Imaging of the pituitary

In the appropriate clinical setting of pituitary hyperfunction or hypofunction, visual field deficit, or cranial nerve palsy, imaging of the pituitary is necessary. This article reviews the normal appearance of the pituitary and its surroundings, emphasizing magnetic resonance imaging. Typical and variant appearances of pituitary pathology are discussed. Because growth of adenoma into surrounding structures is important to surgical management, cavernous sinus invasion and suprasellar spread as well as adenoma mimics are illustrated. Typical examples of pituitary dysfunction from other entities that secondarily affect the gland, hypophysis, or third ventricle are discussed. Some common errors of interpretation are listed.     

Neuroimaging in posttraumatic hypopituitarism

Posttraumatic hypopituitarism is the failure of the hypothalamic-pituitary axis secondary to traumatic brain injury. It can clinically present as decreased muscle mass, concentration, libido, and fertility. It can also present as increased fatigue, depression, and cognitive deficits. In addition, electrolyte abnormalities such as hyponatremia can occur in hypopituitarism. As a result of heightened awareness of posttraumatic hypopituitarism, it is a phenomenon that is becoming more commonly diagnosed. Posttraumatic hypopituitarism is a diagnosis based on clinical evaluation, laboratory testing, and neuroimaging. Of the radiological techniques, magnetic resonance imaging is the preferred technique to image the pituitary gland. This article contains coronal and sagittal magnetic resonance imaging of the posterior fossa, illustrating the normal hypothalamus and pituitary gland as well as adjacent structures. The sequential enhancement pattern of the normal pituitary gland is consistent with its vascular supply. A colored illustration was created to display the vascular supply to the hypothalamus, pituitary stalk, and pituitary gland.     

Magnetic resonance tomography of pituitary tumors

This paper presents a survey of the current status of the diagnosis of pituitary tumors by means of magnetic resonance imaging. It focuses on the clinical and practical aspects. The recommended procedure and the sequences and slice orientations for magnetic resonance imaging of the pituitary gland are presented, and the features that are essential for the diagnosis of pituitary tumors are discussed.     

Magnetic resonance imaging in familial central diabetes insipidus

Summary 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.     

Measurement of temperature changes in cooling dead rats using magnetic resonance thermometry

Magnetic resonance imaging thermometry has been introduced as a technique for measurement of temperature changes in cooling dead rats. Rat pelvic magnetic resonance images were acquired sequentially more than 2 h after euthanasia by halothane overdose. A series of temperature difference maps in cooling dead rats was obtained with calculating imaging phase changes induced by the water proton frequency shift caused by temperature changes. Different cooling processes were monitored by the temperature difference maps in the rats. Magnetic resonance imaging thermometry applied in the study of laboratory animals could theoretically reproduce a variety of causes of death with different environmental conditions. Outcomes from experimental animal studies could be translated into a temperature-based time of death estimation in forensics.     

Normal and abnormal pituitary glands: gadopentetate dimeglumine-enhanced MR imaging

Dynamic magnetic resonance (MR) imaging with a 1.5-T superconductive unit was used in the evaluation of nine normal pituitary glands and 10 pituitary adenomas, including four microadenomas and six macroadenomas. Seven to 10 images were obtained every 20-30 seconds with use of the spin-echo technique after rapid injection of gadopentetate dimeglumine. The earliest contrast material enhancement of normal structures was seen in the infundibulum and posterior lobe of the pituitary gland at 20 seconds, followed by gradual contrast material enhancement of the anterior lobe of the pituitary gland from the junction of the infundibulum to the peripheral portion of the anterior lobe of the pituitary gland within 80 seconds after gadopentetate dimeglumine injection. The peak enhancement of pituitary adenomas occurred at 60-200 seconds, usually after the most marked enhancement of the normal pituitary gland. Microadenomas are best visualized at earlier phases of gadopentetate dimeglumine-enhanced dynamic imaging, with signal intensity lower than that seen on images of normal pituitary glands.     

