Pituitary Magnetic Resonance Imaging for Sellar and Parasellar Masses: Ten-Year Experience in 2598 Patients

Pituitary tumors account for up to 15% of all intracranial masses (1), and pituitary adenomas are reported to account for 90% of sellar and parsellar lesions (2, 3). Clinically active pituitary adenomas occur at a prevalence of 1:1064 to 1:1288 to the general population (4, 5). Other sellar lesions include nonneoplastic cystic lesions, germ cell tumors, gliomas, lymphomas, meningiomas, metastatic tumors, vascular lesions, granulomatous and inflammatory lesions, and infections including bacterial abscesses as well as pituitary hyperplasia (2, 3, 6–8). Of the nonadenomatous masses reported in surgical series, Rathke's cleft cyst is the most commonly encountered (23%), metastatic cancer accounts for 12% of cases, and pituitary lymphoma occurred in one of 83 nonpituitary adenomatous masses observed (2). Because only single case reports of rare nonadenomatous lesions are usually published, it is difficult to assess the true prevalence of such lesions. With advancements in imaging occurring over the past decade as well as the availability of refined endocrine testing techniques, pituitary masses are diagnosed with increased frequency. Increased incidence of pituitary adenomas observed over the second half of an 18-yr study period was due to a 3-fold increased frequency of incidentally discovered pituitary adenomas (9). These pituitary incidentalomas are discovered on computed tomography (CT), or magnetic resonance imaging (MRI) performed for evaluation of unrelated disorders such as head trauma or cancer staging or because of nonspecific symptoms such as headache. MRI scans of clinically normal subjects in the general population have visualized silent pituitary tumors sized 3 mm or greater in diameter in approximately 10% of subjects (10). CT scans of the sellar area in subjects examined for reasons unrelated to pituitary disease revealed sellar lesions sized 3 mm or greater in diameter in 3.7–20% of the subjects (11–13). Pituitary adenomas occur in 1.5–27% of individuals without prior suspected pituitary disease in autopsy series (14). The evaluation and treatment of pituitary incidentalomas are determined by their size and presence of hypersecretory syndromes and/or compressive central symptoms (15, 16). However, further evaluation of these small incidentalomas (<10 mm) may not be cost effective, especially if they are asymptomatic (17). Specific anatomical landmarks of the sella turcica and the surrounding parasellar region may determine presenting symptoms of masses arising in this region. Nonadenomatous parasellar lesions may present with hypopituitarism, or mass effect with compressive symptoms including headache or visual symptoms, especially when endocrinological evaluation does not identify a hypersecretory syndrome (18). Precise imaging with high contrast and topographic resolution is critical in visualizing this small-volume area to determine both location and specific characteristics of masses, which are important for diagnosis (8, 19, 20). To date, two surgical case series have reported the prevalence of nonadenomatous sellar and parasellar masses (2, 3). However, the utility of MRI imaging as a diagnostic tool for screening and diagnosis of sellar masses in a large patient population has not been reported. Pituitary MRI identifies sellar tumors and pituitary masses and offers high contrast and multiplanar, thin pituitary cuts enabling evaluation of small soft tissue changes (20). MRI also allows accurate visualization of mass effects on neighboring soft tissues. The objective of this study was to identify the frequency and diagnosis of pituitary masses in an identified patient population undergoing sellar imaging because diagnoses of pituitary-related masses are not all ultimately made by pathological analysis of surgical specimens. We also sought to identify indications for pituitary imaging and the prevalence of incidentalomas, hypopituitarism, and neuroophthalmic symptoms associated with nonadenomatous lesions, as identified by MRI.