Anterior Subcranial Approach - Trauma 

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 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.

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.

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.

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.

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.

^[2] 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. This 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.^[3] Occasionally, 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.

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.^{[4, 2]} After a follow-up of 15 years, no noticeable growth disturbance was seen in these patients as they grew.

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.

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.