Figure 1: Anterior skull base chondrosarcoma with extensive invasion of the nasal cavities (upper images). This case illustrates appropriate indications for a bifrontal craniotomy. A transnasal approach was deemed inappropriate because the midline septal invasion of the tumor rendered the nasoseptal flap unavailable for skull base reconstruction. The bottom postoperative images demonstrate gross total resection of the mass.

Figure 2: The anatomy of the anterior cranial fossa with the dura removed. Notice the asymmetry of the frontal sinuses (upper image), emphasizing the need to review preoperative imaging. The lower edge of the craniotomy must be at the level of the orbital roof. Note the proximity of the Crista Galli to the olfactory bulbs and cribriform plate that resides in a “valley” as compared with orbital roofs. Extradural dissection of the dura at the level of the crista Galli and cribrifom plate leads to exposure of the intradural space (Images courtesy of AL Rhoton, Jr).

Figure 3: The patient is placed in the supine position with the head slightly extended or flexed based on the vertical extent of the tumor. This head position mobilizes the frontal lobes away from the cranial base using gravity-induced retraction. The head typically does not require rotation for the midline pathologies accessed through this route. The single pin of the skull clamp is just above and behind the pinna, while the contralateral and bisecting two pins are located above the pinna as illustrated. The positions of the pins should be appropriately planned to avoid their interference with the bicoronal skin incision.

Figure 4: A bicoronal incision is designed (dark solid line). This incision should be as anterior as possible while staying behind the hairline. The incision does not always need to reach the tragus, but it at least should reach to the level of the superior edge of the pinna. The extent of the patient’s neck flexion is tailored based on the cranial extension and inferior reach of the tumor into the nasal sinuses.

Figure 5: The scalp incision should leave the pericranium, temporalis muscle, and fascia intact. I routinely elevate a vascularized pericranial graft as a separate layer. The plane between the galea and pericranium is dissected/undermined more posteriorly beyond the incision to allow for elevation of a larger pericranial graft (left image). Monopolar electrocautery disconnects the posterior and lateral attachments of the pericranium (to the superior temporal line). This vascularized graft will be reflected and based anteriorly along the orbital rims.

A generous piece of pericranial flap is elevated, stretched, and kept moist during the operation by covering it with a wet piece of sponge (right image).

Figure 6: Design of the bone flap: A single burr hole is placed over the anterior superior sagittal sinus. The vertical height of the craniotomy is under 10 cm, and the width does not need to spread across the entire width of the orbital rims. Most lesions, regardless of their size, can be reached and removed through a limited “low” bifrontal craniotomy (hashed line).

Some operators prefer a larger craniotomy (gray solid line). If larger bone flaps are infected postoperatively, their removal will leave the patient with a large frontal skull defect. Note the location of the skull clamp pins. More posterior placement of the pins risks fixation failure.

Upon completion of the burr hole and CSF drainage through the lumbar drain, the dura is then dissected off of the calvarium using a #3 Penfield. Burr holes in the region of the forehead are avoided for cosmetic reasons.

Figure 7: The craniotome with its footplate is used to complete the vertical bony cuts (top image). The final horizontal osteotomy over the frontal sinuses is performed using a straight side-cutting burr to first disconnect the anterior and then the posterior walls of the frontal sinus (bottom image).

Upon elevation of the bone flap, the frontal sinus mucosae are thoroughly removed using pituitary rongeurs and coagulated with monopolar electrocautery. I use muscle, betadine, or bacitracin-soaked bone wax to fill the sinuses. Alternatively, the sinuses are filled with betadine-soaked gelfoam and exenteration and cranialization will be completed at the end of the procedure when the dura is closed.

Figure 8: The inferior overhanging edges of the craniotomy and posterior walls of the frontal sinuses are removed to prevent them from obstructing the operator’s view toward the basal frontal lobe.

Figure 9: Pieces of temporalis muscle may also be used to fill the frontal sinuses. Further CSF drainage allows extradural dissection and lobar elevation away from the Crista Galli and exposure of the cribiform plate. The dura is mobilized from the orbital roof and Crista Galli using a #1 Penfield dissector.

Figure 10: I dynamically retract the frontal lobes using the suction apparatus. Sharp dissection is used over the olfactory bulb to disconnect the bulb and expose the anterior extradural extension of the tumor (star). This intraoperative image refers to resection of an anterior skull base chondrosarcoma invading the nasal cavities (See Figure 1 above). Disconnection of the bulb also leads to dural opening and disclosure of the intradural portions of the tumor.

Figure 11: After gross total resection of the tumor and watertight closure of the dural defect using a piece of temporalis fascia graft, a large skull base defect is apparent. The pericranial graft is seen at the top of the image.

Figure 12: If the operator desires to approach purely intradural tumors such as meningiomas through a bifrontal approach, the dura may be opened through two horizontal incisions parallel to upper edge of craniotomy (A and B). The anterior superior sagittal sinus is then ligated with 0-silk sutures in two spots and divided. Although anterior parasagittal bridging veins are considered dispensable, the operator must exercise caution during their sacrifice. The tumor is evident at the tip of suction apparatus (C). The dura is then closed using a piece of temporalis fascia and the pericranium is used to cover the frontal sinuses (D and E).

Figure 13: Excess pericranium is amputated and its edge is sutured to the dura along the floor of the anterior fossa as posteriorly as possible in a running fashion (top image). The pericranial graft provides a sheet of vascularized tissue to separate the intracranial space from the nasal cavity (bottom image).

Figure 14: If a large area of ethmoid sinuses is exposed and a wide bony defect is present at the end of tumor resection, I prepare a split calvarial bone graft from the craniotomy bone flap and place the bone graft over (not under) the pericranial flap that is in place over the skull base defect. This piece of bone may be fixed to the orbital roof using small titanium screws. This bony reconstruction reinforces the skull base construct and avoids displacement of the pericranial graft by the patient’s forceful coughing or sneezing.