Anterior Subcranial Approach - Trauma

Background

The surgeon who manages maxillofacial trauma must be familiar with techniques for the repair of injuries that involve the anterior skull base. Complex high-impact fractures may result in communication between the anterior cranial fossa and the facial or sinus structures. These types of fractures include posterior wall fractures of the frontal sinuses, fractures through the foveae ethmoidale, and fractures through the cribriform plate. These may be associated with cerebrospinal fluid (CSF) leaks, or frank herniation of intracranial structures (dura, brain) may occur. Associated orbital injuries may also be present, including possible trauma to 1 or both optic nerves.

The image below depicts the frontal aspect of the skull.

Skull, anterior view. Skull, anterior view.

History of the Procedure

The subcranial approach is a title applied by Joram Raveh of Bern, Switzerland, to a technique in which the anterior skull base is approached directly by disarticulating the nasal root and glabella to directly access the frontal and ethmoid sinuses and the anterior fossa. In 1997, Jung et al labeled the technique the transglabellar/subcranial approach, and they have used it for tumor resection. [1]

The technique, a logical extension of previously existing approaches, was originally developed by Raveh for skull base access to tumors that involved the paranasal sinuses and anterior fossa. It was a result of continuing the advances in craniofacial resection techniques with the osteotomies used for the repair of congenital craniofacial anomalies. This ultimately led Raveh and others to extend the frontal craniotomy flap inferiorly to include the nasal root and nasal bones, as depicted in the image below, thereby allowing direct access to the nose, sinuses, orbits, and frontal fossa with minimal, if any, retraction of the frontal lobes. A typical subcranial bone flap is shown in the image below.

A typical subcranial bone flap. A typical subcranial bone flap.

Adaptation of this technique to trauma progressed gradually through the transethmoidal approach to the skull base to the more extensive debridement of the frontal and ethmoid areas. This technique may be called the near-subcranial approach, ultimately to include complete disarticulation of the nasal root and nasal bones, thus becoming the complete subcranial approach. This approach allows wide exposure of the anterior fossa, cribriform plates, foveae ethmoidale, and orbits with minimal, if any, frontal lobe retraction.

Problem

The subcranial approach is used to manage complex fractures of the anterior skull base that may include fractures of the floor of the anterior fossa and/or the posterior wall of the frontal sinuses. Cases of severe frontobasal trauma often include injury to the frontal lobes of the brain, which may make retraction of the frontal lobes to repair dural tears and fractures more risky to the patient. Traditionally, because reaching the fractures via a standard bifrontal craniotomy requires significant frontal lobe retraction, repair is delayed, making the ultimate repair more difficult and increasing the risk of interim meningitis. The subcranial approach allows access to these areas with limited, if any, frontal lobe retraction, minimizing the risks of earlier surgical intervention.

Etiology

Most fractures of the nasal root, frontal sinuses, and anterior fossa that are severe enough to benefit from this approach are the result of high-impact trauma (eg, motor vehicle accidents, industrial accidents). Altercations can produce such injuries when a tool, such as a hammer or baseball bat, is swung powerfully enough to generate a sizable impact force.

Presentation

Patients typically present with significant facial swelling and bruising. Often, the patient has associated injuries to one or more organ systems, and the facial plastic surgeon is generally not the first specialist involved. Severe frontobasal trauma often involves injuries to the brain, and neurosurgeons generally stabilize the patient and consult otolaryngologists later. Having the initial brain CT scan include at least a low-resolution survey of the facial bones (when feasible) is beneficial to help in treatment planning.

The patient may have a markedly depressed nasal root, which may indicate a telescoped nasoethmoidal complex and/or an associated Le Fort II or III fracture with facial rotation. Assessing the tension of the medial canthal ligaments is extremely important because late development of telecanthus can create a significant and unsightly deformity if such an injury is missed.

Periorbital edema and ecchymosis are common. Assessing visual function is extremely important; if the patient is awake, he or she may report decreased vision. An afferent pupillary defect (APD) must be detected if present because it may indicate an optic nerve injury. The patient may report diplopia, and evaluating the extraocular movements (EOMs) is extremely important. If any doubt exists about the EOMs, perform a forced duction test.

