This is the most frequent glioma. Just as other brain tumors, it is classified on the basis of its malignancy into: low grade (WHO grades I and II); relatively benign; and high grade (WHO grades III and IV). Grade IV is the most malignant one and also defined as glioblastoma multiforme (GBM). A special kind of this tumor is pilocytic astrocytoma. This is a grade I tumor, benign and generally resectable, if its location is favorable. It is the most frequent in childhood (cerebellar and temporal locations). It may also be located in critical areas: hypothalamus, brainstem; the removal in these cases is technically challenging.
Astrocitoma pilocitico cistico della regione ipotalamica
Fig.5.1: Cystic pilocytic astrocytoma of the hypothalamic region. The yellow arrow points to its cystic part, the red one to the solid part.
RMN postoperatorio
Fig.5.2: Post-operative image of the same case with total removal of the tumor, despite its difficult location.
Pilocytic astrocytomas grow slowly and are clinically evident with intracranial hypertension and hydrocephalus when located in the cerebellum or brainstem, and seizures when located in the cerebral hemispheres. They generally have a large cystic part. Surgery of these tumors must be carried out in qualified centers with the use the most advanced operative and monitoring technologies.
astrocitoma pilocitico
Fig.5.3: Deep left parietal cystic pilocytic astrocytoma (yellow arrow). Right: surgical planning with the neuronavigator combined with CT Scan.
It has some subtypes: fibrillary, gemistocytic and protoplasmatic astrocytoma. This subdivision is rather irrelevant from a clinical point of view. Low-grade astrocytomas grow slowly, but can infiltrate the surrounding brain tissue, sometimes diffusely (gliomatosis).
Astrocitoma di basso grado fronto-temporale sinistro
Fig.5.4: Left fronto-temporal low-grade astrocytoma. It is the dark grey dumbbell area (yellow arrow). The location is critical for language and motor functions.
Low-grade astrocytomas may cause partial and/or generalized seizures (see Figures 4.1, 2, 3) and may be complex if their location is temporal or deep temporal.
astrocitoma pilocitico
Fig.5.5: Left - the red arrow points to an area recalling a low-grade astrocytoma; right - surgical plan at the neuronavigator; the tumor is in red, the motor area in yellow.
Diagnosis at MRI may be difficult. These tumors do not enhance after contrast administration. The lesion may be confused with inflammation, multiple sclerosis and scars secondary to old vascular lesions. Spectroscopic MRI may be of help, as it identifies the biochemical component of the tumor.
astrocitoma pilocitico
Fig.5.6: Spectroscopic MRI, showing a peak of "choline", i.e. an amino acid that is abundant in gliomas.
Risonanza magnetica astrocitoma
Fig.5.7: This MRI shows a right temporal pathological area (yellow arrows), difficult to diagnose. Upon surgery, it turned out to be a low-grade astrocytoma.
Risonanza magnetica dopo asportazione
Fig.5.8: MRI of the same case after surgery. The residual cavity is shown by the red arrows.
Low-Grade Astrocytomas should be removed; the larger the removal, the better the result in terms of survival. This is feasible in non-critical locations. Currently, even tumors in critical areas may be operated upon thanks to adequate pre-operative planning and intra-operative monitoring (functional MRI, neuronavigator, Brain Mapping). Some patients may be operated even in the awake state, to minimize the risks of damaging language areas or the motor cortex and tracts. The patient and the monitors alert the surgeon during the operation.
Nevertheless and despite apparent "radical removal", astrocytomas regrow, generally as more malignant. Their recurrence may occur after many years. In patients undergoing "gross total removal" and not showing any residual tumor upon post-operative MRI, radiotherapy and chemotherapy may be done at a later stage. Correct antiepileptic medication may be crucial to a good quality of life for these patients.