Headache , Meningitis
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Advancements in diagnostic imaging have
revolutionized the practice of modern medicine.
Neuroimaging allows more accurate diagnosis of
central nervous system disorders and analysis of
neuroanatomical differences.
Observation of current practice patterns indicates
that neuroimaging overuse is common in the
clinical evaluation of certain symptoms such as
headache in children and adolescents
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Details of bony structures:
Provides good details about bony structures
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Details of soft tissues:
Less tissue contrast compared to MRI
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Time taken for complete scan:
Usually completed within 5 minutes
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Cost:
from $1,200 to $3,200; they usually cost less than MRIs.
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Helical (spiral) scanners obtain images in fractions of a second and allow rapid, high-quality threedimensional and two-dimensional reformations.
sedation is not necessary for CT scanning
Disadvantages:
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Exposure to high to moderate radiation dose : Doses from a single pediatric CT scan can range from
eabout 5 mSv to 60 mSv. Among children who have undergone CT scans, approximately 1/3 have
had at least 3 scans.
In comparison to some of the Japanese survivors of the atomic bombs who received 5 to 20 mSv .
These survivors, who are estimated to have experienced doses only slightly larger than those
encountered in CT, have demonstrated a small but increased radiation-related excess relative risk for
cancer mortality.
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Pregnant women should not have CT scans .
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Radiation Dose Comparison
Typical
Effective
Dose
(mSv)1
Number of Chest
X rays (PA film)
for Equivalent
Effective Dose2
Time Period for
Equivalent Effective
Dose from Natural
Background
Radiation3
Chest x ray (PA film)
0.02
1
2.4 days
Skull x ray
0.1
5
12 days
Lumbar spine
1.5
75
182 days
I.V. urogram
3
150
1.0 year
Upper G.I. exam
6
300
2.0 years
Barium enema
8
400
2.7 years
CT head
2
100
243 days
CT abdomen
8
400
2.7 years
Diagnostic Procedure
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MRI scans are best for imaging soft tissue.
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Details of bony structures: Less detailed compared to CT scan
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MRI machines can produce in any plane without moving the patient. They also have the
ability to change the contrast of the images making them more clear than CT scan.
Costs range from $1200 to $4000 (with contrast); which is usually more than CT scans
and X-rays, and most examining methods.
Time taken for complete scan: about 30 minutes.
Disadvantages
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People with surgical clips, metallic fragments, cardiac monitors cannot have MRI.
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In cases with pacemakers MRI’s magnetic and radiofrequency fields can disrupt the
pacemaker’s setting or cause wires to overheat, resulting in unintended heart
stimulation, device electrical failure, or tissue damage.and even Trigger rapid pacing.
But in Feb. 2011 FDA approves 1st pacemaker designed to work safely during some
MRI exams (Medtronic's Revo MRI SureScan ) costs $5,000 to $10,000
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Magnetic Resonance Angiography (MRA) and Computed Tomographic Angiography
(CTA):For studies of the intracranial vasculature
Cerebrospinal Fluid Flow Imaging: detects interruptions of normal flow patterns. Useful
In patients with Chiari I and II malformations when they are being considered for
foramen magnum decompressions.
Magnetic Resonance Neurography: highlight nerve fascicles as they course through the
brachial plexus, arms, legs, or neck. excellent for searching for intrinsic pathology in
peripheral nerves
Magnetization Transfer: (MTC) is useful in assessing myelination and demyelination
Perfusion Imaging
Diffusion Tensor Imaging:can be used to assess brain maturation, detects reduced
diffusion in the acute phase after a traumatic, metabolic, or toxic injury to the brain.
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Proton MR Spectroscopy:useful in the assessment of encephalopathic neonates , in
detection and diagnosis of some inborn errors of metabolism , in developmental delay ,
and in post-therapeutic assessment of intracranial tumors
Special Imaging of Brain Function
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Common symptom in children and adolescents.
Has many potential causes, but clinicians generally distinguish primary headache
(ie, pain without evidence of a serious underlying illness) from secondary headache
(ie, pain resulting from a serious pathologic condition).
Neuroimaging can be a valuable diagnostic tool for conditions for which headache is
coupled with other worrisome signs and symptoms.
Practice parameters for the evaluation of children and adolescents with recurrent
headaches, published in 2002, recommend that diagnostic neuroimaging be considered
for children with an abnormal neurologic examination or other historical features that
suggest neurologic dysfunction.
These recommendations emphasized that obtaining a neuroimaging study on a routine
basis is not indicated for children with recurrent headache and a normal neurologic
examination.
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Change in the pattern of headache
Onset of seizures
Headache associated with systemic illness, including fever
Personality change
Symptoms suggestive of raised intracranial pressure, such
as new onset headache in the early morning; or headache
that is worsening with coughing, sneezing, or straining
An abnormal neurological finding, unless the finding is
longstanding.
