Pilocytic astrocyomas (PA) (also known as juvenile pilocytic astrocytomas (JPA)) are low-grade, relatively well-defined astrocytomas (WHO Grade I). They tend to occurs in young patients and have a relatively good prognosis.
Pilocytic astrocytomas are tumours of young people, with 75% occurring in the first two decades of life, typically late in the first decade (9-10 years). There is no recognised gender predisposition.
Although only accounting for between 0.6-5.1% of all intracranial neoplasms (1.7-7% of all glial tumours) they are the most common primary brain tumour of childhood, accounting for 70-85% of all cerebellar astrocytomas.
Presentation depends on location. In the more common posterior fossa tumours, positive mass effect with signs of raised intracranial pressure, especially when hydrocephalus is present predominate. Bulbar symptoms or cerebellar symptoms may also be present.
The term pilocytic refers to the the elongated hair-like projections from the neoplastic cells 4. The presence of eosinophillic Rosenthal fibres are a characteristic feature, and hyalinization of blood vessels a common features.
There is a strong association with neurofibromatosis type 1 (NF1). NF1 associated tumours have a tendency to affect the optic nerves and chiasm and may also have a better prognosis. Pilocytic astrocytomas are seen in up to 15-20% of all patients with NF1 and typically manifest in early childhood. Approximately 1/3 of pilocytic astrocytomas involving the optic nerves have associated NF1.
By far the most common location is the cerebellum (60%). The distribution within the cerebellum varies depending on the study. Safe enough to say that the location within the cerebellum is not very helpful, with many tumours involving both the vermis and the cerebellar hemisphere.
In general they typically they arise from midline structures.
optic nerve / optic chiasm (25-30%)
- very common location in NF1
- hypothalamic / adjacent to third ventricle
- other less common locations
- cerebral hemispheres: more frequent in adults
- cerebral ventricles
- velum interpositum
- spinal cord
- large cystic component with a brightly enhancing mural nodule - 67%
- non enhaning cyst wall - 21%
- enhancing cyst wall - 46%
- heterogenous, mixed solid and multiple cysts and central necrosis - 16%
- completely solid - 17%
Enhancement is almost invariably present (~ 95%). Up to 20% may demonstrate some calcification. Haemorrhage (case 1) is a rare complication.
Signal characterisitics include
- T1 - iso to hypo intense solid component compared to adjacent brain
- T2 - hyper intense solid component compared to adjacent brain
Treatment and prognosis
They are slow growing well circumscribed tumours with an overall good prognosis following treatment (> 90% 5 year survival and > 70% 20 year survival). Cystic tumours have even better prognosis while fibrillary variants tend to do worse.
Surgical resection, if complete, is usually curative. Some surgeons advocate that only the nodule need be resected to effect cure, as the cyst walls are non neoplastic, even if enhancing.
General imaging differential considerations include
- typically arise from the midline (especially vermis and roof of the fourth ventricle) rather than cerebellar hemisphere
- usually seen in younger patients (2-6 years of age)
- atypical teratoid / rhabdoid tumour :-larger heterogenous variably enhancing mass
- tends to fill the fourth ventricle and protrude out of the foramen of Luschka and foramina of Magendie
- large cystic component less common
- usually seen in adults
- associated with von Hippel Lindau disease
- pleomorphic xanthoastrocytoma (PXA)
- cerebellar abscess - has a different clinical presentation and has no enhancing nodule
- WHO classification of CNS tumours
- diffuse astrocytic tumours
- diffuse astrocytoma grading
- low grade astrocytoma
- anaplastic astrocytoma
- glioblastoma multiforme
- giant cell glioblastoma
- gliomatosis cerebri
- localised astrocytic tumours
- specific locations
- 1. Koeller KK, Rushing EJ. From the archives of the AFIP: pilocytic astrocytoma: radiologic-pathologic correlation. Radiographics. 24 (6): 1693-708. doi:10.1148/rg.246045146 - Pubmed citation
- 2. Beni-adani L, Gomori M, Spektor S et-al. Cyst wall enhancement in pilocytic astrocytoma: neoplastic or reactive phenomena. Pediatr Neurosurg. 2000;32 (5): 234-9. Pediatr Neurosurg (link) - Pubmed citation
- 3. Barkovich AJ. Pediatric neuroimaging. Lippincott Williams & Wilkins. (2005) ISBN:0781757665. Read it at Google Books - Find it at Amazon
- 4. Drevelegas A. Imaging of Brain Tumors with Histological Correlations. Springer. (2011) ISBN:3540876502. Read it at Google Books - Find it at Amazon
- 5. Koeller KK, Rushing EJ. From the archives of the AFIP: pilocytic astrocytoma: radiologic-pathologic correlation. Radiographics. 2004;24 (6): 1693-708. Radiographics (full text) - doi:10.1148/rg.246045146 - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Juvenile pilocytic astrocytoma (JPA)||✗|
|Juvenile pilocytic astrocytoma||✗|
|Pilocytic astrocyomas (PA)||✗|
|Pilocytic astrocyoma (PA)||✗|