in two horses, a 12-year-old Standardbred and
B o x
4 4 - 1
Causes of Urinary Outflow Obstruction in Horses Neurologic
Nonneurologic Neoplastic Parasitic Inflammatory/infectious Congenital
Cauda equina syndrome Equine protozoal myeloencephalitis Herpes myeloencephalitis Urolithiasis Tumors Habronemiasis Nonspecific inflammatory swelling (urethritis) Inflammatory urethral webs15 Congenital urethral webs Congenital longitudinal and fenestrated transverse urethral partitions
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SECTION VII III The Abdomen
B
A Figure 44-1 • A, Abdominal sonogram shows a large volume of clear peritoneal fluid, the result of a perforated urinary bladder and resultant chemical peritonitis. B, A second sonogram shows fluid surrounding a testicle.
Table 44–1 • NORMAL UMBILICAL AND UMBILICAL VASCULAR MEAN DIAMETERS IN 1- AND 7-DAY-OLD FOALS Umbilical Element
1-Day-Old Foal
7-Day-Old Foal
Umbilical vein Umbilical stump Urachus plus arteries Umbilical arteries
8.3 15.5 17.7 7.8
5.8 12.5 17.8 6.4
mm mm mm mm
(±3.0) (±2.7) (±2.7) (±1.7)
mm mm mm mm
(±1.5) (±2.3) (±2.6) (±1.5)
Modified from Levan RP, Craychee T, Madigan JE: Practical method of umbilical ultrasonic examination of one-week old foals: the procedure and the interpretation of age-correlated size ranges of umbilical structures, Equine Veterinary Sci.
III SONOGRAPHIC ASSESSMENT OF THE SUSPECT UMBILICUS Sonographic Examination Routine sonographic examination of the foal umbilicus consists of four parts (Figure 44-2): Figure 44-2 • Umbilical diagram showing essential anatomic elements and their spatial relationships.
a 21-year-old Quarter Horse. Common clinical signs included excessive sweating, muscle tremors, tachycardia, tachypnea, hyperglycemia, azotemia, colic, and hemoperitoneum. Retroperitoneal swelling, detected on rectal palpation, was the result of bleeding from the tumor.18
1. Examination of the umbilicus 2. Examination of the umbilical vein 3. Examination of the umbilical arteries and urachal remnant 4. Examination of the umbilical arteries and bladder Several authors have published normal sonometrics for the foal umbilicus and related vasculature, including the (1) umbilical vein, (2) umbilical stump, (3) urachus plus arteries, and (4) umbilical arteries. Lavan and co-workers have provided normal values for both 1- and 7-day-old foals (Table 44-1).19
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Figure 44-3 • Abscessed umbilicus with cavitation and a pair of small air pockets featuring strong through transmission, indicating the fluid nature of the cavity.
A
B
Figure 44-4 • A, Sonographic cross-section of an abscessed umbilical vein and its infected surroundings (center). B, A closeup view of the umbilical vein shows the classic features of severe phlebitis: (1) luminal enlargement, (2) wall thickening, (3) a septic thrombus, and (4) gas.
Umbilical Infection Umbilical infection in young foals can assume a variety of forms: (1) generalized inflammation (omphalitis), (2) abscessation, (3) inflammation of the umbilical vein (ompalophlebitis), (4) inflammation of the umbilical arteries (omphaloarteritis), (5) septicemia, and (6) urachal patency. Contrary to some published
reports, most of the examinations performed in our hospital are prompted by a swollen, nonreducible umbilical swelling. Drainage and pain may also be associated with umbilical infection but are inconstant features. A number of examples follow (Figures 44-3 through 44-5).
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SECTION VII III The Abdomen
Figure 44-5 • Sonographic oblique section of an infected umbilical vein (left center), umbilical artery (far right center), and surrounding tissues.
