Chondrosarcoma – definitive radiosurgery after subtotal resections
SKULL BASE REGION
Petroclival
HISTOPATHOLOGY
Chondrosarcoma
PRIOR SURGICAL RESECTION
Yes
PERTINENT LABORATORY FINDINGS
N/A
Case description
A 32-year-old female presented with left lateral gaze diplopia. Brain magnetic resonance imaging (MRI) demonstrated a 2.5 cm mass in the left petrous bone. She underwent a subtotal resection, which demonstrated a low-grade chondrosarcoma. Due to the low-grade nature of the tumor, the patient was followed closely, and she continued to experience chronic diplopia. Three years later, she developed left facial numbness and worsening diplopia. Imaging demonstrated progression of the partially resected tumor, and a middle fossa craniotomy was performed to achieve a second subtotal resection. Pathology was consistent with persistent low-grade chondrosarcoma, and once again, the patient was observed closely. Two years later, the patient again developed radiographic evidence of local progression ( Figure 6.25.1 ). She was treated with GammaKnife radiosurgery, 16 Gy in a single fraction prescribed to the 50% isodose line ( Figure 6.25.2 ). The target volume measured 4 cm 3 with a maximum diameter of 2.3 cm.
Radiosurgery Machine
Gamma Knife
Radiosurgery Dose (Gy)
16, at the 50% isodose line
Number of Fractions
1
Figure 6.25.1.
Axial, sagittal, and coronal T1-weighted postcontrast images performed at the time of GammaKnife treatment planning. The multilobulated, enhancing mass is located within the left petrous apex, displacing the left carotid artery anteriorly. The mass extends posteriorly into the left prepontine cistern and abuts the pons at the level of the cerebellar peduncle. The mass measures 2.1 cm × 2.0 cm × 1.6 cm.
Figure 6.25.2.
Axial, sagittal, and coronal T1-weighted postcontrast images with target delineated in fuchsia. The 16-Gy prescription isodose line is delineated in yellow and the 13-Gy isodose line is delineated in green.
Critical Structure
Dose Tolerance
Brainstem
Max (0.03 cc) < 15 Gy
Cranial nerves V-VII
Max (0.03 cc) < 15 Gy
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