Ectopic posterior pituitary with agenesis of infundibular stalk

A 17-year-old male patient presented with short stature. On radiographic evaluation, his bone age was less than his chronologic age. The endocrinological investigation revealed the deficiency of both growth hormone (GH) and adrenocorticotropic hormone (ACTH). Decreased blood levels of free thyroxine and thyroid-stimulating hormone (TSH) were also recorded.

Contrast-enhanced pituitary MRI was performed. Pre-contrast T1-weighted coronal and sagittal MR images through medial eminence revealed a small flattened anterior pituitary lobe and an absent pituitary stalk. The ectopic posterior pituitary appeared as a hyperintense nodule at the median eminence (Fig. 1). Post-contrast T1-weighted coronal and sagittal MR images through medial eminence demonstrated the enhancing small anterior pituitary lobe and the ectopic position of the posterior pituitary. The pituitary stalk was still absent on contrast-enhanced images (Fig. 2).

The ectopic posterior pituitary (EPP) is a rare disorder characterised by ectopic location of the posterior pituitary lobe and dysgenesis or agenesis of the infundibular stalk (AIS). Although the aetiology of EPP remains unclear, some recent studies showed that mutations in gene HESX1 cause the development of both EEP and periventricular heterotopia, and suggested that EPP is included in the spectrum of septo-optic dysplasia [1]. Apart from septo-optic dysplasia, several malformations including microcephaly, Chiari I malformation, Kallmann syndrome and basilar impression may be associated with EEP. Regardless of the underlying cause, EPP results from the inadequate downward extension of the infundibulum. This prevents the releasing factors from reaching anterior pituitary by portal circulation and causes the disruption of the hypothalamo-hypophyseal regulation [2].

EPP clinically presents with the findings of isolated growth hormon deficiency, or less commonly with the findings of combined pituitary hormone deficiency [3]. The endocrinological investigation of our patient revealed evidence of GH deficiency accompanied by hypocortisolism and hypothyroidism suggesting an abnormality in the hypothalamo-hypophyseal area. Among patients with congenital combined pituitary hormone deficiency, the prevalence of associated EEP with AIS is reported to reach up to 80% [3].

MRI is the method of choice for the diagnosis of EPP. For the evaluation of pituitary gland and infundibular stalk, sagittal midline T1-weighted images should be chosen [4]. The posterior pituitary lobe is seen as a bright spot on T1-weighted imaging, owing to the presence of phospholipids which have T1-shortening effect [5]. The characteristic MRI findings of EPP are the absence of posterior pituitary bright spot, and the presence of a high T1-signal tissue nodule at varying locations, most commonly along the median eminence [4] (Fig. 3). EPP may be observed in either isolation, or accompanied by varying degrees of infundibular stalk anomalies. The stalk may be smaller than normal, or may be totally absent as it was in the current case.

There is no need for treatment for ectopic pituitary. However, replacement therapy for growth hormone deficiency or combined pituitary hormone deficiency is appropriate [6].

Written informed patient consent for publication has been obtained.