Quantification of the Advantages of the Extended Frontal Approach to Skull Base

This anatomic study evaluated the extent that a fronto-orbital osteotomy (FOO) added to a bilateral frontal craniotomy widened the exposure to the midline compartment of the anterior, middle, and posterior cranial fossae. The goal was to determine if osteotomy would significantly increase angles for two targets: the foramen magnum (FM) and anterior clinoid process (ACP). Stepwise dissections were performed on five cadaveric heads. A bilateral frontal craniotomy was made, followed by FOO. After the ethmoids were removed, the planum sphenoidale was drilled to enter the sphenoid sinus. Further drilling exposed the anterior clivus, which was drilled down to FM. Excellent exposure of the basilar artery, vertebral artery, and brain stem was achieved. With and without FOO, angles of exposure were measured for two targets: the ACP and FM. The angle of exposure after FOO increased markedly with an average gain of 76% for the ACP and of 80% for FM. Compared with a conventional bifrontal craniotomy, the addition of FOO increased the surgical exposure and minimized frontal lobe retraction for accessing lesions of the anterior, middle, and posterior cranial fossae.

KEYWORDS

Brain tumor - extended frontal approach - operative approach - skull base - skull base tumor

REFERENCES

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The authors have quantified the advantages of the extended subfrontal approach by careful measurements. Surgeons who perform subfrontal approaches to access both intradural and extradural lesions should strongly consider the addition of a fronto-orbital osteotomy and, when necessary, a cranial ethmoidectomy to improve exposure and to reduce brain retraction.

The olfaction-preserving approach proposed by Robert Spetzler et al does seem to work,[1] although smell may not recover for almost 3 months (presumably because the olfactory nerves must regenerate). This approach, however, reduces the exposure because a cribriform-frontal block of bone is preserved and retracted toward the frontal lobe. It also makes basal repair using a pericranial vascularized flap difficult. Consequently, I only use this approach if the risk of cerebrospinal fluid leakage is minimal.

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• 1 Spetzler R F, Herman J M, Beals S, Joganic E, Milligan J. Preservation of olfaction in anterior craniofacial approaches.  J Neurosurg. 1993;  79 48-52

The authors performed an anatomic study to quantitate the advantage of the extended frontal approach compared with a conventional bifrontal craniotomy. They provide a clear description of the approach, which has also been described elsewhere.[1] They confirm that the addition of a fronto-orbital osteotomy widens the operative view.

As the authors mention, the advantages and disadvantages of the approach have been reported and illustrated in detail previously.[1] [2] Its advantages lie in improved exposure of the optic nerve, sphenoid sinus, and medial aspect of the cavernous sinuses and, if needed, the ability to unroof the medial wall of the orbit and intracavernous internal carotid artery. The lateral limits of exposure for the extended fronto-orbital approach were neither described nor illustrated. The dorsum sellae and superolateral margin of the maxillary sinuses have been reported to be the anatomic blind spots in this approach.[1] The lower lateral portion of the orbit, located adjacent to the roof of the maxillary sinus, is another relative blind spot in the approach. These disadvantages were not mentioned in the text or diagrammatic representations (the authors’ Fig. [11]).

The authors’ conclusion implies that midline lesions anterior to the foramen magnum (FM) can be excised safely through an extended fronto-orbital approach. However, the extended fronto-orbital approach should not be considered for approaching a tumor strictly localized in the region of the FM. It might be used for an extensive lesion involving the ethmoid and sphenoid sinuses as well as the clivus and FM.

REFERENCES

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• 2 Rhoton Jr A L. The foramen magnum.  Neurosurgery. 2000;  47 S115-S193