= benign slow-growing neoplasm arising from adenohypophysis (= anterior lobe); most common tumor of adenohypophysis
Prevalence: 5–10–18% of all intracranial neoplasms; <3% of patients have underlying MEN 1
- pituitary hyperfunction / hypofunction / visual field defect
Plain film (UNRELIABLE):
- enlargement of sella + sloping of sella floor
- erosion of anterior + posterior clinoid processes
- erosion of dorsum sellae
- calcification in <10%
- may present with mass in nasopharynx
NECT:
- upward convexity of gland
- increased height >10 mm
- deviation of pituitary stalk (nonspecific + unreliable)
- erosion of floor of sella with adenoma >5 mm
- gland asymmetry
CECT (thin section SAG + COR with dynamic bolus injection):
- focal hypodensity (most specific for adenoma) before + after IV contrast administration
- “pituitary tuft” sign = displacement / compression of visualized capillary bed (sinusoids of mid-anterior lobe) of pituitary by adenoma
MR (thin-section SAG + COR with small field of view):
- Highest sensitivity on coronal nonenhanced T1WI (70%) + 3-D FLASH sequence (69%) + combination of both (90%)
- ⅓of lesions are missed with enhancement
- ⅓of lesions are missed without enhancement
- focus of low signal intensity on T1WI
- focus of high-signal intensity on T2WI
- focal hypointensity within normally enhancing gland
DDx: simple pituitary cyst (= Rathke cleft cyst)
◊Adenoma may secrete multiple hormones!
- PROLACTINOMA (30%)
= most common of pituitary adenomas; ~ 50% of all cranial tumors at autopsy; M <<F- prolactin levels do not closely correlate with tumor size
- Any mass compressing hypothalamus / pituitary stalk diminishes the tonic inhibitory effect of dopaminergic factors, which originate there → hyperprolactinemia
Female:- Age: 15–44 years (during childbearing age)
- infertility, amenorrhea, galactorrhea
- elevated prolactin levels (normal <20 ng/mL)
- >75% of patients with serum prolactin levels >200 ng/mL will show a pituitary tumor!
Male:- headache, visual disturbance
- impotence + decreased libido
- characteristic lateral location / anteriorly / inferiorly; variable in size
Rx: bromocriptine - CORTICOTROPHIC ADENOMA (14%)
Function: ACTH-secreting tumor
Age: 30–40 years; M÷F = 1÷3- Cushing disease
- central location; posterior lobe; usually <5 mm in size
- blood sampling of inferior petrosal sinuses (95% diagnostic accuracy compared with 65% for MR)
Rx:- suppression by high doses of dexamethasone of 8 mg/d
- surgical resection difficult because ACTH adenomas usually require resection of an apparently normal gland (tumor small + usually not on surface of gland)
- SOMATOTROPHIC ADENOMA (14%)
- gigantism, acromegaly, elevated GH >10 ng/mL, NO rise in GH after administration of glucose / TRH
Histo:- densely granulated type
- sparsely granulated type: more aggressive
- hypodense region, may be less well-defined, variable size
- GONADOTROPHIC CELL ADENOMA (7%)
secretes follicle-stimulating hormone (FSH) / luteinizing hormone (LH)- slow-growing often extending beyond sella
- THYROTROPHIC CELL ADENOMA (<1%)
secretes thyroid-stimulating hormone (TSH)- often large + invasive pituitary adenoma
- PLURIHORMONAL PITUITARY ADENOMA (>5%)
Nonfunctioning Pituitary Adenoma
- NULL CELL ADENOMA
= hormonally inactive pituitary tumor with no histologic / immunologic / ultrastructural markers to indicate its cellular derivation
Prevalence: 17% of all pituitary tumors
Age: older patient- slow-growing
- ONCOCYTOMA
Prevalence: 10% of all pituitary tumors- clinically + morphologically similar to null cell adenoma
= tumor >10 mm in size
Incidence: 10% (= 70–80% of pituitary adenomas)
Age: 25–60 years; M÷F = 1÷1
- symptoms of mass effect: hypopituitarism, bitemporal hemianopia (with superior extension), pituitary apoplexy, hydrocephalus, cranial nerve involvement III, IV, VI
- usually endocrinologically inactive
Extension into: suprasellar cistern / cavernous sinus / sphenoid sinus + nasopharynx (up to 67% invasive)
- occasionally tumor hemorrhage
- lucent areas ← cysts / focal necrosis
- invasion of cavernous sinus → encasement of carotid artery (SUREST sign)
CT:
- tumor isodense to brain tissue
- erosion of bone (eg, floor of sella)
- calcifications infrequent
MR: (allows differentiation from aneurysm)
- homogeneous enhancement
Cx:
- Obstructive hydrocephalus (at foramen of Monro)
- Encasement of carotid artery
- Pituitary apoplexy (rare)
DDx:
- Metastasis (more bone destruction, rapid growth)
- Pituitary abscess
= very small adenoma <10 mm in size
- usually become clinically apparent by hormone production (20–30% of all pituitary adenomas)
- Prolactin elevation (>25 ng/mL in females)
4–8 x normal: adenoma demonstrated in 71%
>8 x normal: adenoma demonstrated in 100% - incidentaloma = nonfunctioning microadenoma / pituitary cyst
- NO imaging features to distinguish between different types of adenomas
MR:
- small nonenhancing mass of hypointensity on pre- and postcontrast T1WI
- occasionally isointense on precontrast images + hyperintense on postcontrast images
- enhancement on delayed images
- focal bulge on surface of gland
- focal depression of sellar floor
- deviation of pituitary stalk