Medullary sponge kidney and nephrolithiasis

Spilling the beans: an inside scoop on the imaging of renal parenchymal disease

BACKGROUND

Renal parenchymal disease is commonly encountered on imaging, and an understanding of the spectrum of pathology is vital to making correct diagnoses and recommendations for management. These conditions can be categorized based on the presence of calcifications, cysts, solid masses, patterns of enhancement, and other characteristic non-mass findings, as well as on their spatial distribution (i.e., medullary vs. cortical). Making an accurate diagnosis is often challenging, as there is overlap in the features of various diseases, and many benign entities may mimic pathology.

OBJECTIVE

This review broadly discusses imaging features of renal parenchymal disease and provides a systematic approach to characterize findings and appropriately guide further management.

Medullary sponge kidney: A treatment conundrum

Medullary sponge kidney (MSK) is a congenital kidney malformation that is characterized by dilatation of the collecting tubules in the medullary pyramids. Cyst-like areas then form which predispose to nephrocalcinosis, stone formation and recurrent urinary tract infection (UTI). There is an association with defective distal renal tubular acidification and concentration abnormalities such as hypocitraturia. MSK is generally believed to be a sporadic disorder, but an autosomal dominant inheritance is also reported. More recently genetic mutations have been recognised as a possible contributor to the aetiology of the condition. In this article we summarize the available English language literature on the subject of MSK, including its pathogenesis, diagnosis, prognosis and treatment.

Safety and efficacy of minimally invasive percutaneous nephrolithotomy in the treatment of patients with medullary sponge kidney

The purpose of this study was to review the safety and efficacy of the minimally invasive percutaneous nephrolithotomy in the treatment of medullary sponge kidney patients with complex renal calculi. Sixteen medullary sponge kidney patients with complex renal calculi underwent minimally invasive percutaneous nephrolithotomy procedures in our center were entered into this retrospective study. The data analyzed included patients' demographics, stone burden, operative time, operative blood loss, length of hospital stay, complications according to the modified Clavien system, and stone-free rate. All the patients in this study had complex renal stones that included 14 multiple stones and 3 partial staghorn calculi. The mean stone surface area was 779.5 ± 421.1 mm(2). Preoperative urinary tract infection was noted in 5 (31.2 %) patients. Minimally invasive percutaneous nephrolithotomy was successfully completed in 15 renal units in 14 patients. Two patients failed the procedure. The mean operative time was 87.3 ± 32.3 min. Mean hemoglobin drop was 25.3 ± 16.5 g/L. An initial stone-free rate of 60 % was achieved after the procedure, and the final stone-free rate was 86.6 % after auxiliary second look and/or shock-wave lithotripsy. Clavien grade I and II complications occurred in 3 (21.4 %) patients including the one (7.1 %) patient who required transfusion. All the complications were managed conservatively. No major complications occurred. This retrospective analysis confirmed that minimally invasive percutaneous nephrolithotomy was a safe alternative treatment for the medullary sponge kidney patients with complex renal calculi. This procedure provided an acceptable stone-free rate and low incidence of high-grade complications. Stone-free rate further could be further improved with auxiliary procedures.

Nephrolithiasis in medullary sponge kidney: evaluation of clinical and metabolic features

OBJECTIVE

Medullary sponge kidney (MSK) is a disorder characterized by tubular dilation of renal collecting ducts and cystic dilation of medullary pyramids that has been associated with stone disease. The significance of nephrolithiasis and the mechanisms by which it occurs are incompletely understood. We describe clinical and metabolic features of nephrolithiasis in a cohort of patients with MSK.

METHODS

Records were reviewed of 56 patients, all with radiographic diagnosis of medullary sponge kidney and data collected pertaining to presentation, stone events and recurrences, stone composition, and metabolic profile to perform a descriptive study with median 3.7 years follow-up.

