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Published online before print April 15, 2005, 10.1148/radiol.2353040243
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(Radiology 2005;235:999-1004.)
© RSNA, 2005

Neuroradiology

The Pituitary Gland: Changes on MR Images During the 1st Year after Delivery1

Yukio Miki, MD, PhD, Milliam L. Kataoka, MD, PhD, Toshiya Shibata, MD, PhD, Tabassum L. Haque, MBBS, Mitsunori Kanagaki, MD, Taro Shimono, MD, PhD, Tomohisa Okada, MD, PhD, Akira Hiraga, RT, Sadahiko Nishizawa, MD, PhD, Hiroyuki Ueda, MD, Mahbubur Rahman, MBBS, MPH, PhD and Junji Konishi, MD, PhD

1 From the Departments of Nuclear Medicine and Diagnostic Imaging (Y.M., M.L.K., T.S., T.L.H., M.K., T.S., T.O., S.N., H.U., J.K.) and Radiology and Nuclear Medicine Service (A.H.), Kyoto University Hospital, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; and Department of Epidemiological and Clinical Information Management, Kyoto University Graduate School of Medicine, Kyoto, Japan (M.R.). Received February 8, 2004; revision requested April 15; revision received June 20; accepted July 27. Supported in part by a grant from the Ministry of Education Culture, Sports, Science and Technology of Japan. Address correspondence to Y.M. (e-mail: mikiy@kuhp.kyoto-u.ac.jp).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To longitudinally and prospectively investigate changes in the volume and signal intensity on T1-weighted magnetic resonance (MR) images of the pituitary gland up to 1 year after delivery and evaluate whether termination of lactation has an effect on these parameters.

MATERIALS AND METHODS: All participants provided informed consent for participation in the study, which was approved by the institutional review board. Thirteen volunteers (mean age, 28 years; age range, 26–32 years) underwent MR imaging 2 and 4 weeks after delivery and then at intervals of 0.5–2.0 months until 1 year after delivery. Eight participants terminated lactation during the study period. Sagittal and coronal T1-weighted images were obtained. Signal intensities of the anterior and posterior lobes of the pituitary were calculated relative to that of the pons. The volume of the pituitary was also calculated. Two-tailed paired Student t tests and separate simple linear regression analyses were used to test for statistically significant differences.

RESULTS: The mean pituitary volume was 544 mm3 at 2 weeks, 523 mm3 at 4 months, 512 mm3 at 8 months, and 511 mm3 at 12 months after delivery, with significant differences between 2 weeks and 4 months (P = .002) and between 4 and 8 months (P = .003) after delivery. The mean ratio of the signal intensity of the anterior lobe of the pituitary to the signal intensity of the pons was 1.11 at 2 weeks, 1.07 at 4 months, 1.03 at 8 months, and 1.00 at 12 months after delivery, with significant differences between 2 weeks and 4 months (P = .004) and between 4 and 8 months (P = .0001) after delivery. Termination of lactation had no statistically significant effect on pituitary volume or the ratio of the signal intensity of the anterior or posterior lobe of the pituitary to the signal intensity of the pons.

CONCLUSION: The volume of the pituitary gland decreases up to 8 months after delivery, and the T1-weighted signal intensity of the anterior lobe of the pituitary decreases; termination of lactation has no statistically significant effect on these parameters.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Results of several autopsy studies have revealed that the pituitary gland may be enlarged in pregnant and postpartum women (1–4). Pituitary gland enlargement in pregnancy has also been evaluated in vivo with magnetic resonance (MR) imaging (5,6). The signal intensity of the anterior lobe of the pituitary on T1-weighted MR images may also be increased during pregnancy (7).

