CPEB4-CLOCK crosstalk during temporal lobe epilepsy.

OBJECTIVE: Posttranscriptional mechanisms are increasingly recognized as important contributors to the formation of hyperexcitable networks in epilepsy. Messenger RNA (mRNA) polyadenylation is a key regulatory mechanism governing protein expression by enhancing mRNA stability and translation. Previous studies have shown large-scale changes in mRNA polyadenylation in the hippocampus of mice during epilepsy development. The cytoplasmic polyadenylation element-binding protein CPEB4 was found to drive epilepsy-induced poly(A) tail changes, and mice lacking CPEB4 develop a more severe seizure and epilepsy phenotype. The mechanisms controlling CPEB4 function and the downstream pathways that influence the recurrence of spontaneous seizures in epilepsy remain poorly understood. METHODS: Status epilepticus was induced in wild-type and CPEB4-deficient male mice via an intra-amygdala microinjection of kainic acid. CLOCK binding to the CPEB4 promoter was analyzed via chromatin immunoprecipitation assay and melatonin levels via high-performance liquid chromatography in plasma. RESULTS: Here, we show increased binding of CLOCK to recognition sites in the CPEB4 promoter region during status epilepticus in mice and increased Cpeb4 mRNA levels in N2A cells overexpressing CLOCK. Bioinformatic analysis of CPEB4-dependent genes undergoing changes in their poly(A) tail during epilepsy found that genes involved in the regulation of circadian rhythms are particularly enriched. Clock transcripts displayed a longer poly(A) tail length in the hippocampus of mice post-status epilepticus and during epilepsy. Moreover, CLOCK expression was increased in the hippocampus in mice post-status epilepticus and during epilepsy, and in resected hippocampus and cortex of patients with drug-resistant temporal lobe epilepsy. Furthermore, CPEB4 is required for CLOCK expression after status epilepticus, with lower levels in CPEB4-deficient compared to wild-type mice. Last, CPEB4-deficient mice showed altered circadian function, including altered melatonin blood levels and altered clustering of spontaneous seizures during the day. SIGNIFICANCE: Our results reveal a new positive transcriptional-translational feedback loop involving CPEB4 and CLOCK, which may contribute to the regulation of the sleep-wake cycle during epilepsy.

Anaplastic ganglioglioma-A diagnosis comprising several distinct tumour types.

AIMS: Anaplastic ganglioglioma is a rare tumour, and diagnosis has been based on histological criteria. The 5th edition of the World Health Organization Classification of Tumours of the Central Nervous System (CNS WHO) does not list anaplastic ganglioglioma as a distinct diagnosis due to lack of molecular data in previous publications. We retrospectively compiled a cohort of 54 histologically diagnosed anaplastic gangliogliomas to explore whether the molecular profiles of these tumours represent a separate type or resolve into other entities. METHODS: Samples were subjected to histological review, desoxyribonucleic acid (DNA) methylation profiling and next-generation sequencing. Morphological and molecular data were summarised to an integrated diagnosis. RESULTS: The majority of tumours designated as anaplastic gangliogliomas resolved into other CNS WHO diagnoses, most commonly pleomorphic xanthoastrocytoma (16/54), glioblastoma, isocitrate dehydrogenase protein (IDH) wild type and diffuse paediatric-type high-grade glioma, H3 wild type and IDH wild type (11 and 2/54), followed by low-grade glial or glioneuronal tumours including pilocytic astrocytoma, dysembryoplastic neuroepithelial tumour and diffuse leptomeningeal glioneuronal tumour (5/54), IDH mutant astrocytoma (4/54) and others (6/54). A subset of tumours (10/54) was not assignable to a CNS WHO diagnosis, and common molecular profiles pointing to a separate entity were not evident. CONCLUSIONS: In summary, we show that tumours histologically diagnosed as anaplastic ganglioglioma comprise a wide spectrum of CNS WHO tumour types with different prognostic and therapeutic implications. We therefore suggest assigning this designation with caution and recommend comprehensive molecular workup.

A microRNA-129-5p/Rbfox crosstalk coordinates homeostatic downscaling of excitatory synapses.

