Introduction

• Rare condition associated with accumulation of fluid around one or both kidneys. The fluid is usually a transudate between the renal capsule and the renal parenchyma.
• Cause: unknown; associated with renal disease or, more rarely, trauma.
• Signs: asymptomatic, uni- or bilateral renomegaly, abdominal swelling or chronic kidney disease.
• Diagnosis: radiography, ultrasonography.
• Treatment: surgery (omentalization, pseudocyst resection).
• Prognosis: depends on degree of underlying renal disease, some cases recur after drainage.

Pathogenesis

Etiology

• A number of etiologies have been proposed for pseudocyst development in man:
  • Resolving perirenal hematoma.
  • Inflammatory reaction due to extravasated urine (trauma or obstruction).
  • Hypertension Hypertension.
  • Idiopathic.
• In cats:
  • Trauma   →   rupture of part of urinary tract   →   leakage of urine   →   peri-renal urinoma.
  • Renal disease, eg interstitial fibrosis, neoplasia Kidney: neoplasia, hydronephrosis Hydronephrosis / hydroureter, polycystic kidney disease Kidney: autosomal dominant polycystic kidney disease.
    Can occur at any stage of renal disease.

Specific

• Structural renal disease.

Pathophysiology

• A pseudocyst is a fluid-filled cavity with no epithelial lining.
• Three types of peri-renal pseudocysts have been described (maybe uni- or bi-lateral):
  • Intracapsular (most common) - transudate accumulates between the capsule and parenchyma.
  • Extracapsular - transudate accumulates between the renal capsule and the lining of the retroperitoneum.
  • Peri-renal urinoma - leakage of urine from the urinary tract causing an inflammatory response and formation of a fibrous wall around the site of leakage.

• Poorly understood:
  • Transudate may originate from the capsule or the parenchyma.
  • A transudate occurs due to changes in hydrostatic or oncotic pressure in the vasculature or interstitium.
  • Impaired capsular lymphatic drainage has been hypothesized as a cause of transudation from the capsule.
  • Interstitial fibrosis may obstruct lymphatic or venous drainage   →   transudation from parenchyma (a more likely source of transudate).
• Pseudocysts progressively enlarge.

Timecourse

• Insidious onset over months.

Diagnosis

Treatment

Outcomes