Endoscopic Endonasal Petrosectomy: Anatomical Investigation, Limitations, and Surgical Relevance

Abstract

BACKGROUND The endoscopic endonasal approach (EEA) was recently added to the neurosurgical armamentarium as an alternative approach to the petrous apex (PA) region. However, the maximal extension, anatomical landmarks, and indications of this procedure remain to be established. OBJECTIVE To investigate the limitations and suggest a classification of PA lesions for endoscopic petrosectomy. METHODS Five anatomical specimens were dissected with EEA to the PA. Anatomical landmarks for the surgical steps and maximal limits were noted. Pre- and postprocedural computed tomographic scan and image-guidance were used. Relevant surgical cases were reviewed and presented. RESULTS We defined 3 types of petrosectomy: medial, inferior, and inferomedial. Medial petrosectomy was limited within the paraclival internal carotid artery (ICA) anteriorly, lacerum ICA inferiorly, abducens nerve superiorly, and petrous ICA laterally. Among those, abducens nerve and petrous ICA are surgical limits. Full skeletonization of the paraclival ICA and removal of the lingual process are essential for better access to the medial aspect of PA. Inferior petrosectomy was defined by the lacerum foramen synchondrosis anteriorly, jugular foramen inferiorly, internal acoustic canal posteriorly, and PA superolaterally. Those are surgical limits except for the foramen lacerum synchondrosis. The connective tissue at the pterygosphenoidal fissure was a key landmark for the sublacerum approach. Clinical cases in 3 types of PA lesions were presented. CONCLUSION The EEA provides access to the medial and inferior aspects of the PA. Several technical maneuvers, including paraclival and lacerum ICA skeletonization, sublacerum approach, and lingual process removal, are key to maximize PA drilling.

Anatomical Limits of the Endoscopic Contralateral Transmaxillary Approach to the Petrous Apex and Petroclival Region

“…In this context, endonasal approaches to the PA and PCR classically include (1) a medial transphenoidal approach, (2) a medial transpterygoid approach with ICA lateralization, or (3) a transpterygoid infrapetrous approach. 8,9 Cystic lesions protruding into the sphenoid sinus, for example, can be safely treated with the medial transsphenoidal approach. For other tumors, however, a transpterygoid approach with ICA mobilization and ET resection might be necessary.…”

“…[13][14][15] The CTM presents significant advantages over a classical EEA for lesions in the coronal plane, especially if intimately related to the ICA. Borghei-Razavi et al have discussed the limitations of an ipsilateral EEA to the PA. 8 The single most important benefit provided by CTM is the "angle advantage." The difference between the working angles, estimated to be around 25 degrees, permits the surgeons to work behind the ICA while using only 0-degree endoscopes and straight instruments.…”

“…From a purely endonasal point of view, a transpterygoid corridor is often considered sine qua non for reaching the ipsilateral PA and PCR. [6][7][8][9]11 When performing such an approach, the sphenopalatine artery must be sacrificed. Preservation of the sphenopalatine artery, however, is highly desirable for skull base reconstruction following endonasal approaches to the skull base.…”

“…Besides avoiding brain retraction, the EEA can provide a more direct route to some lesions, without crossing the plane of cranial nerves, risking hearing or working through poorly visualized corridors. [6][7][8] In spite of its benefits, the EEA to the PA and PCR is technically demanding. For lesions located below the petrous ICA, for example, an infrapetrous transpterygoid approach is often required, requiring resection of the pterygopalatine fossa (PPF) and the medial Eustachian tube (ET).…”

“…9,10 Lesions located in the superior portion of the PA, on the other hand, require angled instrumentation and risky surgical maneuvers such as bony decompression and lateral displacement of the ICA. 8,11,12 Taking advantage of the paranasal sinuses and combining surgical corridors, a new surgical approach has been proposed. Referred to as contralateral transmaxillary approach (CTM), it provides excellent access to lesions in the coronal plane, including the PA and PCR.…”