Dynamic compression in vertebral artery dissection in children: apropos of a new protocol.

PURPOSE: Our goals are (1) to report a consecutive prospective series of children who had posterior circulation stroke caused by vertebral artery dissection at the V3 segment; (2) to describe a configuration of the vertebral artery that may predispose to rotational compression; and (3) to recommend a new protocol for evaluation and treatment of vertebral artery dissection at V3. METHODS: All children diagnosed with vertebral artery dissection at the V3 segment from September 2014 to July 2020 at our institution were included in the study. Demographic, clinical, surgical, and radiological data were collected. RESULTS: Sixteen children were found to have dissection at a specific segment of the vertebral artery. Fourteen patients were male. Eleven were found to have compression on rotation during a provocative angiogram. All eleven underwent C1C2 posterior fusion as part of their treatment. Their mean age was 6.44 years (range 18 months-15 years). Mean blood loss was 57.7 mL. One minor complication occurred: a superficial wound infection treated with oral antibiotics only. There were no vascular or neurologic injuries. There have been no recurrent ischemic events after diagnosis and/or treatment. Mean follow-up was 33.3 months (range 2-59 months). We designed a new protocol to manage V3 dissections in children. CONCLUSION: Posterior C1C2 fusion is a safe and effective option for treatment of dynamic compression in vertebral artery dissection in children. Institution of and compliance with a strict diagnostic and treatment protocol for V3 segment dissections seem to prevent recurrent stroke.

Reversible Cerebral Vasoconstriction Syndrome: A Novel Mechanism for Neurological Complications in Schimke Immuno-osseous Dysplasia.

BACKGROUND: Schimke immuno-osseous dysplasia is a rare autosomal recessive disease resulting from biallelic SMARCAL1 mutations. It presents in early childhood and is characterized by short stature, nephropathy, and immunodeficiency. Approximately 50% of those affected have neurological complications including migraines, transient ischemic attacks, and strokes. METHODS: We present a six-year-old boy with Schimke immuno-osseous dysplasia without evidence of atherosclerosis with recurrent episodes of severe headache, fluctuating hemiparesis, and aphasia. RESULTS: Magnetic resonance imaging and angiography were normal during the initial episode; multiple areas of reversible restricted diffusion with decreased perfusion and arterial stenosis were seen with subsequent attacks. CONCLUSIONS: This constellation of symptoms and imaging findings is suggestive of reversible cerebral vasoconstriction syndrome, which we propose as a mechanism for the transient ischemic attacks and infarcts seen in some patients with Schimke immuno-osseous dysplasia, as opposed to accelerated atherosclerosis alone. This new insight may provide a basis for novel preventative therapy in this rare disorder.

Correcting B0 Field Distortions in MRI Caused by Stainless Steel Orthodontic Appliances at 1.5 T Using Permanent Magnets - A Head Phantom Study.

Susceptibility artifacts caused by stainless steel orthodontic appliances (braces) pose significant challenges in clinical brain MRI examinations. We introduced field correction device (FCD) utilizing permanent magnets to cancel the induced B0 inhomogeneity and mitigate geometric distortions in MRI. We evaluated a prototype FCD using a 3D-printed head phantom in this proof of concept study. The phantom was compartmented into anterior frontal lobe, temporal lobe, fronto-parieto-occipital lobe, basal ganglia and thalami, brain stem, and cerebellum and had built-in orthogonal gridlines to facilitate the quantification of geometric distortions and volume obliterations. Stainless steel braces were mounted on dental models of three different sizes with total induced magnetic moment 0.15 to 0.17 A·m2. With braces B0 standard deviation (SD) ranged from 2.8 to 3.7 ppm in the temporal and anterior frontal lobes vs. 0.2 to 0.3 ppm without braces. The volume of brain regions in diffusion weighted imaging was obliterated by 32-38% with braces vs. 0% without braces in the cerebellum. With the FCD the SD of B0 ranged from 0.3 to 1.2 ppm, and obliterated volume ranged from 0 to 6% in the corresponding brain areas. These results showed that FCD can effectively decrease susceptibility artifacts from orthodontic appliances.