Elster et al (6) and Dinc et al (8) analyzed the MR imaging appearance of the pituitary in postpartum women up to 6 months after delivery. Elster et al (6) reported that the volume of the pituitary gland rapidly returns to normal beyond the 1st week after delivery. Dinc et al (8) reported no significant differences in pituitary volume between subjects studied 2–6 months after delivery and nonpregnant control subjects. These studies, however, are cross sectional; thus, a small change in volume might have been masked by individual variation in pituitary volume. To overcome the flaw of cross-sectional analysis in detecting such a small change in pituitary volume, longitudinal analysis is mandatory. However, to the best of our knowledge, no investigators have longitudinally investigated changes in the pituitary after delivery.

Moreover, results of several animal studies have revealed regression of the pituitary gland after termination of lactation (9–11). The effect of lactation on the human pituitary gland has not yet been fully studied (4).

In view of the foregoing, the purpose of our study was to longitudinally and prospectively investigate changes in volume and signal intensity on T1-weighted images of the pituitary gland up to 1 year after delivery and determine whether the termination of lactation has an effect on these parameters.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Subjects
Thirteen healthy female volunteers who demonstrated no evidence of pituitary disorder participated in this prospective study after delivering a baby. Subject age at delivery ranged from 26 to 32 years (mean, 28 years). Because previous investigators (4,5) have demonstrated differences in pituitary weights between multi- and primigravid women, our study was limited to primigravid subjects. All subjects underwent neurologic examinination by one of the coauthors (M.L.K., with 1 year of experience as a neurology resident and 9 years of experience as a radiologist) and were free from any neurologic signs or symptoms. Subjects taking any medications were excluded from the study because medication might affect pituitary function. Owing to potential risks to fetuses from MR imaging (12), subjects with a possible second pregnancy were either excluded from the study or left the study. As a consequence, one participant left the study 8 months after delivery. The remaining 12 participants participated in the study until 1 year after delivery. No participants underwent MR imaging within 2 weeks after delivery (0–13 days after delivery) because it was not practical for us to ask the subject to come to our institution for the study (it is widely believed in our country that women are supposed to be at rest for at least 2 weeks after delivery). All participants provided informed consent for participation in the study, which was approved by the institutional review board of Kyoto University Medical School.

After delivering a baby, the subjects underwent MR imaging at 2 and 4 weeks after delivery and then at intervals of 0.5–2.0 months until 1 year after delivery. A total of 132 MR images were obtained. All 13 participants breast-fed their babies until at least 6 months after delivery; eight subjects terminated lactation during the study period. After termination of lactation, MR imaging was performed at intervals of 2 weeks for up to 1 month to identify any rapid changes in pituitary volume or signal intensity.

MR Imaging Technique
MR imaging was performed by using a 1.5-T unit (Signa Horizon; GE Medical Systems, Milwaukee, Wis). Sagittal and coronal T1-weighted images of the pituitary were obtained by using a spin-echo sequence with the following parameters: repetition time msec/echo time msec, 400/14; two signals acquired; 18-cm field of view; image acquisition matrix, 256 x 256; and 3-mm-thick sections without an intersection gap. The polarity of the readout gradient on the sagittal and coronal images was set so that fat was moved posteriorly and inferiorly, respectively, by chemical shift misregistration artifacts. This technique is important for observing the pituitary without overlapping by fatty marrow in the dorsum sellae or clivus (13–17).

Pituitary Gland Measurements
Images were electronically transferred to a personal computer workstation (Personal Station DP500; Plat’Home, Tokyo, Japan). ExaVision LITE (version 1.02d) software (ZIO Software, Tokyo, Japan) was used for image display and quantitative measurements. Measurements were performed by one of the authors (T.L.H., with 4 years of experience in MR imaging of the brain), who was blinded to subject information.

