Review Question - QID 210524

A 6-month-old boy is brought to the pediatrician for multiple swellings on his scalp. His mother reports that she first noticed 3 softened and swollen areas over the child's scalp 2 months ago that have grown in size. The child is also urinating more frequently than usual. He was born by cesarean section at 39 weeks gestation. The mother had appropriate prenatal care. She has a history of gastroesophageal reflux disease for which she takes omeprazole. Her family history is unknown as she was adopted at a young age. The boy's temperature is 99°F (37.2°C), blood pressure is 100/60 mmHg, pulse is 110/min, and respirations are 20/min. On exam, he has 3 areas of soft tissue swelling on his skull that are tender to palpation. Moderate asymmetric exophthalmos is noted. A water deprivation test is performed which demonstrates a urine specific gravity of 1.005. The urine specific gravity rises with desmopression administration. A head computerized tomography (CT) scan is performed which demonstrates multifocal lytic calvarial lesions. A biopsy of one of the lesions is performed. Analysis of the biopsy would most likely reveal which of the following findings?