Minimally invasive image-guided access for drainage of petrous apex lesions: a case report

Abstract

Objective: In this case report, we present a novel, minimally invasive image-guided approach to drainage of a petrous apex lesion.

Patient(s): A 34-year-old man diagnosed with a petrous apex lesion consistent with cholesterol granuloma. The granuloma was large and caused mild compression of the brainstem with associated neurologic symptoms and seizure-like activity.

Interventions: Based on the anatomic location of the lesion, it was determined that the treatment plan would be to surgically drain the lesion via 2 linear paths-one after an infralabyrinthine approach and the other a subarcuate approach. Customized microstereotactic frames that mount on bone-implanted markers and constrain the drill along the desired path were used to accurately drill these desired paths and avoid damage to surrounding critical structures. After a simple mastoidectomy, the petrous apex was successfully reached without damage to vital adjacent structures by drilling the 2 linear channels using 2 custom microstereotactic frames.

Main outcome measures: Viscous brown liquid and debris was recovered by irrigating through one of the channels and suctioning through the other.

Results: Drainage of the petrous apex was successfully performed via 2 linear channels without any complications. Custom microstereotactic frames were used to accurately drill those linear channels. Postoperative CT ensured no complications. Postoperative course of the patient was remarkable with normal hearing and normal facial nerve function.

Conclusion: We presented a successful implementation of an image-guided approach to drain petrous apex.

Figure 1

T1-weighted with contrast (left) and T2-weighted (right) MRI of petrous apex lesion consistent with a cholesterol granuloma. The T2 image demonstrates compression of the brainstem by this lesion.

Figure 2

Traditional approaches to the petrous apex (PA) lesion. (a) Axial view of the CT scan showing a prominent horizontal carotid artery (CA) and thick clival bone preventing a transnasal transphenoidal approach. (b) and (c) show the coronal views of the CT scan indicating the posteriorly located carotid artery and a small infracochlear air cell tract (black arrows) preventing an infracochlear approach. (d) Axial view of the CT scan showing posteriorly located labyrinth (black straight arrows) and anterior endolymphatic duct (ELD) preventing a retrolabyrinthine approach. IAC – internal auditory canal.

Figure 3

Trajectories manually picked by the surgeon are shown as white dotted lines along with the results of automatic segmentation. The boundaries of the 3.8 mm and 1.6 mm wide drilling are shown as white solid lines. (a) Infralabyrinthine approach. The tract is about 2.7 mm from the facial nerve, 1.4 mm from the posterior semicircular canal (PSCC), and 5 mm from the cochlea. Note a tiny area of apparent bony dehiscence adjacent to the carotid canal. (b) Subarcuate approach. The tract is about 3.7 mm from the facial nerve and 1.8 mm from the horizontal semicircular canal (HSCC). The path goes through the center of the superior semicircular canal (SSCC), which is about 4.7 mm wide with a clearance of 1.2 mm.

Figure 4

Steps involved in performing the minimally-invasive, image-guided access to the petrous apex. The gray-filled box indicates that the step is performed prior to surgery.

Figure 5

(a) Fiducial markers – Three anchors were bone-implanted surrounding the temporal bone region. Extenders with spherical ends were attached to each anchor. A simple mastoidectomy was performed to provide the required clearance to attach the microstereotactic frame and drill components. (b) Custom microstereotactic frame for the subarcuate linear path mounted on the spheres. (c) Drill press system attached to the microstereotactic frame. The microstereotactic frame defines the drill path and the drill press controls the linear movement of the drill to a predetermined depth.