Pituitary adenoma is the most common sellar/suprasellar tumor, arising from the adenohypophysis, constituting 10-15% of all intracranial tumors. It is classified by size as microadenoma (<10 mm) and macroadenoma (≥10 mm). It can be functional (hormone-secreting — prolactinoma, GH adenoma, ACTH adenoma) or non-functional. Macroadenomas can cause mass effect with suprasellar extension compressing the optic chiasm, cavernous sinus invasion, and hydrocephalus. Dynamic contrast-enhanced MRI is the gold standard for diagnosing both micro- and macroadenomas.
Age Range
20-70
Peak Age
40
Gender
Female predominant
Prevalence
Common
Pituitary adenomas arise from clonal neoplastic proliferation of the adenohypophysis. Tumor cells represent monoclonal expansion of one of the normal pituitary cell types (lactotrophs, somatotrophs, corticotrophs, gonadotrophs, thyrotrophs). In functional adenomas, cell type-specific hormone overproduction leads to clinical syndromes (prolactinoma → hyperprolactinemia, GH adenoma → acromegaly, ACTH adenoma → Cushing disease). The tumor's behavior on dynamic contrast-enhanced MRI reflects its vascular architecture different from normal pituitary gland: normal pituitary enhances early and intensely through the portal venous system, while adenoma shows delayed enhancement because it has systemic arterial rather than portal venous blood supply. This vascular difference forms the basis of dynamic contrast MRI's diagnostic value.
Delayed enhancement of adenoma compared to early intense enhancement of normal pituitary on dynamic contrast MRI is the gold standard for microadenoma diagnosis. In macroadenoma, the snowman or figure-8 configuration created by waisting at the diaphragma sellae level during suprasellar extension is pathognomonic. The combination of these two findings (dynamic enhancement difference + characteristic morphology) reliably differentiates pituitary adenoma from other sellar/suprasellar lesions (craniopharyngioma, meningioma, Rathke cleft cyst).
On non-contrast CT, macroadenoma appears as an isodense or slightly hyperdense mass in the sellar region. Expansion and floor erosion of the sella turcica are characteristic. In cases of suprasellar extension, suprasellar cistern obliteration may be seen. Microadenomas are generally not detectable on CT. Intratumoral hemorrhage (apoplexy) appears as acutely hyperdense area. Calcification is rare, and if present, craniopharyngioma should be considered.
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On CT, an isodense mass is identified in the sellar region with expansion and floor erosion of the sella turcica.
On T1-weighted images, pituitary adenoma generally appears isointense or slightly hypointense relative to gray matter. In macroadenoma, normal pituitary gland is displaced by the tumor and may be seen as a thin, peripherally located hyperintense structure (bright pituitary). The pituitary stalk may be deviated laterally, providing a clue for tumor lateralization. In microadenoma, a slightly hypointense focus may be seen within the glandular tissue on T1. Intratumoral hemorrhage may show hyperintense area on T1 (methemoglobin).
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On T1-weighted sequence, an iso- to hypointense mass is identified within the sella turcica, with the normal pituitary gland displaced superiorly by the tumor.
On T2-weighted images, pituitary adenoma shows variable signal: solid component generally appears isointense or slightly hyperintense relative to gray matter. Cystic degeneration areas show markedly hyperintense T2 signal, and hemorrhagic areas show T2 hypointense (deoxyhemoglobin/hemosiderin) appearance. In macroadenoma, suprasellar extension, optic chiasm compression, and cavernous sinus relationship are best evaluated on T2. T2 signal varies by adenoma subtype — GH adenomas tend to be T2 hypointense.
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On T2-weighted sequence, the sellar mass shows predominantly iso- to hyperintense signal, with suprasellar extension and relationship to the optic chiasm evaluated.
Dynamic contrast-enhanced MRI (rapid sequential T1-weighted sequences at 15-30 second intervals) is the gold standard for pituitary adenoma diagnosis. Normal pituitary gland enhances early and intensely through the portal venous system, while adenoma enhances later — in the early phase (60-90 seconds), adenoma appears hypointense (non-enhanced) relative to surrounding normal pituitary. In the late phase (5-10 minutes), adenoma shows delayed enhancement and may become isointense to normal pituitary. This vascular dynamic difference is critically important especially for detecting small microadenomas that are invisible on T1/T2.
Report Sentence
On early phase of dynamic contrast MRI, the sellar lesion shows delayed enhancement compared to the intensely enhancing normal pituitary gland, consistent with pituitary adenoma.
On FLAIR, pituitary adenoma generally appears isointense or slightly hyperintense. Cystic degeneration areas may not fully suppress on FLAIR (proteinaceous content). Suprasellar extension of macroadenoma and compression on optic pathways can be evaluated. Hyperintense signal may be seen on FLAIR in pituitary apoplexy (acute hemorrhage). FLAIR appearance of normal pituitary stalk is valuable as reference.
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On FLAIR, the sellar mass shows iso- to slightly hyperintense signal.
In typical pituitary adenoma, no significant diffusion restriction is seen on DWI; ADC values are generally normal or mildly elevated. However, mild diffusion restriction may be seen in densely cellular adenomas and pituitary apoplexy. DWI can be helpful in differential diagnosis of sellar region lesions — used for differentiation from Rathke cleft cyst, epidermoid cyst, and abscess. Increase in ADC values after dopamine agonist treatment in macroprolactinomas may indicate therapeutic response.
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On DWI, no significant diffusion restriction is detected in the sellar mass, with normal ADC values.
On perfusion MRI (DCE), pituitary adenoma shows delayed time-to-peak and low-moderate perfusion compared to normal pituitary gland. This finding reflects the adenoma's systemic arterial rather than portal venous blood supply. Ktrans values are generally low to moderate. Perfusion studies may be used for evaluating tumor biology and treatment response in macroadenomas.