Synaptic downscaling is a homeostatic mechanism that allows neurons to reduce firing rates during chronically elevated network activity. Although synaptic downscaling is important in neural circuit development and epilepsy, the underlying mechanisms are poorly described. We performed small RNA profiling in picrotoxin (PTX)-treated hippocampal neurons, a model of synaptic downscaling. Thereby, we identified eight microRNAs (miRNAs) that were increased in response to PTX, including miR-129-5p, whose inhibition blocked synaptic downscaling in vitro and reduced epileptic seizure severity in vivo Using transcriptome, proteome, and bioinformatic analysis, we identified the calcium pump Atp2b4 and doublecortin (Dcx) as miR-129-5p targets. Restoring Atp2b4 and Dcx expression was sufficient to prevent synaptic downscaling in PTX-treated neurons. Furthermore, we characterized a functional crosstalk between miR-129-5p and the RNA-binding protein (RBP) Rbfox1. In the absence of PTX, Rbfox1 promoted the expression of Atp2b4 and Dcx. Upon PTX treatment, Rbfox1 expression was downregulated by miR-129-5p, thereby allowing the repression of Atp2b4 and Dcx. We therefore identified a novel activity-dependent miRNA/RBP crosstalk during synaptic scaling, with potential implications for neural network homeostasis and epileptogenesis.

Polyadenylation of mRNA as a novel regulatory mechanism of gene expression in temporal lobe epilepsy.

Temporal lobe epilepsy is the most common and refractory form of epilepsy in adults. Gene expression within affected structures such as the hippocampus displays extensive dysregulation and is implicated as a central pathomechanism. Post-transcriptional mechanisms are increasingly recognized as determinants of the gene expression landscape, but key mechanisms remain unexplored. Here we show, for first time, that cytoplasmic mRNA polyadenylation, one of the post-transcriptional mechanisms regulating gene expression, undergoes widespread reorganization in temporal lobe epilepsy. In the hippocampus of mice subjected to status epilepticus and epilepsy, we report >25% of the transcriptome displays changes in their poly(A) tail length, with deadenylation disproportionately affecting genes previously associated with epilepsy. Suggesting cytoplasmic polyadenylation element binding proteins (CPEBs) being one of the main contributors to mRNA polyadenylation changes, transcripts targeted by CPEBs were particularly enriched among the gene pool undergoing poly(A) tail alterations during epilepsy. Transcripts bound by CPEB4 were over-represented among transcripts with poly(A) tail alterations and epilepsy-related genes and CPEB4 expression was found to be increased in mouse models of seizures and resected hippocampi from patients with drug-refractory temporal lobe epilepsy. Finally, supporting an adaptive function for CPEB4, deletion of Cpeb4 exacerbated seizure severity and neurodegeneration during status epilepticus and the development of epilepsy in mice. Together, these findings reveal an additional layer of gene expression regulation during epilepsy and point to novel targets for seizure control and disease-modification in epilepsy.

The DNA copy number landscape of a collision tumor.

Intracranial collision tumors are composed of two histologically distinct but merging components, and are rare. Their genetic profile has rarely been described. Comparative genome hybridization of a combined meningioma and oligodendroglioma demonstrated deletion of chromosome 22q and of 19q in both tumors. Somatic deletion of chromosome 22q and 19q is associated with development of an intracranial collision tumor.
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Absence of 1p/19q codeletion in oligodendroglioma-like areas of pilocytic astrocytomas.

The presence of oligodendroglioma-like areas in pilocytic astrocytoma may give rise to pathologic diagnostic uncertainty. This study aims to determine if the oligodendroglioma-like areas present in some pilocytic astrocytomas (PA) possess the signature 1p/19q codeletion that is characteristic of classical oligodendroglioma. Array comparative genomic hybridization was carried out on 12 PA samples, from which oligodendroglioma-like areas were microdissected and used as the template DNA source. 1p/19q codeletions were not found in any of the oligodendroglioma areas in PAs. We conclude that PAs with oligodendroglioma-like areas do not share the same molecular genetics as classic oligodendroglioma.
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Transient P2X7 Receptor Antagonism Produces Lasting Reductions in Spontaneous Seizures and Gliosis in Experimental Temporal Lobe Epilepsy.

