Contributors: Fraser McConnell

 Species: Canine   |   Classification: Miscellaneous

Introduction

  • Radiography allows evaluation of kidney and bladder number, size, shape and position.
    Significant renal disease may be present despite radiological appearance of normal kidneys.
  • Ureters and urethra are not normally visible without contrast studies.
  • Ovaries and uterus are not visible unless they are enlarged.
  • Radiography of limited value to assess testicular and penile diseases.
  • Contrast radiography is required for full evaluation of the urinary tract.
  • Radiography is of limited value in assessing renal function Renal function assessment.

Radiographic considerations

  • The lateral projection is most useful for evaluation of the bladder and urethra.
  • A low KVp and high mAs should be used to maximize contrast of abdominal radiographs.
  • A grid is necessary if the depth of tissue is >10 cm.
  • Care should be taken to include the entire urinary tract for most investigations.

Restraint

Indications

Radiographic anatomy

  • The kidneys and ureters are retroperitoneal.

Ureters

  • The ureters are not normally visualized unless excretory urography is performed.
  • They are less than 2 mm in diameter.
  • The ureters run in a fold of peritoneum from the renal pelvices to the trigone of the bladder.
  • The left ureter inserts into the bladder slightly caudal to the insertion of the right ureter.
  • The ureters curve cranially in a hook shape as they insert into the dorsal wall of the bladder Ureter ectopic ureter (mild dilatation) - IVU and pneumocystogram.

Bladder

  • The bladder is situated in the caudoventral abdomen ventral to the colon and uterus in female dogs.
  • It sits within the fold of peritoneum.
  • The bladder neck should lie cranial to the pelvic brim.

Urethra

  • The urethra is not normally visible on plain radiographs.
  • In male dogs the urethra runs in a smooth arc from bladder neck to the tip of the penis and is divided into prostatic, membranous and penile portions Urethra normal retrograde urethrogram (male) - lateral. The penile urethra passes ventral to the penis bone.
  • The urethra is shorter in the female dog Urethra normal retrograde vaginourethrogram (female) - lateral.

Prostate

  • Smooth marginated round soft tissue structure caudal to bladder neck, ventral to rectum and dorsal to pubis.
  • Should be barely visible in male castrated dogs.

Vagina

  • Requires positive contrast vaginogram for evaulation.
  • On a postive contrast vaginogram, the vestibulum with clitoris, the vagina propria and the spoon-shaped cervix can be recognized.
  • The height of the vestibulovaginal junction should measure >20% of the vaginal height.

Interpretation

  • The entire urinary tract should be on the radiograph.
    It is often necessary to take separate radiographs of the urethra in male dogs due to superimposition of the hindlimbs.
  • Radiographs may need to be taken with the hindlimbs pulled cranially and caudally if disease of the urethra is suspected.
  • Care should be taken to assess the rest of the abdominal contents carefully for concurrent disease.
  • The lumbar spine, pelvic inlet, retroperitoneal space and sublumbar lymph nodes (which lie ventral to the 6th lumbar vertebra) should be evaluated for signs of metastatic spread of tumors.
  • Poor peritoneal detail may be due to rupture of the bladder or lack of abdominal fat due to weight loss. Poor retroperitoneal detail may be due to rupture of the bladder neck, urethra, ureters or renal trauma and hemorrhage.
  • Mineralization of the renal parenchyma may be difficult to assess due to overlying fecal material in the colon.
  • Air introduced into the colon to create a pneumocolon Radiography: large intestine contrast can help to differentiate true renal mineralization from artifact.
    Contrast radiography is required in most cases to fully evaluate the urinary tract.