References 1. Penninck DG, Eisenberg HM, et al: Ultrasonography: normal and abnormal, Vet Radiol 27:81, 1986. 2. Barratt-Boyes SM, Spensley MS, et al: Ultrasound localization and guidance for renal biopsy in the horse, Vet Radiol Ultrasound 32:121, 1991. 3. Ramirez S, Williams J, et al: Ultrasound-assisted diagnosis of renal dysplasia in a 3-month-old Quarter Horse colt, Vet Radiol Ultrasound 39:143, 1998. 4. Stickle RL, Wilcock BP, Huseman H: Multiple ureteral defects in a Belgian foal, Vet Med Small Anim Clin 70:819, 1975. 5. Jean D, Marcoux M, Louf C-E: Congenital bilateral distal defect of the ureters in a foal, Equine Vet Educ 10:17, 1998. 6. Blikslager AT, Green EM, et al: Excretory urography and ultrasonography in the diagnosis of bilateral ectopic ureters in a foal, Vet Radiol Ultrasound 33:41, 1992.
7. Tomlinson JE, Farnsworth K, et al: Percutaneous ultrasound-guided pyelography aided diagnosis of ectopic ureter and hydronephrosis in a 3-week-old filly, Vet Radiol Ultrasound 42:349, 2001. 8. Wooldridge AA, Seahorn TL, et al: Chronic renal failure associated with nephrolithiais, ureterolithiasis, and renal dysplasia in a 2-year-old Quarter Horse gelding, Vet Radiol Ultrasound 33:121, 1992. 9. Ehnen SJ, Divers TJ, et al: Obstructive nephrolithiasis and ureterolithiasis associated with chronic renal failure in horses: eight cases (1981-1987), J Am Vet Med Assoc 197: 249, 1990. 10. Kisthardt KK, Schumacher J, et al: Severe renal hemorrhage caused by pyelonephritis in 7 horses: clinical and ultrasonic evaluation, Can Vet J 40:571, 1999. 11. Ramirez S, Seahorn TL: Ultrasonography as an aid to diagnosis of renal cell carcinoma in a horse, Vet Radiol Ultrasound 37:383, 1996. 12. Traub-Dargatz JL: Urinary tract neoplasia, Vet Clin N Am Equine Pract 14:495, 1998. 13. Morisset S, Hawkins JF, et al: Surgical management of a ureteral defect with ureterorrhaphy and of ureteritis with ureteroneocystostomy in a foal, J Am Vet Med Assoc 220:354, 2002. 14. Textor JA, Goodrich L, Wion L: Umbilical evagination of the urinary bladder in a neonatal filly, J Am Vet Med Assoc 219:953, 2001. 15. Blikslager AT, Tate LP, Jones SL: Neodymium:yttriumaluminum-garnet laser ablation of a urethral web to relieve urinary outflow obstruction in a horse, J Am Vet Med Assoc 218:1970, 2001. 16. Walesby HA, Ragle CA, Booth LC: Laparoscopic repair of ruptured urinary bladder in a stallion, J Am Vet Med Assoc 221:1737, 2002. 17. Sweeney RW, Hamir AN, Fisher RR: Lymphosarcoma with urinary bladder infiltration in a horse, J Am Vet Med Assoc 199:1177, 1991. 18. Johnson PJ, Goetz GL, et al: Pheochromocytoma in two horsers, J Am Vet Med Assoc 206:837, 1993. 19. Lavan RP, Craychee T, Madigan JE: Practical method of umbilical ultrasonic examination of one-week old foals: the procedure and the interpretation of age-correlated size ranges of umbilical structures, Equine Vet Sci 21:100, 2001.
C h a p t e r
4 4
Urinary Tract
III RENAL SONOGRAPHY Normal Sonographic Anatomy Penninck and co-workers reported the sonographic appearance of the kidneys in three normal horses and a single case of a calcified renal adenoma.1 As in pet animals, the renal cortex of the horse appears relatively bright compared with the medulla but relatively dark compared with the nearby spleen. The deep renal interior is composed of an anechoic pelvis and pelvic recesses, interspersed with echogenic foci corresponding to intrapelvic fat and fibrous tissue. Unlike that of the dog and cat, the equine kidney has a distinctly triangular shape featuring rounded corners.
Renal Biopsy Percutaneous renal biopsy is ideally performed with sonographic assistance. Barratt-Boyes and co-workers have reported their experience obtaining renal biopsies (primarily right-sided) from seven normal horses using both full sonographic guidance and preprocedural renal localization.2 Sonographic localization followed by “blind biopsy” was preferred over constant sonographic surveillance because it required fewer people. The preferred route to the lateral aspect of the right kidney was a transverse approach through the 17th intercostal space. Biopsy of the left kidney proved potentially more hazardous, twice requiring penetration to access underlying kidney.
