Pituitary tumors are abnormal growths that develop in the pituitary gland — a small, pea-sized gland at the base of the brain that controls many of the body's hormonal functions. The vast majority are benign (non-cancerous) and slow-growing, but they can cause significant problems by disrupting hormone production or compressing surrounding structures, including the optic nerves.
Pituitary tumors are among the most common intracranial tumors and are frequently discovered incidentally on MRI performed for other reasons such as headaches. Large tumors that compress the optic chiasm can cause visual symptoms that may initially be attributed to other causes, and those that disrupt normal pituitary function can mimic a wide range of systemic conditions. They are distinct from but sometimes confused with other sellar region lesions including arachnoid cysts and the related condition of partially empty sella.
Causes
Sporadic genetic mutations
Most pituitary tumors arise from spontaneous somatic mutations within pituitary cells that cause unregulated clonal growth. The exact trigger is not fully understood in most cases. The large majority of pituitary tumors are sporadic with no hereditary link and occur in isolation.
Inherited genetic conditions
A small but important minority of pituitary tumors occur as part of inherited syndromes. Multiple Endocrine Neoplasia type 1 (MEN1) causes tumors in the pituitary, parathyroid, and pancreas. Familial Isolated Pituitary Adenoma (FIPA), associated with AIP gene mutations, causes early-onset, often large pituitary tumors — particularly growth hormone-secreting tumors — in affected families. Carney complex and McCune-Albright syndrome are additional rare associations.
Symptoms
Symptoms arise from two distinct mechanisms: hormonal overproduction or underproduction, and mass effect on surrounding structures.
Hormone-secreting tumors cause specific endocrine syndromes: excess prolactin (prolactinoma) causes irregular menstruation, infertility, and inappropriate milk production (galactorrhea); excess growth hormone causes acromegaly in adults (enlarged hands, feet, and facial features) or gigantism in children; excess ACTH causes Cushing's disease (weight gain, hypertension, stretch marks, and easy bruising). These hormonal syndromes often develop slowly and may go unrecognized for years before diagnosis.
Non-functioning tumors grow silently until they compress adjacent structures. Compression of the optic chiasm — which sits directly above the pituitary — produces the characteristic bitemporal hemianopsia (loss of peripheral vision in both eyes, creating tunnel vision). Compression of the normal pituitary tissue causes hypopituitarism with fatigue, sexual dysfunction, and cold intolerance. Headaches are common with larger tumors.
Diagnosis
Comprehensive hormonal blood and urine testing assesses pituitary function and identifies hormonal excess or deficiency — including prolactin, IGF-1 (for growth hormone), morning cortisol and 24-hour urinary free cortisol (for ACTH excess), and thyroid and gonadal hormone panels. A formal visual field examination detects optic chiasm compression even before the patient notices visual symptoms.
MRI of the pituitary with gadolinium contrast is the definitive imaging study. A dedicated pituitary protocol with thin-slice coronal and sagittal sequences through the sella turcica provides the detail needed to detect even small microadenomas (under 5mm), delineate tumor margins, and assess for suprasellar extension toward the optic chiasm, lateral invasion of the cavernous sinuses (which affects surgical resectability), and involvement of the pituitary stalk. Dynamic contrast-enhanced sequences exploit the fact that normal pituitary tissue enhances earlier than adenoma tissue, improving detection of small tumors. Incidentally discovered small pituitary lesions — termed "incidentalomas" — are common on brain MRI and require hormonal evaluation to determine whether they are functioning.
Tumor Classification
Pituitary tumors are classified by size and hormonal activity:
- Microadenoma: Less than 10mm — often discovered incidentally or through hormonal symptoms. Surgical cure rates are high for functioning microadenomas.
- Macroadenoma: 10mm or larger — more likely to cause visual symptoms and hypopituitarism from mass effect on adjacent structures.
- Functioning: Actively secretes hormones, causing specific endocrine syndromes. Prolactinomas are the most common type; GH- and ACTH-secreting tumors are less common but clinically significant.
- Non-functioning: Does not secrete active hormones — symptoms arise primarily from mass effect. These are the most common macroadenomas.
Treatments
Treatment depends on tumor type, size, hormonal activity, and the presence of visual or neurological compromise. Many small, non-functioning tumors with no symptoms or visual compromise can be safely monitored with periodic MRI surveillance and hormonal testing.
Medical therapy:
Prolactinomas — the most common functioning pituitary tumor — are treated first with dopamine agonist medications (cabergoline or bromocriptine), which shrink the tumor and normalize prolactin levels in the majority of patients, frequently avoiding surgery altogether. Somatostatin analogues (octreotide, lanreotide) are used for growth hormone-secreting tumors when surgery is incomplete or not feasible.
Surgery:
Transsphenoidal surgery — performed endoscopically through the nose and sphenoid sinus — is the primary surgical approach for most pituitary tumors. It allows direct tumor removal without craniotomy, with short recovery and high success rates, particularly for microadenomas and non-functioning macroadenomas. For tumors with extensive suprasellar or lateral extension that cannot be reached transsphenoidally, a craniotomy may be required. Surgical cure rates vary significantly by tumor type and size.
Radiation therapy:
Stereotactic radiosurgery (Gamma Knife or CyberKnife) targets residual or recurrent tumor following surgery with high precision. Conventional fractionated radiotherapy is used for larger, more diffuse residual disease. Hormonal normalization after radiation occurs slowly over months to years, so medical therapy is often continued in the interim.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Brain MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.