Characteristics of renal cystic and solid lesions based on contrast-enhanced computed tomography of potential kidney donors

Polycystic kidney disease

Cystic kidneys are common causes of end-stage renal disease, both in children and in adults. Autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are cilia-related disorders and the two main forms of monogenic cystic kidney diseases. ADPKD is a common disease that mostly presents in adults, whereas ARPKD is a rarer and often more severe form of polycystic kidney disease (PKD) that usually presents perinatally or in early childhood. Cell biological and clinical research approaches have expanded our knowledge of the pathogenesis of ADPKD and ARPKD and revealed some mechanistic overlap between them. A reduced 'dosage' of PKD proteins is thought to disturb cell homeostasis and converging signalling pathways, such as Ca²⁺, cAMP, mechanistic target of rapamycin, WNT, vascular endothelial growth factor and Hippo signalling, and could explain the more severe clinical course in some patients with PKD. Genetic diagnosis might benefit families and improve the clinical management of patients, which might be enhanced even further with emerging therapeutic options. However, many important questions about the pathogenesis of PKD remain. In this Primer, we provide an overview of the current knowledge of PKD and its treatment.

Long-Term Surveillance of Complex Cystic Renal Masses and Heterogeneity of Bosniak 3 Lesions

PURPOSE

We sought to better characterize the frequency of Bosniak cyst class changes, identify predictors of change and progression, determine the average growth rate of cysts and validate the safety of active surveillance.

MATERIALS AND METHODS

Consecutive patients referred for the management of complex cysts (Bosniak 2F or greater) were included in analysis. All imaging studies were reevaluated and any stage change was reviewed with a blinded genitourinary radiologist. Bosniak 3 cysts were subclassified as 3s-septated enhancing Bosniak cysts and 3n-cysts with wall or septation-only nodularity. A multivariate Cox proportional hazards model was used to identify predictors of the Bosniak classification change. Kaplan-Meier curves were applied to analyze Bosniak cyst progression and regression.

RESULTS

A total 140 lesions were included in study, necessitating review of a total of 1,011 abdominal scans in 111 patients. Median followup was 46 months (IQR 23-65.5) and patients underwent a mean of 6.8 diagnostic scans. On multivariate analysis nodular cysts progressed (HR 6.16, 95% CI 2.58-14.72, p <0.00004) and entirely endophytic cysts were less likely to progress (HR 0.21, 95% CI 0.05-0.85, p = 0.028). On Kaplan-Meier analysis Bosniak 3s cysts were more likely to regress while Bosniak 3n cysts were more likely to progress than 3s cysts (p = 0.0178 and 0.0002, respectively). The growth rate of 3n and 2F cysts was 0.19 and 0.11 cm per year (p = 0.0493 and 0.0327, respectively). Locally advanced or metastatic disease did not develop in any patient.

CONCLUSIONS

A diagnostic change in Bosniak 3s and 2F cysts is common and Bosniak 3n cysts behave more like Bosniak 4 cysts. Most complex kidney cysts can be safely monitored without intervention and the interval between serial imaging procedures should be increased.

Global glomerulosclerosis with nephrotic syndrome; the clinical importance of age adjustment

Globally sclerotic glomeruli (GSG) occur with both normal aging and kidney disease. However, it is unknown whether any GSG or only GSG exceeding that expected for age is clinically important. To evaluate this, we identified patients with a glomerulopathy that often presents with nephrotic syndrome (focal segmental glomerulosclerosis, membranous nephropathy, or minimal change disease) in the setting of the Nephrotic Syndrome Study Network (NEPTUNE), China-Digital Kidney Pathology (DiKiP), and the Southeast Minnesota cohorts. Age-based thresholds (95th percentile) for GSG based on normotensive living kidney donors were used to classify each patient into one of three groups; no GSG, GSG normal for age, or GSG abnormal for age. The risk of end-stage renal disease or a 40% decline in glomerular filtration rate during follow-up was then compared between groups. Among the 425 patients studied, 170 had no GSG, 107 had GSG normal for age, and 148 had GSG abnormal for age. Compared to those with no GSG, the risk of kidney disease progression with GSG normal for age was similar but was significantly higher with GSG abnormal for age. This increased risk with GSG abnormal for age remained significant after adjustment for interstitial fibrosis, arteriosclerosis, age, hypertension, diabetes, body mass index, glomerulopathy type, glomerular filtration rate, and proteinuria. Thus, in patients with glomerulopathy that often presents with nephrotic syndrome, global glomerulosclerosis is clinically important only if it exceeds that expected for age.

