Review Question - QID 109353

A 6-month-old girl presents with her mother to the pediatrician for a well-child visit. The patient is continuing to breastfeed well and she seems to enjoy the few solids that she has started eating. The child’s stools are becoming firmer, which she attributes to the introduction of solids. The child currently is having a harder time falling asleep at night. The patient’s mother is concerned that a lesion that has been present since birth is now enlarging but the lesion does not seem to bother the patient. Her temperature is 98.7°F (37.1°C), blood pressure is 68/56 mmHg, pulse is 138/min, and respirations are 24/min. On physical exam, the child appears well-developed and well-nourished. She has the physical exam finding seen in Figure A and this lesion blanches with pressure. Which of the following is the most likely cause of this patient’s physical exam finding?