Linear measurements of pedicle dimensions and also axial angles from horizontal and vertical planes may provide some anatomic limitations for subaxial cervical transpedicular screw fixation, and also contribute to the safety of the surgical procedure. One should also rely on tomographic data and computer-assisted guidance systems.

In transcondylar approach, the anatomical landmarks should be well known in order to make a safe occipital condyle resection. The distance between the intracranial edge of the hypoglossal canal and posterior margin of the occipital condyle is important for a safe occipital condyle resection, and it was found to be 12.55 +/-0.05 mm in our study. Approximately 12 mm occipital condyle resection can be made without giving damage to the neural tissue. This value is appropriate to the (1/2) of the occipital condyle.

Knowing the location of the venous sinuses is essential for the localization of the initial burr-hole for a retrosigmoid approach, in order to avoid inadvertent entry into the venous sinuses and limitation of the size of the bony opening. In this anatomic study, external landmarks of the posterolateral cranium have been studied, in order to reveal the relationship with the venous sinuses. Eighty-four dried adult human skulls were studied and study of both sides yielded 168 sides. Morphometric measurements of the posterolateral cranium have been performed and relations of the external landmarks with the venous sinuses have been studied. The anatomic position of the asterion was variable. The superior nuchal line was roughly parallel and below the lower margin of the sulcus of transverse sinus in all specimens. The sigmoid sinus, between the superior and inferior bends, seemed to descend along an axis defined by the junction of the squamosal-parietomastoid suture and the mastoid tip, in a slightly oblique fashion. In conclusion, a burr-hole placed just below the superior nuchal line and posterior to the axis defined by the mastoid tip and the squamosal-parietomastoid suture junction is appropriate for both avoiding inadvertent entry into the sinus and limiting the size of the craniotomy.

No abstract

Summary: Surgical anatomy that provides the basis for dealing with lesions arising in the lower clivus and ventral foramen magnum was reviewed in 8 adult cadaver heads and 76 dry skulls. The extreme lateral transcondylar approach was performed in cadavers; the morphometric analysis was studied in both the cadavers and the skulls. The landmarks, distances and structures were selected in order to guide the surgical operations in this area. In the paper, surgical approaches to this region are reviewed, and the results are discussed from the standpoint of surgical importance.There are many kinds of pathological processes that involve the craniovertebral junction. These lesions include intradural tumors such as meningiomas, neurinomas or vascular lesions such as aneurysms and arteriovenous malformations of the vertebral artery and vertebrobasilar junction, extradural tumors such as chordomas, basilar invagination and other congenital anomalies, nontraumatic (rheumatoid) and traumatic entities with C1-C2 subluxation. Anterior cranial base approaches are appropriate for surgical management of extradural lesions which are localized strictly to the midline. Basilar invagination and congenital anomalies, rheumatoid compression of the craniocervical region, and some traumatic lesions can be treated successfully using the transoral") and transmaxillary1 3) procedures or the mandibular swing-transcervical approach1). For intradural lesions, the transoral, transmaxillary and transmandibular approaches can still be utilized"• 14'16), but are suboptimal because of the lack of proximal and distal vascular control, limited lateral exposure and the possibility of contamination of the cerebrospinal fluid with oral flora resulting in lifethreatening meningeal infection. Suboccipital approach, with or without upper cervical vertebral laminectomy, is the traditional approach used for intradural lesions of the posterior fossa and craniovertebral junction, but in case the lesion is placed ventrally, this approach provide very poor exposure and required retraction of the brainstem.The extreme lateral transcondylar and transjugular approach (ELTCA) offers a very lateral view of the structures located at the lower diva! area and craniovertebral junction. This lateral cranial base approach permits a controlled resection or reconstruction of the lesions in this area through direct view of the vertebral artery, lower cranial nerves, and the interface between the lesion and the brainstem. It is also possible to achieve an occiput-to-C1-3 fusion during the same operation, if necessary. Furthermore, because there is a wellvascularized muscle covering of this area, reconstruction of the operative field is perfect and infectious or vascular complications in the postoperative period oftenly can be managed with good results2,3,5,8,20,2 1). Surgical anatomy of the occipital condyles (0C) is critical for ELTCA, and this study aims to study surgical anatomical and morphometric details of the relevant region.