The safety and efficacy of MPR-CTU combined with precise intraoperative ultrasonography guided flexible ureteroscope in the treatment of renal cystic disease

The safety and efficacy of multi-planar reconstruction (MPR) image post-processing technique-computed tomography (CT) urography (CTU) combined with precise intraoperative ultrasonography guided flexible ureteroscope in renal cyst incision and drainage in the treatment of cystic diseases of kidney were evaluated. A total of 68 patients were randomly divided into control and observation group (n=34). All the patients were treated with renal cyst incision and drainage under flexible ureteroscope. The control group was under ultrasound guidance. The observation group was combined with MPR-CTU, the safety and efficacy was compared. There was no significant difference between the two groups in the success rate and the time of cyst treatment (P>0.05). The incidence of intraoperative and postoperative complications of the observation group was significantly lower than that of the control group. After 1 month follow-up, the total effective rate of the observation group was significantly higher than that of the control group, the difference was statistically significant (P<0.05). Conclusion MPR-CTU technique combined with intraoperative ultrasonography to guide cyst incision and drainage under flexible ureteroscope for renal cystic disease has a high safety and efficacy, and it is worthy of clinical application.

Genetic Complexity of Autosomal Dominant Polycystic Kidney and Liver Diseases

Data indicate significant phenotypic and genotypic overlap, plus a common pathogenesis, between two groups of inherited disorders, autosomal dominant polycystic kidney diseases (ADPKD), a significant cause of ESRD, and autosomal dominant polycystic liver diseases (ADPLD), which result in significant PLD with minimal PKD. Eight genes have been associated with ADPKD (PKD1 and PKD2), ADPLD (PRKCSH, SEC63, LRP5, ALG8, and SEC61B), or both (GANAB). Although genetics is only infrequently used for diagnosing these diseases and prognosing the associated outcomes, its value is beginning to be appreciated, and the genomics revolution promises more reliable and less expensive molecular diagnostic tools for these diseases. We therefore propose categorization of patients with a phenotypic and genotypic descriptor that will clarify etiology, provide prognostic information, and better describe atypical cases. In genetically defined cases, the designation would include the disease and gene names, with allelic (truncating/nontruncating) information included for PKD1 Recent data have shown that biallelic disease including at least one weak ADPKD allele is a significant cause of symptomatic, very early onset ADPKD. Including a genic (and allelic) descriptor with the disease name will provide outcome clues, guide treatment, and aid prevalence estimates.

Structural and Functional Changes in Human Kidneys with Healthy Aging

Aging is associated with significant changes in structure and function of the kidney, even in the absence of age-related comorbidities. On the macrostructural level, kidney cortical volume decreases, surface roughness increases, and the number and size of simple renal cysts increase with age. On the microstructural level, the histologic signs of nephrosclerosis (arteriosclerosis/arteriolosclerosis, global glomerulosclerosis, interstitial fibrosis, and tubular atrophy) all increase with age. The decline of nephron number is accompanied by a comparable reduction in measured whole-kidney GFR. However, single-nephron GFR remains relatively constant with healthy aging as does glomerular volume. Only when glomerulosclerosis and arteriosclerosis exceed that expected for age is there an increase in single-nephron GFR. In the absence of albuminuria, age-related reduction in GFR with the corresponding increase in CKD (defined by an eGFR<60 ml/min per 1.73 m²) has been shown to associate with a very modest to no increase in age-standardized mortality risk or ESRD. These findings raise the question of whether disease labeling of an age-related decline in GFR is appropriate. These findings also emphasize the need for a different management approach for many elderly individuals considered to have CKD by current criteria.

