Ka. Leber et al., DOSE-RESPONSE TOLERANCE OF THE VISUAL PATHWAYS AND CRANIAL NERVES OF THE CAVERNOUS SINUS TO STEREOTAXIC RADIOSURGERY, Journal of neurosurgery, 88(1), 1998, pp. 43-50
As the number of patients treated with stereotactic radiosurgery incre
ases, it becomes particularly important to define with precision adver
se effects on distinct structures of the nervous system. Object. This
study was designed to assess the dose-response tolerance of the visual
pathways and cranial nerves after exposure of the cavernous sinus to
radiation. Methods. A total of 66 sites in the visual system and 210 c
ranial nerves of the middle cranial fossa were investigated in 50 pati
ents who had undergone gamma knife treatment for benign skull base tum
ors. The mean follow-up period was 40 months (range 24-60 months). Fol
low-up examinations consisted of neurological, neuroradiological, and
neuroophthalmological evaluations. The actuarial incidence of optic ne
uropathy was zero for patients who received a radiation dose of less t
han 10 Gy, 26.7% for patients receiving a dose in the range of 10 to l
ess than 15 Gy, and 77.8% for those who received doses of 15 Gy or mon
(p < 0.0001). Previously impaired vision improved in 25.8% and was un
changed in 51.5% of patients. No sign of neuropathy was seen in patien
ts whose cranial nerves of the cavernous sinus received radiation dose
s of between 5 and 30 Gy. Because tumor control appeared to have been
achieved in 98% of the patients, the deterioration in visual function
cannot be attributed to tumor progression. Conclusions. The structures
of the visual pathways (the optic nerve, chiasm, and tract) exhibit a
much higher sensitivity to single-fraction radiation than other crani
al nerves, and their particular dose-response characteristics can be d
efined. Ln contrast, the oculomotor and trigeminal nerves have a much
higher dose tolerance.