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Answers on p 539.
A 72 year old Asian man was transferred to our institution for work-up of hyponatraemia and an intrasellar mass. At an outside hospital, the patient presented with a fever of 40oC (104oF) and mental status changes. The patient had been exposed to ill children and reported symptoms of upper respiratory tract infection a week before presentation. On admission to the outside hospital, he had a serum sodium of 133 mmol/l which decreased to 125 mmol/l with onset of mental confusion. Lumbar puncture findings were normal. Computed tomography of the head done at that point showed a 2.1 cm sellar mass with suprasellar extension, elevating the optic chiasm (fig 1). His fever resolved after treatment with azithromycin. His mental status markedly improved after intravenous infusion of saline and a single dose of hydrocortisone 100 mg given intravenously.
On admission to our hospital, his pulse was 80 beats/min, blood pressure 140/88 mm Hg, temperature 37.3oC, and respiratory rate 20 breaths/min. He was alert and oriented. Systemic examination, including heart, lungs, abdomen, and central nervous system was normal. The neuro-ophthalamic evaluation revealed bitemporal visual field defects with no papilloedema. The endocrine evaluation showed marked abnormalities. Free testosterone was less than 4.9 nmol/l (normal range 76.3–721.1 nmol/l), free and weakly bound testosterone was less than 0.12 nmol/l (2.1–20.1 nmol/l), total testosterone was less than 0.35 nmol/l (7.3–26.0 nmol/l), sex hormone binding globulin was 29 nmol/l (13–71 nmol/l). Luteinising hormone was 0.9 IU/ml (2.0–6.0 IU/ml), follicle stimulating hormone 1.6 IU/ml (1.0–15.0 IU/ml), random cortisol <28 nmol/l (55.2–607.0 nmol/l), total triiodothyronine 0.8 nmol/l (1.2–2.5 nmol/l), total thyroxine 63.1 nmol/l (64.4–154.4 nmol/l), and thyroid stimulating hormone 0.26 mU/l (0.2–5.0 mU/l). His serum prolactin concentration was 9 μg/l (2.0–18.0 μg/l); serum growth hormone was not measured. Serum sodium on admission was 132 mmol/l (136–146 mmol/l), potassium 4.2 mmol/1 (3.5–5.3 mmoll), blood urea nitrogen 6.4 mmol of urea (7.0–22 mmol of urea), and creatinine 97.2 μmol/l (61.9–132.6 μmol/l). Prostate specific antigen was undetectable at 0.
The patient underwent transsphenoidal hypophysectomy with complete removal of the tumour. During the surgery the tumour could be removed easily and was not attached to the dura. The surgical specimen showed a 2.3 × 1.7 × 0.4 cm tumour. The pathology revealed fascicular arrangement of spindle shaped cells with cigar and cigarette shaped nuclei (figs 2 and 3). The tumour cells were S-100 stain positive. Other special stains for prolactin, growth hormone, adenocorticotrophic hormone, epithelial membrane antigen (EMA), as well as glial fibrillary acidic protein were negative. Electron microscopy showed evidence of basal laminae.
Postoperatively, he is doing well on replacement doses of levothyroxine, cortisone, and testosterone. Serum sodium was within the normal range on follow up laboratory analyses. Postoperative magnetic resonance imaging did not reveal any tumour, but did show postoperative changes in the pituitary fossa. Follow up in the ophthalmology clinic did not reveal any visual field defects.
- What is the differential diagnosis of an intrasellar mass?
- What is the cause of the intrasellar mass in this patient and what are its diagnostic features?
- What is the cause of hyponatraemia in this patient?