Hair on end appearance is seen in?
**Core Concept**
Hair on end appearance is a radiological phenomenon observed in certain conditions where there is a significant difference in the attenuation of tissues, leading to an appearance of hairs standing on end. This is typically seen in conditions with a high density of blood vessels or contrast material in the subarachnoid space.
**Why the Correct Answer is Right**
The hair on end appearance is classically seen in subarachnoid hemorrhage (SAH) where blood accumulates in the subarachnoid space, causing a high density area that stands out against the surrounding brain tissue. This is due to the high attenuation of blood, which is visible on computed tomography (CT) scans. The contrast between the blood and the surrounding tissue creates the characteristic "hair on end" appearance.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely to be incorrect as it does not directly relate to the characteristic radiological finding of hair on end appearance.
**Option B:** This option may be related to other radiological findings but does not specifically describe the hair on end appearance seen in SAH.
**Option C:** This option could be a distractor, but it does not accurately describe the hair on end appearance seen in SAH.
**Clinical Pearl / High-Yield Fact**
The hair on end appearance is a classic radiological sign of subarachnoid hemorrhage, and it is essential to recognize this sign to diagnose SAH promptly. Remember that SAH is a medical emergency, and prompt diagnosis and treatment are crucial to prevent further complications.
**Correct Answer: C. Subarachnoid hemorrhage.