# Surgical Approaches to the Anterior Cranial Fossa
## Overview
The anterior cranial fossa (ACF) houses the frontal lobes and is bounded by the orbital roof inferiorly, the lesser wing of the sphenoid posteriorly, and the frontal bone superiorly. Pathology in this region includes olfactory groove meningiomas, planum sphenoidale meningiomas, anterior skull base tumors, CSF leaks, and frontal lobe lesions. Multiple surgical corridors exist, each with specific advantages.
## Relevant Surgical Anatomy
### Bony Anatomy
The frontal bone forms the roof of the ACF. The cribriform plate is a thin, extremely fragile segment of ethmoidal bone through which the olfactory nerves pass. The crista galli is a midline bony projection that anchors the falx cerebri. The planum sphenoidale is a flat surface of the sphenoid bone between the cribriform plate and the tuberculum sellae. The lesser wing of the sphenoid forms the posterior boundary of the ACF and contains the anterior clinoid process.
### Neurovascular Structures
The olfactory nerves and tracts course along the floor of the ACF. The anterior ethmoidal arteries cross the roof of the ethmoid sinuses and serve as landmarks for the cribriform plate. The superior sagittal sinus begins at the crista galli and drains the superior cerebral veins. Frontal bridging veins drain the frontal lobes into the superior sagittal sinus and should be preserved whenever possible. The frontopolar and orbitofrontal arteries are branches of the ACA that supply the base of the frontal lobe.
## Subfrontal Approach
### Indications
The subfrontal approach is used for olfactory groove meningiomas, planum sphenoidale meningiomas, tuberculum sellae meningiomas, anterior cranial base CSF leaks, and selected suprasellar lesions such as craniopharyngiomas and certain pituitary adenomas.
### Technique
The patient is positioned supine with the head elevated 15-20 degrees and slightly extended. A unilateral or bilateral coronal skin incision is made, and a pericranial flap is harvested for later dural and skull base reconstruction. The craniotomy is a unilateral frontal opening with its inferior extent reaching the orbital roof; if the frontal sinus is entered, cranialization is required. The intradural approach involves gentle frontal lobe elevation, with CSF release from the Sylvian or chiasmatic cisterns reducing the need for retraction. A key maneuver is early identification and either division or preservation of the ipsilateral olfactory tract. Tumor devascularization is achieved by coagulating the dural blood supply along the floor of the ACF early in the procedure.
### Advantages
This approach provides direct visualization of the midline anterior skull base, excellent access to the planum and tuberculum sellae, and allows early devascularization of meningiomas from their dural attachment.
### Limitations
Olfactory nerve sacrifice is sometimes necessary, particularly with large olfactory groove meningiomas. There is a risk of frontal sinus violation requiring cranialization, and frontal lobe retraction may cause contusion or venous infarction.
## Bifrontal Craniotomy
### Indications
The bifrontal craniotomy is indicated for large midline anterior skull base tumors (bilateral olfactory groove meningiomas), anterior skull base malignancies (esthesioneuroblastoma, sinonasal carcinoma), bilateral frontal pathology, and cases requiring extensive anterior skull base reconstruction.
### Technique
The patient is positioned supine with the head neutral or slightly extended. A bicoronal incision is made, and a large vascularized pericranial flap based on the supraorbital arteries is harvested. The craniotomy crosses the midline bilaterally; the superior sagittal sinus can be safely ligated anteriorly, where it is small and no significant bridging veins enter. An orbital osteotomy (supraorbital bar removal) may be added for extended approaches, improving the angle of visualization and reducing the need for brain retraction. Skull base reconstruction is achieved by laying the pericranial flap over any dural or bony defect, potentially supplemented with fascia lata, fat, or titanium mesh.
### Advantages
This approach provides wide bilateral exposure of the anterior skull base, allows en bloc resection of skull base tumors with involved dura and bone, and the pericranial flap provides vascularized tissue for watertight reconstruction.
### Limitations
The bifrontal craniotomy carries higher morbidity than unilateral approaches, including the risk of bilateral olfactory nerve injury leading to anosmia, the requirement for frontal sinus cranialization with its attendant risk of mucocele if not properly managed, and the potential for bilateral frontal lobe retraction injury.
## Extended Transfrontal Approaches
### Subcranial (Transbasal) Approach
The subcranial approach combines a bifrontal craniotomy with an orbital osteotomy and nasoethmoidal bone removal. It provides access from the frontal sinus to the clivus and is used for extensive skull base tumors involving the nasal cavity, paranasal sinuses, and anterior skull base simultaneously. It also enables craniofacial resection for malignancies crossing the skull base.
