MR imaging of the posterior hypophysis in children

Diagnosis and Management of pituitary disease with focus on the role of Magnetic Resonance Imaging

Magnetic resonance (MR) imaging is an essential tool in the diagnosis and management of pituitary diseases, indispensable for making correct treatment decisions. Successful management and follow-up of pituitary pathology requires an understanding of the MR appearance of normal and abnormal structures in the sellar region. This review will describe the MR appearance of the normal and abnormal pituitary gland and proposes an algorithm for the management strategy of some of the most common abnormalities in or around the sella.

Autosomal dominant familial neurohypophyseal diabetes insipidus caused by a novel nonsense mutation in AVP-NPII gene

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare single-gene disorder caused by mutations of the arginine vasopressin-neurophysin II (AVP-NPII) gene. These changes impair the release of vasopressin from the posterior pituitary gland. In the present study, the AVP-NPII gene of a Chinese adult patient with central diabetes insipidus, the patient's symptomatic mother and an asymptomatic sister of the patient was sequenced. Examination of the family history revealed cases of FNDI across four generations. Gene sequencing analysis revealed a novel heterozygous mutation, c.268A>T (p.Lys90Ter), in exon 2 of the AVP-NPII gene, in the patient and the patient's mother, which led to the loss of 6 cysteine residues and aberrant disulfide bonds, which is predicted to alter the mature protein structure. The present study identified a novel heterozygous nonsense mutation of the AVP-NPII gene associated with FNDI, which broadens the spectrum of known mutations associated with this disorder and contributes to the understanding of its molecular basis.

A novel AVP gene mutation in a Turkish family with neurohypophyseal diabetes insipidus

PURPOSE

Familial neurohypophyseal diabetes insipidus (FNDI) is a rare, autosomal dominant, inherited disorder which is characterized by severe polydipsia and polyuria generally presenting in early childhood. In the present study, we aimed to analyze the AVP gene in a Turkish family with FNDI.

METHODS

Four patients with neurohypophyseal diabetes insipidus and ten healthy members of the family were studied. Diabetes insipidus was diagnosed by the water deprivation test in affected family members. Mutation analysis was performed by sequencing the whole coding region of AVP-NPII gene using DNA isolated from peripheral blood samples.

RESULTS

Urine osmolality was low (<300 mOsm/kg) during water deprivation test, and an increase more than 50 % in urine osmolality and recovery of the symptoms were observed by the administration of desmopressin in all patients. Plasma copeptin levels were lower than expected according to plasma osmolality. Pituitary MRI revealed partial empty sella with a bright spot in index patient and a normal neurohypophysis in the other affected subjects. Genetic screening revealed a novel, heterozygous mutation designated as c.-3A>C in all patients.

CONCLUSION

c.-3A>C mutation in 5'UTR of AVP gene in this family might lead to the truncation of signal peptide, aggregation of AVP in the cytoplasm instead of targeting in the endoplasmic reticulum, thereby could disrupt AVP secretion without causing neuronal cytotoxicity, which might explain the presence of bright spot. The predicted effect of this mutation should be investigated by further in vitro molecular studies.

Normal dimensions of the posterior pituitary bright spot on magnetic resonance imaging

Object

The normal pituitary bright spot seen on unenhanced T1-weighted MRI is thought to result from the T1-shortening effect of the vasopressin stored in the posterior pituitary. Individual variations in its size may be difficult to differentiate from pathological conditions resulting in either absence of the pituitary bright spot or in T1-hyperintense lesions of the sella. The objective of this paper was to define a range of normal dimensions of the pituitary bright spot and to illustrate some of the most commonly encountered pathologies that result in absence or enlargement of the pituitary bright spot.

Methods

The authors selected normal pituitary MRI studies from 106 patients with no pituitary abnormality. The size of each pituitary bright spot was measured in the longest axis and in the dimension perpendicular to this axis to describe the typical dimensions. The authors also present cases of patients with pituitary abnormalities to highlight the differences and potential overlap between normal and pathological pituitary imaging.

Results

All of the studies evaluated were found to have pituitary bright spots, and the mean dimensions were 4.8 mm in the long axis and 2.4 mm in the short axis. The dimension of the pituitary bright spot in the long axis decreased with patient age. The distribution of dimensions of the pituitary bright spot was normal, indicating that 99.7% of patients should have a pituitary bright spot measuring between 1.2 and 8.5 mm in its long axis and between 0.4 and 4.4 mm in its short axis, an interval corresponding to 3 standard deviations below and above the mean. In cases where the dimension of the pituitary bright spot is outside this range, pathological conditions should be considered.