If the patient reports rhinorrhea or if clear rhinorrhea is noted by a nurse, then the patient should be evaluated for a possible CSF leak. Anosmia similarly may be observed with severe frontobasal trauma.

For the most part, most severe facial fractures are identified more on high-resolution CT scans than on clinical examination.

Indications

High-impact trauma in the central facial region can lead to displacement of the nasal root with telescoping of the nasal bones posteriorly into the ethmoid sinuses, whose thin walls may collapse and accordion posteriorly. [2This has been called the nasoethmoidal complex (NEC) fracture or, more recently, the naso-orbital-ethmoid (NOE) fracture. The cribriform plate and/or ethmoid roofs (foveae ethmoidale) may be fractured, leading to CSF rhinorrhea, with or without herniation of the brain (traumatic encephalocele). These fractures generally disarticulate the medial canthal ligaments, which must be carefully repaired to prevent unsightly telecanthus. Fracture of the posterior walls of the frontal sinuses similarly may lead to CSF leaks, with or without brain herniation. The subcranial approach has been shown to be quite effective for the repair of CSF rhinorrhea. [3Occasionally, fractures may extend into the planum sphenoidale and optic canals.

In some cases, the subcranial approach involves completing existing fractures, and, in severe cases, it may merely be a matter of removing loose fragments, as depicted in the image below. Removal of a free-floating nasal root with resultant exposure of the shattered anterior fossa floor is the beginning of the subcranial approach. Removal of the frontal sinus completes the approach.

A case involving fracture with complete mobility oA case involving fracture with complete mobility of the nasal root and nasal bones. Disarticulating the nasal segment allows access to the anterior subcranial area.

This exposure allows direct access for repair and grafting of the fractures. Wide exposure of the medial orbits enables optic nerve decompression. The frontal sinuses can be easily cranialized, obliterated, or reconstructed. The subcranial approach also can be used for secondary repair of traumatic CSF leaks or traumatic encephaloceles. In these cases, the approach is the same as that used for tumor excision.

Although experience in children is limited, the procedure can be considered a variant of congenital craniofacial surgery. Kellman and Goyal reviewed several cases in which the procedure was used to remove from growing children nasal dermoids with intracranial extension. [42After a follow-up of 15 years, no noticeable growth disturbance was seen in these patients as they grew.

Relevant Anatomy

The subcranial approach involves a bone flap for access that includes the anterior inferior frontal bone, including the medial superior orbital rims and the root of the nose and the nasal bones. Relevant anatomy includes the medial orbits, attachments of the medial canthal ligaments, the relationship of the nasal bones to the upper lateral cartilages and the nasal septum, the location of the ethmoid arteries and the supraorbital and supratrochlear nerves, and the relationship between the bone flap and underlying crista galli and anterior fossa contents. Anyone using this approach should be thoroughly familiar with this anatomy.

The facial skeleton serves to protect the brain; house and protect the sense organs of smell, sight, and taste; and provide a frame on which the soft tissues of the face can act to facilitate eating, facial expression, breathing, and speech. The primary bones of the face are the mandible, maxilla, frontal bone, nasal bones, and zygoma. Facial bone anatomy is complex, yet elegant, in its suitability to serve a multitude of functions. See the images below.

Frontal bone, inferior and posterior aspects. Frontal bone, inferior and posterior aspects.
Zygoma, frontal view. Zygoma, frontal view.

For more information about the relevant anatomy, see Facial Bone AnatomySkull Base AnatomyForehead AnatomyNasal Anatomy, and Orbit Anatomy. See also Facial Nerve Anatomy and Mouth Anatomy.

Contraindications

No absolute contraindications exist that are specific to this procedure. Since repair of the anterior fossa floor can be accomplished without brain retraction, frontal lobe contusions are not a specific contraindication. Ocular injuries that may predispose to blindness (eg, retinal detachment, globe tear) are relative contraindications. In addition, general contraindications remain that are not procedure specific, such as severe brain injury with swelling and danger of herniation, hemodynamic instability, clotting abnormalities, and other medical conditions that are considered contraindications to a major surgical procedure.

Laboratory Studies

Lab studies may be an issue if assessing the presence of a CSF leak. Suggestive rhinorrhea fluid can be sent for a beta2-transferrin test to see if it is indeed CSF.