RESULTS

Nephrolithiasis was confirmed radiographically in 39/56 patients (69.6%). No patient without evidence of nephrolithiasis developed a stone event, whereas 13/39 (33%) of those with nephrolithiasis developed a recurrent stone event. Stones were composed of calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate apatite, and uric acid. Metabolic profile was obtained for 26 of 39 (67%) stone-forming patients demonstrating abnormalities in 22/26 (84.6%). These included hypercalciuria, 58% (15/26); low urine volume, 35% (9/26); hyperuricosuria, 27% (7/26); hypocitraturia, 19% (5/26); elevated urine sodium, 15% (4/26); and hyperoxaluria, 12% (3/26).

CONCLUSION

Many patients with MSK have no evidence of nephrolithiasis. Among those who do, recurrence is common, and metabolic profile and composition are varied as in the general stone-forming population.

A review of the natural progression of medullary sponge kidney and a novel grading system based on intravenous urography findings

PURPOSE

Medullary sponge kidney (MSK) is a developmental abnormality of the medullary pyramids of the kidney, characterised by cystic dilatations of the collecting ducts. We investigated a cohort of patients with MSK to gain further information about its presentation, clinical course and treatment required. We devised a grading system based upon findings at diagnostic intravenous urography (IVU) and established a relationship between severity of IVU findings and severity of disease.

MATERIALS AND METHODS

The clinical notes and imaging of 29 patients with MSK were analysed. The severity of IVU findings was classified as follows: grade 1 (one calyx, unilateral), grade 2 (one calyx, bilateral), grade 3 (more than one calyx, unilateral) and grade 4 (more than one calyx, bilateral).

RESULTS

The age range at diagnosis was 12-69 (mean 39), mean follow-up period was 12.7 years. Increasing grade of IVU findings correlated with more frequent symptomatic stone episodes (grade 1: 0.09 episodes per patient per year; grade 4: 0.34). Higher grade was also related to the number of hospital admissions (grade 1: 0.182 per patient per year; grade 4: 0.282) and the number of procedures required (either surgery or extracorporeal shock wave lithotripsy; grade 1: 0.0 interventions per patient per year; grade 4: 0.24).

CONCLUSIONS

MSK presents over a wide age range and can cause long periods of intermittent episodes. Patients can be graded using a novel system based on IVU findings, which correlates with severity of disease. Management strategies such as intensity of follow-up can be modified using this grading.

Ureteroscopic laser papillotomy to treat papillary calcifications associated with chronic flank pain

OBJECTIVES

To evaluate retrospectively the efficacy and durability of a novel approach using ureteroscopic laser papillotomy for the treatment of painful papillary calcifications. Chronic pain due to renal papillary calcifications has not been addressed by current techniques.

METHODS

Ureteroscopic holmium laser lithotripsy and papillotomy were performed on patients with chronic pain and radiographically visible papillary calcifications without free collecting system calculi. The papillary urothelium overlying all cystic dilations and intraductal calcifications was vaporized. Treated patients answered a telephone survey to assess pain scores, duration of response, use of narcotics, and patient satisfaction. We reviewed the medical records to evaluate for procedure-related complications and serum creatinine measurements.

RESULTS

Of 20 patients who underwent laser papillotomy and responded to the telephone survey, 7 had bilateral procedures, yielding 27 renal units available for analysis. "Much less pain" was reported after 85% of the procedures, with a durable improvement reported after 59% of the procedures, at a median follow-up of 14.5 months. Significant improvements in the median pain scores were seen at 1 month (1.0, P <0.001), 6 months (2.0, P <0.001), and 1 year (1.5, P <0.001) compared with a median preoperative pain score of 9.0. The mean serum creatinine was unchanged after the procedure.

CONCLUSIONS

Ureteroscopic laser papillotomy appears to be an effective treatment option for the chronic pain associated with papillary calcifications. Laser papillotomy offers hope to patients who would otherwise have been denied an attempt at treatment because of a lack of free calculi within the collecting system.

Serial crystalluria determination and the risk of recurrence in calcium stone formers

BACKGROUND

Urinary crystal precipitation is the necessary initial step in kidney stone formation. However, clinical relevance of crystalluria in the evaluation of stone formers is disputed.