Renal Dysplasia Ramirez and co-workers reported the sonographic appearance of renal dysplasia in a 3-month-old Quarter Horse colt.3 548
Ectopic Ureter Congenital and acquired ureteral ectopia has been described in foals.4,5 Blikslager and co-workers described the sonographic and urographic appearance of bilateral ectopic ureter in an incontinent 7-week-old Appaloosa filly.6 Urography was performed under anesthesia, using 300 ml of diagnostic organic iodine solution (Renografin 76, Amfac, Shawnee Mission, Kansas 66203). Distal ureteral contrast was enhanced by catheterizing the bladder, removing as much of the urine as possible and replacing it with air. Films were made at 5, 15, and 40 minutes post injection. The collecting systems of both kidneys were dilated, along with their respective ureters. The bladder failed to opacify, but contrast was observed in the vagina, strong circumstantial evidence of ureteral displacement, which necropsy later confirmed. Tomlinson and co-workers described the use of percutaneous ultrasound-guided pyelography to diagnose hydronephrosis and ectopic ureter in a 3-week-old filly.7
Renal Calculi (Nephrolithiasis, Kidney Stones) Wooldridge and co-workers described the sonographic appearance of renal dysplasia in a 2-year-old Quarter Horse, leading to hydronephrosis, hydroureter, renal and ureteral calculi, and eventually renal failure.8 Ehnen and co-workers described renal and ureteral obstruction caused by kidney stones.9 Common clinical signs in the eight horses included weight loss, poor performance, and decreased appetite. Diagnosis was made with a combination of sonography and rectal palpation. As might be anticipated, the obstructed ureters were urine distended. When identified, the ureteral stones appeared as discrete echogenic objects.
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Hydronephrosis The most common cause of acquired hydronephrosis in horses is nephrolithiasis or ureterolithiasis. Less often, hydronephrosis is caused by infection, tumor, postinflammatory adhesion, or injury related to surgery. Congenital ureteral ectopia is usually associated with hydronephrosis and often infection. Jones and co-workers reported unilateral hydronephrosis in a 4-month-old foal hospitalized because of hematuria. Transabdominal sonography revealed an enlarged, hydronephrotic right kidney, but the ureter and retroperitoneal cavity could not be identified.
Nephritis Kisthardt and co-workers reported the sonographic appearance of pyelonephritis in seven horses initially seen because of hematuria.10 One or more of the following sonographic abnormalities characterized renal infection: ∑ ∑ ∑ ∑ ∑ ∑
Decreased length Increased echogenicity Abnormal contour Poor or absent corticomedullary junction Dilated or distorted renal pelvis and pelvic recesses Focal hypoechoic or hypoechoic cortical defects
549
repeated on the opposite kidney, which showed leakage of contrast from a dilated proximal ureter. After ureteral repair and relocation, postoperative urine leakage, and infection, the foal eventually recovered. The histologic appearance of the resected portion of the left ureter was considered consistent with ureteritis, although there was no proof of infection. The authors did not speculate about how the proposed ureteritis was able to develop so rapidly after birth or whether this might have been an in utero infection.
Umbilical Evagination of the Urinary Bladder Textor and co-workers reported the displacement of the urinary bladder into the umbilicus in an 8-hourold Standardbred filly; this was diagnosed sonographically14 (Box 44-1).
