Onion peel appearance is seen in-
**Core Concept**
The onion peel appearance is a radiological sign associated with a specific condition affecting the brain, characterized by alternating layers of radiodensity and lucency. This appearance is due to the presence of calcifications and gliosis in the brain tissue.
**Why the Correct Answer is Right**
The onion peel appearance is typically seen in neurocysticercosis, a parasitic infection caused by the pork tapeworm Taenia solium. In neurocysticercosis, the larval stages of the parasite (cysticerci) calcify over time, leading to the formation of calcified nodules in the brain. The calcifications are often seen as alternating layers of radiodensity and lucency on CT scans, resembling an onion peel. This appearance is due to the varying stages of calcification and gliosis surrounding the cysts.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the onion peel appearance is not typically associated with cerebral edema or intracranial hemorrhage.
* **Option B:** This option is incorrect because the onion peel appearance is not typically seen in cerebral metastases or primary brain tumors.
* **Option C:** This option is incorrect because the onion peel appearance is not typically associated with cerebral infections such as bacterial or fungal abscesses.
**Clinical Pearl / High-Yield Fact**
The onion peel appearance in neurocysticercosis is a classic radiological sign that should prompt consideration of this diagnosis in patients with seizures, headache, or other neurological symptoms. The presence of calcifications and gliosis in the brain tissue can also be confirmed on MRI or CT scans.
**Correct Answer: D. Neurocysticercosis**