Publications by authors named "Alexander M Khalaf"

2 Publications

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The mammillothalamic tracts: Age-related conspicuity and normative morphometry on brain magnetic resonance imaging.

Clin Anat 2020 Sep 30;33(6):911-919. Epub 2020 Apr 30.

Division of Neuroimaging and Neurointervention, and Stanford Initiative for Multimodality neuro-Imaging in Translational Anatomy Research (SIMITAR), Department of Radiology, Stanford University School of Medicine, Stanford, California, USA.

The mammillothalamic tract (MTT, bundle of Vicq d'Azyr) is a white-matter projection from each mammillary body to the anterior nucleus of the thalamus (ANT). Deep brain stimulation of the MTTs or ANTs is a treatment option for medically refractory focal epilepsy. Since the ANTs may be atrophied in epilepsy, targeting of the MTT terminations could be used as a proxy for ANT locations. However, MTT conspicuity and morphometry on MRI have not been evaluated to date. We investigated normative age- and sex-related MRI morphometrics of the MTTs in healthy individuals. We retrospectively analyzed magnified axial T2-weighted images of 80 subjects for bilateral MTT conspicuity, diameters, areas, shapes, precise locations, and symmetry. We statistically tested the effects of independent variables (sex and MTT side) on measured dependent variables using two-way ANOVA; and performed linear regressions with age as the independent variable for each of the dependent variables. Subjects were F:M = 44:36, with mean age 45.3 years. Only one (0.63%) MTT was inconspicuous. Mean MTT diameter was 1.8 mm, area was 2.0 mm , and distance from third ventricle was 3.1 mm. MTTs were mostly bilaterally symmetrical in shape, equally round, or ovoid. The right MTT diameter was larger than the left, and males had larger MTT areas than females. We found no statistical difference between MTT diameters and areas in young, middle-aged, and older adults. We report normative axial MRI morphometrics of the MTTs to guide neuromodulation treatments. Future detailed analyses will determine if the MTTs atrophy in proportion to the ANTs in refractory epilepsy.
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September 2020

Magnetic resonance imaging anatomy and morphometry of lumbar intervertebral foramina to guide safe transforaminal subarachnoid punctures.

Clin Anat 2020 Apr 23;33(3):405-413. Epub 2019 Dec 23.

Division of Neuroimaging and Neurointervention, Department of Radiology, Stanford University School of Medicine, Stanford, California.

Percutaneous transforaminal lumbar punctures (TFLPs) offer alternative access routes to the lumbar subarachnoid cistern. Safe fluoroscopic insertion of a needle through a lumbar intervertebral foramen (IVF) should ideally avoid the exiting spinal nerve and surrounding vascular pedicles. A crescentic region in the posterior aspect of IVF is the conventional position for needle placement during TFLP, but the underlying anatomic basis for this has not been evaluated fully. To enhance TFLP safety, we defined the morphometry of normal lumbar IVFs and precise locations of neurovascular structures in the IVF posterior crescent. We retrospectively reviewed high-resolution T2-weighted lumbar spine magnetic resonance images of 40 normal adults to establish normative dimensions of each IVF from L1 to L5 bilaterally. We segmented the IVF posterior crescent into three parts, and within each, measured the areas occupied by neurovascular structures. We statistically correlated the presence or absence of neurovascular structures in each crescent segment using a chi-square test. The mean morphometrics for all 304 IVFs in 10 males and 30 females of similar ages were: area 115.3 ± 29.5 mm ; height 18.0 ± 2.4 mm; and width at mid-disc level 5.6 ± 2.1 mm. We found a significant association between crescent segment and presence or absence of neurovascular structures (χ = 95.9, p < .001). A post-hoc calculation of adjusted standardized residuals identified a significant association between the middle crescent segment and absence of neurovascular structures. Thus, the middle segment of the IVF posterior crescent is significantly most devoid of neurovascular structures, and more often would be the safest target for needle placement during TFLP.
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April 2020