Pituitary thyrotropic adenoma associated with congenital hypothyroidism. Report of two cases

Clinical Implications of the New WHO Classification 2017 for Pituitary Tumors

According to the WHO classification 2017 of Pituitary Tumors adenomas are classified not only by structure and immunostaining for pituitary hormones but also by expression of the pituitary transcription factors Pit-1, T-pit and SF-1. By these factors, three cell lineages can be identified: Pit-1 for the GH-, Prolactin- and TSH-cell lineage, T-pit for the ACTH-cell lineage, and SF-1 for the gonadotrophic cell lineage. By this principle, all GH and/or Prolactin producing and all TSH producing adenomas must be positive for Pit-1, all corticotrophic adenomas for T-pit, and all gonadotrophic for SF-1. In adenomas without expression of pituitary hormones immunostainings for the transcription factors have to be examined. If these are also negative the criteria for an endocrine inactive null cell adenoma are fulfilled. If one transcription factor is positive the corresponding cell lineage indicates a potential hormonal activity of the adenoma. So Pit-1 expressing hormone-negative adenomas can account for acromegaly, hyperprolactinemia, or TSH hyperfunction. T-pit positive hormone negative adenomas can induce Cushing's disease, and SF-1 positive hormone negative tumors indicate gonadotrophic adenomas. Instead of the deleted atypical adenoma of the WHO classification of 2004 now (WHO classification 2017) criteria exist for the identification of aggressive adenomas with a conceivably worse prognosis. Some adenoma subtypes are described as aggressive "per se" without necessity of increased morphological signs of proliferation. All other adenoma subtypes must also be designated as aggressive if they show signs of increased proliferation (mitoses, Ki-67 index>3-5%, clinically rapid tumor growth) and invasion. By these criteria about one third of pituitary adenoma belong to the group of aggressive adenomas with potentially worse prognosis. The very rare pituitary carcinoma (0.1 % of pituitary tumors) is defined only by metastases. Many of them develop after several recurrences of Prolactin or ACTH secreting adenomas. The correlation of clinical findings and histological classification of pituitary adenomas is very important since every discrepancy has to be discussed between clinicians and pathologists. Based on data of the German Registry of Pituitary Tumors a table for examinations of correlations is shown in this review.

Cretinism presenting as a pseudotumour

A 43-year-old man from a remote part of India (over 1800 km from our institution), presented with a headache of 3 years duration. He was of short stature, had delayed puberty and was mentally retarded. On evaluation he was detected to have primary hypothyroidism with markedly elevated thyroid-stimulating hormone titres. A CT of the brain revealed a large sellar mass with suprasellar extension into the third ventricle causing obstructive hydrocephalus. Surgical intervention was deferred due to absence of visual impairment and the presence of gross hypothyroidism. The clinical diagnosis of congenital hypothyroidism was confirmed by the absence of radioiodine uptake in the thyroid bed. With thyroid hormone replacement therapy, the 'tumour' underwent significant reduction in size with the resolution of hydrocephalus thereby favouring a potential pituitary pseudotumour. This was an unusual situation of a giant pituitary pseudotumour detected in an adult with untreated congenital hypothyroidism.

Glycoprotein-secreting pituitary adenomas

In the past, pituitary tumours that produce one or more of the glycoproteins (TSH, LH, FSH and alpha subunit) were thought to be rare. However, using modern immunocytochemical and molecular biology techniques, these tumours are being recognized with increasing frequency. Many of these tumours produce glycoprotein alpha and beta subunits in addition to intact glycoproteins. Hormone production is often low compared with tumour size, and serum hormone levels may not be elevated in these patients. Tumours that produce the gonadotrophins (LH or FSH) or alpha subunit account for the majority of clinically non-functioning pituitary adenomas. They do not cause a specific clinical syndrome, and usually present with symptoms of a large mass lesion and/or hypopituitarism. Optimal treatment of these tumours is often difficult. The initial approach is usually transsphenoidal surgery, followed by radiation therapy if there are symptoms due to residual tumour. Medical therapy of gonadotrophin and alpha subunit tumours may include the use of dopamine agonists or somatostatin analogues, although neither has been shown to consistently decrease tumour size. Preliminary trials with experimental GnRH antagonists suggest that these agents may be useful as adjuvant therapy of gonadotrophin tumours. Tumours that produce TSH are rare. Patients present with hyperthyroidism, which is often misdiagnosed as Graves' disease, as well as with symptoms of a pituitary mass lesion. Almost all TSH tumours secrete excess amounts of free alpha subunit. Optimal treatment of these tumours includes transsphenoidal surgery, followed by radiation therapy for residual tumour. The somatostatin analogue octreotide is effective in reducing excess TSH secretion from these tumours, and causes a reduction in tumour volume in a significant minority of patients.