UNLABELLED: Neuroinflammation is thought to contribute to the pathogenesis and maintenance of temporal lobe epilepsy, but the underlying cell and molecular mechanisms are not fully understood. The P2X7 receptor is an ionotropic receptor predominantly expressed on the surface of microglia, although neuronal expression has also been reported. The receptor is activated by the release of ATP from intracellular sources that occurs during neurodegeneration, leading to microglial activation and inflammasome-mediated interleukin 1ß release that contributes to neuroinflammation. Using a reporter mouse in which green fluorescent protein is induced in response to the transcription of P2rx7, we show that expression of the receptor is selectively increased in CA1 pyramidal and dentate granule neurons, as well as in microglia in mice that developed epilepsy after intra-amygdala kainic acid-induced status epilepticus. P2X7 receptor levels were increased in hippocampal subfields in the mice and in resected hippocampus from patients with pharmacoresistant temporal lobe epilepsy. Cells transcribing P2rx7 in hippocampal slices from epileptic mice displayed enhanced agonist-evoked P2X7 receptor currents, and synaptosomes from these animals showed increased P2X7 receptor levels and altered calcium responses. A 5 d treatment of epileptic mice with systemic injections of the centrally available, potent, and specific P2X7 receptor antagonist JNJ-47965567 (30 mg/kg) significantly reduced spontaneous seizures during continuous video-EEG monitoring that persisted beyond the time of drug presence in the brain. Hippocampal sections from JNJ-47965567-treated animals obtained >5 d after treatment ceased displayed strongly reduced microgliosis and astrogliosis. The present study suggests that targeting the P2X7 receptor has anticonvulsant and possibly disease-modifying effects in experimental epilepsy. SIGNIFICANCE STATEMENT: Temporal lobe epilepsy is the most common and drug-resistant form of epilepsy in adults. Neuroinflammation is implicated as a pathomechanism, but the upstream mechanisms driving gliosis and how important this is for seizures remain unclear. In our study, we show that the ATP-gated P2X7 receptor is upregulated in experimental epilepsy and resected hippocampus from epilepsy patients. Targeting the receptor with a new centrally available antagonist, JNJ-47965567, suppressed epileptic seizures well beyond the time of treatment and reduced underlying gliosis in the hippocampus. The findings suggest a potential disease-modifying treatment for epilepsy based on targeting the P2X7 receptor.

Expression and function of the metabotropic purinergic P2Y receptor family in experimental seizure models and patients with drug-refractory epilepsy.

OBJECTIVE: ATP is released into the extracellular space during pathologic processes including increased neuronal firing. Once released, ATP acts on P2 receptors including ionotropic P2X and metabotropic P2Y receptors, resulting in changes to glial function and neuronal network excitability. Evidence suggests an involvement of P2Y receptors in the pathogenesis of epilepsy, but there has been no systematic effort to characterize the expression and function of the P2Y receptor family during seizures and in experimental and human epilepsy. METHODS: Status epilepticus was induced using either intra-amygdala kainic acid or pilocarpine to characterize the acute- and long-term changes in hippocampal P2Y expression. P2Y expression was also investigated in brain tissue from patients with temporal lobe epilepsy. Finally, we analyzed the effects of two specific P2Y agonists, ADP and UTP, on seizure severity and seizure-induced cell death. RESULTS: Both intra-amygdala kainic acid and pilocarpine-induced status epilepticus increased the transcription of the uracil-sensitive P2Y receptors P2ry2 , P2ry4 , and P2ry6 and decreased the transcription of the adenine-sensitive P2Y receptors P2ry1 , P2ry12 , P2ry13 . Protein levels of P2Y1 , P2Y2 , P2Y4 , and P2Y6 were increased after status epilepticus, whereas P2Y12 expression was decreased. In the chronic phase, P2ry1 , P2ry2 , and P2ry6 transcription and P2Y1 , P2Y2 , and P2Y12 protein levels were increased with no changes for the other P2Y receptors. In hippocampal samples from patients with temporal lobe epilepsy, P2Y1 and P2Y2 protein expression was increased, whereas P2Y13 levels were lower. Demonstrating a functional contribution of P2Y receptors to seizures, central injection of ADP exacerbated seizure severity, whereas treatment with UTP decreased seizure severity during status epilepticus in mice. SIGNIFICANCE: The present study is the first to establish the specific hippocampal expression profile and function of the P2Y receptor family after experimental status epilepticus and in human temporal lobe epilepsy and offers potential new targets for seizure control and disease modification.

CHOP regulates the p53-MDM2 axis and is required for neuronal survival after seizures.