Size

  • Enlarged ureters (=hydroureters) can only exceptionally be recognized on survey films and require an excretory urography study for visualization. Dilated ureters are commonly seen with ectopic ureters, ascending infection, ureteral obstruction and/or stricture (urolithiasis Urolithiasis , bladder neck neoplasia Bladder: neoplasia ), extrinsic ureteral compression (eg uterine stump granuloma).
  • Absence of bladder shadow: empty bladder, bladder herniation Bladder: herniation , poor positioning (hind limbs not extended).
  • Small bladder: recent urination, bilateral ectopic ureters, chronic cystitis Cystitis.
  • A very large bladder may indicate polydipsia or high rate IV fluid treatment, urinary obstruction, sacral or pelvic trauma (pudendal and/or pelvic nerve damage), neurogenic bladder disorders or simply lack of opportunity to urinate.
  • An enlarged uterus can be recognized by the presence of a visible tubular soft tissue structure between bladder and colon, multiple large tubular structures in the caudal abdomen with cranial small intestinal displacement and possibly dorsal large intestinal displacement.
  • Most common cause of uterine enlargement is pyometra Pyometra Uterus pyometra - radiograph lateral , pregnancy and post partum uterus. Mucometra, hemometra, and hydrometra are rare. Focal uterine enlargement is also rare and can be caused by stump pyometra in a castrated dog, single horn pregnancy or pyometra, uterine neoplasia Uterus: neoplasia such as leiomyosarcoma Leiomyoma / leiomyosarcoma.
  • Enlarged retained testicles may be seen in the caudoventral or midventral abdomen as an ovoid soft tissue mass. Differential diagnosis includes intra-abdominal testicular neoplasia Testicle: neoplasia (common) and torsion (rare).
  • Large ovarian masses Ovary mass - radiograph may be seen caudal to the caudal pole of a kidney, causing ventral displacement of large and small intestines. Differential diagnosis includes neoplasm Ovary: neoplasia (granulosa cell tumor, teratoma, adenocarcinomas), cystic neoplasm, cysts and abscessation (rare).
  • Prostatomegaly: prostatic shadow protrudes cranially beyond pelvic brim and displaces rectum dorsally on lateral radiograph Prostate prostatomegaly - radiograph lateral. Differential diagnosis in intact male dogs: benign hyperplasia Prostate: benign hyperplasia and hypertrophy , prostatitis, abscessation Prostate: abscessation , cysts Prostate: cyst and neoplasia (namely adenocarcinomas), in castrated male dogs: prostatic neoplasia Prostate: neoplasia.
  • Paraprostatic cysts can be recognized as large ovoid soft tissue structures dorsal and/or lateral to the urinary bladder, possibly reaching cranial to the cranial pole of the bladder Prostate paraprostatic cysts - radiograph lateral Prostate paraprostatic calcified cysts - lateral pneumocystogram.
  • Vaginal and cervix masses may cause urethral obstruction, cystomegaly and hydronephrosis, dorsal displacement of the rectum. Positive contrast vaginogram may outline filling defect caused by vaginal neoplasia Vagina neoplasia - retrograde vaginourethrogram.

Position

  • Ectopic ureter scan enter the urethra, vagina or rectum. Only visible on excretory urography or possibly retrograde vaginogram.
  • Caudal displacement and retroflexion of the bladder can occur with perineal hernias (male dogs); ventral displacement and entrapment in inguinal hernia Inguinal hernia , herniation through body wall rupture may be difficult to delineate without retrograde contrast study.
  • Intrapelvic position of the bladder neck in female dogs is one known factor in the pathophysiology of urethral sphincter mechanism incompetence Urinary incontinence: urethral sphincter mechanism incompetence.
  • A prostatic shadow protruding cranially from the pelvic brim indicates prostatomegaly (see above) Prostate prostatomegaly - radiograph lateral.
    Presence of two ovoid soft tissue structures in the caudoventral abdomen can represent a normal cranial bladder and enlarged caudal prostate, a normal caudal bladder and a large paraprostatic cyst, or a normal bladder and an enlarged retained testicle. Retrograde urethrocystography contrast study or ultrasound is required for differentiation.

Shape

  • Alterations in ureteral wall shape are only visible with excretory urography: ureteral diverticulosis is a rare condition in dogs characterized by multiple small irregular mucosal outpouchings.
  • Alteration in bladder shape are normally due to compression or displacement by adjacent structures.
  • With double (best), positive or negative (worst) contrast cystography the following alterations in bladder wall shape can be recognized:
    • Generalized bladder wall thickening (> 2mm) with irregular mucosal margin:
      • Chronic cystitis
      • Infiltrative neoplasm (less likely).
    • Localized wall thickening with irregular mucosal margin: neoplasia such as transitional cell carcinoma. Most common locations:
      • 1. Trigone
      • 2. Cranial pole.
    • Localized wall thickening (> 2mm) with regular mucosal margin:
      • Polypoid cystitis
      • Submucosal hemorrhage.
    • Focal contrast pooling at ureterovesical junction: ureterocele.
    • Local outpouching of bladder wall: bladder wall diverticulum.
    • Focal outpouching at urachal remnant: vesicourachal diverticulum.
  • Urethra male intact dog: with retrograde positive contrast urethrography distension of the prostatic urethra and extravasation into the prostatic tissue may be seen Urethra normal retrograde urethrogram (male) - lateral. These are non-specific changes.
  • Vagina: positive contrast retrograde vaginography may reveal stenotic vestibulovaginal junction, vaginal wall masses causing filling defects Urethra normal retrograde vaginourethrogram (female) - lateral.

