Access osteotomy - Extended frontal craniotomy

Extended frontal craniotomy gives access to the:

• anterior cranial fossa
• orbital roof on both sides
• entire optic chiasm
• superior portion of the clivus
• anterior aspect of the nasal root

The coronal approach is used to expose the frontal bone.

The craniotomy can be performed in either one step where the suprarobital bandeau is mobilized together with the rest of the frontal bone. Here we will describe a two step procedure.

After the exposure of the frontal bone and the orbits, burr holes are placed at the vertex and nasal frontal area as well as in both temporal regions.

An epidural dissection between these points is made.

A bifrontal craniotomy beginning 1 cm above the superior orbital rim and extending to posterior to the temporal crest is completed by the neurosurgeon, using a craniotome.

After the bone flap is removed, the brain is freed from the anterior fossa in the epidural plane.

Plates are utilized to provide accurate fixation of the supraorbital bar. Prior to creating the osteotomies, 5-hole plates are placed across the planned osteotomy lines of the lateral orbit. A Y-shaped plate is placed in the midline from the nasal bone to the glabella. Two holes are drilled on each side of the osteotomy line and appropriate length screws are placed.

The plates and screws are removed and placed on the back table. It is critical to maintain the plates and screws in the proper anatomical orientation in order to return them in the exact preplanned position.

Malleable retractors are used intracranially to protect the brain and intraorbitally to protect the orbital content.

The supraorbital bar is then osteotomized. A vertical cut posterior to the temporal crest (1) is followed by a horizontal cut to the lateral orbital rim (2). An oblique cut is then made through the orbital rim (3) and a transverse osteotomy is completed at the nasal frontal junction (4).

A right angle saw is then turned intracranially and the orbital roof is cut beginning laterally and ending at the nasal frontal cut medially, joining the cut made extracranially across the nasal frontal region.

An osteotome is then inserted in the osteotomy line liberating the bandeau. It is removed and set aside in a saline soaked gauze for later replacement.

The orbital bar is replaced with the preplanned hardware.

The frontal craniotomy bone is replaced and fixated in the standard fashion.

Care is taken as so to secure that adequate space is left between the frontal bone flap and the supraorbital rim so as not to compress any flap or vascular pedicles.