Extended Transbasal Approach to Skull Base Tumors

In this manuscript, Drs. Chandler and Silva describe the extended transbasal approach as a modification of the commonly used frontoorbital craniotomy, which maximizes anterior skull base exposure while minimizing brain retraction. This concept is now in its ninth decade, having been described by Frazier in rudimentary form in 1913.[1] The approach was subsequently reported in a more formalized fashion in the European literature by Derome and then expanded upon by various surgeons in the United States.[2-4] Throughout the piece, the authors stress that surgical indications are limited by the surgeon's imagination and familiarity with the approach. As lesions in the skull base do not respect one particular region of anatomy vs another, so the authors encourage the operating surgeon to recognize that this approach does not necessarily need to be utilized alone and may best be combined with other approaches to address all regions of pathology. Preoperative Evaluation
Preoperative evaluation is tailored to the individual case based on location and suspected histology of the lesion. Whatever the methods chosen, the surgeon must be cognizant of the location of normal brain, cranial nerve, and vascular structures and their relationship to the pathology being addressed. In most cases, a portion of the preoperative evaluation includes a preliminary biopsy via transnasal, transorbital, and transmastoid approaches. Knowing the pathology will allow the experienced surgeon a better idea of the texture, vascularity, and tenacity of the lesion encountered, to better plan operative time and set proper expectations for removal and risks. These techniques may help minimize complications. The choice of monitoring devices is tailored to the critical structures involved in the dissection, recognizing that no strategy is fail-safe and all such devices are subject to malfunction due to underlying electronic faults and interference, as well as anesthetic and body core temperature alterations. Surgical Technique
The authors provide a well thoughtout set of instructions on the performance of these cases. As they imply, the location of burr holes and osteotomies can be tailored very specifically to the particular case. This allows maximal preservation of normal bony architecture without sacrificing exposure of normal and neoplastic tissue. The posterior wall of the frontal sinus can be quite deep relative to the anterior wall. An alternative to using osteotomes or Gigli saws is simply to score the posterior wall with a dissecting bit of a high-speed drill and fracture the bone along that line with gentle bone flap elevation. This allows direct dural visualization while still guiding bone removal along the trajectory desired. Large frontal sinuses requiring extra care such as this need to be completely cranialized, including removal of mucosa within sinus extensions into the orbital roof. As the authors note, repair of the dural defects is optimal if done primarily; however, dural involvement by tumors may require dural removal. In such cases, secondary closure with free grafts of pericranium, temporalis fascia, or fascia lata is important. As the basal dura is often quite thin, the use of nonresorbable suture such as prolene or nylon may provide the greatest likelihood of long-term strong closure. The addition of fibrin glue or similar alternatives may be helpful, particularly for filling in a potential space between a primary free graft repair and an underlying vascularized graft (pericranium being the most common and versatile type). Planning ahead for possible pedicle or free muscular flaps maximizes the likelihood of closure proceeding successfully and smoothly. Simple details such as improving the likelihood of attached or vascularized free grafts to remain in place by anchoring them to the remaining dura with nonresorbable sutures can make a significant difference in outcome. Removal of the area of pathology is highly dependent on the nature of the lesion, and the authors are properly general in their comments on this issue. The problem of being unable to visualize high posterior extents of lesions in the region of the posterior clinoids is addressed. Any pathology in this location should be sought out ahead of time during the preoperative imaging evaluation, to plan additional approaches to that location. Complications
Although the successful removal of a lesion by this route can be rewarding for the patient and the surgeon, complications are significant and serious. The authors mention risks of cerebrospinal fluid (CSF) leak, infection, and loss of olfaction; however, injuries due to brain retraction- induced contusion and infarcts due to arterial and venous devascularization of brain adjacent to tumor that will manifest as new neurologic deficits also need to be emphasized. With specific concern about CSF leak management, the authors mention overdrainage with lumbar drains, emphasizing that these tools must be used judiciously. An alternative allowing accurate control of CSF drainage, and additionally supporting intracranial pressure monitoring is the use of a ventriculostomy. Although associated with risks of its own, this procedure allows more careful analysis of the intracranial status of patients who may be intubated or otherwise impaired for some time after surgery. Because of the serious problems related to improperly controlled CSF leak along margins of the skull base repair, the managing surgeon must not relent in providing a proper milieu for healing of skull base dural repairs. In the final analysis, a majority of patients will note at least some subjective change in mentation and cranial nerve function in addition to anosmia. Also, the procedure poses a risk of seizures due to cerebral cortical manipulation and alterations in venous drainage. Individualized administration of anticonvulsants must be utilized, depending on the nature of the lesion and the manipulation of the adjacent normal cortical surfaces. Conclusions
In summary, the extended transbasal exposure is a technically feasible approach requiring a surgical and anesthetic team willing to plan and agree on a strategy that will minimize injury to normal structures. Even with this approach, surgical cure may not always be an option, and this procedure is just a first step in the treatment of more difficult cancers and infections. It is absolutely critical that the patient and family have a full understanding of the risks and complications involved and that they understand the likelihood of those most pertinent to their situation. In the long run, this saves considerable anguish for the surgeon, patient, and family.