Key points

Introduction

Management of frontal sinusitis can be challenging for even the most experienced otolaryngologists. The challenges that the treating physician face are deciding whether medical or surgical treatment is needed and if a surgical procedure is necessary, then determining which procedure will serve as the best option. Many times there is no clear-cut solution, and the answer rests with the physician’s clinical judgment and experience.

A thorough understanding of both the pathogenesis of acute and chronic rhinosinusitis (CRS) and the anatomy of the frontal sinus is required in order to properly treat frontal sinusitis and its complications. To the young otolaryngologist, simply understanding the complex anatomy of the frontal sinus and its outflow tract can be difficult. After years of training, frontal sinus surgery remains technically challenging to even the most skilled rhinologists; however, perhaps the most difficult aspect of managing frontal sinusitis is understanding the treatment options available and knowing which approach provides the highest likelihood of success in specific circumstances. When contemplating treatment, one must distinguish between acute and chronic sinusitis. Once that distinction is made, medical and surgical treatment protocols can be initiated. These protocols are determined by severity of disease, patient anatomy, and technical expertise of the operating surgeon. These factors all come into play with both the evaluation and the decision making in frontal sinus surgery.

Introduction

Management of frontal sinusitis can be challenging for even the most experienced otolaryngologists. The challenges that the treating physician face are deciding whether medical or surgical treatment is needed and if a surgical procedure is necessary, then determining which procedure will serve as the best option. Many times there is no clear-cut solution, and the answer rests with the physician’s clinical judgment and experience.

A thorough understanding of both the pathogenesis of acute and chronic rhinosinusitis (CRS) and the anatomy of the frontal sinus is required in order to properly treat frontal sinusitis and its complications. To the young otolaryngologist, simply understanding the complex anatomy of the frontal sinus and its outflow tract can be difficult. After years of training, frontal sinus surgery remains technically challenging to even the most skilled rhinologists; however, perhaps the most difficult aspect of managing frontal sinusitis is understanding the treatment options available and knowing which approach provides the highest likelihood of success in specific circumstances. When contemplating treatment, one must distinguish between acute and chronic sinusitis. Once that distinction is made, medical and surgical treatment protocols can be initiated. These protocols are determined by severity of disease, patient anatomy, and technical expertise of the operating surgeon. These factors all come into play with both the evaluation and the decision making in frontal sinus surgery.

Relevant anatomy/pathophysiology

Anatomy

In most adults, 2 frontal sinuses exist and are separated by an intersinus septum that can vary in location. Each sinus consists of a thick anterior plate that serves as a buffer in the setting of trauma and a thinner posterior plate. The posterior plate separates the frontal sinus from the anterior cranial fossa, and below the frontal sinus floor is the orbit. For this reason, infection in the frontal sinus has the potential to spread to both the orbit and the intracranial cavity.

The frontal sinus outflow tract (FSOT) is described as an hourglass. It consists mainly of 3 structures: the frontal sinus infundibulum, ostium, and recess. The frontal sinus infundibulum is a funnel-shaped area at the inferior aspect of the frontal sinus that leads to the frontal sinus ostium. The ostium opens into the frontal sinus recess. The frontal recess is bounded laterally by the lamina papyracea, medially by the middle turbinate, anteriorly by the agger nasi, and posteriorly by the ethmoid bulla. The superior attachment of the uncinate process determines whether the frontal sinus has a medial or lateral drainage pathway. Most commonly, the uncinate attaches to the lamina papyracea, leading to a medial drainage pathway ( Fig. 1 ). In cases where the uncinate attaches to the skull base, the frontal sinus drains lateral to the uncinate.

Arrow demonstrates uncinate attaching to lamina papyracea signifying a medial frontal sinus drainage pathway.

Preoperative evaluation of the computed tomographic (CT) scan is in many ways the most critical aspect of surgical decision making for frontal sinus surgery. Identification of the drainage pathway helps direct a surgeon to dissect in a way that minimizes mucosal trauma. In addition, depending on frontal sinus aeration, a purely endoscopic approach may not be feasible or, if entertained, an extended approach such as a modified Lothrop procedure (LP) may be needed.

Many cells have been described that can obstruct the FSOT. Bent and colleagues have described 4 types of frontal infundibular cells that can obstruct the anterior aspect of the FSOT. A type I frontal cell is an individual anterior ethmoid cell located superior to the agger nasi. Type II frontal cells consist of a tier of anterior ethmoid cells located superior to the agger nasi. A type III frontal cell is a cell arising superior to the agger nasi and extending into the frontal sinus. A type IV cell is an isolated cell arising within the frontal sinus. Other cells that can obstruct the posterior aspect of the FSOT include suprabullar and frontal bullar cells. The most common air cell in the frontal recess is the agger nasi that has variable degrees of posterior aeration. The more posterior it aerates, the further posterior the origin of the FSOT will be ( Fig. 2 ).

Arrow demonstrates agger nasi cell. One can see how increased levels of posterior aeration could displace frontal recess outflow posteriorly.

Normal mucosal function, termed mucociliary clearance, plays a critical role in protecting the frontal sinus against infectious agents. The ciliated epithelium allows for coordinated movement of mucus through the sinus cavity, and mucociliary flow in the frontal sinus has been described to occur in a spiral pattern. Mucociliary flow progresses superiorly along the intersinus septum, laterally across the roof, and inferiorly along the lateral wall before traveling medially along the floor to drain into the frontal recess ( Fig. 3 ). This concept is crucial to understand, and surgical techniques should be performed in a way that minimizes damage to the delicate ciliary apparatus and incorporates the mucociliary clearance pathway into the surgical approach.

