Gamma Knife Management of Skull Base Chordomas: Is it a Choice?

Skull base chordomas are locally invasive tumors which able to extend in different directions with skull base invasion. Although they are histologically benign, they have invasive nature makes total resection virtually impossible to achieve in most cases and this lead to residual tumors after surgery. To decrease postoperative surgical resection morbidity of these tumors, gamma knife radiosurgery (GKRS) was performed as alternative management for these residual chordomas to evaluate its safety and efficacy.

A retrospective study was made on eight residual skull base chordomas treated with GKRS between 2011 and 2015. The mean patient age was 49 years (range 30-73 years). Four patients harboring chordoma were male, and four patients were females with 1:1 ratio. All patients had undergone one prior surgery. Patients were treated with peripheral dose ranged between 12-15 gray (Gy) (mean 13.75 Gy) usually at 35% to 50% isodose curve (mean 38.8%). The maximum dose to the adjacent brain stem area ranged between 10 and 12 Gy. All patients were followed up from 8 to 39 months (mean 18 months).

The tumor control rate was 50% and 25% after 18 and 36 months, respectively, but we found that their wasdeclined in the tumor control rate with long follow-up time. Four tumors were stable in their size just for 18 months, and then there two of these tumors were progressed in their size, the other four patients showed progression in their tumors in their 1^st year of treatment without sign of central tumor necrosis.

Skull base chordoma patients complained from symptoms due to tumor mass effect which were not prospected to respond to GKRS alone as the aim of this type of treatment was the local tumor control, the tumor control rate declined with long follow-up time and this correlated with radioresistant nature of skull base chordoma. We advise a gross total resection to decrease the tumor volume, and this making gamma knife a reasonable treatment modality.