Pre-operative renal artery embolization and suprarenal IVC filter placement for prevention of fat embolization in renal angiomyolipoma with venous extension

Though generally considered benign, angiomyolipomas can invade through the renal vein into the inferior vena cava, putting patients at risk of catastrophic pulmonary fat embolization. Venous invasion is thus an indication for surgical resection but is thought to increase the risk of adverse operative outcomes including intraoperative hemorrhage and embolization of fat and/or tumor thrombus. We report a novel approach to mitigating these complications illustrated in the case of a 43-year-old woman with IVC-invasive renal AML who underwent successful radical nephrectomy after concurrent pre-operative renal artery embolization and placement of a retrievable suprarenal IVC filter.

Correlation of computed tomography characteristics of cystic renal cell carcinoma with histopathology

Background

Renal cysts are common incidental findings in computed tomography (CT) of the abdomen and range from benign to cystic renal cell carcinoma (RCC). Cystic RCC has various pathology, clinical prognosis, and treatment options.

Objectives

To compare preoperative CT of cystic RCC with histopathology.

Methods

Preoperative CT of histopathologically proven cystic RCCs were retrospectively reviewed in this single-center cross-sectional observational study. Two investigators recorded consensus CT features for each cystic RCC. The means of descriptive continuous data were calculated. A chi-square test, Fisher’s exact test, or an ANOVA were used for compare the frequency of findings for each histopathological subtype.

Results

Of 38 cystic RCCs, 25 were clear cell RCC, 5 were papillary RCC, 4 were multilocular cystic RCC, 1 was chromophobe RCC, and 3 were mixed type/other type (papillary/chromophobe, clear cell/chromophobe, and sarcomatoid type). We classified 36 lesions as Bosniak category IV and 2 lesions as Bosniak category III. There was no significant difference in cyst attenuation in any phase. Solid attenuation of the tumors was significantly different for each type in corticomedullary and nephrogenic phases (P = 0.001 and 0.042, respectively). Clear cell RCC was enhanced the most on corticomedullary and nephrogenic phases (means 135.5 and 112.1 Hounsfield Units, respectively). Septal thickening, enhancement, and multilocularity were significantly different between subtypes, particularly in multilocular cystic RCCs (P = 0.018, 0.018, and 0.02, respectively).

Conclusion

Preoperative CT findings may help clinicians and radiologists to predict tumor subtypes and aid treatment planning.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

Sorting the Alphabet Soup of Renal Pathology: A Review

Diseases of the kidney often have their names shortened, creating an arcane set of acronyms which can be confusing to both radiologists and clinicians. This review of renal pathology aims to explain some of the most commonly used acronyms within the field. For each entity, a summary of the clinical features, pathophysiology, and radiological findings is included to aid in the understanding and differentiation of these entities. Discussed topics include acute cortical necrosis, autosomal dominant polycystic kidney disease, angiomyolipoma, autosomal recessive polycystic kidney disease, acute tubular necrosis, localized cystic renal disease, multicystic dysplastic kidney, multilocular cystic nephroma, multilocular cystic renal cell carcinoma, medullary sponge kidney, paroxysmal nocturnal hemoglobinuria, renal papillary necrosis, transitional cell carcinoma, and xanthogranulomatous pyelonephritis.

Detection and Clinical Patterns of Nephron Hypertrophy and Nephrosclerosis Among Apparently Healthy Adults

BACKGROUND

Even among ostensibly healthy adults, there is often mild pathology in the kidney. The detection of kidney microstructural variation and pathology by imaging and the clinical pattern associated with these structural findings is unclear.

STUDY DESIGN

Cross-sectional (clinical-pathologic correlation).

SETTING & PARTICIPANTS

Living kidney donors at Mayo Clinic (Minnesota and Arizona sites) and Cleveland Clinic 2000 to 2011.

PREDICTORS

Predonation kidney function, risk factors, and contrast computed tomographic scan of the kidneys. These scans were segmented for cortical volume and medullary volume, reviewed for parenchymal cysts, and scored for kidney surface roughness.