### Fronto-orbital Approach
This approach combines a unilateral frontal craniotomy with removal of the supraorbital bar. It improves the angle of approach to the sellar and suprasellar region, reduces the need for frontal lobe retraction, and is useful for anterior communicating artery aneurysms and suprasellar tumors.
## Dural Reconstruction Principles
Watertight closure is essential to prevent CSF leak, which is the most common complication of anterior skull base surgery. The pericranial flap is the workhorse for reconstruction and must be harvested carefully with its blood supply intact. Dural substitutes such as fascia lata, collagen matrix, and synthetic grafts may supplement the pericranial flap. A multilayer closure consisting of a fat graft, fascial layer, pericranial flap, and fibrin glue provides optimal results. A lumbar drain may be placed for 3-5 days postoperatively if a large dural defect was repaired.
## Comparison of Anterior Cranial Fossa Approaches
| Feature | Subfrontal | Bifrontal | Subcranial (Transbasal) | Fronto-orbital |
|---------|-----------|-----------|------------------------|----------------|
| Indications | Olfactory groove/planum meningiomas, CSF leaks | Large midline ACB tumors, malignancies | Extensive tumors involving nasal/sinus/ACB | AComA aneurysms, suprasellar tumors |
| Exposure | Unilateral midline ACB | Wide bilateral ACB | Frontal sinus to clivus | Sellar/suprasellar |
| Retraction | Unilateral frontal | Bilateral frontal | Minimal (bone removal replaces retraction) | Reduced (orbital bar removal) |
| Olfactory preservation | Possible (small tumors) | Rarely achievable | Difficult | Possible |
| Key risk | Frontal sinus violation | Bilateral anosmia, sinus mucocele | Complex reconstruction | Orbital complication |
## Complications
CSF leak is the most common major complication and may require re-exploration or lumbar drainage. Frontal sinus mucocele can develop from incomplete cranialization and is prevented by stripping all sinus mucosa and packing with fat or vascularized tissue. Olfactory loss is nearly universal in bilateral approaches for olfactory groove tumors. Frontal lobe contusion from excessive retraction can be minimized with CSF drainage and intermittent relaxation. Venous infarction may result from bridging vein sacrifice, so as many veins as possible should be preserved. Pneumocephalus is expected postoperatively, though tension pneumocephalus is a surgical emergency. Meningitis may occur secondary to CSF leak or sinus communication.
Stepwise illustration of a unilateral subfrontal craniotomy approach to an olfactory groove meningioma. Panel A shows the coronal skin incision and planned craniotomy outline on the skull. Panel B shows the craniotomy completed with the frontal lobe gently retracted and the olfactory groove meningioma visible on the floor of the anterior cranial fossa. Panel C shows the dural blood supply being coagulated at the base of the tumor. Key structures labeled include olfactory tract, crista galli, and anterior ethmoidal arteries. Clean surgical illustration style.
Bifrontal craniotomy with orbital bar osteotomy for extended anterior skull base access. The illustration shows a superior view of the skull base after the bifrontal bone flap and supraorbital bar have been removed. The anterior cranial fossa floor is exposed bilaterally with the crista galli, cribriform plates, planum sphenoidale, and lesser wings of the sphenoid labeled. A large vascularized pericranial flap is shown reflected posteriorly, ready for later reconstruction. Medical illustration with labeled bony landmarks.
## Clinical Pearls
The superior sagittal sinus can be safely ligated in its anterior third, anterior to the coronal suture, where it is small and receives few critical bridging veins. A pericranial flap should always be harvested before performing the craniotomy, as it is the most reliable reconstructive option for the anterior skull base. Early CSF drainage through opening the Sylvian fissure or chiasmatic cistern dramatically reduces the need for brain retraction. When the frontal sinus is entered, all mucosa must be stripped, the nasofrontal ducts plugged, and the sinus cranialized to prevent delayed mucocele formation. Olfactory nerve preservation is possible in small unilateral tumors but is rarely achievable with large bilateral olfactory groove meningiomas. The anterior ethmoidal arteries mark the lateral extent of the cribriform plate and are key landmarks during skull base dissection.
## References
- Dehdashti AR, et al. "Modified Bifrontal Craniotomy for Anterior Skull Base Tumors." *Neurosurgery*. 2009;64(ONS Suppl 2):ons287-ons296.
- Spektor S, et al. "Olfactory Groove Meningiomas from Neurosurgical and Ear, Nose, and Throat Perspectives." *Neurosurgery*. 2005;57(4):635-646.
- Rhoton AL Jr. "The Anterior and Middle Cranial Base." *Neurosurgery*. 2002;51(Suppl 1):S273-S302.
- Sekhar LN, Janecka IP. "Surgery of Cranial Base Tumors." Raven Press, 1993.