17 Frontal Sinus Obliteration and Cranialization

Managing pathology of the frontal sinus has been and remains a complex issue for otolaryngologists. Etiologies such as acute and chronic infection, trauma, mucoceles, tumors, and osteomas may require surgical intervention. Before the advent of antibiotics and, more recently, endoscopy, the majority of frontal sinus pathology was managed surgically through external approaches. The first reports of frontal sinus surgery are from the latter half of the 16th century,1 but it was not until the 1880s that Ogston and Luc outlined trephination.² They described drilling into the frontal sinus and widening the frontal recess using an external anterior ethmoid approach. Breiger and Schonborn, among other surgeons, further described the use of the osteoplastic flap to access the frontal sinus.² Riedel detailed frontal sinus ablation by removing the anterior frontal table and supraorbital rim entirely in treating frontal sinus pathology.³ In the early 20th century, Lothrop described resecting the intersinus septum, medial floor of the frontal sinus, and the superior nasal septum through an external approach described by Lynch.^1,4 Obliteration of the frontal sinus with fat was first described by Tato et al⁵ and then performed using an osteoplastic flap procedure by Goodale and Montgomery in 1956.⁶

With the advent of endoscopy and approaches to the frontal sinus through an endonasal approach, the need to obliterate the frontal sinus has become much less frequent. However, it remains a useful tool for various disease processes and this chapter intends to detail the surgical methodology and clinical usefulness of this technique.

Common indications for frontal sinus obliteration or cranialization are as follows:

1. After fracture with posterior table involvement, either comminuted or displaced (Fig. 17.1).

2. After neoplasm removal (i.e., large osteoma or inverted papilloma) with extensive mucosal injury, bone loss, or impaired outflow.

3. After failure of endoscopic transnasal management for mucocele, chronically dysfunctional mucosa (i.e., cystic fibrosis and ciliary dysfunction), or persistent chronic infectious sinusitis.

Surgical Anatomy

The frontal sinus is an air-filled space that is usually formed in the later teenage years. It can be thought of as an inverted pyramid with the frontal outflow tract representing the apex. Typically, the sinuses are paired right and left; however, in approximately 10% of people, there will be a variation of this anatomy with either a unilateral frontal sinus only or complete agenesis of both frontal sinuses. Furthermore, the extent of pneumatization of the frontal sinus can vary from a volume occupying the area just superior to the midline to one that may extend laterally past the lateral orbital rim. There may also be variation in the superior extension. The sinus is bordered anteriorly by a bone known as the anterior table and posteriorly, the posterior table. The mucosa of the frontal sinus is ciliated pseudostratified columnar epithelium. Posterior to the posterior table is dura mater. The floor of the frontal sinus is typically adjacent to or part of the superior orbital roof. The mucus produced within the sinus drains through the frontal outflow tract that is located inferomedially. The typical outflow of the frontal sinus is into the middle meatus, posterior to the anterior ethmoid cell known as the agger nasi, anterior to the ethmoid bulla, medial to lamina papyracea, and lateral to the middle turbinate. Variations of this outflow pattern exist. As such, a thorough understanding of a patient’s frontal sinus anatomy is imperative before operating.

To preoperatively assess the frontal sinus anatomy, the traditional approach was through radiography. Historically, a 6-foot Caldwell frontal X-ray was taken. A coin would be taped to the X-ray cassette and after developing, this would be used as a size template for the frontal sinus. If the X-ray was performed correctly, then the size match of the frontal sinuses could be used as an exact template for the frontal borders. The X-ray film was sterilized and used during the procedure to aid in the accuracy of osteotomies. Today, however, digital X-rays have made the process of acquiring a Caldwell view with the coin template difficult. Additionally, the wide availability of computed tomography (CT) of the sinuses has made Caldwell views less necessary. CTs allow for a highly accurate assessment of the frontal anatomy. Furthermore, image guidance systems that use the CT for an individual patient in coordination with infrared or electromagnetic localization have allowed for highly accurate mapping of the borders of the frontal sinus. It is important to remember that no technology can replace the surgeon’s understanding of the anatomy specific to each patient; and proper preoperative planning is imperative.

Various surgical approaches to the frontal sinus have been described previously; however, a coronal incision, often referred to as a bicoronal incision, is standard if obliteration or cranialization is being performed. Not only is a coronal flap relatively easy and fast to elevate, it allows for the formation of a pericranial tissue flap that can be fashioned from the overlying periosteum (pericranium) of the frontal skull bone and pedicled inferiorly. Pericranium is especially useful during cranialization as there are often defects in the dura and possible cerebrospinal fluid (CSF) leaks that can be repaired with a high degree of success using this hardy pedicled flap. The pericranial flap receives its blood supply from the deep branches of the supratrochlear and supraorbital vessels and can be harvested up to 40 mm in length.7

An incision is planned approximately 2 cm posterior to the hairline with an anterior curve that mimics the natural hairline. The incision is created parallel to the direction of the hair follicles and brought down to the subgaleal plane and elevation is commenced. When elevating the coronal flap great care should be taken not to puncture the pericranium as it may be necessary for dural repair, and holes in the flap may make it unusable. It is important to elevate the flap to the level of the supraorbital rims and nasion. Care is also taken not to damage the supraorbital neurovascular bundles. The lateral extension of the flap should be lateral to the lateral orbital rim and over the zygomatic arches. If there is difficulty getting the proper lateral extension, consider that the incision of the coronal flap may need to be extended inferiorly. As access to the frontal sinus is often needed after frontal sinus trauma, the coronal flap may be tethered in a fracture line. Careful dissection should be performed over the fracture as not to further perforate the pericranium.

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