The IGF-I receptor sub-membrane domain is intact in GH-secreting pituitary tumours

BACKGROUND AND OBJECTIVE

Clinical acromegaly is characterized by dysregulation of somatotroph GH secretion in the presence of high circulating serum IGF-I levels. Physiologically, IGF-I exerts a negative feedback on GH secretion at both the hypothalamic and the pituitary levels. We have previously shown that the 943 and 950 tyrosine residues in the IGF-I receptor beta-subunit are required for ligand signalling to the GH gene, as substitution of these residues abrogates IGF-I signal transduction. To determine whether a mutation within the IGF-I receptor submembrane domain may be involved in the pathogenesis of GH secreting tumours, we studied this region in these tumours.

DESIGN

Exon 15 of the IGF-I receptor containing both the 943 and 950 tyrosines was analysed in 19 GH-secreting tumours by single-strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR) products. Tumour DNA and patients' lymphocyte DNA, which served as normal controls, were analysed.

RESULTS

All samples exhibited normal migration patterns in the SSCP analysis which was further confirmed by direct DNA sequencing.

CONCLUSIONS

We conclude that mutations in the IGF-I receptor sub-membrane domain which disrupt the negative feedback loop are not involved in the pathogenesis of acromegaly.

MR imaging of pituitary hypertrophy due to juvenile primary hypothyroidism: a case report

We present a case of pituitary hypertrophy due to juvenile primary hypothyroidism with subsequent return to normal size after therapy. This clinical entity is well known, but there are few reports on its magnetic resonance (MR) findings. We stress the usefulness of Gadolinium-DTPA-enhanced (Gd-DTPA-enhanced) MRI in the differential diagnosis of pituitary hypertrophy and pituitary adenoma.

Surgical treatment of thyrotropin-secreting pituitary adenomas

Thyrotropin-secreting pituitary adenomas have been diagnosed more frequently as radiographic techniques and biochemical assays have improved; however, they remain uncommon and are unfamiliar to most neurosurgeons. This report concerns eight patients with hyperthyroidism, inappropriately elevated levels of serum thyrotropin and alpha-subunit, and radiographic evidence of pituitary tumor. All underwent surgery and had pathological confirmation of a thyrotropin-secreting adenoma, and most had been subjected to prior ablation of the thyroid gland. Only one tumor was a microadenoma; the others ranged in size from 1.4 to 12 cm, and invasion of parasellar structures was common. Thyrotropin, triiodothyronine, thyroxine, and alpha-subunit were measured preoperatively and at intervals postoperatively. Coexistent hormonal abnormalities (which occurred in all patients) included acromegaly and hyperprolactinemia and were also monitored. All four patients who had tumors less than 2 cm in diameter remain alive. Complete extirpation of tumor in these patients produced rapid correction of all hormonal abnormalities and resolution of clinical hyperthyroidism. The other four patients had larger invasive tumors: two died soon after surgery, one died of disseminated tumor 8 years after presentation, and one remains alive with residual tumor. Tumors secreting thyroid-stimulating hormone are less easily cured by surgery than are other types of pituitary adenoma because of the large size and invasive features that many attain during the delay to diagnosis; medical therapy can subdue the tumor but not cure it. The experience with these patients establishes the importance of early diagnosis and surgical excision for successful treatment, and demonstrates the utility of modern diagnostic techniques for finding these lesions. As occurs in Nelson's syndrome after adrenalectomy for Cushing's disease, ablation of the target organ may allow the tumor to convert to a more clinically malignant form which is resistant to cure.

