Pituitary Stalk

Pituitary stalk interruption syndrome (PSIS) is a distinct developmental defect of the pituitary gland identified by magnetic resonance imaging and characterized by a thin, interrupted, attenuated or absent pituitary stalk, hypoplasia or aplasia of the adenohypophysis, and an ectopic posterior pituitary.

From: Handbook of Clinical Neurology , 2021

Pituitary Physiology and Diagnostic Evaluation

Ursula Kaiser , Ken K.Y. Ho , in Williams Textbook of Endocrinology (Thirteenth Edition), 2016

Pituitary Stalk Interruption Syndrome

PSIS is a congenital defect of the pituitary gland characterized by a thin or interrupted pituitary stalk, anterior pituitary hypoplasia, and an ectopic posterior pituitary. Patients may present with an isolated pituitary hormone deficiency or with combined hypothalamic-pituitary hormone deficiencies. Accompanying midline defects and eye abnormalities suggest involvement of developmental processes. Mutations or single nucleotide variants in HESX1, LHX4, OTX2, SOX3, and PROKR2 have been associated with PSIS. A homozygous missense mutation was identified in a family with PSIS in GPR161, an orphan G protein–coupled receptor expressed in the hypothalamus and pituitary and implicated in the SHH signaling pathway. 536 Mutations have been identified in less than 5% of patients with PSIS, suggesting that there is much more to be learned about the pathogenesis of this disorder.

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The Human Hypothalamus

Antonis Voutetakis , in Handbook of Clinical Neurology, 2021

Magnetic Resonance Imaging findings

PSIS is a distinct developmental defect characterized by a thin, interrupted, attenuated or absent pituitary stalk, hypoplasia or aplasia of the adenohypophysis, and an ectopic posterior pituitary ( Fujisawa et al., 1987; Pinto et al., 1997). Nevertheless, besides this classic triad, the definition of PSIS has widened to include patients with a subset of these features such as isolated lack of a visible pituitary stalk or an ectopic posterior pituitary "bright spot" (i.e., outside the sella turcica). However, we must underline that isolated absence of a visible posterior pituitary with a normal pituitary stalk may not be considered as PSIS since the "bright spot" may be absent in 10% of normal individuals (Di Iorgi et al., 2012). Although this developmental pituitary disorder may be clinically and hormonally suspected, it is identified and diagnosed through MRI (Maghnie et al., 1991a,b, 1996; Argyropoulou and Kiortsis, 2005; Di Iorgi et al., 2012).

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Neuroimaging Part II

Hisham M. Dahmoush , ... Arastoo Vossough , in Handbook of Clinical Neurology, 2016

Pituitary stalk interruption syndrome

Pituitary stalk interruption syndrome is characterized by absence or marked thinning of the pituitary stalk, nonidentification of the normal posterior bright spot of the neurohypophysis, the presence of the bright spot in the floor of the third ventricle in the region of the median eminence or along the infundibulum (ectopic posterior pituitary), and commonly small size of the adenohypophysis ( Abernethy, 1998) (Fig. 63.25). Isolated growth hormone deficiency or multiple pituitary hormone deficiencies occur. Mutations of HESX1, LHX4, OTX2, and SOX3 genes have been occasionally implicated. The severity of abnormality of the stalk (absence versus thinning) correlates with the severity and multiplicity of hormone deficiencies (Wang et al., 2014).

Fig. 63.25. Pituitary stalk interruption syndrome with nonvisualization of the pituitary infundibulum, small pituitary adenohypophysis, and an ectopic posterior pituitary bright spot at the floor of the third ventricle (arrow).

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Atlas of Pituitary Imaging

Kevin M. Pantalone DO , ... Amir H. Hamrahian MD , in MRI Atlas of Pituitary Pathology, 2015

Pituitary Stalk Transection

Pituitary stalk transection was described after the introduction of MRI and comprises a small anterior pituitary gland, thin or absent infundibulum after gadolinium administration, and an ectopic location of the posterior pituitary [12].

