Rathke’s cleft cyst
Summary
- Benign midline sellar cyst.
- Midline, pars intermedia–centred cyst, non‑enhancing “waxy” intracystic nodule (T1 bright, T2 dark), and rare calcification.
- Most are incidental; symptomatic when large.
Clinical
- Most asymptomatic and stable; mean age at presentation ≈ 45 y.
- Adamantinomatous craniopharyngioma: more paediatric.
- If symptomatic: headache, visual field defect, hypopituitarism.
- Diabetes insipidus is uncommon but possible.
Pathology
- Epithelium‑lined cyst from Rathke’s pouch (oral ectoderm in origin); mucinous/proteinaceous content.
- Intracystic nodule = inspissated mucin/“waxy” material.
- Squamous metaplasia of the cyst wall is associated with higher risk of post‑op re‑accumulation.
Imaging
Well‑delineated round/ovoid lesion within or just above the sella, centred in the pars intermedia (midline). Pituitary stalk may be displaced rather than invaded.
CT
- ~75% hypodense, ~20% mixed density, ~5–10% hyperdense.
- Calcification is rare (contrast with craniopharyngioma where calcification is common).
MRI
- T1‑weighted imaging (T1WI): ~50% hyperintense, ~50% hypointense (depends on protein/mucin).
- T2‑weighted imaging (T2WI): Usually hyperintense; ~25–30% hypointense.
- FLAIR (fluid‑attenuated inversion recovery): almost always hyperintense.
- Intracystic nodule (“waxy nodule”): classically T1 hyperintense, T2 hypointense, non‑enhancing. Frequency variable.
- Enhancement: thin peripheral rim only; no solid enhancing component.
- “Claw sign”: enhancing compressed normal pituitary tissue partially surrounds the non‑enhancing cyst.
- Diffusion: variable; not a reliable discriminator.
Differentials
- Adamantinomatous craniopharyngioma:
- “Machinery/motor oil” cyst fluid
- Calcifications common
- Solid/mural enhancement
- More frequent suprasellar/hypothalamic involvement.
- Non‑functioning cystic microadenoma: overlap exists but
- Often off‑midline/asymmetric
- Enhancing mural/solid tissue
- Haemorrhagic/proteinaceous cyst with possible fluid–fluid levels.
- Arachnoid cyst: CSF signal on all sequences; no nodule, no enhancement.
- Epidermoid: insinuating margins and diffusion restriction.
Management
- Asymptomatic/small: observation.
- Symptomatic/large:
- Transsphenoidal fenestration/marsupialisation is typical
- Many surgeons avoid aggressive capsule stripping to preserve pituitary function.
Recurrence / Follow‑up
- Not intrinsically “recurrent,” but re‑accumulation can occur if the epithelial wall remains after fenestration.
- Risk is higher with
- Residual capsule
- Squamous metaplasia
- Suprasellar extension
- Routine clinical + MRI follow‑up after surgery; earlier imaging if symptoms recur.
Common traps
T1‑bright content ≠ haemorrhage by default. Corroborate with a non‑enhancing intracystic nodule and lack of susceptibility. Calcification, restrict diffusion, or a true enhancing mural nodule should push you away from RCC (consider craniopharyngioma or pituitary adenoma).