Imaging Studies

When assessing central facial trauma, high-resolution CT scanning is key to the proper assessment of the extent of the fractures.

  • Whenever possible, obtain both axial and coronal scans; however, if only axial scans are possible (eg, if an associated cervical spine injury is present, if 3-dimensional reconstructions are desired), then 1.5-mm cuts should be used to maximize the quality of the coronal reconstruction.

  • Careful assessment of the orbits, optic canals, ethmoid roofs, cribriform plate, and posterior walls of the frontal sinuses helps determine the surgical plan.

If an osteoplastic bone flap is being considered, obtain and copy a 6-foot anteroposterior Caldwell view. A cutout of the frontal sinus is made from the copy and used to create the osteoplastic flap. As an alternative, image guidance may assist with defining the outlines of the frontal sinuses.

When evaluating a patient for possible CSF rhinorrhea from a previously managed trauma, the site of the leak may not be obvious. Generally speaking, finding the bony defect with high-resolution CT scanning is the most dependable way of identifying the site of a probable leak. However, if this is not possible, a metrizamide CT scan may occasionally reveal the site of a CSF leak.

Other Tests

Consider a gamma-cisternogram when CSF rhinorrhea is a possibility and the patient is unable to produce any fluid for testing for beta2-transferrin. This test is very sensitive for finding a CSF leak, but, while it may indicate which side of the nose is involved, it is not particularly good for further identifying the site of an identified leak. It involves injecting a radioactive isotope into the CSF. Cotton pledgets are placed in the nasal cavities, and, after an appropriate time interval, these are removed and tested for radioactivity. The presence of radioactive material on the cotton pledgets indicates CSF rhinorrhea.

Diagnostic Procedures

Consider performing a forced duction test to assess the mobility of the globe to determine if entrapment of extraocular muscles exists.

Consider performing a traction test on the medial canthal ligaments to assess the stability of the ligaments and their bony attachments.

Obtain an ophthalmology consult to assess the globe and orbital contents as well as for visual acuity testing on any patient who has sustained periorbital or orbital trauma. Visual field testing may also be indicated.

Olfactory testing is usually performed fairly grossly, though formal testing is possible if indicated.


Treatment & Management


Surgical Therapy

A coronal incision is used, generally extending from auricle to auricle, with an extension in the preauricular crease to the level of the tragus (as needed for flap development). This incision should be a wavy line or multiple Z s so that the resultant scar is less likely to part the hair and is, therefore, less visible. Note that the decision to shave the scalp, either minimally or completely, is at the surgeon's discretion, as the recent literature fails to demonstrate a benefit of shaving. [5]

The length of the coronal flap from the forehead varies depending on how far back the anterior fossa floor defect extends, since the location of the coronal incision determines the length of pericranial flap available for lining the anterior fossa floor defect. The incision is down to bone from temporalis to temporalis so that the pericranium is elevated with the flap. The flap is elevated forward off the bone medially and off the temporalis fascia laterally. A more anteriorly positioned skin incision can be dissected to (but not through) the periosteum; then, a supraperiosteal elevation can be carried posteriorly to create a longer pericranial flap.

If the flap needs to be elevated laterally to and/or beyond the zygomas, at the temporal line of fusion, the superficial layer of the temporalis fascia may be incised and the dissection continued inferiorly between the 2 fascial layers, thereby reducing the likelihood of injury to the temporal branch of the facial nerve. Dissection may be carried over or under the temporal fat pad. Medially, the flap is elevated to the supraorbital rims, taking care not to injure the supraorbital and supratrochlear nerves and vessels. These are generally in foramina above the rims, and they must be brought inferiorly with the flap to preserve them. If the rims are notched, the supraorbital and supratrochlear nerves and vessels can be carefully dissected out through them. If they are in complete foramina, then the bone between the orbit and each foramen must be cut away with a fine osteotome or a small rongeur.

The flap is then elevated inferiorly off the glabella and nasal bones to the level of the upper lateral cartilages, exposing the lacrimal crests and lacrimal sacs bilaterally. The orbital periosteum is carefully dissected from the bone, exposing the ethmoid vessels, which are generally cauterized with bipolar cautery.

