Endocrine Abstracts

Introduction: Pituitary tumours, and perhaps particularly suprasellar tumours or where surgery threatens the infundibulum, require vigilant peri-operative monitoring for salt and water complications such as arginine vasopressin deficiency (AVP-D), and syndrome of inappropriate antidiuretic hormone secretion (SIADH). In this case, an 18-year-old male with a craniopharyngioma demonstrates a potentially challenging example, with a distinct ‘triple-phase’ AVP response to transsphenoidal surgery (TSS).

Case Summary: A 15-year-old male presented with partial hypopituitarism. MRI demonstrated a suspected craniopharyngioma (cystic lesion with calcification and heterogeneous enhancement). Growth hormone and testosterone were replaced and, in the absence of compressive symptoms (vision was intact), conservative management (surveillance) was favoured. In view of subsequent growth of the lesion (8 x9 mm to 23 x13 mm over a 2-year interval), he underwent transsphenoidal cyst decompression with partial tumour resection at age 18.

Post-operative Course and Timeline: Day 1:

Postoperatively, he developed significant polyuria(>400 mL/hour) with thirst and polydipsia (24-hour intake 5194 mL; urine output 6380 mL/24 h). With this negative balance, serum sodium transiently rose to152 mmol/l (reference133–146 mmol/l). With urine osmolality 89 mOsm/kg and serum osmolality 306 mOsmol/kg, post-operative AVP-D was diagnosed and dDAVP (0.5 mg SC) was given. Continued oral desmopressin and drinking to thirst (his thirst was intact) led to normalisation of balance and biochemistry.

Day 6:

Serum sodium dropped to a nadir of 126 mmol/l, with elevated urine sodium, no thirst, little urine output and modest reported positive balance (albeit with suboptimal records initially). DDAVP was stopped and it was then with fluid intake restriction (to 750 mL/24 hours) for presumed SIADH. Serum sodium normalised by day 8, with appropriate off-loading of excess water.

Day 11:

After a period of stability, polyuria recurred (fluid intake 2050 mL/24 h; urine output 5123 mL/24 h) with significant thirst and serum sodium rising within the reference range. Recurrence of AVP-D was diagnosed, and he was started on oral dDAVP 100 mg twice daily. With this, his salt and water balance remains controlled. He has also required ongoing glucocorticoid and thyroxine replacement.

Discussion: This case illustrates the ‘triple-phase’ AVP response following TSS in pituitary tumours.

1. Transient AVP-D phase: Polyuria, thirst and hypernatremia, requiring dDAVP. 1. SIADH phase: Hyponatremia due to inappropriate ADH secretion, managed with fluid restriction and stopping dDAVP. 2. Permanent AVP-D: Ongoing dDAVP requirement.

Conclusion: This case underscores the potentially complex salt and water disturbances after peri-operative surgery. Close monitoring of fluid balance and serum sodium, with appropriate response is crucial. Management is aided by awareness of the potential for such a triphasic response.