TITLE: FRONTAL SINUS
SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds
DATE: February 22, 1995
RESIDENT PHYSICIAN: Kelly D. Sweeney, M.D.
FACULTY: Brian P. Driscoll, M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.
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The arterial blood supply of the frontal sinus is primarily diploic branches of the supraorbital artery which arise from the ophthalmic artery and from branches of the anterior ethmoid artery. Superficial venous drainage is by the angular and facial veins. The deep venous drainage is through the ophthalmic vein to the cavernous sinus. In addition, there are veins present in the mucosa of the frontal sinus which communicate with the dura and the diploe of the cranium. The perforations in the bone containing these veins are known as Breschet's canals, and blood may flow in a retrograde fashion into the anterior cranial fossa because of the lack of valves in these veins. Spread of infection through these veins can then lead to development of a subdural or brain abscess. Sensory innervation is provided by the ophthalmic division of the trigeminal nerve.
The frontal sinus begins as an evagination of the anterior- superior portion of the middle meatus known as the frontal recess. This is first recognizable during the end of the third month of fetal life. A furrow develops in the frontal recess around the fifth month which progresses to form a larger pit or several smaller ones from which the sinuses develop. The sinuses may develop as a large direct extension of this area (no true duct) or may push upward maintaining communication with the nasal cavity by a formed nasofrontal duct.
Between the ages of 1 and 2 years, this developing sinus begins to grow between the anterior and posterior tables of the frontal bone. By age 3, it extends several millimeters above the frontonasal suture line. The frontal sinus becomes recognizable radiographically by age 7, but is not clinically significant until age 10. It usually reaches adult size by age 18, and may continue to grow slowly throughout adulthood.
The drainage pattern of the frontal sinus is variable. In 15% of the population, a true nasofrontal duct exists. These ducts are located in the posterior-medial portion of the floor of the sinus. They vary in length from a few millimeters to 2-3 centimeters and are lined with respiratory mucosa. Longer ducts are more susceptible to traumatic disruption. These ducts travel in an anterior-inferior direction to empty into the anterior end of the middle meatus. More commonly (85%), the frontal sinus drains directly into the middle meatus via an ostium without a true nasofrontal duct.
The primary purpose of the frontal sinus is to serve as a mechanical barrier to protect the brain from trauma. The frontal sinuses are positioned more anteriorly than the other paranasal sinuses and are situated to absorb anterior cranial facial trauma.
In any patient sustaining significant maxillofacial injury, the cervical spine should be suspect and should be evaluated both radiographically as well as clinically prior to other studies or examinations requiring hyperflexion or other manipulation in the head and neck. The c-spine should be stabilized in a cervical collar until a cross-table lateral radiograph is obtained and demonstrates that all seven cervical vertebrae are normal.
A thorough neurologic examination is extremely important. Significant intracranial injury occurs more commonly with injury to the frontal sinus (12-17% of the time) that with injury to the mandible or midface due to the proximity of the frontal sinus to the brain and the great forces required to cause a frontal sinus fracture. Neurosurgical consultation should be obtained promptly if abnormal neurologic studies or brain CT changes are observed. Changes in mental status as well as nausea or vomiting are suggestive of intracranial injury. It is important to search for cerebrospinal fluid leakage from the nose or directly from lacerations and exposed bone which could signify dural displacement coupled with a posterior table fracture. A traumatic CSF fistula of the frontal sinus is a life threatening process deserving urgent attention.
Early ophthalmologic consultation should be obtained in the emergency department for any fractures of the frontal sinus when they concomitantly involve the orbit and should be considered in every case of frontal sinus fractures. It is important to document visual acuity, pupillary function, and ocular mobility and to inspect the anterior chamber for blood (hyphema) and the fundus for gross disruption. In one study by Holt, of 787 patients with facial fractures who were evaluated by an ophthalmologist in the emergency department, 89% of those with frontal sinus fractures had associated eye injuries!
A general head and neck examination should be performed promptly, carefully palpating and exploring locally all wounds and lacerations. Note any crepitance, bony step-offs, point tenderness, soft tissue swelling, rhinorrhea, epistaxis, or abrasions and contusions around the neck. The extent of soft tissue injury overlying the sinus can be misleading and may not reflect the degree of injury to the sinus. Soft tissue swelling is often seen over the frontal region and may not allow for the diagnosis of a depressed fracture on palpation.
CT scans may not clearly define fractures or injuries to the nasofrontal ostia or ductal drainage system. It will, however, provide enough detail to make fairly accurate predictions of nasofrontal duct involvement. Isolated fractures of the anterior table of the frontal sinus and transverse linear fractures through the anterior and posterior table above the floor of the sinus are not usually associated with damage to the nasofrontal duct. However, CT evidence for fractures involving the floor of the sinus, the nasoethmoid complex, inferiorly located fractures of the posterior wall, or depressed fractures of the posterior table almost always signify injury to the frontal sinus drainage system and must be evaluated further.
CT scanning can also be helpful in anticipating possible dural disruptions. Findings on CT that usually signify torn dura include: a wide gap in the posterior wall or any marked displacement of fragments; a fracture passing across both sinuses; a large projecting fragment posteriorly; a fracture that widens as it progresses inferiorly; or tilting of the crista galli.
Although a treatment plan may be formed on the basis of pre-op evaluation and CT scan findings, the surgeon must be ready to modify this plan based on the findings at the time of the exploration. A risk to benefit evaluation must be made to determine the least operative intervention that will achieve the optimal result. This is particularly important to remember in dealing with frontal sinus fractures in children in order to avoid interfering with the growth centers and causing iatrogenically induced deformities.
