Hyponatremia as the Initial Sign of Rathke’s Cleft Cyst-Related Hypopituitarism

A 76-year-old woman presenting with profound dizziness and severe euvolemic hyponatremia was ultimately diagnosed with panhypopituitarism and a Rathke’s cleft cyst (RCC), according to a medical case report. Doctors initially discharged the patient with a diagnosis of peripheral vertigo before secondary adrenal insufficiency and a 0.7 cm by 1 cm by 0.8 cm sellar lesion were identified on subsequent hospital admission.

How an Incidental Sellar Cyst Masks Itself as Peripheral Vertigo

Rathke’s cleft cysts are benign epithelial lesions originating from remnants of Rathke’s pouch, an embryologic structure involved in anterior pituitary gland development, according to autopsy studies showing a prevalence between 13% and 22%. While most lesions remain asymptomatic, cyst enlargement can compress adjacent structures and cause headaches, visual disturbances, or endocrine dysfunction. In this case, the patient presented to the emergency department with two days of dizziness and normal blood pressure readings. Medical staff initially treated her for peripheral vertigo and discharged her from the hospital.

Uncovering Severe Hyponatremia and Pituitary Dysfunction

When symptoms persisted, the patient returned to the medical ward one week later, where laboratory tests revealed a serum sodium level of 112 mmol/L. According to the diagnostic workup, her serum osmolality measured 241 mOsm/kg, urine osmolality reached 244 mOsm/kg, and urine sodium was 63 mmol/L. An 8 am cortisol test showed a severely depressed level of 32 nmol/L, and a high-dose short Synacthen test confirmed hypocortisolism. Additional blood panels revealed a low adrenocorticotropic hormone (ACTH) level of 3.4 pg/mL, low-normal thyroid-stimulating hormone (TSH), low free T4, and suppressed gonadotropin levels.

Brain magnetic resonance imaging (MRI) revealed a hypointense lesion on T1-weighted imaging and a hyperintense lesion on T2-weighted imaging within the pituitary fossa. The imaging demonstrated a slight suprasellar extension without optic chiasmal compression, alongside a leftward deviation of the pituitary stalk. Despite the cyst measuring under one centimeter, it produced multi-axis endocrine deficiencies.

Treatment Decisions and Conservative Management Outcomes

Following the diagnosis of hypopituitarism due to an RCC, physicians initiated hormone replacement therapy starting with hydrocortisone 10 mg twice daily, followed by thyroxine 75 µg once daily. Although neurosurgeons recommended transsphenoidal pituitary surgery, the patient declined the operation due to her age and personal preference.

At a six-month follow-up evaluation, she experienced no compressive symptoms, and her hormone tests and imaging findings remained stable under conservative management. Retrospective data from Zhang et al. cited in the report indicate that pituitary dysfunction occurs in roughly one-quarter of symptomatic patients, and hormone deficits do not always correlate directly with cyst dimensions.

Frequently Asked Questions

What is a Rathke’s cleft cyst?

A Rathke’s cleft cyst is a benign, non-cancerous fluid-filled pouch located in the pituitary gland region that develops from embryological tissue remnants.

Why does an RCC cause low sodium levels?

Compression of the pituitary gland can trigger secondary adrenal insufficiency. Cortisol deficiency impairs renal free-water clearance and promotes vasopressin secretion, leading to dilutional hyponatremia.

Can Rathke’s cleft cysts be managed without surgery?

Yes. Patients who lack visual impairment or acute neurological decline can be managed conservatively using targeted hormone replacement therapy and serial monitoring.

What are the classic symptoms of a symptomatic sellar cyst?

Common symptoms include headaches, vision changes, and endocrine imbalances, though atypical presentations like dizziness from profound electrolyte disturbances can also occur.