Contributors: Alison Dickie

 Species: Canine   |   Classification: Miscellaneous

Introduction

Uses

Advantages

Disadvantages

  • May require patient's coat to be clipped.
  • Normal sonographic appearance does not exclude disease.
  • Abnormal sonographic appearance does not always indicate significant disease.
  • Similar sonographic appearance with different diseases.

Potential problems

  • Poor transducer-skin contact:
    • Inadequate clipping.
    • Insufficient coupling medium.
  • Inadequate patient restraint.
  • Operator inexperience.
  • Patient has urinated prior to examination so bladder is empty.

Alternatives

Equipment

Ultrasound machine

  • Enter patient identification, date and other relevant information on the screen.
  • Alter time-gain, depth and focal point settings throughout the examination to optimize the images obtained.
  • Keep power setting low to reduce noise.

Transducer

  • High frequency (7.5 MHz).
  • Linear, curvilinear or sector.
  • Small scan face most convenient for small patients.

Image production and storage

  • Any of the following are acceptable:
    • Thermal printer.
    • Video recorder.
    • Multiformat camera.
    • Disk drive.

Skin preparation

  • Clippers.
  • Coupling medium:
    • Ultrasound gel.
    • Alcohol or spirit.

Environmental factors

  • Quiet room with reduced lighting.
  • Table, preferably with comfortable surface, eg blanket or foam pad.
    A relaxed patient will avoid the need for sedation.
  • Assistant to restrain patient.

Patient preparation

Prior to examination

Where to clip

  • Female: caudal ventral midline of abdomen.
  • Male: caudal ventral abdomen to either side of prepuce.
  • Extend cranially to umbilicus.

Positioning

Technique

  • Swab clipped area of skin with alcohol.
  • Apply ultrasound gel to the skin surface and the transducer before commencing with the examination.
  • Place the transducer on the ventral midline of the caudal abdomen using a longitudinal imaging plane.
  • Angle the ultrasound beam caudo-dorsally until the bladder is identified.
  • Angling further caudo-dorsally towards the pelvic brim will allow the bladder neck to be imaged.
  • Move the transducer cranially along the abdominal surface until the cranial wall of the bladder is imaged.
  • Rotate the transducer through 90° to image the bladder in short axis.
  • Alter the angle of the ultrasound beam relative to the skin surface and move the transducer up the abdominal wall to examine the bladder from a series of different positions.

Normal Anatomy

  • Urinary bladder is pear shaped, tapering to the bladder neck caudally.
  • Location of the cranial bladder wall will depend on the distention of the bladder.
  • The wall appears as a smooth, hyperechoic line 1-2 mm thick when the bladder is distended - 3 layers may be visible if high resolution transducer is used Bladder normal - ultrasound.
  • The wall appears thick and corrugated after urination.
  • Bladder contents should be anechoic.
  • The ureteral papillae may be imaged as small echogenic mounds at the trigone.
  • Ureteral jets are occasionally visualized as short-lived streams of echogenic material arising at intervals from the papillae.
  • Normal ureters not visible.
  • Proximal urethra may be followed from bladder neck until it enters pelvic cavity.

Common problems or artifacts

  • More than one condition may be present concurrently.
  • The bladder must be distended before wall thickness can be accurately assessed. If the bladder is empty, then re-scan the patient a few hours later once it has refilled.
  • Increased frequency of urination associated with many bladder diseases may make it difficult to perform examination in presence of full bladder.
    Can introduce sterile saline via a urinary catheter to distend bladder, however, air introduced during catheterization may interfere with imaging.
  • Bladder wall in near field often does not image well due to close aposition to transducer.
    Alteration of transducer position will ensure entire wall imaged well. Alternatively, a sonolucent stand-off pad may be used.
  • Slice thickness and reverberation artifacts produce appearance of echogenic material within lumen and should not be mistaken for intraluminal or mural abnormalities.
  • Distal acoustic enhancement commonly observed in region beyond bladder.
  • Pressure on transducer may cause colon to become indented into bladder wall producing appearance similar to that of a urinary calculus.