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 (embryologic precursor of the anterior pituitary). The pathognomonic histological finding is **"wet keratin"** — compact, eosinophilic, anucleate keratin debris that appears as laminated sheets, often described as having a "machine oil" appearance on gross examination. This keratinous material is virtually diagnostic and distinguishes craniopharyngioma from all other sellar/suprasellar masses. The tumor's suprasellar location explains both visual disturbances (compression of optic chiasm → bitemporal hemianopia) and endocrine dysfunction (growth hormone deficiency → delayed growth, short stature). In Indian pediatric practice, craniopharyngioma accounts for 5–14% of intracranial tumors in children and is the most common non-glial, non-neuronal tumor in the sellar region. Peak incidence is 5–14 years. The combination of visual symptoms, growth retardation, and suprasellar mass location with wet keratin on histology makes craniopharyngioma the only defensible answer. Treatment in India typically involves neurosurgical resection (transcranial or transsphenoidal approach) followed by radiation if incomplete resection or recurrence occurs. ## Why the other options are wrong **A. Pituitary adenoma** — While pituitary adenomas (prolactinoma, growth hormone-secreting) present with growth disturbance and visual symptoms in children, they do NOT show wet keratin on histology. Adenomas show chromophobic, acidophilic, or basophilic cells with intact nuclei. Adenomas are intrasellar; craniopharyngioma is suprasellar. This is the NBE trap — both cause growth and vision problems, but histology is the discriminator. **B. Glioma** — Optic pathway gliomas (pilocytic astrocytomas) can present with visual disturbance and suprasellar location, but they show fibrillary astrocytes with Rosenthal fibers and eosinophilic granular bodies — NOT wet keratin. Gliomas lack the keratinous material and epithelial architecture that define craniopharyngioma. Histology rules this out definitively. **D. Medulloblastoma** — Medulloblastoma is a posterior fossa tumor (cerebellum) in children, not a suprasellar mass. It presents with ataxia, hydrocephalus, and raised ICP — not visual disturbance from chiasmal compression. Histologically, it shows small round blue cells with high mitotic activity, never wet keratin. Location and histology both exclude this. ## High-Yield Facts - **Wet keratin** (compact, eosinophilic, anucleate laminated keratin) is pathognomonic for craniopharyngioma and distinguishes it from all other sellar tumors. - **Suprasellar location** causes bitemporal hemianopia (optic chiasm compression) and growth hormone deficiency (delayed growth, short stature) — the classic pediatric presentation. - **Rathke's pouch origin**: craniopharyngioma arises from embryologic remnants; it is the most common non-glial, non-neuronal sellar tumor in Indian children (5–14% of pediatric intracranial tumors). - **Peak age 5–14 years** in children; bimodal distribution with a second peak in adults (50–74 years). - **Treatment**: neurosurgical resection (transsphenoidal or transcranial) ± adjuvant radiation for incomplete resection or recurrence; Indian guidelines favor maximal safe resection to reduce recurrence. ## Mnemonics **CRANK for Craniopharyngioma** **C**ystic/solid mass, **R**athke's pouch origin, **A**denohypophyseal dysfunction, **N**on-glial tumor, **K**eratin (wet) on histology. Use this to recall the defining features when you see a suprasellar mass in a child. **WET KERATIN = Craniopharyngioma** **W**et (compact, eosinophilic), **E**pithelial origin, **T**umor of Rathke's pouch. When histology mentions wet keratin, the answer is craniopharyngioma — this is the single most discriminating feature. ## NBE Trap NBE pairs craniopharyngioma with pituitary adenoma because both cause growth disturbance and visual symptoms in children. The trap is that students may choose adenoma based on endocrine dysfunction alone. The discriminator is **histology**: wet keratin is pathognomonic for craniopharyngioma and absent in adenoma. ## Clinical Pearl In Indian pediatric practice, a child presenting with short stature, visual disturbance, and a suprasellar mass on imaging should raise immediate suspicion for craniopharyngioma. The wet keratin finding on biopsy is virtually diagnostic and guides urgent neurosurgical referral. Early recognition prevents permanent vision loss and allows optimization of growth hormone replacement post-resection. _Reference: Robbins Ch. 28 (Nervous System); Harrison Ch. 375 (Pituitary Disorders); OP Ghai Ch. 15 (Pediatric Neurology)_