Pituitary tumors are tumors that occur in the pituitary gland, also commonly referred to as pituitary adenomas, and are one of the common neuroendocrine tumors, accounting for approximately 10-15% of central nervous system tumors. The vast majority of pituitary adenomas are benign tumors. And according to the different hormone secretion, the types of pituitary adenoma are also different.
Functional classification: Functional pituitary tumors and non-functional pituitary tumors. Functional pituitary tumors are further classified into PRL tumors, GH tumors, ACTH tumors, TSH tumors, LH/FSH tumors and mixed tumors and unclassified adenomas according to the hormones secreted by tumor cells. This classification method is most commonly used in clinical practice.
2.Tumor size classification: according to tumor diameter, <1 cm is called microadenoma; 1~100px is macroadenoma; >100px is giant adenoma.
3.Biological behavior classification: it is divided into invasive pituitary adenoma and non-invasive pituitary adenoma. Invasive pituitary adenoma is defined as “pituitary adenoma that grows through its envelope and invades the dura mater, optic nerve, bone and other adjacent structures. It is a tumor between benign pituitary adenoma and malignant pituitary adenoma, with a benign histologic pattern but a malignant biology. The clinical presentation and prognosis of invasive and non-invasive pituitary adenomas are significantly different. The incidence of necrosis, stroke, and cystic transformation is significantly higher in aggressive pituitary adenomas than in non-invasive pituitary adenomas. One study showed that 70% of pituitary strokes occur in invasive pituitary adenomas. Invasive pituitary adenoma has a high recurrence rate after surgery because it is difficult to cut cleanly and the proliferation index is high, and the tumor residual tissue grows quickly.
4. WHO classification criteria: After studying 8000 cases of surgically resected pituitary adenomas, it is believed that the classification method of pituitary adenomas should include 5 aspects, namely clinical manifestations and hormone levels in blood, neuroimaging and intraoperative findings, performance of tumor sections under light microscopy, immunohistochemical typing and ultrastructural features of tumor cells under electron microscopy. Each of these classification criteria is valuable in determining the diagnosis and analyzing the biological manifestations of the tumor, and has been recommended as the World Health Organization classification criteria for pituitary adenomas. However, the classification is complex and has not been widely promoted in clinical work.
5. Classification according to the staining properties of cytoplasm: Based on the light microscopic observation results of hematoxylin and eosin staining ((HE staining)), pituitary adenomas can be classified into four categories: eosinophilic, basophilic, suspicious and mixed. In the past, eosinophilic adenomas were thought to present as acromegaly or gigantism, basophilic adenomas were associated with Cushing’s syndrome, and chromophobic adenomas had no obvious clinical endocrine symptoms. In fact, the classification based on the chromophobic characteristics of pituitary adenoma cells alone does not reflect the endocrine characteristics of pituitary adenoma and the relationship between clinical and pathology.
6.Classification according to tissue structure: that is, according to the arrangement of tumor cells and the number of blood vessels, they are classified into diffuse, sinus-like, papillary and mixed types.