Hippocampal sclerosis is a frequent pathological finding in patients with temporal lobe epilepsy and can be caused by prolonged single or repeated brief seizures. Both DNA damage and endoplasmic reticulum stress have been implicated as underlying molecular mechanisms in seizure-induced brain injury. The CCAAT/enhancer-binding protein homologous protein (CHOP) is a transcriptional regulator induced downstream of DNA damage and endoplasmic reticulum stress, which can promote or inhibit apoptosis according to context. Recent work has proposed inhibition of CHOP as a suitable neuroprotective strategy. Here, we show that transcript and protein levels of CHOP increase in surviving subfields of the hippocampus after prolonged seizures (status epilepticus) in mouse models. CHOP was also elevated in the hippocampus from epileptic mice and patients with pharmacoresistant epilepsy. The hippocampus of CHOP-deficient mice was much more vulnerable to damage in mouse models of status epilepticus. Moreover, compared with wild-type animals, CHOP-deficient mice subject to status epilepticus developed more spontaneous seizures, displayed protracted hippocampal neurodegeneration and a deficit in a hippocampus-dependent object-place recognition task. The absence of CHOP was associated with a supra-maximal induction of p53 after status epilepticus, and inhibition of p53 abolished the cell death-promoting consequences of CHOP deficiency. The protective effect of CHOP could be partly explained by activating transcription of murine double minute 2 that targets p53 for degradation. These data demonstrate that CHOP is required for neuronal survival after seizures and caution against inhibition of CHOP as a neuroprotective strategy where excitotoxicity is an underlying pathomechanism.

Migrating partial seizures of infancy: expansion of the electroclinical, radiological and pathological disease spectrum.

Migrating partial seizures of infancy, also known as epilepsy of infancy with migrating focal seizures, is a rare early infantile epileptic encephalopathy with poor prognosis, presenting with focal seizures in the first year of life. A national surveillance study was undertaken in conjunction with the British Paediatric Neurology Surveillance Unit to further define the clinical, pathological and molecular genetic features of this disorder. Fourteen children with migrating partial seizures of infancy were reported during the 2 year study period (estimated prevalence 0.11 per 100,000 children). The study has revealed that migrating partial seizures of infancy is associated with an expanded spectrum of clinical features (including severe gut dysmotility and a movement disorder) and electrographic features including hypsarrhythmia (associated with infantile spasms) and burst suppression. We also report novel brain imaging findings including delayed myelination with white matter hyperintensity on brain magnetic resonance imaging in one-third of the cohort, and decreased N-acetyl aspartate on magnetic resonance spectroscopy. Putaminal atrophy (on both magnetic resonance imaging and at post-mortem) was evident in one patient. Additional neuropathological findings included bilateral hippocampal gliosis and neuronal loss in two patients who had post-mortem examinations. Within this cohort, we identified two patients with mutations in the newly discovered KCNT1 gene. Comparative genomic hybridization array, SCN1A testing and genetic testing for other currently known early infantile epileptic encephalopathy genes (including PLCB1 and SLC25A22) was non-informative for the rest of the cohort.

Immunoproteasome deficiency results in age-dependent development of epilepsy.

The immunoproteasome is a central protease complex required for optimal antigen presentation. Immunoproteasome activity is also associated with facilitating the degradation of misfolded and oxidized proteins, which prevents cellular stress. While extensively studied during diseases with increasing evidence suggesting a role for the immunoproteasome during pathological conditions including neurodegenerative diseases, this enzyme complex is believed to be mainly not expressed in the healthy brain. In this study, we show an age-dependent increase in polyubiquitination in the brains of wild-type mice, accompanied by an induction of immunoproteasomes, which was most prominent in neurons and microglia. In contrast, mice completely lacking immunoproteasomes (triple-knockout mice), displayed a strong increase in polyubiquitinated proteins already in the young brain and developed spontaneous epileptic seizures, beginning at the age of 6 months. Injections of kainic acid led to high epilepsy-related mortality of aged triple-knockout mice, confirming increased pathological hyperexcitability states. Notably, the expression of the immunoproteasome was reduced in the brains of patients suffering from epilepsy. In addition, the aged triple-knockout mice showed increased anxiety, tau hyperphosphorylation and degeneration of Purkinje cell population with the resulting ataxic symptoms and locomotion alterations. Collectively, our study suggests a critical role for the immunoproteasome in the maintenance of a healthy brain during ageing.

Alzheimer's disease brain-derived amyloid-ß-mediated inhibition of LTP in vivo is prevented by immunotargeting cellular prion protein.

