Headache
Imaging Strategies
Autho Dugald Chisolm MS 4
Editor: Ashley Davidoff
Copyright 2006
UNDER CONSTRUCTION
HEADACHE ? WHEN SHOULD I ORDER AN IMAGING STUDY?
Clinical Background:
Headache is an extremely common complaint seen by physicians in all fields, but especially in the emergency department. There are many different etiologies of headaches and determining the cause of your patient?s headache can be quite a daunting task. Headache can present as one of many symptoms or it may be a sole complaint. Most often the headache is benign and primary without obvious etiology. The difficulty lies in identifying the small subset of patients with a serious or potentially life-threatening disorder.
The first step in determining the potential cause of a headache is to obtain a thorough and systematic history and physical. Often the physical exam will be completely normal, even in the presence of significant pathology, so history plays a vital role in developing the differential diagnosis.
The clinical approach to identifying the patient that needs imaging is beyond the scope of this module, but questioning should include the characterization of the pain including precipitating factors, duration, acuity of onset, location, severity, aggravating and relieving factors. Associated symptoms of neurologic deficit, fever, nausea must also be elicited. A remote or recent history of a similar headache should be sought including a chronology of the headache. Medical history with a focus on the trivial such as a recent viral infection, exposure to anybody who may have had an infection, to the more serious such as a history of cancer have relevance to the headache. Lastly family history, drug use and substance abuse history are also relevant.
Benign primary causes of headache include migraine, cluster headache, and tension headache.
Primary causes of headache are not an indication for imaging as was determined in 1992 by Weingarten et al. In their study of a large population of adults presenting with ?chronic isolated headaches,? meaning no neurologic abnormalitites, no head trauma, and no known cancer, they found that CT scanning of all patients changed neither the diagnosis nor the management. Although imaging is not used for diagnosis of primary causes of headaches, it may be useful in helping to rule out possible secondary causes.
For the secondary causes of headache the answer is not simple. In these cases further workup is almost always warranted. Secondary, or potentially life-threatening, causes may include vascular disorders, trauma, nonvascular intracranial disorders (i.e. intracranial mass, elevated ICP), substance usage or withdrawal, infection, and metabolic disorders.
The clinical concerns for secondary headache are raised when the following symptoms or signs are present
– Focal neurologic finding on physical or change in mental status
– Headache starting after exertion, Valsalva?s maneuver, or sexual activity
– Acute onset (within a few minutes) of severe headache or ?the worst headache of my life?
– Headache awakens patient at night
– Change in well established pattern of headaches – progressive or new daily, persistent headache
– New-onset headaches in patient >35
– New-onset headaches in HIV
– New-onset headache in patient with previously diagnosed cancer
Imaging Strategies:
When do I get an imaging study?
Once the decision has been made to get a study it should be ordered immediately particularly when a bleed is suspected. The study in turn should be read and reported immediately.
What study should I order?
In general a head CT scan (without and with contrast) is likely to be sufficient in most patients [30]. An MRI along with MRA are indicated when posterior fossa or vascular lesions are suspected.
In the context of ?acute headache suspect bleed? the study of choice is a non-contrast head CT, which has >90% sensitivity of detecting a bleed less than 24 hours old.
In the context of ?acute headache suspect mass? an MRI with contrast is the study of choice. If MRI is not available then a CT with and without contrast is recommended.
The major benefit of the non-contrast head CT as the first study in the context of an acute headache suspect bleed is because of its high sensitivity to detect blood. Additionally it is available in almost all emergency setting environments, mostly is not operator dependant, is quick ? (less than 10 seconds once the patient is on the table and can lie still) and consistently provides a diagnostic study.
In the setting of ?acute headache suspect vascular abnormality? a CT or MRI with IV contrast (CTA or MRA) is indicated.
In the setting of ?acute headache suspect soft tissue mass?, an MRI with contrast is indicated.
In the setting of ?acute headache suspect infection?, MRI with its innate sensitivities to edema and soft tissue changes is indicated.
Specific Disease Entities
Subarachnoid Hemorrhage
Subarachnoid hemorrhage presents classically with ?thunderclap? or ?worst headache of life?. The study of choice is a head CT because it is fast, the patient only has to lie still for 8-10 seconds it is sensitive to the presence acute blood.
Noncontrast head CT
Highly sensitive for acute bleed (<24 hrs), but should be performed with thin cuts through the base of the brain to increase the sensitivity to small amounts of blood.
