A 2-month-old girl is brought to the office by her father for a well child visit. He is concerned about right-sided flattening of the back of his child's head that he noticed 3 weeks ago. The patient also seems to prefer turning her head to the right while tilting her head to the left. She was born full-term via Cesarean delivery for breech positioning. She is breastfed exclusively and receives vitamin D supplementation. She is placed to sleep on her back as instructed, and her parents have not yet started "tummy time" since they are nervous she may fall asleep. The patient spits up frequently and appears most comfortable when held upright after feeding. Physical examination reveals flattening of the right occiput with anterior displacement of the right ear and forehead. Her head is turned to the right, and there is a palpable, firm mass that does not transilluminate in the inferior portion of the left side of the neck. The patient's hips are stable with no clicks or clunks.
Which of the following is the most likely underlying cause of this patient's presentation?
A. Congenital lymphatic malformation
B. Fracture of the clavicle
C. Premature closure of a cranial suture
D. Postural deformity of the neck
E. Tumor of posterior fossa