In some previous studies, pituitary volume was estimated from the length, width, and height of the gland (5,18). This method, however, may lead to substantial error because the sella differs from person to person and the sella floor can be shallow or deep—which substantially alters the morphologic characteristics of the pituitary. Error may also result because the width and length of the pituitary may not substantially change because of the bony sella, whereas the height is very dependent on factors such as the curvature of the gland. Thus, we measured gland volume by means of outright segmentation. The segmentation was manually and carefully performed on coronal T1-weighted images. In addition, the mean signal intensities of the anterior lobe of the pituitary gland and the pons were measured by placing regions of interest. We fixed the sizes of these regions of interest at 6, 3, and 12 mm2 for the anterior lobe of the pituitary, posterior lobe of the pituitary, and pons, respectively, because we believed these sizes to be small enough to set within each region. Because the signal intensity of the pons did not substantially change in our study, signal intensities of the anterior and posterior lobes of the pituitary gland were evaluated by using ratios of the signal intensities of those lobes to that of the pons on T1-weighted images, according to methods used in previous studies (7,18). We did not measure the signal intensity of the pituitary on T2-weighted images because, to our knowledge, there have been no reports describing a change in the signal intensity of the pituitary on T2-weighted images that is associated with pregnancy.

In addition to obtaining quantitative measurements, we visually assessed the shape of the pituitary gland on MR images; this was performed by two experienced neuroradiologists (Y.M. and T.L.H.), who were blinded to subject information. Pituitary shape was assessed on sagittal T1-weighted images by using the five-point scoring system proposed by Elster et al (6). In this scoring system, grade 1 represents a gland with a markedly concave superior surface; grade 2, a gland with a mildly concave superior surface and less than 2 mm of depression centrally; grade 3, a gland with a flat superior surface; grade 4, a gland with a mildly (<2 mm) convex superior surface; and grade 5, a gland with a markedly convex superior surface that appears nearly spherical on sagittal images (6). The superior surface of the pituitary was defined as the surface that is in contact with cerebrospinal fluid. Initial evaluations were made independently, and any disagreements over final conclusions (which occurred with five of the 132 MR images [3.8%]) were resolved by consensus.

Statistical Analyses
The statistical analyses were performed by a statistician (M.R.). Data are presented as means ± standard deviations. Two-tailed paired Student t tests were used to evaluate differences in pituitary volumes and relative signal intensity ratios of the anterior and posterior lobes between MR images obtained at 2 weeks and those obtained at 4 months (n = 13), between those obtained at 4 and those obtained at 8 months (n = 13), and between those obtained at 8 months and those obtained at 1 year (n = 12) after delivery. The Wilcoxon signed rank test was used to evaluate if there was a difference in pituitary shape score between MR images obtained at 2 weeks and those obtained at 4 months (n = 13), between those obtained at 4 and those obtained at 8 months (n = 13), and between those obtained at 8 months and those obtained at 1 year (n = 12) after delivery. The Bonferroni adjustment procedure was applied for multiple comparisons to keep the type I error less than .05. Thus, P values less than .0167 (.05 divided by three, the number of comparison groups) were considered to indicate statistically significant differences.

Simple linear regression analyses (one model for one patient) were performed by using the following variables: the time after delivery (independent variable), pituitary volume, and relative signal intensity ratios of the anterior and posterior lobes (dependent variables). In addition, time-series analysis was performed by using forced (because the time of measurement was not equally spaced) generalized least-squares regression to determine whether pituitary volume or signal intensity ratios of the anterior and posterior lobes changed significantly after delivery. Separate simple linear regression analyses were conducted to examine the relationship between the time of termination of lactation (independent variable) and pituitary volume or relative signal intensity ratios of the anterior and posterior lobes of the pituitary (dependent variables). All statistical analyses were performed by using either Stata Intercooled version 7 (Stata, College Station, Tex) or JMP statistical software version 5.0.1 (SAS Institute, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Volume
The mean pituitary volume was 544 mm3 ± 41 at 2 weeks, 523 mm3 ± 40 at 4 months, 512 mm3 ± 41 at 8 months, and 511 mm3 ± 41 at 12 months after delivery. Volumes differed significantly between 2 weeks and 4 months (P = .002) and between 4 and 8 months (P = .003) after delivery but not between 8 and 12 months after delivery. Changes in pituitary volume showed good fits with the time after delivery for all participants (Fig 1).



