A 42-year-old man presents with progressive gait ataxia and headaches for 6 weeks. MRI brain shows a well-demarcated, round mass in the cerebellar hemisphere with homogeneous T2 hyperintensity, minimal surrounding edema, and marked enhancement after gadolinium. There is no cystic component. Cerebrospinal fluid analysis shows elevated protein. What is the most likely diagnosis?

## Diagnosis: Hemangioblastoma ### Clinical Presentation **Key Point:** Hemangioblastomas are benign vascular tumors of the cerebellum that present with progressive ataxia, headache, and hydrocephalus due to mass effect and CSF obstruction. ### Imaging Characteristics - **Well-demarcated, round lesion** in cerebellar hemisphere - **Homogeneous T2 hyperintensity** (cystic or solid) - **Marked gadolinium enhancement** (due to rich vascularity) - **Minimal surrounding edema** (benign nature) - **No necrosis or hemorrhage** in typical cases - May show associated cyst with mural nodule (classic but not always present) ### Pathophysiology Hemangioblastomas are WHO Grade I benign tumors arising from angioblastic mesenchyme. They are highly vascular with prominent feeding arteries and draining veins. In 20% of cases, they are associated with von Hippel–Lindau (VHL) syndrome. ### Key Distinguishing Features | Feature | Hemangioblastoma | Pilocytic Astrocytoma | Medulloblastoma | Metastasis | |---------|------------------|----------------------|-----------------|------------| | Age | 30–50 years | Children/young adults | Children (peak 5–9) | Any age | | Location | Cerebellar hemisphere | Cerebellar peduncle/4th ventricle | 4th ventricle midline | Variable | | Enhancement | Marked, homogeneous | Moderate, variable | Heterogeneous | Variable | | Edema | Minimal | Minimal to moderate | Moderate to marked | Marked | | Cystic component | Common (cyst + nodule) | Common | Rare | Variable | | Vascularity | High (feeding/draining vessels) | Low | Low | Variable | | WHO Grade | I | I–II | IV | **High-Yield:** The combination of **minimal edema + marked enhancement + well-demarcated borders** in a cerebellar mass is classic for hemangioblastoma. The absence of necrosis or hemorrhage helps exclude higher-grade tumors. ### Clinical Pearl Hemangioblastomas may present with polycythemia (erythropoietin production) and are associated with VHL syndrome in 20% of cases. Always screen for other VHL manifestations (renal cysts, pheochromocytoma, retinal angiomas). ### Management Surgical resection is curative for sporadic hemangioblastomas. In VHL-associated cases, surveillance imaging is essential to detect multiple lesions. **Mnemonic: HEMANGIO** — **H**ighly vascular, **E**nhances markedly, **M**inimal edema, **A**ngioblastic origin, **N**o necrosis, **G**rade I, **I**ntra-axial cerebellar, **O**ften cyst + nodule.