Ruptured Urinary Bladder Bladder rupture in adult horses has been attributed to a variety of causes, including (1) dystocia in the mare, (2) urethral obstruction due to calculi, (3) urethral hematoma, (4) structural weakening subsequent to surgery, (5) infectious perforation related to umbilical infection, (6) torn bladder adhesions, (7) blunt trauma, and (8) iatrogenic rupture: overdistension during endoscopy or catheter perforation (Figure 44-1).16
Bladder Tumor Renal Carcinoma (Renal Adenocarcinoma) Ramirez and Seahorn described the sonographic appearance of a renal carcinoma in a 15-year-old Tennessee Walking Horse mare.11 The tumor appeared as a large, eccentric, relatively hyperechoic mass protruding from the caudal pole. Other than some distortion at the junction between the tumor and kidney, the latter appeared sonographically normal, with a discrete cortex and medulla. In their discussion, the authors point out that renal tumors occur rarely in horses and do not show any gender preference. Renal carcinomas develop in the polar cortex within the tubular epithelium and gradually expand, often leading to adhesions. The tumor eventually spreads via the lymph or blood systems to the regional lymph nodes and lungs. The presence of renal carcinoma is often signaled clinically by polyuria and polydipsia combined with an abnormal urine/creatinine ratio. There is no cure.12
Ureteral Stenosis Morisset and co-workers reported a case of congenital ureteral stenosis in a 2-day-old foal with uroperitoneum.13 Sonographically, the left renal pelvis appeared dilated, but retrograde urography failed to determine the cause. Guided by ultrasound, diagnostic iodine solution was injected directly into the left renal pelvis (unilateral antegrade urography), eventually revealing distal ureteral stenosis. The procedure was
Lymphosarcoma. Sweeney and co-workers described a large pelvic lymphosarcoma that infiltrated the wall of the urinary bladder, obstructing a ureter and causing hydronephrosis. The tumor also invaded the uterus.17 The renal lesion was detected with transabdominal ultrasound; the bladder lesion was identified using rectal sonography. Adrenal Glands. Johnson described pheochromocytoma in two horses, a 12-year-old Standardbred and
B o x
4 4 - 1
Causes of Urinary Outflow Obstruction in Horses Neurologic
Nonneurologic Neoplastic Parasitic Inflammatory/infectious Congenital
Cauda equina syndrome Equine protozoal myeloencephalitis Herpes myeloencephalitis Urolithiasis Tumors Habronemiasis Nonspecific inflammatory swelling (urethritis) Inflammatory urethral webs15 Congenital urethral webs Congenital longitudinal and fenestrated transverse urethral partitions
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SECTION VII III The Abdomen
B
A Figure 44-1 • A, Abdominal sonogram shows a large volume of clear peritoneal fluid, the result of a perforated urinary bladder and resultant chemical peritonitis. B, A second sonogram shows fluid surrounding a testicle.
Table 44–1 • NORMAL UMBILICAL AND UMBILICAL VASCULAR MEAN DIAMETERS IN 1- AND 7-DAY-OLD FOALS Umbilical Element
1-Day-Old Foal
7-Day-Old Foal
Umbilical vein Umbilical stump Urachus plus arteries Umbilical arteries
8.3 15.5 17.7 7.8
5.8 12.5 17.8 6.4
mm mm mm mm
(±3.0) (±2.7) (±2.7) (±1.7)
mm mm mm mm
(±1.5) (±2.3) (±2.6) (±1.5)
Modified from Levan RP, Craychee T, Madigan JE: Practical method of umbilical ultrasonic examination of one-week old foals: the procedure and the interpretation of age-correlated size ranges of umbilical structures, Equine Veterinary Sci.
III SONOGRAPHIC ASSESSMENT OF THE SUSPECT UMBILICUS Sonographic Examination Routine sonographic examination of the foal umbilicus consists of four parts (Figure 44-2): Figure 44-2 • Umbilical diagram showing essential anatomic elements and their spatial relationships.
a 21-year-old Quarter Horse. Common clinical signs included excessive sweating, muscle tremors, tachycardia, tachypnea, hyperglycemia, azotemia, colic, and hemoperitoneum. Retroperitoneal swelling, detected on rectal palpation, was the result of bleeding from the tumor.18
1. Examination of the umbilicus 2. Examination of the umbilical vein 3. Examination of the umbilical arteries and urachal remnant 4. Examination of the umbilical arteries and bladder Several authors have published normal sonometrics for the foal umbilicus and related vasculature, including the (1) umbilical vein, (2) umbilical stump, (3) urachus plus arteries, and (4) umbilical arteries. Lavan and co-workers have provided normal values for both 1- and 7-day-old foals (Table 44-1).19
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Figure 44-3 • Abscessed umbilicus with cavitation and a pair of small air pockets featuring strong through transmission, indicating the fluid nature of the cavity.
A
B
Figure 44-4 • A, Sonographic cross-section of an abscessed umbilical vein and its infected surroundings (center). B, A closeup view of the umbilical vein shows the classic features of severe phlebitis: (1) luminal enlargement, (2) wall thickening, (3) a septic thrombus, and (4) gas.