Is technetium-99m-MIBI taken up by the normal pituitary gland? A comparison of normal pituitary glands and pituitary adenomas

PURPOSE: The aim of this study was to compare the behavioral uptake of a normal gland and a pituitary adenoma and to assess the ability to diagnose pituitary adenoma by means of technetium-99m-hexakis-2-methoxy-isobutyl-isonitrile (MIBI) single photon emission computed tomography (SPECT). METHODS: The study included 15 patients with pituitary adenomas (mean age = 44.0 years, range 19-63) and 15 control subjects (mean age = 50.7 years, range 20-67). SPECT was performed 15 minutes after an intravenous injection of MIBI 600 MBq. The shape and location of MIBI uptake were evaluated on a magnetic resonance (MR) imaging/SPECT registration image. The shape patterns and location were classified as follows: Shape C (circular); LO (longitudinal oval); T/R (triangular or rectangular) and location P (pituitary gland or adenoma); D/C (dorsum sellae and/or clivus). RESULTS: Analysis of the uptake showed that 10 (67%) adenomas were C, and 5 (33%) were LO. Of the controls, 5 (33%) were C, and 10 (69%) were T/R. With regard to location, all patients with pituitary adenomas were classified as P, and all control subjects (93%) but one showed uptake in the dorsum sellae and clivus (D/C). CONCLUSION: MIBI was taken up in the dorsum sellae or clivus but not the normal pituitary gland and had a strong affinity for the pituitary adenoma. This result implies that MIBI SPECT may be a useful new auxiliary examination technique for the location diagnosis of pituitary adenoma.     

In vivo manganese MR imaging of calcium influx in spontaneous rat pituitary adenoma

BACKGROUND AND PURPOSE: Rapid uptake of the calcium analog manganese (Mn2+) into spontaneous pituitary adenoma during MR imaging of aged rats generated the hypothesis that neuroendocrine tumors may have a corresponding increase in calcium influx required to trigger hormonal release. A goal of this study was to investigate the potential for clinical evaluation of pituitary adenoma by MR imaging combined with administration of Mn2+ (Mn-MR imaging). MATERIALS AND METHODS: Mn-MR imaging was used to characterize the dynamic calcium influx in normal aged rat pituitary gland as well as spontaneous pituitary adenoma. To confirm the validity of Mn2+ as a calcium analog, we inhibited Mn2+ uptake into the olfactory bulb and pituitary gland of normal rats by using the calcium channel blocker verapamil. Rats with adenomas received fluorodeoxyglucose-positron-emission tomography (FDG-PET) scanning for characterization of tumor metabolism. Mn2+ influx was characterized in cultured pituitary adenoma cells. RESULTS: Volume of interest analysis of the normal aged pituitary gland versus adenoma indicated faster and increased calcium influx in adenoma at 1, 3, 11, and 48 hours. Mn2+ uptake into the olfactory bulb and pituitary gland of normal rats was inhibited by calcium channel blockers and showed dose-dependent inhibition on dynamic MR imaging. FDG-PET indicated correlation between tumor energy metabolism and Mn2+ influx as well as tumor size. CONCLUSION: These results indicate that adenomas have increased activity-dependent calcium influx compared with normal aged pituitary glands, suggesting a potential for exploitation in the clinical work-up of pituitary and other neuroendocrine tumors by developing Mn-MR imaging for humans.     

Magnetic resonance imaging evaluation of radiation-induced changes in experimentally implanted renal cell carcinoma

The effect of radiation on the magnetic resonance imaging appearance and relaxation parameters of human renal cell tumors implanted in male white-Swiss athymic nude mice was evaluated. Twenty-three mice were treated with external beam radiation, receiving a total dose of 2,500 rads administered in a single treatment limited to subcutaneous tumor. Twenty-two tumor-bearing mice served as control animals. Experimental and control mice were studied with MRI at four (n = 9), seven (n = 20), 14 (n = 8), and 28 (n = 8) days following experimental radiotherapy. A 0.35 tesla superconductive MRI system was employed. Images were generated using spin-echo technique with repetition times (TR) of 500 and 2,000 ms and echo-delay times (TE) of 28 to 30 and 56 to 60. Relaxation time calculations were made on the basis of tumor signal-intensity measurements in assigned regions of interest. The MRI appearances and relaxation times of irradiated tumors that decreased in size following treatment, irradiated tumors that grew, and control tumors were similar, as were their histologic features. No statistically significant differences could be detected in relaxation times of the four experimental and four control groups. Statistical evaluation was performed using analysis of variance. Further investigation of MRIs potential in tissue characterization following radiotherapy is warranted, but evaluation of change in tumor dimensions remains the most reliable indicator of therapeutic response.     

