**5. Frontal sinus pathology and concept of "safe sinus"**

Pathology of FS is rare but most commonly is associated with trauma, which causes fracture of the frontal sinus walls.

Fractures of FS have many forms and a variety of classifications. Basically, they can be classified as anterior or posterior wall fractures. These fractures can be simple with no displacement, or complex displaced and comminuted with or without brain injury. Displaced anterior wall fracture usually leads to a simple aesthetic deformity. Posterior wall fracture usually results from high impact injury and bears a risk of placing the intracranial content in direct commu‐ nication with the nasal cavity. A complicating factor is involvement of the NFOT. Its obstruc‐ tion can lead to mucus retention and late infectious complications. [21]

A more detailed classification of the frontal sinus fractures which is suggested by many authors [22-25] and can be as follows:

#### **Anterior wall fractures:**

pattern is seen in 66-88 % of cases. When the uncinate process attaches superiorly to more medial structures (middle turbinate, cribriform, or skull base), the drainage of the sinus is lateral to the uncinate process. This type of drainage pattern is seen in 12-34% of cases. A true identifiable duct may be absent in up to 85% of FSs. In this situation, the FS drains indirectly through ethmoid air cells to the middle meatus. Therefore, some investigators chose the term *nasofrontal outflow tract* (NFOT) or *frontal sinus outflow tract* (FSOT) for the drainage path of the

**Figure 3.** Opposite extremes of frontal sinus development; aplasia (left) versus hypertrophy (right).

The mucosa of the frontal sinus consists of pseudostratified ciliated epithelium, mucus producing goblet cells, a thin basement membrane, and a thin lamina propria that contains seromucous glands. It covers the entire surface of the sinus and ranges in thickness from 0.07 to 2.0 mm. When the mucosa is healthy, a blanket of mucin overlies the epithelium. The cilia beat at 250 cycles/min. The mucin blanket flows in a spiral fashion in a medial-to-lateral direction; the flow is slowest at the roof and fastest at the NFD. The mucin empties at the NFD

The frontal sinus is unique in that it is the only sinus that has a recirculation phenomenon. The mucus travels along the lateral side of the sinus and turns medially over the sinus floor and down the lateral frontal recess wall. Of the secretion, 60% is directed back into the sinus cavity as it reaches the frontal recess. [13] Clinically significant anatomical structures of the mucosa of the frontal sinus are the foramina of Breschet, first described over 60 years ago. These foramina are sites of venous drainage of the mucosa and can serve as the route of intracranial spread of infection. The mucosa is found deeply penetrating these foramina. If mucosa is not completely removed microscopically from these foramina in obliteration or cranialization

FS (Figure 3). [7, 12-18]

440 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

**4. Frontal sinus physiology**

at a daily rate of 5.0 g/cm2. [14, 19, 20,]

procedures, there is a high risk of mucocele formation. [13]

Anterior wall fractures with no displacement

Anterior wall fractures with displacement and intact FSOT.

Anterior wall fracture with displacement and FSOT injury.

#### **Posterior wall fractures:**

Posterior wall fracture without displacement and no cerebro-spinal fluid (CSF) leak.

Posterior wall fractures without displacement and positive CSF leak.

Posterior wall fracture with displacement and no CSF leak.

Posterior wall fracture with displacement and positive CSF leak.

Infection of the sinus, which causes sinusitis, may give rise to serious complications due to the proximity of FS to the cranial cavity, orbit, and nasal cavity. Complications can develop into orbital cellulitis, epidural abscess, subdural abscess, meningitis, and in long-term into muco‐ pyocele.

Mucocele formation is a complication, which can develop years after trauma and the symptoms may go unnoticed for a long period of time. [26] Therefore it is desirable to treat injured FS in such way as to make it "safe". This means either to obliterate it completely including all mucosa lining, or to restore it to the functional state with unobstructed NFOT.
