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In addition to reviewing each CT slice for its anatomical landmarks,
an organized search should be made for signs of various disorders
that can cause headache. These include (1) aneurysmal SAH, (2) an
intracranial mass such as a tumor, abscess, or hematoma (intracerebral
or subdural), (3) arteriovenous malformation (AVM), (4) cerebral
venous sinus thrombosis, or (5) sinusitis (Table 1).
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First, compare the left and right
cerebral hemispheres for symmetry and
look for midline shift indicative
of an intracranial mass.
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Second, examine the basilar cisterns for evidence of SAH.
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Third, examine the ventricles. Ventricular enlargement
may represent obstructive (noncommunicating) hydrocephalus due to
a mass causing obstruction to CSF flow. Enlargement of all the four
ventricles (communicating hydrocephalus) is associated with SAH
and meningitis or may be a chronic condition. Small ventricles may
be seen in idiopathic intracranial hypertension (pseudotumor cerebri)
or diffuse cerebral edema.
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Fourth, examine the brain parenchyma for anatomical distortion
or altered attenuation indicative of a mass lesion, bleed or vascular
malformation.
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Fifth, examine the major cerebral venous sinuses, particularly
the superior sagittal sinus and transverse sinuses, for increased
attenuation (hyperdensity) indicative of thrombosis. The superior
sagittal sinus is seen in the midline where the falx attaches to
the skull in the superior CT slices and in the occipital region.
The transverse sinuses are visible where the tentorium attaches
to the occipital region of the skull.
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Sixth, the paranasal sinuses, in
particular the sphenoid sinus and ethmoid air cells should be examined
for signs of sinusitis, i.e., filling with fluid. Sinus aeration
is more easily assessed on bone windows.
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Finally, a careful search should be made for disorders that can
have subtle CT findings that are easily
missed. These include SAH (CT is occasionally entirely normal),
an intracerebral mass or AVM (causing only subtle parenchymal irregularity),
an isodense SDH (particularly if bilateral and not causing midline
shift), and cerebral venous sinus thrombosis.
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The initial diagnostic test in the evaluation of ED patients
with headache is generally a noncontrast
CT. Other tests ...