OBJECTIVE: We aimed to identify the factors that can predict the risk of occipital lobe damage preoperatively when resecting tumors located at the tentorial or pineal regions with the occipital-transtentorial approach (Poppen approach). - METHODS: In 27 consecutive patients who underwent tumor resection with the Poppen approach for tentorial or pineal region meningiomas, the following morphologic parameters were assessed on a preoperative magnetic resonance imaging: (1) tentorial angle, (2) tentorial length, and (3) the shortest distance from the confluence of the sinus to the tumor. These parameters, together with tumor size, texture, and resection extent, were correlated with occipital lobe damage by using the one-way analysis of variance, chi(2), or Fisher's exact tests. RESULTS: The mean value was 55.3 degrees +/- 5.6 degrees (range, 45 degrees - 66 degrees) for the tentorial angle, which was significantly associated with the occipital lobe damage grades (P = 0.008), but this was not the case for the tentorial length (P = 0.802) and the shortest distance from the confluence of the sinus to the tumor (P = 0.695). Interestingly, age was also strongly associated with occipital lobe damage risk (P = 0.020). The patients in the subgroup with no occipital damage (grade 4) were the youngest (aged 47.3 years), compared with other grades, with age of 58.0 years for grade 1, 54.3 years for grade 2, and 58.6 years for grade 3. These 2 parameters were also significant after multivariate analysis. No correlation was observed between either tumor nature or the extent of resection and damage grades. CONCLUSIONS: The risk of occipital lobe damage increases in the presence of a steep tentorial angle during the Poppen approach for tentorial or pineal area tumors. Awareness of such anatomic features preoperatively is important for minimizing operative complications.