Advances in surgical technique as well as strategies to deliver adjuvant radiation therapy in the last few decades have drastically improved outcomes in patients with malignant tumors invading the skull base. Tumors of the upper aerodigestive tract and neck involving the intracranial space can now be addressed with the combined expertise of head and neck surgeons and neurological surgeons.
Procedures are classified as anterior, middle, and posterior according to the cranial fossa to which the surgery is directed. In addition, lesions of the midline such as the region of the sella turcica and clivus require a central approach. Far lateral approaches are utilized for access to the region of the brain stem and medulla. (Figure 49-1). Expanded endonasal approaches to sinonasal malignancies involving the skull base have also been described for select anterior skull base malignancies.
(A) Diagram outlining the various regions of cranial base surgery. (Reproduced with permission from Donald PJ: Surgery of the Skull Base. Philadelphia, PA: Lippincott-Raven; 1998.) (B) The far lateral approach.
The anterior skull base is defined as the bony partition between the frontal lobes in the anterior cranial fossa and the midline and paramedian facial structures including nasal cavity and eyes.
The gyri of the frontal lobes overlie most of the anterior cranial fossa, the ocular gyri, and gyrus rectus lie lateral to the midline. The floor of the anterior cranial fossa is composed of ethmoid, sphenoid, and frontal bones. Anteriorly it forms the crista galli and cribriform plate of the ethmoid bone and covers the upper nasal cavity. The crista galli defines the midline of the anterior skull base. Posteriorly it forms the planum sphenoidale. Laterally the frontal bone and lesser wing of the sphenoid form the roof of the orbit and the optic canal; blending medially into the anterior clinoid process. The cribriform plate is the thinnest portion of the ethmoid bone and transmits the first cranial nerve to the olfactory fossa through multiple foramina.
The infratemporal fossa is located inferiorly to the temporal fossa. The temporalis muscle is located in the temporal fossa and inserts into the coronoid process and down the mandibular ramus. Distally the temporalis muscle traverses deep to the zygomatic arch forming the lateral wall of the infratemporal fossa. The roof of the infratemporal fossa is the floor of the middle cranial fossa.
The boundaries of the infratemporal fossa include the maxillary sinus anteriorly, the parotid gland posteriorly, the ascending ramus of the mandible and the temporalis muscle laterally, the zygomatic arch and the greater wing of the sphenoid superiorly as well as the pterygoid fascia medially. It ...