Background
A minority of headache patients have a secondary headache disorder, yet identifying these cases is critical as they may represent life-threatening conditions [1]. The systematic use of red flags helps clinicians distinguish between benign primary headaches and concerning secondary etiologies that warrant urgent evaluation [2,4].
The SNNOOP10 Systematic Framework
The SNNOOP10 mnemonic provides a comprehensive screening tool for identifying secondary headaches that may require neuroimaging [1,5]:
S - Systemic Symptoms and Signs
- Fever [1]
- Constitutional symptoms suggesting systemic illness [1]
N - Neoplasm History
- Known history of cancer requiring evaluation for metastatic disease [1]
N - Neurologic Deficit
- Focal neurologic signs on examination [1]
- Decreased consciousness or impaired consciousness [1,5]
N - New/Recent Onset
- Recent onset of new headache, particularly in specific populations [1]
O - Older Age
- Onset after 65 years of age [1]
O - Other Features
- Pattern change in existing headache [1]
- Positional headache (worse with position changes) [1]
- Precipitated by sneezing, coughing, or exercise (suggesting raised intracranial pressure) [1]
P - Papilledema
- Papilledema on fundoscopic examination [1]
- When accompanied by focal neurologic signs, this warrants immediate evaluation [5]
Additional Red Flags (10-15):
- Progressive headache and atypical presentations [1]
- Pregnancy or puerperium [1]
- Painful eye with autonomic features (concerning for acute glaucoma or other ophthalmologic emergencies) [1,5]
- Posttraumatic onset of headache [1]
- Pathology of the immune system (such as HIV) [1]
- Painkiller overuse or new drug at onset of headache [1]
Emergent Red Flags Requiring Immediate Evaluation
According to available evidence, the following warrant immediate neuroimaging [5]:
Critical Presentations:
- Acute thunderclap headache (sudden, severe onset) [5]
- Fever with meningeal irritation on physical examination [5]
- Papilledema with focal neurologic signs [5]
- Impaired consciousness [5]
- Concern for acute glaucoma [5]
Specific Clinical Contexts
Pregnancy-Related Headaches
Headache during pregnancy requires particular vigilance as it can indicate life-threatening conditions [7]. Secondary causes requiring urgent evaluation include:
- Stroke [7]
- Cerebral venous thrombosis [7]
- Subarachnoid hemorrhage [7]
- Pituitary tumor [7]
- Choriocarcinoma [7]
- Eclampsia/preeclampsia [7]
- Idiopathic intracranial hypertension [7]
- Reversible cerebral vasoconstriction syndrome [7]
Additional diagnostic studies that may be necessary include brain MRI and MR angiography, ophthalmoscopy, and lumbar puncture [7].
Pediatric Populations
Current American Academy of Neurology (AAN) guidelines recommend against routine neuroimaging in pediatric patients with no headache red flags by history and a normal neurologic examination [3]. This emphasizes that red flags are essential screening criteria even in children.
Recommended Imaging Approaches
For Emergent Evaluation:
Noncontrast computed tomography (CT) of the head is recommended to exclude:
- Acute intracranial hemorrhage [5]
- Mass effect [5]
Lumbar puncture is also needed to rule out subarachnoid hemorrhage if the CT scan result is normal [5].
For Less Urgent Cases:
Magnetic resonance imaging (MRI) of the brain is preferred for evaluating headaches with concerning features [5].
Clinical Recommendations
Systematic Screening Approach
Using the systematic SNNOOP10 list to screen new headache patients will presumably increase the likelihood of detecting a secondary cause [1]. A systematic diagnostic approach using red flags can help reduce unnecessary testing and shift attention to patient care [4].
When Neuroimaging is NOT Indicated
According to available evidence, primary headache disorders without red flags or abnormal examination findings do not require neuroimaging [5]. The AAN specifically recommends against routine neuroimaging in patients with no red flags and normal neurologic examination [3].
Differential Diagnosis Considerations
A thorough history and physical examination, along with comprehensive differential diagnosis, may alert physicians to secondary headache diagnosis, particularly when accompanied by the red flag clinical features described above [2].
Limitations & Considerations
Evidence Gaps
Several important limitations exist in the current evidence base:
- Lack of prospective validation: The lack of prospective epidemiologic studies on red flags and the low incidence of many secondary headaches leave many questions unanswered and call for large prospective studies [1].
- Limited sensitivity/specificity data: While the literature presents and promotes red flags, data on sensitivity, specificity, and predictive value of individual red flags for secondary headaches remains limited [1].
- Need for validated tools: A validated screening tool could reduce unneeded neuroimaging and costs [1], but such validation is still needed to properly introduce these concepts for clinical use [4].
- Scarcity of biomarkers: Initial suspicion and diagnostic workup of secondary headache currently relies heavily on patient's medical history due to a scarcity of validated biomarkers [4].
Clinical Judgment Required
Despite these systematic approaches, clinical judgment remains essential. The absence of red flags does not absolutely exclude secondary headache, and conversely, the presence of a single red flag does not automatically indicate pathology requiring imaging. The decision for neuroimaging should integrate the complete clinical picture, including the pattern and severity of symptoms, examination findings, and individual patient risk factors.