Rathke Cleft Cyst

Rathke cleft cyst is a benign, epithelium lined cyst of the sella or suprasellar region arising from remnants of Rathke pouch, between the anterior and posterior pituitary lobes.

It is found in 11 to 33% of autopsies and about 1 to 2% of MRI scans. Most are asymptomatic. Symptomatic cysts present in adults aged 30 to 60 years, with a female predominance.

Pathophysiology. The cyst contains mucoid or serous fluid, and enlargement compresses the pituitary gland, stalk, optic chiasm and hypothalamus. Inflammation or haemorrhage can cause sudden enlargement.

Presentation is headache, visual field loss (bitemporal), hypopituitarism (low gonadotrophins, thyroid and adrenal deficiency), hyperprolactinaemia from stalk compression, diabetes insipidus (more common than with pituitary adenoma) and, rarely, apoplexy or aseptic meningitis. Most cysts are found incidentally.

Red flags.

• Sudden severe headache with visual loss or ophthalmoplegia (apoplexy).
• Progressive visual field loss or reduced acuity.
• Polyuria and polydipsia, or features of adrenal insufficiency.

MRI of the pituitary with contrast shows a non-enhancing, well circumscribed sellar or suprasellar cyst with variable signal (T1 hyperintense with protein rich content), and an intracystic nodule (T1 hyperintense, T2 hypointense) that is characteristic. Measure pituitary function: 9 am cortisol (or short corticotropin stimulation test), free thyroxine and thyroid stimulating hormone, luteinising and follicle stimulating hormones, testosterone or oestradiol, prolactin and IGF-1. Perform formal visual fields and acuity if the cyst abuts the chiasm.

Differential diagnosis.

• Cystic pituitary adenoma, craniopharyngioma and arachnoid cyst.
• Pituitary abscess, hypophysitis and epidermoid cyst.

Asymptomatic. Observation with MRI at 6 to 12 months, then every 1 to 2 years if stable, and endocrine review.

Surgery. For visual loss, progressive growth, intractable headache, apoplexy or hypothalamic compression: transsphenoidal drainage with a limited biopsy of the wall (avoid radical wall resection to reduce pituitary damage and diabetes insipidus). Recurrence is 10 to 30%. Postoperative diabetes insipidus and CSF leak are risks.

Hormone replacement.

• Hydrocortisone 15 to 25 mg daily in two or three divided doses (for example 10 mg on waking, 5 mg at noon and 5 mg late afternoon), with stress dosing and an emergency card. Start before levothyroxine.
• Levothyroxine 1.6 microgram/kg daily, adjusted to free thyroxine (and not to thyroid stimulating hormone) in central hypothyroidism.
• Sex steroid replacement as indicated.
• Desmopressin 0.1 mg orally at night or twice daily, titrated to urine volume and sodium (monitor sodium for hyponatraemia).

Monitoring. Visual fields, pituitary function and MRI.

Referral and escalation. Refer to endocrinology and neurosurgery. Refer as an emergency for apoplexy or visual deterioration.

Special groups. In pregnancy, monitor for visual change and adjust hydrocortisone and levothyroxine with endocrinology.