• Primary tumor of the adenohypophysis of various cell line differentiations, ≤10 mm in size

• Low-grade tumors, WHO grade I
• Well differentiated, slow growing or nongrowing
• Can secrete hormones according to the cell of origin, most commonly prolactin

• Usually incidental (nonfunctioning)
• Can have symptoms related to hormone secretion (secretory)
  • Prolactinoma is most common
    • Women: irregular menses, amenorrhea, galactorrhea
    • Men: hypogonadism, decreased libido
  • Growth hormone secreting (acromegaly)
  • Adrenocorticotropic hormone (ACTH) secreting (Cushing disease)
  • Thyroid-stimulating hormone (TSH) secreting (hyperthyroidism)
• 10% of all patients on autopsy series
• More common in syndromes such as multiple endocrine neoplasia type 1 (MEN1) syndrome, McCune-Albright syndrome, Carney complex, familial isolated pituitary adenoma (FIPA) syndrome
• Pituitary apoplexy is a rare but serious complication

• General
  • Small intrasellar mass, <10 mm in size
  • Can be cystic, proteinaceous, or hemorrhagic
  • Can demonstrate elevated contour on the superior margin of the affected side of the pituitary gland
  • Can deviate the infundibulum away from the side of the microadenoma
• CT Imaging
  • Usually not visible, nonrevealing
  • Cystic or hemorrhagic lesions can be visible as tiny hypodense or hyperdense lesions
  • Can see slight deviation of the infundibulum
  • Thin-cut CT imaging might be helpful for delineating sphenoid sinus bony anatomy for surgical planning
• MRI
  • T1WI: usually not visible unless cystic (hypointense) or hemorrhagic/proteinaceous (hyperintense)
  • T2WI: variable, hyperintense if cystic
  • FLAIR: variable, hyperintense if cystic
  • DWI: usually not visible or obscured by adjacent sphenoid sinus/bone susceptibility artifact
  • T1WI+C: usually enhances similar to surrounding pituitary gland on routine postcontrast imaging; on dynamic postcontrast images through the sella, microadenomas might be more visible at a time point during which they enhance less than normal pituitary tissue because of their comparatively delayed enhancement pattern
  • Advanced imaging: these lesions are too small to appear on most advanced imaging modalities (MR spectroscopy, MR perfusion)
• Conventional Angiography
  • Inferior petrosal sinus sampling (IPSS) is more accurate for identifying ACTH-secreting microadenomas than imaging alone

• MRI without and with contrast with detailed images of the sella, including dynamic coronal postcontrast sequences
• Thin-cut CT imaging of the sinuses or sella can be helpful for delineating sphenoid sinus anatomy before transsphenoidal resection and during intraoperative navigation

For more information, please see the corresponding chapter in Radiopaedia.

Contributor: Rachel Seltman, MD

DOI: https://doi.org/10.18791/nsatlas.v1.03.01.34