Characterization of experimental spinal cord injury with magnetization transfer ratio histograms

This study was designed to characterize the severity of tissue damage in experimental spinal cord injury using magnetization transfer (MT) histogram analysis. Seven Sprague-Dawley rats were subjected to laminectomy and standard weight-drop injury to the spinal cord (four rats at 15 cm drop-height and three rats at 2.5 cm). Three control animals underwent laminectomy without weight-drop. After sacrifice, the animals were scanned at 1.9 T with a pulsed off-resonance MT technique. Following magnetic resonance (MR) imaging, the cords were embedded in paraffin and sectioned into 5-microm sections for semiquantitative histopathological analysis. Composite histograms were generated using data spanning an axial distance of 3 cm centered on the injury site. MT histogram parameters, such as the amount of tissue with statistical correspondence to normal white matter, were highly predictive of histopathological results, including myelination state and neurofilament damage. Less correlation with edema was observed, suggesting that the technique was most sensitive to true tissue alteration.     

Effect of tamoxifen in an experimental model of breast tumor studied by dynamic contrast-enhanced magnetic resonance imaging and different contrast agents

OBJECTIVES: The aim of this study was to compare the efficacy of gadoteridol, B22956/1 (a new protein binding blood pool contrast agent), and (Gd-DTPA)37-albumin in detecting, by dynamic contrast-enhanced magnetic resonance imaging (MRI), the effect in vivo of tamoxifen in an experimental model of breast tumor implanted in rats. MATERIALS AND METHODS: Tumors were induced by subcutaneous injection of 10 mammary adenocarcinoma cells (13762 MAT B III). Treatment with tamoxifen (or vehicle) started on day 4 after implantation. On day 10 after implantation, animals were observed by MRI using B22956/1 (or gadoteridol) and, 24 hours later, using (Gd-DTPA)37-albumin. RESULTS: Dynamic contrast-enhanced magnetic resonance imaging data showed that tamoxifen treatment decreased vascular permeability to B22956/1, whereas no difference was detectable in permeability to gadoteridol or to (Gd-DTPA)37-albumin. No effect on fractional plasma volume was detected with either of contrast agents. CONCLUSIONS: B22956/1 is superior to both small Gd chelates and macromolecular contrast agents in the assessment of the effect of tamoxifen treatment on tumor vasculature.     

超急性脑梗死及灌注功能磁共振成像研究的实验模型制作

目的：用改良线栓法制作鼠大脑中动脉阻塞超急性脑梗死及其再灌注功能磁共振成像的实验模型。材料和方法：22只SD大,同分成5组,其中2只为假手术A组,其余按栓塞时间30min及1、3、6h均分为B、C、D、E四组。A组于2、24h后,B、C、D、E组分别于栓塞后30min,1、3、6h以及线栓拔出后2、24h行弥散加权成像和灌注成像扫描;并将成像所见与病理观察对比。结果：A组弥散加权成像、灌注成像无异常信号,病理观察无变化。B、C、D、E组弥散加权成像、灌注成像均见阻断侧大脑中动脉供血区异常信号区,病理观察见该供血区脑组织坏死和缺血改变。结论：该方法制作超急性脑梗死及再灌注功能磁共振成像研究的实验模型是稳定的、可行的。     

Magnetic resonance imaging of the pituitary gland

Magnetic resonance imaging (MRI), a nonionizing, biologically safe imaging technique, is bringing the desired goal of directly imaging the pituitary gland very close to reality. The exquisite anatomic demonstration of the gland and hypophyseal stalk and the perisellar structures and the usefulness of tissue characterizations (T1 and T2 values) firmly establish the role of MRI in imaging of pituitary gland abnormalities, with the potential of becoming the procedure of choice.     

