Introduction: Neuronavigation allows localizing brain lesions more accurately and planning a safe surgical corridor for pathology. This is especially crucial in areas with limited space like posterior fossa. Compared to Intraoperative MRI, Intraoperative Ultrasound (IOUS) - with its newly advanced micro transducers - is a more economical and user-friendly device in posterior fossa operations. Higher expenses of Intraoperative MRI is a limiting factor in developing nations like Egypt.

Methods: Intraoperative Ultrasound probe GE i12l with frequency 6-10 MHz is used in an ongoing descriptive study on patients with intraaxial posterior fossa lesions. twelve patients have been operated so far, with more enrolments underway. A surgeon oriented quesionnaire was designed to assist IOUS efficacy. Patients had IOUS scans done at several stages: During craniectomy, before durotomy, during tumor resection and finally to determine the residual lesion. MRI with contrast was done to compare the residual lesion with that detected by IOUS, a postoperative CT brain was carried in cases where MRI wasn’t possible.

Results: Lesions pathology of patients included medulloblastoma, epidermoid, hemangioblastoma, astrocytoma and abscess. The mean age for patients was 28. IOUS helped modifying the craniectomy in 7 patients. Localization of tumor and site of durotomy was achieved in all cases, in addition to defining tumor borders and differentiating solid and cystic parts. Residual part was found to be almost identical to that detected by postoperative scan in 9 cases. Trajectory of intraoperative corridor was modified with help of IOUS in 7 cases.

Conclusions: IOUS is a promising utility for posterior fossa tumors resection. It helps in determining the extent of craniectomy and durotomy. It accurately detects residual lesion intraoperatively compared to postoperative scans. Although most posterior fossa lesions have a well defined plane of cleavage with the surrounding cerebellar tissue, IOUS modifies the trajectory of lesion resection and enables an optimal surgical corridor.

Patient Care: This research will help to evaluate the value of usage of IOUS in resection of posterior fossa lesion as regards: 1) Craniectomy and durotomy modification, 2) Choosing the best surgical corridor to the pathology, 3) Detection of residual pathology intraoperative and compare it to Post operative scan, 4) The use of IOUS as a cheap neuronavigation tool in developing nations.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) compare cost and benifits of Intaoperative MRI and Intraoperative Ultrasound(IOUS), 2) Identify that IOUS is an intraoperative neuronavigation tool that tailor craniectomy in posterior fossa tumor resection, 3) describe How the IOUS modifies the surgical corridor in posterior fossa tumors operations, 4) Identify different items of IOUS efficacy quesionnaire

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