Synthetic amyloid-ß protein (Aß) oligomers bind with high affinity to cellular prion protein (PrP(C)), but the role of this interaction in mediating the disruption of synaptic plasticity by such soluble Aß in vitro is controversial. Here we report that intracerebroventricular injection of Aß-containing aqueous extracts of Alzheimer's disease (AD) brain robustly inhibits long-term potentiation (LTP) without significantly affecting baseline excitatory synaptic transmission in the rat hippocampus in vivo. Moreover, the disruption of LTP was abrogated by immunodepletion of Aß. Importantly, intracerebroventricular administration of antigen-binding antibody fragment D13, directed to a putative Aß-binding site on PrP(C), prevented the inhibition of LTP by AD brain-derived Aß. In contrast, R1, a Fab directed to the C terminus of PrP(C), a region not implicated in binding of Aß, did not significantly affect the Aß-mediated inhibition of LTP. These data support the pathophysiological significance of SDS-stable Aß dimer and the role of PrP(C) in mediating synaptic plasticity disruption by soluble Aß.

Microvascular stabilization via blood-brain barrier regulation prevents seizure activity.

Blood-brain barrier (BBB) dysfunction is associated with worse epilepsy outcomes however the underlying molecular mechanisms of BBB dysfunction remain to be elucidated. Tight junction proteins are important regulators of BBB integrity and in particular, the tight junction protein claudin-5 is the most enriched in brain endothelial cells and regulates size-selectivity at the BBB. Additionally, disruption of claudin-5 expression has been implicated in numerous disorders including schizophrenia, depression and traumatic brain injury, yet its role in epilepsy has not been fully deciphered. Here we report that claudin-5 protein levels are significantly diminished in surgically resected brain tissue from patients with treatment-resistant epilepsy. Concomitantly, dynamic contrast-enhanced MRI in these patients showed widespread BBB disruption. We show that targeted disruption of claudin-5 in the hippocampus or genetic heterozygosity of claudin-5 in mice exacerbates kainic acid-induced seizures and BBB disruption. Additionally, inducible knockdown of claudin-5 in mice leads to spontaneous recurrent seizures, severe neuroinflammation, and mortality. Finally, we identify that RepSox, a regulator of claudin-5 expression, can prevent seizure activity in experimental epilepsy. Altogether, we propose that BBB stabilizing drugs could represent a new generation of agents to prevent seizure activity in epilepsy patients.

Recessive mutations in RYR1 are a common cause of congenital fiber type disproportion.

The main histological abnormality in congenital fiber type disproportion (CFTD) is hypotrophy of type 1 (slow twitch) fibers compared to type 2 (fast twitch) fibers. To investigate whether mutations in RYR1 are a cause of CFTD we sequenced RYR1 in seven CFTD families in whom the other known causes of CFTD had been excluded. We identified compound heterozygous changes in the RYR1 gene in four families (five patients), consistent with autosomal recessive inheritance. Three out of five patients had ophthalmoplegia, which may be the most specific clinical indication of mutations in RYR1. Type 1 fibers were at least 50% smaller, on average, than type 2 fibers in all biopsies. Recessive mutations in RYR1 are a relatively common cause of CFTD and can be associated with extreme fiber size disproportion.

Percutaneous renal cryoablation: local control at mean 26 months of followup.

PURPOSE: We retrospectively determined the efficacy of percutaneous renal cryoablation based on a mean followup of more than 2 years. MATERIALS AND METHODS: Institutional review board approval was obtained for this Health Insurance Portability and Accountability Act compliant retrospective study. Informed consent was waived. From March 2003 through March 2007, 91 patients with 93 tumors underwent 92 percutaneous cryoablation procedures. Technical success was defined as extension of the ice ball beyond the tumor margin and post-ablation images showing no contrast enhancement in the area encompassing the original tumor within 3 months of the procedure. Local tumor progression was defined as new enhancement in the ablated tumor or an increase in ablated tumor size beyond 3 months after the procedure. Complications were defined using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0. RESULTS: Mean followup was 26 months (range 5 to 61, SD ±13) and mean tumor size was 3.4 cm (range 1.5 to 7.3, SD ±1.2). Major complications occurred in 6 of 91 patients (7%) or after 8 of 92 (9%) procedures. Technically successful ablation was performed in the treatment of 89 of the 93 (96%) tumors or 87 of the 91 patients (96%). Of the 83 tumors with followup longer than 3 months only a single case (1%) of local tumor progression occurred. Overall local control was achieved in 86 of 91 (95%) patients or 88 of 93 (95%) tumors. CONCLUSIONS: Midterm followup of percutaneous renal cryoablation shows durability of this treatment method with a low incidence of tumor recurrence beyond 3 months.

