Patients with isolated growth hormone deficiency have a thin or truncated pituitary stalk (the stalk is rarely absent or normal), normal or small anterior pituitary, and an ectopic posterior pituitary.
Patients with multiple pituitary hormonal deficiencies, on the other hand, may have a small or absent pituitary stalk, a small or absent anterior pituitary, and an ectopic or absent posterior pituitary.
To sum up the above: A thin stalk is strongly suggestive of isolated growth hormone deficiency, while an absent stalk is strongly suggestive of multiple pituitary hormonal deficiencies.
A contrast-enhanced MRI is needed to fully define the infundibulum.
The above case is a non-contrast MRI with an absent posterior pituitary bright spot (yellow arrow), an absent or thin stalk (green arrow), and an ectopic bright spot in the region of the median eminence (pink arrow). Without contrast, we can't tell if the stalk is absent or very thin.
An ectopic posterior pituitary lobe can also be seen in cases of pituitary stalk transection and septo-optic dysplasia and as an asymptomatic variant.
- Fujisawa I, Kikuchi K, Nishimura K, Togashi K, Itoh K, Noma S, Minami S, Sagoh T, Hiraoka T, Momoi T, et al. Transection of the pituitary stalk: development of an ectopic posterior lobe assessed with MR imaging. Radiology. 1987 Nov;165(2):487-9.
- Grossman RI and Yousem DM. Chapter 11. in Neuroradiology: The Requisites (second edition). Mosby, 2003. pp 539-541.