Endocrine Abstracts

Introduction: Thyrotroph adenomas are extremely rare accounting for only 0.5–2.8% of paediatric pituitary adenomas. Almost 90% of thyrotropinomas are macroadenomas.

Case report: A 9-year-old boy presented with acute onset of a right divergent squint on a background of 6 months of visual disturbance. Opthalmological assessment confirmed reduced visual acuity and visual field defects.

MRI revealed a large macroadenoma invading the cavernous and sphenoid sinuses. Pre-operative pituitary function assessment showed low cortisol (74 nmol/l), normal gonadotrophins and testosterone, mildly raised prolactin and borderline low free T₄ (10.7 pmol/l) with normal TSH (6.39 mU/l) and marginally raised T₃ (7.7 pmol/l).

On extended biopsy histology showed an atypical pituitary adenoma which, based on its hormone expression profile, was classified as a thyrotroph pituitary adenoma.

The patient was critically unwell postoperatively with polyuria up to 10 l/day (13 ml/kg per h), hyponatraemia (lowest value 121 mmol/l) with high urinary sodium losses (290 mmol/l). Serum osmolality was initially low and then normalised (lowest value 256 mosm/l). He was diagnosed with severe cerebral salt wasting (CSW) requiring high-volume fluid replacement with hypertonic saline and high dose fludrocortisone. His condition was exacerbated by diabetes insipidus (DI) requiring an infusion of vasopressin. Both of these resolved 2–3 weeks postoperatively. On discharge he had partial hypopitutitarism with secondary hypothyroidism and ACTH deficiency. He is currently under follow-up with plans for resective surgery.

Conclusions: Thyrotropinomas classically present with clinical hyperthyroidism and / or neuro-opthalmological signs due to mass effect. Surgery is usually considered first line therapy but results in cure for only a third of patients as they are often difficult to resect due to their marked fibrosis and proximity to vital structures, as illustrated in our case. This case highlights the post-operative complication of CSW which can co-exist with DI, making diagnosis and management very challenging.