Structures involved

Each wall of the frontal sinus serves a dual function. The anterior wall of the frontal sinus, formed by the frontal bone, is responsible for the aesthetic contours of the forehead and the superior orbital rims. In addition, this structure serves as the frontal bar, one of the key horizontal buttresses of the facial skeleton ( Fig. 1 ). The frontal bar helps to maintain the horizontal dimension of the face and to provide a stable foundation for the vertically oriented facial buttresses (see Fig. 1 ) that support the forces of mastication. Fractures of the anterior table may be clinically important either by disrupting the aesthetic contour of the forehead or by destabilizing the frontal bar from which the other facial bones are suspended . The posterior wall of the frontal sinus forms the anterior wall of the anterior cranial fossa, and serves to separate the sinus contents from the cranial vault. Posterior table fractures are therefore skull fractures, and must be recognized and managed as such. The floor of the frontal sinus forms the medial orbital roof; it also houses the ostium to the nasofrontal duct in its posteromedial aspect . The nasofrontal duct forms the drainage pathway of the frontal sinus into the nose, so obstruction of this pathway can lead to mucocele, mucopyocele, osteomyelitis, and epidural or subdural abscess .

The buttress system of the midface. The buttress system of the midface is formed by the strong frontal, maxillary, zygomatic, and sphenoid bones and their attachments to one another. The central midface consists of several fragile bones that easily “crumple” when subjected to strong forces. These more fragile bones are surrounded by the thicker bones of the buttress system, which provide structure and absorb the forces applied to the face. Most of the forces absorbed by the face are masticatory, therefore the vertical buttresses are the most well developed. These include the medial nasomaxillary buttress and the lateral zygomaticomaxillary buttress. Three horizontal buttresses interconnect and provide support for the vertical buttresses: the frontal bone and supraorbital rims (frontal bar), the nasal bones and inferior orbital rims, and the maxillary alveolus. ( From Linnau KF, Stanley RB Jr, Hallam DK, et al. Imaging of high-energy midfacial trauma: what the surgeon needs to know. Eur J Radiol 2003;48:17–32; with permission.)

Variables affecting treatment

There are three main variables to consider when assessing the need for surgical intervention for frontal sinus fractures. These are involvement of the anterior table, disruption of the nasofrontal duct, and involvement of the posterior table. When assessing the involvement of the anterior or posterior tables, the degree of fracture displacement and comminution are also important. An additional factor involved when assessing the posterior table is the likelihood of dural penetration or nasofrontal duct disruption.

Posterior table fractures

The management of posterior table fractures remains somewhat controversial. Nondisplaced posterior table fractures are frequently treated conservatively with close follow-up . Follow-up should include early and repeated CT scans of the sinuses . In contrast, comminuted or displaced posterior table fractures are generally felt to increase the risk of complications and thus merit exploration . The presence of pneumocephalus, although not specific, may indicate dural violation, and also may be an indication for surgical exploration of the fracture . Posterior table fractures may be managed with sinus obliteration if the floor of the sinus is not comminuted and there is not a large amount of bone missing ( Fig. 2 ). Severely comminuted or displaced posterior wall fractures frequently require cranialization ( Fig. 3 ) .

Frontal sinus obliteration. ( A ) Axial CT scan demonstrates fractures of both anterior ( arrowheads ) and posterior ( arrow ) tables of the frontal sinuses. At exploration, the dura was found to be intact and there was no evidence of CSF leak, therefore cranialization was not performed. However, the presence of an associated severe NOE fracture suggested disruption of the nasofrontal ducts bilaterally, and therefore the sinuses were obliterated bilaterally with concominant plugging of the nasofrontal ducts with calvarial bone grafts (CBGs) and free pericranium. ( B ) Postoperative axial CT scan showing reduction of the posterior table with fixation of the anterior table fractures. ( C ) Coronal CT scan demonstrating the CBGs used to plug the nasofrontal ducts ( wide arrows ). Additional CBGs were required in this patient to reconstruct the floor, medial wall, and roof of the left orbit ( thin black arrows ).

