**Core Concept**
The patient's symptoms, particularly the new onset of headaches, jaw pain, and transient visual loss, suggest a diagnosis of Giant Cell Arteritis (GCA), an inflammatory condition of the large and medium-sized arteries, often involving the temporal artery.

**Why the Correct Answer is Right**
Giant Cell Arteritis is characterized by granulomatous inflammation of the arterial wall, leading to stenosis or occlusion of the affected artery. The biopsy would likely show a mixture of lymphocytes, plasma cells, and multinucleated giant cells, which are a hallmark of the disease. The inflammation can lead to damage to the temporal artery, resulting in symptoms such as jaw claudication and visual disturbances. The initiation of corticosteroids, such as prednisone, is a common treatment approach to reduce inflammation and prevent further complications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because GCA typically involves the large and medium-sized arteries, not the small arteries or arterioles.
**Option B:** This option is incorrect because while vasculitis can involve a range of blood vessels, the specific involvement of the temporal artery and the presence of giant cells are characteristic of GCA.
**Option C:** This option is incorrect because while there may be some overlap in symptoms, the presence of giant cells and the specific involvement of the temporal artery are more suggestive of GCA.
**Option D:** This option is incorrect because while inflammation can be seen in many conditions, the presence of multinucleated giant cells and the specific involvement of the temporal artery are more characteristic of GCA.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to remember that GCA often presents with jaw claudication (pain in the jaw when chewing) and visual disturbances, particularly transient vision loss, which can be a "red flag" for this diagnosis.

**Correct Answer:** C. A mixture of lymphocytes, plasma cells, and multinucleated giant cells.