What is the preferred imaging modality to rule out secondary causes of cluster headaches in patients presenting with this condition?

Preferred Imaging for Ruling Out Secondary Causes of Cluster Headache

MRI of the brain without contrast is the preferred initial imaging modality to rule out secondary causes of cluster headache, with contrast administration added if the non-contrast study reveals abnormalities. 1

Primary Imaging Recommendation

MRI brain without IV contrast should be obtained in all patients presenting with cluster headache to exclude structural mimics. 2 The American College of Radiology guidelines establish that for secondary headache evaluation, MRI head without IV contrast is the appropriate initial study, with postcontrast imaging indicated if the noncontrast study is abnormal. 1

Why MRI is Superior

• MRI provides superior soft-tissue resolution for detecting the structural lesions most commonly associated with secondary cluster headache, including pituitary/suprasellar masses (which account for 77.3% of brain mass-like lesions causing cluster-like headache), tumors, and inflammatory lesions. 3, 4

• MRI is more sensitive than CT for identifying clinically significant intracranial pathology in non-emergent headache evaluation, particularly for detecting small masses, optic nerve pathology, and demyelinating lesions that CT would miss. 3, 5

• MRI avoids radiation exposure, which is particularly important given that cluster headache patients may require follow-up imaging, as neuroimaging is as necessary at follow-up visits as at initial presentation. 4

Specific Imaging Protocol

The MRI should include: 1

• Standard brain sequences (T1-weighted, T2-weighted, FLAIR)
• Thin-slice imaging through the sella/suprasellar region, as pituitary pathology is the most common structural cause of secondary cluster headache 4
• Contrast administration if any abnormality is detected on the non-contrast study 1

When to Add Vascular Imaging

MRA (magnetic resonance angiography) should be added to the initial MRI if there is clinical suspicion for vascular pathology, particularly: 1

• Internal carotid artery dissection (the third most common cause of secondary cluster headache at 14.3% of cases) 4
• Aneurysm or arteriovenous malformation 1
• Cerebral venous thrombosis (requires particular attention as it can mimic primary cluster headache) 4

MRV (magnetic resonance venography) is indicated if venous sinus thrombosis is suspected, as this can perfectly mimic primary cluster headache. 1, 4

When CT is Appropriate Instead

Non-contrast CT head should be ordered first only in acute emergency scenarios: 1, 3

• Thunderclap (sudden severe) headache requiring immediate exclusion of subarachnoid hemorrhage 1
• Suspected acute intracranial hemorrhage requiring rapid assessment 1
• Patient unable to undergo MRI due to contraindications (pacemaker, metallic implants, severe claustrophobia) 3

CT is inferior to MRI for cluster headache evaluation because it misses the structural lesions most commonly responsible for secondary cluster headache, including small pituitary masses, inflammatory lesions, and subtle vascular abnormalities. 3, 5

Red Flags Requiring Urgent Imaging

The following atypical features substantially increase suspicion for secondary cluster headache and mandate neuroimaging: 4, 6

• Late age at onset (present in at least one-third of secondary cases) 4
• Abnormal neurological examination, particularly impaired cranial nerves (the most significant red flag, with likelihood ratio of 5.3) 4, 7
• Change in headache pattern or development of continuous interictal pain 6
• Cluster headache type itself has a positive likelihood ratio of 11 for significant intracranial abnormality 7
• Headache aggravated by exertion or Valsalva (likelihood ratio 2.3) 7

Common Structural Causes to Exclude

Neuroimaging should specifically evaluate for: 4, 8

1. Pituitary/suprasellar masses (28.6% of all secondary cluster headache cases, with 77.3% of brain mass-like lesions located in this region) 4
2. Vascular pathology (37.7% of cases): internal carotid artery dissection, aneurysms, arteriovenous malformations, cerebral venous thrombosis 4
3. Tumors (32.5% of cases): both primary brain tumors and metastases 4, 8
4. Inflammatory lesions (27.2% of cases) 4
5. Sinusitis (19.5% of cases—this has risen dramatically and requires particular attention) 4

Critical Pitfalls to Avoid

• Do not skip imaging based on treatment response. Cluster-like headache patients may be responsive to typical cluster headache treatments (oxygen, triptans); therefore, treatment response does not exclude secondary causes. 4, 6

• Do not order CT when MRI is appropriate. CT misses the majority of structural lesions causing secondary cluster headache, particularly pituitary masses and inflammatory lesions. 3, 5

• Do not assume primary cluster headache without imaging. Since secondary headache can perfectly mimic primary cluster headache, neuroimaging should be conducted in all patients presenting with cluster headache symptoms. 4

• Do not skip contrast if the non-contrast study shows abnormalities. Many vision-threatening and life-threatening lesions require contrast for proper characterization. 1, 3

• Do not forget that contralateral structural pathologies can trigger cluster-like headache. The structural lesion may not be ipsilateral to the headache. 4

Follow-Up Imaging Considerations

Repeat neuroimaging should be considered if there is any change in headache pattern, development of new neurological signs, or failure to respond to appropriate prophylactic therapy, as demonstrated by the case of a patient with initially normal MRI who later developed a pituitary cyst. 6