Brain Imaging in Psychiatry
I. Introduction
Neuroimaging methodologies allow measurement of the structure, function, and chemistry of the living human brain. Computer tomography (CT) scanners, the first widely used neuroimaging devices, allowed assessment of structural brain lesions, such as tumors or strokes. Magnetic resonance imaging (MRI) scans, developed next, distinguish gray and white matter better than CT scans do and allow visualizations of smaller brain lesions as well as white matter abnormalities. In addition to structural neuroimaging with CT and MRI, a revolution in functional neuroimaging has enabled clinical scientists to obtain unprecedented insights into brain function using positron emission tomography (PET) and single photon emission computer tomography (SPECT).
II. Uses of Neuroimaging
A. Indications for ordering neuroimaging in clinical practice
Neurological deficits. In a neurological examination, any change that can be localized to the brain or spinal cord requires neuroimaging. Consider neuroimaging for patients with new-onset psychosis and acute changes in mental status.
Dementia. The most common cause of dementia is Alzheimer’s disease, which does not have a characteristic appearance on routine neuroimaging but, rather, is associated with diffuse loss of brain volume. One treatable cause of dementia that requires neuroimaging for diagnosis is normal pressure hydrocephalus, a disorder of the drainage of cerebrospinal fluid (CSF).
Strokes. Strokes are easily seen on MRI scans. In addition to major strokes, extensive atherosclerosis in brain capillaries can cause countless tiny infarctions of brain tissue; patients with this phenomenon may develop dementia as fewer and fewer neural pathways participate in cognition. This state, called vascular dementia, is characterized on MRI scans by patches of increased signal in the white matter.
Degenerative disorders. Certain degenerative disorders of basal ganglia structures, associated with dementia, may have a characteristic appearance on MRI scans. Huntington’s disease typically produces atrophy on the caudate nucleus; thalamic degeneration can interrupt the neural links to the cortex.
Space-occupying lesions can cause dementia and are apparent with neuroimaging techniques (e.g., chronic subdural hematomas, cerebral contusions, brain tumors).
Chronic infections. Chronic infections, including neurosyphilis, cryptococcosis, tuberculosis, and Lyme disease, may produce a characteristic enhancement of the meninges, especially at the base of the brain. Serological studies are needed to complete the diagnosis. Human immunodeficiency virus (HIV) infection can cause dementia directly, in which case is seen a diffuse loss of brain volume, or it can allow proliferation to the Creutzfeldt–Jakob virus to yield progressive multifocal leukoencephalopathy, which affects white matter tracts and appears as increased white matter signal on MRI scans. Multiple sclerosis plaques are easily seen on MRI scans as periventricular patches of increased signal intensity.
Clinical Hint
The clinical examination always assumes priority, and neuroimaging is ordered on the basis of clinical suspicion of a central nervous system (CNS) disorder.
III. Brain Imaging Methods
A. Computed tomography (CT)
Clinical indications—dementia or depression, general cognitive and medical workup, and routine workup for any first-break psychosis.
Research
Differentiating subtypes of Alzheimer’s disease.
Cerebral atrophy in alcohol abusers.
Cerebral atrophy in benzodiazepine abusers.Related posts:
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