You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
pituitary hyperplasia secondary to primary hypothyroidism ( pph ) has been described in case reports [ 13 ] .
reported that pituitary hyperplasia was present in 90% of primary hypothyroidism children with serum thyrotropin ( tsh )
primary hypothyroidism is also a well - recognized etiology of low growth hormone ( gh ) levels .
regression of the pituitary hyperplasia and low gh levels after adequate thyroid hormone replacement therapy have been reported separately [ 2 , 7 ] . to our knowledge ,
only a few cases of children with pph accompanied by low gh levels have been reported in the literature .
few studies have investigated changes in gh secretion in short - stature children with pph . to clarify this issue
, we analyzed clinical , hormonal , and imaging changes in a cohort of short - stature children with pph accompanied by low gh levels before and after 3 months of thyroid hormone replacement therapy .
this retrospective study was carried out at the department of pediatrics of shandong provincial hospital , shandong university , between march 2010 and october 2013 .
the study was approved by the ethical committee of the hospital . written informed consent was obtained from parents .
the diagnosis of pph was based on typical symptoms and signs of hypothyroidism , low free thyroxine ( ft4 ) level with high tsh level , and regression of the hyperplastic pituitary after thyroid hormone replacement therapy .
we excluded children with sexual precocity or history of other endocrine disorders or systemic diseases .
children who had taken thyroid hormones and/or recombinant human growth hormone ( rhgh ) before the study were also excluded .
11 children with low gh levels ( gh peak  10  ng / ml ) were included in the final analysis .
the following parameters were collected at baseline : chronological age ( ca ) , bone age ( ba ) , height , weight , pituitary height , and serum levels of gh peak , free triiodothyronine ( ft3 ) , ft4 , tsh , thyroid peroxidase antibody ( tpoab ) , thyroglobulin antibody ( tgab ) , insulin - like growth factor-1 ( igf-1 ) , and prolactin ( prl ) .
all children were treated with levothyroxine ( l - t4 ) ( 60100  g /
height was measured to the nearest 0.1  cm by a standard stadiometer with the subjects wearing no shoes .
weight was measured to the nearest 0.1  kg by an electronic scale with the subjects wearing light clothing .
height was expressed as height standard deviation scores ( htsds ) using normative values for chinese children .
body mass index ( bmi ) was calculated as weight ( kg)/height ( m ) .
breast stages ( b1b5 ) , genital stages ( g1g5 ) , and pubic hair stages ( ph1ph5 ) were evaluated according to tanner criteria .
girls with stages of b1 ( no breast development ) and ph1 ( no pubic hair ) and boys with stages of g1 ( testicular volume  3  ml ) and ph1 were considered prepubertal .
serum ft3 , ft4 , tsh , tpoab , and tgab levels were measured using chemiluminescence assay ( advia centaur , siemens healthcare diagnostics , usa ) .
the intra- and interassay coefficients of variation ( cvs ) for thyroid hormones were < 4.0% and < 3.0% , respectively .
reference ranges for ft3 , ft4 , tsh , tpoab , and tgab were 3.56.5  pmol / l , 11.522.7  pmol / l , 0.355.5  miu / l , 060  iu / ml , and 060  iu / ml , respectively .
the sensitivity of ft3 , ft4 , tsh , tpoab , and tgab was 0.3 
pmol / l , 1.3  pmol / l , 0.001  miu / l , 0.1  iu / ml , and 10  iu / ml , respectively .
serum igf-1 levels were measured using chemiluminescence assay ( immulite 2000 , siemens healthcare diagnostics , usa ) .
the sensitivity was 20  ng / ml . serum gh and prl levels were measured using chemiluminescence assay ( cobas e170 , roche diagnostics , germany ) .
the intra- and interassay cvs for the assays were < 5.0% and < 8.0% , respectively .
serum gh levels were determined at 0 , 30 , 60 , 90 , 120 , and 150  min after two stimulation tests ( arginine test and levodopa test ) .
ba was determined by radiograph of the left hand and wrist according to the method of greulich and pyle .
ultrasound examination of the thyroid was performed on a logiq 9 scanner ( ge medical systems , milwaukee , wi , usa ) with a 512  mhz transducer .
mri scans of the pituitary were obtained in the sagittal and coronal planes on t1- and t2-weighted images using a 3.0 t scanner ( siemens , erlangen , germany ) , with 3  mm slice thickness .