Definitive management of facial fractures should be delayed until the patient is stable and optimum conditions exist for a good surgical result and recovery. Frontal sinus fractures do not require immediate surgical attention unless they are associated with a neurosurgical or ophthalmologic emergency. Patients not requiring operative treatment for associated injuries should be observed for head trauma for 48 hours prior to frontal sinus exploration.
In selected cases, a frontoethmoidectomy via a Lynch incision may be used for limited access to the frontal sinus. An incision is extended from below the medial border of the eyebrow inferiorly midway between the medial canthus and nasal dorsum. This is carried down to the periosteum and the sinus is entered using a chisel or drill. This allows combined access to the ipsilateral ethmoid and frontal sinus.
The osteoplastic flap allows a direct approach through the anterior wall of the frontal sinus but preserves the anterior wall by hinging it inferiorly on the blood supply coming through the periosteum and soft tissue. The forehead contour is preserved by replacement of the bone-periosteal flap over the sinus at the completion of the procedure. This approach provides wide exposure to the frontal sinus and can be used to explore both sides, repair anterior table fractures, obliterate the sinus with fat, or remove the posterior wall with cranialization and ablation of the sinus. This may be done via an overlying laceration, a brow incision, or a coronal incision. The coronal incision is preferred because it provides the best exposure, it allows the neurosurgeon access to perform an anterior craniotomy if findings warrant, and it hides the scar in hair-bearing skin. An exception to the use of a coronal incision would be a male patient with a predilection to male pattern baldness. In these patients, a brow incision (gull-wing) might heal with a more acceptable scar (controversial).
The frontal sinus ablation procedure (Reidel procedure) allows the overlying soft tissue to obliterate the sinus by collapsing inward to meet the posterior table after removal of the anterior table and the mucosa. This can be accomplished via a brow incision or a coronal incision. Reconstruction of the forehead defect can be performed 6-12 months later using metal plates, calvarial bone graft, or synthetic materials.
The cranialization procedure preserves forehead contour. This is done via an osteoplastic sinusotomy. The entire posterior table is removed and the brain is allowed to expand forward. For this procedure to be successful, the dura must be intact or repaired carefully and patched with fascia if indicated, all mucosa must be removed, and the nasofrontal duct must be well plugged with fat and fascia. These patients require perioperative IV antibiotics. In cases of severe head trauma, this allows the brain to decompress into the frontal sinus defect.
Hybels and Newman evaluated the natural history of posterior fractures using a cat model. They demonstrated that mucocele formation occurred in the presence of nasofrontal duct obstruction and when mucosa was inadequately removed in an obliterated sinus. They were able to demonstrate that with adequate drainage of the sinus, mucosa did not grow into the fracture lines. They also showed that healing of the posterior wall occurred with new bone formation if the fracture line was depressed less than the width of the posterior table. Fractures with loss of bone or separation between the fragments greater than the width of the posterior table healed by fibrous tissue filling the defect. Hybels concluded that nondisplaced or minimally displaced fractures of the posterior table may be treated conservatively if there is no CSF leak or NFD injury.
In contrast, Donald states that nondisplaced posterior wall fractures may not heal by bony union. Additionally, dural tears often exist adjacent to these posterior wall defects which may predispose the patient to meningitis if an episode of sinusitis develops. He supports fat obliteration of the frontal sinus in all cases of posterior wall fractures.
For displaced posterior wall fractures, surgical exploration is generally agreed upon, but the optimal surgical treatment is controversial. In moderately displaced fractures of the posterior table, mucosa may become trapped in the suture line. These require surgical attention because continued growth of the mucosa may result in mucocele formation, or if sinusitis occurs, meningitis, cerebritis, or a brain abscess may occur. Also damage to the NFD is frequently associated with displaced fractures of the posterior table and should be evaluated at the time of exploration. Most authors recommend fat obliteration of the frontal sinus as treatment for displaced frontal sinus fractures. The rationale for obliteration is to provide a secure barrier between the unsterile nasal cavity and the intracranial area. Complete removal of mucosa is imperative to prevent potential mucocele formation. A bicoronal craniotomy is used, providing optimum exposure for evaluation and repair of both dural and bony injuries. The dura is repaired either with a simple suture closure or using a fascial graft. Once the dura is closed, the bony fragments are reduced. In most instances, simple reduction is sufficient. If instability exists, a reduction plate is applied from the intracranial side to provide fixation. If >50% of the posterior wall is fractured, then a cranialization procedure should be performed. This is because the extensive bone debridement and dural grafts required to repair a severely comminuted fracture may not have the vascular bed to support a fat graft.
Attempts at treating unilateral obstruction to the NFD by removing the intersinus septum and allowing drainage down the contralateral side have proven unsuccessful due to the unpredictability of the drainage system and fibrous tissue ingrowth at the site of the removed septum. Catheter placement in the NFD has also been abandoned due to ductal stenosis.
Reconstruction of the NFD may be attempted for frontal sinus fractures when the pre-op assessment has shown that the posterior wall does not require surgical attention. This can be done via a frontoethmoidectomy approach with or without the use of temporary stents. Advocated of this argue that it is a lesser procedure with fewer complications than the osteoplastic flap and allows direct access to the ethmoid air cells. This can be done bilaterally if both NFD are injured.
For NFD injuries associated with posterior wall fractures, the best treatment is an osteoplastic flap approach with complete mucosal removal, fat obliteration of the sinus, and plugging of the NFD.
Follow-up is extremely important in any patient who sustains a frontal sinus fracture. Complications may not develop for many years after the injury, and this fact must be emphasized to these patients. At any time in the patient's life when complaints of frontal sinusitis, frontal sinus pressure, visual changes, unexplained fevers, and persistent frontal headaches arise, he should be evaluated for complications and should undergo a CT scan.
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