Endoscopic transsphenoidal anterior petrosal approach for locally aggressive tumors involving the internal auditory canal, jugular fossa, and cavernous sinus
Authors: Shin Masahiro , Kondo Kenji , Hanakita Shunya , Hasegawa Hirotaka , Yoshino Masanori , Teranishi Yu , Kin Taichi , Saito Nobuhito 
Published: April 2016

OBJECTIVE
Reports about endoscopic endonasal surgery for skull base tumors involving the lateral part of petrous apex remain scarce. The authors present their experience with the endoscopic transsphenoidal anterior petrosal (ETAP) approach through the retrocarotid space for tumors involving the internal auditory canal, jugular fossa, and cavernous sinus.

METHODS
The authors performed the ETAP approach in 10 patients with 11 tumors (bilateral in 1 patient) that extensively occupied the lateral part of petrous apex, e.g., the internal auditory canal and jugular fossa. Eight patients presented with diplopia (unilateral abducens nerve palsy), 3 with tinnitus, and 1 with unilateral hearing loss with facial palsy. After wide anterior sphenoidotomy, the sellar floor, clival recess, and carotid prominence were verified. Tumors were approached via an anteromedial petrosectomy through the retrocarotid triangular space, defined by the cavernous and vertical segments of the internal carotid artery (ICA), the clivus, and the petrooccipital fissure. The surgical window was easily enlarged by drilling the petrous bone along the petrooccipital fissure. After exposure of the tumor and ICA, dissection and resection of the tumor were mainly performed under direct visualization with 30° and 70° endoscopes.

RESULTS
Gross-total resection was achieved in 8 patients (9 tumors). In a patient with invasive meningioma, the tumor was strongly adherent to the ICA, necessitating partial resection. Postoperatively, all 8 patients who had presented with abducens nerve palsy preoperatively showed improvement within 6 months. In the patient presenting with hearing loss and facial palsy, the facial palsy completely resolved within 3 months, but hearing loss remained. Regarding complications, 3 patients showed mild and transient abducens nerve palsy resolving within 2 weeks, 3 months, and 6 months. Postoperative CSF rhinorrhea requiring surgical repair was observed in 1 patient. No patient exhibited hearing deterioration, facial palsy, or symptoms of lower cranial nerve palsy after surgery.

CONCLUSIONS
The ETAP approach can offer a simple, less invasive option for invasive skull base tumors involving petrous regions, including the internal auditory canal, jugular fossa, and cavernous sinus. The ETAP approach can reach more extensive areas in the extradural regions around the petrous bone. The authors' results indicate that the transsphenoidal retrocarotid route is sufficient to approach the petrosal areas in select cases. Further expansion of the surgical field is not always necessary. However, experience with intradural lesions remains limited, and the extent of tumor resection largely depends on tumor characteristics. Application of the ETAP approach should thus be carefully determined in each patient, taking into consideration the size of the retrocarotid window and tumor characteristics.