The typical subcranial bone flap includes a portion of the frontal bone, the medial portions of both supraorbital rims, and the nasal bones, as depicted in the first image below. In patients with primary trauma, this exposure may sometimes require piecemeal removal of fractured bone fragments, as depicted in the second image below. The ultimate exposure is essentially the same, though in some trauma patients, the full bone removal may not require total removal of the nasal root, and a transethmoidal access to the anterior fossa floor may be adequate for repair; this technique may be called the near-subcranial approach. The bone flap may include the entire frontal sinus, or the frontal sinus may be outlined using an osteoplastic flap.

A typical subcranial bone flap. A typical subcranial bone flap.
A case involving fracture with complete mobility oA case involving fracture with complete mobility of the nasal root and nasal bones. Disarticulating the nasal segment allows access to the anterior subcranial area.

Once the planned bone cuts have been marked, microplates are positioned across the frontal osteotomies at 2 or 3 points and screwed in place. (Note that all of the holes are drilled, though only the first 2 screws in each plate need to be placed to ensure the position.) Leave 1 screw in each plate and rotate the plates so that the osteotomies can be made. The osteotomies extend horizontally across the frontal bone either along the superior frontal sinus in osteoplastic fashion or across and above the frontal sinus.

The approach is similar for the vertical cuts, which extend through the supraorbital rims into the orbits. When an osteoplastic flap is used, the frontal sinus floors are entered from below, and the incision is extended laterally to the supraorbital rim cuts and medially toward the nasal bones. If the sinus is to be included in the flap, the bone cuts behind the supraorbital rims are made just posterior to the sinuses. Taking care to avoid the lacrimal sacs, the cuts extend inferiorly either anterior to or behind the anterior lacrimal crests. They then extend inferiorly through the area of the junction of the nasal bones with the frontal processes of the maxillae. They can extend to the inferior limit of the nasal bones, which can then be separated from the upper lateral cartilages, as described by Raveh. Some prefer to leave 3-5 mm of distal nasal bone intact to support the upper lateral cartilages, as depicted in the image below.

The subcranial bone flap has been removed. Note thThe subcranial bone flap has been removed. Note the remaining portion of the distal nasal bones in situ.

Before completion of the frontal osteotomies, which mobilize the bone flap, a posterior bone cut must be made with an osteotome to separate the flap from the crista galli. If an osteoplastic flap has been used, the cut is actually behind the glabella through the intersinus septum. The nasal bones are similarly divided from the bony nasal septum. The osteotomies are then completed, and the bone flap should come out in 1 piece, including the frontal bone and nasal bones, unless they were fractured by the injury. This provides exposure of the nose and either the anterior fossa dura or the back wall of the frontal sinuses. It also provides a direct view of the floor of the anterior fossa.

Additional exposure is developed as needed to manage the specific patient problem. Fractures of the back wall of the frontal sinuses allow visualization of the dura, and the posterior wall defect can be extended to allow for easier dural repair. When the posterior wall is severely comminuted, cranialization can be performed. If it is relatively intact, then reconstruction of the posterior wall is preferred because it provides an additional layer between the dura and the nasal cavity.

Performing a direct exenteration of the ethmoid sinuses extends access to the floor of the anterior fossa. The cribriform plate is thereby directly exposed, as are both foveae ethmoidale (ie, roofs). The anterior fossa dura is easily elevated off of the ethmoid roofs and, as needed, 1 or both cribriforms to allow for complete repair of the anterior fossa floor. This can be extended posteriorly into the sphenoid sinuses to expose the planum sphenoidale as well.

If optic nerve decompression is indicated, the medial wall of the orbit can be removed posteriorly, allowing for direct exposure of the medial wall of the optic canal. This allows for wide decompression of the optic nerve in its canal under direct vision. The medial orbital wall is then reconstructed with bone grafts to support the orbital contents.

The frontal sinuses can be managed by stenting or by obliteration, which some may prefer. All mucosa must be carefully removed, and the surface of the bone must be drilled with a polishing burr to minimize the risk of later mucocele formation. Many materials have been used to obliterate the frontal sinuses. Autogenous fat grafts have been the most frequently used obliteration material.

However, bone grafts are now commonly used as well. As depicted in the image below, calcium phosphate cements have been used, but they are not generally recommended for this purpose because of what seems to be a higher infection risk. [6Some advocate leaving the sinus empty, with the expectation that bone will spontaneously regenerate and fill the sinuses (called osteoneogenesis). When a pericranial flap is used to repair the anterior fossa floor, some of the flap can be used to obliterate the sinus.

An example of obliteration of the frontal sinuses An example of obliteration of the frontal sinuses using calcium phosphate bone cement.

If needed to repair the anterior fossa dura, a pericranial flap or a thicker galeal-pericranial flap is elevated from the skin flap and laid over the anterior fossa dura as posteriorly as necessary. Note that this flap effectively separates the nose from the brain and precludes replacement of the nasal bone. Therefore, making a hole in the central portion of the flap anterior to the ethmoid area is necessary to allow inferior positioning of the nasal bone portion of the bone flap. This incision must not be carried laterally, or it could interfere with the blood supply to the flap.

Before the bone flap is replaced, the medial canthal ligaments must be addressed. A permanent suture (eg, 2-0 or 3-0 Mersilene, Ethibond) is passed once or twice through a medial canthal ligament. This suture is passed through the medial orbital wall (native or graft) and then through the bony nasal septum if present. A similar suture is placed through the opposite medial canthal ligament so that the 2 sutures cross in the midline. The bone flap is then replaced so that these sutures pass posterior to it. Tightening of these sutures allows independent positioning of each medial canthus. Each suture is then tied either to a screw placed in the contralateral frontal bone (medial supraorbital rim) or through a hole in the bone. Raveh has called this centripetal suspension, and it allows excellent control of medial canthal position, as depicted in the image below.

The sutures seen in this figure each are attached The sutures seen in this figure each are attached to the contralateral medial canthal ligaments and passed behind the nasal bones. They then can be secured to the frontal bones to maintain the desired positions of the medial canthi.

The bone flap is then fixed in position using the previously applied plates and predrilled holes. This ensures precise repositioning of the bone flap. Note that deficient areas of nasal bones generally are grafted using split calvarial bone grafts. Frontal bone defects may be grafted or repaired using calcium phosphate cements. The skin flap is then repositioned and closed, taking care to resuspend the incised temporalis fascia to prevent facial drooping. A suction drain may be used; however, if a large dural tear was repaired, many neurosurgeons prefer a tight pressure dressing instead.

If necessary, the lacrimal system is stented with silicon tubes.

Preoperative Details

Careful analysis of high-resolution preoperative CT scans allows for fairly accurate prediction of the extent of the injuries and, therefore, helps in planning the repair. Ophthalmology evaluation and close cooperation with neurosurgery colleagues are important.

If image guidance will be used in surgery, appropriate preoperative scanning with fiducial markers on the patient should be performed.

In the presence of an extensive CSF leak, a lumbar drain may be desirable.

Intraoperative Details

The key steps of the procedure involve the following, although not all are used in every patient:

  • Incision and flap development, including preservation of supraorbital and supratrochlear nerves and vessels and the temporal branch of the facial nerve

  • Outline of the bone flap (in trauma, variable depending on the fractures involved)

  • Plating across planned bone cuts followed by plate removal

  • Making of bone cuts and osteotomies, with removal of the bone flaps

  • Repair of skull base injuries including debridement of necrotic brain, dural repair, optic nerve decompression, medial canthal repositioning, and obliteration or stenting of frontal sinuses

  • Placement of pericranial flap

  • Replacement and fixation of bone flap, including repair of fractured fragments

  • Skin closure

Postoperative Details

Carefully monitor patients for visual loss and deterioration in neurologic status. All patients have pneumocephalus after a craniotomy, but a tension pneumocephalus can be life-threatening and must be recognized and treated.

Follow-up

When patients are neurologically stable, they can generally be discharged within a few days (assuming other organ systems are intact). Coronal sutures or staples are generally removed in 7-10 days. The actual cosmetic and functional result is observed as the swelling recedes, generally over 3-6 weeks. Outcomes can then be assessed, and, if needed, revision surgery can be contemplated thereafter, although waiting 3-6 months to assess the final result is often wise.

Complications

The most common complications include hematoma and localized wound infection. These are usually minor and easily managed.

Less frequent, though more worrisome, complications include intracranial problems (eg, tension pneumocephalus, hemorrhage, infarction), some of which may more likely be related to the injury. Meningitis can occur and must be managed aggressively. Persistent or recurrent CSF leak may require revisional surgery.

