The petrous apex is a pyramid-shaped structure, located medial to the inner ear and the intrapetrous segment of the internal carotid artery. Lesions of the petrous apex can be surgically treated through different surgical routes. Because of the important neurovascular structures located inside the temporal bone, anatomical 3D knowledge is paramount. For this reason, image-guided surgery could represent a useful tool. We report the case of a young woman who came to our observation for a trigeminal neuralgia due to a petrous apex cholesterol granuloma. The lesion was treated through the placement of a drainage tube via an infracochlear approach, with the aid of neuronavigation and intraoperative MRI. Preoperative CT scan images and intraoperative MRI images were fused for surgical planning. The accuracy of the neuronavigation system has proved to be good, and the safety of the procedure was enhanced. Therefore, neuronavigation and intraoperative MRI, though not available in all neurootological centres, should be considered useful tools in these challenging procedures. 1. Introduction The petrous apex is a pyramid-shaped structure that represents the most medial part of the temporal bone [1, 2]. It is located medially to the intrapetrous segment of the internal carotid artery, inner ear, and Eustachian tube [1–3]. Several types of lesions may involve the petrous apex, such as cholesterol granuloma, cholesteatoma, dermoid cyst, mucocele, abscess, primary benign, or malignant neoplasms and metastases [3]. Because of the complex anatomical relationships with the adjacent neurovascular structures (internal carotid artery, jugular bulb, VII and VIII CN, and inner ear), surgery may be highly challenging. In order to respect the aforementioned structures and to achieve a macroscopically total resection of petrous apex lesions, different surgical approaches have been described in the literature. Image-guided surgery could represent a useful tool for surgical planning; therefore [4], we report the case of a young woman who underwent surgical treatment of a petrous apex cholesterol granuloma via an infracochlear approach, with the aid of neuronavigation and intraoperative MRI. 2. Case Presentation A 36-year-old woman came to our observation because of a three-month history of left trigeminal neuralgia with pain distributed along the ophthalmic division of the fifth cranial nerve. The neurological examination revealed the absence of neurological deficits. MRI with gadolinium showed a hyperintense lesion on both T1- and T2-weighted images, with no postcontrast
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