Background: Pituitary adenomas may be associated with hormonal hypersecretion (functional) or be clinically silent (non-functional – NFPA). In 2017, revised WHO guidelines incorporated both cell lineage and transcription factor immunohistochemistry (IHC) to better characterise NFPAs as either silent pituitary neuroendocrine tumours (PitNETs) or null-cell adenomas. Most silent PitNETs are gonadotrophinomas while silent prolactinomas are rare, with limited literature on their natural history, therapeutic response and impact on fertility. We present a case report of this unusual pathology.
Case Description: In 2016, a 29-year-old female presented with a 2-year history of amenorrhoea and headache. MRI-pituitary identified a macroadenoma (24x19x23mm) with optic chiasm compression. Biochemistry confirmed hypogonadotropic hypogonadism (oestradiol 71 pmol/L, FSH 3.9 IU/L, LH 1.0 IU/L). Prolactin level was not elevated at 61 mIU/L (70-570), with hook effect excluded with serial dilution. Other pituitary hormones were unremarkable. She subsequently had transsphenoidal resection (TSR). Unexpectedly, tumour IHC stained positive for prolactin and was negative for other hormones. The Ki67 index was 2%. Thus, the diagnosis was a silent sparsely granulated lactotroph adenoma. Transcription factor IHC has been performed routinely at our centre since 2021, however was added retrospectively in this case, demonstrating was PIT1 positivity (SF1- and TPIT-). Postoperative imaging revealed a 15x7x14 mm residual tumour with a prolactin of 62 mIU/L. The woman conceived spontaneously shortly after surgery and delivered a healthy child, despite the need for emergency caesarean section for pre-eclampsia and failed induction of labour. Over the next 2 years, there was gradual tumour growth to 16x9x15mm. Cabergoline was commenced shortly before she again conceived spontaneously. She recommenced cabergoline post-partum for the residual tumour (13x9x13mm) contacting the optic chiasm, with marked tumour size reduction (9x5x10mm). Most recently, she gave birth to a third child after a pregnancy complicated by intrapartum pre-eclampsia and gestational diabetes.