A patient shows symptoms typical of a viral infection following the development of a mass in the pituitary gland. What is the most probable initial resource for determining the nature of her condition?

In the scenario presented, a patient exhibits symptoms indicative of a viral infection alongside the presence of a mass in the pituitary gland. The most appropriate initial resource for determining the nature of her condition is imaging studies.

Imaging studies, such as MRI or CT scans, are essential for visualizing the mass in the pituitary gland. They help identify the size, shape, and location of the mass, and can also reveal whether it is compressing surrounding structures such as nearby blood vessels or brain tissue. This initial step is crucial in differentiating between various types of pituitary pathologies, including tumors, cysts, or other abnormalities, some of which may be associated with infectious processes.

While other tests like a complete blood count or thyroid function panel may provide helpful information regarding the patient's generalized health and hormonal status, they do not offer direct insight into the physical characteristics of the pituitary mass. Biopsies, although definitive for determining the cellular nature of a mass, are typically not the first-line investigation due to their invasive nature and the need for imaging guidance to obtain an appropriate sample. Thus, imaging studies are fundamental to the initial assessment and diagnosis in cases involving masses in the pituitary gland.