KEYWORDS

Skull base;

Skull base fractures; Frontal fractures; Frontal sinus fractures

Frontal sinus fractures have long been considered controversial and, to this day, no absolute guidelines exist for management. However, it is generally agreed that complications are more likely to occur when there is either blockage of active outflow from the frontal sinus or when there is communication between the anterior cranial fossa and the sinonasal cavities. The following discussion will focus on the latter problem when fractures involve the anterior skull base in addition to frontal sinus and cranial fractures.

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Frontal sinus fractures can occur with significant impact to the lower frontal region. They can be in combination with other frontocranial fractures and also may be commonly associated with naso-orbital-ethmoidal fractures. A plethora of literature exists discussing the evaluation and management of frontal sinus fractures, yet this topic remains a controversial one. It is generally accepted, however, that acute and chronic complications such as abscesses or mucoceles will occur when there is either inadequate re-establishment of drainage between a reconstructed or “functioned” frontal sinus during fracture repair or when communication persists between a fractured anterior skull base, such as in the region of the cribriform plate of the ethmoid or other reasons of the central skull base such as the planum sphenoidale.1-3 A variety of algorithms and other recommendations have been made to differentiate severity of injury, but fracture patterns are not necessarily consistent, and it is difficult at times to determine what is the least amount of intervention that will be effective in attaining the above goals.

It has been stated that the goal for frontal sinus fracture repair is to “create a safe sinus” and, with this statement in mind, the surgeon can generally optimize the management of these frontal sinus fractures. The options generally include allowing the sinus to “function” by allowing continued drainage from this frontal sinus into the sinonasal cavities, to obliterate the sinus with a variety of material options (in itself, a controversial topic) or, in more severe situations, to cranialize the frontal sinus by removal of the posterior

Address reprint requests and correspondence: John L. Frodel, Jr, MD, FACS, Geisinger Medical Center Facial Plastic Surgery and Otolaryngology, 100 N. Academy Ave, Danville, PA.

E-mail address: jlfrodel@geisinger.edu.

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table of the sinus after obliteration of the outflow of the frontonasal outflow tracts into the sinonasal cavity. Further controversy is added when computed tomography (CT) scans suggest fracture and comminution of the important aspects of the anterior skull base such as the orbital roof, cribriform plate, and planum sphenoidale regions. Oftentimes, if the orbital roof is fractured it can either be ignored or limited reconstruction will be adequate. Pulsatile exophthalmus has been described for larger orbital roof defects but this is quite uncommon.4 Fractures of the cribriform plate in particular are relatively common and as many of these fracture, when isolated, are evaluated and managed by the specialty of neurosurgery, it is the author’s experience that this subspecialty commonly observes these fractures without intervention if no other significant injuries are involved. The premise is that these fractures will most commonly heal spontaneously and even if a cerebral spinal fluid (CSF) leak occurs, this can be managed conservatively using a lumbar drain, with secondary operative procedures to repair this leak only occasionally being required. However, on rare occasions severe intracranial infections can occur from this communication between the intracranial cavity and the sinonasal cavities and, accordingly, it is my belief that when possible, these fractures should be addressed in the acute setting, particularly if CSF leak is documented. In this review, we will discuss the evaluation and options for management of anterior skull base fractures.

Indications

On occasion, a linear skull fracture will continue through the anterior skull base, particularly when it is isolated to the

orbital roof or into the temporal region. If no other symptoms exist and there are no other related fractures requiring intervention, this type of fracture usually does not cause problems or require intervention. It is only when there is a severe displacement of such skull fractures that intervention is necessary and, in these cases, the patient often has a severe brain injury that takes precedence over fracture repair. More commonly, a situation exists in which fractures are present in the frontal region involving, in particular, the frontal sinus commonly combined with frontal bone, orbital rim, internal orbital, and naso-orbital ethmoidal fractures. The specific indications for management of these related fractures is discussed elsewhere in this issue, but suffice to say that this combination of fractures will most likely lead to the need for surgical intervention.

