Chapter 4 Frontal Sinus and Draf Approaches

10.1055/b-0037-143510

Chapter 4 Frontal Sinus and Draf Approaches

Eugenio Cárdenas, Ariel Kaen, Isam Alobid, Manuel Bernal-Sprekelsen

Introduction

The endonasal approach to the frontal sinus is considered one of the most difficult parts of endoscopic sinus surgery. At the same time, benign or malignant lesions located anteriorly along the skull base require a maximum visualization of the frontal sinus and anterior skull base for which a Draf type III (also known as modified endoscopic Lothrop) procedure needs be performed. This technique is a well-established approach for refractory chronic rhinosinusitis involving the frontal sinus disease, mucoceles, bone-derived tumors (osteomas, fibrous dysplasia), and exposure of the anterior skull base.

A Draf type III is indicated as a prior step for the transcribriform approach (tumors along the anterior skull base, such as esthesioneuroblastomas, carcinomas, and adenocarcinomas of the anterior ethmoid, tumors involving the olfactory bulb, etc.).

This chapter deals with surgical anatomy of the frontal sinus, preoperative imaging needed, and different surgical steps to complete the Draf approaches. Illustrated cases and guidelines on how to avoid complications during surgery are included.

4.1 Anatomy of the Frontal Recess and Frontoethmoid Cells

The frontal sinus is localized in the anterior cranial vault between two thick layers of cortical bone. The frontal sinus shares a common embryologic and anatomic relationship with the ethmoid sinus; several authors refer to this sinus as a “large ethmoidal cell.” In an adult, two frontal sinuses are usually seen. Each frontal sinus cavity takes on the shape of a pyramid, with a thick anterior table and a thinner posterior table. This posterior wall forms the most anteroinferior boundary of the anterior cranial fossa. It has a superior vertical, and a smaller inferior horizontal, portion. The horizontal portion will form part of the orbital roof. Both are in close contact with the frontal lobes, separated only by the dura. An intersinus septum divides the frontal sinuses into separately draining sinus cavities and almost always is closed to the midline in the most inferior portions.1

The frontal sinus narrows down inferiorly and medially into a funnel-shaped point, which is defined as the frontal infundibulum. The latter ends in an almost circular area called frontal sinus ostium or frontal sinus opening.

The frontal ostium/opening is defined as the narrowest area of the transition zone from the frontal sinus to the frontal recess with its anterior edge formed by the frontal sinus beak (best seen on the parasagittal computed tomography [CT] scan).2

The angulation (posteromedially) and maximum diameter of this funnel may vary greatly between patients, or even between sides, and this funnel is surrounded by an intricate complex area covered by ethmoid cells and other anatomic structures. The frontal recess is the three-dimensional (3D) space below the frontal sinus that does include the drainage pathway. This space is usually occupied by several ethmoidal cells which affect the direction and position of this drainage pathway. The medial wall of the frontal recess is formed by the lateral lamella of the cribriform plate and the vertical lamella of the middle turbinate, and the lateral wall is formed by the lamina papyracea and lacrimal bone. The anterior ethmoidal artery may be situated in the posterior region of the roof of the frontal recess, right at the level of the attachment of the anterior wall of the bulla or right behind. It can be at risk if it runs in a mesentery off the skull base ( Fig. 4.1 ).

**Fig. 4.1** Schematic sagittal drawing of the frontal infundibulum, ostium, and recess. Black arrows indicate the extension of the frontal recess (irrespective of existing cells). Please note that the frontal recess encompasses all, but the frontal outflow tract encompasses only the drainage pathway of the frontal. AEA, anterior ethmoidal artery; EB, ethmoidal bulla; IT, inferior turbinate; UP, uncinate process.

The frontal recess drains into the superior end of the ethmoidal infundibulum in anatomic variants in which the uncinate process is attached to the skull base or the superoanterior portion of the middle turbinate. The ethmoidal infundibulum then communicates with the middle meatus via the hiatus semilunaris. However, when the uncinate process attaches to the lamina papyracea, the frontal recess drains directly into the middle meatus. In this case, the ethmoidal infundibulum terminates in a blind-ending recess known as the recessus terminalis ( Fig. 4.2 ).3

**Fig. 4.2** Schematic drawing of the three most frequent variations of attachments of the uncinate process (UP) in coronal sections and its relationship with the frontal recess and frontal outflow tract as proposed by Stammberger and Hasler.3 IT, inferior turbinate; MT, middle turbinate; UP, uncinate process.