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On perfusion MRI, the sellar lesion shows delayed contrast kinetics and low-moderate perfusion values compared to normal pituitary gland.
On SWI, no significant findings are seen in uncomplicated pituitary adenoma. However, in pituitary apoplexy (intratumoral hemorrhage), prominent blooming artifact and areas of low signal are detected on SWI — reflecting the magnetic susceptibility effect of hemorrhagic products (hemosiderin, deoxyhemoglobin). SWI detects small hemorrhagic foci much more sensitively than conventional sequences. Multiple blooming foci may be seen on SWI in adenomas with recurrent microhemorrhages.
Report Sentence
On SWI, blooming artifact/low signal areas consistent with hemorrhagic products are identified within the sellar mass (suspected apoplexy).
Criteria
Adenoma with diameter <10 mm. Sellar expansion is usually absent. Dynamic contrast MRI is gold standard — small focus showing delayed enhancement compared to normal pituitary. Despite small size, may cause significant endocrine symptoms when functional (especially prolactinoma and ACTH adenoma).
Distinct Features
May show minimal signal difference from normal pituitary on T1 and T2 — diagnosis generally depends on dynamic contrast sequences. Indirect signs: lateral deviation of pituitary stalk, focal erosion of sellar floor, pituitary gland asymmetry.
Criteria
Adenoma with diameter ≥10 mm. Sellar expansion and floor erosion are common. Suprasellar extension with optic chiasm compression (bitemporal hemianopia). Cavernous sinus invasion (Knosp classification). Snowman/figure-8 configuration is characteristic.
Distinct Features
Mass effect is prominent — visual symptoms (visual field defects), hypopituitarism, headache. Heterogeneous enhancement (cystic degeneration, hemorrhage). No dural tail sign (unlike meningioma). ICA is usually displaced, not encased (unlike meningioma).
Criteria
Adenoma with cavernous sinus invasion (Knosp grade 3-4), bone invasion, extension into sphenoid sinus and nasal cavity. Ki-67 proliferation index >3%. Aggressive behavior requiring recurrent surgery and/or radiotherapy. Defined as 'atypical adenoma' or 'high-risk' in WHO classification.
Distinct Features
Knosp classification is used for evaluating cavernous sinus invasion on MRI (Grade 0-4). At Grade 3-4, >50% of internal carotid artery is encased — complete surgical resection is difficult. ICA narrowing is rare and raises suspicion of malignant transformation. Perfusion studies may help predict aggressive behavior.
Criteria
Acute hemorrhage and/or infarction within pre-existing adenoma. Presents with sudden severe headache, visual loss, ophthalmoplegia, and acute hypopituitarism. MRI shows T1 hyperintense signal (subacute blood — methemoglobin), heterogeneous T2 signal, prominent blooming on SWI.
Distinct Features
Emergency — risk of acute hormonal crisis (adrenal crisis). DWI may show diffusion restriction in hemorrhage/infarction areas. Heterogeneous or ring-like enhancement on contrast MRI (peripheral viable tissue). May mimic subarachnoid hemorrhage in acute phase. Treatment: urgent corticosteroid replacement + surgical decompression may be needed.
Distinguishing Feature
Craniopharyngioma shows calcification (in 90%) and T1 hyperintensity of cystic component (machine oil appearance — cholesterol content). Calcification is rare in pituitary adenoma, T1 hyperintensity only with hemorrhage. Rim enhancement in craniopharyngioma vs solid/homogeneous enhancement in adenoma.
Distinguishing Feature
Sellar/suprasellar meningioma shows dural tail sign, enhances homogeneously and intensely, and encases the ICA (ICA is displaced in adenoma). Meningioma generally does not cause sellar expansion. On dynamic contrast MRI, meningioma and normal pituitary show similar enhancement kinetics.
Distinguishing Feature
Sellar region schwannoma is very rare, trigeminal schwannoma may show parasellar extension. Schwannoma is markedly hyperintense on T2, enhances heterogeneously and typically originates from outside the sella (cavernous sinus or Meckel cave). Adenoma originates from within the sella turcica.
Distinguishing Feature
Pituitary lymphoma is rare and shows pituitary stalk thickening (infundibulohypophysitis-like) and homogeneous enhancement. Lymphoma shows marked DWI restriction (high cellularity), generally not seen in adenoma. Lymphoma shows periventricular predilection and edema in surrounding parenchyma.
Urgency
variable — apoplexy is emergency, microadenoma may be observedManagement
medical (dopamine agonist for prolactinoma) or surgical (transsphenoidal resection)Biopsy
Not NeededFollow-up
Every 6-12 months MRI for microadenoma; 3-6 months initially for macroadenoma post-treatmentTreatment of pituitary adenoma varies by subtype and functional status. First-line treatment for prolactinoma is dopamine agonists (cabergoline) — tumor shrinkage is achieved in 80-90% with medical treatment. Transsphenoidal surgery is first-line for non-functional macroadenomas and other functional adenomas (GH, ACTH). Radiotherapy (stereotactic radiosurgery) may be applied for residual tumor post-surgery. Pituitary apoplexy is an emergency requiring urgent corticosteroid replacement due to acute hormonal insufficiency (especially adrenal crisis) and surgical decompression when needed. Imaging follow-up is recommended for all adenomas.
Prolactinomas are primarily treated with dopamine agonists (cabergoline) — surgery not required. Non-functional macroadenomas and other functional types (GH, ACTH-secreting) require surgical treatment (transsphenoidal approach). Pituitary apoplexy may require emergent surgical decompression. Postoperative follow-up includes hormonal assessment and serial MRI.