[Martin Heinrich Rathke (1793–1860), professor of physiology and pathology at the University of Dorpat (Tartu), Estonia and professor of zoology and anatomy in Königsberg, Germany]

= usually asymptomatic benign cystic sellar lesion

Histo: lined with single layer of epithelial cells; CSF / mucopolysaccharide content

• often asymptomatic
• hypopituitarism, visual disturbance, headache (in older patients)

Location: commonly midline at junction of anterior + posterior pituitary lobes anterior to infundibular stalk; intra- and suprasellar (71%); purely suprasellar (rare)

• may contain thick mucinous material
• no contrast enhancement
• calcifications rare

MR:

• round well-demarcated lesion
• variable SI ranging from hypo- to hyperintense on T1WI ← dependent on biochemical content:
  • homogeneously high T1 SI (50%) ← high protein content
  • low T2 intensity (30%) ← low intracystic water content
  • simple / complex cyst content ± fluid-fluid level
  • NO central enhancement / hemorrhagic component
• small intracystic nodules of lower T2 + higher T1 SI (75%)← proteinaceous concretions
• wall enhancement due to squamous metaplasia / displaced rim of pituitary tissue

DDx: craniopharyngioma, macroadenoma (hemorrhagic fluid-debris level)