When evaluating frontal sinus fractures, it is important to look for anterior skull base involvement. Involvement of the orbital roof is common and generally clearly observed on both axial and coronal CT scans. The latter view is optimal for determining involvement along the cribriform plate, lateral to the crista galli, and more posteriorly onto the planum sphenoidale of the sphenoid bone. These latter fractures generally imply significant impact and greater significance of injury. Although direct open repair of the anterior skull base components of these frontal bone fractures is not always necessary, it is important then that during the evaluation process that the patient is observed for CSF leak and, in addition to review of the CT scans for involvement of these important anterior skull base regions, the presence of intracranial air may imply rupture or displacement of at least the cribriform plate. It is this fracture scenario that the surgeon should be prepared to also explore the anterior cribriform plate region for fracturing during the frontal sinus exploration. The concern is that by either isolated reconstruction and restoration of the frontal nasal outflow tracks or, conversely, obliteration of these tracts along with the frontal sinus may leave a persistence of communication

between the anterior cranial fossa and the sinonasal region, leading to secondary problems such as CSF leak and subsequent intracranial contamination.

Accordingly, the indications for exploration through the frontal sinus of the anterior cranial fossa are relatively liberal in the presence of fractures on CT scan and reconstruction is likely indicated when a relatively large defect exists without obvious integrity of the structures in the anterior skull base. As will be discussed, a variety of approaches exist for obtaining access to the anterior skull base and these include low frontal craniotomies, a subcranial or orbital rim/bar osteotomy, or the combination of both.4-8

Figure 2 Lines demonstrate one form of a supraorbital bar osteotomy including the anterior table of the frontal sinus.

Technique

When the patient with frontal region trauma demonstrates findings that are suggestive of anterior skull base trauma on the CT scan, the amount of anterior table and frontal bone fracture comminution should be evaluated. The anterior skull base most commonly can be approached through the frontal sinus fracture but, on occasion, other osteotomies may be required, and neurosurgical assistance may be desirable. When the fracture includes a posterior table of the frontal sinus fracturing and comminution, the plan would generally include the availability of neurosurgery to assist in exploration of anterior cranial fossa structures in case intervention such as dural repair or deeper frontal lobe intervention is necessary. However, it often is possible to approach the anterior cranial fossa without the use of frontal craniotomy. In particular, the posterior table and anterior aspect of the anterior skull base may be approached through via the removal of the anterior table fragments, and this is further facilitated by removal or retraction of medial supraorbital rim and nasal root segments.

Figure 1 demonstrates the theoretical advantage of viewing the anterior fossa contents through anterior or subcranial approach as has been described by many authors.5-8 The advantage of a more anterior approach as opposed to ap-

proaches through a traditional craniotomy is that a traditional craniotomy is performed by many surgeons above the level of the frontal sinus, thus leading to an obstructed view and limited access to the anterior aspect of the anterior cranial fossa. These limitations can be addressed by removal of the frontal sinus itself, either by removing the existing bony fragments and/or performing an osteotomy that removes the entire anterior table of the frontal sinus and the medial aspect of the supraorbital rim and nasal root (or the so-called supraorbital bar). The design of one such osteotomy is seen in Figure 2, and whether the nasal bone requires removal or not is up to the discretion of the surgeon. However, oftentimes the fracture pattern allows removal of the central supraorbital bar segment of bone without removal of the proximal nasal bones. Once these bony segments have been removed, the posterior table and siphon into the frontal nasal outflow tracts can be identified and evaluated.

In the scenario of cribriform plate fractures, there is generally comminution in the region of the outflow tracts that extends alongside the crista galli which can be readily identified through this anterior approach. Comminuted fracture segments can be readily removed by careful dissection off the dura to allow retraction of the anterior/inferior aspect of the frontal lobes to determine the extent of injury along the cribriform plate and orbital roof regions. Conversely, if there is not significant fracturing in the posterior table, small

telescoped nasal root and glabelar region.

Figure 5 Anterior reflection of the nasal root and crista galli.

osteotomies facilitated by the use of neurosurgical rongeurs can provide removal of the bone and improved access to the anterior cranial fossa.