Frontal sinus cranialization. This patient was involved in a high-velocity motor vehicle collision that resulted in combined anterior and posterior sinus fractures with displacement of the posterior table, dura injury, and frontal contusion. Frontal sinus cranialization was performed using an anteriorly based pericranial flap and CBGs to plug the nasofrontal ducts. The anterior table fractures were managed with open reduction and fixation. ( A ) Preoperative axial CT scan demonstrating anterior and posterior table fractures and associated pneumocephalus ( arrow ). ( B ) Postoperative axial CT scan demonstrating cranialization (note the absence of the posterior table). ( C ) Postoperative sagital CT scan demonstrating cranialization. The arrow indicates the window made in the frontal bone to allow intracranial passage of the pericranial flap. The pericranial flap was draped over the anterior skull base to reinforce the dura.

Clinically relevant radiology reports: Frontal sinuses

• 1.
  

  Indicate whether the fracture involves the anterior wall, posterior wall, or both, as well as the degree of displacement and comminution of the fracture.

  
  
• 2.
  

  For posterior wall fractures, indicate the presence or absence of pneumocephalus with an estimation of the likelihood of dural violation and the degree of bone loss in the posterior wall and floor of the sinus.

  
  
• 3.
  

  Indicate the likelihood of nasofrontal duct obstruction based on the fracture location.

  
  
• 4.
  

  Comment on any associated brain injury. This is especially important for posterior table fractures.

Structures involved

The zygoma is an approximately quadrilateral-shaped bone. The body of the zygoma forms the malar prominence, which is an important aesthetic feature of the face. A prominent malar eminence has been described as “a sign of youth and beauty” . Through its attachments to the surrounding facial bones, the zygoma also helps to determine midfacial height and width . From the laterally oriented malar prominence, the zygoma sends four projections that articulate with the surrounding facial bones. Superiorly, the zygoma articulates with the frontal bone at the narrow frontozygomatic suture; medially, it has a wider articulation with the maxilla, involving both the anterior and lateral walls of the antrum. The curved bony strut of the zygoma lying between these superior and medial projections forms the lateral orbital wall and the lateral aspect of the infraorbital rim and orbital floor. Posteriorly, the zygoma articulates with the sphenoid bone, and laterally it extends as the zygomatic arch to attach to the temporal bone at the zygomaticotemporal suture.

The presence of the thick bone of the zygoma at the lateral corner of the midface allows it to act as a cornerstone to provide support to the other facial bones . The maxilla directly contacts the frontal bone at the frontomaxillary suture line and the sphenoid bone posteriorly above the maxillary tuberosity and anterior to the sphenopalatine foramen. The zygoma then overlies and reinforces this area through its attachments to the underlying frontal, maxillary, sphenoid, and temporal bones.

Variables affecting treatment

The goal of reconstruction in ZMC fractures is to restore the height, width, and projection of the malar eminence. The degree of fracture displacement and comminution determines the extent of the surgical exposure needed for repair. Nondisplaced and minimally displaced fractures frequently do not require surgical intervention . Displaced and comminuted fractures generally require open reduction and fixation. The first and most critical step in management of ZMC fractures is achieving adequate reduction . When fractures are not significantly comminuted, as is the case in a classic tripod fracture, the entire zygoma may be reduced as a single unit. In such cases, ZMC fractures may be managed through the use of limited incisions, in particular an upper gingivobuccal (UGB) incision and a lateral upper blepheroplasty (LUB) incision. Reduction can, in these cases, be accurately assessed by confirming reduction at the ZM suture (through the UGB incision), the ZF suture (through the LUB incision), and the ZS suture (through the LUB incision).

Accurate depiction of ZMC fracture displacement can be accomplished with CT ( Fig. 5 ). The malar eminence is often displaced posteriorly, but the degree of displacement may be masked clinically by soft tissue swelling (see Fig. 5 A). The malar eminence may be rotated internally or externally (see Fig. 5 B, C). Occasionally, the zygomatic arch fracture that accompanies ZMC fractures will not be evident radiographically as a discrete linear hypodensity. Abnormal curvature of the zygomatic arch should be considered equivalent to a discrete fracture in this setting (see Fig. 5 D).

ZMC variants. ( A ) Axial CT shows posterior displacement of the ZMC ( double arrow ). This displacement would be masked clinically by soft tissue swelling (note symmetry of facial soft tissues). ( B ) Internal rotation ( arrow ) of a ZMC fracture. Note the increased interzygomatic distance. ( C ) External rotation ( arrow ) of a ZMC fracture. Note the decreased interzygomatic distance. ( D ) Zygomatic arch angulation. Although no discrete fracture line is seen through the arch, it is abnormally angulated ( arrow ), which is sufficient for the diagnosis of ZMC fracture.