Effects of protracted hypothyroidism on pituitary function and structure in endemic cretinism

Pituitary function and structure were assessed in 69 endemic cretins from western China. In hypothyroid cretins (TSH greater than 10 mIU/l), CT imaging of the pituitary revealed adenoma in five of 20 (25%) and partially empty sella (PES) in a further eight of 20 (40%). The majority of tumours were microadenomas and showed a relation with higher levels of serum TSH but not with duration of hypothyroidism. Dynamic pituitary testing with TRH and GnRH in four patients with adenoma on CT gave a flat TSH response but significant rises in serum PRL, GH, LH and FSH concentrations. Hyperprolactinaemia (greater than 350 mIU/l) was present in hypothyroid cretins only (13 of 26; 50%) and serum PRL showed a curvilinear relation with serum TSH levels (r = 0.7, P less than 0.0001). Hypogonadism was seen in approximately half the cretins with high PRL levels. Our data suggest that severe protracted thyroid hormone deficiency may result in thyrotrophin adenomas of the pituitary gland. Disturbances of growth, puberty, and sexual function in endemic cretins are explained by the secondary effects of thyroid hormone deficiency on pituitary function.

Combined thyrotroph and lactotroph cell hyperplasia simulating prolactin-secreting pituitary adenoma in long-standing primary hypothyroidism

Primary hypothyroidism accompanies more than 50% of clinically significant pituitary thyrotroph adenomas. Hypothyroidism may also produce pituitary enlargement secondary to thyrotroph hyperplasia and present with a sellar mass and hyperprolactinemia. Three hypothyroid patients who presented with presumed prolactin-producing adenomas are reported. Although laboratory and radiologic abnormalities of pituitary enlargement may resolve after corrective thyroid therapy, our patients showed no such response and underwent operation. Histologic examination revealed no adenomas, but thyrotroph and lactotroph hyperplasia were present. Thyrotroph hyperplasia probably results from lack of negative feedback of thyroid hormone upon the anterior pituitary. Whether this is due to hypothalamic release of thyrotropin-releasing hormone (TRH) or another mechanism is unclear. Lactotroph hyperplasia may result from excess TRH, which stimulates lactotrophs with resultant hyperprolactinemia, or from reduced hypothalamic dopamine, thereby facilitating prolactin secretion. This study suggest that (a) hyperprolactinemia in hypothyroidism is not necessarily due to the "stalk section effect" secondary to pituitary enlargement, and (b) patients with primary hypothyroidism and sellar mass should initially be managed medically so that potentially reversible pituitary hyperplasia is not mistaken for adenoma.

Response of thyrotropin-secreting pituitary adenomas to a long-acting somatostatin analogue

Thyrotropin-secreting pituitary adenomas are aggressive, invasive tumors that respond poorly to available surgical and medical treatments. Inappropriate release of thyrotropin by these tumors can result in hyperthyroidism. We treated five patients who had thyrotropin-secreting pituitary adenomas with the long-acting somatostatin analogue SMS 201-995, which was administered by subcutaneous injection in doses of 50 to 100 micrograms every 8 to 12 hours. Serum levels of thyrotropin were dramatically reduced by treatment in four of the five patients, and levels of another tumor marker, the alpha-subunit of thyrotropin, were reduced in all five. In two patients with hyperthyroidism due to production of excess thyrotropin by the tumor, treatment with the somatostatin analogue resulted in a sustained euthyroid state. One patient who was treated for more than 16 months had a persistent reduction in serum levels of thyrotropin and iodothyronines. We conclude that SMS 201-995 is an effective means of controlling hypersecretion of thyrotropin and the associated hyperthyroidism due to thyrotropin-secreting pituitary tumors.