OUTCOMES

Nephrosclerosis (glomerulosclerosis, interstitial fibrosis/tubular atrophy, and arteriosclerosis) and nephron size (glomerular volume, mean profile tubular area, and cortical volume per glomerulus) determined from an implantation biopsy of the kidney cortex at donation.

RESULTS

Among 1,520 living kidney donors, nephrosclerosis associated with increased kidney surface roughness, cysts, and smaller cortical to medullary volume ratio. Larger nephron size (nephron hypertrophy) associated with larger cortical volume. Nephron hypertrophy and larger cortical volume associated with higher systolic blood pressure, glomerular filtration rate, and urine albumin excretion; larger body mass index; higher serum uric acid level; and family history of end-stage renal disease. Both nephron hypertrophy and nephrosclerosis associated with older age and mild hypertension. The net effect of both nephron hypertrophy and nephrosclerosis associating with cortical volume was that nephron hypertrophy diminished volume loss with age-related nephrosclerosis and fully negated volume loss with mild hypertension-related nephrosclerosis.

LIMITATIONS

Kidney donors are selected on health, restricting the spectrum of pathologic findings. Kidney biopsies in living donors are a small tissue sample leading to imprecise estimates of structural findings.

CONCLUSIONS

Among apparently healthy adults, the microstructural findings of nephron hypertrophy and nephrosclerosis differ in their associations with kidney function, macrostructure, and risk factors.

Structural and Functional Changes With the Aging Kidney

Senescence or normal physiologic aging portrays the expected age-related changes in the kidney as compared to a disease that occurs in some but not all individuals. The microanatomical structural changes of the kidney with older age include a decreased number of functional glomeruli from an increased prevalence of nephrosclerosis (arteriosclerosis, glomerulosclerosis, and tubular atrophy with interstitial fibrosis), and to some extent, compensatory hypertrophy of remaining nephrons. Among the macroanatomical structural changes, older age associates with smaller cortical volume, larger medullary volume until middle age, and larger and more numerous kidney cysts. Among carefully screened healthy kidney donors, glomerular filtration rate (GFR) declines at a rate of 6.3 mL/min/1.73 m(2) per decade. There is reason to be concerned that the elderly are being misdiagnosed with CKD. Besides this expected kidney function decline, the lowest risk of mortality is at a GFR of ≥75 mL/min/1.73 m(2) for age <55 years but at a lower GFR of 45 to 104 mL/min/1.73 m(2) for age ≥65 years. Changes with normal aging are still of clinical significance. The elderly have less kidney functional reserve when they do actually develop CKD, and they are at higher risk for acute kidney injury.

Influence of vascular endothelial growth factor inhibition on simple renal cysts in patients receiving bevacizumab-based chemotherapy

Purpose

Although angiogenesis has been implicated in the promotion of renal cyst growth in autosomal dominant polycystic kidney disease, no studies have investigated the role of angiogenesis in the growth of simple renal cysts. The aim of current study was to investigate the effect of chemotherapy with the antivascular endothelial growth factor antibody bevacizumab on renal cyst development and growth in cancer patients.

Materials and Methods

We retrospectively reviewed the medical records of 136 patients with a variety of cancers that were treated with bevacizumab-based chemotherapy for metastatic disease. The presence of and changes in renal cysts were evaluated by retrospective analysis of computed tomography scans performed for assessment of tumor response to bevacizumab-based therapy.

Results

The median age of the patients was 64 years. Renal cysts were identified in 66 patients, in whom 33 (50%) had a single cyst and the rest had 2 or more cysts. The average dose of bevacizumab was 2.68 mg/kg per week. Median duration of treatment was 33 weeks. Average cyst size was 1.9±2.4 cm at the beginning of the study and the majority of the cysts (54 patients, 84%) did not change in size or shape during bevacizumab treatment. No patients were identified with new cysts. Cyst size changed in 10 patients (16%): an increase of 15% to 40% from the baseline size in 5 patients and a decrease in size of 10% to 70% in another 5 patients. The duration of bevacizumab therapy was significantly longer in the subgroup of patients with diminished or increased cyst size than in the patients with stable cyst size: 62 weeks versus 29 weeks, respectively (p=0.0002).

