**Core Concept:** Osteoid osteoma is a benign bone tumor, typically smaller than 1 cm in diameter, characterized by a central nidus and surrounded by reactive bone formation. It usually presents with nighttime pain, relieved by salicylic acid.

**Why the Correct Answer is Right:** Osteoid osteomas are clinically characterized by nocturnal pain, which is relieved by non-steroidal anti-inflammatory drugs (NSAIDs) like salicylic acid. This is because the nidus, a small, central area of cartilage or bone, stimulates the production of prostaglandins, leading to pain. Salicylic acid works by inhibiting the cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis and alleviating the pain.

**Why Each Wrong Option is Incorrect:**

A. False: Osteoid osteomas do involve a central nidus and reactive bone formation, making this statement incorrect.
B. False: Pain is not specifically relieved by salicylic acid, which is a misconception. While salicylic acid does alleviate pain, it is not the primary treatment for osteoid osteomas.
C. False: Pain can occur at any time of day, not exclusively at night. Although nocturnal pain is common, it is not a universal feature.
D. False: Osteoid osteomas are benign bone tumors, not malignant lesions.

**Clinical Pearl:** Pain relief by salicylic acid is a crucial aspect of diagnosing osteoid osteoma, as it points towards the nidus-induced prostaglandin synthesis. This information is essential for making an accurate diagnosis and guiding treatment decisions.

**Correct Answer:** D. Osteoid osteomas are benign bone tumors, not malignant lesions.