METHODS

We serially determined crystalluria in first-voided morning urine samples, together with full 24-hour urine biochemistry, in 181 patients with idiopathic calcium nephrolithiasis who had formed at least one calcium-oxalate stone and were followed for at least 3 years under our care. All stone events which occurred prior to referral, then after entry in the study were recorded.

RESULTS

As compared with 109 patients who had no evidence of stone recurrence during follow-up, the 72 patients who experienced >/= one recurrent stone event had a lower daily urine volume (1.74 +/- 0.06 vs. 2.26 +/- 0.05 L/day (mean +/- SEM) (P < 0.0001), higher urine calcium and oxalate concentrations, and daily calcium excretion, and they had more frequent crystalluria (68% vs. 23% of urine samples) (P < 0.0001). By multivariate Cox regression analysis, the hazard ratio for stone recurrence was 0.32 (95% CI 0.16-0.62) for 1 L increase in daily urine volume, 1.12 (1.09-1.24) for 1 mmol/L increase in urine calcium concentration, 1.24 (1.02-1.50) for 0.1 mmol/L increase in urine oxalate concentration and 27.8 (10.2-75.6) for crystalluria index.

CONCLUSION

These data provide evidence that crystalluria, when repeatedly found in early morning urine samples, is highly predictive of the risk of stone recurrence in calcium stone formers. Serial search for crystalluria, a simple and cheap method, may be proposed as a useful tool for the monitoring of calcium stone formers, in addition to urine biochemistry.

Renal stone disease in autosomal dominant polycystic kidney disease

Nephrolithiasis is an important manifestation of autosomal dominant polycystic kidney disease (ADPKD), which occurs in approximately 20% of patients. It should always enter the differential diagnosis of flank pain in patients with ADPKD. The diagnosis is hindered by the distorted anatomy of the polycystic kidneys and the frequent occurrence of parenchymal and cyst wall calcifications, and requires demonstration of the relationship to the collecting system by intravenous urography and/or computed tomography. Computed tomography is the most sensitive imaging technique for detection of stones or calcifications, whereas intravenous urography is the most sensitive for visualization of the intrarenal collecting system. Precaliceal tubular ectasia can be detected in 15% of patients with ADPKD and nephrolithiasis, but this association may not be specific to ADPKD. The composition of the stones is most frequently uric acid and/or calcium oxalate. Metabolic factors are important in their pathogenesis. Distal acidification defects may be important in a few patients, while an abnormal transport of ammonium, low urine pH, and hypocitruria are the most common abnormalities. The treatment of nephrolithiasis in patients with ADPKD is not different from that in patients without ADPKD. Extracorporeal shock wave lithotripsy and percutaneous nephrostolithotomy in patients with early disease and normal renal function are not contraindicated.

Role of extracorporeal shock-wave lithotripsy in treatment of urolithiasis in patients with medullary sponge kidney

In an effort to identify the role of extracorporeal shock-wave lithotripsy (ESWL) in the treatment of patients with medullary sponge kidney, a retrospective review of our experience with the Dornier HM-3 lithotriptor is presented. From 1986-1991 17 patients with medullary sponge kidney ranging in age from twenty-eight to fifty-eight years received 31 treatments to a total of 24 renal units. Follow-up ranged from four to fifty-six months with an average follow-up of twenty-five months. ESWL appears to have a role in the treatment of symptomatic urolithiasis in patients with medullary sponge kidney. There may also be some benefit in treating parenchymal calcifications. No significant side effects from the treatment were noted.

