Pφ

Rupture of a cerebral artery aneurysm leads to a sudden, dramatic increase in ICP. The subarachnoid space rapidly fills with blood. In severe hemorrhages, this blood may also leak into the intraventricular space or into the parenchyma. Both genetic and environmental factors predispose patients to formation of saccular aneurysms, the most common form of aneurysm. Saccular aneurysms tend to occur at arterial branch points, most commonly in the anterior communicating artery. Less common forms of aneurysms include mycotic aneurysms (formed by septic or neoplastic emboli that lodge in the arterial wall) and fusiform aneurysms.

TP

Classically a patient with subarachnoid headache will experience an explosive, generalized headache that will often be described as “the worst headache of my life.” Associated symptoms can include neck stiffness (usually), vomiting, photophobia, confusion, and loss of consciousness. Depending on whether there is parenchymal hemorrhage, the patient may also exhibit focal motor or sensory signs. Before aneurysmal rupture, patients are usually asymptomatic. However, they may present with a third-nerve palsy, which involves the pupil; the pupil will be asymmetrically enlarged and poorly reactive to light. This is caused by direct pressure from the aneurysm, most often from the posterior communicating artery, on the third-nerve fibers. This is an important syndrome not to be missed by the clinician because identification can be lifesaving.

Dx

A noncontrast head CT scan has >90% sensitivity in SAH in the first 24 hours. If the head CT scan is negative but there is still a high suspicion for SAH, LP must be performed. LP typically reveals a high opening pressure, is grossly bloody with a very high RBC count, and is positive for xanthochromia—a yellow appearance to the supernatant.

Pφ

Meningitis is an infection of the arachnoid, the pia, and the subarachnoid space. Encephalitis is an infection of the brain parenchyma. When there are symptoms that seem to indicate infection of both meninges and brain, this is termed meningoencephalitis. CNS infections produce an intense inflammatory response. This response is often more detrimental than the pathogen itself and may lead to acute and chronic complications.

TP

The two most common treatable life-threatening types of CNS infections seen are bacterial meningitis and herpes simplex virus (HSV) encephalitis. A patient with acute bacterial meningitis will typically present with severe generalized headache and neck stiffness. Fevers, chills, nausea, and vomiting are common. Level of consciousness may range from normal to confused or comatose. On exam, meningismus is prominent, although this sign may be absent in coma. Kernig and Brudzinski signs may also be present.

HSV encephalitis may have a similar presentation. There is usually fever, headache, and alteration in mental status. Patients can also exhibit prominent symptoms not often appreciated in meningitis, including olfactory hallucinations, aphasia, recurrent partial seizure, hemiparesis, and ataxia.

Dx

The diagnosis of meningitis is made by analysis of CSF. Opening pressure will be elevated. CSF will be cloudy upon visual examination. WBC count in fluid usually ranges from 1000 to 10,000 cells/μL with a neutrophilic predominance. Protein will usually be elevated and glucose decreased. Gram stain and culture reveal the pathogen in a large percentage of patients, although the likelihood of identifying the organism depends upon the concentration of organisms in spinal fluid. Blood cultures should be done as well. Importantly, before LP is performed (particularly if there is any sign of increased ICP or focal neurologic deficit), a head CT scan should be done to rule out a mass lesion.

HSV encephalitis is also diagnosed via the CSF. There is a CSF lymphocytic pleocytosis with elevated protein and normal glucose. In some cases there are increased RBCs or xanthochromia, but this sign is not reliable. HSV PCR is highly sensitive and specific, and is used to establish the diagnosis. The most common abnormalities on MRI are characteristic changes in the temporal lobes.

Pφ

The etiology of migraine is not completely understood. There is certainly a genetic component, as migraine tends to run in families. Currently it is thought that migraine occurs as the result of excitability in the trigeminal nerve system, which sets off a chain reaction resulting in the release of neurochemical transmitters, including serotonin and calcitonin gene–related peptide (CGRP), resulting in vascular dilatation. At the same time, this hyperexcitability also causes a phenomenon that has been termed “spreading cortical depression” in which decreased neural activity spreads across both hemispheres from the occiput forward in a continuous pattern.