Arrows demonstrate mucociliary flow through the frontal sinus. Mucus progresses in a coordinate fashion superiorly along the intersinus septum, laterally across the roof, and inferiorly along the lateral wall before traveling medially along the floor to drain into the frontal recess.

Clinical presentation/examination/diagnosis

Acute viral sinusitis is diagnosed in patients with purulent nasal discharge along with nasal obstruction and/or facial pain-pressure-fullness lasting less than 4 weeks. Acute bacterial sinusitis is diagnosed when symptoms last greater than 10 days or when symptoms acutely worsen within 10 days after an initial period of improvement ( Table 1 ).

Acute frontal sinusitis is most common in adolescent men, and it is commonly preceded by an upper respiratory illness. The most common symptom in acute frontal sinusitis is frontal headache. One should consider the diagnosis in anyone with signs of acute rhinosinusitis and frontal headache. In addition, the diagnosis should be considered in anyone with no prior history of headaches who develops new onset frontal headache. No diagnostic criteria specific for frontal sinusitis exists; rather, the criteria for diagnosing acute sinusitis are used, and involvement of the frontal sinus is assessed based on symptomatology and examination findings.

On nasal endoscopy, purulent drainage in the frontal recess indicates involvement of the frontal sinus but is not always present. When possible, cultures should be obtained to guide antimicrobial therapy. In uncomplicated cases of acute sinusitis, imaging is not required to confirm the diagnosis.

Orbital complications are more likely to arise from the ethmoid cells but can develop from the frontal sinus due to its proximity to the orbital roof. Intracranial complications such as epidural abscess, subdural abscess, and meningitis can present with subtle findings; therefore, a high index of suspicion is necessary for early and accurate diagnosis of these complications. Patients may complain of lethargy, change in personality, or in severe cases, seizures with severe headache or generally toxic appearance. Other signs may include periorbital edema or erythema, extraocular movement restrictions, vision changes, nausea, vomiting, altered mental status, photophobia, or neurologic deficits.

Diagnosis of acute frontal sinusitis can be confirmed with CT scan of the sinuses. In cases where extrasinus spread to the orbit or brain is suspected, an MRI with and without contrast is indicated.

Treatment of complicated acute frontal sinusitis includes aggressive medical and surgical management. Appropriate cultures should be obtained if possible. In the event of meningitis, an LP may be obtained after CT confirms the lack of an intracranial mass or space-occupying process. Following these diagnostic measures, broad spectrum intravenous antibiotics should be initiated. Surgical treatment of the frontal sinus is necessary either via frontal sinus trephination, via endoscopic frontal sinusotomy, or both. Endoscopic frontal sinusotomy is more difficult to perform in the acutely inflamed sinus and is often delayed in this setting.

CRS is diagnosed in patients with 2 or more of the following: nasal obstruction, purulent nasal drainage (rhinorrhea or postnasal drip), anosmia/hyposmia, and facial fullness-pressure-pain lasting longer than 12 weeks in addition to either radiographic evidence of sinusitis, purulent nasal drainage, or middle meatus edema or polyps. CRS can further be classified as chronic sinusitis with polyposis and chronic sinusitis without polyposis; the mechanisms underlying the development of each seem to be distinct.

Most patients with chronic frontal sinusitis do not have isolated frontal disease. However, chronic frontal sinusitis is diagnosed in patients with CRS who are found to have involvement of the frontal sinus. In addition, certain pathologies may predispose patients to developing isolated frontal disease. Examples include the presence of frontal sinus osteomas, mucoceles, or tumors that obstruct the FSOT. In addition, many patients who have previously undergone functional endoscopic sinus surgery may continue to have or may develop chronic frontal sinusitis as a result of neo-osteogenesis or scarring resulting in a narrowed FSOT. Aberrations in technique and/or complications of healing are often responsible for iatrogenic cases.

Diagnosis can be confirmed with nasal endoscopy. The use of angled endoscopes (30°, 45°, and 70°) allows for the evaluation of the frontal sinus and its outflow tract in most patients. It is important to note the presence or absence of the middle turbinate and its location, scarring or synechiae from previous operations, and the location of any polyps. In addition, CT of the paranasal sinuses using thin (<3 mm) cuts is a necessary adjunct. It is common practice to obtain imaging only after the patient has completed a course of aggressive medical management unless complications are suspected. MRI may be particularly useful to evaluate suspected orbital or intracranial extension. Thorough review of all imaging with careful attention paid to the FSOT is absolutely crucial to identify factors leading to the development of frontal sinusitis. Particular attention should be paid to the size and pneumatization of the frontal sinus, the presence of any anatomic abnormalities predisposing to frontal sinusitis (eg, frontal cells, supraorbital cells, suprabullar cells, intersinus septal cells, osteomas, or other benign tumors involving the frontal sinus), the anterior-posterior dimension from the nasal root to the anterior cranial fossa including the nasal beak, the presence or absence of the middle turbinate or its remnant, and the attachment site of the uncinate. The frontal recess anatomy dictates the choice of surgical approach necessary to treat the frontal sinus.