Sachin K. Gujar

Presurgical brain mapping of the language network in patients with brain tumors using resting-state fMRI: Comparison with task fMRI

To compare language networks derived from resting‐state fMRI (rs‐fMRI) with task‐fMRI in patients with brain tumors and investigate variables that affect rs‐fMRI vs task‐fMRI concordance.

Multiphase computed tomography for localization of parathyroid disease in patients with primary hyperparathyroidism: How many phases do we really need?

BACKGROUNDnMultiphase computed tomography (CT) involves multiple cervical CT acquisitions to accurately identify hyperfunctional parathyroid glands, thus increasing radiation exposure to the patient. We hypothesized that only 2 cervical acquisitions, instead of the conventional 4, would provide equivalent localization information and halve the radiation exposure.nnnMETHODSnWe identified 53 consecutive patients with primary hyperparathyroidism who underwent multiphase CT before parathyroidectomy. All scans were reinterpreted first using 2 phases then using all 4 phases. The accuracies of interpretations were determined with surgical findings serving as the standard of reference.nnnRESULTSnSixty-four hyperfunctional parathyroid glands were resected with a mean weight of 394.3 mg. Two-phase CT lateralized the hyperfunctional glands in 38 patients with a sensitivity, positive predictive value (PPV), and accuracy of 100%, 71.7%, and 71.7%, respectively. Four-phase CT lateralized the hyperfunctional glands in 39 patients with a sensitivity, PPV, and accuracy of 95.1%, 76.5%, and 73.6%, respectively. For quadrant localization, the accuracy of 2-phase and 4-phase CT was 50.9% and 52.8%, respectively.nnnCONCLUSIONnOur results suggest that 2-phase and 4-phase CT provide an equivalent diagnostic accuracy in localizing hyperfunctional parathyroid glands. The reduced radiation exposure to the patient may make 2-phase acquisitions a more acceptable alternative for preoperative localization.

Presurgical fMRI and DTI for the Prediction of Perioperative Motor and Language Deficits in Primary or Metastatic Brain Lesions.

To determine whether lesion to activation distance (LAD) on presurgical blood‐oxygen‐level‐dependent functional magnetic resonance imaging (fMRI) and degree of white matter involvement by primary or metastatic brain lesions predict perioperative motor and language deficits.

Delayed posthypoxic leukoencephalopathy: a case series and review of the literature.

Delayed posthypoxic leukoencephalopathy (DPHL) is a rare and underrecognized entity where patients manifest a neurological relapse after initial recovery from an acute hypoxic episode. We sought to describe the magnetic resonance imaging (MRI) findings in a group of patients with DPHL and review the available literature.

Congenital Malformations of the Orbit

This article discusses the embryologic development of the eye and orbital structures. Among the defects presented are anophthalmia and microphthalmia, coloboma, persistent hyperplastic primary vitreous, Coats disease, vascular malformations, encephalocele and nasolacrimal mucocele. Clinical and imaging features of the diseases are presented, along with radiographic images.

Special Considerations/Technical Limitations of Blood-Oxygen-Level-Dependent Functional Magnetic Resonance Imaging

In this review, limitations affecting the results of presurgical mapping with blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) are discussed. There is a great need to standardize fMRI acquisition and analysis methods and establish guidelines to address quality control issues. Several national and international organizations are formulating guidelines and standards for both clinical and research applications of BOLD fMRI. Consensus regarding management of these issues will likely both improve the clinical standard of care and enhance future research applications of fMRI.