Once the extent of the fracture along the cribriform plate region is evaluated, the extent of intervention is further determined by the extent of injury and the concern that the surgeon might have for the previously discussed connection between the anterior cranial fossa and the sinonasal regions. In less-severe situations, minimal intervention is required, including doing nothing, placing soft-tissue grafts into the region (such as temporalis fascia or muscle, which will also assist in closure of the disruption of the frontal nasal ducts), or placing a variety of different types of fibrin tissue glues. Other forms of intervention might include placement of vascularized tissue flaps such as pericranial flaps that are traditionally brought over either through the fractures in the supraorbital bar region or over the supraorbital rim osteotomy of the frontal craniotomy. The author prefers to perform a unilateral or bilateral flap and deliver the flap through medial orbital roof defects that are almost always present into the region of the skull base. These flaps can then both serve to separate the dura of the anterior cranial fossa in the region of the cribriform plate and the underlying defect into the ethmoid regions as well as being extended so as to in part or completely obliterate the frontal sinus cavity. This can be further facilitated and augmented by the use of fibrin glue.

Finally, further security in separation of the anterior cranial fossa from the ethmoid sinus can be obtained by placement of rigid bone grafts which essentially reconstruct the anterior cranial fossa floor. Oftentimes, the defect is not large enough to place significant size bone grafts so the use of the pericranial flap alone should be adequate.

Figure 3 demonstrate a patient involved in a motor vehicle accident with a severe frontal blow. Notable on Figure 3 is the severe retrodisplacement of the nasal root and fracture displacement of the cribriform plate into the anterior cranial fossa. A significant amount of intracranial air is noted whereas the superior aspect of the anterior table of the frontal sinus is relatively intact. At the time of exploration,

Figure 7 After reposition of the osteotomized frontal table anterior and telescoped nasal root with fixation with titanium mesh.

the patient was noted to have a severely impacted root of the nose, including the frontonasal attachment. Figure 4 demonstrates this segment after reduction to the approximate desirable anteriorly projected region whereas Figure 5 shows a photograph during the further anterior retraction of the nasal root segment demonstrating the intact crista galli that was impaled into the anterior cranial fossa structures. At this point, the anterior table is osteotomized and removed. With inferior retraction allowing a more inferior and anterior view at the lower aspect of the anterior frontal region, the comminuted posterior table is usually visualized and, in this case, because of severe comminution, the entire posterior table was removed to allow for cranialization of the frontal lobe. Bone removal continued inferiorly to the region where the impaled crista galli was removed and now a relatively large defect existed.

Accordingly, pericranial flaps, elevated at the time of the initial coronal approach, and visualized in Figure 6, were prepared for insertion. Before this, small calvarial bone grafts were placed alongside region of the crista galli (which was still reflected but would be trimmed and replaced). These bone grafts and other smaller bone grafts also serve to obliterate the frontonasal outflow tracks. In this particular case, minimal fixation was required, followed by positioning of the pericranial flaps as seen in Figure 6, which also in

part served to fill the dead space created by removal of the posterior table and cranialization cavity. Fibrin tissue glue was then used to further secure this region and the flaps into the anterior skull base. Finally, the osteotomized anterior table was repositioned and the nasal root/frontal bar region was repositioned and fixated (Figure 7). The postoperative

CT demonstrates separation between the anterior fossa and the intracranial contents (Figure 8). This is optimally demonstrated with coronal CT scan, which was not performed in this particular patient.

This represents a common scenario for frontal sinus fracturing with anterior skull base involvement. The situa-

tion commonly arises where there is remarkably minimal disruption of the frontal bone and anterior table itself due to impaction at the root of the nose. Conversely, there are other injuries with a wider area of impact that will involve the frontal region. It is in these cases that the approach is simplified by bone fragment removal, thus alleviating the need for elective osteotomies in this region.