statistical analyses were conducted using spss version 17.0 program ( chicago , il , usa ) .
nonparametric variables were expressed as median ( interquartile range ) . paired t - test ( parametric test )
was used to determine the significance of clinical , hormonal , and imaging changes before and after therapy .
baseline characteristics of the 11 children ( 8 boys and 3 girls ) are displayed in table 1 .
patients 7 ( tanner 2 ) , 8 ( tanner 4 ) , and 11 ( tanner 2 ) were in puberty .
growth retardation was the most common manifestation ( n = 11 , 100% ) , followed by dry skin ( n = 9 , 81.8% ; 6 boys and 3 girls ) . other symptoms and signs were fatigue , sluggish speech , and slow movement ( n = 7 , 63.6% ; 5 boys and 2 girls ) , weight gain ( n = 6 , 54.5% ; 4 boys and 2 girls ) , puffy face and mental retardation ( n = 5 , 45.5% ; 4 boys and 1 girl ) , and anemia ( n = 4 , 36.4% ; 3 boys and 1 girl ) .
liver dysfunction was suggested by elevated aminotransferases ( n = 8 , 72.7% ; 7 boys and 1 girl ) ; five of the seven boys had elevated cholesterol and low - density lipoprotein ( ldl ) cholesterol levels .
visual symptoms and signs were not found in all children . as shown in table 1 ,
all children had decreased gh peak and ft3 and ft4 levels , elevated tsh levels , and delayed ba .
serum igf-1 levels were decreased in seven ( 63.6% ) children and normal in four children ( patients 1 , 6 , 9 , and 11 ) .
serum prl levels were elevated in 10 ( 90.9% ) children and normal in one child ( patient 3 ) .
mri scans showed homogeneously enlarged pituitary gland with suprasellar extension in 11 children ( 100% ) .
of the 11 children , two children ( 18.2% ) had increased thickness of pituitary stalk , two children ( 18.2% ) had invisible pituitary stalk , 3 children ( 27.3% ) had compressed optic chiasm , and one child ( 9.1% ) had rathke 's cleft cyst .
the clinical symptoms and signs of hypothyroidism improved after 3 months of l - t4 treatment .
serum ft3 , ft4 , and igf-1 levels were significantly higher than before treatment ( p < 0.001 , p < 0.001 , and p = 0.004 ) .
serum tsh and prl levels were significantly lower than before treatment ( p < 0.001 , p < 0.001 ) .
the pituitary height was significantly less than before treatment ( p < 0.001 ) ( table 2 ) .
mri scans showed complete resolution of the hyperplastic pituitary in eight children ( patients 1 , 2 , 3 , 7 , 8 , 9 , 10 , and 11 ) . in three children ( patients 4 , 5 , and 6 ) , the pituitary height after 3 months of therapy decreased by 7  mm , 7.5  mm , and 7.7  mm , respectively .
reassessment of pituitary mri scans after 6 months of therapy revealed normal size of pituitary in those three children .
two children ( patients 5 and 6 ) still had subnormal gh peak levels ( 5.5  ng / ml and 7.1  ng / ml , resp . ) despite resolution of both thyroid function and pituitary height .
in other children , repeat gh peak levels returned to normal and were more than 10  ng / ml .
gh peak levels increased from 5.0  2.7  ng / ml to 13.8  4.0  ng / ml after l - t4 therapy ( figure 1 ) .
in the present study of short - stature children with pph accompanied by low gh levels , decreased ft3 , ft4 , igf-1 , and gh levels and elevated values of tsh , prl , and pituitary height were observed .
low growth hormone levels could be resolved after thyroid hormone replacement therapy in most short - stature children with pph .
thyroid hormone replacement therapy led to improvement of thyroid hormones , igf-1 , gh and prl levels , and the enlarged pituitary .
the association of pituitary hyperplasia and primary hypothyroidism was first reported by niepce in 1851 .
sporadic cases of pituitary hyperplasia in patients with primary hypothyroidism have been published since then .
insufficient production of thyroid hormones directly or indirectly leads to overproduction of tsh and thyrotropin - releasing hormone ( trh ) due to the loss of thyroxine feedback inhibition [ 13 , 14 ] . elevated trh levels stimulate both pituitary thyrotrophs and lactotrophs hypertrophy and subsequent enlargement of the pituitary gland , resulting in oversecretion of tsh and prl levels .
