Guy Cosnard

Pediatric diffusion tensor imaging: Normal database and observation of the white matter maturation in early childhood

Recent advances in diffusion tensor imaging (DTI) have made it possible to reveal white matter anatomy and to detect neurological abnormalities in children. However, the clinical use of this technique is hampered by the lack of a normal standard of reference. The goal of this study was to initiate the establishment of a database of DTI images in children, which can be used as a normal standard of reference for diagnosis of pediatric neurological abnormalities. Seven pediatric volunteers and 23 pediatric patients (age range: 0-54 months) referred for clinical MR examinations, but whose brains were shown to be normal, underwent anatomical and DTI acquisitions on a 1.5 T MR scanner. The white matter maturation, as observed on DTI color maps, was described and illustrated. Changes in diffusion fractional anisotropy (FA), average apparent diffusion constant (ADC(ave)), and T2-weighted (T2W) signal intensity were quantified in 12 locations to characterize the anatomical variability of the maturation process. Almost all prominent white matter tracts could be identified from birth, although their anisotropy was often low. The evolution of FA, shape, and size of the white matter tracts comprised generally three phases: rapid changes during the first 12 months; slow modifications during the second year; and relative stability after 24 months. The time courses of FA, ADC(ave), and T2W signal intensity confirmed our visual observations that maturation of the white matter and the normality of its architecture can be assessed with DTI in young children. The database is available online and is expected to foster the use of this promising technique in the diagnosis of pediatric pathologies.

Apparent diffusion coefficient measurements within intracranial epidermoid cysts in six patients

Abstract. The purpose was to determine whether a strong decrease in apparent diffusion coefficient (ADC) within epidermoid cysts (ECs) is actually responsible for their bright signal intensity on diffusion-weighted (DW) trace images. We studied six patients with surgically proven ECs in whom ADC calculation from T2-weighted DW-EPI-SE data were performed within the ECs and within the deep white matter and cerebrospinal fluid (CSF) as references. All ECs displayed highest signal intensity on the DW trace images. ADC values ranged from 1,280 to 807×10–6xa0mm2/s within cysts (with a mean value of 1,070), from 849 to 698×10–6xa0mm2/s within white matter (with a mean value of 764) and from 3,370 to 2,980×10–6xa0mm2/s within CSF (with a mean value of 3,185). ECs exhibited slightly higher ADC values than white matter, and not the strongly decreased ones which would have been expected if diffusion-weighting were the prominent mechanism for bright signal intensity of the ECs on DW images. However, the EC ADC values are much lower than those of the CSF. Other mechanisms must therefore be involved, i.e. the T2 shine-through effect. Reduced ADC is not the only explanation of the EC bright signal intensity on the DW trace images.

Fast FLAIR sequence for detecting major vascular abnormalities during the hyperacute phase of stroke : a comparison with MR angiography

Abstract In the hyperacute phase of stroke, occluded vessels can be seen as high signal on fast-FLAIR images or as absence of flow-related enhancement in maximum-intensity projection (MIP) MR angiography (MRA). To compare these techniques, we examined 53 patients within 6 h of a stroke, using a standardised MRI protocol including fast-FLAIR and 3D time-of-flight TOF MR to detect vessel occlusion or reduced flow corresponding to the suspected ischaemic territory. Brain infarcts were confirmed on MRI after 1–5 days in 41 cases (77 %). The overall accuracy of 3D-TOF MRA was 68 % and sensitivity, specificity, positive and negative predictive values were 67 %, 71 %, 87 %, and 43 % respectively. Values for the fast-FLAIR sequence were: 65 %, 85 %, 93 % and 44 %, with an overall accuracy of 70 %. The fast-FLAIR sequence was thus able to show occluded vessels or reduced flow with about the same accuracy as 3D-TOF MRA and enabled better prediction of the ischaemic area.

High signal in cerebrospinal fluid mimicking subarachnoid haemorrhage on FLAIR following acute stroke and intravenous contrast medium

Abstract We describe five cases of high signal in the cerebrospinal fluid (CSF) on fast-FLAIR images 24–48 h after onset of stroke. All the patients had undergone perfusion-weighted MRI within 6 h of the onset of the symptoms. The CSF was far brighter than the cortical gyri. The high signal was diffusely around both cerebral hemispheres in two cases and around one hemisphere in two others; it was focal, around the acute ischaemic lesion, in one. CT was normal in all cases. The CSF high signal was transient, decreasing in extent and intensity with time and resolving completely within 3–6 days. It was not associated with worsening of the clinical state or poor outcome. Our explanation of this phenomena is hypothetical: we speculate that it could be due to disruption of the blood-brain barrier resulting in leakage of protein, gadolinium chelates, or both in to the subarachnoid space. It should not be confused with subarachnoid haemorrhage.

