A 9-year-old girl is admitted to the emergency department with a painful swelling behind her ear. An MRI examination reveals mastoiditis. Which of the following structures is most likely to be affected by the inflammation?

(a) Source: GAS 907, 909; GA 474-475 Mastoiditis is an infection of the air cells within the mastoid process of the temporal bone, often caused by untreated acute otitis media. A known complication of mastoiditis is inflammation of the transverse sinus. Necrosis of the bone due to untreated infection will often affect the transverse sinus. The petrous part of the temporal bone is unlikely to experience inflammation. Infection in the middle ear is usually the preceding event to mastoiditis rather than occurring as a result of it. The occipital sinus is located far posteriorly to the mastoid process and is unlikely to be affected. Because of its position, the internal carotid artery will not be affected by this inflammation.