The sensitivity of head CT for detecting SAH is highest in the first 12 hours after SAH (nearly 100 percent) and then progressively declines over time to about 58 percent at day five [92,9496].
MRI is recommended if the presentation is delayed for greater than 24 hours
The sensitivity of head CT is also reduced with more minor bleeds. In one study, for example, a minor SAH was not diagnosed by CT scan in 55 percent of patients; lumbar puncture was positive in all cases [Leblanc R].
Note: If there is a high suspicion of SAH and CT is negative, LP is the examination of choice to r/o SAH.
Cerebral angiography or CTA/MRA
Cerebral angiography or CTA/MRA may be located and if current bleeding is happening.Most lesions responsible for SAH can be identified using
CT/MR
CT/MR coupled with cerebral angiography that includes injections of the external carotid circulation and deep cervical branches, which may supply a cryptic dural AV fistula. Angiographic imaging of key branch points, including the proximal posterior circulation, is essential to definitively rule out aneurysm.
Note: Angiography may not be indicated if CT and LP are negative
- Repeat study may be required after 12 weeks to account for small possibility of false (Gershon).
MRI FLAIR and T2*
MRI FLAIR and T2* sequences on MRI have a high sensitivity in patients with a subacute presentation of SAH (eg, >4 days from the bleed) [107].
CVA
Noncontrast head CT
Noncontrast head CT Obtain as soon as patient is medically stable.If within first 1224 hours after onset of symptoms used to confirm/exclude intracranial hemorrhage. Immediate CT scanning of all patients with suspected stroke is the most costeffective strategy when compared with alternate strategies such as scanning selected patients or delayed rather than immediate imaging [1].
Using noncontrast CT along with CT Perfusion scanning and CTA has been shown to improve detection of acute infarction when compared with CT evaluation using any of the single techniques alone [2,3].
MRI
Brain MRI protocols that combine conventional T1 and T2 sequences with diffusionweighted imaging (DWI), perfusionweighted imaging (PWI), and GRE can reliably diagnose both acute ischemic stroke and acute hemorrhagic stroke in emergency settings. These MRI techniques may obviate the need for emergent CT in centers where brain MRI is readily available. As an example, one specialized stroke center found that routine use of these MRI sequences to screen patients prior to intravenous thrombolysis for suspected ischemic stroke was practical and safe [37]. Furthermore, MRI screening did not cause excessive treatment delays or lead to worse outcomes. On the other hand, MRIspecific selection criteria for acute thrombolysis of ischemic stroke have not been validated, and no randomized studies have compared CT and MRI screening in this setting. The utility of MRI lies in the availability at any given institution as well as patient characteristics. Many more patients have contraindications or are intolerant to MRI than to CT (stroke severity or pacemakers). [Schramm]
Ultrasound
Carotid Duplex ultrasound (CDUS) and transcranial Doppler (TCD) ultrasound are noninvasive methods for neurovascular evaluation of the extracranial and intracranial large vessels. There have been some studies that suggest the utilization of both methods together is a good method for detecting lesions amenable to interventional treatment if U/S technicians with sufficient experience are available. [Chernyshev] Availability of these experienced techs is one of the major limitations of routine utilization of these methods.
Angiography
Angiography is not typically used in the acute setting except for situations where there is a probable large vessel occlusion that may benefit from ?insitu? repair.
TIA
Brain imaging is indicated in all patients w/ TIA symptoms ASAP
MRI DWI
DWI reliably confirms whether only ischemia has occurred or if there has also been an element of infarction. Differentiation of stroke from TIA is possible within the first hours after onset of symptoms. [Kidwell, Winbeck]
CT
CT may be used if MRI is not readily available at a given institution.
Carotid Ultrasound
Carotid Ultrasound indicated to help determine location of the ischemia as well as the possibility of definitive treatment if the lesion lies in the carotid.
CTA/MRA/Angiography
For further evaluation similar to that described under CVA may be indicated to identify lesions for prognostication.
AV Malformation
AVM usually presents from age 1040 w/ signs of ICH, seizures, HA, or focal neurological deficit
Noncontrast CT
Noncontrast CT initial study to r/o acute hemorrhage. May also identify flow voids in and around the nidus of AVM. Patients presenting with acute hemorrhage often have the AVM compressed by the hematoma, thus not allowing definitive diagnosis of AVM by CT.