Corticospinal dysgenesis and upper-limb deficits in congenital hemiplegia : a diffusion tensor imaging study

OBJECTIVES. Precision grasping critically relies on the integrity of the corticospinal tract as evidenced in congenital hemiplegia by the correlation found between corticospinal dysgenesis and hand-movement deficits. Therefore, corticospinal dysgenesis could be used to anticipate upper-limb deficits in young infants with congenital hemiplegia. However, most studies have quantified corticospinal dysgenesis by measuring the cross-sectional area of cerebral peduncles on T1 MRI, a measure biased by other structures present in the peduncles. The purpose of this study was to evaluate the extent to which this may have hampered the conclusions of previous studies. We also aimed to investigate the relationship between upper-limb deficits and a more accurate measure of corticospinal dysgenesis to provide a tool for anticipating upper-limb deficits in infants with congenital hemiplegia. METHODS. To address this issue, we measured corticospinal tract areas in 12 patients with congenital hemiplegia and 12 matched control subjects by using the diffusion tensor imaging technique. Corticospinal dysgenesis was quantified by computing a symmetry index between the area of the contralateral and ipsilateral corticospinal tracts. This value was then compared with that resulting from the conventional MRI method. RESULTS. The symmetry indexes gathered with these 2 methods were highly correlated, although the diffusion tensor imaging symmetry indexes were significantly smaller. This indicates that, in patients with congenital hemiplegia, the conventional MRI measurement has led to a systematic underestimate of corticospinal dysgenesis. These 2 estimates of corticospinal dysgenesis were also correlated with upper-limb impairments and disabilities. Although the symmetry index computed from peduncle measurements was correlated solely with deficits in stereognosis, the diffusion tensor imaging index correlated with stereognosis, digital and manual dexterities, and ABILHAND-Kids, a measure of manual ability in daily life activities. CONCLUSIONS. The diffusion tensor imaging symmetry index provides a useful prognostic tool for anticipating upper-limb deficits and their consequences in daily life activities.

Reproducibility of osseous landmarks used for computed tomography based three-dimensional cephalometric analyses

PURPOSEnThe aim of this paper was to measure the reproducibility of osseous landmark identification from two recently described three-dimensional (3D) cephalometric analyses: 3D-ACRO and 3D-Swennen analyses. The study population consisted of 13 patients examined with spiral 3D computed tomography (CT). We used a previously validated low-dose CT protocol. For each analysis, 22 cephalometric reference landmarks were identified on 3D CT surface renderings. Forty-four reference landmarks were identified per patient. Two series of identifications were performed by two independent observers. In total, 3432 imaging measurements were completed. The intra-observer reconstructed mean log was 1.210+/-1.042mm for the 3D-ACRO analysis, and 1.311+/-1.042mm for 3D-Swennen analysis (comparison: p=0.17 NS). The inter-observer reconstructed mean log was 1.799+/-1.037mm for the 3D-ACRO analysis, and 2.465+/-1.036mm for 3D-Swennen analysis (comparison: p=0.000000002). The difference between the intra- and inter-observer reconstructed mean logs were 1.486+/-1.057mm for 3D-ACRO and 1.880+/-1.056mm for 3D-Swennen analysis. In conclusions: 3D-ACRO analysis was significantly more reproducible than 3D-Swennen analysis (p=0.0027) due to the use of a majority of highly reproducible cephalometric landmarks. Finally, we propose a classification scheme and exclusion criteria for reference landmarks used in 3D cephalometrics, based on inter-observer reproducibility and anatomical reality.

Intraoperative magnetic resonance imaging at 3-T using a dual independent operating room-magnetic resonance imaging suite: development, feasibility, safety, and preliminary experience.

OBJECTIVEA twin neurosurgical magnetic resonance imaging (MRI) suite with 3-T intraoperative MRI (iMRI) was developed to be available to neurosurgeons for iMRI and for independent use by radiologists. METHODSThe suite was designed with one area dedicated to neurosurgery and the other to performing MRI under surgical conditions (sterility and anesthesia). The operating table is motorized, enabling transfer of the patient into the MRI system. These two areas can function independently, allowing the MRI area to be used for nonsurgical cases. We report the findings from the first 21 patients to undergo scheduled neurosurgery with iMRI in this suite (average age, 51 ± 24 yr; intracranial tumor, 18 patients; epilepsy surgery, 3 patients). RESULTSTwenty-six iMRI examinations were performed, 3 immediately before surgical incision, 9 during surgery (operative field partially closed), and 14 immediately postsurgery (operative field fully closed but patient still anesthetized and draped). Minor technical dysfunctions prolonged 10 iMRI procedures; however, no serious iMRI-related incidents occurred. Twenty-three iMRI examinations took an average of 78 ± 20 minutes to perform. In three patients, iMRI led to further tumor resection because removable residual tumor was identified. Complete tumor resection was achieved in 15 of the 18 cases. CONCLUSIONThe layout of the new complex allows open access to the 3-T iMRI system except when it is in use under surgical conditions. Three patients benefited from the iMRI examination to achieve total resection. No permanent complications were observed. Therefore, the 3-T iMRI is feasible and appears to be a safe tool for intraoperative surgical planning and assessment.