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In this present study neuroimaging findings in 400 nonacute pediatric headache
patients from the most recent study years 2000 and 2004 were analysed
neuroimaging results were categorized as normal, remarkable without clinical action,
remarkable with clinical follow-up action, and abnormal.
185 of 400 patients (46%) had neuroimaging.
Of these, 78.4% of neuroimaging studies were normal, and none was considered
abnormal.
21.5% had remarkable findings in the neuroradiology report.
One third of these patients received further consultation or neuroimaging because of
incidental findings.
Conclusion: In the evaluation of nonacute pediatric headache, overuse of
neuroimaging leads to frequent discovery of incidental findings and increased
testing.
Urgent scan if any of the following:
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Witnessed loss of consciousness >5 minutes
worsening level of consciousness
Amnesia (antegrade or retrograde) >5 minutes
Abnormal drowsiness
≥3 Discrete episodes of vomiting
Clinical suspicion of nonaccidental injury
Post-traumatic seizure
GCS <14 in emergency room
(Paediatric GCS <15 if aged <1)
Suspected open or depressed skull fracture or tense fontanelle
Signs of base of skull fracture
Focal neurological deficit
Aged <1 - bruise, swelling or laceration on head >5 cm
Dangerous mechanism of injury (high-speed RTA, fall from >3 m, highspeed projectile)
MRI is particularly indicated in patients with one or more of the following.
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Onset of seizures at any age with evidence of focal onset in history or
EEG.
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Onset of unclassified or apparently generalised seizures in the first year
of life or in adulthood.
Evidence of a focal fixed deficit on neurological or neuropsychological
examination.
Difficulty in obtaining control of seizures with first-line anti-epileptic
drug treatment.
Loss of control of seizures with anti-epileptic drugs or a change in the
seizure pattern that may imply a progressive underlying lesion.
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Imaging studies are not the means by which meningitis is
diagnosed;
therefore, imaging is not performed routinely other than to ensure
the absence of hydrocephalus or abscess before a lumbar puncture
is performed.
Neuroimaging is indicated if the clinical diagnosis is unclear, if
neurologic deterioration occurs secondary to increased
intracranial pressure, if the meningitis is associated with persistent
seizures or focal neurologic deficits, or if patient recovery from the
disease is slow
And finally imaging is best reserved to look for complications of
meningitis in children with complicated clinical courses.
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Computed tomography and MR studies in uncomplicated
cases of purulent meningitis are usually normal.
Occasionally, some enhancement of the meninges will be
seen on postcontrast scans .
In granulomatous meningitis, enhancement is most typically
seen in the basal meninges
In bacterial meningitis typically shows enhancement over
the cerebral convexities.
In either type of meningitis, contrast-enhanced MR is more
sensitive than contrast-enhanced CT in detecting
inflammatory changes in the meninges
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Clinicians are reliant on CT to detect patients where LP should be
avoided .
In a series of 445 children by Rennick, 4.3% of patients had clinical
signs of herniation. CT was performed at the time of herniation in
14 patients and five (36%) of the scans were normal despite the
clinical picture. In another study, approximately 50% of patients
with clinical features suggestive of raised intracranial pressure
had a normal CT scan
There is evidence to show that performing a CT prior to lumbar
puncture may delay the institution of antibiotics with the time
delay ranging from 2 to 4.9 hours
A thorough clinical assessment prior to imaging is important as
the imaging findings may not be supportive of raised intracranial
pressure and may provide false reassurance for clinicians.
Hydrocephalus
evaluated well by all imaging modalities; MR is
the most effective at localizing the level of the
obstruction
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Thrombosis of deep veins, cortical veins, and venous sinuses is an
uncommon complication of meningitis.
Develops more often in the presence of superimposed
dehydration.
In the acute phase (when the clot is dense), thrombus can be seen
on CT as high density in the sagittal sinus on a noncontrast scan .
Subacute sinus thrombosis is recognizable on CT by the so-called
“empty delta sign,” which is a triangle of decreased density in the
posterior portion of the affected sinus on a contrast enhanced scan.
On MR, sinus thrombosis is readily diagnosed when the thrombus
is subacute
Figure 11-16 Sagittal sinus thrombosis secondary to meningitis. A: Noncontrast CT scan shows high attenuation in the torcular herophili (arrows)
at the junction of the straight sinus (also hyperdense and thrombosed) and the superior sagittal sinus. The presence of high density within blood
vessels in a child beyond the first few months of life is extremely suspicious for sinus thrombosis. B: Sagittal SE 600/11 image shows high signal
intensity in the posterior half of the superior sagittal sinus (black arrows). The straight sinus (white arrowheads) also appears thrombosed. C:
Coronal FLAIR image shows high signal intensity (arrow) within the superior sagittal sinus, supporting the diagnosis of sagittal sinus thrombosis.