Pituitary fossa: chemical shift effect in MR imaging

The effect of chemical shift on magnetic resonance (MR) imaging of the pituitary fossa was studied. Healthy volunteers underwent conventional MR imaging of the pituitary fossa and then imaging with the frequency-encoding gradient reversed or with the phase- and frequency-encoding gradients interchanged. Comparison of the image pairs in each subject showed that the thin, black stripe evident at the water-fat interface within the pituitary fossa was altered when the gradients were changed. Therefore, the low-intensity signal within the pituitary fossa is a chemical shift misregistration effect.     

Imaging of the pituitary in children with growth disorders

Magnetic resonance imaging reveals the anatomy of the pituitary and hypothalamus with unique detail. The clinical and biochemical investigation of short stature in childhood may be difficult and complex; magnetic resonance imaging of the pituitary is a non-invasive technique which can help to clarify the diagnosis of growth hormone insufficiency and to determine its cause. Most cases of growth hormone insufficiency have previously been considered to be idiopathic; in about 60% of these children, magnetic resonance imaging shows a characteristic structural abnormality which has been termed pituitary stalk interruption syndrome. The most important role of magnetic resonance imaging is in the diagnosis of destructive lesions of the hypothalamic-pituitary axis which may initially present with growth failure.     

MR imaging with ultrasmall superparamagnetic iron oxide particles in experimental soft-tissue infections in rats

PURPOSE: To investigate the feasibility of macrophage magnetic resonance (MR) imaging in rats by using an experimental soft-tissue infection model. MATERIALS AND METHODS: Thirteen rats with unilateral calf-muscle infection were imaged with a 4.7-T MR imager at an early chronic stage of infection (day 4 before contrast material injection, days 4-7 after injection). Eleven animals were imaged before and 3 and 24 hours after intravenous application of ultrasmall superparamagnetic iron oxide (USPIO), and eight animals were additionally imaged 48 hours and three animals 72 hours after USPIO application. Two infected rats served as controls. T1- and T2-weighted spin-echo and T2*-weighted gradient-echo sequences were applied. All animals were sacrificed, and histopathologic findings were correlated with findings on MR images. Electron microscopy was performed in two rats. For quantitative analysis, signal intensities on T2*-weighted images and T2 values on T2 maps were measured within regions of interest, and the temporal variation was analyzed by using the signed rank test. RESULTS: Visualization of USPIO-loaded macrophages was most sensitive with a T2*-weighted sequence. USPIO distribution pattern and quantitative analysis of T2 and T2* effects 3 hours after USPIO application were significantly different (P <.05) from those at 24 and 48 hours, reflecting the dynamic transit of the particle accumulation from the intravascular to the intracellular compartment by means of macrophage phagocytosis. Local signal intensity alterations could be correlated with iron-loaded macrophages at histopathologic examination. CONCLUSION: Activated macrophages in acute soft-tissue infection can be labeled with USPIOs and detected with MR imaging because of susceptibility effects.     

Expression of Hsp27 and Hsp70 and vacuolization in the pituitary glands in cases of fatal hypothermia

Hypothermia causes systemic cellular stress. The pituitary gland is an endocrine gland and plays an important role in thermoregulation. When the core body temperature drops, the pituitary gland is activated by stimulation of hypothalamic hormones. In this study, we investigated morphological alterations of the pituitary gland in cases of fatal hypothermia. Several morphological alterations of the anterior lobe of the pituitary gland, such as hemorrhage, vacuolization, and hyperemia, have been previously described in fatal hypothermia. However, the diagnostic value of these findings is controversial. We compared 11 cases of fatal hypothermia with 10 cases lacking antemortem hypothermic influences. In the presence of thermal cellular stress, the expression of heat shock proteins increases to protect cellular structures. Therefore, we immunohistochemically analyzed Hsp27 and Hsp70. Hsp27 expression was detected in 27.3% of the cases of fatal hypothermia and in 10.0% of the control cases, whereas Hsp70 expression was not detected in any case. Additionally, Sudan staining was performed to quantify fatty degeneration. A positive reaction was found in 45.5% of the study group and in 10.0% of the control group. This indicates that fatty degeneration might be a valuable marker when other macroscopic signs of hypothermia are absent.     

