Review Question - QID 210650

A 17-year-old girl presents to her primary care doctor with knee pain. She reports a 6-month history of mild progressive pain on the proximal posterior portion of her right knee that does not change with position or activity. She has tried taking ibuprofen and naproxen without any significant change in her pain level. She plays volleyball for her high school. She has a history of mild intermittent asthma and uses an albuterol inhaler as needed. Her mother has a history of adolescent idiopathic scoliosis requiring spinal fusion at the age of 13 years old. Physical examination reveals a healthy, well-appearing girl in no acute distress. There is mild tenderness to palpation along the proximal posterior knee. A lateral radiograph of the affected knee is shown in Figure A. The physician estimates that the lesion is approximately 3 cm in diameter. A biopsy of this patient's lesion would most likely reveal which of the following findings?