Conclusions

The pituitary bright spot should always be demonstrated on T1-weighted MRI, and its dimensions should be within the identified normal range in most patients. Outside of this range, pathological conditions affecting the pituitary bright spot should be considered.

Influence of age and sex on signal intensities of the posterior lobe of the pituitary gland on T1-weighted images from 3 T MRI

PURPOSE

To elucidate the influence of age and sex on the signal intensity (SI) of the posterior lobe of the pituitary gland (PPG) on T1-weighted images (T1WI) from 3 T MRI.

MATERIALS AND METHODS

Sagittal T1WI acquired from three-dimensional fast spoiled gradient recalled acquisition in the steady state in 1,634 subjects without conditions affecting antidiuretic hormone were evaluated retrospectively. The presence or absence of a bright signal in the PPG was assessed qualitatively. The SI ratio of the PPG to the pons (SIR) was obtained from quantitative measurements. We statistically analyzed these data, creating 14 subject groups categorized according to age and sex, and applied a Poisson generalized linear model to the SIR data.

RESULTS

The characteristic bright signal was absent in 47 subjects (2.8 %), with no significant difference in incidence among the groups. The SIR was inversely related to age in both males (r > 0.7) and females (r > 0.9), and was significantly higher in females in the third to the eighth decades (p < 0.05). Analysis of the whole SIR dataset using a generalized linear model showed that the estimated SIR decreased by 1.7 % per decade and is higher in females.

CONCLUSION

Age and sex influence the SI of the PPG on T1WI. These findings may aid the recognition of PPG signal abnormalities on T1WI.

Pediatric disorders of water balance

Fluid homeostasis requires adequate water intake, regulated by an intact thirst mechanism and appropriate free water excretion by the kidneys, mediated by appropriate secretion of arginine vasopressin (AVP, also known as antidiuretic hormone). AVP exerts its antidiuretic action by binding to the X chromosome-encoded V2 vasopressin receptor (V2R), a G protein coupled receptor on the basolateral membrane of renal collecting duct epithelial cells. After V2R activation, increased intracellular cyclic adenosine monophosphate mediates shuttling of the water channel aquaporin 2 to the apical membrane of collecting duct cells, resulting in increased water permeability and antidiuresis. Clinical disorders of water balance are common, and abnormalities in many steps involving AVP secretion and responsiveness have been described. This article focuses on the principal disorders of water balance, diabetes insipidus, and the syndrome of inappropriate antidiuretic hormone secretion.

Clinical features and molecular analysis of arginine-vasopressin neurophysin II gene in long-term follow-up patients with idiopathic central diabetes insipidus

INTRODUCTION: Central diabetes insipidus (DI) characterized by polyuria, polydipsia and inability to concentrate urine, has different etiologies including genetic, autoimmune, post-traumatic, among other causes. Autosomal dominant central DI presents the clinical feature of a progressive decline of arginine-vasopressin (AVP) secretion. OBJECTIVE: In this study, we characterized the clinical features and sequenced the AVP-NPII gene of seven long-term follow-up patients with idiopathic central DI in an attempt to determine whether a genetic cause would be involved. METHODS: The diagnosis of central DI was established by fluid deprivation test and hyper-tonic saline infusion. For molecular analysis, genomic DNA was extracted and the AVP-NPII gene was amplified by polymerase chain reaction and sequenced. RESULTS: Sequencing analysis revealed a homozygous guanine insertion in the intron 2 (IVS2 +28 InsG) of the AVP-NPII gene in four patients, which represents an alternative gene assembly. No mutation in the code region of the AVP-NPII gene was found. CONCLUSIONS: The homozygous guanine insertion in intron 2 (IVS2 +28 InsG) is unlikely to contribute to the AVP-NPII gene modulation in DI. In addition, the etiology of idiopathic central DI in children may not be apparent even after long-term follow-up, and requires continuous etiological surveillance.

Pediatric disorders of water balance

Fluid homeostasis requires adequate water intake, regulated by an intact thirst mechanism and appropriate free water excretion by the kidneys, mediated by appropriate secretion of arginine vasopressin (AVP, also known as antidiuretic hormone). AVP exerts its antidiuretic action by binding to the X chromosome-encoded V2 vasopressin receptor (V2R), a G protein-coupled receptor on the basolateral membrane of renal collecting duct epithelial cells. After V2R activation, increased intracellular cyclic adenosine monophosphate mediates shuttling of the water channel aquaporin 2 to the apical membrane of collecting duct cells, resulting in increased water permeability and antidiuresis. Clinical disorders of water balance are common, and abnormalities in many steps involving AVP secretion and responsiveness have been described. This article focuses on the principal disorders of water balance, diabetes insipidus, and the syndrome of inappropriate antidiuretic hormone secretion.

