## Core Concept
The "onion peel" appearance on radiographs is a characteristic feature associated with certain bone lesions. It is caused by layers of reactive bone formation around a lesion, resembling the layers of an onion. This appearance is typically seen in benign bone lesions.

## Why the Correct Answer is Right
The correct answer, Ewing's sarcoma, does not typically present with an "onion peel" appearance. Ewing's sarcoma is a malignant bone tumor that often presents with a "moth-eaten" or permeative appearance on radiographs due to its aggressive nature and lack of significant reactive bone formation.

## Why Each Wrong Option is Incorrect
* **Option A: Osteosarcoma** - While osteosarcoma can have a variety of radiographic appearances, it is not typically associated with the "onion peel" appearance. However, this option might seem confusing because osteosarcoma can cause bone formation.
* **Option B: Fibrous dysplasia** - This condition can cause a range of radiographic appearances but is not characteristically associated with the "onion peel" sign.
* **Option C: Non-ossifying fibroma** - This benign bone lesion can present with a characteristic "onion peel" or layered appearance due to periosteal reaction.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the "onion peel" appearance is most commonly associated with benign bone lesions that cause a periosteal reaction, such as **non-ossifying fibroma** or **osteomyelitis**. Ewing's sarcoma, being a malignant tumor, tends to have a more aggressive and permeative appearance on radiographs.

## Correct Answer: D. Ewing's sarcoma.