Autism Syndromes: Clinical issues behind the label.Lorene E A Amet, Pippa Line (12 May 2010)BMJ 2010; 340: c1127 Brain Imaging in AutismParents often ask me whether a brain scan would be beneficial to understand their child’s condition better. Such investigations are indeed valuable, even if in most cases no abnormalities can be found. I would like to review here the main conclusions reached across various brain imaging studies conducted in autism and also explain a little more what these techniques can and cannot show.
CT-scan Computerised Tomography (CT) scan uses special X-ray and a computer to generate cross sections across the body. A brain CT scan examines various structures of the brain, allowing the identification of potential mass, stroke, areas of bleeding or blood vessel abnormality. It can also be used to look at the skull. The patient is exposed to radiation during the scan, though it is at safe levels. The resolution of this technique is about 1mm. It does not allow identifying subtle structural features and is not indicative of brain function.
MRI Magnetic Resonance Imaging. This technique gives a much greater contrast between different soft tissue area of the brain than a CT-scan, and sections can be performed in any directions throughout a structure, not solely horizontal as it is for the CT-scan. There are various ways to change the contrast of various brain area, which enable to detect, white and gray matters, the cerebro-spinal fluid area. It enables the measurement of the volume of various brain regions, potential tumours, mass, bleeding, stroke areas, inflammation and encephalitis as well as problem of demyelination such as seen in MS. As for a CT-scan, it is not indicative of brain function. A MRI scan takes about 40 min to be completed; it required absolute stillness by lying down inside a substantially large piece of equipment, causing a confinement that tends to bring claustrophobic responses. For this reason, children with autism will need to receive a general anaesthesia, which is the only aspect of the procedure that might cause potential side effect. fMRIFunctional MRI. This technique detects signal changes in the brain that are due to changes of neuronal activity. Increased neuronal activity causes an increased demand of oxygen and this demand can be measured from the magnetic properties of oxygenated haemoglobin that are distinct from those of the deoxygenated form. It enables to map various brain regions involved in specific brain processes, for example face recognition, listening to music or to a human voice. In this technique, the subject is awake and undergoing a specific cognitive task. For this reason, only high functioning autistic individuals able to cope with the stress of the procedure as well as the tasks requested can be assessed by fMRI.
PET and SPECT PET stands for Positron Emission Tomography and SPECT stands for Single Photon emission computed tomography which both rely on the injection of radioactive component into the blood stream. Depending of the nature of the radioactive component, one can measure with this technique the blood flow across various brain regions as well as the localisation of certain receptors or liguands which have specific brain function. This technique does not require the subject to be awake. Most commonly it is used in autism to detect areas of increased (hyperperfusion) or decreased (hypoperfusion) blood flow. Hyperperfusion can be indicative of epilepsy, a tumour or increased neuronal activity, whilst hypoperfusion can be suggestive of reduced neuronal activity, that may be related to abnormal brain function and/or mitochondrial dysfunction issues.
Main findings in autism What has been published in autism with regard to brain imaging is rather confusing, in as much as there is little consensus obtained across studies; some studies suggest no anatomical abnormalities, whilst other identifies abnormalities in virtually any brain area that had received a focus: for example, frontal cortex, parietal cortex, brain stem, cerebellum, amygdala, hippocampus, gray matter, white matter. Some studies suggest enlargement of the brain regions whilst others suggest size reduction. There are several potential problems in the studies conducted that could explain these disparities. One is that generally speaking, the studies published so far include a small number of subjects. Second is that autism is a very heterogeneous conditions that is known to include individuals presenting with unrelated aetiologies. As for fMRI findings, the major drawback is that these studies apply only to certain autistic individuals and it is unknown if the finding are relevant to the rest of the spectrum. Commonly also these are done on adults, some of whom might be based in hospital settings and be receiving a pharmacological intervention, which further introduce variability and more confounding factors.
What you might be able to identify in your child and how this might help you to understand or treat his condition? Rule out possible conditions of encephalitis, tumours, stroke, cysts, intracranial pressure abnormality. Look for possible structural abnormalities, some of which can be addressed if need be by surgery, others which are not amendable. Identify a possible loci of infection or epileptic foyer. Identify potential issues of hypo or hyper perfusion.
Further Links: ATT video of going through a SPECT scan experience, child with autism and parent:
ATT video reviewing the various brain imaging techniques and main findings in autism:
Other ATT Articles: |
