Monday 11 May 2015

Understanding Primary Dystonia with Advanced MRI Sequences

A 13 year old male patient resident of UK came with complaints of Dystonic hand movements on activity, right more than Left.
No history of seizures. No obvious cognitive impairment. No prior investigations were done.

Routine MRI brain imaging

Conventional MRI Brain normal 

Arterial Spin Labelled Perfusion MRI images of Brain

What is Arterial Spin Labelled Perfusion MRI ? 
Uses magnetically labelled endogenous blood  water. 
Ideal in  brain as the arterial supply is  well defined &  perfusion to brain tissue is high.
Higher magnet strengths give improved ASL
Gives an idea of tissue perfusion without using contrast
Estimates cerebral blood flow in ml/gm/min

Diffusion Tensor Imaging and Fibre Tracking images of Brain

What is Diffusion Tensor Imaging ? 
A form of diffusion-weighted imaging
Analyzes the microstructural integrity of white matter
Fractional anisotropy -The major index for this discrepant diffusion 
Higher FA values correlate with more ordered tissue containing a larger number of aligned axons
Higher FA values reflect tissue integrity and coherence

Fractional Anisotropy Maps

Average fractional Anisotropy ( FA) values:

Putamen                      (Right) 0.293             (Left) 0.328
Posterior limb of IC    (Right) 0.616             (Left) 0.709
Genu of IC                  (Right) 0.693             (Left) 0.637
Corpus callosum         (Right) 0.697             (Left) 0.880
Thalamus                    (Right) 0310              (Left) 0.321

Thalamo cortical tract fibers appear relatively sparse on right side compared to left.
Corpus callosal and cortico spinal tract fibres appears more ore less symmetrical on both sides.


Average fractional Anisotropy values are more in putamen, Posterior limb of left internal capsule, Corpus callosum and left thalamus.
In the genu of internal capsules, the values are greater on right side.

Segmented Brain Volumes

Volumetry was performed using 3DSPGR acquisition.
Whole brain and segmented brain volumes were calculated.

Left putaminal volume is approximately 13 % more than right.

MR Spectroscopy

To summarize the findings in this case..
Structural MRI is normal.
MR spectroscopy is normal.
Arterial Spin Labelled MR Perfusion (ASL) show increased cerebral blood flow in left parietal cortex and caudate nuclei.
DTI and FA maps show Relatively dense Thalamo cortical tracts on left.
Segmented Brain Volume show 13 % increased putamen volume on left.

Review of Literature:

Primary Dystonias is a hyperkinetic movement disorder characterized by involuntary, repetitive twisting movements.
Early onset - prior to 26 years of age.
Associated with a known gene carrier status (e.g., DYT1).
Symptoms more likely  begin in  one extremity and have a tendency to be generalized.

Conventional MRI does not typically reveal brain abnormalities.

Segmented Brain Volumes
Putamen has been predominantly involved in focal hand dystonias.
The involved side show > 10% increase in putaminal volume.
Other areas which may be involved are thalami and caudate nucleus.

Summarization of Literature…
Gray matter changes are not restricted to the basal ganglia.
Sensorimotor cortices, thalamus, and cerebellum may also be involved
White matter aberrations mainly involve cortico-striato-pallido-thalamic and cerebello-thalamo-cortical pathways.
Whether these changes are causative or compensatory remains unknown.
Newer MRI sequences may provide an insight in understanding disease pathophysiology and intricate brain networks involved.

To conclude…
Advanced MRI sequences like ASL, DTI, Segmented brain volumes may provide more comprehensive insight into pathophysiology of dystonia.
Further studies in this regard are needed to understand these findings and link them to disorder-specific clinico-behavioral characteristics.

Newer advances in the pathophysiology of focal dystonias  Brain (2006), 129, 6–7
Thalamocortical Connectivity Correlates with Phenotypic Variability in Dystonia; May 2014 An Vo1,Wataru Sako1, Martin Niethammer1, Maren Carbon
Primary Dystonia: Conceptualizing the Disorder Through a Structural Brain Imaging Lens  Ritesh A. Ramdhani & Kristina Simonyan
Cortical somatosensory reorganization in children with spastic cerebral palsy: a multimodal neuroimaging study Front. Hum. Neurosci., 12 September 2014 Christos Papadelis1,2*†, Banu Ahtam1,2†, Maria Nazarova

Dr.Deepak Patkar (HOD Radiology) Nanavati Superspeciality Hospital, Mumbai
Dr.Mitusha Verma SR DNB Radiology Nanavati. 

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