In more complex fractures such as those from severe avulsive or blast type of injuries, the disruption of the

anterior skull base is greater and more widespread, often involving significant defects in the orbital roof with extension posteriorly, sometimes including the planum sphenoidale. When more complex fracture scenarios with obvious involvement of the skull base are present, neurosurgical consultation is a must and discussion should take place as to the extent of the approach. Although many of these even more complex fractures can be addressed through a subcranial approach with or without bony fragment removal or

Figure 13 Patient involved in motor vehicle accident. Note the obvious left canthal displacement.

orbital bar osteotomy, including the anterior table of the frontal sinus, some neurosurgeons are more comfortable with an additional frontal craniotomy. The latter is obviously acceptable if this allows an increased comfort level for the neurosurgeon and should not lead to any further requirement for brain retraction and subsequent brain edema if there is still an anterior subcranial access performed. It is generally recommended that a low frontal craniotomy is performed in addition to the orbital bar osteotomy or subcranial approach in this situation.

Figure 9 demonstrates a sagittal view of a severe disruption of the anterior cranial fossa noting a defect onto the planum sphenoidale with simulated brain herniation which is unusual. It suggestions violation of the dura and intracranial contents, however, and this must be addressed in these more severe situations. This figure also demonstrates removal of the supraorbital orbital bar/nasal root along with the low frontal craniotomy segment for a more direct anterior access to the central anterior cranial fossa. This is again diagrammatically demonstrated in Figure 10, whereby the supraorbital bar, which in this case contains a portion of the anterior cranial fossa defect, is removed to demonstrate access to a large central cranial defect. Subsequent reconstruction with bone grafting of such defects is recommended by this author as these defects can be quite large. This is demonstrated in Figure 11 and Figure 12 along with repositioning of the frontal bar and frontal osteotomy segments noting bridging of the defect and separation of the anterior cranial fossa contents from the sinonasal contents.

Although more severe frontobasilar injuries, such as those from blast or avulsive injuries (such as from industrial accident), present the obvious need for intracranial or subcranial intervention, less-severe frontal trauma can produce a similarly devastating anterior skull base injuries. This is demonstrated in Figure 13, in which a patient presented after sustaining a frontal and nasal blow in a motor vehicle accident. Figure 14 demonstrates CT scans showing a large orbital roof blowout into the anterior cranial fossa on 3-di- mensional CT along with significant disruption along the cribriform plate on the 2 axial CTs. Note the severe disruption of the orbital roof in crista galli on these views. This was though to be a remarkably extensive disruption for what appeared to be an isolated naso-orbital-ethmoidal and left orbital fracture. Because of the extent of disruption, and the

decision was made with the neurosurgeon to make a low frontal osteotomy with frontal orbital bar osteotomy (an isolated orbital bar osteotomy would have likely been adequate). Such an orbital bar osteotomy is demonstrated in Figure 15 noting the lateral extent of the orbital rim osteotomies being to the level of the supraorbital foramina, the structures of which being released into the orbit for retraction purposes. Figure 16 demonstrates the disruption of the anterior fossa floor just posterior to and including the frontonasal outflow tracts whereas Figure 17 shows the anterior cranial fossa floor after multiple levels of reconstruction, including bone grafting along the anterior cranial fossa floor on the left side and orbital roof reconstruction, which also

Figure 14 (A) 3-dimensional CT demonstrating blow-out fracture into the anterior cranial fossa. (B) Coronal CT showing disruption of crista galli. (C) Coronal CT demonstrating disruption of planum sphenoidale.

Figure 16 After low frontal craniotomy and removal of the supraorbital bar osteotomy segment with the 2 lateral retractors reflecting the orbital contents, defects are shown in the anterior cranial fossa floor extending from the frontal nasal ducts.

facilitated obliteration of the frontonasal outflow tracts. The left naso-orbital-ethmoid canthal repair was also facilitated through this subcranial approach.

A unilateral left-sided pericranial flap had been elevated earlier and now is delivered through the orbital roof defect into the anterior cranial fossa floor (Figure 18). It should be noted that posterior table had been removed earlier in the procedure. This is placed both along the anterior cranial

Figure 19 After repositioning the supraorbital bar and after craniotomy, bone segments are secured with titanium mesh and plates.

fossa floor superior to the bone grafts and then layered into the space created by removal of the posterior table. This supraorbital bar osteotomy and frontal osteotomy, frontal craniotomy bone segments are repositioned and this is repositioned and plated (Figure 19). Postoperative photos at 6 months after surgery demonstrate good frontal contours, orbital position, and canthal position (Figure 20. In the