4 Approaches to Thalamic, Pineal, and Brainstem Lesions Figure 4.1. Anterior skull base approaches. (a) The various anterior and anterolateral skull base approaches that can be used to access lesions in the brainstem. These approaches constitute a continuum, and they include unilateral and bilateral subfrontal, eyebrow/supraorbital or orbitopterional, pterional, orbitozygomatic, and Kawase approaches. With improvements in endoscopy, anterior transclival approaches can be used for ventral pontine and pontomedullary lesions. Figure 4.1. (b) The various skin incisions used to perform the anterior skull base craniotomies in (a). (c) The various working trajectories afforded by anterior skull base approaches to the top of the brainstem. The extent of the lesion plays an important role in the choice of actual approach used and the degree of bony removal necessary to achieve the exposure. All of the various approaches to the brainstem are summarized at the end of the section (Table 4.1). Figure 4.3. Unilateral subfrontal or frontolateral approach. (a) The patient’s head is rotated 30 degrees off the vertical axis, with the neck slightly extended. The skin incision should be placed behind the hairline from the midline to the zygomatic process. This craniotomy is performed along the floor of the frontal fossa, extending to the pterion. Drilling the anterior fossa floor flush provides a flat and unhindered exposure to the basal cisterns. (b) The relationship between the craniotomy and the underlying neural structures. Figure 4.6. Pterional and mini-pterional approaches. (a) The pterional craniotomy is the mainstay skull base approach for lesions in the anterior cranial fossa and for ventral mesencephalic lesions. The skin incision and craniotomies for the standard (solid line) and mini-pterional (dashed line) approaches are illustrated. (b) The relationship between the craniotomy and the underlying neural structures. Figure 4.7. Cadaveric dissection demonstrating the mini-pterional craniotomy. (a) A curvilinear incision is centered on the extension line of the sphenoid groove (blue dashed line) 1 cm behind the hairline. (b) The subcutaneous tissue, frontal branch of the superficial temporal artery, and superficial fat pad are exposed after the galeal flap is reflected toward the temporal fossa. Figure 4.8. (e) The zygoma and orbital rim are covered by two layers of temporal fascia, which must be (f) incised and (g) mobilized to enable the osteotomies to be performed. In total, six osteotomies must be performed to enable removal of the orbitozygomatic unit.