title: The World Health Organization classification of adenohypophysial neoplasms. A proposed five-tier scheme.
abstract: BACKGROUND
  Although numerous attempts have been made, the classification of pituitary neoplasms remains controversial.
  
  
  METHODS
  The present proposal is based on correlative clinical and pathologic (histologic, immunocytochemical, and electron microscopic) studies of more than 8000 surgically removed human pituitary tumors.
  
  
  RESULTS
  Anterior pituitary tumors have been variously classified on the basis of their clinical presentation, biochemical findings, histology (growth pattern, tinctorial characteristics), proliferation indices, immunocytochemical profile, and ultrastructural features. Herein we propose a five-tier classification, clinicopathologic in nature, which focuses on endocrine activity, imaging, operative findings, histology, immunocytochemistry, and ultrastructure. The integration of these five complementary approaches into what is fundamentally a pathologic classification is as practical as it is novel. Its importance lies in the fact that the collected data provide valuable information to the clinical endocrinologist, neurosurgeon, and oncologist involved in the assessment of a tumor's biologic behavior, growth potential, therapeutic responsiveness, and prognosis. Due to financial restraints, lack of facilities, and unavailability of well trained personnel, we realize that at present the five approaches cannot be fully implemented in all institutions. Nonetheless, clinical and biochemical data, imaging, and operative findings, as well as basic histologic parameters are generally readily available. Collectively they are indispensable in establishing the correct diagnosis and in directing patient management. Conversely, the cost-effectiveness of immunocytochemistry and electron microscopy is debatable in that their performance and interpretation requires time, financial resources, and expertise. Nonetheless, it should be clear that any correlation between endocrine activity, growth potential, morphologic features, immunocytochemical profile, and ultrastructural features provides greater insight into the pathobiology of adenohypophysial tumors than is gained by routine histology alone. Thus we feel justified in including immunocytochemical and ultrastructural investigation of pituitary tumors in a modern classification. At present, more sophisticated molecular biologic methods represent investigative tools that play no significant role in the classification.
  
  
  CONCLUSIONS
  A five-tier classification of adenohypophysial neoplasms based on clinical and biochemical results, imaging, operative findings, histology, immunocytochemistry, and electron microscopy is proposed. It is recommended to the World Health Organization for acceptance.
authors.affiliation: Department of Pathology, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Kovacs
authors.forename: B W
authors.initials: BW
authors.lastname: Scheithauer
authors.forename: E
authors.initials: E
authors.lastname: Horvath
authors.forename: R V
authors.initials: RV
authors.lastname: Lloyd
mesh_terms: D006801:Humans; D010903:Pituitary Gland, Anterior; D010911:Pituitary Neoplasms / Q000737:chemistry / Q000145:classification* / Q000473:pathology / Q000648:ultrastructure; D014944:World Health Organization