A 32-year-old woman undergoes MRI brain for progressive visual loss and is found to have a sellar-suprasellar mass with mixed T1 signal, T2 hyperintensity, and heterogeneous enhancement. All of the following imaging features would support a diagnosis of craniopharyngioma EXCEPT:

Explanation

## Craniopharyngioma — Imaging Characteristics and Differential ### Classic Imaging Profile **Key Point:** Craniopharyngioma is a benign epithelial tumor arising from remnants of Rathke's pouch, with distinctive imaging features that aid diagnosis. | Feature | Craniopharyngioma | |---------|-------------------| | **Location** | Sellar-suprasellar (90%) | | **Calcification** | Present in ~90% of cases (pathognomonic) | | **Cystic component** | ~75% have cystic portions | | **Cyst fluid signal** | T1 hyperintense (cholesterol-rich, proteinaceous) | | **Solid component** | T1 iso-hypointense, T2 variable | | **Enhancement** | Heterogeneous (solid portions enhance) | | **Diffusion restriction** | **NOT typically restricted** — benign lesion | | **Mass effect** | Compression of optic chiasm, pituitary stalk | ### Why Restricted Diffusion is NOT Expected **High-Yield:** Restricted diffusion (low ADC) is a feature of **high cellularity** and is seen in malignant or aggressive tumors (glioblastoma, lymphoma, medulloblastoma). Craniopharyngioma, being a benign cystic-solid lesion, does **not** show restricted diffusion in typical cases. **Clinical Pearl:** If you encounter a sellar-suprasellar mass with calcification and cystic components but see restricted diffusion, consider alternative diagnoses such as: - Pituitary adenoma with hemorrhage or necrosis - Sellar lymphoma - Metastatic disease ### Differential Diagnosis: Sellar-Suprasellar Masses | Tumor | Calcification | Cystic | Restricted DWI | Enhancement | |-------|---------------|--------|-----------------|-------------| | **Craniopharyngioma** | ~90% | Yes | No | Heterogeneous | | **Pituitary adenoma** | Rare | Rare | No | Homogeneous | | **Meningioma** | ~20% | No | No | Homogeneous | | **Germinoma** | ~10% | Rare | **Yes** | Homogeneous | | **Lymphoma** | Rare | Rare | **Yes** | Homogeneous | **Mnemonic:** **CCCCC** = Craniopharyngioma Calcification, Cyst, Cholesterol-rich fluid, Chiasm compression, **Cellular restriction (absent)** ### Clinical Correlation The patient's progressive visual loss is explained by mass effect on the optic chiasm, which is a common presenting symptom. Endocrine dysfunction (hypopituitarism, diabetes insipidus) may also occur due to compression of the pituitary stalk. [cite:Robbins 10e Ch 28; Osborn's Brain Imaging, Pathology, and Anatomy]