Less worrisome complications include hair loss along the incision, paresis or paralysis of 1 or both temporal branches of the facial nerve, forehead numbness, and lateral facial asymmetry.

Diplopia generally resolves over time, though it occasionally may necessitate extraocular muscle surgery.

Although rare, visual loss is a feared complication, and early recognition may lead to intervention for a reversible cause such as hematoma.

Cosmetic deformity (eg, inadequate dorsal nasal height, persistent malposition of the medial canthus) is generally the result of inability to obtain ideal repair, although bone graft resorption may also contribute.

Epiphora results if a lacrimal system injury is not recognized or if recanalization failed to occur despite cannulation.

Late complications include sinusitis, and frontal sinus mucoceles may occur as long as 20 years after injuries of this type.

Outcome and Prognosis

Experience with the subcranial approach for trauma has been extensively reported by Raveh et al and Kellman. [78In 1995, Gliklich and Lazor reported anecdotal experience. [9]

In 1988, Raveh et al published their results of 395 cases of frontobasal injuries. [10They separated their results into 2 groups, those of early experience (1978-1983, 176 cases) and those of later experience (1983-1987, 219 cases), noting a marked decrease in surgically related complications in the later group. They noted a 3.9% incidence of recurrent CSF leaks after surgery in the early group and none in the later group. No cases of surgically related meningitis occurred. The incidence of orbital apex compression was 1.6% in the early group; none occurred in the later group.

Raveh et al never obliterated the frontal sinuses, and the incidence of frontal sinus complications, including mucocele development, was 2.8% in the early group and 1.9% in the later group. No local infections or bone or cartilage graft rejections occurred. However, 17% of bone grafts in the early group and 14% of the grafts in the later group resulted in 30-50% resorption. Only 3 patients (0.8%) required revision surgery because of persistent pseudohypertelorism, and 9 required revision surgery for repair of the nasal buttresses. No persistent anosmia was attributed to the surgery. The 5 deaths were attributed to associated injuries.

In 1992, Raveh et al published a review of 355 cases with similar results. [7Presumably, overlap between the patients in the 2 reports was significant. In this series, they reported a 1.9% incidence of insufficient reduction of the medial canthal ligaments and a 2.5% incidence of inadequate repair of the nasal frame. Incidence of CSF leak was 2.8%; that of meningitis was 1.1%. The 4 deaths were attributed to causes other than the surgery. The incidence of frontal sinus mucocele was 3.0%; that of frontal sinus infection was 1.7%. The incidence of postoperative orbital apex syndrome was 0.8%.

In 1998, Kellman reported an experience with 28 patients, including 9 complete primary subcranial dissections for frontobasal trauma, 14 near-subcranial dissections in primary trauma, and 5 complete subcranial approaches for secondary repair of traumatic CSF leaks and meningoencephaloceles. [8This included 7 children aged 4-17 years; the follow-up period was 4-58 months. In this series, no meningitis or tension pneumocephalus occurred, and no brain injuries or blindness was secondary to the surgery. Two optic nerve decompressions resulted in some visual improvement. Nasal dorsal height was satisfactory or better in 26 of 28 cases, and medial canthal position was judged excellent in 25 cases (less than 1-mm discrepancy), satisfactory in 2 cases (discrepancy of 2 mm or less), and unsatisfactory in 1 case. Thus far, no frontal sinus complications have occurred.

Future and Controversies

The subcranial approach is fairly new and is yet to be widely used, though published experiences are increasing. [111213It remains controversial and has its detractors. It seems particularly invasive at a time when minimally invasive surgical techniques are being developed. Still, despite the fairly aggressive nature of the surgical exposure, this approach actually allows a more conservative approach to the intracranial component of severe frontobasal trauma by allowing access to the anterior fossa floor with minimal, if any, brain retraction.

Certain specific aspects of the procedure, such as the issue of stenting the nasofrontal ducts versus frontal sinus obliteration, also remain controversial. Similarly controversial is the issue of how to manage posttraumatic blindness and optic nerve injury.

The knowledge hoped to be gained from this approach may ultimately be combined with the technology of minimally invasive surgery to lead to the best results with the most conservative techniques possible.