Angiography
Angiography is considered the gold standard for diagnosis, treatment planning, and follow up of AVM.
MRI
MRI very sensitive for identifying location of AVM. Useful in following changes after therapy.
Cerebral Aneurysm
Usually identified after SAH
Noncontrast CT
Noncontrast CT look for acute SAH
CTA or Angiography
CTA or Angiography Identify aneurysm Can be used as screening tool in patients with strong family history of aneurysm
Transcranial Doppler
Transcranial Doppler detect vasospasm
Brain Tumor
MRI with and without contrast.
MRI with and without contrast. Usually the only imaging study necessary to diagnose a brain tumor
MR Spectroscopy
MR Spectroscopy can help to determine extent of infiltration into brain tissue
Functional MRI can help differentiate normal brain from tumor tissue during preop planning
CT
CT Can be useful in identifying bone involvement. Also useful if there is emergent concern about tumor hemorrhage.
PET Scan
PET Scan may guide neurosurgeon to biopsy most biologically active area of tumor
May differentiate new tumor growth from radiation necrosis in previously treated patient
Along with functional MRI may help with mapping
Can help to differentiate highgrade from lowgrade
Temporal Arteritis
Arterial biopsy is going to be the definitive modality of diagnosis
Ultrasound
Ultrasound can be performed on temporal artery or occipital artery.
Sensitivity and specificity range from 0.690.88 and 0.770.82, respectively. [Karassa]
Acute Sinusitis
Imaging studies are not indicated in the usual case of acute communityacquired sinusitis, unless intracranial or orbital complications are suspected.
CT
CT is the study of choice if imaging is deemed necessary (has failed 2 courses of Abx therapy)
MRI
MRI May be helpful if extrasinusoidal involvement is suspected
Chronic Sinusitis
Limited CT
Limited CT Screening tool that provides select coronal views through each of the sinuses for patients that are suspected of having chronic sinusitis. Has basically replaced the use of plain films of sinuses
CT Sinuses
CT Sinuses provides useful information on the extent of sinusitis
Infectious
(Meningitis, Toxoplasmosis and others).
MRI
MRI is the most useful study in determining inflammation of the meninges, but is not able to make diagnosis of meningitis. Ring enhancing lesions may be found in multiple scenarios of CNS infection, and MRI is more sensitive than CT in identifying these lesions. Effusion, hydrocephalus, cerebritis, and abscess can be evaluated well by using CT and ultrasonography (US) in infants; however, MRI is the most effective modality for localizing the level of the obstructio
Spect Imaging
Spect Imaging Thallium single photon emission computed tomography Is useful in differentiating an infectious process from CNS lymphoma
CT
CT Is useful in ruling out signs of elevated ICP prior to performing LP.
Cerebral Venous Thrombosis
MR venography
MR venography is an excellent method of visualizing the dural venous sinuses and larger cerebral veins.
Singleslice phasecontrast angiography (SSPCA) Many neurologists now consider it to be the procedure of choice in diagnosing CVT.
CT
CT useful in ruling out other etiologies. CT of the mastoids may be helpful in lateral sinus thrombosis.
CT Venography
CT Venography a useful alternative to MR venography
Trauma
In the patient with neurological deficit the procedure of choice is a non contrast head CT. In the absence of neurological deficit, is a topic of debate and there are not currently any well defined criteria for who should or should not receive imaging.
Non contrast CT
Non contrast CT may identify hemorrhage, skull fracture
MRI
MRI more sensitive than CT and should be considered if patient continues to have concerning symptoms after a negative CT.
Elevated ICP
CT or MRI may show midline shift, large ventricle size, or signs of edema, but also may be initially normal in some
HOW TO ORDER?
We want to promote accurate wording and appropriate clinical content ?Ordering the study should include the relevant symptom ie ?dyspnea on effort? , a provisional diagnosis ie “suspect sarcoidosis” and a specific intentif possible ie “evaluate for interstial lung disease.
PREPARING THE PATIENT
Red Flags
Sudden explosive headache or ?the worst headache of my life?.
New-onset headache after the age of 50.
Headache associated with papilledema or focal neurologic symptoms.
Headache status post trauma.
Sub-acute headache with increasing severity or frequency.
Headache associated with fever, cancer, or immunosuppression.
References:
Texts
Pubmed
Links intact
Web