July 6, 2017
A 23-year-old man with recurrent headaches associated with photophobia. Additional symptoms include a mildly unsteady gait and intermittent tingling of the hands and feet.
Pilocytic Astrocytoma
- Background:
- Pilocytic astrocytoma (PA) is the most common pediatric glioma and the most common pediatric cerebellar neoplasm.
- The tumor is most often WHO grade I, with a high 10-year survival rate of over 90%.
- Many PAs have abnormalities in the Ras/RAF/MAPK/ERK pathway, as did this tumor, which contained an ERC2-RAF1 translocation.
- Clinical Presentation:
- Most (75%) PAs present in the first 2 decades, therefore making the age of this patient slightly older than usual.
- Symptoms are reflective of tumor location. For example, tumors within the cerebellum often cause headache, hydrocephalus, truncal ataxia, gait disturbance, and appendicular dysmetria.
- Key Diagnostic Features:
- This particular case of pilocytic astrocytoma is atypical in that the tumor is both completely solid and nonenhancing. However, certain features are helpful in arriving at the correct diagnosis.
- First, the cerebellar hemisphere is one of the most common locations of PAs (the other being vermis).
- Lack of surrounding edema and well-demarcated, smooth margins are typical, reflecting the benign behavior of the tumor.
- Characteristic hyperintensity on T2 sequence and lack of diffusion restriction due to low cellularity also provide clues to the low tumor grade.
- Unfortunately, the calcification seen in this case is not particularly helpful; one study of 80 PAs found a calcification rate of only 14%.
- Differential Diagnoses:
- Due to the unusual appearance of this PA, the standard differential does not apply. Instead, the differential should include:
- nonenhancing, solid masses of the cerebellum, such as subependymoma (rarely intraparenchymal)
- low-grade astrocytomas, such as diffuse fibrillary astrocytoma (more often supratentorial)
- hamartoma: seen in patients with tuberous sclerosis or neurofibromatosis 1
- dysplastic cerebellar gangliocytoma: thickened cerebellar folia with “tigroid” pattern, plus characteristic clinical syndromes
- ganglioglioma: more likely to have cystic change and enhancement)
- Due to the unusual appearance of this PA, the standard differential does not apply. Instead, the differential should include:
- Treatment:
- Surgical resection is usually curative.
- Radiation and/or chemotherapy is used for tumors of the hypothalamic region or optic chiasm and for recurrent or disseminated tumors, which are rare.
