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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).

Table 1 What to Look for on a Head CT in a Patient with Headache

First, compare the left and right cerebral hemispheres for symmetry and look for midline shift indicative of an intracranial mass.

Second, examine the basilar cisterns for evidence of SAH.

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.

Fourth, examine the brain parenchyma for anatomical distortion or altered attenuation indicative of a mass lesion, bleed or vascular malformation.

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.

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.

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.

The initial diagnostic test in the evaluation of ED patients with headache is generally a noncontrast CT....

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