Presurgical Brain Mapping of the Ventral Somatomotor Network in Patients with Brain Tumors Using Resting-State fMRI

BACKGROUND AND PURPOSE: Resting-state fMRI readily identifies the dorsal but less consistently the ventral somatomotor network. Our aim was to assess the relative utility of resting-state fMRI in the identification of the ventral somatomotor network via comparison with task-based fMRI in patients with brain tumor. MATERIALS AND METHODS: We identified 26 surgically naïve patients referred for presurgical fMRI brain mapping who had undergone both satisfactory ventral motor activation tasks and resting-state fMRI. Following standard preprocessing for task-based fMRI and resting-state fMRI, general linear model analysis of the ventral motor tasks and independent component analysis of resting-state fMRI were performed with the number of components set to 20, 30, 40, and 50. Visual overlap of task-based fMRI and resting-state fMRI at different component levels was assessed and categorized as full match, partial match, or no match. Rest-versus-task-fMRI concordance was calculated with Dice coefficients across varying fMRI thresholds before and after noise removal. Multithresholded Dice coefficient volume under the surface was calculated. RESULTS: The ventral somatomotor network was identified in 81% of patients. At the subject level, better matches between resting-state fMRI and task-based fMRI were seen with an increasing order of components (53% of cases for 20 components versus 73% for 50 components). Noise-removed group-mean volume under the surface improved as component numbers increased from 20 to 50, though ANOVA demonstrated no statistically significant difference among the 4 groups. CONCLUSIONS: In most patients, the ventral somatomotor network can be identified with an increase in the probability of a better match at a higher component number. There is variable concordance of the ventral somatomotor network at the single-subject level between resting-state and task-based fMRI.

Hypoxic-Ischemic Encephalopathy Mimicking Acute Necrotizing Encephalopathy

BACKGROUNDnAcute necrotizing encephalopathy is a rare childhood syndrome associated with distinct and unifying neuroimaging features that are often used for the diagnosis of this entity.nnnPATIENTnWe describe a previously healthy 9-month-old girl who presented with upper respiratory symptoms, suspected seizures, and positive nasopharyngeal rapid antigen test for influenza A virus. Magnetic resonance imaging revealed signal abnormality in both thalami, bilateral caudate nuclei, brainstem tegmentum, subcortical white matter, and cerebellar hemispheres, suggestive of acute necrotizing encephalopathy. She subsequently had a cardiac arrest, was placed on extracorporeal membrane oxygenation, and treated with methylprednisone, intravenous immunoglobulin, and plasmapheresis without apparent clinical response. On autopsy, neuropathology showed evidence of hypoxic-ischemic injury but lacked evidence of hemorrhagic necrosis, which is typically associated with acute necrotizing encephalopathy.nnnCONCLUSIONnCombined clinical and neuroimaging features may be suggestive but not sufficient for the diagnosis of acute necrotizing encephalopathy.

Repeatability of language fMRI lateralization and localization metrics in brain tumor patients

To assess the within‐subject intra‐scan session repeatability of language functional MRI (fMRI) activation maps in patients with brain tumors who were undergoing presurgical fMRI as part of their preoperative clinical workup. Sentence completion (SC) and silent word generation (SWG) tasks were used for language localization and hemispheric lateralization for identifying the primary language cortex. Within‐subject repeatability for each of these paradigms was assessed in right‐handed patients—37 for SC and 78 for SWG. Repeatability of activation maps between consecutive runs of the same task within the same scan session was evaluated by comparing lateralization indexes in holohemispheric and regional language areas. Displacement of center of activation between consecutive runs was also used to assess the repeatability of activation maps. Holohemispheric and regional language lateralization results demonstrated high intra‐subject intra‐scan repeatability when lateralization indices were calculated using threshold‐dependent and threshold‐independent approaches. The high repeatability is demonstrated both when centers of mass of activation are considered within key eloquent regions of the brain, such as Brocas area and Wernickes area, as well as in larger more inclusive expressive and receptive language regions. We examined two well‐known and widely accepted language tasks that are known to activate eloquent language cortex. We have demonstrated very high degree of repeatability at a single‐subject level within single scan sessions of language mapping in a large cohort of brain tumor patients undergoing presurgical fMRI across several years at our institution.

Quantitative assessment of changes in diffusion tensor imaging (DTI) metrics along the courses of the cortico-ponto-cerebellar tracts secondary to supratentorial human brain glial tumors

The cortico‐ponto‐cerebellar tract (CPCT) is the largest projection pathway, which synapses at the pons. Remote effects of supratentorial brain tumors have not been evaluated along the infratentorial course of the CPCT.