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  		Figure 1. Graph shows changes in pituitary volume after delivery for all participants. Different symbols indicate different participants. Adjusted R2 values were between 0.46 and 0.96, coefficients were negative, and P values were less than .05 in all cases.

 
Signal Intensity
The mean ratio of the signal intensity of the anterior lobe of the pituitary to the signal intensity of the pons was 1.11 ± 0.06 at 2 weeks, 1.07 ± 0.07 at 4 months, 1.03 ± 0.08 at 8 months, and 1.00 ± 0.09 at 12 months after delivery. The signal intensity of the anterior lobe of the pituitary relative to the signal intensity of the pons differed significantly between 2 weeks and 4 months (P = .004) and between 4 and 8 months (P = .0001) after delivery. However, the relative signal intensity of the anterior lobe did not differ significantly between 8 and 12 months, although overall relative signal intensities showed good fits in linear regression models (Fig 2).



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  		Figure 2. Graph shows changes in the signal intensity of the anterior lobe of the pituitary relative to the signal intensity of the pons for all participants. Different symbols indicate different participants. Adjusted R2 values were between 0.54 and 0.91, coefficients were negative, and P values were less than .05 for 12 of the 13 subjects. One subject had an R2 value of 0.40 and a P value of .15.

 
The mean ratio of the signal intensity of the posterior lobe of the pituitary to the signal intensity of the pons was 1.62 ± 0.16 at 2 weeks, 1.60 ± 0.17 at 4 months, 1.59 ± 0.17 at 8 months, and 1.59 ± 0.17 at 12 months after delivery. The signal intensity of the posterior lobe of the pituitary relative to the signal intensity of the pons did not differ significantly between any of the compared periods. Relative signal intensities of the posterior lobe of the pituitary were within 5% of each other (Fig 3). Results of linear regression, however, showed good fits in some subjects.



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  		Figure 3. Graph shows changes in the signal intensity of the posterior lobe of the pituitary relative to the signal intensity of the pons for all participants. Different symbols indicate different participants. Adjusted R2 values were between 0.45 and 0.65, coefficients were negative, and P values were less than .05 in four of the 13 subjects.

 
Relationship between Time after Delivery and Volume and Signal Intensity Ratio
Results of time-series analysis with generalized least-squares regression showed that pituitary volume decreased during the time (in months) after delivery (regression coefficient, –2.0; P = .001), as did the ratios of the signal intensity of the anterior lobe of the pituitary to the signal intensity of the pons (regression coefficient, –0.007; P = .001), although the changes in the relative signal intensities of the posterior lobes were not statistically significant (regression coefficient, –0.002; P = .072).

Shape
At 2 weeks after delivery, the superior surface of the pituitary gland was classified as grade 3 (n = 3), grade 4 (n = 3), or grade 5 (n = 7). At 4 months after delivery, the surface was classified as grade 2 (n = 2), grade 3 (n = 4), grade 4 (n = 4), or grade 5 (n = 3). At 8 months after delivery, the surface was classified as grade 2 (n = 2), grade 3 (n = 4), grade 4 (n = 4), or grade 5 (n = 3). At 1 year after delivery, the surface was classified as grade 2 (n = 2), grade 3 (n = 3), grade 4 (n = 5), or grade 5 (n = 2) (Table). The Wilcoxon signed rank test revealed a statistically significant difference in pituitary gland shape score between 2 weeks and 4 months after delivery (P = .004). However, this score did not differ significantly between 4 and 8 months (P > .99) or between 8 and 12 months (P = .50) after delivery (Figs 4, 5).


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  		Grades for Superior Contour of Pituitary Gland after Delivery

 


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  		Figure 4a. Subject 1. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 26-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is markedly convex (grade 5). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface (arrow) displays mild convexity (grade 4). The anterior lobe of the pituitary is hyperintense to the pons at 2 weeks (a), slightly hypointense to the pons at 4 months (b), and markedly hypointense to the pons at 8 (c) and 12 (d) months after delivery.

