19 Medial Petrous Apex Approach

The petrous apex, a complex bony area located between the middle and posterior cranial fossa, is surrounded by a number of important neurovascular structures, including the petrous and paraclival tract of the internal carotid artery, trigeminal nerve, Gasserian ganglion, abducens nerve, acoustic-facial bundle, and all the vessels and nerves of the jugular foramen. Topographically, the petrous apex is the anteromedial portion of the petrous bone and is enclosed between the internal acoustic meatus and the petroclival junction. The petrous apex can be schematically divided into three subunits, which can be variably exposed through the transnasal routes. The superior portion lies above the axial plane passing through the superior surface of the petrous horizontal tract of the internal carotid artery. The anteroinferior and posteroinferior portions lie below the aforementioned plane, anteromedially and posterolaterally to the vertical portion of the petrous internal carotid artery, respectively. ¹

Several endoscopic transnasal surgical routes have been designed to reach the petrous apex, namely, the medial petrous apex approach, the infrapetrous approach, and the suprapetrous (Meckel’s cave) approach. The medial petrous apex approach exploits the transclival pathway through the midclivus to reach the medial segment of the superior and anteroinferior portions of the petrous apex. ^{2 , 3} This approach has been employed either alone or as lateral extension of the middle transclival approach to manage several diseases of the petroclival area, including fluid-containing lesions requiring surgical drainage such as cholesterol granuloma and petrous apicitis, ^{2 – 5} as well as solid tumors such as chondrosarcomas, ^{3 , 6} chordomas, ^{3 , 7 , 8} and meningiomas. ^{9 , 10} The infrapetrous and suprapetrous corridors are described in Chapters 20 and 21, respectively. Skull base teams treating lesions of the petroclival area should master both the transnasal and the lateral transcranial/transpetrosal surgical techniques, which are selected or combined depending on the extension and nature of the disease.

From an anatomical–topographical perspective, the medial petrous apex approach exploits the narrow bony area (called “carotid-clival window”) between the paraclival internal carotid artery, anteriorly, and the periosteum of the posterior cranial fossa, posteriorly. ^{11 , 12} This area corresponds to the petroclival junction, thus being the floor of Dorello’s canal, where the abducens nerve runs below the petroclinoid ligament (also called petrosphenoidal or Gruber’s ligament), passing from the basilar plexus to the cavernous sinus. In addition, the tract of the nerve passing through the basilar plexus runs with an ascending trajectory immediately behind the petroclival junction. As a consequence, the dissection of this anatomical space should be performed carefully to avoid damaging the abducens nerve. ¹³ In cases requiring a large exposure, the paraclival tract of the internal carotid artery can be uncovered from the surrounding bone and subsequently lateralized to widen the window of the medial petrous apex approach. ³

The network of dural sinuses and plexuses between the periosteum and the dura of this anatomic area is exceedingly intricate, including the basilar plexus, the inferior and superior petrosal sinus, and the cavernous sinus. Therefore, intense venous bleeding should be expected when the petroclival periosteum is entered.

Laboratory dissection including all three transnasal routes toward the petrous apex is strongly recommended to fully understand potentials and limitations of these pathways.

Related posts:

1 Classification of Endoscopic Transnasal Approaches to the Skull Base and Adjacent Areas 9 Transsellar Approach 10 Transsellar Transdorsal Approach 17 Medial Transcavernous Approach 22 Transcondylar/Transjugular Tuberculum (“Far-Medial”) Approach 18 Lateral Transcavernous Approach

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