Year : 2004 | Volume
: 14 | Issue : 4 | Page : 353--354
Primary headache and radiologist
Shrinivas B Desai
Shrinivas B Desai
|How to cite this article:|
Desai SB. Primary headache and radiologist.Indian J Radiol Imaging 2004;14:353-354
|How to cite this URL:|
Desai SB. Primary headache and radiologist. Indian J Radiol Imaging [serial online] 2004 [cited 2019 Jun 19 ];14:353-354
Available from: http://www.ijri.org/text.asp?2004/14/4/353/29519
Headaches are one of the most common symptoms that neurologists evaluate.
Although most are caused by primary disorders, the list of differential diagnoses is one
of the longest, with over 300 different types and causes. The cause or type of most headaches can be determined by a careful history supplemented by a general and neurologic examination. Reasons for obtaining neuroimaging include medical indications as well as anxiety of patients, families and medico-legal concerns. The yield of neuroimaging in the evaluation of patients with headache and normal neurologic examination is quite low.
As routine outpatient neuroimaging became available more than 20 years ago, controversy arose over appropriate selection of patients for computed tomography studies and subsequently magnetic resonance imaging studies. Nowhere is this more apparent than in headache. Because headache is a truly ubiquitous condition with a lifetime prevalence rate reaching 90%, it is clear that it is not possible to scan all patients with headache. Review of the pertinent literature, expert consensus, and a Practice Parameter issued by the American Academy of Neurology all suggest that routine neuroimaging is not necessary in patients with migraine headaches as defined
by the International Headache Society criteria. The literature would also support the belief that imaging is not necessary in patients with typical recurrent cluster headaches. However, patients with new-onset headaches, headaches with a progressive course, headaches with a significant change in pattern, headaches that never alternate sides, and headaches associated with any neurologic findings or seizures have a substantially higher likelihood of a secondary cause such as tumor, arteriovenous malformation, or other structural lesion. In these situations, imaging must be considered as part of the workup. The literature does not provide enough data to make any statistically predictive observations in patients with headaches other than migraine or cluster headache with symptoms but no findings on neurologic examination.
Combining the results of multiple studies performed reveal the overall percentages of various pathologies as: brain tumors, 0.8%; arteriovenous malformations, 0.2%; hydrocephalus, 0.3%; aneurysm, 0.1%; subdural hematoma, 0.2%; and strokes, including chronic ischemic processes, 1.2%. EEG is not useful in the routine evaluation
of patients with headache. Similarly, the yield of neuroimaging in the evaluation of migraine is quite low. Combining the results of multiple studies performed in patients with various types of migraine, the overall percentages of various pathologies are: brain tumor, 0.3%; arteriovenous malformation, 0.07%; and saccular aneurysm, 0.07%.
The "first or worst" headache has a long list of possible causes and always includes the possibility of acute subarachnoid hemorrhage. Headaches--especially the sentinel type caused by SAH--often are misdiagnosed. The probability of detecting an aneurysmal hemorrhage on CT scans performed at various intervals after the ictus is: day 0.95%; day 3, 74%; 1 week, 50%; 2 weeks, 30%; and 3 weeks, almost nil. The location of a ruptured saccular aneurysm often is suggested by the predominant site of the SAH. The probability of detecting xanthochromia with spectrophotometry in the CSF at various times after a subarachnoid hemorrhage is: 12 hours, 100%; 1 week, 100%; 2 weeks, 100%; 3 weeks, more than 70%; and 4 weeks, more than 40%. The management of thunderclap headaches with normal CT scan and CSF examinations is controversial. Most patients have a benign course but an unruptured saccular aneurysm occasionally may be responsible for the headache. MR angiography may be a reasonable test to obtain instead of a cerebral arteriogram in many of these cases. About 30% to 90% of patients have headaches of various types and causes after mild head injury.
Although most headaches are relatively benign, perhaps 1% to 3% of these patients have life-threatening pathology, including subdural and epidural hematomas, that are detected on CT and MRI scans. Headaches caused by subdural hematomas can be nonspecific. When new-onset headaches begin in patients over the age of 50 years, the physician always should consider whether it may be a secondary headache disorder requiring specific diagnostic testing and treatment. Up to 15% of patients 65 years and over who present to neurologists with new-onset headaches may have serious pathology such as stroke, TIA, neoplasm, and subdural hematoma
White Matter Abnormalities have been reported on MRI 354 SB Desai studies of patients with all types of migraine, ranging from 12% to 46%. The cause of WM Abnormalities in migraine is not certain. Cerebral atrophy has been reported as more frequent and no more frequent in patients with migraine compared to controls. It has been found that during acute episodes one might have focal areas of ischemia detected by combination of diffusion & perfusion imaging which reverse with time. They may also have small infarcts at the gray-white matter junction.
Dr. Moskowitz's of Massachusetts general hospital evaluated four migraine patients during episodes of spontaneous visual aura by diffusion-perfusion weighted magnetic imaging. They noted moderate focal reductions in cerebral blood flow and volume in the occipital lobes during multiple spontaneous migrainous visual auras in these subjects. They observed a 16 to 53 % decrease in relative cerebral blood flow, and a 6 to 33 % decrease in cerebral blood volume in these patients. They also noted a 10 to 54% increase in tissue mean transit time in the gray matter of occipital cortex contralateral to the visual field disturbances. No changes in the apparent diffusion coefficient were observed either during the symptoms or after resolution of the visual symptoms but before the onset of headache. Dr. Moskowitz's team points that diffusion-perfusion weighted functional MRI offers advantages over other imaging techniques.
Functional imaging has shed light on the genesis of both syndromes, documenting activation in the midbrain and pons in migraine and in the hypothalamic gray in cluster headache. These areas are involved in the pain process in a permissive or triggering manner rather than as a response to pain impulses. Functional imaging can be done by MRI & PET. MRI has the advantage of excellent structural detail. In the case of visual cortex experiments, volunters wore glasses with lights attached to them in the magnet, and the lights were flashed during certain portions of an imaging sequence. By looking for differences of intensity between task periods and relaxation periods, it was possible to identify areas of the brain that were stimulated by these tasks.
Idiopathic or primary headache, including migraine, tension-type headache and cluster headache, are due to abnormal brain function with completely normal brain structure. Cluster headache is one such idiopathic headache with many similarities to migraine, including normal brain structure on magnetic resonance imaging and abnormal function in the hypothalamic grey matter ,well studied by PET and/or FUNCTIONAL MRI. Given the consistency of the positron emission tomography findings with the clinical presentation, study was carried out to assess whether the brains of such patients were structurally normal. Voxel-based morphometry, an objective and automated method of analyzing changes in brain structure, was carried out to study the structure of the brains of patients with cluster headache. Researches found a co-localization of structural changes and changes in local brain activity with positron emission tomography in the same area of the brain in the same patients. These results indicate that the current view of the neurobiology of cluster headache requires complete revision and that this periodic headache is associated with a hitherto unrecognized brain abnormality in the hypothalamic region. It is believed that voxel-based morphometry on MRI has the potential to change our concept of primary headache disorders, requiring a radical reappraisal of the tenet of structural normality.