Endoscopic Correction of Frontal Sinus Fractures

Patrick Colley

Kibwei A. McKinney

Brent A. Senior

ANATOMY

The frontal bone has both vertical and horizontal components.
- The vertical component is the bone of the forehead and is composed of the anterior and posterior tables.
- The horizontal component makes up the superior orbital roof and floor of the frontal sinus.
The vertical portion of the frontal bone contains a pneumatized frontal sinus in greater than 90% of the population.
The frontal sinus begins its development at 4 years of age and continues to develop until the late teenage years.
The anterior table of the frontal sinus is a bicortical structure made of cancellous bone that begins at the nasofrontal suture line inferiorly and averages 4 to 12 mm in thickness.
The posterior table of the frontal sinus is thinner than the anterior table, with an average thickness of 0.1 to 4 mm. Its inner cortex is closely adherent to the underlying dura.
The anterior and posterior tables of the frontal sinus converge inferiorly to form the frontal recess or frontal sinus drainage pathway (FSDP), where the frontal sinus drains into the middle meatus or ethmoid infundibulum, depending on where the uncinate process inserts superiorly (FIG 1A,B).
- At the superior-most portion of the FSDP is the frontal recess, a three-dimensional (3D) structure with the following boundaries:
  - Anterior—the agger nasi cell and/or the uncinate process
  - Posterior—the anterior wall of the ethmoid bulla and any suprabullar ethmoid cells
  - Lateral—lamina papyracea of the orbit
  - Medial—the lateral lamellae of the skull base and attachment of the middle turbinate to the skull base

The soft tissue overlying the frontal bone consists of skin, subcutaneous soft tissue, frontalis muscle, and pericranium.

At the glabella and medial portion of the supraorbital rim, the soft tissue is thicker than it is at the superior portion of the forehead due to the presence of the orbicularis oculi, procerus, and corrugator muscles.

FIG 1 • A. Sagittal drawing of the frontal sinus drainage pathway (FSDP). The pathway passes posterior to the agger nasi cell and anterior to the ethmoid bulla before draining into the middle meatus. B. Coronal drawing showing the most common relationship of the FSDP to the lamina papyracea and middle turbinate.

FIG 1 (Continued) • C. Anterior view of the face showing the location of the supratrochlear and supraorbital neurovascular bundles. The supratrochlear bundle can be located approximately 1.5 cm from midline, while the supraorbital exits its foramen approximately 2.5 cm from midline. CSM, corrugator supercilii muscle; PrM, procerus muscle; StN, supratrochlear nerve; StA, supratrochlear artery; StV, supratrochlear vein; SoN; supraorbital nerve; SoA, supraorbital artery; SoV, supraorbital vein; FrM, frontalis muscle. D. Endoscopic view of the supratrochlear and supraorbital bundles. StN, supratrochlear nerve; SoN, supraorbital nerve; DSM, depressor supercilii muscle; CSM, corrugator supercilii muscle; Ant. Table, anterior table of the frontal sinus. External palpation can aid in orientation while dissecting inferiorly and alert the surgeon when the supraorbital rim is near.

The subpericranial plane constitutes a bloodless space and provides access to the underlying anterior table of the frontal sinus.

The supraorbital and supratrochlear nerves supply sensation to the forehead skin and course from the superior orbital rim, inferiorly, to the vertex of the scalp, superiorly (FIG 1C,D).
- The supraorbital nerve, the more lateral of these two structures, is a branch of V1 that passes through the supraorbital foramen and travels deep to the corrugator muscles, before penetrating the frontalis muscle and traveling within the subcutaneous tissue in its superior course.
- The supratrochlear nerve passes just above the superior oblique muscle and its trochlea before coursing in a similar plane to the supraorbital nerve superiorly along with the supratrochlear artery.
Injury to these nerves via trauma or surgical incision leads to a loss of sensation superior to the site of injury.

PATHOGENESIS

The frontal bone is one of the stronger bones in the human body, and fracturing it requires a pressure of 800 to 1600 ft-lb. However, an aerated frontal sinus reduces the ability of the frontal bone to withstand pressure, thus making pneumatized areas more susceptible to fractures than other regions of the frontal bone.
The most common mechanisms of injury resulting in frontal sinus fracture are motor vehicle collision (42%), assaults (14%), motorcycle collisions (10%), pedestrians struck by motor vehicles (8%), and ballistic injuries (7%).¹
The most common type of fracture is a combined fracture involving the anterior and posterior tables as well as the FSDP, occurring between 55% and 67% of the time. Isolated anterior table fractures are seen in 33% of frontal sinus fractures, with isolated posterior table fractures making up less than 5%.¹

NATURAL HISTORY

Injury to the frontal sinus can lead to complications from cerebrospinal fluid (CSF) rhinorrhea, damage to the FSDP, or changes in the aesthetic structure of the facial skeleton.
The posterior table of the frontal sinus is thin and adherent to the underlying dura, making a tear and subsequent CSF leak more likely when the posterior table has been significantly injured or displaced.
The FSDP is the only pathway of egress for mucus produced by the frontal sinus mucosa. Obstruction of this space can lead to chronic sinus disease and frontal mucocele formation.
The frontal bone supplies the height and contour of the entire forehead. Fractures of the frontal bone as small as 2 to 3 mm can lead to significant alteration in the appearance of the forehead, particularly in the superior portion, where the overlying soft tissue is thinner.

PATIENT HISTORY AND PHYSICAL FINDINGS

The history obtained from a patient with a suspected frontal sinus fracture should focus on the method of injury, neurologic complaints, visual changes, and the possibility of a CSF leak.
- Because of the large amount of force required to produce a frontal sinus fracture, loss of consciousness is associated with over 70% of these injuries, while intracranial injuries are seen in 39%.²
- Ophthalmologic injuries can be seen in 26% of frontal sinus fractures.²
The physical examination in patients suspected of having a frontal sinus fracture involves a complete trauma assessment and typically requires consultation with otolaryngology, plastic surgery, neurosurgery, and ophthalmology.
A thorough head and neck examination should be conducted including assessment of the airway and the neck, prior to focusing on maxillofacial injuries.
Examination of the entire maxillofacial skeleton should be conducted, as 87% of patients with a frontal sinus fracture have other maxillofacial injuries.³
- The forehead should be examined for abnormalities in contour, tenderness, crepitus, and paresthesias.
- Lacerations should be examined under sterile conditions and probed carefully until the integrity of the underlying frontal bone can be assessed on imaging.
- The orbital rims and integrity of the medial canthal tendon (MCT) can be assessed with palpation and by placing a thumb and index finger over the nasal root and carefully applying lateral tension on each lower lid. Minimal movement of 2 to 3 mm with a defined endpoint is normal, while excessive movement or orbital movement means that the integrity of the MCT has been compromised.
  - MCT injuries are often seen with naso-orbital-ethmoid fractures
CSF leaks should be suspected in all patients with frontal sinus fractures.
- The nasal cavity should be cleared of debris and examined using nasal endoscopy
- Any rhinorrhea should be examined using the halo test or sent for beta-2-transferrin analysis.¹^,³^,⁴^,⁵^,⁶
  - The halo test consists of capturing fluid from the nasal secretions on a cloth or gauze and observing whether a clear “halo” is visible around a central pool of blood within the drainage (CSF migrates faster than does blood). This test is suggestive of the presence of CSF but is not diagnostic as saline and mucus can also lead to false-positive results.
  - Testing of fluid for beta-2-transferrin is the mainstay of evaluation for CSF. This protein can be found in CSF, vitreous humor of the eye, and perilymph.