Rathke pouch

**Embryology** - Around week 4, an upward outpouching of oral ectoderm from the roof of the stomodeum (primitive mouth) forms Rathke pouch. - It grows toward the floor of the diencephalon (infundibulum), loses its connection with the oral cavity, and differentiates into the adenohypophysis (anterior pituitary): pars distalis, pars tuberalis, and pars intermedia. - The posterior pituitary (neurohypophysis) comes from neuroectoderm, a downgrowth of the diencephalon (infundibulum). It stores and releases ADH and oxytocin, which are made in the hypothalamus. - Memory aid: "Rathke = Rathke's pouch = Roof of mouth = Right (anterior) pituitary." The anterior pituitary is derived from oral ectoderm, and the posterior pituitary is derived from neuroectoderm.

**Clinical correlates** 1. **Craniopharyngioma** - Benign but locally aggressive tumor arising from remnants of Rathke pouch (the craniopharyngeal duct). - Most common supratentorial tumor in children. It has a bimodal age distribution (children 5-15 yr, adults 50-60 yr). - Location: suprasellar. - Presentation: bitemporal hemianopia from chiasm compression, hypopituitarism, growth failure in children, and headache. Diabetes insipidus can occur from compression of the posterior pituitary or hypothalamus. - Imaging: calcifications and cystic components, with "motor-oil" cystic fluid. - Histology: adamantinomatous type (children) with wet keratin, calcifications, and cholesterol clefts. Papillary type (adults) has BRAF V600E mutations, while the adamantinomatous type has CTNNB1 (β-catenin) mutations. - Treatment: surgical resection with or without radiation. 2. **Rathke cleft cyst** - Benign cystic remnant of the pouch lumen lined by cuboidal or ciliated epithelium. - Usually asymptomatic and found incidentally. It can cause headache, visual disturbance, or pituitary dysfunction if large. - It differs from craniopharyngioma by lacking calcifications and solid components, and it is typically intrasellar or between the anterior and posterior lobes. 3. **Pituitary (adenohypophyseal) hypoplasia or aplasia**, and combined pituitary hormone deficiency, can result from defects in transcription factors such as PROP1 and POU1F1 (Pit-1) that guide differentiation of the pouch. 4. **Ectopic pharyngeal pituitary tissue** can persist along the migration path of the pouch (craniopharyngeal canal).

**Boards pearls** - Anterior pituitary (adenohypophysis) = oral ectoderm (Rathke pouch). It secretes FSH, LH, ACTH, TSH, prolactin, and GH. - Posterior pituitary (neurohypophysis) = neuroectoderm. Hormones are made in the hypothalamus (supraoptic and paraventricular nuclei). - Suprasellar calcified mass in a child with bitemporal hemianopia = craniopharyngioma. - Don't confuse with pituitary adenoma, which arises from adenohypophyseal cells (not remnants) and is the most common cause of bitemporal hemianopia in adults.