histological examination of the enlarged pituitary gland in patients with primary hypothyroidism has shown hyperplasia of both thyrotrophs and lactotrophs [ 15 , 16 ] .
the reported incidence of hyperprolactinemia was 75% in patients with pph . in our study ,
90.9% of short - stature children with pph accompanied by low gh levels had elevated prl levels .
the normal pituitary gland undergoes dramatic changes in size and shape due to physiological alterations in hormones during puberty .
pituitary enlargement is much more prominent in girls in puberty , but it can also occur in boys . the pituitary gland can reach a height of 810  mm in girls and 7  mm in boys .
regression in pituitary hyperplasia after l - t4 therapy on follow - up mri scans can be distinguished from pituitary adenoma .
gh secretion could be decreased in short - stature children with pph and accompanied by delayed ba . in our small number of short - stature children with pph
upward convexity of the pituitary gland results in thick or invisible pituitary stalk on mri .
compression of the pituitary stalk and infundibulum in patients with pph might contribute to the influence on gh secretion .
transformation of somatotrophs to thyrotrophs in the pituitary of patients with primary hypothyroidism might also reduce gh secretion . moreover , thyroid hormones are essential for growth , development , and metabolism .
reduced gh secretion and decreased activity of thyroid hormones in the synthesis of proteins cause short stature and delayed ba . serum igf-1 level
is influenced by multiple factors , such as age , gender , puberty , nutrition , thyroid status , and prolactin status [ 22 , 23 ] .
thyroid hormones regulate basal metabolic rate of hepatocytes , increase degradation of blood lipids , and stimulate erythropoiesis .
ht is considered to be the most common cause of primary hypothyroidism in children . a positive correlation between pituitary size and tsh levels has been previously reported . in this study ,
our children had a long duration of symptoms probably due to early unconspicuous symptoms and lack of clinical awareness about the disease and neonatal screening of congenital hypothyroidism in remote rural areas .
as a result , remarkably high tsh levels followed by pituitary hyperplasia were found in children with primary hypothyroidism .
after thyroid hormone replacement therapy , clinical symptoms improved , liver function , blood lipids , and blood routine examinations returned to normal , thyroid hormones and prl levels resolved to the normal range , and mri scans showed regression in the size of the enlarged pituitary .
although gh secretion increased in all short - stature children with pph after regression in hormonal levels and pituitary size , there were two boys in our study whose gh secretion remained abnormal .
based on the resolution in clinical , hormonal , and imaging changes after thyroid hormone replacement therapy , the diagnosis of primary hypothyroidism was definite .
the time interval varied from one week to 12 months in different cases [ 5 , 25 ] . in our children , all abnormalities resolved after 6 months of therapy .
primary hypothyroidism is associated with low gh levels and reversible pituitary hyperplasia in addition to abnormal thyroid function and prl levels .
the recognition of these associations between primary hypothyroidism and pituitary size as well as gh secretion can avoid misdiagnosis and eliminate unnecessary harmful therapy .
additional studies with larger samples are needed to clarify more the associations between primary hypothyroidism and hormonal and imaging abnormalities .
objective . 
 the follow - up of gh levels in short - stature children with pituitary hyperplasia secondary to primary hypothyroidism ( pph ) is reported in a few cases . 
 we aimed to observe changes in gh secretion in short - stature children with pph . 
 methods . 
 a total of 11 short - stature children with pph accompanied by low gh levels were included . 
 they received levothyroxine therapy after diagnosis . 
 their thyroid hormones , igf-1 , prl , and pituitary height were measured at baseline and 3 months after therapy . 
 gh stimulation tests were performed at baseline and after regression of thyroid hormones and pituitary . results . at baseline 
 , they had decreased gh peak and ft3 and ft4 levels and elevated tsh levels . 
 decreased igf-1 levels were found in seven children . 
 elevated prl levels and positive thyroid antibodies were found in 10 children . 
 the mean pituitary height was 14.3  3.8  mm . 
 after 3 months , ft3 , ft4 , and igf-1 levels were significantly increased ( all p < 0.01 ) , and values of tsh , prl , and pituitary height were significantly decreased ( all p < 0.001 ) . 
 after 6 months , pituitary hyperplasia completely regressed . 
 gh levels returned to normal in nine children and were still low in two children . 
 conclusion . 
 gh secretion can be resolved in most short - stature children with pph .