Authors have described the frontal sinus drainage pathway (FSDP) in many ways and have given all sorts of names, depending on the surgical approach or perspective by which the frontal sinus is visualized. However, most authors would agree this to be the most difficult anatomic region to manage in endoscopic frontal sinus surgery due to the extreme variability of cell patterns observed in this area. Surgeons often lack confidence when exploring this area, which can result in an inadequate removal of disease. This is why, the frontal recess is the most likely area for the recurrence of sinus disease.2

To facilitate the understanding of this complex frontal sinus drainage area, we recommend the study of cell classifications in the literature, particularly the one recently published by Wormald et al.4,5

4.2 Preoperative Evaluation

4.2.1 Preoperative Study

The first, and possibly the most important, step in this area is to make an accurate surgical planning. A complete and individualized study is required in each patient. The study of the anatomy in three planes and their correlation with the disease to be treated is crucial. There are different 3D viewers such as Osirix or Carestream designed for navigation and visualization of multimodality and multidimensional images.

Successful surgery in the frontal recess relies critically on a detailed knowledge of the complex anatomy in this region.6 Programs specially designed for handling images have been proven useful to increase knowledge of this anatomy. These 3D viewers usually offer all modern rendering modes—multiplanar reconstruction, surface rendering, volume rendering, and maximum intensity projection—allowing a better surgical planning.

4.2.2 Computed Tomography

CT scans offer the most accurate images to study the frontal recess and the frontoethmoidal cells.7 Slices of 1 mm are necessary to avoid losing relevant information. The preoperative evaluation of the frontal recess can also avoid severe complications related with vital structures around the sinus.

The configuration of the following structures must be checked in the preoperative CT before a frontal sinus procedure:

Ostiomeatal complex anatomy.
The width of the lateral lamella of the cribriform plate, which articulates with the roof of the ethmoids (see Keros classification).
Insertion of the superior portion of the uncinate process that could have superior attachment to different structures ( Fig. 4.2 ).
Pneumatization of the frontoethmoid cells (agger nasi and other cells).
Presence of supraorbital, frontobullar, suprabullar, and interfrontal sinus septal cells.
Position of the anterior ethmoidal artery.
Check the relationship between the nasal septum and the head of the middle turbinate (septal deviation or nasal spine).
Thickness of the nasofrontal beak.

CT scan has proved to be useful in the postoperative evaluation of the frontoethmoidal cells and frontal recess.8 The sinuses may display persistent opacification, residual anterior ethmoidal and agger nasi cells, and a new bone formation (osteoneogenesis) obstructing the FSDP.

4.2.3 Magnetic Resonance Imaging

The ability of magnetic resonance imaging (MRI) to better discern the soft tissue becomes an ideal supplementary test to CT. Sometimes the anterior fossa approach allows a better planning with the CT scan, but the tumor resection is easiest to design with the MRI as it depicts soft tissues. The surgeon must review the preoperative images and evaluate the extent of the tumor along the parasagittal plane. Lesions located at the anterior cranial base along the anterior ethmoidal artery region require maximum visualization of the frontal sinus and skull base ( Fig. 4.3a, b ).

**Fig. 4.3** (a) Coronal and (b) parasagittal MR scans demonstrate a large olfactory groove meningioma in contact with the posterior table of the frontal sinus.

4.3 Indications

Table 4.1 summarizes the indications and respective surgical extensions of the approach to the frontal sinus as exposed by Draf.9

**Table 4.1 Indications of surgical approach to the frontal sinus following Draf8**
Draf I Acute sinusitis Chronic sinusitis	Failure of conservative surgery Orbital and endocranial complications First time surgery No risk factors (aspirin intolerance, asthma, triad) Revision after incomplete ethmoidectomy
Draf II type IIa drainage Type IIb drainage	Serious complications of acute sinusitis Medial mucopyocele All indications of type IIa if the drainage is too small in regard to the underlying pathology
Draf III	Persistent chronic frontal sinusitis with failure of appropriate medical therapy and after unsuccessful primary endoscopic frontal sinusotomy Primarily in patients with prognostic risk factors and severe polyposis Mucoviscidosis Kartagener′s syndrome Ciliary immotility syndrome Benign and malignant tumors (lesions close to the anterior ethmoidal artery region)