Management of male cats with urethral obstruction (Proceedings)
Aug 01, 2009
CVC IN KANSAS CITY PROCEEDINGS
Pathophysiology of urethral obstruction
Urethral plugs consist of proteins and embedded constituents of the urine in varying proportion. They contain little internal structure, and most commonly form in the penile urethra. Lower urinary tract inflammation, caused by either idiopathic cystitis/urethritis or bladder stones, precedes the formation of urethral plugs. Struvite still comprises the major crystal in plugs, despite the emergence of calcium oxalate crystalluria. Inflammatory exudates of white blood cells and proteins, red blood cells from hemorrhage, sloughed epithelial cells, fibrin, calcium oxalate crystals, and calici-like viral particles may also become trapped if present in urine at the time of plug formation.
Most plugs cause obstruction within the penile urethra, but obstructions can also occur at more proximal sites. The predominant mineral composition in most plugs is magnesium ammonium phosphate (struvite). Secondary components can contribute to plug formation including inflammatory exudate ( WBC and proteins), red blood cells, cellular debris, sloughed tissue (epithelial cells), struvite crystals and combinations. Virus-like particles resembling calicivirus and bacteria have also been observed within urethral plugs examined by transmission electron microscopy. Primary inflammatory changes ( exudates, blood, and edema) or changes within the urethral wall secondary to intraluminal urethral plugs may contribute to the obstructive process. These changes may be magnified following instrumentation with catheters and back-flushing solutions used in therapeutic endeavors.
Diagnostics and management