Background: Neuronavigation is based on the stereotactic principle which involves applying coordinate values to points in a reference frame. In situations where a navigation system is unaffordable but digital image data in the hospital’s data bank are available, a desired entry point location can be calculated by measuring the coordinate values in the image processing software on the computer’s intranet. In this report, a virtual orbito-meatal (OM) image study plane was used as the reference for localization of entry point instead of the actual study plane which can vary in angle.
Objective: The present study proposes a new technique to localize the desired entry point on the calvarium using a virtual (OM) study plane as reference. Herein, the technique is described, and the results in the operative theatre, which were confirmed by neuronavigation, are presented as a case report.
Material and Method: The author reported a case of left fronto-temporal intra-parenchymal brain tumor in a 56-year-old male who presented with headache, nausea, vomiting, disorientation, dysphasia and right side motor weakness. The patient underwent uneventful craniotomy and tumor biopsy, and the pathologic report revealed lymphoma. In the operative room, freehand entry point localization was performed using virtual OM plane as the reference, and outcomes were confirmed by a navigation system before the operation was started.
Results: In the present study, the desired entry point location was confirmed by a navigation system with good clinical results. In cases of intra-parenchymal lesions like this one, a navigation system is necessary until the overall operation is finished.
Conclusion: A virtual OM study plane can be used as the reference for localizing the desired entry point, but the procedure needs to be conducted on a computer with capable image processing software, which is usually bundled with the computerized tomography (CT) machine. A long-term study entailing neuronavigation supervision should be conducted in the future.

Keywords: Entry point, Calvarium, Brain tumor, Orbito-meatal, Image processing, Stereotactic, Neuronavigation