Q. A child presents with visual disturbances and delayed growth. Imaging reveals a suprasellar mass, and histopathology shows the presence of wet keratin compact, eosinophilic anucleate keratin. What is the most likely diagnosis?

Explanation

## Correct Answer: C. Craniopharyngioma Craniopharyngioma is a benign epithelial tumor arising from remnants of Rathke's pouch along the pituitary stalk. The pathognomonic histological finding is **wet keratin** (compact, eosinophilic, anucleate keratin debris), which is virtually diagnostic. This keratinous material accumulates within cystic spaces lined by stratified squamous epithelium, often with calcification visible on imaging. The suprasellar location is classic—the tumor grows upward from the sella turcica, compressing the optic chiasm (causing visual disturbances) and the pituitary gland (causing growth hormone deficiency and delayed growth). Craniopharyngiomas are the most common suprasellar mass in children in India, presenting typically between 5–14 years. The combination of visual symptoms (bitemporal hemianopia from chiasmal compression), growth delay (GH deficiency), and the pathognomonic wet keratin on histology makes this diagnosis certain. Imaging typically shows a mixed cystic-solid mass with calcification in 80% of cases. ## Why the other options are wrong **A. Rathke pouch cyst** — While Rathke pouch cysts also arise from Rathke's pouch remnants and can be suprasellar, they are lined by simple cuboidal or columnar epithelium and contain clear serous fluid, NOT wet keratin. Rathke cysts are typically asymptomatic incidental findings on MRI and do not cause the degree of mass effect or growth hormone deficiency seen here. The wet keratin is the discriminating feature. **B. Pituitary adenoma** — Pituitary adenomas are intrasellar masses arising from anterior pituitary cells and show histology of neuroendocrine cells with chromophobic, acidophilic, or basophilic patterns—never wet keratin. While adenomas can cause visual disturbances and growth delay, they lack the characteristic keratinous material. Adenomas are rare in children; craniopharyngioma is far more common in this age group. **D. Medulloblastoma** — Medulloblastoma is a malignant cerebellar tumor arising from the posterior fossa, not the suprasellar region. Histology shows small round blue cells with high mitotic activity, not stratified squamous epithelium or wet keratin. Medulloblastoma typically presents with hydrocephalus and ataxia, not visual disturbances from chiasmal compression. The location and histology are entirely different. ## High-Yield Facts - **Wet keratin** (compact, eosinophilic, anucleate debris) is the pathognomonic histological finding of craniopharyngioma. - **Suprasellar location** and **bitemporal hemianopia** from optic chiasm compression are the classic clinical presentation. - **Growth hormone deficiency** is the most common endocrine abnormality, causing delayed growth in children. - **Calcification** is present on imaging in ~80% of cases; mixed cystic-solid appearance is typical. - Craniopharyngioma is the **most common suprasellar tumor in children** in India, peak age 5–14 years. - **Stratified squamous epithelium** lining the cyst with keratinization distinguishes it from Rathke pouch cysts (simple epithelium, serous fluid). ## Mnemonics **CRANK for Craniopharyngioma** **C**yst suprasellar, **R**athke remnant, **A**nucleate keratin (wet), **N**eeds imaging (calcified), **K**eratinous debris. Use when you see wet keratin + suprasellar + child with growth delay. **WET KERATIN = Craniopharyngioma** **W**et keratin, **E**pithelial origin, **T** Tumor suprasellar. Whenever you see 'wet keratin' or 'anucleate eosinophilic keratin' in a histology stem, think craniopharyngioma immediately. ## NBE Trap NBE often pairs Rathke pouch cyst with craniopharyngioma because both arise from Rathke's pouch remnants and both can be suprasellar. The trap is forgetting that Rathke cysts contain clear serous fluid and simple epithelium, NOT wet keratin—the wet keratin is the discriminating feature that locks in craniopharyngioma. ## Clinical Pearl In Indian pediatric practice, any child presenting with growth failure + visual disturbance + suprasellar mass on imaging should raise suspicion for craniopharyngioma until proven otherwise. The wet keratin on biopsy is virtually diagnostic and guides definitive surgical management, which is the gold standard treatment in Indian tertiary centers. _Reference: Robbins Ch. 28 (Endocrine System); Harrison Ch. 375 (Pituitary Disorders)_