Substitution of 11C-methionine PET by perfusion MRI during the follow-up of treated high-grade gliomas: Preliminary results in clinical practice.

PURPOSEnOur aim was to compare perfusion magnetic resonance imaging (MRI) and positron emission tomography (PET) using carbon-11 labelled methionine (MET) in gliomas and their value in differentiating tumour recurrence from necrosis.nnnMATERIALS AND METHODSnWe retrospectively reviewed 28 patients with a high-grade glioma. A total of 33MR perfusions and MET-PET were ultimately analysable for comparison between the relative cerebral blood volume (rCBV) and MET-PET examinations. Intra- and interobserver reproducibility was assessed and diagnostic value of rCBV compared to MET-PET and histology was assessed by the area under the receiver operating characteristic (ROC) curve.nnnRESULTSnROC curve analysis showed that rCBV had at least equal performances in differentiating tumour recurrence and necrosis than MET-PET. Cut-off value of rCBV for differentiating tumour from necrosis was 182% with a sensitivity of 81.5% and a specificity of 100%.nnnCONCLUSIONnIn clinical practice, perfusion MRI could replace MET-PET for differentiating necrosis from tumour recurrence.

IDH1 mutation, a genetic alteration associated with adult gliomatosis cerebri

Recently, mutations in IDH1 and IDH2 have been reported as an early and common genetic alteration in diffuse gliomas, being possibly followed by 1p/19q loss in oligodendrogliomas and TP53 mutations in astrocytomas. Lately, IDH1 mutations have also been identified in adult gliomatosis cerebri (GC). The aim of our study was to test the status of IDH1/2, p53 and of chromosomes 1 and 19 in a series of 12 adult and three pediatric GC. For all tumors, clinico‐radiologic characteristics, histopathologic features, status of IDH1/2, p53 and of chromosomes 1 and 19 were evaluated. IDH1 mutations were detected only in GC of adult patients (5/12). They all corresponded to R132H. Additional 1p/19q losses were observed in two of them with histological features of oligodendroglial lineage. Other copy number alterations of chromosomes 1 and 19 were also noticed. The median overall survival in adults was 10.5 months in non‐mutated GC and 43.5 months in mutated GC. IDH1 mutations were present in GC of adult patients, but not in those of children. There was a trend toward longer overall survival in mutated GC when compared to non‐mutated ones. Concomitant 1p/19q loss was observed in IDH1‐mutated GC with oligodendroglial phenotype. These observations contribute toward establishing a stronger link between GC and diffuse glioma. In addition, these results also emphasize the importance of testing for IDH1/2 mutations and 1p/19q deletions in GC to classify them better and to allow the development of targeted therapy.

Gliomatosis cerebri, imaging findings of 12 cases.

BACKGROUND AND PURPOSEnWe report 12 cases of Gliomatosis cerebri (GC), a rare brain neoplasm, to define its semeiologic criteria. Literature was reviewed to clarify its physiopathology.nnnPATIENTS AND METHODSnFrom 1997 to 2008, 12 histologically proven cases with GC were retrospectively reviewed. Of the 12 patients, nine were male. The mean age was of 54 years. Were performed CT-Scan (n=6), MRI (n=12), diffusion and perfusion weighted images (n=12 and n=4), MR Spectroscopy (n=3), a FDG and a Methionin PET-Scan (n=2 and n=3 respectively).nnnRESULTSnPrimary diagnosis was missed in six cases. Most frequent clinical signs were seizure and mental changes. Imaging criteria were: area of high signal intensity on FLAIR and T2-weighted images, involving three or more contiguous lobes with conserved architecture. Frequently a bilateral widespread invasion with involvment of the corpus callosum or the anterior white commissure or both was observed. At diagnosis and in the classical form (type I) of GC, no significant contrast enhancement and decreased rCBV were observed. Focal enhancement and increased rCBV were observed in the focal mass in type II GC. MR Spectroscopy showed an increase of the Cho/Cr ratio and a decrease in the NAA/Cr one. FDG PET showed in type I a decreased avidity for the FDG whereas in type II a increased avidity was observed. MET-PET showed an increased avidity for the tracer in a GC type II and a slight avidity in a GC type I.nnnCONCLUSIONnGC is a rare brain entity. Primary diagnosis is often missed. The imaging findings of GC I, a WHO grade III tumor, should be known and include classical MRI but also PWI, MRS and scintigraphic findings.