Opacity
Reduced opacity

  • Gas accumulation in the bladder may be iatrogenic (previous catheterization), infection by gas-forming organisms (most commonly associated with diabetes mellitus) Bladder emphysematous cystitis - radiograph lateral abdomen.
  • Gas may also track into bladder wall and extravasate into broad ligament.
  • Urethra: with retrograde positive contrast urethrography urethral calculi may cause filling defects (=dark).
    Ensure complete filling of the urinary catheter with contrast medium prior to insertion to avoid misinterpretation of injected gas bubbles as filling defects caused by calculi.

Increased opacity

  • Urolith opacity depends on composition:

Calculus composition

Opacity on survey radiograph

Ca oxalate

Mineral

Triple phosphate

Mineral small calculi may be soft tissue opaque

Cystine

Soft tissue to mineral

Uric acid and urate

Soft tissue

Xantine

Soft tissue

Matrix Concretions

Soft tissue

Most calculi are of mixed composition and their radiopacity is therefore not predictable.In positive or double contrast cystography, the radiopacity of the calculus is relative to the opacity of the surrounding contrast medium. A radiopaque calculus on a survey film may appear lucent on a contrast study.

  • Ureters: ureteral calculi may appear as small radiopaque lesions in the dorsal and medial retroperitoneal space Ureter calculi - radiograph. IVU or ultrasound is required to confirm their location and obstructive nature.
    The branching of the caudal vena cava at the level of the 6th lumbar vertebra creates some end-on vascular shadows in the retroperitoneal space which should not be confused with radiopaque ureteral calculi.
  • Bladder: focal mineralized opacities within the bladder lumen are most often due touroliths. Usually roughly spherical and accumulate in dependent part of the bladder (usually the center on a lateral projection) Bladder calculi - radiograph lateral.
  • Dystrophic mineralization- linear mineralization of bladder wall in severe chronic cystitis Cystitis , neoplasia Bladder: neoplasia or chronic inflammation.
    In male dogs linear mineralization is more commonly seen with paraprostatic cysts than the bladder wall.It is important to evaluate the entire urinary system if uroliths are detected.
  • Radiographs taken with hindlimbs pulled cranially and caudally will aid detection of urethral calculi in males.
  • Prostatic mineralization is more commonly seen with neoplasia than with infection. In castrated male dogs highly suspicious for neoplasia, i rregular periosteal reaction along the ventral aspect of the pelvis, sacrum and caudal lumbar vertebrae together with prostatomegaly are pathognomonic for metastatic prostatic neoplasia.

Radiographic signs of pregnancy, dystocia and fetal death

  • Normal gravid uterus may be visible as uterine enlargement in mid term.
  • Fetal mineralization is visible > 42 to 45 days of gestation.
  • Fetal oversize: single fetus pregnancy has higher risk of dystocia Uterus dystocia - radiograph lateral.
  • Fetal malpresentation may be seen on survey radiographs.
  • Pelvic narrowing (old malunion fracture) can cause fetal obstruction.
  • Fetal death Uterus fetal death (physometra) - radiograph VD : fetal and/or uterine gas, hyperextension of pelvic limbs, overlap of cranial bones at fontanel, demineralization of fetal bones, compact dense fetus (mummification) Abdomen fetal ossification - radiograph lateral.

Pitfalls

  • The os penis may have a seperate center of ossification which may be mistaken for a urethral calculi.
    Urine samples should be obtained prior to contrast studies as the contrast media will alter the urinalysis.
  • Nipples overlying the kidneys or bladdder may be mistaken for calculi.
    To identify postion of nipples paint them with barium or attach a paper clip.