**9.2 Proptosis**

Proptosis, the most common sign encountered in patients with SOM, may be explained by different, yet interrelated, factors. From a mechanical point of view, the bony involvement of the orbital walls and the intraorbital tumor extension exert a direct mass effect on the eyeball. From a vascular point of view, the meningioma invasion of the SOF is responsible for a decrease in venous drainage and subsequently exacerbates the proptosis by increasing the intraorbital venous engorgement [32, 33]. This multifactorial physiopathology may explain the varied results from retrospective clinical series, which report improvements ranging from 50 to 100% [34–39]. Thus, if mechanical compression is relieved by surgical opening of the orbit and resection of the intraorbital portion of the tumor, exophthalmos will certainly improve. Nevertheless, it is rare that the proptosis recovers completely, likely due to persistent disturbances of venous drainage and potential trophic disorders of the oculomotor muscles. Removal of the periorbit appears to have a beneficial effect and seems to be a key factor in reducing proptosis [29].