Conclusions

Our data demonstrated that simple renal cysts were stable in size and number in the vast majority of cancer patients treated with bevacizumab.

Rationale for early treatment of polycystic kidney disease

In hereditary cystic disorders, renal injury begins with the formation of the first cyst. Renal injury may manifest as large kidneys, abdominal pain, hypertension and hematuria in children and young adults with autosomal dominant polycystic kidney disease (ADPKD). In autosomal recessive PKD (ARPKD) and ADPKD, cysts form primarily in collecting ducts and expand progressively. Collecting duct cysts that block urine flow have the potential to block urine formation in large numbers of upstream nephrons. In an ARPKD rat congenitally lacking vasopressin, only a few cysts developed until exogenous arginine vasopressin (AVP) was administered. AVP elevates cyclic AMP in vulnerable tubule cells to stimulate mitogenesis and fluid secretion, thereby causing cysts to form and enlarge indefinitely. The administration of an AVP-V2 receptor inhibitor or the consumption of sufficient water to persistently lower plasma AVP levels will ameliorate disease progression. Renal volume measurements provide the most reliable way to forecast long-term outcome in individual children and adult patients with ADPKD. Many drugs that have demonstrated efficacy in small clinical trials, preclinical trials and cell-based studies are in the treatment pipeline. Counseling, regular exercise, limitation of dietary calories, salt, protein and fat, increased fluid intake throughout the day and treatment of hypertension are components of a rational treatment program that can be offered at an early age to those with, or at risk for developing PKD.

Copeptin is associated with kidney length, renal function, and prevalence of simple cysts in a population-based study

Arginine vasopressin (AVP) has a key role in osmoregulation by facilitating water transport in the collecting duct. Recent evidence suggests that AVP may have additional effects on renal function and favor cyst growth in polycystic kidney disease. Whether AVP also affects kidney structure in the general population is unknown. We analyzed the association of copeptin, an established surrogate for AVP, with parameters of renal function and morphology in a multicentric population-based cohort. Participants from families of European ancestry were randomly selected in three Swiss cities. We used linear multilevel regression analysis to explore the association of copeptin with renal function parameters as well as kidney length and the presence of simple renal cysts assessed by ultrasound examination. Copeptin levels were log-transformed. The 529 women and 481 men had median copeptin levels of 3.0 and 5.2 pmol/L, respectively (P<0.001). In multivariable analyses, the copeptin level was associated inversely with eGFR (β=-2.1; 95% confidence interval [95% CI], -3.3 to -0.8; P=0.002) and kidney length (β=-1.2; 95% CI, -1.9 to -0.4; P=0.003) but positively with 24-hour urinary albumin excretion (β=0.11; 95% CI, 0.01 to 0.20; P=0.03) and urine osmolality (β=0.08; 95% CI, 0.05 to 0.10; P<0.001). A positive association was found between the copeptin level and the presence of renal cysts (odds ratio, 1.6; 95% CI, 1.1 to 2.4; P=0.02). These results suggest that AVP has a pleiotropic role in renal function and may favor the development of simple renal cysts.

Structure, not just function

Although kidney size can be important in the evaluation of renal disease, it has not been carefully studied and true volume is rarely measured, and good normative data are lacking. Wang et al. measured both cortical and medullary volumes in potential transplant donors and correlate these with physiologic, morphometric, and metabolic parameters. The results reveal interesting and potentially important correlations and differential responses between the two compartments, providing a framework for future investigation.

Diagnosis and evaluation of renal cysts

Renal cysts are commonly encountered in clinical practice. Although most cysts found on routine imaging studies are benign, there must be an index of suspicion to exclude a neoplastic process or the presence of a multicystic disorder. This article focuses on the more common adult cystic diseases, including simple and complex renal cysts, autosomal-dominant polycystic kidney disease, and acquired cystic kidney disease.

