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  • Updated 04.30.2021
  • Released 06.03.1997
  • Expires For CME 04.30.2024

Pituitary aplasia, dysplasia, and ectopic neurohypophysis

Introduction

Key points

• Anterior pituitary aplasia or dysplasia is associated with endocrinopathies and often with malformations of the eyes, brain, or somatic anomalies; multiple genes are implicated, particularly LHX4, OTX2, and HESX1.

• Ectopic neurohypophysis and posterior pituitary dysplasia is mainly associated with anterior pituitary endocrine defects because of early neural induction of the Rathke pouch; the HESX1 gene is mostly implicated.

• Pituitary aplasia and dysplasias may occur as isolated anomalies or as part of major brain malformations, most frequently with septo-optic dysplasia, holoprosencephaly, and Joubert syndrome.

• Clinical manifestations largely are related to the endocrinopathies but also may involve intellectual deficits and visual problems.

• Diagnosis is based on clinical history, physical examination, endocrine function studies, and neuroimaging, particularly MRI.

• Treatment addresses correction of endocrine deficiencies.

• Growth hormone deficiency is the most frequent endocrinopathy of infancy, but other pituitary hormonal insufficiencies may appear later in childhood, so vigilant monitoring is recommended in follow-up.

• Numerous genes are reported in isolated growth hormone deficiency, but most frequently due to GH1 and GHRHR mutations.

Historical note and terminology

Pituitary aplasia (absence) is a rare condition first described in the 1950s and 1960s (27; 168; 196). It has been related to ciliary gene mutations, exemplified in patients with type 9 oral-facial-digital syndrome (03).

Pituitary hypoplasia, in which the pituitary gland is diminutive and leads to congenital hypopituitarism, is not always an anatomical anomaly of the adeno- or neurohypophysis (anterior and posterior pituitary) identified in neuroimaging studies to correlate with functional neuroendocrine disorders. Ectopic (ie, displaced) neurohypophysis is a common anatomical anomaly, with or without other brain malformations.

The term pituitary dysplasia may be associated with abnormalities in the adenopituitary cells (94; 175; 121), abnormalities in the neuropituitary cells (124; 09), or other abnormalities in the tissue components that are vital for the organ. Ectopic adenopituitary tissue was found pharyngeally (141), and ectopic neuropituitary tissue has been described in cases where the neuropituitary gland is either absent or underdeveloped (06; 36).

The diagnoses of pituitary aplasia, hypoplasia, and dysplasia are difficult to make. In the diagnostic process, 3 principal methods are used: (1) endocrinological, (2) radiological, and (3) autopsy methods. In extremely preterm neonates, serum hormonal levels differ significantly from those of late preterm and full-term neonates; therefore, it is important that hospital laboratory has reference concentrations at different gestational ages of preterm infants (76).

The diagnosis of pituitary agenesis (the absence of pituitary gland primordium) can be made only after the pharyngeal side of the cranial base has been examined for adenopituitary tissue and the brain has been investigated for neuropituitary tissue by MRI or neuropathological examination.

The diagnosis of pituitary aplasia, in which no pituitary gland tissue is found where the gland is normally located in the sella turcica, necessitates a description of the morphology of the sella turcica. In abnormal sella turcica morphology, (such as that observed when a craniopharyngeal canal has formed in the floor of the sella turcica), glandular tissue may be found in the osseous canal (107; 111; 110). Similar precautions are necessary in order to make the diagnosis of hypoplasia and dysplasia. The nomenclature of pituitary abnormalities should take into account the complicated normal embryological origin of the gland (30). The sella turcica, a superior depression in the sphenoid bone, also has a complex embryology and is altered in size and shape with developmental structural defects of the pituitary (203).

In this review, the term “pituitary aplasia” will be used to refer to the condition observed when the pituitary gland is absent or where a rudimentary gland in a normally developed sella turcica is recorded. Accordingly, this condition does not include cases in which pituitary tissue is found in localities other than the sella turcica.

“Pituitary dysplasia” is understood to be all forms of defect in the organ caused by defective development, including malposition of pituitary tissue and ectopic neurohypophysis. The “pituitary stalk interruption syndrome” is characterized by a triad of interrupted pituitary stalk, absent or ectopic neurohypophysis, and anterior pituitary hypoplasias or aplasia, the latter often leading to panhypopituitarism; the diagnosis is confirmed by MRI (166; 215). This triad is really just a variant of the ectopic neurohypophysis syndrome.

Rarely, by contrast with agenesis, the pituitary may be duplicated (33; 72). Hyperplasia of the single midline pituitary may occur in hypothyroidism (221).

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