Initial Headache

New headache is a common complaint in the outpatient or emergency room setting. Distinguishing between headaches due to a potentially dangerous cause and those that are benign is paramount. Speed of onset of the headache, associated medical conditions, and neurologic examination findings are important factors to consider.

A.

Headaches commonly follow concussion. Decisions about imaging in this scenario are reviewed in Chapter 63 . Cervical arterial dissection of the internal carotid or vertebral arteries may also be associated with headache following trauma; often there is a delay between injury and development of pain. There may be associated neck pain, and the headache is often notably focal over just one region (such as retroorbital). When suspicion for dissection is present, computed tomography angiogram (CTA) or magnetic resonance angiogram (MRA) of the neck are indicated.
B.

A sudden-onset (“thunderclap”) headache is one that reaches maximum intensity within 1 minute. The intensity is not as significant as the rapidity of onset. This type of headache warrants emergent evaluation, starting with noncontrast head CT to evaluate for subarachnoid hemorrhage (SAH).
C.

In addition to SAH, head CT may identify other causes of thunderclap headache, such as intracerebral or intraventricular hemorrhage, pituitary apoplexy, or third ventricular colloid cyst. Presence of ischemic changes on CT should raise concern for arterial dissection, reversible cerebral vasoconstriction syndrome (RCVS), or cerebral venous thrombosis (CVT). A hyperdense artery sign suggests ischemic stroke, and hyperdense venous sinuses suggest CVT.
D.

With modern-generation scanners and expert neuroradiology interpretation, the sensitivity of head CT for SAH approaches 99% when done within 6 hours of headache onset. However, sensitivity diminishes with time from headache onset and with less skilled CT readers. Given this and the catastrophic results of failing to identify SAH (i.e., aneurysmal rebleeding), if CT is negative, lumbar puncture should be performed. Xanthochromia, a yellow tinge to cerebrospinal fluid (CSF) caused by red blood cell (RBC) degradation, or elevated RBCs that do not decrease in successive tubes of CSF samples suggest the presence of SAH. Xanthochromia is reliably present 12 hours after occurrence of SAH and may persist for 2 weeks.
E.

Headaches developing slowly over hours to days are common and most often benign. Certain features suggest an increased likelihood of a dangerous cause. As most primary headaches (e.g., migraine) present in the second to third decade of life, older patients (> 50 years) presenting with new headache should undergo brain magnetic resonance imaging (MRI). Similarly, imaging is indicated in the immunocompromised and those with recent dental, head or neck, or neurosurgical procedures (concern for infection), in those with known malignancy (concern for metastasis), and in women who are pregnant or postpartum (concern for preeclampsia, RCVS, CVT). Additional testing, such as sedimentation rate to evaluate for giant cell arteritis or lumbar puncture to evaluate for a chronic meningeal process, may be needed depending on the clinical context. Postural headache that consistently worsens with lying down or headache precipitated by Valsalva maneuvers (e.g., coughing) suggest increased intracranial pressure and warrants brain imaging.
F.

Lumbar puncture should include measurement of opening pressure, protein, glucose, and cell counts. While infectious and inflammatory processes rarely present with thunderclap headache, marked inflammation in the CSF should raise concern. RCVS and CVT can be associated with mild elevations in white blood cells (< 15 per mm ³) and/or protein (< 100 mg/dL). Opening pressure is often elevated in patients with CVT.
G.

Characteristic clinical features suggest a specific underlying cause of thunderclap headache; however, even in the absence of these, a high suspicion for secondary cause of headache should be maintained. Multiple recurrent thunderclap headaches strongly suggest RCVS; this is a common feature of this condition. While very rare, pheochromocytoma may present similarly. Catheter angiography is typically necessary to diagnose RCVS, given involvement of smaller- caliber vessels that are unreliably imaged with CT or MR angiography. CVT can present with thunderclap headache. There are often additional neurologic findings on examination; superimposed slowly progressive headache is typical. Diagnosis is with MR or CT venography. Pituitary apoplexy is due to either hemorrhage into or infarction of the pituitary gland. The former is visible on head CT, while the latter typically requires brain MRI with contrast to identify. Ocular movement abnormalities due to cranial neuropathies and visual loss due to compression of the optic nerves, chiasm, or tracts point to this diagnosis. Arterial dissection should be suspected in the setting of coexistent neck pain, recent trauma, or when focal neurologic deficits are present. Horner syndrome may be present with carotid dissection. Diagnosis is with neck MRA or CTA. Spontaneous intracranial hypotension is characterized by postural headache with improvement when lying flat. The presence of subdural fluid collections, meningeal enhancement, venous engorgement, pituitary hyperemia, or brain sagging on contrast MRI suggests the diagnosis. More involved testing to identify a spinal CSF leak may be needed.