**Question:** A 15-year-old boy presents with a mass in the distal femur. X-ray from the lesion shows features of Codman's triangle and Sunray appearance. The diagnosis is:

A. Osteosarcoma
B. Ewing's sarcoma
C. Fibrosarcoma
D. Chondrosarcoma

**Core Concept:**

Codman's triangle and Sunray appearance are specific radiological findings in bone lesions, which help in differentiating between various bone sarcomas. Codman's triangle is a characteristic appearance of an osteosarcoma. It is characterized by a "triangle" shape formed by the tumor, the greater trochanter, and the tip of the patella. Sunray appearance refers to the radiopaque "rays" emanating from the tumor periphery, which is seen in chondrosarcoma.

**Why the Correct Answer is Right:**

The correct answer is D. Chondrosarcoma, as it is the type of sarcoma that exhibits both Codman's triangle and Sunray appearance on X-rays. Osteosarcoma (option A) usually presents with a "punched-out" lesion, while Ewing's sarcoma (option B) typically shows a diffuse infiltrative pattern. Fibrosarcoma (option C) generally presents with a well-defined, sclerotic border on X-rays.

**Why Each Wrong Option is Incorrect:**

A. Osteosarcoma usually presents with a "punched-out" lesion, which is not observed in this case.
B. Ewing's sarcoma shows a diffuse infiltrative pattern on X-rays, not seen in this case as it has specific radiological findings like Codman's triangle and Sunray appearance.
C. Fibrosarcoma has a well-defined, sclerotic border on X-rays, which is not seen in this case as it exhibits specific radiological findings like Codman's triangle and Sunray appearance.

**Clinical Pearl:**

In a 15-year-old boy presenting with a mass in the distal femur, radiological findings like Codman's triangle and Sunray appearance on X-rays strongly suggest a chondrosarcoma. These features help differentiate it from other types of bone sarcomas, which usually exhibit different radiological patterns. Clinical correlation and imaging findings are crucial in arriving at a definitive diagnosis in such cases, as it can aid in selecting the appropriate treatment and prognosis.