title: Image-guided surgical planning using anatomical landmarks in the retrosigmoid approach.
abstract: OBJECTIVE
  The suboccipital lateral or retrosigmoid approach is the main neurosurgical approach to the cerebellopontine angle (CPA). It is mainly used in the treatment of CPA tumors and vascular decompression of cranial nerves. A prospective study using navigation registered with anatomical landmarks in order to identify the transverse and sigmoid sinuses junction (TSSJ) was carried out in a series of 30 retrosigmoid craniotomies. The goal of this study was to determine the accuracy of this navigation technique and to establish the relationship between the location of the asterion and the TSSJ.
  
  
  METHODS
  From March through November 2008, 30 patients underwent a retrosigmoid craniotomy for removal of CPA tumors or for surgical treatment of neurovascular syndromes. Magnetic resonance imaging (MRI) T1 sequences with gadolinium (FSPGR with FatSst, 1.5 T GE Signa) and frameless navigation (Vector vision, Brainlab) were used for surgical planning. Registration was performed using six anatomical landmarks. The position of the TSSJ indicated by navigation was the landmark to guide the craniotomy. The location of the asterion was compared with the position of the TSSJ. After craniotomy, the real TSSJ position was compared with the virtual position, as demonstrated by navigation.
  
  
  RESULTS
  There were 19 cases of vestibular schwannomas, 5 petroclival meningiomas, 3 trigeminal neuralgias, 1 angioblastoma, 1 epidermoid cyst and 1 hemifacial spasm. In all cases, navigation enabled the location of the TSSJ and the emissary vein, with an accuracy flaw below 2 mm. The asterion was located directly over the TSSJ in only seven cases. One patient had a laceration of the sigmoid sinus during the craniotomy.
  
  
  CONCLUSIONS
  Navigation using anatomical landmarks for registration is a reliable method in the localization of the TSSJ for retrosigmoid craniotomies and thereby avoiding unnecessary sinus exposure. In addition, the method proved to be fast and accurate. The asterion was found to be a less accurate landmark for the localization of the TSSJ using navigation.
authors.affiliation: Departament of Neurosurgery, Instituto de Neurologia de Curitiba, Rua Jeremias Maciel Perretto 300, Curitiba, Paraná, Brazil. teeth@uol.com.br
authors.forename: Erasmo Barros
authors.initials: EB
authors.lastname: da Silva
authors.forename: André G
authors.initials: AG
authors.lastname: Leal
authors.forename: Jerônimo B
authors.initials: JB
authors.lastname: Milano
authors.forename: Luis F Moura
authors.initials: LF
authors.lastname: da Silva
authors.forename: Rogério S
authors.initials: RS
authors.lastname: Clemente
authors.forename: Ricardo
authors.initials: R
authors.lastname: Ramina
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000601:surgery; D002530:Cerebellopontine Angle / Q000033:anatomy & histology / Q000601:surgery*; D002561:Cerebrovascular Disorders / Q000601:surgery; D003388:Cranial Fossa, Posterior / Q000033:anatomy & histology / Q000098:blood supply / Q000601:surgery; D003390:Cranial Nerve Neoplasms / Q000601:surgery; D003392:Cranial Sinuses / Q000033:anatomy & histology / Q000601:surgery; D003399:Craniotomy / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D038361:Neuronavigation / Q000295:instrumentation / Q000379:methods*; D009777:Occipital Bone / Q000033:anatomy & histology / Q000601:surgery*; D011300:Preoperative Care / Q000295:instrumentation / Q000379:methods; D011446:Prospective Studies; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult