Background: The ectopic posterior pituitary (EPP) is a rare condition characterized by the ectopic location
of posterior pituitary lobe associated with varying degree of stalk anomalies. The arachnoid cysts (AC) are
benign lesions of the arachnoid, which account for 1% of all intracranial space-occupying lesions.
Sellar/suprasellar ACs account for approximately 1% of all ACs. This is the first case of coexistence EPP
with sellar/suprasellar AC.
Case Report: A 67-year-old woman presented with 6 months history of fatique. Her medical history was
positive for irregular menstruation. Her endocrine examinations indicated low free thyroxine level with
low TSH level, low oestradiol with low gonadotrophin level, slightly elevated prolactin level. Her Insulinlike growth factor-1 was below the normal levels. Dynamic contrast hypophysis MRIrevealed a sellar cystic
lesion with a dimension of 18 × 14 × 14 mm, extending from the suprasellar cistern, traversing the
diaphragma sellae and reaching the level of the floor of the 3rd ventricle, consistent with
sellar/suprasellar AC. There was no wall enhancement. The optic chiasm was compressed. The precontrast
T1-weighted magnetic resonance images did not demonstrate the characteristic bright spot of posterior
pituitary within the sella which was higher in position, in the region of median eminence. The pituitary
stalk was not present.
Conclusion: Although speculative, we have a hypothesis to explain how the EPP and sellar/suprasellar AC
coexist in this patient. Due to absence of stalk, CSF may enter the sella tursica from central aperture of
the diaphragma sellae through which normally the stalk pass.