Osteochondroma

Grossly, the lesion may be flat, pedunculated, or cauliflower-shaped. The cortex and periosteum covering the tumor are continuous with that of the underlying bone. The lesion has a smooth cartilage cap (seen at the top of this image) which is usually 2 to 3 mm thick. If the cap is irregular or excessively thick, especially in an adult, one has to exclude secondary chondrosarcoma. Image courtesy of Dr. Jean-Christophe Fournet, Paris, France; humpath.com; Used with permission