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Pituitary MRI (Sella / Dynamic Contrast)

Dedicated pituitary MRI is the gold standard for imaging the sella and parasellar region. A small field-of-view, thin-section protocol with dynamic post-contrast imaging exploits the differential enhancement kinetics of normal gland and adenoma to detect small lesions that determine endocrine management and surgical planning.

Indications

  • Biochemically suspected functioning adenoma (prolactinoma, GH-secreting, ACTH-secreting)
  • Non-functioning macroadenoma with mass effect, visual failure or hypopituitarism
  • Investigation of hyperprolactinaemia, acromegaly and Cushing disease
  • Central diabetes insipidus and assessment of the posterior pituitary bright spot and stalk
  • Suspected pituitary apoplexy, Rathke cleft cyst, craniopharyngioma or hypophysitis
  • Post-operative and post-radiotherapy surveillance of pituitary tumours

Contraindications & Cautions

  • Non-conditional pacemakers, ICDs, neurostimulators and ferromagnetic aneurysm clips
  • Cochlear implants and unstable metallic intra-ocular foreign bodies
  • Severe claustrophobia without sedation
  • Gadolinium caution with eGFR <30 mL/min/1.73 m2 (NSF risk)
  • Pregnancy: perform unenhanced imaging where possible; avoid gadolinium unless essential

Patient Preparation

  • MRI safety screening and removal of ferromagnetic objects
  • Intravenous cannula for dynamic gadolinium administration
  • Explain the need to remain still during the rapid dynamic acquisition
  • Correlate with endocrine results (prolactin, IGF-1, cortisol axis) to focus interpretation
  • For suspected microadenoma, ensure the dynamic sequence timing is set up before contrast injection

Technique & Parameters

  • Small field-of-view (16-20 cm) dedicated sella coil positioning
  • Thin-section (2-3 mm, no or minimal gap) coronal and sagittal T1 pre-contrast and coronal T2
  • Dynamic thin-section coronal spoiled gradient-echo or fast spin-echo T1 acquired repeatedly during gadolinium bolus (temporal resolution ~20-30 s)
  • Delayed post-contrast coronal and sagittal T1 for macroadenoma extent and cavernous sinus assessment
  • Optional 3T high-resolution and volumetric sequences for very small lesions
  • Include the optic chiasm, cavernous sinuses and suprasellar cistern in coverage

Systematic Review

  • Assess gland height, superior margin convexity and symmetry (upper limit ~9-10 mm, higher in pregnancy/puberty)
  • Confirm the posterior pituitary bright spot and midline infundibulum position
  • On dynamic images, look for a focus enhancing later/less than the avidly enhancing normal gland (microadenoma)
  • Evaluate suprasellar extension, optic chiasm compression and third ventricle
  • Assess cavernous sinus invasion using the Knosp grading relative to the internal carotid arteries
  • Review sphenoid sinus, clivus and parasellar structures

Key Findings & Significance

  • Microadenoma (<10 mm): focal region of delayed/reduced enhancement on dynamic imaging, often T1 hypointense
  • Macroadenoma (>10 mm): sellar mass with suprasellar extension and a figure-of-eight or snowman configuration at the diaphragma
  • Optic chiasm compression producing bitemporal hemianopia
  • Cavernous sinus invasion with encasement of the cavernous internal carotid artery (higher Knosp grade)
  • Pituitary apoplexy: haemorrhage/infarction with fluid level and heterogeneous signal in an enlarged gland
  • Loss of the posterior pituitary bright spot and thickened stalk in central diabetes insipidus/hypophysitis

Differential Considerations

  • Sellar mass: pituitary adenoma, Rathke cleft cyst, craniopharyngioma, meningioma, hypophysitis
  • Suprasellar mass: craniopharyngioma, meningioma, hypothalamic glioma, germinoma, aneurysm
  • Cystic sellar lesion: Rathke cleft cyst, cystic adenoma, arachnoid cyst, craniopharyngioma
  • Thickened stalk: lymphocytic hypophysitis, sarcoidosis, Langerhans cell histiocytosis, germinoma, metastasis
  • Physiological gland enlargement in puberty, pregnancy and lactation mimicking pathology

Pearls & Pitfalls

  • Timing is critical: on dynamic imaging the normal gland enhances first, so a microadenoma is seen as a transient relative filling defect
  • A convex upper gland border and stalk deviation are supportive but non-specific signs of a microadenoma
  • Prolactin levels correlate with tumour size; a large macroadenoma with only modest prolactin elevation suggests a non-functioning tumour with stalk effect
  • The Knosp grade predicts the likelihood of surgical cavernous sinus residual disease
  • Always exclude an aneurysm before diagnosing a parasellar mass; flow void and MRA help

Structured Report

  • State protocol, field strength and whether dynamic contrast was performed
  • Report gland dimensions, lesion size, location and enhancement characteristics
  • Describe suprasellar and parasellar extension, chiasm compression and Knosp cavernous sinus grade
  • Comment on the posterior bright spot and infundibulum where relevant
  • Provide an impression correlated with endocrine data and surgical/medical recommendation

References

  • Bonneville F, et al. Radiographics: Imaging of the pituitary gland and sellar region
  • Knosp E, et al. Pituitary adenomas with invasion of the cavernous sinus space
  • ACR-ASNR-SNIS-SPR Practice Parameter for the Performance of MRI of the Brain
  • FitzPatrick M, et al. Dynamic contrast-enhanced pituitary MRI. AJNR

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.