Pituitary Adenoma

Pituitary adenomas are tumours that occur in the pituitary gland. Most are benign, though some can be invasive or carcinomas. They represent 10% to 25% of all intracranial neoplasms and have an estimated prevalence of 17% in the general population.

Classification

Adenomas are classified by size: those exceeding 10 mm are macroadenomas, while those smaller are microadenomas. Most adenomas are microadenomas and often remain undiagnosed, discovered incidentally during imaging studies.

Signs and Symptoms

Physical Symptoms

Hormone-secreting pituitary adenomas cause hyperpituitarism, with effects depending on the hormone type. The most common combination is growth hormone (GH) and prolactin, presenting as unexpected bone growth and lactation in both sexes.

Patients may present with visual field defects, typically bitemporal hemianopsia, due to compression of the optic chiasm. Lateral expansion can compress the abducens nerve, causing lateral rectus palsy. Symptoms of increased intracranial pressure and various headaches are common, especially in macroadenomas.

Psychiatric Symptoms

Pituitary disorders, including adenomas, can cause psychiatric symptoms such as depression, anxiety, apathy, emotional instability, irritability, and hostility.

Complications

Morphological facial changes caused by acromegaly; frontal bossing, enlarged nose, prognathism, maxillary widening with separation of teeth, and macroglossia

Complications include acromegaly, Cushing's syndrome, hyperpituitarism, pituitary apoplexy, and central diabetes insipidus. Acromegaly results from excess GH and can lead to severe disfigurement and premature death. Cushing's syndrome, often caused by corticotropic adenomas, results in hypercortisolism, causing symptoms like weight gain, hypertension, and psychiatric manifestations.

Risk Factors

Multiple Endocrine Neoplasia (MEN1)

Adenomas are a major feature of MEN1, affecting various endocrine glands and causing benign or malignant tumours. About 25% of MEN1 patients develop pituitary adenomas.

Carney Complex

Carney complex is an autosomal dominant condition causing myxomas, skin hyperpigmentation, and endocrine overactivity. Patients often develop GH-producing pituitary tumours.

Familial Isolated Pituitary Adenoma (FIPA)

FIPA is characterised by pituitary adenomas within families, with known genetic causes including mutations in the AIP gene and duplications in chromosome Xq26.3.

Mechanism

The pituitary gland controls most endocrine functions via hormone secretion. It is divided into the anterior lobe, which secretes six hormones, and the posterior lobe, which stores and releases vasopressin and oxytocin.

Diagnosis

Diagnosis involves assessing hormone levels and imaging studies like CT or MRI. Differential diagnosis includes conditions like pituitary tuberculoma. Adenomas are classified anatomically by size and histologically by hormone production.

Treatment

Prolactinomas

Prolactinomas are treated primarily with dopamine agonists like cabergoline or bromocriptine. Surgery is considered if medical therapy fails.

Thyrotropinomas

These are treated first with transsphenoidal surgery, followed by somatostatin receptor ligands if necessary.

Somatotrophic Adenomas

Primarily treated with surgery, followed by medical therapy such as somatostatin analogues or pegvisomant if residual tumour or symptoms persist.

Corticotropinomas

These require surgical intervention, with medication therapy and radiation therapy as secondary options.

Surgery and Radiation

Surgical options include trans-sphenoidal adenectomy. Radiation therapies like external beam radiation and proton therapy are also used, though they carry risks including hypopituitarism and increased mortality due to cerebrovascular disease.

Incidentalomas

Pituitary incidentalomas are often discovered incidentally during unrelated imaging studies. They require comprehensive evaluations, including visual field and endocrine testing, followed by regular monitoring if not surgically removed.

Ectopic Pituitary Adenomas

These rare tumours occur outside the sella turcica and are often found in regions like the sphenoid sinus or nasopharynx.

Metastases

Carcinomas metastasizing to the pituitary gland are uncommon, with breast and lung cancers being the most prevalent sources. Symptoms include diabetes insipidus, visual field defects, and anterior pituitary dysfunction.

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Self-assessment MCQs (single best answer)

What percentage of all intracranial neoplasms do pituitary adenomas represent?

What is the size threshold that distinguishes a pituitary macroadenoma from a microadenoma?

Which hormone combination is most commonly secreted by hormone-secreting pituitary adenomas?

Which visual defect is commonly associated with pituitary adenomas?

What genetic condition is characterised by pituitary adenomas and myxomas, skin hyperpigmentation, and endocrine overactivity?

Which imaging studies are commonly used in the diagnosis of pituitary adenomas?

What is the first-line treatment for prolactinomas?

Which surgical approach is most commonly used for the removal of pituitary adenomas?

What condition results from excess growth hormone and can lead to severe disfigurement and premature death?

Which of the following is a potential complication of radiation therapy for pituitary adenomas?