A low-angle trans-magendie foraminal approach to the fourth ventricle and dorsal brainstem

Traditional transvermian (TvA) and telovelar approaches (TelA) for accessing tumors of the fourth ventricle (FV) are associated with the need to dissect the cerebellar vermis or with traction and dissection of the uvulotonsilar fissure, which often leads to postoperative cerebellar disorders. A surgical approach to the fourth ventricle (59 patients) and the brainstem (18 patients) through the foramen of Magendie utilizing a low angle of surgical attack is proposed. Depending on their localization, the tumors were divided into 4 main groups: 1) upper region, 8 cases; 2) middle region, 14 cases; 3) lower region, 20 cases; and 4) tumors of the lower region of the fourth ventricle with extension into the cisterna magna, 12 cases; and various combinations of these localizations, 23 cases. All surgeries were performed using minimally invasive techniques with a 4 cm soft tissue incision and 0-21 mm of occipital bone resection (median of 12 mm). Total tumor resection was achieved in 55 (71.4%; 95% CI [60%, 81%]) patients, including 48 (81.4%; 95% CI [69%, 90%]) with fourth-ventricle tumors and 7 (41.2%; 95% CI [18%, 64%]) with brainstem tumors (p <.001). Among fourth-ventricle tumors, the extent of tumor resection decreased depending on the tumor localization level (p = 0.05). Postoperative cerebellar disorders manifested or deteriorated significantly rarely, with tumors located at the upper levels of the fourth ventricle or brainstem (p=0.05), as well as with smaller dorsoventral tumor sizes (p=.004). The low-angle trans-Magendie foraminal approach is an effective technique for the surgical treatment of space-occupying lesions of the fourth ventricle and dorsal brainstem.