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This report describes the diagnostic, morbid, anatomical and histopathological features of pyelocalyceal cysts with hydrotic nephritis of the kidney in a 3-year-old boy, and discusses the pathogenesis. Calyceal cysts gave rise to a ‘large blue cystic lobulated kidney’ with microscopic changes in nephrons identifiable as ‘hydrotic nephritic glomerulosclerosis’. Pelvic and calyceal cysts were identifiable by location, number, arrangement, and morbid anatomical and microscopic features of their lining walls. Such cysts may develop due to partial or complete obliterate adhesions at the uretero-pelvic and pyelocalyceal junctions. Patent calyceo-tubulonephric junctions in such cases may give rise to hydrotic nephritis. Pyelocalyceal cystic disease with hydrotic nephritis of the kidney needs to be distinguished from megacalycosis and hydronephrosis and deserves recognition. Observations in this case may provide the basis for future classifications of cystic renal diseases.
Renal calyceal cysts, or diverticula or pyelogenic cysts as they are also known, are not uncommon findings.1 However, they rarely require the pathologist’s attention.2 In radiological diagnostic opinion, the calyceal cyst is not a true cystic condition but a structural abnormality observed on ultrasonography and confirmed by intravascular ultrasound (IVUS), while the ultimate diagnosis remains confusing and erroneous,3 and the pathogenesis speculative.2 This report presents diagnostic morbid, anatomical and histopathological features of pyelocalyceal cysts with hydrotic nephritis of the kidney and discusses the pathogenesis.
An excised left renal mass from a 3-year-old male child, with a history of (1) abdominal distension for the previous 1.5 years, (2) abdominally palpable and radiographically cystic lump on the left side, and (3) perioperative finding of uretero-pelvic obliteration, was submitted for pathological diagnosis. In gross appearance, the kidney was enlarged with a smooth cyanosed congested surface showing cystic lobulations (large blue cystic lobulated kidney) adherent to a dirty white pyelocyst (fig 1A). On cut surface the pyelocyst measured 10 cm in infundibular diameter; it was filled with a clear watery content, lined by a thickened dirty white parchment cyst wall adherent to the pelvic curvature of kidney from the upper to the lower pole, and showing multiple narrow calyceal openings of <5 mm diameter on the inner surface (fig 1B). The ureteric opening was relatively higher up and obliterated. Renal parenchyma was almost entirely occupied by five cysts of varying sizes arranged parallel to the line of adhesion of the pyelocyst along the renal curvature, each with an independent narrow calyceal opening into the pelvis. The upper lobe was occupied by a large confluent cyst with three diverticular lobulations. The lower and middle lobes showed four unilocular cysts measuring 2–3 cm in diameter. The cysts’ contents were watery. Their walls were thin, parchment-like, and lined externally by a 1–2 mm thick grey brown strip of dark, congested, compressed, atrophied renal parenchyma sub-adjacent to the capsule.
On microscopic examination, the pyelocyst wall in conjunction with renal parenchyma showed an identifiable fibromuscular coat lined on the cystic side by attenuated oedematous transitional epithelium with intraepithelial bullous formations (fig 2A). Part of the pyelocyst epithelium was attenuated to a single cell layer lined externally by a fibromuscular coat and serosa (fig 2B). Calyceal cysts were lined by oedematous vacuolated low transitional epithelium attenuated to a single cell layer in most parts (fig 2C). Nephrons around the calyceal cysts revealed hydrotic dilation along the entire tubular length with cystic ballooning of the glomerular space, collapse of the glomerular tuft, congestion of tuft capillaries, focal necrosis, glomerulosclerosis, and periglomerular mononuclear inflammatory infiltration (fig 2D). The ureteric lumen was obliterated (fig 2, panel U).
The family history was negative. A computed tomography scan revealed a 15×20 cm cystic renal mass with a non-functioning kidney. Blood test results were: haemoglobin 10.6 g/dl, total leucocyte count 1800 cells/cubic mm, differential leucocyte count P20 L76 E2 B2, platelets 3.5 cells/cubic mm, fasting blood sugar 90 mg/dl, blood urea 28 mg/dl, serum creatinine 0.83 mg/dl, serum Na 133 mEq/l, serum K 3.9 mEq/l, bleeding time 1.48 min, and clotting time 3.8 min. Urinalysis findings were normal.
The patient is currently doing well, and a follow-up is planned.
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.
Assistance in histopathology by Dr Vanesa T John and Dr Amit Kumar (residents histopathology), and contribution of clinical notes by Professor Imran Ghani (paediatric surgery) are acknowledged.
Competing interests: None.
Patient consent: Patient/guardian consent was obtained for publication.