 


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  		Figure 4b. Subject 1. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 26-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is markedly convex (grade 5). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface (arrow) displays mild convexity (grade 4). The anterior lobe of the pituitary is hyperintense to the pons at 2 weeks (a), slightly hypointense to the pons at 4 months (b), and markedly hypointense to the pons at 8 (c) and 12 (d) months after delivery.

 


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  		Figure 4c. Subject 1. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 26-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is markedly convex (grade 5). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface (arrow) displays mild convexity (grade 4). The anterior lobe of the pituitary is hyperintense to the pons at 2 weeks (a), slightly hypointense to the pons at 4 months (b), and markedly hypointense to the pons at 8 (c) and 12 (d) months after delivery.

 


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  		Figure 4d. Subject 1. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 26-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is markedly convex (grade 5). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface (arrow) displays mild convexity (grade 4). The anterior lobe of the pituitary is hyperintense to the pons at 2 weeks (a), slightly hypointense to the pons at 4 months (b), and markedly hypointense to the pons at 8 (c) and 12 (d) months after delivery.

 


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  		Figure 5a. Subject 7. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 32-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is essentially flat (grade 3). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface is mildly concave (grade 2). The anterior lobe of the pituitary appears hyperintense to the pons 2 weeks after delivery (a) and appears almost isointense to the pons 4 (b), 8 (c), and 12 (d) months after delivery.

 


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  		Figure 5b. Subject 7. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 32-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is essentially flat (grade 3). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface is mildly concave (grade 2). The anterior lobe of the pituitary appears hyperintense to the pons 2 weeks after delivery (a) and appears almost isointense to the pons 4 (b), 8 (c), and 12 (d) months after delivery.

 


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  		Figure 5c. Subject 7. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 32-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is essentially flat (grade 3). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface is mildly concave (grade 2). The anterior lobe of the pituitary appears hyperintense to the pons 2 weeks after delivery (a) and appears almost isointense to the pons 4 (b), 8 (c), and 12 (d) months after delivery.

 


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  		Figure 5d. Subject 7. Sagittal T1-weighted spin-echo MR images (400/14) of pituitary gland in 32-year-old woman who delivered a baby. Arrowhead indicates the pons. (a) Image obtained 2 weeks after delivery shows that the superior surface of the pituitary gland (arrow) is essentially flat (grade 3). (b-d) Images obtained 4, 8, and 12 months after delivery, respectively, show that the superior surface is mildly concave (grade 2). The anterior lobe of the pituitary appears hyperintense to the pons 2 weeks after delivery (a) and appears almost isointense to the pons 4 (b), 8 (c), and 12 (d) months after delivery.

 
Relationship to Termination of Lactation
Results of simple linear regression analyses showed no statistically significant relationship between termination of lactation and pituitary volume or relative signal intensity ratios of the anterior or posterior lobes of the pituitary gland in separate models.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
 
To the best of our knowledge, this is the first study in which the changes in the pituitary gland after delivery were longitudinally investigated, revealing that the volume of the pituitary gland decreases after delivery up to 8 months after delivery. Thus, the volume of the pituitary gland decreases for a longer period than previously thought. Analysis of MR imaging findings led Elster et al (6) to report that the volume of the pituitary gland rapidly returns to normal beyond the 1st week after delivery. Dinc et al (8) also reported no significant differences in pituitary volume between subjects studied 2–6 months after delivery and control subjects. Differences between the results of the present study and those reported by Elster et al (6) and Dinc et al (8) are probably attributable to the cross-sectional nature of those earlier studies. Because there is substantial interindividual variation in pituitary gland volume (19), cross-sectional studies may fail to reveal subtle changes in volume.

In the present study, the pituitary shape scores showed significant differences between 2 weeks and 4 months after delivery; however, these scores did not differ significantly between 4 and 8 months or between 8 and 12 months. This may be contradictory with our finding that pituitary volume significantly differed between 4 and 8 months after delivery; however, we believe the reason the pituitary shape scores did not significantly differ between 4 and 8 months after delivery is that the volume change in this period is too small to be noticed visually.