Identification, characterization and rescue of a novel vasopressin-2 receptor mutation causing nephrogenic diabetes insipidus

OBJECTIVE

X-linked nephrogenic diabetes insipidus (XNDI), caused by mutations in the V2 vasopressin receptor (V2R), is clinically distinguished from central diabetes insipidus (CDI) by elevated serum vasopressin (AVP) levels and unresponsiveness to 1-desamino-8-d-arginine vasopressin (DDAVP). We report two infants with XNDI, and present the characterization and functional rescue of a novel V2R mutation.

PATIENTS

Two male infants presented with poor growth and hypernatraemia. Both patients had measurable pretreatment serum AVP and polyuria that did not respond to DDAVP, suggesting NDI. However, both also had absent posterior pituitary bright spot on MRI, which is a finding more typical of CDI.

METHODS

The AVPR2 gene encoding V2R was sequenced. The identified novel missense mutation was re-created by site-directed mutagenesis and expressed in HEK293 cells. V2R activity was assessed by the ability of transfected cells to produce cAMP in response to stimulation with DDAVP. Membrane localization of V2R was assessed by fluorescence microscopy.

RESULTS

Patient 1 had a deletion of AVPR2; patient 2 had the novel mutation L57R. In transiently transfected HEK293 cells, DDAVP induced detectable but severely impaired L57R V2R activity compared to cells expressing wild-type V2R. Fluorescence microscopy showed that myc-tagged wild-type V2R localized to the cell membrane while L57R V2R remained intracellular. A nonpeptide V2R chaperone, SR121463, partially rescued L57R V2R function by allowing it to reach the cell membrane.

CONCLUSIONS

L57R V2R has impaired in vitro activity that can be partially improved by treatment with a V2R chaperone. The posterior pituitary hyperintensity may be absent in infants with XNDI.

A case of lymphocytic infundibuloneurohypophysitis: histophathological studies

A 57-year-old woman presented with 2-year history of polyuria and polydipsia. Hormonal studies revealed almost normal anterior pituitary function and central diabetes insipidus. Magnetic resonance imaging showed thickening of the pituitary stalk and enlargement of the neurohypophysis without high intensity of the posterior lobe on T1-weighted images, which were compatible with lymphocytic infundibuloneurohypophysitis. Transsphenoidal biopsy was done and histological examination disclosed moderate fibrosis and lymphocytic infiltration not only in the posterior pituitary, but also in the adjacent anterior pituitary part of the gland. The lymphocytes both in the anterior and posterior pituitary were mainly T cells that were positive for UCHL 1, CD 3, and CD 8. Immunofluorescence of frozen tissue detected immunecomplex deposition in small vessels and the interstitium. These findings suggested that allergic reactions may play an important role in the pathogenesis of lymphocytic infundibuloneurohypophysitis.

Occult neurohypophyseal germinomas in patients presenting with central diabetes insipidus

Although neurohypophyseal germinoma is known be a common initial symptom in cases of diabetes insipidus (DI), its radiological detection may take months or years even by a high-resolution magnetic resonance (MR) imaging. The term “occult neurohypophyseal germinoma” denotes such cases, but its clinical picture remains obscure.

Of seven patients with neurohypophyseal germinoma presenting with DI during the last 5 years, three patients showed no evidence of tumor at the onset of DI and were treated as “idiopathic” DI. Neurohypophyseal germinoma was eventually diagnosed in these three patients as the tumor became evident on sequential MR imaging studies and the patients were successfully treated with chemotherapy and radiation therapy. To delineate the clinical features of the occult neurohypophyseal germinoma, the authors analyzed endocrinological aspects and MR images in these patients and compared them with those in two patients with true idiopathic DI and four patients with overt neurohypophyseal germinoma and DI. Nine previously reported cases in the literature were reviewed. During the stage at which the germinoma gave no notable change on MR images, patients often displayed anterior pituitary dysfunction, particularly growth hormone (GH) deficiency, or an elevation of serum or cerebrospinal fluid human chorionic gonadotropin-beta. Preceding the appearance of an obvious tumor mass, a slight swelling of the pituitary stalk with loss of normal hyperintensity of the posterior pituitary lobe was a common finding on MR imaging.

Central DI associated either with an enlarged stalk, decreased GH secretion, or an elevated serum human chorionic gonadotropin-beta should prompt the diagnosis of an occult germinoma.