Pituitary adenomas and normal pituitary tissue: enhancement patterns on gadopentetate-enhanced MR imaging

A dynamic study of magnetic resonance (MR) imaging was used to obtain successive heavily T1-weighted coronal images (spin-echo [SE] 100/15 [repetition time msec/echo time msec]) of normal pituitary glands and pituitary adenoma immediately after patients were given an intravenous bolus injection of gadopentetate dimeglumine. The images were obtained every minute for 5-8 minutes at 1.5 T. Usual T1-weighted images (SE 600/15) were also obtained before and after the dynamic study was performed. The study group consisted of 18 patients, 10 with normal pituitary glands, and eight with pituitary adenoma. Normal pituitary glands showed maximum enhancement on the first or second image following the administration of gadopentetate dimeglumine, followed by gradual signal reduction through the later images, whereas pituitary adenomas reached a peak of enhancement later and showed slower signal reduction than normal pituitaries. The difference of enhancement patterns between the normal pituitary gland and the pituitary adenoma produced prominent image contrast on the first or second image after administration of gadopentetate dimeglumine, which improved the visualization of one microadenoma and four normal pituitary glands that had been displaced by large adenomas. Dynamic MR imaging is a useful diagnostic procedure not only for detection of microadenomas, but also for visualization of pituitary glands that have been displaced by large pituitary adenomas.     

Rapid progression of pituitary hyperplasia in humans with primary hypothyroidism: demonstration with MR imaging.

PURPOSE: To use magnetic resonance (MR) imaging to evaluate the morphologic changes of the pituitary gland during the development of hypothyroidism. MATERIALS AND METHODS: Fourteen patients who had undergone thyroidectomy were evaluated before radioactive iodine 131 therapy. In each patient, MR imaging and measurement of serum hormone levels were performed twice: 5 weeks before 131I treatment as the "euthyroid state" with thyroid hormone supplementation and on the day of 131I treatment as the "hypothyroid state" after a 3-week depletion of thyroid hormone supplements. Nine healthy volunteers also underwent MR imaging twice at an interval of 5 weeks. Pituitary volume and the relative signal intensity ratio of the anterior pituitary to the pons were measured. The shape and signal intensity of the pituitary gland were also visually assessed. The paired Student t test was used to evaluate the significance of the data. A P value less than .05 indicated a statistically significant difference. RESULTS: The patients had significantly larger pituitary volume in the hypothyroid state than in the euthyroid state both quantitatively (P < .001) and visually. No significant differences were found in the relative signal intensity ratios of the anterior pituitary to the pons. In healthy volunteers, no significant differences in pituitary volumes or signal intensity were found between the two MR images. CONCLUSION: Rapid progression of hyperplasia of the anterior pituitary may occur with acute development of hypothyroidism.     

Evaluation of pituitary microadenomas with dynamic MR imaging.

PURPOSE: To evaluate the use of keyhole dynamic magnetic resonance (MR) imaging in the evaluation of women with borderline hyperprolactinemia. PATIENTS and METHODS: We investigated 30 patients (mean age 31.6+/-4.3 years) with moderate hyperprolactinemia and clinically suspected microadenomas on T1-weighted spin echo (SE) sequences (repetition time (TR)/echo time (TE) 625/15 ms) with keyhole dynamic imaging and contrast enhancement of the pituitary gland. The probability of lesion presence according to MR criteria was ranked on a five-grade scale and compared with standard examinations of the hypophysis before and after intravenous administration of contrast media. RESULTS: The probability for lesion presence showed a trend toward lower scores on standard SE sequences and higher scores with dynamic imaging (P=0.067). CONCLUSION: Dynamic keyhole imaging of the pituitary gland could help establish a diagnosis of microadenomas with a higher probability.