How simple are 'simple renal cysts'?

The increasing use of medical imaging as an investigative tool is leading to the incidental and frequent finding of renal cysts in the general population. The presence of a solitary or multiple renal cysts has been generally considered benign in the absence of a family history of renal cystic disease or evidence of chronic kidney disease. Nonetheless, a number of recent studies have questioned this consensus by reported associations with the development of hypertension or malignant change. For these reasons, some clinicians consider the presence of renal cysts to be a contraindication to kidney donation. The situation is complicated by the different usage of the term 'simple' by some radiologists (to indicate non-complex lesions) or nephrologists (to indicate age-related non-hereditary lesions). We propose that the term 'simple' be replaced with the morphological description, Stage I renal cyst (Bosniak Classification). The presence of a Stage I renal cyst should not preclude kidney donation. However, occult renal disease should be excluded and appropriate donor assessment performed.

New modalities for evaluation and surveillance of complex renal cysts

PURPOSE

The increased use of abdominal imaging has led to more frequent detection of incidental renal cysts. Since the inception of the Bosniak classification system, management of Bosniak I, III and IV cysts has been clearly defined, while evaluation and management of Bosniak II and IIF cysts have remained a clinical dilemma. Discussions of new imaging modalities are becoming increasingly prevalent in the radiological literature. In this context we performed a comprehensive review of the recent literature on complex renal cysts focusing on new imaging modalities, surveillance strategies and biopsy.

MATERIALS AND METHODS

We performed a comprehensive literature review of articles published from January 1, 1998 through December 31, 2013 via MEDLINE(®), EMBASE and the Cochrane Collection using a predetermined search strategy. All studies included were performed in humans older than 18 years, were written in English and had an abstract available for review. We grouped studies into 1 of 5 categories, ie computerized tomography, magnetic resonance imaging, ultrasound, biopsy and surveillance.

RESULTS

While computerized tomography and magnetic resonance imaging with and without contrast enhancement remain the gold standard to evaluate cystic lesions of the kidney, diffusion-weighted magnetic resonance imaging and contrast enhanced ultrasound have surfaced as new tools for assessment of complex cysts. Comparative effectiveness studies on these new imaging modalities are limited. Image guided biopsy has increasingly been shown to be useful for evaluation of intermediate (Bosniak II and IIF) complex cysts. We found few studies providing guidance on the duration and/or intensity of surveillance required for intermediate complex renal cysts.

CONCLUSIONS

Although new and enhanced techniques are in development and may be useful in the future management of complex renal cysts, there is a paucity of data regarding the value of these new techniques. Future research should focus on surveillance of intermediate complex renal cysts, particularly on the ideal frequency and type of imaging required.

Multiple kidney cysts in thin basement membrane disease with proteinuria and kidney function impairment

Background

Some patients with thin basement membrane disease (TBMD) develop proteinuria, hypertension and different degrees of CKD, besides the persistent microhaematuria characteristic of the disease. Little is known about factors associated with this unfavourable outcome.

Methods

We reviewed clinical, pathological and radiological features of 32 patients with biopsy-proven TBMD. Patients were divided in two groups: those with persistent normal kidney function and negative or minimal proteinuria (n = 16) and those with persistent proteinuria >0.5 g/day (n = 16).

Results

Patients with proteinuria had a worse kidney function at baseline than those with negative proteinuria. Global or segmental glomerulosclerosis, together with interstitial fibrosis, was found in 37% of patients with proteinuria. All proteinuric patients were treated with renin–angiotensin system blockers. At the end of follow-up (198 months in proteinuric patients and 210 months in patients with negative proteinuria) the prevalence of hypertension was 68% in proteinuric patients (12% at baseline), compared with 12 and 6%, respectively, in non-proteinuric patients. A slow decline of renal function was observed in proteinuric patients, although no patient developed end-stage kidney disease. Ultrasound studies showed bilateral kidney cysts in nine patients (56%) with proteinuria. Cysts were bilateral and countless in six patients, and bilateral but with a limited number of cysts in the three remaining patients. No cysts were found in patients with negative proteinuria.