Variability of Ponto-cerebellar Fibers by Diffusion Tensor Imaging in Diverse Brain Malformations.

To describe pontine axonal anomalies across diverse brain malformations. Institutional review board-approved review of magnetic resonance imaging (MRI) and genetic testing of 31 children with brain malformations and abnormal pons by diffusion tensor imaging. Anomalous dorsal pontocerebellar tracts were seen in mid-hindbrain anomalies and in diffuse malformations of cortical development including lissencephaly, gyral disorganization with dysplastic basal ganglia, presumed congenital fibrosis of extraocular muscles type 3, and in callosal agenesis without malformations of cortical development. Heterotopic and hypoplastic corticospinal tracts were seen in callosal agenesis and in focal malformations of cortical development. There were no patterns by chromosomal microarray analysis in the non-lissencephalic brains. In lissencephaly, there was no relationship between severity, deletion size, or appearance of the pontocerebellar tract. Pontine axonal anomalies may relate to defects in precerebellar neuronal migration, chemotactic signaling of the pontine neurons, and/or corticospinal tract pathfinding and collateral branching not detectable with routine genetic testing.

Induced magnetic moment in stainless steel components of orthodontic appliances in 1.5 T MRI scanners.

PURPOSE: Most orthodontic appliances are made of stainless steel materials and induce severe magnetic susceptibility artifacts in brain MRI. In an effort for correcting these artifacts, it is important to know the value of induced magnetic moments in all parts of orthodontic appliances. In this study, the induced magnetic moment of stainless steel orthodontic brackets, molar bands, and arch-wires from several vendors is measured. METHODS: Individual stainless steel brackets, molar bands, and short segments of arch-wire were positioned in the center of spherical flask filled with water through a thin plastic rod. The induced magnetic moment at 1.5 T was determined by fitting the B0 map to the z-component of the magnetic dipole field using a computer routine. RESULTS: The induced magnetic moment at 1.5 T was dominated by the longitudinal component mz, with a small contribution from the transverse components. The mz was insensitive to the orientation of the metal parts. The orthodontic brackets collectively dominated the magnetic dipole moment in orthodontic appliances. In brackets from six vendors, the total induced mz from 20 brackets for nonmolar teeth ranged from 0.108 to 0.158 (median 0.122) A ⋅ m(2). The mz in eight molar bands with bracket attachment from two vendors ranged from 0.0004 to 0.0166 (median 0.0035) A ⋅ m(2). Several full length arch wires had induced magnetic moment in the range of 0.006-0.025 (median 0.015) A ⋅ m(2). CONCLUSIONS: Orthodontic brackets collectively contributed most to the total magnetic moment. Different types of brackets, molar bands, and arch wires all exhibit substantial variability in the induced magnetic moment.

Signal-to-noise assessment for diffusion tensor imaging with single data set and validation using a difference image method with data from a multicenter study.

PURPOSE: To describe a quantitative method for determination of SNR that extracts the local noise level using a single diffusion data set. METHODS: Brain data sets came from a multicenter study (eight sites; three MR vendors). Data acquisition protocol required b=0, 700 s/mm2, fov=256×256 mm2, acquisition matrix size 128×128, reconstruction matrix size 256×256; 30 gradient encoding directions and voxel size 2×2×2 mm3. Regions-of-interest (ROI) were placed manually on the b=0 image volume on transverse slices, and signal was recorded as the mean value of the ROI. The noise level from the ROI was evaluated using Fourier Transform based Butterworth high-pass filtering. Patients were divided into two groups, one for filter parameter optimization (N=17) and one for validation (N=10). Six white matter areas (the genu and splenium of corpus callosum, right and left centrum semiovale, right and left anterior corona radiata) were analyzed. The Bland-Altman method was used to compare the resulting SNR with that from the difference image method. The filter parameters were optimized for each brain area, and a set of "global" parameters was also obtained, which represent an average of all regions. RESULTS: The Bland-Altman analysis on the validation group using "global" filter parameters revealed that the 95% limits of agreement of percent bias between the SNR obtained with the new and the reference methods were -15.5% (median of the lower limit, range [-24.1%, -8.9%]) and 14.5% (median of the higher limits, range [12.7%, 18.0%]) for the 6 brain areas. CONCLUSIONS: An FT-based high-pass filtering method can be used for local area SNR assessment using only one DTI data set. This method could be used to evaluate SNR for patient studies in a multicenter setting.

