Endocrine Abstracts

TSH-expressing pituitary neuroendocrine tumours (PitNETs) are a rare entity with a spectrum of clinical features. These range from functioning TSH-producing adenomas associated with thyrotoxicosis to clinically silent TSH-expressing adenomas that are unassociated with thyrotoxicosis and present with symptoms of mass effect. We present the case of a 28 year-old woman in whom pre-operative imaging was consistent with a craniopharyngioma but histopathology revealed a TSH-expressing PitNET. The patient presented after an ophthalmic examination showing significant visual field defects. She reported amenorrhoea of 15 months duration. She did not have any clinical features of thyrotoxicosis. Biochemistry showed a mildly elevated prolactin of 552 (102-496) mIU/l, along with hypogonadotropic hypogonadism (FSH 5.2 IU/l, LH 1.0 IU/l, oestradiol 27 pmol/l), but otherwise normal pituitary profile. MRI pituitary demonstrated a 3.7cm suprasellar solid-cystic mass with mass effect, suggestive of an adamantinomatous craniopharyngioma. She was transferred to a neurosurgical centre for emergent endoscopic transsphenoidal excision of this lesion. Histopathological examination revealed a PitNET with positive immunohistochemistry staining for PIT1, TSH, chromogranin and CAM5.2, consistent with a thyrotroph PitNET. The patient experienced interval improvement in her vision and return of menses post-operatively. Thyroid function tests remained within normal limits. Prolactin normalised but there was persistent biochemical evidence of hypogonadotropic hypogonadism, whilst interval imaging is pending. The post-operative diagnosis is consistent with a silent TSH-expressing adenoma. The functional status of a silent PitNET can change during the course of disease with interval development of enhanced secretory activity, and our patient will remain under close surveillance.