Clinically nonfunctioning
pituitary adenomas (CNFPAs) consist of several histological subtypes, including null cell
adenoma (NCA), silent gonadotroph cell
adenoma (SGA), silent
corticotroph adenoma (SCA), and other silent
adenomas (OSA) (i.e., GH, TSH, and
prolactin adenomas). To detect possible correlations between MRI findings and the subtypes, we retrospectively studied 390 consecutive patients with CNFPA who underwent surgery between 2008 and 2010. They were classified into three groups: NCA/SGA (313 cases), SCA (39 cases), and OSA (36 cases); in addition there were two unusual cases of plurihormonal
adenoma. Three MRI findings were less common in NCA/SGA than in the other groups (P < 0.0001): giant
adenoma (>40 mm), marked cavernous sinus invasion (Knosp grade 4), and lobulated configuration of the suprasellar
tumor. When these MRI findings were negative in patients older than 40 years old, 91.0% (212/233) were NCA/SGA. These MRI findings were frequently noted despite a low MIB-1 index in SCA. OSA showed a high MIB-1 index and a preponderance in younger patients. In conclusion, although SCA and OSA consisted of only 20% of CNFPAs, their frequency significantly increased when the
tumor was large, invasive, and lobulated, and the patient was younger than 40 years old.