Accurate reduction is more difficult to assess in comminuted fractures. When the zygoma itself is comminuted, it cannot be reduced as a single unit, and accurate reduction at one suture line does not imply adequate reduction at the others. In such cases, additional incisions may be necessary for fracture reduction and fixation. Eyelid incisions (ie, transconjunctival incision with a lateral canthotomy or subciliary incision) provide exposure to the orbital rim. A coronal access incision may be necessary for wider exposure of the zygomatico-sphenoid suture line, lateral orbit, and zygomatic arch. In addition, the high-energy trauma required to create comminuted zygoma fractures frequently also results in comminuted fractures of the surrounding bones. Le Fort, NOE, and panfacial fractures frequently coexist with ZMC fractures . Identification of these coexisting fractures is critical for determining accurate reduction of the ZMC. Failure to recognize coexisting fractures may mislead the surgeon into aligning the ZMC with another segment of the buttress system that is itself displaced; this in turn may result in postoperative cosmetic deformity .

Another major variable affecting the surgical management of ZMC fractures is the status of the orbital floor. The zygoma contributes to both the lateral and the inferior orbital walls. Displacement of these walls frequently occurs in ZMC fractures, and may result in an increased volume of the bony orbit. This increase in orbital volume is the most common cause of posttraumatic enophthalmos . Restoration of the pretrauma orbital volume is therefore a primary goal of ZMC fracture management. Before the advent of routine CT scanning for these injuries, the decision of whether or not to explore the orbit was made on a clinical basis. CT scan has been shown to be a reliable method of making the decision of which orbits require exploration . The ability to make this determination based on the CT scan allows those patients without significant orbital volume expansion to be spared the morbidity of a subcilliary or transconjunctival incision. Some degree of ectropion and scleral show may complicate as many as 20% of these incisions . Radiologic criteria suggesting the need for orbital exploration include severe comminution or displacement of the orbital rim, displacement of greater than 50% of the orbital floor with prolapse of the orbital contents into the maxillary sinus, an orbital floor fracture greater than 2 cm ² , and the combination of an inferior and medial wall fracture . Based on these or similar criteria, approximately 30% to 44% of patients with ZMC fractures require an orbital incision .

A final variable to consider in ZMC fractures is the status of the orbital apex. The orbital apex is the posterior portion of the orbit that contains the optic nerve and lies in close apposition to the internal carotid arteries and cavernous sinuses. Injury to this area may result in a number of serious injuries resulting from injury to the carotid arteries and to cranial nerves II, III, IV, V1, and VI . The lateral wall of the orbital apex is formed by the greater wing of the sphenoid. This bone also contributes to the lateral orbital wall and articulates anteriorly with the zygoma. ZMC fractures may result in displacement of the greater wing of the sphenoid . It is important to note whether this displacement occurs laterally or medially (into the orbital apex). The medial wall of the orbital apex is formed by contributions from the ethmoid and palatine bones and the body of the sphenoid bone. Fractures in these areas should also alert the radiologist to possible orbital apex involvement.

Clinically relevant radiology reports: ZMC fractures

• 1.
  

  Recognize that a range of injuries from an isolated zygomatic arch fracture, to a classic tripod fracture, to a displaced, comminuted zygoma all represent fractures of the zygomaticomaxillary complex (ZMC).

  
  
• 2.
  

  Comment on the degree of displacement and comminution of the ZMC fracture. The more displaced and the more comminuted the involved bones are, the more complex the surgical repair with a need for wider surgical exposure and more points of fixation.

  
  
• 3.
  

  Comment on the extent of orbital involvement. Fractures involving more than 50% of the orbital floor will likely require open reconstruction.

  
  
• 4.
  

  Identify whether the medial orbital wall (lamina papyracea) is involved. An isolated medial orbital wall fracture is generally not a cause of clinically significant orbital volume loss; however, when found in combination with a floor fracture, it may require repair.

  
  
• 5.
  

  Comment on the involvement of the orbital apex and the direction of displacement of the lateral orbital wall.