Pituitary adenoma is a benign tumor originating from the anterior pituitary gland, accounting for approximately 10%–15% of intracranial tumors, with an autopsy detection rate as high as 10%. The typical age of onset is between 30 and 50 years, and the incidence is higher in females than in males. Most pituitary adenomas are benign, while pituitary carcinomas are rare (approximately 0.1%–0.2%). Based on whether the tumor invades the cavernous sinus, nerves, brain tissue, or sellar bone structures, pituitary adenomas can be classified as invasive or non-invasive.
Clinical Classification
Pituitary adenomas are typically divided into two categories based on clinical symptoms: functional (or secretory, accounting for 65%–85%) and non-functional (15%–35%). Functional pituitary adenomas are further classified based on the hormones they secrete:
- Prolactinomas (PRL cell adenomas): The most common type, often leading to Forbes-Albright syndrome (amenorrhea-galactorrhea syndrome) in women or sexual dysfunction in men.
- Growth hormone-secreting adenomas (GH cell adenomas): Responsible for acromegaly in adults and gigantism in children or adolescents.
- Adrenocorticotropic hormone-secreting adenomas (ACTH cell adenomas): May cause Cushing's disease.
- Thyrotropin-secreting adenomas (TSH cell adenomas): A rare type that can lead to hyperthyroidism.
Non-functional pituitary adenomas, such as gonadotroph adenomas and null-cell adenomas, generally do not present with symptoms of endocrine hyperfunction.
Clinical Presentation
Pituitary adenomas often lead to endocrine-related symptoms due to hyperfunction or hypofunction of the pituitary gland or its target organs. Larger pituitary adenomas may cause mass effect symptoms, such as visual impairment or visual field defects caused by compression of the optic nerve, and headaches due to the tumor stretching the dura mater. Hemorrhage or necrosis within the tumor can lead to pituitary apoplexy, resulting in sudden-onset headache and rapidly worsening vision.
Imaging Studies
MRI is the primary diagnostic modality for pituitary adenomas, with dynamic contrast-enhanced imaging of the sellar region aiding in the detection of microadenomas. CT imaging may show an enlarged sella turcica.
Pituitary and Target Gland Function Tests
Tests of pituitary function include assessments of PRL, GH, insulin-like growth factor-1 (IGF-1), TSH, follicle-stimulating hormone/luteinizing hormone (FSH/LH), and ACTH. Target gland function tests evaluate thyroid function, adrenal cortical function, and gonadal function. A clinical diagnosis of pituitary adenoma is typically made based on a combination of these laboratory results and imaging studies.
Treatment
Surgical Treatment
Surgery is the preferred treatment for most pituitary adenomas. Indications for surgery include:
- Large non-secreting tumors causing mass effect symptoms.
- Pituitary apoplexy.
- Prolactinomas unresponsive to bromocriptine treatment or in cases where medication side effects are intolerable.
- GH-secreting adenomas.
- ACTH-secreting adenomas.
- Pituitary adenomas associated with cerebrospinal fluid leakage.
Most pituitary adenomas can be removed through minimally invasive transnasal-transsphenoidal neuroendoscopic surgery.
Medical Treatment
Medical therapy is the first-line treatment for prolactinomas. Bromocriptine can reduce tumor size and PRL levels in 90% of cases. For patients with pituitary or target gland insufficiency, replacement therapy is based on the specific hormonal deficiency and may include medications such as prednisone, thyroxine, testosterone, or female hormones.
Radiotherapy
Radiotherapy is typically used for tumors that cannot be surgically removed. Techniques include Gamma Knife radiosurgery or conventional radiation therapy. However, radiotherapy carries a risk of inducing pituitary insufficiency.