Ans. B. Intrauterine malposition
Explanation: This infant has congenital torticollis, which typically develops by 2 to 4 weeks of age. It is most commonly caused by malposition of the head in utero or birth trauma (eg, breech delivery), both of which can result in sternocleidomastoid muscle (SCM} injury and fibrosis. Rarely, it can be due to cervical spine deformities (eg, cervical hemivertebrae, C1-C2 subluxation, or cervical vertebral fusion}. Children with congenital torticollis may have additional musculoskeletal anomalies, including hip dysplasia, metatarsus adductus, and talipes equinovarus. The diagnosis of congenital torticollis is made clinically. On physical examination, the head is tilted toward the affected side with the chin pointed away from the contracture. A soft-tissue mass may be palpable in the inferior one-third of the affected SCM. Plagiocephaly and facial asymmetry may be seen in severe cases. Radiographs of the cervical spine should be performed to rule out associated vertebral abnormalities.