Show image difference of, difference between normal pituitary MRI with stalk transaction and ectopic hot spot.
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pituitary MRI normal vs stalk transection vs ectopic posterior pituitary bright spot comparison images
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pituitary stalk transection MRI T1 bright spot absent ectopic neurohypophysis median eminence radiology images
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normal pituitary MRI T1 sagittal posterior bright spot sella turcica stalk radiopaedia
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I now have all the images needed for a thorough comparison. Here is the full visual and conceptual breakdown:
Pituitary MRI: Normal vs. Stalk Transection vs. Ectopic Posterior Pituitary (Hot Spot)
All comparisons below are on unenhanced T1-weighted sagittal MRI, which is the key sequence for evaluating posterior pituitary pathology.
1. NORMAL Pituitary MRI
What to look for:
| Feature | Normal Finding |
|---|---|
| Posterior pituitary bright spot | Present within the sella turcica - bright (hyperintense) T1 signal at the posterior/inferior aspect of the gland |
| Pituitary stalk | Visible as a thin midline structure connecting hypothalamus to pituitary, tapers inferiorly (3.5 mm at median eminence, 2 mm at apex) |
| Anterior pituitary | Isointense to gray matter |
| Sella | Pituitary gland fills the sella normally |
- The bright spot reflects high neurophysin/phospholipid content of neurosecretory granules in the neurohypophysis
- Present in ~90% of normal individuals on T1
2. STALK TRANSECTION (Pituitary Stalk Interruption Syndrome - PSIS)
What to look for:
| Feature | Stalk Transection Finding |
|---|---|
| Pituitary stalk | Absent, interrupted, or markedly thinned - the defining feature |
| Posterior bright spot in sella | Absent from normal posterior sellar location |
| Ectopic bright spot | May or may not develop at median eminence (depends on timing - congenital vs. acquired) |
| Anterior pituitary | Often hypoplastic |
| Sella | Often small/empty |
- In congenital PSIS: the transected stalk causes the posterior pituitary to remain stranded at the median eminence - producing the classic triad of: ectopic bright spot + absent/thin stalk + hypoplastic anterior pituitary
- In acquired traumatic transection (e.g. road traffic accident): the bright spot typically does NOT migrate back to the median eminence; instead it simply disappears from the sella
3. ECTOPIC POSTERIOR PITUITARY (Ectopic Hot Spot / Ectopic Neurohypophysis)
Caption from source: Ectopic posterior pituitary bright spot seen in suprasellar location near the floor of third ventricle and optic chiasma. The infundibulum and pituitary stalk are not seen. Anterior pituitary is deficient/hypoplastic.
What to look for:
| Feature | Ectopic Hot Spot Finding |
|---|---|
| Posterior bright spot | Absent from sella - but present at/near the median eminence (floor of 3rd ventricle/hypothalamus) |
| Pituitary stalk | Absent or markedly hypoplastic |
| Anterior pituitary | Hypoplastic (often very thin sheet at sellar floor) |
| Location of bright spot | Suprasellar - at the tuber cinereum/median eminence |
- This represents failure of the posterior pituitary to descend into the sella during development
- The ectopic tissue retains ADH-synthesizing capacity, so diabetes insipidus is usually absent or mild
- The anterior pituitary, however, is hypoplastic - causing growth hormone deficiency and often panhypopituitarism
Side-by-Side Comparison Table
| Feature | Normal | Stalk Transection | Ectopic Hot Spot |
|---|---|---|---|
| Posterior bright spot location | In sella (posterior gland) | Absent from sella | Absent from sella |
| Ectopic bright spot | Not present | Usually absent (acquired); may be present (congenital) | Present at median eminence |
| Stalk | Normal, tapers 3.5 → 2 mm | Absent / interrupted / thin | Absent or markedly hypoplastic |
| Anterior pituitary | Normal size, isointense | Hypoplastic | Hypoplastic |
| Sella size | Normal | Small/empty | Small |
| ADH function (DI) | Normal | Often DI (acquired); spared (congenital) | Usually preserved |
| GH/hormonal axis | Normal | GHD, panhypopituitarism | GHD, may progress to panhypopituitarism |
| Typical cause | - | Trauma, surgery, or congenital | Congenital (failed descent) |
Key Clinical Pearl
The classic triad of PSIS (which encompasses both stalk transection + ectopic hot spot in the congenital form):
- Ectopic posterior pituitary at median eminence (T1 bright spot displaced superiorly)
- Absent/interrupted pituitary stalk
- Hypoplastic anterior pituitary
This triad is seen on T1-weighted sagittal and coronal unenhanced MRI, as shown in the images above. The Radiopaedia article on pituitary MRI approach and the Barrow Neurological Institute review are excellent further reading resources.
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