Sorry to hear about your husband's symptoms, but glad the workup so far is
normalNormal saline flush. There is something called "thunderclap headache," which is described as the worst headache ever that comes on suddenly. Usually when doctors hear about such a headache, immediately we all think of an aneurysm that burst or is about to, causing a very serious brain
hemorrhageChronic subdural hematoma
Extradural hemorrhage
Hemorrhagic stroke
Intracerebellar hemorrhage - ct scan
Intracerebral hemorrhage
Scurvy, periungual hemorrhage
Stroke
Subarachnoid hemorrhage
Subconjunctival hemorrhage
Subdural hematoma . However, as recently reported in an article by Dr. Dodick on the subject, other things can cause thunderclap headache, such as pituitary gland problems like a stroke there,
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Tears renewed in the arteries of the neck, blood clots in the veins throughout the brain,vasculitis, and leaks in the cerebrospinal fluid called intracranial hypotension. But what's also very interesting is that it may just be a type of headache in itself with no other serious condition behind it. An MRI and spinal tap are necessary to rule out anything serious. Then, based on the clinical exam and history, further testing may include an MRI of the arteries and veins in your husband's brain called an MRA and MRV to see if there is narrowing or blood clots. Finally, if they suspect vasculitis and the MRA is inconclusive, an angiogram may help as well as routine blood studies.
If everything turns out normal still, then consider a headache specialist at a major academic or clinical center for further evaluation and treatment options. Good luck.