1.Classification according to tumor size: microadenoma: tumor diameter <10mm; macroadenoma: tumor diameter 10-30mm; giant adenoma: tumor diameter >30mm 2.Classification according to cell chromophobia: based on hematoxylin and eosin staining ((HE staining)) light microscopic observation results, can be divided into eosinophilic cell tumor, basophilic cell tumor, suspicious cell tumor and mixed cell tumor. This classification has limited clinical guidance value and is now used sparingly. (1) Pituitary tumors with secretory function, accounting for 65% to 80% of pituitary tumors: Hormone-secreting tumors are the most complex pituitary tumors in terms of clinical manifestations, various treatment options and different clinical prognosis. Prolactin-secreting pituitary tumors (PRL tumors), the most common of the pituitary secretory adenomas, manifest mainly as amenorrhea, lactation, and infertility in most female patients and as hypogonadism in male patients. In non-selective autopsies, PRL microadenomas account for 23% to 27% of cases, most of which were asymptomatic before birth. Growth hormone-secreting pituitary tumors (GH tumors) are more common in young and middle-aged adults. The main manifestation is gigantism or acromegaly. Adrenocorticotropic hormone-secreting pituitary tumor (ACTH tumor), which mainly manifests as centripetal obesity, full-moon face, acne, hirsutism, and purple lines. Thyrotropic hormone-secreting pituitary tumor (TSH tumor). The main symptoms of hypermetabolism are feverishness, excessive sweating, weight loss, and atrial fibrillation with heartburn. Other types of pituitary tumors are FSH and LH. The main clinical manifestations are menstrual disorders and infertility in women and male hypogonadism and infertility in men. Mixed tumors: Hormone-secreting tumors can occur alone or be mixed tumors with increased secretion of two or more hormones, and the clinical manifestations have corresponding mixed symptoms. Unclassified adenoma. (2) Non-functional adenoma: It accounts for 20% to 35% of pituitary tumors, and the serum hormone concentration does not increase when measured by conventional methods. Non-functioning adenoma is the only adenoma that develops in old age, especially in males with an increasing trend. (3) Classification by biological behavior: Invasive pituitary adenoma, which breaks through its envelope and invades adjacent structures such as dura mater, optic nerve and bone, is a tumor between benign pituitary adenoma and malignant pituitary carcinoma, and its histological pattern is benign but its biological characteristics are malignant. The incidence of necrosis, stroke, and cystic degeneration is significantly higher in invasive pituitary adenomas than in non-invasive pituitary adenomas. Non-invasive pituitary adenomas.