Calcium and calcium magnesium carbonate specimens submitted as urinary tract stones

Of 8,129 specimens submitted as urinary stones from 6,095 patients, 67 from 15 patients were predominantly calcium carbonate or calcium magnesium carbonate (dolomite) by infrared analysis. Detailed study of 1 man and 4 women who submitted 3 or more such specimens showed that all were of aragonite calcium carbonate crystal form in 2 women and all calcite in the man. All 3 patients had a long history of nephrolithiasis preceding submission of calcium carbonate stones. There was frequent and often painful spontaneous passage of many small stones. Medullary sponge kidney was reported in 2 patients. Specimens submitted by the other 2 women included dolomite and quartz artifacts. Of the other 10 patients 4 had calcite and 1 had aragonite (possibly true stones). Five patients had artifacts with dolomite in 3 and mixed specimens in 2. True calcium carbonate kidney stones and calcium carbonate artifacts may be difficult to distinguish, and dolomite and quartz artifacts may require x-ray diffraction for clear-cut diagnosis.

Medullary sponge kidney on axial computed tomography: comparison with excretory urography

To evaluate features of medullary sponge kidney (MSK) on computed tomography (CT), 4-mm-thick axial slices without intravenous contrast material were first made in 13 patients through 24 kidneys which showed images of MSK on excretory urograms. On CT, papillary calcifications were found in eleven kidneys. In five of these kidneys, the calcifications were not detectable on plain films. Some hyperdense papillae (attenuation value 55-70 Hounsfield units) without calcification were found in four other kidneys. Nine kidneys appeared normal. Ten of these 24 kidneys were reexamined by a second series of 4-mm-thick axial slices, 5 min after intravenous injections of 50 ml of Urografin. Images suggesting possible ectasia of precaliceal tubules were found in only four kidneys. These images appear much less obvious and characteristic on CT than on excretory urogram and do nothing more than suggest the possibility of MSK. In conclusion, the sensitivity of CT in the detection of MSK is markedly lower than that of excretory urography. In the most florid cases of the disease, CT can only show images suggesting the possibility of MSK. On the other hand, CT appears much more sensitive than plain films and tomograms of excretory urography in the detection of papillary calcifications, the most frequent complication of MSK.

Tubulopathy in nephrolithiasis: consequence rather than cause

To address whether a renal tubular dysfunction is encountered in a particular patient subgroup with urolithiasis, the following parameters of tubular function were measured in urine taken in the morning from 214 stone formers after fasting: pH, excretion of lysozyme and gamma-glutamyl transferase (gamma-GT); fractional excretion (FE) of glucose, insulin, Mg, K, and HCO3 after an alkali loading; and the renal threshold for phosphate (TmP/GFR). The following diagnoses were made in the patient group: primary hyperparathyroidism (N = 8), medullary sponge kidneys (N = 21), hyperuricemia (N = 10), cystinuria (N = 2), struvite stone disease (N = 6), idiopathic hypercalciuria of the absorptive (N = 25), dietary (N = 69) or renal (N = 7) type, and normocalciuric idiopathic urolithiasis (N = 66). In 31% of the patients TmP/GFR was below 0.80 mmole/liter and in 13% of the patients, FE HCO3 after alkali loading was above normal. Urinary excretion of lysozyme and that of gamma-GT both were elevated in 17% of the patients. FE glucose, FE insulin, FE Mg, and FE K were elevated in 8, 9, 3, and 7% of the patients, respectively. This study demonstrates that a significant number of stone formers present with signs of renal tubular dysfunction, primarily involving the proximal tubule since apparent leaks of phosphate and of bicarbonate were most frequently encountered. The defects were not specific for a given etiologic group of patients; on the other hand, occurrence was related to the presence of large stones in the pyelocaliceal system at the time data were gathered. Taken together these data suggest that the tubulopathy in nephrolithiasis is the consequence rather than the cause of the stone.

Medullary sponge kidney presenting with hypokalaemic paralysis

Medullary sponge kidney associated with a defect in urine acidification is rare and usually of no clinical significance. We report a case presenting as hypokalaemic paralysis due to associated congenital distal renal tubular acidosis.

Medical evaluation and management of calcium nephrolithiasis

Stone disease is a common medical problem, frequently recurs, and is associated with significant morbidity. Because appropriate medical therapy significantly decreases stone recurrence, this disorder must not be ignored by nonurologists. Even the single stone-former should be offered a metabolic evaluation.