Measures of pituitary gland and stalk: from neonate to adolescence

Introduction

Magnetic resonance imaging (MRI) is the modality of choice in the evaluation of pituitary morphology and the use of this modality has increased dramatically over the last three decades (1). Pituitary stalk (PS) and pituitary gland (PG) abnormalities, such as empty sella, tumors, and midline malformations, can easily be assessed by MRI (2). However, assessment of some abnormalities, such as pituitary hypoplasia, might be difficult, therefore, normative data about PG and PS have become more necessary (3).

The PG forms in the sixth to seventh embryonic weeks and is situated in a protective sella turcica. The anterior PG arises from an invagination of the oral ectoderm and forms Rathke’s pouch, whereas the posterior PG originates from neuroectoderm (4). The sizes of PG vary with age and physiologic status and it becomes its largest size during hormonally active conditions (such as puberty or pregnancy) (5, 6). In the literature, it has been reported that the height of the PG may reach 8 mm in pubertal boys (7). There are some reports about pituitary measurements in children with different age groups, however, these data pertain to a limited number of subjects and to low MRI technology (8, 9).

The PS shows similar changes depending on age and hormonal status (5, 6, 10–12). The ratio of PS to basilar artery (diameter) is used as a screening method for PS thickening and if the ratio is close to 1, further investigation is needed for tumoral thickening (e.g., germinoma, histiocytosis) (13). To the best of our knowledge, measurements of the PS in childhood and adolescence using 1.5- or 3-T MRI have not been studied until now. Accordingly, the aim of our study was to provide data regarding the PG size and PS/basilar artery (BA) ratio in healthy children according to age and gender.

Materials and methods

This study was submitted and approved by the Local Research Ethics Committee.

MR measurements

Four radiologists (S.S., V.A., E.O., and S.I.) were initially trained for the measurements by a pediatric radiologist (M.K.) experienced in cranial/pituitary MR assessment. Before performing the measurements, we selected 20 patients for a pilot study. In the pilot study, four radiologists performed all measurement and discussed the difference between them. They worked on this issue until they have reached a consensus on measurements. At the beginning, 120 randomly selected patients were evaluated by all radiologists to determine interclass correlation coefficient as an interobserver reliability measure. Then, all 517 images were examined by one of the four radiologists. The flowchart diagram of the study is given in Figure 1.

Figure 1

Flowchart of the study group.

Measurements

The PG and PS were measured on mid-sagittal and coronal images (Figure 2A). The coronal width and height of PG were evaluated on coronal images. Sagittal width of the PG is shown in Figure 2B. PG volume was calculated with the height×coronal width×sagittal width×0.5 formula (1). The diameters of the PS and BA were measured on axial images on the same plane in the middle of the PS (Figure 2C). PS/BA ratio was calculated.

Figure 2

(A) Height and coronal width of the pituitary gland on coronal plane. (B) Width of the pituitary gland on sagittal plane. (C) Pituitary stalk and basilar artery on axial plane.

Results

There were 10–22 children in each age group and there were 517 children in total, with 261 girls. Pituitary diameters, volume and PS thickness were determined in all subjects. All PG dimensions were showing an increase with advancing age. Due to different findings between girls and boys, the results were given separately by gender. The median height of the pituitary gland was 3.81±0.68 and 8.48±1.08 mm for girls in the younger than 1-year-old group and 18-year-old age group, respectively, for boys, it was 3.91±0.75 and 6.19±0.88 mm, respectively. The maximum and minimum PS/BA for girls were 0.73±0.12 mm in younger than 1-year-old age group and 0.59±0.10 mm in the 8-year-old age group. The ratios for boys were 0.70±0.12 mm in the 18-year-old age group and 0.56±0.11 in the 9-year-old age group. The results are shown in Tables 1 and 2. Figures 3 and 4 include diagrams for the standard deviation scoring system.

Figure 3

Pituitary height plotted against age for girls.

Figure 4

Pituitary height plotted against age for boys.

Discussion

In this study, we have reported the MRI data of the pituitary gland and stalk in healthy children from neonate to adolescent. Although MRI of the pituitary gland is advocated as part of the essential investigations to be performed in children with diagnosis and follow-up of those endocrine diseases, its interpretation as regards the pituitary imaging is difficult and subjective. Therefore, standardization in these diameters are considered necessary.

Craniocaudal, transverse, and anteroposterior diameters are named as height, coronal width, and width, respectively. Indirect volume calculations were performed for pituitary volume, height×coronal width×width×0.5 derived from the volume calculation of ellipsoid (1). However, the shape of PG can be disrupted due to pituitary pathologies and ellipsoid appearance might be distorted. In these circumstances, the formula can cause misinterpretation. In general, pituitary height is accepted to reflect pituitary growth. During puberty, there is a spike of pituitary height followed by a plateau when it reaches adult values. In our study, increasing time of PG volume and height was 11 years old for girls and 13 years old for boys. The time was consistent with pubertal onset. Again, in our study, the PG size was significantly larger in girls than in boys, which was similar to the study of Takano et al. (14). Although volumetric studies from indirect volume calculation had some different results (15, 16), we suggest that this simple formula can be used to predict the pituitary volume.

PS also shows similar changes depending on age or physiologic status, such as PG dimensions (5, 6, 10–12). Many pathologic entities have been shown to lead enlargement of the PS, including diabetes insipidus due to histiocytosis and other causes, such as tumors, metastases, sarcoidosis, and infections. Therefore, assessment of the normal appearance of the PS is important for an accurate diagnosis. The appearance of PS lesions may be a radiologic challenge, therefore, standardization of the PS diameter is also necessary. The PS to BA ratio is a readily applied visual screening tool that enables easy recognition of the possibly abnormal PS and ratio close to one should alert the clinician. Classically accepted PS to BA ratio is <1 and our results support this ratio where maximum ratios were 0.73 and 0.70 in girls and boys, respectively.

The main limitation of our study is its retrospective style of reviewing previous MR scans. There has not been any consideration concerning the clinical and laboratory data of the subjects. Another minor drawback could be the lack of percentile curves (for age and sex) that was due to an insufficient number of subjects for such an analysis.

In conclusion, our study demonstrated the PG size and PS thickness data of children in various age groups from newborn to adolescent. Future prospective studies with larger samples that correlate the structural findings with the clinical and laboratory results are awaited.