A 54-year-old woman presents to the emergency department complaining of the abrupt onset of what she describes as the worst headache of her life. You are concerned about the possibility of subarachnoid hemorrhage. What is the most appropriate initial test for diagnosis?
A. Cerebral angiography
B. Computed tomography (CT) of the head with intravenous contrast
C. CT of the head without intravenous contrast
D. Lumbar puncture
E. Transcranial Doppler ultrasound
The answer is C. (Chap. 440e) Appropriate and timely evaluation is needed to determine whether a subarachnoid hemorrhage is present because it can be rapidly fatal if undetected. The procedure of choice for initial diagnosis is a computed tomography (CT) of the head without intravenous (IV) contrast. On the CT, blood in the subarachnoid space would appear whiter compared to the surrounding brain tissue. The head CT is most sensitive when it is performed shortly after the onset of symptoms, but sensitivity declines over several hours. It can also demonstrate significant mass effect and midline shift, factors that increase the severity of the underlying hemorrhage. In the situation where the head CT is negative but clinical suspicion is high, a lumbar puncture can be performed. This may demonstrate increased numbers of red blood cells that do not clear with successive aliquots of cerebrospinal fluid (CSF). If the lumbar puncture is performed more than 12 hours after a small subarachnoid hemorrhage, then the red blood cells may begin to decompose, leading to xanthochromia—a yellow to pink coloration of CSF that can be measure spectrographically. A basic head CT with IV contrast is rarely useful in subarachnoid hemorrhage because the brightness of the contrast material may make it difficult to identify blood in the subarachnoid space. However, a CT angiography that is performed with IV contrast can be useful in identifying the aneurismal vessel leading to the bleeding. Classic angiography is a more direct way to visualize the anatomy of the cranial vasculature and is now often combined with interventional procedures to coil a bleeding vessel. Transcranial Doppler ultrasound is a test that measures the velocity of blood flow through the cranial vasculature. It is used in some centers following subarachnoid hemorrhage to assess for the development of vasospasm, which can worsen ischemia leading to increased damage to brain tissue following subarachnoid hemorrhage.