Reversible endocrine dysfunction and pituitary stalk enlargement

We report 4 patients (3 of which were children) with diabetes insipidus and different degrees of hypopituitarism in whom a pituitary stalk enlargement was disclosed on imaging techniques, and in whom radiological and functional recovery was observed during follow-up. Pituitary substitution therapy with desmopressin, thyroxine, hydrocortisone, growth hormone and/or oral contraceptives was prescribed. During follow-up, regression of the stalk lesion was seen which was spontaneous in 2 cases, following a short course of corticosteroids in another and an empirical trial of tuberculostatic drugs in the fourth. A partial recovery of pituitary function was also observed. These cases illustrate that pituitary stalk enlargement and associated hypopituitarism may be reversible; however, this morphological and functional recovery has rarely been described in adults and has not been previously reported in children.

Dystopic neurohypophysis

A dystopic neurohypophysis was noted incidentally at autopsy in a 51 -year-old man with no endocrine abnormality. The dystopic gland was situated in the upper region of the tuber cinereum and macroscopically simulated a neoplasm. The pituitary fossa contained only anterior hypophyseal elements. Review of the literature disclosed 19 such cases discovered at autopsy; 11 occurred in normal individuals with no endocrine abnormality. Radiological study revealed 145 additional cases. Except for the 6 occurrences described in normal individuals, the rest occurred in patients with anterior pituitary dysfunction. No instance of isolated diabetes insipidus has been reported due to dystopia of the neurohypophysis. Dystopia of the neurohypophysis in normal individuals should be distinguished from those occurring in patients with anterior pituitary abnormalities. The former represent a true dystopia and are not associated with perinatal injury, in contrast to the latter, which are acquired dystopias secondary to regeneration of the neurohypophysis and are associated with perinatal injury. Although anterior and posterior pituitary glands are formed by appositional growth, their development and functional status are entirely independent. Finally, the most significant clinical feature of dystopic neurohypophysis is the absence of any related symptoms and this condition should always be considered in the clinical differential diagnosis of hypothalamic lesions. In such patients, a surgical procedure may be avoided because other hypothalamic lesions, such as hamartomas and astrocytomas, are more frequently symptomatic.

Lymphocytic infundibuloneurohypophysitis as a cause of central diabetes insipidus

BACKGROUND

Central diabetes insipidus may be familial, secondary to hypothalamic or pituitary disorders, or idiopathic. Idiopathic central diabetes insipidus is characterized by selective hypofunction of the hypothalamic-neurohypophysial system, but its cause is unknown.

METHODS

We studied 17 patients with idiopathic diabetes insipidus, in whom the duration of the disorder ranged from 2 months to 20 years. Only four patients had been treated with vasopressin before the study began. All the patients underwent endocrinologic studies and magnetic resonance imaging (MRI) with a 1.5-T superconducting unit, and two patients had biopsies of the neurohypophysis or the pituitary stalk.

RESULTS

Nine of the 17 patients had thickening of the pituitary stalk, enlargement of the neurohypophysis, or both and lacked the hyperintense signal of the normal neurohypophysis. In the remaining eight patients, the pituitary stalk and the neurohypophysis were normal, although the hyperintense signal was absent. The abnormalities of thickening and enlargement were seen on MRI only in the patients who had had diabetes insipidus for less than two years, and the abnormalities disappeared during follow-up, suggesting a self-limited process. In addition to vasopressin deficiency, two patients had mild hyperprolactinemia and nine had impaired secretory responses of growth hormone to insulin-induced hypoglycemia. The two biopsies revealed chronic inflammation, with infiltration of lymphocytes (mainly T lymphocytes) and plasma cells.

CONCLUSIONS

Diabetes insipidus can be caused by lymphocytic infundibuloneurohypophysitis, which can be detected by MRI. The natural course of the disorder is self-limited.