D: Axial SE 2500/70 image shows hyperintensity in the superior sagittal sinus, suggesting the presence of extracellular deoxyhemoglobin, present
in subacute clot. E: Two-dimensional time of flight MR venogram shows absence of flow-related enhancement in the superior sagittal sinus and
straight sinus, confirming the diagnosis of thrombosis.
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On CT, venous infarcts are usually poorly delimited, hypodense or mixed
attenuation areas involving the subcortical white matter and producing a
slight mass effect on ventricular structures
The low attenuation is probably due to localized cerebral edema, whereas
high attenuation areas usually represent hemorrhage.
On MR, early venous infarcts may be identified by visualization of
prolonged T1 and T2 relaxation times.
Another early imaging sign is visualization of thrombus in the deep
medullary veins with surrounding cavitatio
25 % of venous infarcts are hemorrhagic and have an imaging
appearance that varies from large subcortical hematomas to petechial
hemorrhages within edematous brain parenchyma
The hemorrhages are generally subcortical and often multifocal with
irregular margins. They are occasionally linear in nature, indicating
hematoma in and around the vein.
Figure 11-19 Periventricular venous infarctions in meningitis. A: Noncontrast CT early in the course of
the disease shows subtle hyper- and hypodensity (arrows) in the periventricular white matter. B: Axial
SE 3000/120 image the following day shows linear T2 shortening (arrows) in the deep frontal and
parietal white matter bilaterally. C: Coronal FSE 3500/95 image shows small areas of cavitation between
and around the thrombosed medullary veins. D: Follow-up noncontrast CT one week later shows
increasing hypodensity (arrows) in the deep white matter.
Figure 11-20 Bilateral middle cerebral artery infarcts secondary to meningitis. A:
Noncontrast CT shows low attenuation bilaterally in the distribution of the
middle cerebral arteries. B: At a higher level, the low attenuation is seen to
involve the entire middle cerebral artery distribution (arrows) bilaterally.
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Arterial infarctions in the setting of meningitis are usually the
result of arteritis secondary to involvement of the perivascular
spaces and, subsequently, the arterial walls by the infection.
CT or MR can reliably diagnose arteritis in the setting of
meningitis by identifying the resulting infarcts, which tend to be
sharply marginated and confined to a specific arterial vascular
territory
Diffusion weighted imaging is useful in this setting, as it will
detect infarctions earlier .
Frequently, multiple lacunar type infarcts are seen in the
distribution of perforating vessels in the brainstem, basal ganglia ,
and white matter, presumably resulting from involvement of the
basilar cisterns and vessels contained therein.
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Infants with meningitis, particularly H. influenzae,
frequently develop subdural effusions
Effusions are iso-intense to CSF on CT, may be slightly
hyperintense to CSF on MR , and are most commonly
located over the frontal and temporal regions of the brain.
Occasionally, a portion of the medial surface (the cerebral
surface), of an effusion will show enhancement
These effusions typically regress along with the signs of
meningitis over several days.
Subdural empyemas show reduced diffusion compared
with CSF, whereas effusions do not.
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It is a common complication of neonatal meningitis.
The organisms enter the ventricles via the choroid plexuses.
The best imaging sign of ventriculitis is the presence of proteinaceous
debris in the dependent portion of the ventricle, usually the trigone or
occipital horn of the lateral ventricle .
If contrast is administered, intense enhancement of the inflamed
ependyma is seen on both CT and MR
Magnetic resonance has, perhaps, a greater sensitivity to the
inflammatory process. The ventricles are nearly always dilated from
reduced CSF absorption. A more ominous complication of ventriculitis is
necrosis of periventricular white matter. Ultimately, multiple loculations
form in the brain, separated by thin septae
The septae are likely formed by astroglial response to the infection.
Ultrasound and MR detect the septae better than CT.
Figure 11-23 Subdural empyemas and ventriculitis secondary to meningitis. Utility of diffusion weighted imaging. A: Axial noncontrast CT
show asymmetrical fluid collections over the frontal convexities. Although large CSF spaces are normal in the first year of life, they are
normally symmetrical. The frontal horns are disproportionately large, suggesting injury to the frontal white matter. B: Axial SE 3000/120
image shows abnormal heterogeneity (white arrows) in the asymmetrical CSF spaces over the frontal convexities. In addition, the frontal
white matter is abnormally hyperintense. C: Postcontrast SE 600/11 image shows abnormal enhancement of the frontal cortex and
leptomeninges. D: Axial apparent diffusion coefficient image shows abnormally low diffusion in the fluid collections over the frontal
convexities; the CSF in normal brains is hyperintense on these images. E: Axial postcontrast SE 600/11 image shows a possible fluid-fluid
level (arrow) in the left occipital horn. F: Axial apparent diffusion coefficient image shows reduced diffusion (manifested as low signal
intensity, arrows), diagnostic of blood or, in this case pus, layering in the occipital horns of both lateral ventricles.
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