gms | German Medical Science

Objective: The growth pattern of pilocytic brainstem astrocytomas remains challenging in these rare lesions, but its understanding in the individual patient is essential for a tailored approach, complete removal and quality of life.

Method: From a series of 500 patients operated upon for posterior fossa lesions between 2002 and 2013, 21 pediatric and young adult patients were identified with pilocytic astrocytomas and evaluated with respect to growth pattern, extent of resection on MRI and functional outcome.

Results: A dorsally exophytic growth pattern could not be identified in any of the cases. Three each harbored focal endophytic and cerebellar tumors. 15 peduncular lesions (midline approach n=9, retrosigmoid n=4, combined n=2) were identified and further investigated. Out of these 15 cases a growth pattern from the peduncle into the 4^th ventricle, mimicking a dorsally exophytic growth was seen in 9, a lateral growth towards the CPA in 4 cases. In two cases a lateral to medial growth pattern from the peduncle was encountered, pushing the floor of the ventricle dorsally. Tumor removal was complete in all cases but two. Additional morbidity was seen with the midline and combined approach.

Conclusions: The understanding of growth patterns in peduncular astrocytomas provides a safe surgical corridor and is essential for complete removal and functional integrity. The entity of a dorsally exophytic pattern needs to be discussed, since all cases, appearing as dorsally exophytic on MRI, eventually had a peduncular origin with respect to the vascular supply, predominantly coming from the peduncles and not from the ventricular floor.