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Ectopic posterior pituitary

Ectopic posterior pituitary reflects an disruption of normal embryogenesis and is one of the more common causes of pituitary dwarfism. Although it can be an isolated abnormality, numerous other congenital central nervous system malformations have been identified.

Epidemiology

Ectopic posterior pituitary is a congenital abnormality due to faulty embryogenesis (see below).

Clinical presentation

Patients with ectopic posterior pituitary glands often present with features of growth hormone deficiency (pituitary dwarfism), and may have additional features referable any one of numerous associated malformations 1,3.  Neonatal hypoglycemia is also common 1.

Associations include 1:

Pathology

The clear underlying aetiology of an ectopic posterior pituitary has not been established although recent reports suggests that it may share a similar pathogenesis as septo-optic dysplasia 1-2. The HESX1 gene has been implicated in both conditions 1. Regardless of the underlying cause, an ectopic posterior pituitary results from incomplete downward extension of the diencephalon (Infundibulum). As a result releasing factors released by the hypothalamus which usually travel down the portal circulation to the anterior pituitary can only reach their target via the general circulation. This results in frequent growth hormone deficiency, and in some instances panhypopituitarism 5.

For more details on development of the pituitary please refer to the pituitary gland article.

Radiographic features

MRI

MRI is the only modality adequately able to identify ectopic posterior pituitary. The diagnosis is best made on sagittal midline T1 images, and features consist of 3:

  • high T1 signal 3-8-mm tissue nodule at the median eminence (floor of third ventricle)
  • absent normal posterior pituitary bright spot
    • It is important to note that a posterior pituitary bright spot is not identified in 100% of patients, but rather somewhere between 50-90% 4.  In addition there may be age related atrophy 4.

The exact cause of high T1 signal is uncertain, and may relate to neurosecretory granules or high lipid content of the posterior pituitary tissue 3.

As numerous abnormalities have been associated with ectopic posterior pituitary glands, a careful survey of the rest of the intracranial content should be performed.

Treatment and prognosis

No treatment is required for the ectopic pituitary per se, but rather for the frequently associated growth hormone deficiency, or less frequently panhypopituitarism 5. Growth hormone replacement is available in selected patients and can improve adult height.

Differential diagnosis

The differential for an ectopic posterior pituitary is limited and essentially boils down to a subset of pituitary region mass with intrinsic high T1 signal. Possibilities include:


Related articles

Neuroanatomy

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