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  • Updated 01.28.2021
  • Released 04.18.1994
  • Expires For CME 01.28.2024

Pituitary adenoma

Introduction

Overview

Pituitary adenomas represent 9% of intracranial neoplasms. Typical presenting manifestations include amenorrhea, infertility, visual field abnormalities, and headache. Diagnosis is often made with brain MRI, visual field testing, and serum hormone assay. Prolactinoma, the most common type of pituitary adenoma, usually responds to therapy with a dopamine agonist such as bromocriptine or cabergoline. Transsphenoidal surgery, particularly the endoscopic approach, has evolved to become the preferred approach to refractory prolactinoma, other functioning adenomas, and macroadenomas. Stereotactic radiosurgery is emerging as a second-line option.

Key points

• Pituitary adenomas represent 9% of intracranial neoplasms.

• Typical presenting manifestations include amenorrhea, infertility, visual field abnormalities, and headache.

• Diagnosis is often made with brain MRI, visual field testing, and serum hormone assay.

• Prolactinoma, the most common type of pituitary adenoma, usually responds to therapy with a dopamine agonist such as bromocriptine or cabergoline.

• Rare refractory cases, large tumors, and pituitary adenomas that secrete other hormones are treated with transsphenoidal surgical resection first-line.

• Stereotactic radiosurgery has largely replaced external-beam radiotherapy as a second-line treatment option.

Historical note and terminology

The pathologic classification of pituitary adenomas has changed considerably over time and has been influenced by advances in physiology, molecular biology, and genetics. The initial attempts at classification relied on hematoxylin and eosin staining of resected tissue. They were categorized as acidophilic, basophilic, or chromophobic. This scheme, however, failed to account for clinical manifestations or hormone secretion. Further attempt at a functional classification of these tumors utilized immunoperoxidase staining techniques to identify the hormones within adenoma cells. This form of analysis proves that acidophil and chromophobe cells may produce the same hormones (prolactin, growth hormone, or thyroid-stimulating hormone), whereas basophil cells produce any of the other anterior pituitary hormones (adrenocorticotropic hormone, beta-lipotropin, luteinizing hormone, or follicle-stimulating hormone). A more recent classification scheme, based on the cell lineage delineation, uses a combination of immunohistochemical biomarkers which includes pituitary transcription factors, hormones and low molecular weight keratins (03). This scheme not only identifies hormone producing tumors but subclassifies the nonfunctioning adenomas, with the identification of the hormone and transcription factor negative tumor named null cell adenoma, which has distinct characteristics from the most common gonadotroph adenomas (04). Of the hormone-secreting adenomas, 60% to 70% secrete prolactin, 10% to 15% secrete growth hormone, a small number secrete adrenocorticotropic hormone, and rare tumors secrete gonadotropins or thyroid-stimulating hormone (57).

The classification of neoplasms of the anterior adenohypophyseal cells by malignancy has not been clinically useful. Although pituitary adenocarcinoma characterized by metastases is extremely uncommon, these predominantly benign tumors have varying aggressive behavior with capacities for invading surrounding tissues (02). The attempt at a clear definition of this heterogenous group of tumors has led to the drop of the term atypical adenomas in the 2016 WHO revision of the classification of pituitary adenomas, such that proliferative and invasive markers will be used to define these high risk adenomas. There has also been a recommendation of the use of the term pituitary neuroendocrine tumors rather than adenomas (02).

Tumor size is frequently used to categorize pituitary tumors as microadenomas (less than 10 mm in diameter) and macroadenomas (10 mm or greater in diameter). Tumors greater than 30 mm along any plane are regarded as large adenomas, whereas tumors greater than 40 mm or with a volume of 10 cm2 or more are regarded as huge adenomas. The differing sizes portend different challenges. This radiologically based classification continue to be relevant particularly to the neurosurgeon in the era of evolving high-resolution neuroimaging.

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