Though a known clinical entity, the pathology and pathogenesis of pyelocalyceal cysts has remained poorly understood and speculative.1–4
In the case documented here, pyelocalyceal cysts presented anatomically as a large blue cystic lobulated kidney adherent to a dirty white pelvic cyst. Pelvic and calyceal cysts were differentiated by location, number, arrangement, and morbid anatomical and microscopic features of the lining of their walls. Findings suggested that calyceal cystic pressure severely compressed the venous channels leading to congestive cyanotic atrophied renal tissue around the cysts, giving rise to the large blue cystic lobulated kidney. Hydrotic nephritis with glomerulosclerosis of the nephrons suggested patency at the calyceo-tubular junctions. A large blue cystic lobulated kidney with hydrotic nephritis had not been previously reported in cases of pyelocalyceal cysts in the literature.
During embryonic development, as the ureteric bud (evaginated from the mesonephric duct) approaches the metanephrons it undergoes ampullation and serial branching under the influence of chondroitin sulphate proteoglycans and glycol aminoglycans present in the mesenchymal matrix, while adhesion molecules (such as syndecan, cadherin, laminin, collagen) regulate adhesions, mesothelial to epithelial transformation, and fusion of nephric tubules with ureteric duct branches.5
Simultaneously, as the first ureteric divisions fuse to form the pelvis and the subsequent divisions evolve into the major and minor calyces and collecting tubules, respectively, the budding points marking the ureteropelvic, pelvicalyceal, and calyceo-nephro-tubular junctions are left as distinctly narrow segments. Such segments, in an adhesive biomolecular environment, before functioning of the metanephric nephrons starts, are liable to result in the development of obliterate urothelial adhesions, leading to pelvic, calyceal, ductular, tubular, and glomerular nephric cysts depending on the site(s) of obliteration. Ureteropelvic obliteration with partial obliterations at the pelvicalyceal and calyceo-nephro-tubular junctions may give rise to congenital developmental pyelocalyceal cysts with hydrotic nephritis, as observed in the present case. The condition differs from megacalycosis which is characterised by non-obstructive dilatation of renal calyces, with normal pelvis and hypoplastic renal medullary pyramids.6
It also needs to be distinguished from hydronephrosis which is a term indicating retention of urine up to the kidney, irrespective of the disease causing obstruction of urinary flow, leading to dilatation of orifices besides the (reno-pelvi-ureteric) channels, with no universally accepted value or definition.7
In this case the renal pelvis was transformed into the cyst, drawing the ureteric junction higher up, and communicating through narrow openings with the calyceal cysts, which in turn communicated with the hydronephritic nephrons, but with no outlet for the fluid contents on either side—hence, satisfying the definition of cysts. Pyelocalyceal cystic disease with hydrotic nephritis of the kidney therefore deserves to be recognised by pathologists.
Confusion persists in the classification of cystic diseases of the kidney. The Potter classification was simple and reasonable;4
however, it later appeared that it did not fit the recent mutant gene oriented classification8
for which there may be a need for a new consensus based on the origin (mainly genetic), pathogenesis and clinical manifestation. The observations made in the present case may therefore help to provide material for future classification.
- In this case pyelocalyceal cysts presented as a ‘large blue cystic lobulated kidney’, adhering to dirty white pelvic cyst, and microscopically evident hydrotic nephritis.
- Such cysts are lined by transitional epithelium which have undergone hydrotic degenerative changes with bullous formations, and attenuation from multilayered to single cell lining.
- Cysts may be differentiated as pelvic, calyceal, tubular, or nephric by their number, location, arrangement and communications.
- Partial or complete adhesive obliteration(s) at the budding points of the ureteric bud may give rise to congenital developmental pyelocalyceal cysts.
- Observations made in the present case may help to provide material for the future classification of cystic diseases of the kidney.