IOC for sub-arachnoid hemorrhage
**Core Concept**
Non-contrast computed tomography (CT) scan is the initial imaging modality of choice for suspected subarachnoid hemorrhage (SAH) due to its high sensitivity and rapid availability. SAH is characterized by bleeding into the subarachnoid space, which surrounds the brain.
**Why the Correct Answer is Right**
The non-contrast CT scan is particularly useful in SAH as it can detect blood in the subarachnoid space, even if it is as small as 1 mL. This is because blood in the subarachnoid space has a higher density than the surrounding cerebrospinal fluid (CSF), making it visible on CT scans. The sensitivity of non-contrast CT scans for SAH is around 90-95%.
**Why Each Wrong Option is Incorrect**
**Option A:** Magnetic Resonance Imaging (MRI) is not the initial imaging modality of choice for SAH due to its longer scan time and lower availability compared to CT scans.
**Option B:** Lumbar puncture (LP) is not typically used as an initial diagnostic tool for SAH, as it can be delayed and may not accurately diagnose SAH if performed too soon after the bleed.
**Option C:** Angiography is not the initial imaging modality of choice for SAH, although it may be used to identify the source of bleeding in some cases.
**Clinical Pearl / High-Yield Fact**
In cases of suspected SAH, it is essential to perform a non-contrast CT scan as soon as possible, ideally within 6 hours of symptom onset, to maximize detection sensitivity.
**Correct Answer:** C. Angiography is not the initial imaging modality of choice for SAH, although it may be used to identify the source of bleeding in some cases.