Anterior pituitary function and computed tomography/magnetic resonance imaging in patients with Langerhans cell histiocytosis and diabetes insipidus

In order to document anterior pituitary dysfunction in patients with biopsy-proven Langerhans cell histiocytosis (LCH) and diabetes insipidus and to correlate this with structural changes on imaging, we performed an insulin tolerance test, enhanced computed tomography (CT), and unenhanced magnetic resonance imaging (MRI) in nine patients. Six of the nine patients had growth hormone deficiency, which in two patients was part of panhypopituitarism and in one was associated with poor cortisol response to insulin hypoglycemia. One patient had an exaggerated growth hormone response and one who had had neck irradiation as an infant, had a high resting thyroid stimulating hormone (TSH) suggesting compensated primary hypothyroidism. All enhanced CTs were abnormal, bony defects being the only abnormality in two patients and opaque mastoids in one. The remaining six patients all had structural changes in the hypothalamic/pituitary region. Unenhanced MRI confirmed the CT findings except in one child who had been treated with radiotherapy in the intervening period, but, in addition, confirmed diabetes insipidus by showing absence of the posterior pituitary bright signal and picked up white matter changes in a child with clinical neurological dysfunction. Our findings indicate that the development of diabetes insipidus in LCH is commonly associated with anterior pituitary dysfunction and is usually associated with structural changes in the hypothalamic/pituitary axis.

Central diabetes insipidus resulting from a nonneoplastic tiny mass lesion localized in the neurohypophyseal system

With the advent of magnetic resonance imaging (MRI), the neurohypophyseal system can be clearly delineated and its functional integrity can be predicted. The authors describe seven cases of central diabetes insipidus (DI) that occurred spontaneously. MRI revealed that the normal hyperintensity of the pituitary posterior lobe, which has been thought to be the neurosecretory material containing antidiuretic hormone, was absent in all cases. In addition, enlargement of a part of the neurohypophyseal system was recognized in five of seven cases on MRI. Three of the five patients with enlargement of a part of the neurohypophyseal tract underwent biopsy and were demonstrated to have chronic inflammation of the neurohypophyseal system. It was demonstrated that the enlarged parts of the neurohypophyseal system had shrunk either spontaneously or after the biopsy in four of the five cases. All patients are alive and have not experienced progression or remission of the disease. This study indicates that some cases of idiopathic DI result from a tiny mass lesion, usually nonneoplastic, localized in the neurohypophyseal system.

MR imaging of the pituitary gland in central precocious puberty

Cranial magnetic resonance imaging was performed in 17 children with central precocious puberty (CPP) and 19 aged-matched controls to compare the appearance of the pituitary gland. Gland size was measured on T1-weighted sagittal and coronal images. The gland was graded according to the concavity or convexity of the upper surface, and the signal intensity of the gland was assessed visually. The mean pituitary volume in 13 CPP children without hypothalamic tumor (292.6 mm3) was significantly greater than that in normal controls (181.35 mm3). The mean volume for the four CPP children with hypothalamic tumor was smaller (145.0 mm3). Compared to controls, the upper pituitary surface in CPP patients appeared convex in a higher proportion. The anterior pituitary was isointense to pons in all patients and controls. Although the posterior pituitary bright spot was present in 14 controls and 11 CPP patients, none with hypothalamic tumor showed it.

Magnetic resonance imaging in familial central diabetes insipidus

More detailed examinations of the pituitary gland in central diabetes insipidus (CDI) has been possible with magnetic resonance imaging (MRI). Compared to the high signal findings in the posterior lobes of normal subjects, the absence of such signal in adults and children with primary CDI has been reported. Familial CDI is a hereditary form of primary CDI with a variety of clinical expressions among affected individuals which is said to be related to varying degrees of an arginine vasopressin (AVP) deficiency. However, the structural correlates have yet to be documented by MRI technique. This report describes the pituitary gland MRI findings (using a superconducting magnet; 3 mm-slice thickness; spinecho, repetition time 400 ms, echo time 25 ms) in five patients in one family with familial CDI. A signal of high intensity was detected in the posterior part of the pituitary gland in 2 patients but not in 3 others. We concluded that MRI of the posterior pituitary lobe in familial CDI seem to vary in members of the same family.

Brain MR in patients with Langerhans cell histiocytosis: findings and enhancement with Gd-DTPA

The brains of eight patient with Langerhans Cell Histiocytosis (LCH) were studied with magnetic Resonance Imaging (MRI). One scan was normal and a spectrum of abnormalities was seen in the others. Five patients had absence of the posterior pituitary bright spot, and four with evidence of pituitary dysfunction had a lesion in the region of the hypothalamus. An orbital extraconal mass was noted in one child with exopthalmus. This decreased in a follow-up study after Vinblastine therapy. The cerebellum was abnormal in two patients; the area of the dentate nuclei exhibited abnormal signal in one asymptomatic child and the MRI of another boy with a ten year history of progressive cerebellar dysfunction showed cerebral and cerebellar atrophy. Three of the five patients with deficiency of antidiuretic hormone (ADH) were studied both before and after the administration of intravenous Gadolinium-DTPA. In all three, after administration of the contrast agent, there was enhancement of involved areas.