High-grade astrocytoma with piloid features

High-grade astrocytoma with piloid features is a recently described rare tumour most commonly encountered in the posterior fossa of adults, especially those with neurofibromatosis type 1. It appears heterogeneous and has a dismal prognosis. 

Epidemiology

Due to the small number of patients so far reported, it is difficult to make strong pronouncements on the epidemiology of this tumour, however, cases so far appear to be primarily in middle-aged and elderly individuals ^1,3. Neurofibromatosis type 1 appears to be an association ¹. 

Pathology

This rare tumour was first included in the 5th Edition (2021) of the WHO classification of CNS tumours as a circumscribed astrocytic glioma ². 

It is defined by a characteristic DNA-methylation profile. 

Location

The small number of tumours reported have occurred throughout the brain, brainstem and spinal cord with a predilection for the posterior fossa, and especially the cerebellum ¹. 

Microscopic appearance

The histological appearance of these tumours is varied with reported cases having histological diagnoses of anaplastic pilocytic astrocytoma or glioblastoma ¹.  

Molecular characteristics

Alterations are commonly encountered in ¹: 

• NF1
• BRAF
• FGFR1
• CDKN2A/B deletion
• ATRX (mutations or loss)a
• MGMT promoter methylation

Radiographic features

MRI

Due to the small number of cases reported to date, specific or even suggestive imaging features are not yet evident especially as the tumours that have been described are heterogeneous in location (see above) and appearance ¹. 

Generally, they appear to be peripherally enhancing lesions with high T2 signal but without diffusion restriction of either central or peripheral components ¹. 

Treatment and prognosis

No tumour specific treatments are available at this time with treatment being empirical consisting of maximal safe surgical resection with concurrent chemoradiotherapy (e.g. temozolomide) ¹. 

Prognosis is poor, similar to glioblastoma (IDH-wildtype) ¹.