Role of intraarterial embolization before cryoablation of large renal tumors: a pilot study.

A retrospective review of patients who underwent percutaneous cryoablations of renal tumors (> or = 5 cm) with/without previous selective intraarterial embolization from March 2003 to January 2008 was performed to compare periprocedural complications. Of 129 treated tumors, 11 (8.5%) were larger than 5 cm. One patient was lost to follow-up. Of the remaining 10 follow-up patients, four (40%) underwent selective intraarterial tumor embolization before cryoablation. The mean hematoma volume in patients who underwent embolization before cryoablation (n = 4) was 18.3 mL +/- 25.9, whereas that in patients who underwent cryoablation alone (n = 6) was 357.3 mL +/- 460.9 (P< .01). Only one patient required transfusion and prolonged hospitalization. Combination therapy can provide a decrease in postprocedural cryoablation-related hemorrhage.

Percutaneous cryoablation of masses in a solitary kidney.

OBJECTIVE: The purpose of this study was to determine the effect of percutaneous cryoablation of tumors in a solitary kidney on renal function, treatment-related complications, and local tumor control. MATERIALS AND METHODS: A retrospective review of the cases of patients with a solitary kidney treated with percutaneous renal cryoablation from March 2003 through November 2008 was performed. Renal function was analyzed with serum creatinine concentration and glomerular filtration rate measured before ablation, on the first day after ablation, 3-6 months after ablation, and at the most recent evaluation on record at our institution. Index tumor size, ice ball size, and local tumor control were tabulated after review of preablation and postablation images. RESULTS: Thirty-one patients with 38 tumors (mean maximum diameter, 3.0 cm; range, 1.7-7.3 cm) were treated with 35 cryoablation procedures. After a mean follow-up period of 14 months (range, < 1-42 months), 29 patients had a 0.1-mg/dL median increase in creatinine concentration (p = 0.0089) and 4.7-mL/min/1.73 m(2) median decrease in glomerular filtration rate (p = 0.0335) from preablation levels. Fifteen of 25 patients with 3 months or more of renal function follow-up had a decrease in renal function. Ten of these 15 patients (67%) had a history of previous renal ablation or partial nephrectomy involving the same solitary kidney. No patient needed dialysis. Seven grade 3 or greater complications (Common Terminology Criteria for Adverse Events) occurred after the 35 procedures (20% complication rate). The median hospital stay was 1 day (range, 1-19 days). The local tumor control rate was 92%. CONCLUSION: Percutaneous cryoablation is effective in the management of renal tumors in patients with a solitary kidney, causing minimal loss of renal function. Patients who have previously undergone partial nephrectomy or ablation in a solitary kidney may be more susceptible to renal function loss than patients who have not undergone these procedures.

Hydrodisplacement in the percutaneous cryoablation of 50 renal tumors.

OBJECTIVE: The purpose of this article is to describe the technique, safety, and effectiveness of percutaneous hydrodisplacement during the course of percutaneous renal cryoablation. MATERIALS AND METHODS: We retrospectively reviewed our experience in performing percutaneous hydrodisplacement during the cryoablation of renal tumors. In this subset of patients, we addressed tumor location within the kidney, tumor position relative to critical structures, effectiveness of hydrodisplacement, and complications in performing this adjunct technique. Comparisons between the two groups were made using Wilcoxon's rank sum test or chi-square test, as appropriate. RESULTS: Hydrodisplacement was attempted 52 times in 50 (24%) of 206 percutaneous renal tumor cryoablations. Tumors that were located anteriorly (p < 0.0001) or in the lower pole (p = 0.001) of the kidney were more likely to require hydrodisplacement. The colon required displacement most often (n = 41), followed by the body wall (n = 3), duodenum (n = 2), jejunum and ileum (n = 2), ureter (n = 1), and psoas muscle (n = 1). There was a single complication of hemorrhage resulting from injury to an intercostal artery branch that required termination of the procedure before fluid infusion. When fluid was infused, the critical structure was displaced in 50 (96%) of 52 attempts, displacing the critical structure from its initial location by a mean distance of 16 mm (range, 3-46 mm). Both failures occurred early in our experience with hydrodisplacement, and both required balloon displacement. CONCLUSION: Hydrodisplacement is a safe, effective, and commonly needed technique for displacement of critical structures before percutaneous cryoablation of renal tumors, particularly for tumors located anteriorly or in the lower pole of the kidney.