Discussion
Perinephric pseudocyst formation, characterized by the accumulation of a variable amount of serous fluid in fibrous sacs surrounding
one or both kidneys, is a relatively uncommon disease in cats.1-3 Because the cyst is not lined with epithelium, the term pseudocyst is used. The pathogenesis of the perinephric fluid accumulation is not completely understood, but underlying renal parenchymal
disease may be a factor.2-5 Chronic interstitial renal disease is often present in association with pseudocysts, and progressive renal parenchyma contraction
that impairs venous or lymphatic drainage could result in transudation. The fluid may accumulate in a subcapsular or an extracapsular
location and is usually characterized as a transudate, having a low protein content, a low specific gravity, and a low cell
count.6,7 It is also possible to find urine (uriniferous pseudocyst) or blood within the pseudocyst. Uriniferous pseudocysts occur
from extravasation of urine between the kidney and renal capsule usually because of urinary tract trauma or an obstruction.
Blood that accumulates in pseudocysts may be secondary to blood dyscrasias, blood vessel damage from neoplasia, external trauma,
aneurysm rupture, or surgery.
Perinephric pseudocysts occur primarily in male cats with a mean age of 11 years.1-7 Cats usually appear outwardly healthy with an increasingly distended, nonpainful abdomen, but signs of concomitant renal
failure may be present.3,4 While abdominal palpation reveals what may seem like dramatic renomegaly, radiography demonstrates a large, fluid-filled
mass (or masses) in the area occupied by the kidneys, and ultrasonography shows the anechoic fluid surrounding the renal parenchyma.
Treatments for perinephric pseudocysts are ultrasound-guided aspiration of the fluid, combined nephrectomy and cyst resection,
and resection of the cyst wall with or without adjunctive omentalization.1,8,9 Because of continual fluid production, needle drainage provides only temporary relief to the patient, lasting from days to
months, and should be repeated as needed. Instilling tetracycline into the pseudocysts can prolong the period between recurrences
but is associated with extremely high fever in some patients.10 Nephrectomy should be avoided, if possible, when underlying renal disease is present or suspected because of the potential
for rapid progression of underlying chronic renal failure in the remaining kidney.1,3 Renal biopsy of the contralateral kidney is useful to identify underlying parenchymal disease, but complications such as
hemorrhage and deterioration of renal function must be considered.
Currently, resecting the cyst wall is the most common treatment. If the cyst wall is insufficiently removed, a new pseudocyst
may form, necessitating dissection to the renal hilus.9 Because of the continued fluid production from the cyst remnants after capsulectomy and the inability of the peritoneum to
remove the excess fluid, ascites can occur.11 Using the omentum to enhance physiologic draining of the fluid has been reported and may be useful in minimizing abdominal
distention.8,9 Surgically resecting the pseudocyst wall is often effective in relieving clinical signs, but renal disease will continue
to progress. The patient's prognosis is related to the severity of renal dysfunction at the time the perinephric pseudocyst
is diagnosed.
The photographs and information for this case were provided by Becky L. Morrow, DVM, Biology Department, College of Natural
Sciences and Mathematics, Indiana University of Pennsylvania, Indiana, PA 15705.
REFERENCES
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3. Osborne CA, Finco DR. Diseases of the kidney. In: Canine and feline nephrology and urology. Philadelphia, Pa: Lippincott Williams & Wilkins, 1995;466-470.
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10. Mattoon J. Renal ultrasound. Available at:
http://www.vet.osu.edu/docs/ClinSci/radiology/urinary/renalus.html. Accessed March 3, 2005.
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