Differential Diagnosis for Rapid Onset Headache
Given the scenario of a 45-year-old female with a rapid onset headache and a normal CT head done 7 hours after onset, the differential diagnosis can be categorized as follows:
Single Most Likely Diagnosis
- Migraine or tension headache: These are common causes of sudden onset headaches in adults and can present with severe pain, though they typically do not have the "thunderclap" characteristic often associated with subarachnoid hemorrhage. The normal CT head makes a hemorrhagic cause less likely, but not impossible.
Other Likely Diagnoses
- Thunderclap headache due to other causes (e.g., cervical artery dissection, reversible cerebral vasoconstriction syndrome): These conditions can mimic subarachnoid hemorrhage in terms of the sudden onset of severe headache but have different underlying pathologies.
- Idiopathic thunderclap headache: This is a diagnosis of exclusion for a severe headache that reaches its maximum intensity within a minute, without an identifiable cause.
Do Not Miss Diagnoses
- Subarachnoid hemorrhage (SAH): Despite the normal CT head, SAH remains a critical diagnosis not to miss due to its high morbidity and mortality. The sensitivity of CT scans for detecting SAH decreases with time, and a lumbar puncture may be necessary to rule out SAH if clinical suspicion remains high.
- Cervical artery dissection: This can lead to stroke or other neurological deficits and may present with headache as an initial symptom.
- Venous sinus thrombosis: Although less common, this condition can cause sudden onset headache and has significant implications if not treated promptly.
Rare Diagnoses
- Pituitary apoplexy: A rare condition involving hemorrhage or infarction of the pituitary gland, which can present with sudden, severe headache.
- Spontaneous intracranial hypotension: Characterized by a low-pressure headache, often postural, due to spontaneous leakage of cerebrospinal fluid.
- Arteriovenous malformation (AVM) or other vascular anomalies: While less common, these can cause sudden onset headaches due to hemorrhage or other mechanisms.
Each of these diagnoses carries different implications for management and prognosis, highlighting the importance of a thorough diagnostic workup in the setting of a sudden onset headache, even with a normal initial CT scan.