Imaging characteristics of atypical teratoid-rhabdoid tumor in children compared with medulloblastoma.

OBJECTIVE: The purpose of our study was to compare the imaging characteristics of atypical teratoid-rhabdoid tumor with medulloblastoma and seek distinguishing features that can aid in preoperative diagnosis. MATERIALS AND METHODS: Preoperative MRI examinations of 55 patients (36 medulloblastomas and 19 atypical teratoid-rhabdoid tumors) were analyzed retrospectively. Imaging characteristics of atypical teratoid-rhabdoid tumor and medulloblastoma were assessed with conventional MRI and CT. Diffusion-weighted imaging (DWI) was available in 27 patients (19 medulloblastomas and eight atypical teratoid-rhabdoid tumors). Apparent diffusion coefficient (ADC) values were calculated for 14 medulloblastomas and six atypical teratoid-rhabdoid tumors. RESULTS: Both atypical teratoid-rhabdoid tumors in general and infratentorial atypical teratoid-rhabdoid tumors presented at a younger age than medulloblastomas. Eleven of 19 atypical teratoid-rhabdoid tumors were infratentorial. Cerebellopontine angle (CPA) involvement was more frequent (8/11, 72.7%) in atypical teratoid-rhabdoid tumor than in medulloblastoma (4/36, 11.1%) (p < 0.001). Intratumoral hemorrhage was more common in atypical teratoid-rhabdoid tumor (9/19, 47.4%) than in medulloblastoma (2/36, 5.6%) (p < 0.0001). All atypical teratoid-rhabdoid tumors and all medulloblastomas for which DWI was available displayed increased signal intensity on DWI compared with normal brain parenchyma. The mean ADC values for tumor types were not significantly different. CONCLUSION: Atypical teratoid-rhabdoid tumor presents at a younger age than medulloblastoma. Although atypical teratoid-rhabdoid tumor and medulloblastoma display similar imaging characteristics on conventional MRI, CPA involvement and intratumoral hemorrhage are more common in atypical teratoid-rhabdoid tumor. If a pediatric posterior fossa mass that displays restricted diffusion is involving the CPA, atypical teratoid-rhabdoid tumor is a more likely consideration than medulloblastoma.

Pre- and postnatal MR imaging of hypothalamic hamartomas associated with arachnoid cysts.

We describe two cases of hypothalamic hamartoma associated with arachnoid cysts. One case was initially documented on prenatal MR images. Because of the rarity of the association and resultant distortion in regional anatomy, the solid component of the mass may be overlooked. This would certainly be true when using lower-resolution diagnostic studies such as fetal MR imaging. The lesion could also be confused with a cystic tumor such as pilocytic astrocytoma. Thorough evaluation is required in patients with precocious puberty, gelastic seizures, and the presence of a suprasellar arachnoid cyst.

MR imaging of the spine in epidermal nevus syndrome.

We report two cases of epidermal nevus syndrome (ENS) involving the spine. MR imaging of the spine demonstrated intraspinal lipomas in both cases. Abnormal, enhancing, enlarged cervical and lumbosacral nerve roots were present in one patient. Spinal imaging for patients with ENS may help in the diagnosis of subtle intracranial manifestations, as it did in both of our cases. ENS has features similar to those of other neurocutaneous syndromes, such as neurofibromatosis type 1 and encephalocraniocutaneous lipomatosis.