The accompanying images (Figures 1.31A–D) were obtained from a 36-year-old woman who presented to the adult endocrinologist with multiple anterior pituitary hormone deficiencies. GH deficiency was diagnosed after she stopped growing around the age of 5. GH therapy was initiated and was continued until the patient was 18 years of age. She subsequently developed hypothyroidism in her early 20s, requiring progressively higher doses of levothyroxine. In addition, she did not develop secondary sexual characteristics or have menstrual cycles until she was started on oral contraceptives in her early 20s. She was diagnosed with polyglandular autoimmune deficiency in her early 30s and was started on dexamethasone 0.5   mg at bedtime. This was subsequently changed to therapy with hydrocortisone, 10   mg in morning and 5   mg in the afternoon (an appropriate daily dose based on her body habitus).

Figure 1.31. Pituitary stalk transection: (A) T1-weighted coronal image precontrast, (B) T1-weighted coronal image precontrast, (C) T1-weighted sagittal image precontrast, and (D) T1-weighted sagittal image postcontrast.

The T1-weighted coronal image precontrast demonstrated an ectopic posterior pituitary along the floor of the hypothalamus (white dashed line). The pituitary stalk was very small and demonstrated only minimal enhancement following the administration of contrast. A small rim of anterior pituitary tissue was noted along the floor of the sella (solid white arrow). This clinical case and some of the images were previously published by Ioachimescu et al. [13] (Figure 1.31).

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THE HYPOTHALAMUS AND PITUITARY PART I

Joy Hinson BSc PhD DSc FHEA , ... Shern Chew BSc MD FRCP , in The Endocrine System (Second Edition), 2010

Connection between the hypothalamus and pituitary

The pituitary stalk, which connects the hypothalamus to the pituitary gland, carries both blood vessels and nerve fibres. The anterior pituitary is connected to the hypothalamus by a vascular connection through the hypophyseal portal system. A portal system is a vascular connection with two sets of capillary beds. The first set of capillaries is in the hypothalamus and blood passes through the portal veins in the pituitary stalk to the second set of capillaries in the anterior pituitary ( Fig. 3.4). In this way, agents released from the hypothalamus can be delivered to the pituitary where they act on pituitary cells to control hormone synthesis and release.

The posterior pituitary consists of fibres of the magnocellular and parvocellular neurons, which carry the posterior pituitary hormones from the hypothalamus.

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The Human Hypothalamus: Anterior Region

Milica Perosevic , ... Nicholas A. Tritos , in Handbook of Clinical Neurology, 2021

Congenital Abnormalities (Pituitary Stalk Interruption Syndrome, Hamartomas)

The pituitary stalk interruption syndrome has been reported since 1987 and includes the following triad: absence or hypoplasia of the anterior adenohypophysis, ectopic neurohypophysis, and thin (<  1   mm) or interrupted pituitary stalk. The diagnosis is made by genetic testing (genes that are involved in pituitary development), MRI, and endocrine testing (with the growth hormone deficiency being the most common, followed by TSH and gonadotropin deficiency). The clinical presentation often includes short stature, craniofacial abnormalities, delayed puberty, and micropenis. Treatment is lifelong hormonal supplementation (Voutetakis et al., 2016; Gosi et al., 2019; Vergier et al., 2019).

Hypothalamic hamartomas (HH) are congenital benign lesions, typically recognized by gelastic (laughing) seizures. These seizures are difficult to treat and failure of medical therapy is high, up to 50%. Treatment options include surgery; however, this should be cautiously considered due to lesion location. The most common endocrine abnormality associated with HH is precocious puberty (up to 40%), commonly associated with cognitive impairment (Harrison et al., 2017; Kerrigan et al., 2017; Scholly et al., 2017). Typical imaging features of HH include being isointense with gray matter on T1-weighted imaging and isointense or hyperintense with gray matter on T2-weighted imaging (Boyko et al., 1991) (Fig. 6.20). These lesions do not enhance after contrast administration.

Fig. 6.20

Fig. 6.20. Large hamartoma. Isointense lesion on T1-weighted image, sagittal view. The lesion did not enhance after contrast administration (not shown).