Umbilical Infection Umbilical infection in young foals can assume a variety of forms: (1) generalized inflammation (omphalitis), (2) abscessation, (3) inflammation of the umbilical vein (ompalophlebitis), (4) inflammation of the umbilical arteries (omphaloarteritis), (5) septicemia, and (6) urachal patency. Contrary to some published
reports, most of the examinations performed in our hospital are prompted by a swollen, nonreducible umbilical swelling. Drainage and pain may also be associated with umbilical infection but are inconstant features. A number of examples follow (Figures 44-3 through 44-5).
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SECTION VII III The Abdomen
Figure 44-5 • Sonographic oblique section of an infected umbilical vein (left center), umbilical artery (far right center), and surrounding tissues.
References 1. Penninck DG, Eisenberg HM, et al: Ultrasonography: normal and abnormal, Vet Radiol 27:81, 1986. 2. Barratt-Boyes SM, Spensley MS, et al: Ultrasound localization and guidance for renal biopsy in the horse, Vet Radiol Ultrasound 32:121, 1991. 3. Ramirez S, Williams J, et al: Ultrasound-assisted diagnosis of renal dysplasia in a 3-month-old Quarter Horse colt, Vet Radiol Ultrasound 39:143, 1998. 4. Stickle RL, Wilcock BP, Huseman H: Multiple ureteral defects in a Belgian foal, Vet Med Small Anim Clin 70:819, 1975. 5. Jean D, Marcoux M, Louf C-E: Congenital bilateral distal defect of the ureters in a foal, Equine Vet Educ 10:17, 1998. 6. Blikslager AT, Green EM, et al: Excretory urography and ultrasonography in the diagnosis of bilateral ectopic ureters in a foal, Vet Radiol Ultrasound 33:41, 1992.
7. Tomlinson JE, Farnsworth K, et al: Percutaneous ultrasound-guided pyelography aided diagnosis of ectopic ureter and hydronephrosis in a 3-week-old filly, Vet Radiol Ultrasound 42:349, 2001. 8. Wooldridge AA, Seahorn TL, et al: Chronic renal failure associated with nephrolithiais, ureterolithiasis, and renal dysplasia in a 2-year-old Quarter Horse gelding, Vet Radiol Ultrasound 33:121, 1992. 9. Ehnen SJ, Divers TJ, et al: Obstructive nephrolithiasis and ureterolithiasis associated with chronic renal failure in horses: eight cases (1981-1987), J Am Vet Med Assoc 197: 249, 1990. 10. Kisthardt KK, Schumacher J, et al: Severe renal hemorrhage caused by pyelonephritis in 7 horses: clinical and ultrasonic evaluation, Can Vet J 40:571, 1999. 11. Ramirez S, Seahorn TL: Ultrasonography as an aid to diagnosis of renal cell carcinoma in a horse, Vet Radiol Ultrasound 37:383, 1996. 12. Traub-Dargatz JL: Urinary tract neoplasia, Vet Clin N Am Equine Pract 14:495, 1998. 13. Morisset S, Hawkins JF, et al: Surgical management of a ureteral defect with ureterorrhaphy and of ureteritis with ureteroneocystostomy in a foal, J Am Vet Med Assoc 220:354, 2002. 14. Textor JA, Goodrich L, Wion L: Umbilical evagination of the urinary bladder in a neonatal filly, J Am Vet Med Assoc 219:953, 2001. 15. Blikslager AT, Tate LP, Jones SL: Neodymium:yttriumaluminum-garnet laser ablation of a urethral web to relieve urinary outflow obstruction in a horse, J Am Vet Med Assoc 218:1970, 2001. 16. Walesby HA, Ragle CA, Booth LC: Laparoscopic repair of ruptured urinary bladder in a stallion, J Am Vet Med Assoc 221:1737, 2002. 17. Sweeney RW, Hamir AN, Fisher RR: Lymphosarcoma with urinary bladder infiltration in a horse, J Am Vet Med Assoc 199:1177, 1991. 18. Johnson PJ, Goetz GL, et al: Pheochromocytoma in two horsers, J Am Vet Med Assoc 206:837, 1993. 19. Lavan RP, Craychee T, Madigan JE: Practical method of umbilical ultrasonic examination of one-week old foals: the procedure and the interpretation of age-correlated size ranges of umbilical structures, Equine Vet Sci 21:100, 2001.