Conclusions

Some patients with TBMD develop hypertension, proteinuria and CKD. Multiple bilateral kidney cysts were found in a majority (56%) of these patients. Further studies are needed to investigate the pathogenesis and the influence on long-term outcome of this TBMD-associated multiple kidney cysts.

Age, kidney function, and risk factors associate differently with cortical and medullary volumes of the kidney

The kidney atrophies in patients with advanced chronic kidney disease (CKD) but factors influencing kidney size in normal adults are less clear. To help define this we measured kidney volumes on contrast-enhanced CT images from 1344 potential kidney donors (ages 18 to 75 years). Cortical volume per body surface area progressively declined in both genders with increased age. Statistically, this was primarily dependent on the age-related decline in glomerular filtration rate (GFR). Independent predictors of increased cortical volume per body surface area were male gender, increased GFR, increased 24-hour urine albumin, current smoker, and decreased high-density lipid cholesterol. Medullary volume per body surface area increased with age in men while it increased with age in women until age 50 followed by a subsequent decline. Independent predictors of increased medullary volume per body surface area were older age, male gender, increased GFR, increased 24-hour urine albumin, increased serum glucose, and decreased serum uric acid. Thus, while cortical volume declines with age along the same biological pathway as the age-related decline in GFR and albuminuria some CKD risk factors are actually associated with increased cortical or medullary volume among relatively healthy adults. Underlying hypertrophy or atrophy of different nephron regions may explain these findings.

Evidence of a third ADPKD locus is not supported by re-analysis of designated PKD3 families

Mutations to PKD1 and PKD2 are associated with autosomal dominant polycystic kidney disease (ADPKD). The absence of apparent PKD1/PKD2 linkage in five published European or North American families with ADPKD suggested a third locus, designated PKD3. Here we re-evaluated these families by updating clinical information, re-sampling where possible, and mutation screening for PKD1/PKD2. In the French-Canadian family we identified PKD1: p.D3782_V3783insD, with misdiagnoses in two individuals and sample contamination explaining the lack of linkage. In the Portuguese family, PKD1: p.G3818A segregated with the disease in 10 individuals in three generations with likely misdiagnosis in one individual, sample contamination, and use of distant microsatellite markers explaining the linkage discrepancy. The mutation, PKD2: c.213delC, was found in the Bulgarian family, with linkage failure attributed to false positive diagnoses in two individuals. An affected son but not the mother, in the Italian family had the nonsense mutation, PKD1: p.R4228X, which appeared de novo in the son; with simple cysts probably explaining the mother’s phenotype. No likely mutation was found in the Spanish family, but the phenotype was atypical with kidney atrophy in one case. Thus, re-analysis does not support the existence of a PKD3 in ADPKD. False positive diagnoses by ultrasound in all resolved families shows the value of mutation screening, but not linkage, to understand families with discrepant data.

GFR estimating equations: getting closer to the truth?

The application of serum creatinine and cystatin C in patients with CKD has been limited to using estimated glomerular filtration rate (eGFR). Criteria for choosing the best GFR estimating equation are 1) accuracy in estimating measured GFR, 2) optimal discrimination of clinical outcomes, and 3) association with CKD risk factors and outcomes similar to that of measured GFR. Notably, these criteria are often not in agreement; and while the last criterion is the most important, it has been widely overlooked. The primary problem with eGFR is that the non-GFR determinants of serum creatinine and cystatin C, as well as their surrogates (age, sex, and race), associate with CKD risk factors and outcomes. This leads to a distorted understanding of CKD, though eGFR based on serum creatinine appears to be less biased than eGFR based on cystatin C. Because of this problem, the use of eGFR should be limited to settings where knowing actual GFR is relevant and eGFR is more informative about GFR than serum creatinine or cystatin C alone. Such settings include staging CKD severity by GFR and dosing medications cleared by glomerular filtration. Alternatively, the diagnosis of CKD, the longitudinal progression of CKD, and prognostic models for CKD are settings where serum creatinine and cystatin C can be better applied and interpreted without eGFR.