TP

The two types of migraine most commonly encountered are migraine with aura (classic migraine) and migraine without aura (common migraine). In the patient who has migraine with aura, a stereotyped aura will precede the headache by a period of minutes. The aura commonly is a visual phenomenon of an expanding, shimmering blind spot (scintillating scotoma). In some the scotoma may morph into a colored zigzag line (fortification spectra). Interestingly, the progression of the visual aura across the visual field seems to parallel the spreading cortical depression described above. Less commonly, aura can consist of unilateral sensory or motor symptoms. The aura symptoms last between 20 and 25 minutes, and usually resolve before the headache occurs.

The headache in migraine usually increases to a maximum over 30 minutes to 2 hours. Pain is classically unilateral; however, it may also be generalized. It is throbbing in nature. Usually there is photophobia and/or phonophobia. Physical activity will exacerbate the symptoms, and thus the patient will prefer to lie down in a dark, quiet place until the headache improves, usually over hours to days. Neurologic examination should be normal except in rare cases in which focal deficits accompany migraine symptoms.

Dx

Migraine is diagnosed by history. In cases in which a person with migraine presents to the ED, it may be necessary to exclude other more dangerous entities with imaging and/or LP.

Pφ

Brain, blood, and CSF are the three elements that reside in the finite space of the cranial vault. If a fourth element is introduced into this space, such as an intracranial mass, then the equilibrium between the preexisting elements is altered. Localized headache may be caused by distension of pain-sensitive structures. If the tumor continues to grow, there will be a rise in ICP, which may then cause generalized headache.

TP

Patients with brain tumor will present in a variety of ways, including headache, seizure, or focal symptoms. Headaches from an intracranial mass can range from dull and constant to sharp and intermittent. Some patients will localize their headache to the approximate location of the mass; however, others will complain of generalized headaches. Patients will often describe headaches that awaken them from sleep. This is because lying in the recumbent position causes a transient increase in ICP. In the same manner other maneuvers that transiently increase ICP, such as coughing or straining, can worsen the headache. On exam there may be papilledema or focal signs referring to the mass.

Dx

An intracranial mass is most readily identified with MRI. The addition of contrast can aid in elucidating what type of mass is present. If MRI is not available, CT can be used, but it is not as sensitive or informative. Further attempts to identify the mass noninvasively can be made using either MRI–single photon emission CT (MRI-SPECT) or PET scan. However, most often a brain biopsy is necessary for definitive identification of the mass. The differential diagnosis of an intracranial mass should include brain abscess, which can have a similar presentation and appearance on imaging studies.

Pφ

Venous sinus thrombosis is the occlusion of an intracerebral venous sinus by thrombus. Sagittal, lateral, and cavernous sinuses are the most common sites for thrombosis. The thrombosis is presumably caused by a hypercoagulable state, whether that is from a genetic predisposition, medications such as oral contraceptives, an autoimmune process, the postpartum period, intracranial infection, or malignancy. Dehydration has also been implicated. Venous sinus thrombosis can lead to a host of complications such as venous infarction, seizure, and increased ICP.

TP

Depending on the site of thrombosis, the presentation can vary. The superior sagittal sinus (SSS) is the most commonly affected sinus; patients with SSS thrombosis most often present with headache, which is usually constant and generalized, but can be located in the occipital region. Headache may be exacerbated by coughing, straining, or lying down. Patients with cavernous sinus thrombosis may also present with chemosis, exophthalmos, and ophthalmoplegia.

Dx

Head CT both with and without contrast suggests the diagnosis, although it is by no means a sensitive test for this condition. MRV is the initial test of choice when venous sinus thrombosis is suspected. Further information can be gained by the more invasive conventional angiogram, although this is not always necessary. Once the diagnosis is confirmed, the cause of thrombosis should be pursued.