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Hypothalamus☆

J.P. Card , L. Rinaman , in Reference Module in Neuroscience and Biobehavioral Psychology, 2017

Abstract

The hypothalamus is a remarkable region of the central nervous system. This small subdivision of the ventral diencephalon communicates extensively with other regions of the neuraxis via classical synaptic interactions, and plays an essential role in coordinating behavioral and emotional state with peripheral physiology through its regulatory influences over the autonomic nervous system and pituitary gland. In essence, it is directly responsible for the regulation of homeostatic systems essential for the survival of the parent organism and perpetuation of the species. The ability of this subdivision of the diencephalon to exert such profound influences over behavioral state and physiology is reflected in both the properties of hypothalamic neurons and the mechanisms through which they communicate. This article reviews basic organizational principles fundamental to hypothalamic function, focusing upon well-studied hypothalamic systems that illustrate the functional diversity of this small but influential region of the brain. We begin with a brief historical perspective, progress to a description of basic features of hypothalamic structure and connectivity, and finish with a consideration of four regulatory systems through which hypothalamic neurons exert their influence. Throughout we emphasize the cooperative interactions among functionally diverse systems that permit precise adjustments of physiology in support of adaptive behavior.

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Endocrine Glands

Peter Greaves MBChB FRCPath , in Histopathology of Preclinical Toxicity Studies (Fourth Edition), 2012

Diffuse hyperplasia of the intermediate lobe

Following transection of the pituitary stalk or presence of hypothalamic lesions which destroy the supraoptic and paraventricular nuclei, the intermediate lobe of the rat and other species may show hypertrophy and hyperplasia. 67 Hypertrophy and hyperplasia can also result from interference with dopaminergic-control mechanisms by administration of xenobiotics. Chronic treatment of rats with haloperidol, a dopamine receptor antagonist, stimulates the secretion of α-MSH and β endorphin and accelerates the synthesis of pro-opiomelanocortin. This is associated with an increase in the number of cell layers in the intermediate lobe. The thickened gland contains many dark melanotrophs which do not appear increased in size but contain more mRNA for pro-opiomelanocortin than controls as shown by in situ hybridization. 36 Hyperplasia of the intermediate lobe is also observed spontaneously in Syrian hamsters with advancing age. 68

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Pituitary and Sellar Region Lesions

Eric C. Bourekas , ... H. Wayne Slone , in Handbook of Neuro-Oncology Neuroimaging (Second Edition), 2016

Pituitary Stalk Lesions

The thickness of the normal pituitary stalk is approximately 2  mm. The normal stalk enhances markedly on CT and MRI with contrast. The most common clinical problem associated with disease of the pituitary stalk is diabetes insipidus. When this is present, there usually is absence of the normal hyperintensity of the posterior pituitary noted on T1-weighted MRI. Diabetes insipidus may also occur as a result of transection of the pituitary stalk.

The differential diagnosis of a thickened stalk includes sarcoidosis, tuberculosis, histiocytosis X, germinoma, lymphoma (see Figure 26), leukemia, metastasis (Figures 17 and 18), and ectopic posterior pituitary. A thickened stalk can also be due to an extension of a glioma from the hypothalamus.

Figure 26. Lymphoma. (A) Coronal and (B) axial T1-weighted images following the administration of contrast demonstrate an enhancing lesion involving the pituitary stalk in a patient with a history of systemic lymphoma. Findings resolved following chemotherapy for lymphoma.

Clinical findings may help in sorting out the etiology for pituitary stalk thickening. For example, in patients with neurosarcoidosis or tuberculous infiltration of the stalk, the chest radiograph is generally abnormal and may be helpful in the differentiation from histiocytosis X. Clinically, patients with histiocytosis X may have skin lesions, otitis media, or bone lesions, in addition to interstitial lung disease. 95

Neurosarcoidosis causing clinical symptoms is an uncommon manifestation of sarcoidosis. It has been reported that symptomatic neurosarcoidosis occurs in up to 5% of patients. 96 The most common clinical symptoms include cranial nerve dysfunction, aseptic meningitis related to leptomeningeal spread, hydrocephalus, and dysfunction of the hypothalamic–pituitary axis such as diabetes insipidus. 96,97 Neurosarcoidosis commonly affects the leptomeninges with findings of basilar leptomeningitis affecting the pituitary gland region and subjacent structures. 97 Mass lesions as a result of sarcoid are less common (Figure 27).

Figure 27. Neurosarcoidosis. (A) Sagittal T1-weighted image. (B) Coronal T1-weighted image after contrast administration. Images show a lobulated mass involving the sellar and suprasellar region, which enhances on postcontrast images. The patient was a 62-year-old male complaining of visual disturbances with known sarcoidosis. His symptoms improved following a steroid regimen.