The results of our study also demonstrated that the signal intensity of the anterior lobe of the pituitary on T1-weighted MR images also decreases up to 8 months after delivery. Miki et al (7) reported that the anterior lobe of the pituitary may be hyperintense on T1-weighted MR images during pregnancy or in the postpartum period. Although the mechanisms of the association between hyperintensity of the anterior pituitary gland on T1-weighted images and pregnancy are not fully understood, they are believed to be related to histologic changes within the lobe (7). The most striking histologic change in the anterior lobe of the pituitary that is associated with pregnancy is hyperplasia of prolactin cells (4,20,21). If it is assumed that the hyperintensity of the anterior lobe of the pituitary on T1-weighted images is related to an increase in the number of prolactin cells, our results concur with those from the pathology study by Scheithauer et al (4), who reported that hyperplasia of prolactin cells gradually disappears within several months after delivery. Because we used T1-weighted images to measure signal intensities, the T2 effect may have partially caused signal intensity changes; in the future, it may be useful to measure true T1 and T2 relaxation times. Other methods, including fat-suppression imaging, T2*-weighted susceptibility imaging, or MR spectroscopy, may also be useful for evaluating the characteristics of the neurochemical changes in the anterior lobe of the pituitary.

The signal intensity of the posterior lobe of the pituitary did not differ significantly between 2 weeks and 4, 8, and 12 months after delivery. The posterior lobe of the pituitary is usually hyperintense to the pons on T1-weighted images, and this high signal intensity is well known to be due to neurosecretory granules that contain antidiuretic hormone (13,15,22,23). Our results suggest that the number of neurosecretory granules that contain antidiuretic hormone does not change significantly after delivery. To the best of our knowledge, there are no reports in the literature in which the relationship between oxytocin and high signal intensity in the posterior lobe of the pituitary has been described; oxytocin might not have a substantial effect on signal intensity in the posterior lobe of the pituitary.

In this study, we failed to identify any statistically significant effect of termination of lactation on volume and T1-weighted signal intensity of the pituitary gland. This finding agrees with those of Elster et al (6), who found no significant differences in height or convexity of the pituitary between lactating and nonlactating women. Further investigation, however, is needed to determine the effect of lactation on the volume of the pituitary gland and the signal intensity of the anterior lobe of the pituitary because the subject population in the current study may have been too small to enable us to detect minor variations.

There were a few drawbacks to this study. Owing to ethical considerations and practical limitations, MR imaging was not performed during pregnancy or within 2 weeks after delivery. The volume of the pituitary gland is reportedly maximal at term or within 1 week after delivery (6,8,24). Therefore, the current investigation does not reveal the percentage decrease in pituitary volume compared to maximum volume. Because we did not measure the volume of the anterior and posterior lobes of the pituitary separately, the change in the volume of the posterior lobe may partly have affected the total pituitary volume, although we believe that this change (if any) is small. Prolactin levels were not measured in this study because we wished to make this study minimally invasive. However, future studies are needed to reveal any correlation between a decrease in gland volume or T1-weighted signal intensity and a decrease in prolactin levels.

The results of our longitudinal in vivo study revealed that both the volume of the pituitary gland and the signal intensity on T1-weighted MR images of the anterior lobe decrease until 8 months after delivery; the termination of lactation had no statistically significant effect on volume and T1-weighted signal intensity. It may be useful to be aware of this physiologic change in the pituitary gland when interpreting MR images in postpartum patients.


   FOOTNOTES
 
Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, Y.M.; literature research, Y.M.; clinical studies, M.L.K.; data acquisition, all authors; data analysis/interpretation, Y.M., M.L.K., T.L.H., M.K.; statistical analysis, Y.M., M.R.; manuscript preparation, Y.M.; manuscript definition of intellectual content, revision/review, and final version approval, all authors; manuscript editing, Y.M., M.L.K., T.L.H., M.K., T.S., T.O., M.R.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 

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