Pφ

The cause of pseudotumor cerebri, also known as idiopathic intracranial hypertension (IIH), is not known. Theories include increased rate of CSF production, decreased rate of CSF absorption secondary to venous hypertension, slowed absorption of CSF by arachnoid villi, and increased brain volume due an increase both in intracranial blood volume and extravascular space. Pseudotumor is most commonly associated with obesity and menstrual irregularities. Other risk factors include excessive vitamin A ingestion, endocrine abnormalities, remote head trauma, and venous sinus thrombosis.

TP

The headache in pseudotumor is most often constant and generalized; it may wake the patient up from sleep and worsens upon coughing or straining. There may be associated visual symptoms including blurring of vision, diplopia, or recurrent episodes of transient visual loss. In severe cases there may be complete visual loss. Exam can reveal papilledema and possibly retinal hemorrhage. There may be bilateral cranial nerve VI palsy. Visual fields may be constricted, and/or there may be an enlargement of the physiologic blind spot. More often, however, bedside visual testing will appear normal, and formal visual testing will have to be performed to identify abnormalities. The rest of the neurologic exam is normal.

Dx

In a patient with headache and papilledema, neuroimaging with CT or MRI must be done initially to rule out a structural cause such as a mass lesion. Depending on the clinical scenario, MRV may also be appropriate. If neuroimaging proves unrevealing, LP is performed. Normal opening pressure is <180 mm H2O in nonobese patients and <250 mm H2O in obese patients. Thus, an opening pressure above these levels is diagnostic; however, these minimum thresholds for diagnosis may well be exceeded.

Pφ

The etiology of cluster headache is unknown. Some believe it is secondary to abnormal parasympathetic activity, mediated through the superior petrosal nerve and the sphenopalatine ganglion. Others have implicated the hypothalamus and its pathways because of the daily rhythmicity of attacks and their relationship to the circadian rhythm.

TP

The headaches typically occur in “clusters,” every day at the same time for a 4- to 6-week period, before remitting for months to years, when the cycle repeats. The pain, usually localized over one eye, is deep, stabbing, and unbearable. Prominent symptoms associated with cluster headache include ipsilateral ptosis, conjunctival injection and tearing, nasal stuffiness, and facial flushing. In contrast to the migraneur who prefers to lie in a quiet, dark environment, a cluster headache patient will often pace about until the pain stops. The headache will last between 15 minutes and 2 hours. Alcohol can trigger a headache in 70% of patients; however, if the patient is not in the midst of a cycle, alcohol has no effect.

Dx

The diagnosis is made by a careful history and, if possible, observation during an attack.

Pφ

Temporal arteritis is an autoimmune vasculitic syndrome of unknown cause that affects the superficial temporal artery exclusively in the majority of cases, and less commonly affects other larger arteries. It is thought that T cells invade the internal elastic lamina initially in response to an unknown antigen. Lymphokines are then released and attract monocytes, which carry out a full-thickness arterial invasion. In foci of inflammation there is frequent granuloma and giant cell formation. With progression of the disease, there is luminal proliferation causing stenosis of the artery and distal ischemia.

TP

Patients with temporal arteritis usually present with increasingly severe, constant unilateral pain centered over the temporal artery. The pain can be dull, throbbing, or stabbing in character. Associated symptoms can include jaw claudication (pain with chewing), fatigue, anemia, and low-grade fever. If myalgias are a prominent feature, there may be coexistent polymyalgia rheumatica. The dreaded complication of temporal arteritis is visual loss due to involvement of the central retinal artery; this can occur with a prodrome of transient episodes of amaurosis fugax, or it can occur suddenly without warning. On exam a tender, nodular, enlarged, and erythematous superficial temporal artery may be present. If vision has been affected, it may manifest in abnormal visual fields, decreased visual acuity, or blindness. Otherwise the neurologic exam is usually normal.

Dx

ESR is the initial test for temporal arteritis. While an ESR > 50 mm/hr is diagnostic, it is important to note that a normal ESR is seen in a minority of cases. In these cases, C-reactive protein (CRP) level may be more sensitive and should be checked. Temporal artery biopsy should then be performed for confirmation.