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Neuroendocrinology

Malcolm J. Low , in Williams Textbook of Endocrinology (Thirteenth Edition), 2016

Pituitary Isolation Syndrome

Destructive lesions of the pituitary stalk, as occur with head injury, surgical transection, tumor, or granuloma, produce a characteristic pattern of pituitary dysfunction. 324,325 Central diabetes insipidus (DI) develops in a large percentage of patients, depending on the level at which the stalk has been sectioned. If the cut is close to the hypothalamus, DI is almost always produced, but if the section is low on the stalk, the incidence is lower. The extent to which nerve terminals in the upper stalk are preserved determines the clinical course. The classic triphasic syndrome of initial polyuria followed by normal water control and then by AVP deficiency over a period of 1 week to 10 days occurs in fewer than half of the patients. The sequence is attributed to an initial loss of neurogenic control of the neural lobe, followed by autolysis of the neural lobe with release of AVP into the circulation, and finally by complete loss of AVP. However, full expression of polyuria requires adequate cortisol levels; if cortisol is deficient, AVP deficiency may be present with only minimal polyuria. DI can also develop after stalk injury without an overt transitional phase. When DI occurs after head injury or operative trauma, varying degrees of recovery can be seen even after months or years. Sprouting of nerve terminals in the stump of the pituitary stalk may give rise to sufficient functioning tissue to maintain water balance. In contrast to the effects of stalk section, nondestructive injury to the neurohypophysis or stalk, as during surgical resection of sellar tumors, can sometimes give rise to transient or delayed SIADH. 326

Although head injury, granulomas, and tumors are the most common causes of acquired DI, other cases develop in the absence of a clear-cut cause. 327 Autoimmune disease of the hypothalamus may be the cause in some instance, as was suggested by the finding of autoantibodies to neurohypophyseal cells in a third of cases of idiopathic DI in one series. 328 However, autoantibodies were also frequently found in association with histiocytosis X. Later reports suggested the importance of continued vigilance in cases of idiopathic DI. A definite cause is frequently uncovered in time, including a high proportion of occult germinomas, whose detection by MRI may be preceded by elevated levels of hCG in CSF. 329 Congenital DI can be part of a hereditary disease. DI in the Brattleboro rat is due to an autosomal recessive genetic defect that impairs production of AVP but not of oxytocin. In contrast, inherited forms of DI in humans have been attributed to mutations in the vasopressin V2 receptor gene or less frequently in the aquaporin or the AVP genes. 330-332

Menstrual cycles cease after stalk section, although gonadotropins may still be detectable, unlike the situation after hypophysectomy. Plasma glucocorticoid levels and urinary excretion of cortisol and 17-hydroxycorticoids decline after hypophysectomy and stalk section, but the change is slower after stalk section. A transient increase in cortisol secretion after stalk section is believed to be due to release of ACTH from preformed stores. The ACTH response to the lowering of blood cortisol is markedly reduced, but ACTH release after stress may be normal, possibly because of CRH-independent mechanisms. Reduction in thyroid function after stalk section is similar to that seen with hypophysectomy. The fall in GH secretion is said to be the most sensitive indication of damage to the stalk, but the insidious nature of this endocrinologic change in adults who have suffered traumatic brain injuries may cause it to be overlooked and therefore contribute to delayed rehabilitation. 333

Humans with stalk sections or with tumors of the stalk region have widely varying levels of hyperprolactinemia and may have galactorrhea. 334 PRL responses to hypoglycemia and to TRH are blunted, in part because of loss of neural connections with the hypothalamus. PRL responses to dopamine agonists and antagonists in patients with pituitary isolation syndrome are similar to those in patients with prolactinomas. Interestingly, PRL secretion continues to show a diurnal variation in patients with either hypothalamic-pituitary disconnection or micro­prolactinoma. 268 Both forms of hyperprolactinemia are characterized by a similarly increased frequency of PRL pulses and a marked rise in nonpulsatile or basal PRL secretion, although the disruption is greater in the tumoral hyperprolactinemia.

An incomplete pituitary isolation syndrome may occur with the empty sella syndrome, intrasellar cysts, or pituitary adenomas. 335,336 Anterior pituitary failure after stalk section is in part due to loss of specific neural and vascular links to the hypothalamus and in part due to pituitary infarction.

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