Struvite crystalluria

Magnesium ammonium phosphate – (struvite) crystals typically appear as colourless, orthorhombic (i.e. with three unequal axes that crosses each other in right angles ) coffin-like prisms. They often have three until six or more sides and often have blunt ends (Fig. 32-39). Six ‘til eight sided struvite crystals in cats are considered sometimes by mistake as cystine crystals (Fig. 40-41). But in contrast to cystine they occur together with other forms of struvite and dissolve themselves immediately after acidification with diluted acetic acid. Struvite crystals occasionally agglomerate themselves to fern-like objects. The sharp profile from struvite crystals which are characteristic for fresh urine may become feather-like or moth-eaten during the dissolving.

Interpretation
Struvite crystals often occur in dogs and occasionally in cats together with free ammonia that is produced during the microbially by urease triggered hydrolysis of urine urea. Struvite crystals also appear very often in cats and occasionally in dogs in combination with no detectable urease. In this case the ammonia component from the struvite is probably produced in the kidney tubules. Composited urinary calculus which contain various amounts of sulfonamides had been found in dogs and cats. Other forms of crystalluria related to medicates are only described for humans. Roentgen contrast agent like Urografin® (Schering) and Uromiro® (Heyden) may precipitate in the urine as pleomorphic needles that occur single or in bundles. Ampicillin may precipitate in acid urine as thin colourless needles. Primidone may precipitate as hexagonal plate which resemble to calcium oxalate monohydrate. Ciprofloxacin may precipitate in alkaline urine as a bundle with eccentric bond.

Fig. 32)
Microphotographic picture from magnesium ammonium phosphate crystals in the urine sediment from an eleven-year-old male English Cocker Spaniel with bladder calculus of struvite.

Fig. 33)
Scanning electron microscope picture from a magnesium ammonium phosphate crystal in the urine sediment from a one-year-old Dwarf Schnauzer with bladder calculus of struvite.

Fig. 34)
Microphotographic picture from magnesium ammonium phosphate crystals in the urine sediment from a thirteen-weeks-old male Springer Spaniel with urinary infection caused by Proteus mirabilis.

Fig.35)
Scanning electron microscope picture from magnesium ammonium phosphate crystals in the urine sediment from the dog from fig. 34.

Fig 36)
Microphotographic picture from the accommodation of magnesium ammonium phosphate crystals in the urine sediment from a dog.

Fig.37)
Scanning electron microscope picture from magnesium ammonium phosphate crystals in the urine sediment from a four-year-old longhair cat.

Fig.38)
Microphotographic picture from magnesium ammonium phosphate crystals in the urine sediment from five-year-old cow.

Fig.39)
Scanning electron microscope picture from magnesium ammonium phosphate crystals related to medicaments in the urine sediment from the cow from fig. 38. crystalluria.