THE POTENTIAL ROLE OF MYOFIBROBLASTS IN THE OBLITERATION OF ARTERIOVENOUS-MALFORMATIONS AFTER RADIOSURGERY

OBJECTIVES: To examine the structural changes in arteriovenous malform ations (AVMs) after stereotactic radiosurgery and to identify the cyto skeletal antigen phenotype of the proliferating cells to gain informat ion about the possible mechanism of obliteration. METHODS: We conducte d immunohistochemical and electromicroscopic investigations of surgica l material that was removed from seven patients. The patients were har boring cerebral AVMs that had been previously treated with gamma knife irradiation, and they experienced subsequent bleeding 10 to 52 months after treatment. RESULTS: Light microscopy revealed spindle-shaped ce ll proliferation in the connective tissue stroma and in the subendothe lial region of the vessels. The ultrastructural and immunohistochemica l characteristics of these spindle cells were identical to those desig nated as myofibroblasts in wound healing processes and pathological fi bromatoses. Whereas in nonirradiated specimens of AVMs, similar cells expressed vimentin and desmin positivity, in irradiated cases, alpha-s mooth muscle actin activity was also observed. CONCLUSION: In view of the contractile activity of myofibroblasts, the proliferation generate d by irradiation and the transformation of the resting cells into an a ctivated form could be relevant to the shrinking process and eventual occlusion of AVMs after radiosurgery.